Optimizing the immobilization of gold nanoparticles on functionalized silicon surfaces: amine- vs thiol-terminated silane

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1 Optimizing the immoiliztion of gold nnoprtiles on funtionlized silion surfes: mine- vs thiol-terminted silne Mrou Ben Hddd, Juliette Blnhrd, Sndr Csle, Jen-Mr Krfft, Anne Vllée, Christophe Méthivier, Souhir Boujdy To ite this version: Mrou Ben Hddd, Juliette Blnhrd, Sndr Csle, Jen-Mr Krfft, Anne Vllée, et l.. Optimizing the immoiliztion of gold nnoprtiles on funtionlized silion surfes: mine- vs thiol-terminted silne. Gold ulletin : qurterly review of reserh on gold nd its pplitions in industry, World Gold Counil, 2013, 46 (4), pp < /s y>. <hl > HAL Id: hl Sumitted on 18 Mr 2015

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3 Gold Bull (2013) 46: DOI /s y ORIGINAL PAPER Optimizing the immoiliztion of gold nnoprtiles on funtionlized silion surfes: mine- vs thiol-terminted silne Mrou Ben Hddd & Juliette Blnhrd & Sndr Csle & Jen-Mr Krfft & Anne Vllée & Christophe Méthivier & Souhir Boujdy Pulished online: 17 Novemer 2013 # The Author(s) This rtile is pulished with open ess t SpringerLink.om Astrt Immoiliztion of gold nnoprtiles on plnr surfes is of gret interest to mny sientifi ommunities; hemists, physiists, iologists, nd the vrious ommunities working t the interfes etween these disiplines. Controlling the immoiliztion step, espeilly nnoprtiles dispersion nd overge, is n importnt issue for ll of these ommunities. We studied the prmeters tht n influene this intertion, strting with the nture of the terminl hemil funtion. Thus, we hve refully grfted silnes terminted y either mine or thiol groups strting from minopropyltriethoxysilne (APTES) or merptopropyltriethoxysilne. We lso hnged the hin length for thiol-terminted lyers through ovlent grfting of merptoundenoi id (MUA) on APTESmodified lyers, nd the protool of nnoprtiles deposition to evlute whether other ftors must e tken into onsidertion to rtionlize this intertion. The formed lyers were hrterized y X-ry photoeletron spetrosopy nd gold nnoprtiles deposition ws monitored y snning eletron mirosopy nd surfe-enhned Rmn sttering. We oserved signifint differenes in terms of nnoprtiles dispersion nd density depending on the nture of the hemil lyer on silion. The use of ultrsounds during the deposition proess Eletroni supplementry mteril The online version of this rtile (doi: /s y) ontins supplementry mteril, whih is ville to uthorized users. M. Ben Hddd: J. Blnhrd : S. Csle : J.<M. Krfft : A. Vllée: C. Méthivier : S. Boujdy UPMC Univ Pris 6, UMR CNRS 7197, Lortoire de Rétivité de Surfe, Pris, Frne M. Ben Hddd: J. Blnhrd : S. Csle : J.<M. Krfft : A. Vllée: C. Méthivier : S. Boujdy (*) Lortoire de Rétivité de Surfe, UMR CNRS 7197, Université Pierre et Mrie Curie-Pris VI, 4 Ple Jussieu, Pris edex 05, Frne e-mil: souhir.oujdy@upm.fr ws very effiient to limit ggregtes formtion. The optiml deposition proedures were otined through the use of APTES nd APTES/MUA funtionliztion. They were ompred in terms of overge, dispersion, nd densities of isolted nnoprtiles. The APTES/MUA surfes lerly showed etter results tht my rise from oth the longer hin nd the dilution of thiol end groups. Keywords Gold nnoprtiles. Silion surfe. Silne grfting. Surfe funtionliztion. XPS. Snning eletron mirosopy Introdution The frition of solid sustrtes with gold nnoprtiles ssemlies immoilized on their surfe is urrently the sujet of growing interest euse of the key role these sustrtes ould ply in the development of severl devies [1 3]. The physil nd hemil properties of these devies will depend not only on the size nd shpe of the gold nnoprtiles ut lso on their sptil rrngement nd on the nture of their intertion with the sustrte surfe [4 6]. Biosensors represent one of the res for whih the use of nnoprtiles is ooming. Indeed, iosensors re nlytil tools whose effetiveness is highly dependent on the ury of the mesurement nd thus on its reproduiility [7, 8]. Input from gold nnoprtiles in this re is twofold: on the one hnd, they llow mplifition of the signl trnsdution for mny tehniques nd, on the other hnd, they n provide surfe nnostruturtion [9, 10]. In oth ses, hieving densely pked lyer nd regulr rrngement is ruil to ensure n optiml mplifition while preserving reproduile nd quntittive response of trnsdution tehniques [11, 12].

