Orientational Behavior of Thermotropic Liquid Crystals on

Orientational Behavior of Thermotropic Liquid Crystals on Surfaces Presenting Electrostatically Bound Vesicular

Stomatitis Virus

Luis A.Tercero Espinoza,Kate R.Schumann,?Yan-Yeung Luk,

Barbara A.Israel,?and Nicholas L.Abbott*

Department of Chemical and Biological Engineering,University of Wisconsin s Madison,

1415Engineering Drive,Madison,Wisconsin53706

Received September22,2003.In Final Form:December23,2003

We report the orientational behavior of nematic phases of4-cyano-4′-pentylbiphenyl(5CB)on cationic, anionic,and nonionic surfaces before and after contact of these surfaces with solutions containing the negatively charged vesicular stomatitis virus(VSV).The surfaces were prepared on evaporated films of gold by either adsorption of poly-L-lysine(cationic)or formation of self-assembled monolayers(SAMs)from HS(CH2)2SO3-(anionic)or HS(CH2)11(OCH2CH2)4OH(nonionic).Prior to treatment with virus,we measured the initial orientation of5CB(? ) |- ⊥>0)to be parallel to the cationic surfaces(planar anchoring) but perpendicular(homeotropic)after equilibration for5days.A similar transition from planar to homeotropic orientation of5CB was observed on the anionic surfaces.Only planar orientations of5CB were observed on the nonionic surfaces.Because N-(4-methoxybenzylidene)-4-butylaniline(MBBA,? ) |- ⊥<0) exhibited planar alignment on all surfaces,the time-dependent alignment of5CB on the ionic surfaces is consistent with a dipolar coupling between the5CB and electrical double layers formed at the ionic interfaces.Treatment of poly-L-lysine-coated gold films(cationic)with purified solutions of VSV containing 108-1010plaque-forming units per milliliter(pfu/mL)led to the homeotropic alignment of5CB immediately after contact of5CB with the surface.In contrast,treatment of anionic surfaces and nonionic surfaces with solutions of VSV containing～1010pfu/mL did not cause immediate homeotropic alignment of5CB.These results and others suggest that homeotropic alignment of5CB on cationic surfaces treated with VSV of titer g108pfu/mL reflects the presence of virus electrostatically bound to these surfaces.

Introduction

Several recent studies have exploited the delicate balance of intermolecular forces underlying the anchoring of thermotropic liquid crystals(e.g.,4-cyano-4′-pentylbi-phenyl(5CB))on surfaces to amplify and report a range of molecular interactions,including the presence of proteins specifically bound to functionalized surfaces of gold.1-3The objective of the study reported herein was to investigate the response of thermotropic liquid crystals to viral particles bound to solid surfaces and to determine if there exists an orientational response of the liquid crystal that permits the presence of bound viral particles to be distinguished from other biological species(e.g.,proteins). We hypothesized that the anchoring of liquid crystals on surfaces presenting proteins or viruses might reflect the structural differences between these species.Virus particles have sizes ranging from tens to hundreds of nanometers and are composed of assemblies of proteins and nucleic acids(either RNA or DNA).Hence,viruses are considerably larger and more complex than individual proteins.4,5Also,in the case of enveloped viruses,the surfaces of the viral particles comprise phospholipid bilayers studded with viral membrane proteins.4Whereas thermotropic liquid crystals on gold and glass surfaces decorated with proteins have been reported to align the liquid crystals parallel to the supporting surfaces,1-3,6-8 surfaces presenting monolayers of phospholipids have been reported to induce planar,tilted,or homeotropic alignment of thermotropic liquid crystals depending on the surface pressure,organization,and tilt of the phos-pholipids comprising the monolayer.9,10We note also that studies of the anchoring of5CB on cells have found homeotropic or near-planar alignment on the surfaces of adhered cells,depending on the type of cell.11

In this paper,we report a study of the interactions of nematic liquid crystals with vesicular stomatitis virus (VSV),a member of the Rhabdoviridae family.VSV is a widely studied virus that has a well-defined structure. The virus causes periodic outbreaks of disease in cattle, horses,and swine in Central and North America.12-14Its main structural features have been established by electron microscopy.12,15-17The infectious VS virion is bullet-shaped

*To whom correspondence should be addressed.Phone:(608) 265-5278.Fax:(608)262-5434.E-mail:abbott@https://www.sodocs.net/doc/2f16662653.html, ?Department of Pathobiological Science,School of Veterinary Medicine.

(1)Gupta,V.K.;Skaife,J.J.;Dubrovsky,T.B.;Abbott,N.L.Science 1998,279,2077.

(2)Skaife,J.J.;Brake,J.M.;Abbott,https://www.sodocs.net/doc/2f16662653.html,ngmuir2001,17,5448.

(3)Luk,Y.-Y.;Tingey,M.L.;Hall,D.J.;Israel,B.A.;Murphy,C. J.;Bertics,P.J.;Abbott,https://www.sodocs.net/doc/2f16662653.html,ngmuir2003,19,1671.

(4)Flint,S.J.;Enquist,L.W.;Krug,R.M.;Racaniello,V.R.;Skalka,

A.M.Principles of Virology:Molecular Biology,Pathogenesis,and Control;ASM Press:Washington,DC,2000.

(5)Lodish,H.;Berk,A.;Zipursky,S.L.;Matsudaira,P.;Baltimore,

D.;Darnell,J.Molecular Cell Biology;W.H.Freeman:New York,2000.

(6)Kim,S.-R.;Abbott,N.L.Adv.Mater.2001,13,1445.

(7)Kim,S.-R.;Abbott,https://www.sodocs.net/doc/2f16662653.html,ngmuir2002,18,5269.

(8)Tingey,M.L.;Luk,Y.-Y.;Abbott,N.L.Adv.Mater.2002,14, 1224.Skaife,J.J.;Abbott,https://www.sodocs.net/doc/2f16662653.html,ngmuir2001,17,5595.

(9)Fang,J.;Gehlert,U.;Shashidhar,R.;Knobler,https://www.sodocs.net/doc/2f16662653.html,ngmuir 1999,15,297.

(10)Hiltrop,K.;Stegemeyer,H.Liq.Cryst.Ordered Fluids1984,4, 515.

(11)Fang,J.;Ma,W.;Selinger,J.V.;Shashidhar,https://www.sodocs.net/doc/2f16662653.html,ngmuir2003, 19,2865.

(12)Howatson,A.F.Adv.Virus Res.1970,16,195.

(13)de Mattos,C.A.;de Mattos,C.C.;Rupprecht,C.E.Rhabdovi-ruses.In Fields Virology;Knipe,D.M.,Howley,P.M.,Eds.;Lippincott Williams&Wilkins:Philadelphia,PA,2001.

(14)Rose,J.K.;Whitt,M.A.Rhabdoviridae:The Viruses and Their Replication.In Fields Virology;Knipe,D.M.,Howley,P.M.,Eds.; Lippincott Williams&Wilkins:Philadelphia,PA,2001.