4 336 Gold Bull (2013) 46: Usully, the nhoring of gold nnoprtiles on the solid sustrtes is rried out y using n intermedite lyer of orgni moleules grfted on the solid surfe, whose terminl funtionl groups re seleted for their eletrostti or hemil intertions with the nnoprtiles [11 16]. These pltforms should lso e stle over time nd the intertion of the nnoprtiles with the surfe should e strong enough to ensure tht the nnoprtiles remins tthed to the surfe during further funtionliztion nd upon utiliztion. The moleules ommonly used for the funtionliztion of oxidized silion wfer or glss slides re orgnosilne with up to three hydrolysle groups (either OR or Cl) tht would ret with the silnols groups from the sustrte surfe nd (t lest) nonhydrolysle group ering the terminl funtion responsile for the intertion with the gold nnoprtiles [17]. Among the lrge vriety of ville orgnosilnes, minopropyltriethoxysilne (APTES; NH 2 (CH 2 ) 3 Si(OCH 2 CH 3 ) 3 ) is, y fr, the most studied surfe modifier (referenes [18 21] nd referenes therein). APTES is reltively esy to hndle thnks to its moderte retivity. Its three hydrolysle ethoxy groups ensure roust nhoring of the silne to the surfe (silniztion step), wheres the mine funtion of the minopropyl group remins ville for further retion. Terminl mine funtions re extensively used for surfe funtionliztion euse they esily ret with id, ldehyde, or thioyntes through ovlent ond. Moreover, mine groups hve ffinity to gold nnoprtiles nd re widely used to immoilize them through eletrostti intertions [4, 11, 14]. The numerous studies deling with the funtionliztion of sili/oxidized silion surfe with APTES hve shown tht the silniztion step is very sensitive towrd experimentl onditions nd tht the finl surfe stte of the modified sustrte depends strongly on temperture, presene of wter, onentrtion of APTES, nd the durtion of the grfting step [18]. In this work, we studied the orgni lyer influene on the grfting of gold nnoprtiles on funtionlized silion sustrtes. Our im ws to find the optiml experimentl onditions for oth n optiml density nd dispersion of gold nnoprtiles on silion surfes. For this purpose, we explored some of the prmeters tht n influene this intertion, strting with the nture of the terminl hemil funtion. In first step, APTES ws used to form mine-terminted silne lyers. Then, strting from merptopropyltriethoxysilne (MPTES), thiol-terminted silne lyers were onstruted. We lso hnged the hin length for thiol-terminted lyers through ovlent grfting of merptoundenoi id (MUA) on APTES-modified lyers. This ltter funtionliztion proedure ws suessfully used y Kminsk et l. to immoilize CTAB-overed nnoprtiles on silion nd reh densely pked lyer [22]. X-ry photoeletron spetrosopy (XPS) nd ontt ngle mesurements were used to hrterize the formed lyers nd the protool of nnoprtile deposition ws modified, prtiulrly using ultrsonition during the deposition of the spheril gold nnoprtiles. The grfting of nnoprtiles ws monitored y surfeenhned Rmn sttering (SERS). Finlly, snning eletron mirosopy (SEM) ws used to ompre gold nnoprtiles overge nd dispersion for the onsidered surfe funtionliztions. Experimentl setion Mterils N-ethyl-N -(3-(dimethylmino) propyl) rodiimide hydrohloride (EDC; 98 %), sodium itrte (HOC(COON) (CH 2 COON) 2 2H 2 O; 99 %), nd gold(iii)hloride trihydrte (HAuCl 4.H 2 O; 99.9 %) were purhsed from Sigm Aldrih. N-hydroxysuinimide (NHS; 97 %), 11-merptoundenoi id (MUA; 95 %), (3-minopropyl)triethoxysilne (APTES; 99 %) nd (3-merptopropyl)trimethoxysilne (MPTES; 95 %) were purhsed from Aldrih nd ethylenedimine (EDA; 99.5 %) from Fluk. Silion wfer <100> from Sigm Aldrih ws ut into 1 1 m 2 piees. Sulfuri id, 96 % (H 2 SO 4 ) nd hydrogen peroxide, 30 % in wter (H 2 O 2 ) were supplied y Crlo Er. Toluene, etone, nd ethnol were purhsed from Anlr Normpur. MilliQ wter (18 MΩ, Millipore, Frne) ws used for the preprtion of the solutions nd for ll rinses. All hemils were regent grde or higher nd were used without further purifition. Surfe hemistry First, silion surfes were lened following proedure whih inludes severl wshing step, tretment with pirnh solution, nd finlly tretment with UV ozone. A detiled desription of this proedure is given in referene [18]. The sme experimentl onditions were pplied for silne grfting for the mine-terminted silne (APTES) nd for the thiol-terminted one (MPTES): the surfe oxidized nd lened silion wfer ws immersed in 50 mm solution of silne in nhydrous toluene t 75 C for 24 h. After silniztion step, the smples were wshed twie, sonited for 10 min in nhydrous toluene, dried under nitrogen, nd heted t 90 C for 2 h. The MUA grfting ws hieved fter APTES deposition on silion surfes. First, MUA solution ws tivted using mixture of EDC nd NHS in ethnol during 90 min nd then the APTES-modified silion surfes were pled in the tivted solution of MUA for 90 min, then wshed twie in ethnol nd dried under nitrogen.

5 Gold Bull (2013) 46: Gold nnoprtiles preprtion nd deposition Citrte-stilized gold nnoprtiles (GNPs) were prepred ording to the stndrd method developed y J. Turkevih nd o-workers nd refined y G. Frens. Detils on solution storge nd prtiles dispersion re given in referenes [11, 12]. Freshly synthesized Au NPs were then deposited, with no further dilution, on the modified silion surfes for 2 h either using gentle gittion or using sonition th (Elm, 90 W, 45 khz). Silion sustrtes were then wshed twie in wter nd dried under nitrogen. Chrteriztion tehniques TEM Trnsmission eletron mirosopy mesurements were performed using JEOL JEM 1011 mirosope operting t n elerting voltge of 100 kv. The trnsmission eletron mirosopy (TEM) grids were prepred s follows: typilly 1.5 ml of the solution ws entrifuged t 10,000 rpm (equivlent to 11,200 reltive entrifugl fores) for 10 min to preipitte the prtiles. The olorless superntnt ws disrded. The hevy residue ws redispersed in suitle volume of deionized wter depending on the quntity of the residue. Of this redispersed prtile suspension, 2 μl ws pled on ron-oted opper grid nd dried t room temperture. SEM Snning eletron mirosopy imges of the gold nnoprtiles on the modified silion wfers were otined using SEM FEG Hithi SU-70 snning eletron mirosope with low voltge of 1 kv nd distne of mm; the seondry eletron detetor in Lens ws used. The distriution of gold nnoprtiles on the surfes ws estlished onsidering 1,000 1,500 prtiles. Contt ngle mesurements Stti wter ontt ngles were mesured t room temperture using the sessile drop method nd imge nlysis of the drop profile. The instrument, whih uses CCD mer nd n imge nlysis proessor, ws purhsed from Krüss (Germny). The wter (Milli-Q) droplet volume ws 1 μl nd the ontt ngle (θ) ws mesured 5 s fter the drop ws deposited on the smple. For eh smple, the reported vlue is the verge of the results otined on three droplets nd the overll ury in the mesurements ws etter thn ±5. XPS XPS nlyses were performed with PHOIBOS 100 X- ry photoeletron spetrometer from SPECS GmH (Germny) with n monohromted Al Kα X-ry soure (hν=1,486.6 ev), operting t Torr or less, in fixed nlyzer trnsmission nlysis mode with 7 20 mm entrne slit, leding