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Langmuir2004,20,2375-2385

and consists of an internal helical structure (RNA and nucleocapsid protein)surrounded by a protein matrix and a phospholipid bilayer studded with fine projections (VSV-G protein).12,17The virion is approximately 173nm (range 125-205nm)in length and 75nm (range 45-85nm)in diameter.15,17A schematic illustration of the infectious VS virion is shown in Figure 1.Electrokinetic studies have determined that VSV has an isoelectric range from pH 4.7to pH 7.0.18

In the study reported in this paper,we immobilized VSV on surfaces by taking advantage of the net negative surface charge of VSV at slightly basic solution pHs.We prepared cationic surfaces by adsorption of poly-L -lysine from aqueous solutions onto the surfaces of gold films.We exploited electrostatic interactions to capture the virus particles onto these surfaces.We further examined the interactions of virus particles with anionic and neutral surfaces.The anionic surfaces comprised SAMs formed from 2-mercaptoethanesulfonic acid (HS(CH 2)2SO 3-Na +),whereas the neutral surfaces comprised SAMs formed from 1-mercaptoundec-11-yltetra(ethylene glycol)(HS-(CH 2)11(OCH 2CH 2)4OH).Although electrostatic capture of VSV lacks the specificity of antibody-decorated surfaces,such specificity was not required in this study because the principal goal of the study was to understand how nematic liquid crystals orient in response to virions bound to surfaces and to compare this response to that observed for proteins.We did not seek to selectively capture viruses from mixtures onto surfaces.We also note that cationic surfaces have been used to concentrate and purify viruses engineered to express vesicular stomatitis virus glyco-protein (VSV-G)on their surfaces.19

Materials and Methods

Materials.Aluminum oxide and glass microscope slides (Fisher’s Finest,premium grade)were purchased from Fisher Scientific (Pittsburgh,PA).The nematic liquid crystal 4-cyano-4′-pentylbiphenyl (5CB),manufactured by BDH,was purchased from EM Industries (Hawthorne,NY).Ethanol was purchased from AAPER Alcohol and Chemical Co.(Shelbyville,KY).Antibiotic -antimycotic solution,minimum essential medium Eagle (MEM)(with Earle’s salts and L -glutamine),non-essential amino acid solution,and Hank’s balanced salt solution (HBSS)were purchased from Mediatech,Inc.(Herndon,VA).Heat-inactivated fetal bovine serum was purchased from

GibcoBRL (Carlsbad,CA).Poly-L -lysine (0.1%w/v,aqueous)was purchased from Ted Pella,Inc.(Redding,CA).Phosphate-buffered saline (PBS),crystal violet,and formaldehyde were purchased from Sigma-Aldrich Co.(St.Louis,MO).Octyltrichlorosilane,n -heptane,2-mercaptoethanesulfonic acid (sodium salt)(HS(CH 2)2SO 3-Na +),decanethiol,hexadecanethiol,and the ne-matic liquid crystal N -(4-methoxybenzylidene)-4-butylaniline (MBBA)were purchased from Aldrich Chemicals (Milwaukee,WI)and used as received.HS(CH 2)11(OCH 2CH 2)4OH was syn-thesized using procedures reported by Whitesides and co-workers.20

Cell Culture.Vero cells (CCL-81,ATCC,Manassas,VA)were grown using minimum essential medium Eagle (MEM),with Earle’s salts and L -glutamine,supplemented with heat-inacti-vated fetal bovine serum,antibiotic -antimycotic solution,and a solution containing nonessential amino acids for MEM.Cell culture was carried out using polystyrene flasks with a growth area of 150cm 2to allow for the cultivation of ～2×107cells per flask.The cells were infected with VSV Indiana strain (VR-1238,ATCC,Manassas,VA)using a proportion of approximately one infectious virus particle per 100cells.After incubation for ～48h at 37°C (100%relative humidity,5.5%CO 2),the supernatant was collected for purification.

Purification of Virus.The supernatant from infected Vero cells was collected and spun at 10500rpm in a Beckman J2-21M centrifuge (Beckman,Fullerton,CA)fitted with a JA 20rotor for 30min at 4°C.The supernatant was collected and spun again at 27500rpm for 1h at 4°C onto a 30%“sucrose cushion”using a Beckman L8-70M centrifuge fitted with an SW 28rotor.The “sucrose cushion”(2-3mL of 30%w/v solution of sucrose in Tris buffer saline (TBS),10mM Tris-NaCl,0.1M NaCl,1mM EDTA,pH 8.0)helped to separate the viral particles,which pellet through the cushion,from cellular fragments that stay in solution after the first centrifugation step and that do not readily penetrate the cushion.After the sample was spun,the supernatant was discarded and the remaining pellet was resuspended in TBS buffer.This solution was then stored at -80°C in working aliquots until needed.

We prepared control solutions using the procedure described above except that supernatant from uninfected Vero cells was used as the starting material.Approximately equal numbers of cells were used to produce the virus and control solutions.Determination of Virus Titer.The titer or concentration of infectious virus particles in solution was determined by means of a plaque assay,as described elsewhere.21Briefly,Vero cells were grown in six-well plates (Corning,Acton,MA)until a monolayer of cells was formed.The cells were rinsed twice with HBSS,and then 100μL of serial dilutions of the virus solution was added to each well and incubated for ～1h at room temperature in a rocker.The virus solutions were then removed,and the cells were covered with a 1:1mixture of 1.5%agar and MEM.After ～5min,the mixture solidified and the samples were placed in an incubator (37°C,100%relative humidity,5.5%CO 2)

(15)Bradish,C.J.;Kirkham,J.

B.J.Gen.Microbiol.1966,44,359.(16)(a)Chow,T.L.;Chow,F.H.;Hanson,R.P.J.Bacteriol.1954,68,724.(b)Howatson,A.F.;Whitmore,G.F.Virology 1962,16,466.(c)Reczko,E.Arch.Gesamte Virusforsch.1961,10,588.(17)Nakai,T.;Howatson,A.F.Virology 1968,35,268.(18)Miki,T.Microbiol.Immunol.1981,25,585.

(20)Pale-Grosdemange,C.;Simon,E.S.;Prime,K.L.;Whitesides,Figure 1.Schematic representation of vesicular stomatitis virus (VSV).The structural components are the following:G,viral glycoprotein (～1200per virion,variable);M,matrix protein (～1800per virion);P,polymerase subunit (～466per virion),N,nucleocapsid protein (～1250per virion);L,polymerase subunit (～50per virion);a phospholipid bilayer membrane;negative sense RNA genome.P and L proteins,complexed,form the viral RNA-dependent RNA polymerase.Adapted from Flint 4and Rose.14

2376Langmuir,Vol.20,No.6,2004Tercero Espinoza et al.

for4days.After the4-day incubation,～1mL of crystal violet stain was added to each well and incubated overnight at room temperature.

After incubation,the plugs of agar were removed with a stream of water and each well was drained of any residual water.Since the agar overlay restricts the spread of progeny virus to surrounding cells,localized areas of cell death are formed in the monolayer.These areas are called“plaques”and are not stained by crystal violet,allowing for direct visualization of the sites of infection.The plaques were then counted,and the titer of the solution was calculated according to the relation

where the titer is given in plaque-forming units per milliliter (pfu/mL),N plaques refers to the number of plaques in an individual well,d is the dilution of the virus solution used to inoculate the well(e.g.,10-6),and V is the volume of solution used for inoculation in milliliters.For statistical reasons,dilutions that yielded20-100plaques per well were used for calculation of the titer.