to resolution of 0.1 ev. A 10 ev pss energy for the survey sn nd 10 ev pss energy for the smll regions were pplied. The spetr were fitted using Cs XPS softwre (version , Cs Softwre, UK). SERS Surfe-enhned Rmn sttering spetr were reorded in the 500 1,900 m 1 rnge on modulr Rmn spetrometer (Model HL5R of Kiser Optil Systems, In.) equipped with high-powered ner-ir lser diode working t 785 nm. Before spetr quisition, n optil mirosope (Olympus; ojetive, 50) ws used to fous the lser em. Mesurements were rried using n ojetive 100. The lser output power ws 10 mw, whih orresponds to 1 mwon smples. For eh spetrum, 30 quisitions of 5 s were reorded to improve the signl-to-noise rtio. To ensure representtive hrteriztion of surfes, minimum of three mesurements were tken on different prts of the surfe. Results nd disussion Silne grfting nd surfe hrteriztion Gold nnoprtiles re ommonly immoilized on mineterminted lyers, through eletrostti intertion or on thiol-terminted lyers through ovlent onds. These two termintions were ompred herein through the use of APTES or MPTES for silniztion. Adding MUA on the APTES lyer would led to longer hin terminted lso y thiol funtion, nd thus enling us to estlish the influene of n dditionl prmeter, nmely, the hydroron hin length. The three hemil modifition of silion surfes re shown in Fig. 1. In first stge, the effiieny of silne inding nd further hemil grfting ws investigted through ontt ngle mesurements nd XPS nlysis of the funtionlized silion surfes. Contt ngle mesurements were performed to investigte the hydrophili hrter of the three funtionlized silion surfes. The pitures otined with the CCD mer nd the orresponding ngles re shown in Fig. 2. The initil len silion surfe (Fig. 2) ws very hydrophili nd the ontt ngle (<10 ) ould not e mesured due to drop spreding. This result onfirms the effiieny of the pplied lening proedure to remove the orgni ontminnts from the surfe [23]. Upon APTES grfting (Fig. 2), the mesured ontt ngle ws 83, inditing hydrophoi lyer. This result is in greement with previously oserved vlues [18], the hydrophoi hrter, in pprent ontrdition with the hydrophili terminl mine funtions, is proly due to the folding of mine terminl funtion to form H onds with free silnol groups [24]. For the MPTES funtionliztion, the ontt ngle ws lower thn for

6 338 Gold Bull (2013) 46: Fig. 1 Shemti desription of the three funtionlized surfes NH 2 NH 2 NH 2 SH SH SH SH SH SH APTES MPTES APTES/MUA APTES-modified surfes ( 61 ). This higher hydrophiliity my e due to the lower tendeny of sulfur to form hydrogen onds; whih ould indue less folding of the silne hins. But nother possiility, tht will e disussed herefter, on XPS dt sis, is the inomplete overge of silion surfe y MPTES; this would indeed lower ontt ngle vlues s the mesured vlue will inlude ontriution of the hydrophili-re silion oxide. Finlly, upon grfting MUA on the APTES-modified lyer, n even lower ontt ngle ws reorded, 40, suggesting higher hydrophili hrter of the resulting surfes. The inrese of hydrophili hrter with hin length ws oserved likewise y Wssermn et l. upon ssemling hlorolkylsilnes on silion surfes [25]. The most likely explntion is the inrese of the lyer rystllinity nd orgniztion due to the inrese of Vn der Wls intertions etween lkyl hins [26]. This higher rystllinity would redue the folding of the terminl groups, thus exhiiting the hydrophili prt of the grfted moleule on the upmost of the surfe [27]. The modified silion surfes were lso hrterized y XPS nlysis. The min XPS spetr re shown in Fig. 3.On ll the survey spetr, in ddition to the silion nd oxygen peks rising from silion wfers nd the sili lyer, ron, nitrogen, nd sulfur for APTES/MUA- nd MPTES-modified surfes were present. On the Si 2p peks, shown in Fig. 3, two ontriutions were oserved; the first one t 99 ev, rises from ulk silion wfer Si 0, nd the seond ontriution t higher inding energy, 103 ev is ttriuted to Si IV in oth oxide lyer nd grfted silnes. The rtio Si ox /Si 0 ws lulted to ompre silne overge, ssuming the sili lyer ws similr in ll ses. For the three surfes, the vlues were very lose, 0.64, 0.62, nd 0.56, for APTES, MPTES, nd APTES/MUA, respetively, suggesting similr verge overges with silnes, nd not enling preise omprison of the mounts of grfted silnes. The N 1s peks inluded two ontriutions ttriuted to mine groups [C NH 2 ] (t ev) nd protonted mines C NH 3 + (t ev). The shpe of this pek ws modified Fig. 2 Stti wter ontt ngles pitures, nd orresponding ngles; lened (oxidized) silion wfer, silion-grfted APTES, silion-grfted MPTES, nd d silion-grfted APTES/MUA

7 Gold Bull (2013) 46: ps Si2p N1s Binding Energy (ev) 400 ps 1000 ps S2p lrge exess of MUA in solution, only. 24 % of mine groups hve reted with the id funtion of MUA. Therefore, thiol-end groups on these surfes re diluted nd four times less numerous thn mine funtions on APTESmodified surfes. In ddition, the integrtion of the S2p for oth APTES/MUA nd MPTES led to similr mounts of sulfur. Therefore, the use of MPTES would hve led to silne overge four times lower thn the use of APTES. This low vlue is not surprising s it ws estlished thn the terminl mine groups of APTES t s tlysts for silne retion with silnols, thus enhning the effiieny of grfting [24, 29]. We onfirmed these oservtions y performing the MPTES grfting using smll mount of ethylenedimine s tlyst. The XPS results (see Eletroni supplementry mteril (ESM) 1) showedninreseof sulfur mount y ftor of 3.7, inditing silne over lose to tht otined for APTES. Gold nnoprtiles deposition nd hrteriztion Binding Energy (ev) Binding Energy (ev) Fig. 3 XP spetr Si 2p, N1s, nd S2p signls fter APTES (), APTES/ MUA (), nd MPTES () grfting on silion surfes upon grfting MUA, ut it is diffiult to disriminte the ontriution of mide nitrogen [C=O) NH] from the mine one [28]. The S 2p spetr showed the S 2p doulet t nd ev for S 2p 3/2 nd 2p 1/2, respetively, orresponding to the sulfur in the SH groups. For the APTES/MUA-modified surfe, the rtio S/N lulted using S 2p nd N 1s pek ws Thus, despite the Before interting with the silne lyers, the solution of gold nnoprtiles ws hrterized y UV visile spetrosopy. On this spetrum (see ESM), nrrow plsmon nd ws present t 525 nm, inditing homogeneous prtile size of 13 nm [30, 31]. Gold nnoprtiles size nd distriution were lso onfirmed y TEM imges (see ESM 1). Figure 4 shows the Rmn spetr of funtionlized silion surfes efore nd fter gold nnoprtiles deposition. On the Rmn spetrum of the funtionlized silion surfe efore the deposition of GNPs, the virtion nds of silnes ould not e seen nd only silion signl ws oserved round 500 nd 1,000 m 1 for the sili lyer. After gold nnoprtiles deposition, SERS effet is expeted [32, 33]. For the three funtionlized surfes, Rmn signl ws oserved, evidening the grfting of gold nnoprtiles [34, 35]. Fig. 4 Rmn spetr otined for gold nnoprtiles deposited on silion surfes modified y APTES/MUA (), APTES (), nd MPTES (). d Silne lyers prior to gold nnoprtiles deposition E-4 (u) d Rmn Shift (m -1 )