Glass Cleaning.Glass slides were immersed in piranha solution(70:30v/v%H2SO4/H2O2)at60-80°C for45min to1 h.Warning:piranha solution reacts strongly with organic compounds and should be handled with extreme caution;do not store the solution in closed containers.The slides were then rinsed at least10times with18.2M??cm water(Milli-Qplus,Millipore, Bedford,MA)and immersed in a base bath(70:30v/v%3M KOH/H2O2)at60-80°C for approximately30min.The slides were then rinsed sequentially with18.2M??cm water,ethanol (200proof),and methanol.The slides were thoroughly dried under a stream of nitrogen and placed overnight in an oven at110°C.

Electron Beam Deposition of Metals.Thin films of gold were deposited onto clean glass slides using a thin layer(～80?)of titanium to promote adhesion between the gold and glass (metal purity99.999%,International Advanced Materials,New York,NY).The process was carried out at a maximum pressure of4×10-6Torr in a VES-3000C electron beam evaporator manufactured by Tek-Vac Industries(Brentwood,NY).The rate of deposition was0.02nm/s and was controlled by a quartz crystal microbalance(QCM).“Uniformly deposited”films of gold were prepared by rotating the slide holders in an epicyclical manner, thereby removing all preference in the direction of deposition of the metals.“Obliquely deposited”gold films were prepared by using a fixed angle of incidence of the metals and stationary substrates.The angle of incidence used in this study was60°, measured from the normal of the substrate.“Obliquely deposited”gold films with thicknesses of～200?were used as substrates for optical cells,while“uniformly deposited”gold films with thicknesses of～500?were used as a substrate for ellipsometric measurements.

Optical Cells Containing Liquid Crystal.The orientational behavior of liquid crystals on surfaces supporting bound VSV was determined by preparing optical cells that were filled with liquid crystal(LC cells).The LC cells were formed by spacing apart two solid substrates using Saran wrap(thickness of～13μm).One of the substrates was a glass slide treated with octyltrichlorosilane to give homeotropic alignment of the liquid crystal.The other substrate was the surface of interest.The LC cell was placed in an oven set to55-60°C for～5min;5CB heated above its clearing temperature(～35°C)was then introduced into the LC cell and allowed to cool to room temperature.Alternatively,MBBA,heated above its clearing temperature(～43°C),was used instead of5CB.

Optical Examination of Liquid Crystals.The orientations of5CB were examined by using plane-polarized light in trans-mission mode on an Olympus BX60microscope with crossed polarizers.The LC cells were placed on a rotating stage located between the polarizers.In-plane birefringence was determined by rotating the stage by45°and observing the extent of modulation in the intensity of transmitted light.Homeotropic alignment was determined by first observing no transmission of sample stage and a Bertrand lens above the stage.The condenser produced convergent incident light,and the Bertrand lens permitted imaging of the back focal plane of the microscope. When a liquid crystal was homeotropically aligned,an interfer-ence pattern consisting of two crossed isogyres was observed in the back focal plane.22The isogyres were parallel to the crossed polars.The reader is referred to ref22for a detailed discussion of conoscopy.Optical images were captured using a digital camera (Olympus C2020Zoom)mounted on the microscope.

Treatment of Glass Microscope Slides with Octyl-trichlorosilane.A solution of n-heptane was passed through a column of aluminum oxide to remove residual water from n-heptane.Glass slides cleaned with piranha solution were immersed in a10mM solution of octyltrichlorosilane in n-heptane for～30min at room temperature,rinsed with methylene chloride, and dried under a stream of nitrogen.We confirmed that each glass slide treated with octyltrichlorosilane caused homeotropic orientation of5CB.Any slide not causing homeotropic orientation of5CB was discarded.

Deposition of Poly-L-lysine.Poly-L-lysine was deposited onto the gold surfaces from aqueous drops of0.1%poly-L-lysine.The drops were incubated in a water-saturated environment for～30 min.The surfaces were then rinsed with water and dried under a stream of nitrogen.Alternatively,poly-L-lysine-treated gold films were rinsed with water and submerged in PBS buffer (Sigma,St.Louis,MO)for storage.Prior to use,the stored gold films were rinsed again with water.

Self-Assembled Monolayers(SAMs).SAMs formed from HS(CH2)2SO3Na,HS(CH2)11(OCH2CH2)4OH,HS(CH2)9CH3,or HS(CH2)15CH3were prepared by soaking gold substrates in ethanolic solutions containing the corresponding alkanethiols (1mM)overnight.The SAMs were then rinsed with ethanol and dried under a stream of nitrogen prior use.

Deposition of Vesicular Stomatitis Virus(VSV).Poly-L-lysine-treated gold substrates were contacted with solutions of

VSV for about4-6h at room temperature by placement of a10μL drop of virus solution on the surface.Incubation took place in a water-saturated environment to prevent evaporation.For these experiments,stock virus solutions with titers of2.5×109 and2×1010pfu/mL were used,as determined by plaque titration (see above);control solutions were prepared as described above.

Ellipsometry.Ellipsometry was performed using uniformly deposited films of gold with thicknesses of500?because these gold films are optically reflective.Ellipsometric constants were measured at three locations on each sample using a Rudolph Research Auto EL II ellipsometer(wavelength632nm,angle of incidence70°,Rudolph Technologies,Flanders,NJ).The ellip-sometric constants for the gold surfaces were determined before each experiment by using decanethiol and hexadecanethiol self-assembled monolayers(SAMs)as standards of known thickness (～15and～23?,respectively).23A simple slab model was used to interpret the ellipsometric constants of the SAMs and poly-L-lysine films formed on the gold surfaces.The slab was assumed to have an index of refraction of1.46.

Results and Discussion Characterization of Capture Surfaces.First,we sought to fabricate cationic,anionic,and nonionic surfaces for the capture of VSV.For this purpose,we chose to use poly-L-lysine(cationic),a sulfonate-terminated alkanethiol (anionic),and a tetra(ethylene glycol)-terminated al-kanethiol(nonionic)to functionalize the gold surfaces. For the last two surfaces,we used procedures that have been reported previously to form SAMs of these compounds on the surfaces of films of gold.3Here,we report the characterization of gold surfaces that were incubated with solutions of poly-L-lysine.Past studies have reported that proteins and polypeptides adsorb onto the surfaces of gold films.24,25

(22)Hartshorne,N.H.;Stuart, A.Crystals and the Polarizing Microscope;Edward Arnold&Co.:New York,1970.

titer)N

plaques

(d)(V)

(1)

Behavior of Liquid Crystals on Surfaces Langmuir,Vol.20,No.6,20042377

Visual inspection of the behavior of water on gold

surfaces treated with poly-L-lysine revealed the treated

surfaces to be hydrophilic.In contrast,untreated slides

were hydrophobic(when measured1h or more after

removal from the evaporator)because adventitious ad-

sorbates collect on the gold(see below).We used ellip-

sometry to determine the optical thickness of poly-L-lysine

adsorbed on the gold films.Because of the presence of the

adventitious adsorbates on the gold surfaces,our mea-

surements of optical thicknesses reflect both the adsorbed

contaminants and adsorbed poly-L-lysine.We measured

the ellipsometric thickness of the poly-L-lysine layer(plus

adventitious adsorbates)to be～1.7nm.Prior to adsorption

of poly-L-lysine,the ellipsometric thickness of the adven-

titious adsorbates was～1.0nm.Thus,we conclude that

the ellipsometric thickness of the layer of poly-L-lysine is ～0.7nm and that poly-L-lysine adsorbs onto the surface of gold from aqueous solutions of poly-L-lysine.The

ellipsometric results described above were obtained when

using gold films with ages(measured from the time of

removal from the evaporator)that were between1h and

2weeks.

Anchoring of Thermotropic Liquid Crystals on

Cationic Surfaces at Short Times.Because the non-

ionic surfaces we used are known to induce a planar

alignment of5CB,3we explored the alignment of5CB on

the cationic and anionic surfaces prepared on obliquely

deposited gold films.First,we prepared cationic surfaces by adsorption of poly-L-lysine to gold surfaces as described above.We prepared optical cells by pairing the gold surfaces treated with poly-L-lysine with glass slides treated with octyltrichlorosilane.The glass slides treated with octyltrichlorosilane induce homeotropic alignment of thermotropic liquid crystals.The surfaces were spaced apart by using thin films of Saran wrap(thickness of～13μm)and secured together with binder clips.Hereafter,we refer to an optical cell prepared by pairing the surface of interest with a slide of octyltrichlorosilane-treated glass as an“asymmetric optical cell”(Figure2).Next,we introduced5CB above its clearing temperature into the optical cell and imaged the optical texture of the liquid crystal in transmission through crossed polarizers after it cooled into its nematic phase.Our initial observations were made within10min of filling the optical cells with liquid crystal.

We observed a uniformly dark optical texture,except for line defects,when the sample was oriented with the direction of gold deposition parallel to either of the polarizers(Figure3a).Upon rotation of the sample by 45°,the optical texture appeared bright,and we observed domains of two distinct colors(Figure3b).The domains were encircled by the line defects.These defects were also visible when the second polarizer(analyzer)was removed from the light path in the microscope,indicating that the defects correspond to localized regions where the nematic order was lost,causing scattering of light.The uniformly dark texture observed when the sample was oriented parallel to one of the polarizers,when combined with the observation of strong modulation of light upon rotation of the sample between crossed polarizers,indicates that the nematic director points in a uniform azimuthal direction throughout the sample and that the alignment is either parallel to the surface(planar alignment)or tilted from it.We attributed the appearance of domains of two distinct colors to two distinct tilt angles of the nematic director on the surface of the treated gold.These colors are close to each other in a Michel-Le′vy color chart.On the basis of calculations discussed below,we concluded that the tilt angles differ from each other by less than5°.

Because the capture of viruses on these surfaces required the contact of the surfaces with solutions of VSV in TBS buffer for several hours,we investigated the effect that incubation of the poly-L-lysine-coated gold surfaces in TBS buffer had on the alignment of5CB on those

Figure2.Geometry of the asymmetric liquid crystal cell

comprising octyltrichlorosilane-treated glass and poly-L-lysine-

treated gold film.The director field of5CB is shown schemati-

cally between the surfaces.

Figure3.Optical textures of5CB on poly-L-lysine-treated

gold films(obliquely deposited)(a,b)and on poly-L-lysine-

treated gold films incubated in TBS buffer for>3h(c-f).The

images(cross polars)were obtained with the direction of

deposition of the gold film oriented at an angle of0°(a,c,e)or

45°(b,d,f)from one of the polarizers.Scale bars)500μm. 2378Langmuir,Vol.20,No.6,2004Tercero Espinoza et al.

temperature.We rinsed the surfaces with water,dried them under a stream of nitrogen,and then prepared asymmetric optical cells as described above.We imaged the optical cells under crossed polarizers shortly after contacting the cationic surfaces with5CB.When a sample was oriented with the direction of gold deposition parallel to one of the polarizers,we observed a uniformly dark texture with the exception of line defects(Figure3c).Most, but not all,defects formed closed loops of irregular shape and varying size.Upon rotation of the sample by45°under crossed polarizers,we observed a bright texture consisting of two colors separated almost always by line defects (Figure3d).The colors lie next to each other in a Michel-Le′vy chart and indicate that the domains possessed tilt angles that differed by less than5°(see below for details). These optical textures are very similar to those observed for surfaces of gold treated with poly-L-lysine that had not been contacted with TBS buffer(Figure3a,b).

We note that we observed some variability in the shape and abundance of line defects on surfaces of gold treated with poly-L-lysine,independent of whether they had or had not been contacted with TBS buffer.For example,the defects observed in Figure3e did not form closed loops. When the sample was rotated by45°under crossed polarizers,we observed a bright texture of a single color across the entire sample(Figure3f).In contrast to the textures shown in parts b and d of Figure3,the color was

the same for the inside and outside areas bounded by line defects.We also note that the interference colors in Figure 3depend on the thickness of the film of liquid crystal in each optical cell.Thus,it is not possible to directly compare interference colors between samples.However,colors can be compared within the same optical cell.Abrupt changes in color,like those seen in parts b and d of Figure3,indicate two different tilt angles of the nematic director,but a gradual change in color across an optical cell most likely reflects small changes in the thickness of the liquid crystal film across the sample.

To determine if5CB assumes planar alignment on at least some regions of the surfaces of gold treated with poly-L-lysine,we prepared asymmetric optical cells with a continuously varying thickness of the film of liquid crystal across the length of the sample(wedge cells,Figure 4a).As before,the top surface of the optical cell was prepared from octyltrichlorosilane-treated glass.The bottom surface of the optical cell was a gold surface patterned along the length of the sample(parts b and c of Figure4).The pattern was made by first submerging half of the gold slide in an ethanolic solution of n-hexadecanethiol for～2h.The sample was then rinsed with ethanol and dried under a stream of nitrogen.SAMs formed from n-hexadecanethiol on the surfaces of gold films are known to cause planar alignment of5CB.26Next, we incubated the other half of the gold film with poly-L-lysine solution for～30min;the sample was then rinsed with water and dried under a stream of nitrogen.The poly-L-lysine solution did not contact the SAM formed from hexadecanethiol.

We compared the progression of the interference colors generated by5CB across the two areas of the optical cell. By patterning poly-L-lysine and hexadecanethiol on the same substrate,we ensured identical thicknesses of the film of liquid crystal in the two regions of surface(Figure 4).Thus,the same progression of interference colors across the sample would imply the same anchoring of liquid crystals on the two areas of the surface.Because the length of the sample was greater than the field of view of our

microscope,we obtained a series of overlapping images

along the length of the sample and assembled them into

a composite image.The images shown in Figure4b,c were

obtained from areas fully contained within each patterned

https://www.sodocs.net/doc/2f16662653.html,parison of the progression of interference colors

along the length of the slide revealed that they were nearly

identical.Because SAMs formed from hexadecanethiol

cause planar anchoring of5CB,this result leads us to

conclude that gold films treated with poly-L-lysine cause

planar anchoring of5CB immediately after contact of the

surface and the liquid crystal.

Anchoring of Thermotropic Liquid Crystals on

Cationic Surfaces at Long Times.Whereas the results

above demonstrate that gold surfaces treated with poly-L-lysine cause planar or near-planar anchoring of5CB shortly after contact of the liquid crystal with the surface,

we observed homeotropic alignment of5CB when the

samples were examined a week later.Thus,below we

characterize this time-dependent behavior of5CB on gold

surfaces treated with poly-L-lysine.

Figure5a shows a series of images of a sample

(asymmetric optical cell)oriented45°from either polarizer

(crossed polarizers).During the first day of observation,

the sample exhibited a pale-orange to pale-green color.

These colors changed very little during the first2days.

By the third day,however,the colors had changed to light-

blue and yellow.By the fourth day,the color of the sample

had turned gray.On the fifth day,the sample was dark

and exhibited no modulation of light upon rotation under

crossed polarizers.By using conoscopy,we observed an

interference pattern consisting of two crossed isogyres,

which confirmed the alignment to be homeotropic.

We interpreted the progression of interference colors to

indicate a continuous transition from planar to homeo-

tropic anchoring on the surface of gold treated with poly-L-lysine.Past studies have demonstrated that it is possible to quantitatively relate the interference colors generated by the liquid crystal to the tilt angle on one of the surfaces comprising the LC cell,provided the anchoring at the

Figure4.(a)Side view of the patterned wedge cell and top view of the gold film patterned with areas of n-hexadecanethiol and poly-L-lysine.Shown are optical textures of5CB in the wedge cell in regions(b)treated with n-hexadecanethiol and (c)poly-L-lysine.The images of the liquid crystal cells were obtained within10min of filling the cell with5CB.Scale bar )1mm.

Behavior of Liquid Crystals on Surfaces Langmuir,Vol.20,No.6,20042379

effective birefringence,?n eff ,of a tilted material,27-29

where n |is the refractive index parallel to the director,n ⊥is the refractive index perpendicular to the director,and θis the tilt of the liquid crystal,and by noting that minimization of the elastic energy stored in the splay and bend distortion of the liquid crystal (Figure 2)leads to a linear variation of the tilt angle across the thickness of the sample,27

we estimate the effective birefringence of the sample as

where θ2is the tilt angle of the liquid crystal at the

polylysine-treated surface.From knowledge of the optical properties of 5CB 27and the geometry of the sample,we

estimated the tilt angle of 5CB at the surface of gold treated with poly-L -lysine by determining the birefringence cor-responding to the colors in Figure 5(using a Michel -Le ′vy chart)and then solving for θ2using eq 3.The results are shown in Figure 5b.

The results reported above reveal that poly-L -lysine causes homeotropic alignment of 5CB after 5days of contact of the liquid crystal with the surface.A past study using gold surfaces supporting sodium carboxylate salts has demonstrated that the electric field of electrical double layers formed by dissociation of surface-immobilized salts can influence the orientations of supported nematic liquid crystals.30In that study,the authors reported planar alignment of 5CB (? ) |- ⊥>0,where |is the dielectric constant parallel to the director and ⊥is the dielectric constant perpendicular to the director)on surfaces presenting low densities of sodium carboxylate salts but homeotropic alignment on surfaces presenting high den-sities of sodium carboxylate groups.This observation and other past studies 31are consistent with reorientation of the liquid crystals under the influence of an electric field normal to the surface.Planar alignment of MBBA (? ) |- ⊥<0)on gold surfaces presenting low and high densities of sodium carboxylate groups was also observed,consistent with the larger ( ⊥)aligning parallel to the electric field.

We hypothesized that the time-dependent behavior of the orientation of 5CB on surfaces of gold decorated with poly-L -lysine may also arise from the formation of an electrical double layer.To test this proposition,we prepared asymmetric optical cells as described above,

(27)Brake,J.M.;Mezera,A.D.;Abbott,N.

https://www.sodocs.net/doc/2f16662653.html,ngmuir 2003,19,8629.

(28)Van Doorn,C.Z.;Gerritsma,C.J.;de Klerk,J.J.M.J.Influence of the Device Parameters on the Performance of Twisted-Nematic Liquid-Crystal Matrix Displays.In The Physics and Chemistry of Liquid Crystal Figure 5.Temporal evolution of the optical textures of (a)5CB and (c)MBBA on poly-L -lysine-treated gold films.(b)Progression of tilt angle corresponding to textures in (a).Scale bars )250μm.

?n eff )

n |n ⊥

n |

2

cos 2θ+n ⊥2sin 2

θ

-n ⊥

(2)

θ(x ))x

h

θ2)x ?θ2(3)

?n eff ≈

∫0

1

(n |n ⊥

n ⊥2

sin 2

(x ?θ2)+n |2

cos 2

(x ?θ2)

-n ⊥)

d x ?

(4)

2380Langmuir,Vol.20,No.6,2004Tercero Espinoza et al.

substituting MBBA for 5CB,and observed the evolution of the optical textures of MBBA over a period of 5days (Figure 5c).Initially (on day 1),we observed a uniformly dark texture virtually free of line defects when the sample was oriented parallel to one of the polarizers (crossed polarizers).As in the case of 5CB,we observed strong modulation of light upon rotation of the sample under crossed polarizers.We measured the interference colors to remain virtually unchanged over the course of 5days,indicating that the anchoring of MBBA remained planar.This observation is consistent with the formation of an electrical double layer on the surface of gold treated with poly-L -lysine because the presence of an electric field perpendicular to the surface would favor planar alignment of MBBA,in which the larger ( ⊥)is aligned parallel to the electric field in the electrical double layer.Finally,we note that Fang and co-workers have reported homeotropic anchoring of 5CB on glass substrates coated with poly-D -lysine,although the time dependence of the anchoring was not discussed.11

Anchoring of Thermotropic Liquid Crystals on Anionic Surfaces.Next,we characterized the anchoring of 5CB on the anionic surfaces prior to treatment of VSV.Anionic surfaces were formed by soaking gold substrates in a 2mM ethanolic solution of HS(CH 2)2SO 3-Na +.We then assembled asymmetric optical cells with the anionic surfaces and examined them under crossed polarizers immediately (<10min)after contacting the liquid crystal with the surfaces.When the samples were oriented parallel to either of the polarizers,the optical textures of the samples were uniformly dark with the exception of some line defects.When the sample was rotated 45°under crossed polarizers,the optical texture appeared bright and exhibited largely a uniform color (Figure 6a).After 6h,the optical textures of 5CB became uniformly dark corresponded to homeotropically aligned 5CB.The ob-servation of near-planar alignment of 5CB shortly after contacting the surfaces with the liquid crystal and of homeotropic alignment after 6h of contact is similar to the anchoring of 5CB on surfaces of gold decorated with poly-L -lysine but with a faster transition from planar to homeotropic anchoring.These observations are consistent with the formation of an electrical double layer on the anionic surfaces.Although we do not yet understand why the transition occurs more quickly on the anionic surfaces than on the surfaces treated with poly-L -lysine,we note that the density of charge on the anionic surfaces may be greater than that on the surfaces treated with poly-L -lysine.

To further characterize the anionic surfaces,we ex-amined the orientation of MBBA in the asymmetric optical cells.At short times,we observed modulation of the intensity of the polarized light under cross polars (Figure 6c).We then examined the samples every 2h but observed no distinguishable change in the textures (Figure 6d).This observation is similar to that observed on the cationic surfaces and provides further support for the proposition that the time-dependent anchoring of 5CB on the anionic surfaces is caused by the formation of an electrical double layer.

Cationic Surfaces Incubated with VSV.Next,we measured the orientation of nematic 5CB on surfaces treated with poly-L -lysine and then solutions of VSV.The surfaces were incubated for approximately 4h in TBS buffer with a VSV titer of 109pfu/mL.We assembled asymmetric optical cells with these surfaces and observed the alignment of 5CB immediately after contacting the surfaces with the liquid crystal.When examined in transmission through crossed polarizers,we observed uniformly dark textures that were free of line defects (samples oriented parallel to either polarizer,Figure 7a).Upon rotation by 45°,we observed no modulation of the intensity of transmitted light,suggesting homeotropic alignment (Figure 7b).Under conoscopic examination,we observed an interference pattern consisting of two crossed isogyres,which confirmed the orientation of 5CB to be perpendicular to the surface (inset in Figure 7b).

Next we prepared control solutions from the superna-tant of uninfected Vero cells (the same cell line used to grow the virus stock)and subjected them to the same purification procedure as the supernatant containing VSV.We contacted the control solutions with cationic surfaces for approximately 4h.After rinsing them with water and drying them under a stream of nitrogen,we assembled the surfaces into asymmetric optical cells as described above.Examination of the optical cells under crossed polarizers,shortly after contact of the surfaces with 5CB,revealed a dark texture (with defects)when the sample was oriented parallel to either polarizer (Figure 7g).Upon rotation of the sample by 45°,we observed a bright texture of largely uniform color (Figure 7h).We interpreted the variations in color in Figure 7h as small variations in the tilt angle of 5CB on these surfaces,similar to that observed for 5CB supported on the cationic surfaces prior to treatment with virus.We concluded that the alignment of 5CB on cationic surfaces contacted with control solutions was not homeotropic.This result suggested that the homeotropic alignment of 5CB on cationic surfaces treated with VSV was due to the presence of virus particles on those surfaces.

We performed an additional experiment to obtain further evidence for the homeotropic alignment of 5CB on Figure 6.Optical textures of nematic liquid crystals with positive (5CB)and negative (MBBA)dielectric anisotropy supported on SAMs formed from HS(CH 2)2SO 3-Na +(anionic surfaces).Shown are images of 5CB obtained shortly (a)and 6h (b)after assembly of optical cells and images of MBBA obtained shortly (c)and 6h (b)after assembly of optical cells.All images (cross polars)were obtained with the direction of deposition of the gold film oriented at an angle of 45°from one of the polarizers.Scale bars )500μm.

Behavior of Liquid Crystals on Surfaces Langmuir,Vol.20,No.6,2004

2381

cationic surfaces as both the top and bottom surfaces of an optical cell.Examination of the samples under crossed polarizers revealed uniformly dark textures with no defects when the sample was oriented parallel to either of the polarizers(Figure8a).We observed a similar texture when the sample was rotated by45°,consistent with homeotropic orientation of5CB(Figure8b).Homeotropic alignment of 5CB on these surfaces was confirmed by conoscopy(inset in Figure8b).Thus,we conclude that5CB does assume

Next,we investigated the influence of the titer of the virus solutions contacted with the cationic surfaces on the orientation of the liquid crystal.We diluted the virus solutions10-fold(to108pfu/mL)and contacted them with cationic surfaces,as described above.Examination of asymmetric optical cells formed with these surfaces revealed optical textures identical to those observed for samples incubated with virus solutions of titer109pfu/ mL.These textures are shown in parts c and d of Figure 7.However,we observed different textures for samples incubated with virus solutions of titer107pfu/mL.When those samples were examined under crossed polarizers and oriented parallel to either polarizer,we observed uniformly dark textures with line defects(Figure7e).Upon rotation of the sample by45°under crossed polarizers,we observed a bright texture of nearly uniform color present-ing line defects(Figure7f).The absence of transmitted light in Figure7e indicates that the nematic director points in a uniform azimuthal direction across the sample. Furthermore,the strong modulation of the intensity of transmitted light observed upon rotation of the sample under crossed polarizers indicates that the anchoring of 5CB on these surfaces is tilted or planar.

The results above,when combined,lead to two conclu-sions.First,contact of cationic surfaces with VSV solutions of titer greater than108pfu/mL causes homeotropic orientations of5CB.Second,the homeotropic alignment is not caused by the presence of cell fragments in the

Figure7.Optical textures of5CB sandwiched in an asym-metric optical cell consisting of poly-L-lysine-treated gold films (obliquely deposited)treated with VSV on one surface and octyltrichlorosilane-treated glass on the other.The samples were oriented such that the direction of deposition of the gold film was oriented at an angle of0°(a,c,e,g)or45°(b,d,f,h) from one of the polarizers:The concentration of VSV was the following:(a,b)109pfu/mL;(c,d)108pfu/mL;(e,f)107pfu/mL; (g,h)control,0pfu/mL.The insets correspond to conoscopic images of the samples in parts b and d.All images(crossed polars)were obtained immediately after assembly of the liquid crystal cell.Figure8.Optical texture of5CB sandwiched between two poly-L-lysine-treated gold films(obliquely deposited)treated with VSV(109pfu/mL).The sample was oriented such that the direction of deposition of the gold film was oriented at an angle of0°(a)or45°(b)from one of the polarizers.The inset in part b is a conoscopic image.All images(crossed polars)were obtained immediately after assembly of the liquid crystal cell.

2382Langmuir,Vol.20,No.6,2004Tercero Espinoza et

al.

We conclude that the presence of virus in the supernatant of the Vero cells is required for attainment of homeotropic alignment.These conclusions are supported by images of these interfaces that were obtained by using atomic force microscopy(AFM).We observed cationic surfaces incu-bated in solutions of VSV to support both infectious and truncated VS virions.The density of infectious virions was approximately1per square micrometer.The trun-cated form of the virion was more numerous on the surface than the infectious form.A full account of our observations using AFM will be reported elsewhere.

Finally,we note that since the anchoring of5CB on gold surfaces incubated with poly-L-lysine was found to be time-dependent(see above),the anchoring of5CB on cationic surfaces after incubation with virus and control solutions was only investigated immediately(within10 min)after contacting the surfaces with the liquid crystal. Anionic and Nonionic Surfaces Incubated with VSV.We further tested the proposition that the homeo-tropic alignment reported above was caused by VSV captured on the cationic surfaces by preparing anionic (SAMs formed from HS(CH2)2SO3-Na+)and nonionic (SAMs formed from HS(CH2)11(OCH2CH2)4OH)surfaces. If the virus particles were captured on the cationic surfaces by electrostatic interactions between the negatively charged virion and the cationic poly-L-lysine,we hypoth-esized that the anionic and nonionic surfaces would not capture the virus and thus would not give rise to an immediate homeotropic alignment of5CB after exposure of the surfaces to virus.The anchoring of5CB on the anionic surfaces prior to contact with solutions of VSV was discussed above,and the anchoring of5CB on the nonionic surfaces(planar)has been reported elsewhere.3 First,we incubated the anionic surfaces prepared from HS(CH2)2SO3-Na+with solutions containing a titer of1010 pfu/mL of VSV(100times the concentration of VSV required to trigger the planar-to-homeotropic transition of5CB on cationic surfaces)for～4h.We then prepared asymmetric optical cells with these substrates.Examina-tion of these samples under crossed polarizers revealed a dark optical texture when the sample was oriented parallel to either polarizer(Figure9a).A high density of line defects was also visible to the naked eye.Upon rotation of the samples by45°,we observed bright textures.In the case of the sample shown in Figure9b,the texture comprised mainly two colors dispersed across the sample. We attribute these colors to small variations in the tilt angle(<10°)of5CB on the surface.These results lead us to conclude that the anchoring of the liquid crystal on these surfaces is planar or near-planar.

We also contacted anionic surfaces with control solutions prepared as described above and examined the optical textures of5CB supported on these surfaces by using asymmetric optical cells.The textures that we observed under crossed polarizers,when the samples were oriented parallel to either polarizer,were similar to those observed for anionic surfaces contacted with VSV solutions(Figure 9c).Additionally,the textures we observed upon rotation of the samples by45°were bright and exhibited a uniform color.The high density of defects and small color variations

may reflect electrostatic capture of positively charged components from both the control and virus solutions(but likely not VSV because of unfavorable electrostatic interactions).

We performed similar experiments with the nonionic surfaces prepared from HS(CH2)11(OCH2CH2)4OH.For the case of nonionic surfaces incubated with solutions con-were oriented parallel to either polarizer(Figure9e).These textures possessed very few defects.When the samples were rotated by45°,we observed uniformly bright textures consisting of two closely related colors(<5°difference in tilt)(Figure9f).We observed nearly identical textures for 5CB supported on nonionic surfaces incubated with VSV and with control solutions(Figure9g,h).

Figure9.Optical textures of5CB supported on VSV-treated SAMs formed on obliquely deposited gold films.One optical cell comprised a SAM formed from HS(CH2)2SO3-Na+and a second surface formed from octyltrichlorosilane-treated glass (a-d).The second optical cell comprised a SAM formed from HS(CH2)11(OCH2CH2)4OH and octyltrichlorosilane-treated glass (e-h).The samples were oriented such that the direction of deposition of the gold film was oriented at an angle of0°(a,c, e,g)or45°(b,d,f,h)from one of the polarizers.For samples a,b,e,and f,the concentration of VSV was1010pfu/mL;the control samples c,d,g,and h were free of VSV.All images (crossed polars)were obtained immediately after assembly of the liquid crystal cell.

Behavior of Liquid Crystals on Surfaces Langmuir,Vol.20,No.6,2004

2383

within the liquid crystal.It is likely that these differences in defect densities reflect the capture of proteins and other biomolecules on the anionic surface but not on the ethylene glycol terminated surface.The optical textures observed with the anionic and nonionic surfaces incubated with virus and control solutions,however,are both consistent with planar or near-planar alignment of5CB.The planar or near-planar alignment of5CB on the anionic and nonionic surfaces incubated with virus solutions contrasts with the alignment observed on cationic surfaces incubated with VSV solutions(homeotropic).Thus,we conclude that the alignment observed on cationic surfaces after incuba-tion with VSV likely arises from electrostatically bound virus particles(truncated and infectious VSV particles).

Discussion

The principal finding of the study reported in this paper is the observation of homeotropic alignment of liquid crystals on cationic surfaces treated with VSV.The homeotropic anchoring of liquid crystals on cationic surfaces decorated with VSV contrasts to past reports of the anchoring of liquid crystals on proteins bound to surfaces of gold,glass,and polymers.1-3,6-8,32,33In our past studies of proteins specifically bound to functionalized SAMs on gold films,we observed planar or near-planar alignment of5CB in contact with the protein-laden surfaces.1-3Other studies by us have reported planar or near-planar alignment of5CB on surfaces of gold pre-senting a layer of physisorbed protein,and this alignment persisted after a second monolayer of protein was bound to the surface via specific protein-protein inter-actions.8,32,33Similarly,our past studies of the alignment of5CB on glass surfaces with covalently linked proteins have revealed planar or near-planar alignment of the liquid crystal on those surfaces.6,7

In contrast to the above studies of proteins,studies of the alignment on5CB on surfaces supporting other biological materials,such as cells and phospholipids monolayers,have revealed tilted or homeotropic anchoring on those surfaces.9-11,34-36Hiltrop and Stegemeyer have reported that the anchoring of a nematic liquid crystal on Langmuir-Blodgett monolayers of lecithin supported on quartz and glass substrates depends on the surface pressure of the amphiphiles.10,34,35At low surface pressure, the alignment of the liquid crystal was homeotropic and changed to a tilt with increasing surface pressure.These observations were explained in terms of steric interactions between the hydrophobic tails of the amphiphiles with the mesogens comprising the liquid crystal.Fang and co-workers have reported a similar observation of tilted anchoring of5CB on Langmuir monolayers of1-mono-palmitoyl-rac-glycerol,which are closed-packed.9Fur-thermore,the anchoring of the liquid crystal reflected the tilt of the underlying layer of amphiphiles.A possible cause of the homeotropic orientation induced by VSV could be, therefore,interactions between the lipid coat of the virus and the liquid crystal.We note,however,that in the case of Langmuir monolayers of phospholipids,the hydrophobic tails of the phospholipids were directed away from the supporting surface into the liquid crystal.In contrast,the hydrophobic tails of the phospholipids in the viral membrane are directed away from the liquid crystal into the viral membrane(at least prior to contact with the liquid crystal).

Another mechanism that may give rise to homeotropic alignment of5CB on virus-laden surfaces is the formation of an electrical double layer.In the case of the cationic surfaces,we observed homeotropic alignment of5CB after a period of a few days.We interpreted this observation in terms of the formation of an electrical double layer on the cationic surfaces.However,other studies using liquid crystals have reported the formation of electrical double layers on much shorter time scales.30,31Our observations of homeotropic alignment of5CB on virus-laden surfaces could plausibly reflect the formation of an electrical double layer associated with the charge of the virus.

A third possible cause of the homeotropic alignment observed on virus-laden surfaces could be the introduction of relatively large topographical features onto the surface by binding of the virus particles.The theoretical basis for this mechanism was formulated by Berreman in terms of minimization of the elastic energy of the liquid crystal anchored on solid surfaces.37If a nematic liquid crystal aligns parallel to a wavy surface,the geometry of the surface will influence the azimuthal orientation of the nematic director because it is energetically favorable for the director to lie parallel to the grooves(or in the direction of minimum roughness).However,if the surface is equally rough in all azimuthal directions,the liquid crystal may avoid the energetic penalty associated with distortion of the nematic director on the rough surface by aligning perpendicular to the surface(even though it may align parallel to a smooth surface of the same material at the same temperature).AFM measurements performed using surfaces of gold treated with poly-L-lysine and incubated with VSV do show that the surfaces become rough. Incubation of a cationic surface in a solution containing a titer of VSV of109pfu/mL leads to an increase in the root-mean-square(rms)roughness of the interface from ～1.4to12nm(area characterized was5μm×5μm). Surfaces incubated with control solutions possessed an rms roughness of～6nm.A detailed report of the characterization of these interfaces by AFM will be published elsewhere.

Conclusion

In conclusion,we have found that gold films treated with poly-L-lysine(cationic surfaces)induce planar align-ment of5CB immediately after contact with the liquid crystal but progressively change to homeotropic alignment over5days.Similarly,the anchoring of5CB on surfaces of gold supporting SAMs formed from HS(CH2)2SO3-was observed to be initially near-planar but to progressively turn homeotropic over several hours.Because the orien-tation of MBBA was always found to be planar on these surfaces,we conclude that the evolution of5CB to the homeotropic alignment is consistent with the gradual formation of an electrical double layer at these surfaces. In contrast,we found that the surfaces of gold films treated with poly-L-lysine and then incubated with virus solutions of titer g108pfu/mL cause homeotropic align-ment of5CB immediately after contact of5CB with the surface.The anchoring of5CB on negatively charged or neutral surfaces was observed to be planar or near-planar after incubation with virus solutions having concentra-10

(32)Kim,S.-R.;Teixeira,A.I.;Nealey,P.F.;Wendt,A.E.;Abbott,

N.L.Adv.Mater.2002,14,1468.

(33)Skaife,J.J.;Abbott,https://www.sodocs.net/doc/2f16662653.html,ngmuir2000,16,3529.

(34)(a)Hiltrop,K.;Stegemeyer,H.Ber.Bunsen-Ges.1978,82,883.

(b)Hiltrop,K.;Stegemeyer,H.Ber.Bunsen-Ges.1981,85,582.

2384Langmuir,Vol.20,No.6,2004Tercero Espinoza et al.

and nonionic)initially produced planar or near-planar

anchoring of5CB after incubation with solutions depleted

of virus particles.Thus,we conclude that the homeotropic

alignment of5CB on poly-L-lysine-treated gold surfaces

that have been contacted with solutions of VSV of titer

g108pfu/mL reflects the presence of virus particles on the surfaces.The homeotropic alignment of5CB on virus-

laden surfaces contrasts to the alignment of5CB on

protein-laden surfaces(planar).Thus,homeotropic align-

ment of5CB appears to be a signature of the presence of

a critical density of VSV particles on a surface.This

observation suggests that virus particles immobilized on

surfaces via specific antibody-antigen interactions could give rise to homeotropic alignment and thus form the basis of a viral diagnostic.

Acknowledgment.This research was supported by funding from the Office of Naval Research(Presidential Early Career Award for Science and Engineering to N.L.A., Grant N00014-99-1-0250),Materials Research Science and Engineering Center on Nanostructured Materials and Interfaces(Grant NSF-DMR-0079983)at University of Wisconsin,and the Biophotonics Partnership Initiative of NSF(Grant ECS-0086902).The authors thank Maren Daschner for helpful discussions.

LA035774I

Behavior of Liquid Crystals on Surfaces Langmuir,Vol.20,No.6,20042385

如何写先进个人事迹

如何写先进个人事迹 篇一：如何写先进事迹材料 如何写先进事迹材料 一般有两种情况：一是先进个人，如先进工作者、优秀党员、劳动模范等；一是先进集体或先进单位，如先进党支部、先进车间或科室，抗洪抢险先进集体等。无论是先进个人还是先进集体，他们的先进事迹，内容各不相同，因此要整理材料，不可能固定一个模式。一般来说，可大体从以下方面进行整理。 (1)要拟定恰当的标题。先进事迹材料的标题，有两部分内容必不可少，一是要写明先进个人姓名和先进集体的名称，使人一眼便看出是哪个人或哪个集体、哪个单位的先进事迹。二是要概括标明先进事迹的主要内容或材料的用途。例如《王鬃同志端正党风的先进事迹》、《关于评选张鬃同志为全国新长征突击手的材料》、《关于评选鬃处党支部为省直机关先进党支部的材料》等。 (2)正文。正文的开头，要写明先进个人的简要情况，包括：姓名、性别、年龄、工作单位、职务、是否党团员等。此外，还要写明有关单位准备授予他(她)什么荣誉称号，或给予哪种形式的奖励。对先进集体、先进单位，要根据其先进事迹的主要内容，寥寥数语即应写明，不须用更多的文字。 然后，要写先进人物或先进集体的主要事迹。这部分内容是全篇材料

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TPO4-leture1-animal behavior

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主要事迹简介怎么写

员工主要事迹写法： ｘｘ，一个普通的名字。一个平凡的身影，经常出现在酒店的各个区域巡视。他是保安部副主管。 ｘｘ，自20ｘｘ年x月份进入酒店工作以来，一直表现出色，爱岗敬业，努力学习业务知识，也因此由一名普通保安员逐步成长为酒店一名管理人员，在20ｘｘ年x月正式接手保安部副主管一职。同年6月，参加宁波消防安全管理员的培训，并拿到了相应的资格证书。 作为酒店一名基层管理者，他处处起到了模范带头的作用，他的工作态度会影响整个团队，正所谓：火车跑得快，全靠车头带。在日常工作中他不怕困难，勇于承担责任，用在工作上，就是那份执着、坚定、信念。每当这时，他总是憨厚的笑笑：“还是领导有方，我只是一个执行者罢了”！ 20ｘｘ年x月份，根据国家气象局预报的台风预测消息，第9号强台风“梅花”正向本地移动，可能在6日夜间在浙江省中北部沿海登陆，或紧擦宁波市沿海北上，但不管哪种路线都将对宁波造成严重影响。我酒店在林总经理的号召下，立即由工程部张经理带领工程保安部及各部门相关人员迅速成立临时抗台小组。ｘｘ也同时参加了前期各项准备工作，并同相关人员一同在酒店蹲守两个日夜，直至“梅花”绕道离开。他还开玩笑说：“这个日子很特别，七夕情人节碰上了梅超风”。

20ｘｘ年，对于酒店保安部来说，是较为艰辛的一年，由于市场原因，使得保安部人力处于紧张状态，即使如此，他还是较为圆满的完成了部门的各项培训及其它各项工作，并在ｘｘ月份对酒店全员进行了为期三天的消防知识培训，用自己所学到的知识来跟大家一起分享。同月底，在酒店各层领导的组织与鼓励下圆满的完成了消防模拟演习，事后他说：“大家都比我做的好，我还要努力加强学习啊”。 20ｘｘ年底，酒店餐饮客情非常好，餐饮部自身人员不能满足服务需求，需要其他部门帮工跑菜，这个问题也就落在了工程保安部的肩上。每天在厨房都能看到那一身保安制服的跑菜员，不用问，那肯定是ｘｘ。仅x月份，他在做好自己本职工作的同时，利用非当班时间帮工累计56小时。当然也有其他部门的帮工人员，他们都是优秀的，正是有这些非常优秀的员工，使得酒店营业部门顺利完成了各项任务。每当这时，他又会说：“我虽然是过来帮忙的，但我要把它当成自己的本职工作来做”。 20ｘｘ年底，临近春节，好多员工都想回家过年，保安部员工也不例外，但人员紧张怎么办呢，他又给大家做思想工作，同时分开安排人员回家的假期，以保证春节期间的正常排班，保障酒店的正常运行。但谁能知道他在酒店工作三年多了，每年的春节都是在酒店过的，每年的中秋节也都是在酒店过的，难道他不想在佳节时与家人团聚吗?每当这时，他又说：“人员紧张，名额有限，让给他们。呵呵，再说，我是以店为家”，也许这时，他的笑容里带有一丝让人难以察觉的苦涩！