8 340 Gold Bull (2013) 46: Fig. 5 SEM imges of silion surfes fter nnoprtile deposition without () nd with ( nd ) sonitiononaptes, MPTES, nd APTES/MUA APTES MPTES APTES/MUA 500 nm 500 nm 500 nm The min nds oserved on SERS spetr rise from the hrteristi nds of itrtes nd minly of the roxylte groups etween 1,200 nd 1,600 m 1 [11, 36]. The ν (C C) rising from itrtes nd silne ron hin formed mssif of nds in the region 900 1,100 m 1. Some differenes, relted to the different underlyer ompositions, were oserved nd highlighted on the figure. On APTES/MUA, nds were present orresponding to ν (C S) G t 630 m 1 nd ν (C S) T t 700 m 1, whih is sent from the APTES spetrum. The intensities of the nds t 800 nd 1,040 m 1 rising from mine funtions were modified upon MUA grfting on APTES nd n dditionl nd, mide II, ppered t 1,552 m 1 [37]. Considering the itrtes nds, the intensity of the signl ws dependent on the system: While APTES- nd APTES/ MUA-modified surfes led to similr intensities; the MPTES-modified surfes exhiited lower exlttion. This my e due to lower overge of GNPs s disussed elow. Figure 5 shows SEM imges reorded fter deposition of gold nnoprtiles on APTES-, APTES/MUA-, nd MPTESmodified silne surfes. In Fig. 5, the imges otined when nnoprtile deposition ws rried out with gentle gittion re shown. The highest overge in gold nnoprtiles ws lerly oserved on APTES/MUA-modified surfes. However, for the three surfe funtionliztion nnoprtiles, ggregtes re lerly oservle with this deposition proedure. When gold nnoprtiles deposition ws done under sonition, the lrgest nnoprtiles ggregtes were removed on oth APTES nd APTES/MUA surfes. On these two systems, the dispersion ws lso lerly improved. The GNPs overge on APTES ws onsiderly inresed. On MPTES lyers, no signifint improvement ws oserved using the sonition th. The sme results were otined upon depositing the nnoprtiles on the MPTES tlyzed y ethnedimine with or without sonition (imges in the ESM 1). The sulfur density t silion surfe is therefore not determining ftor for this system. Despite the improved dispersion nd the removl of the lrgest ggregtes, loser inspetion of the SEM imges t higher mgnifition (Fig. 5) showed the presene of smll ggregtes espeilly on APTES lyers. To ompre effiiently the dispersion on APTES nd APTES/MUA lyers, prtile distriutions were quntified for these two funtionliztions nd re presented s histogrms in Fig 6. % of prtiles Fig. 6 Gold nnoprtiles distriution on APTES/MUA (drk) nd on APTES (right)-modified lyers

9 Gold Bull (2013) 46: The omprison of the ggregte size distriution for the two funtionlized surfes lerly showed tht the APTES/ MUA funtionliztion llowed etter dispersion of the gold nnoprtiles with lrge frtion of isolted prtiles wheres, on the APTES funtionlized surfe, the nnoprtiles formed higher mount of lrge ggregtes. This etter dispersion of gold nnoprtiles on the MUA/APTES lyer my result from the dilution of terminl funtions on this system, 24 % SH on MUA/APTES vs 100 % NH 2 on APTES. Indeed, similr ehvior ws oserved using mixed thiol selfssemled monolyers to immoilize proteins: the dispersion ws etter when the terminl funtions were diluted [38, 39]. The length of the lkyl hin indues lso etter flexiility of the orgni lyer tht proly fvors nnoprtiles inding ompred to the MPTES lyer [8]. Conlusion We studied the orgni lyer influene on the grfting of gold nnoprtiles on funtionlized silion sustrtes. To this im, we grfted silnes terminted y either mine or thiol groups strting from APTES or MPTES. A third lyer, lso terminted y thiol funtion, ws onstruted y ovlent tthment of MUA on APTES-modified lyers. XPS hrteriztions onfirmed the suessful grfting of APTES nd MPTES on silion surfes. Upon dding MUA to the APTES-modified lyers, only 24 % of the mine funtions reted. Spheril gold nnoprtiles were then deposited on these lyers. SEM reveled tht sonition during the deposition proedure limited the presene of ggregtes on the surfes. The higher overge in gold nnoprtiles ws oserved on APTES nd APTES/MUA lyers. SEM imges lso showed tht gold nnoprtiles dispersion ws etter on APTES/MUA thn on APTES, with lrger frtion of isolted prtiles nd few ggregtes. This system likely enefits from oth the dilution of terminl funtions, 24 % SH, nd the flexiility of the orgni lyer. Aknowledgments This work finnilly supported y the Agene Ntionle de l Reherhe NArBIoS projet (ANR-DFG progrm; grnt numer: ANR-11-INTB-1013). The uthors re grteful to Clire- Mrie Prdier for her interest in the work. Open Aess This rtile is distriuted under the terms of the Cretive Commons Attriution Liense whih permits ny use, distriution, nd reprodution in ny medium, provided the originl uthor(s) nd the soure re redited. Referenes 1. Srdr R, Funston AM, Mulvney P, Murry RW (2009) Lngmuir 25: Ho XD, Kirk AG, Trizin M (2007) Biosens Bioeletron 23: Dniel MC, Astru D (2004) Chem Rev 104: Zheng J, Zhu Z, Chen H, Liu Z (2000) Lngmuir 16: Hes AJ, Vn Duyne RP (2004) Anl Bionl Chem 379: Ghosh SK, Pl T (2007) Chem Rev 107: Lupp PB, Sokoll LJ, Chn DW (2001) Clin Chim At 314: Boujdy S, Bntegnie A, Brind E, Mrnet P-G, Slmin M, Prdier C-M (2008) J Phys Chem B 112: Hutter E, Fendler JH (2004) Adv Mter 16: Llnder CH, Zheng Y, Dhuey S, Crini S, Bh U (2010) ACS Nno 4: Morel A-L, Boujdy S, Méthivier C, Krfft J-M, Prdier C-M (2011) Tlnt 85: Morel A-L, Volmnt R-M, Méthivier C, Krfft J-M, Boujdy S, Prdier C-M (2010) Colloids Surf B Biointerfes 81: Zhong Z, Ptskovskyy S, Bouvrette P, Luong JHT, Gednken A, Phys J (2004) Chem B 108: Aureu D, Vrin Y, Roodenko K, Seitz O, Pluhery O, Chl YJ (2009) J Phys Chem C 114: Khire VS, Lee TY, Bowmn CN (2007) Mromoleules 40: MNlly H, Jnes DB, Ksihtl B, Kuik CP (2002) Superlttie Mirost 31: Gooding JJ, Cimpi S (2011) Chem So Rev 40: Aissoui N, Bergoui L, Lndoulsi J, Lmert JF, Boujdy S (2012) Lngmuir 28: Kim J, Cho J, Seidler PM, Kurlnd NE, Ydvlli VK (2010) Lngmuir 26: Psternk RM, Rivillon Amy S, Chl YJ (2008) Lngmuir 24: Howrter JA, Younglood JP (2006) Lngmuir 22: Kminsk A, Iny-Agh O, Forster RJ, Keyes TE (2008) Phys Chem Chem Phys 10: Mittl KL (1979) Surfe ontmintion. In: Mittl KL (ed). Springer, New York, pp Knn SM, Tze WTY, Tripp CP (2002) Lngmuir 18: Wssermn SR, To YT, Whitesides GM (1989) Lngmuir 5: Love JC, Estroff LA, Krieel JK, Nuzzo RG, Whitesides GM (2005) Chem Rev 105: Vllée A, Humlot V, Al Housseiny R, Boujdy S, Prdier C-M (2013) Colloids Surf B Biointerfes 109: Merier D, Boujdy S, Anni C, Villnneu R, Prdier C-M, Proust A (2012) J Phys Chem C 116: Blitz JP, Murthy RSS, Leyden DE (1987) J Am Chem So 109: Turkevih J, Hillier J, Stevenson PC (1951) Disuss Frdy So 11: Seitz O, Chehimi MM, Cet-Deliry E, Truong S, Felidj N, Perruhot C, Greves SJ, Wtts JF (2003) Coll Surf A: Physiohem Eng Aspets 218: Grr KC, Freemn RG, Hommer MB, Ntn MJ (1995) Anl Chem 67: Chumnov G, Sokolov K, Gregory BW, Cotton TM (1995) J Phys Chem 99: Moskovits M (2005) J Rmn Spetros 36: Tin ZQ (2005) J Rmn Spetros 36: Bntz KC, Nelson HD, Hynes CL (2012) J Phys Chem C 116: Rihrd Allen N (2001) Interpreting infrred, Rmn, nd nuler mgneti resonne spetr. Ademi, Sn Diego, pp Brind E, Gu C, Boujdy S, Slmin M, Herry JM, Prdier CM (2007) Surf Si 601: Théult P, Boujdy S, Sénéhl H, Prdier C-M (2010) J Phys Chem B 114: