Control of fluorescence in quantum emitter and metallic nanoshell hybrids for medical applications

Transcription

1 Cotol of fluoesee i quatum emitte ad metalli oshell hyids fo medial appliatios Mahi R. Sigh 1, Jiaoha Guo 1, José M. J. Cid 1,, Jesús E. De Hoyos M. 1 Depatmet of Physis ad Astoomy, The Uivesity of Weste Otaio, Lodo N6A K7, Cada Posgado, Faultad de Aquitetua y Diseño Uivesidad Autóoma del Estado de Méxio, Tolua 50110, Méxio Astat: We study the light emissio fom quatum emitte ad doule metalli oshell hyid systems. Quatum emittes at as loal soues whih tasmit thei light effiietly due to a doule oshell ea field. The doule oshell osists a dieleti oe ad two oute oshells. The fist oshell is made of a metal ad the seod spae oshell is made of a dieleti mateial o huma seum alumi. We have alulated the fluoesee emissio fo a quatum emitte-doule oshell hyid whe it is ijeted i a aimal o huma ody. Sufae plasmo polaito esoes i the doule oshell ae alulated usig Maxwell s equatios i the quasi-stati appoximatio ad the fluoesee emissio is evaluated usig the desity matix method i the pesee of dipole-dipole iteatios. We have ompaed ou theoy with two fluoesee expeimets i hyid systems i whih the quatum emitte is Idoyaie Gee o ifaed fluoeset moleules. The oute spae oshell of doule metalli oshells osist of silia ad huma seum alumi with vaiale thikesses. Ou theoy explais the ehaemet of fluoesee speta i oth expeimets. We fid that the thikess of the spae oshell laye ieases the ehaemet whe the fluoesee deeases. The ehaemet of the fluoesee depeds o the type of quatum emitte, spae laye ad doule oshell. We also foud that the peak of the fluoesee spetum a e shifted y hagig the shape ad size of the oshell. The fluoesee speta a e swithed fom oe peak to two peaks y emovig the degeeay of exitoi states i the quatum emitte. Hee usig these popeties oe a use these hyids as sesig ad swithig devies fo appliatios i mediie. I: Itodutio Nole-metal opatiles ae kow to ehae emissio ates of quatum emittes (s) sigifiatly y deeasig thei adiative lifetime ad ieasig thei quatum yield [1-7]. The ehaemet of the emissio i s suh as moleula fluoophoes is a highly useful stategy fo impovig detetio sesitivity ad seletivity i may emegig appliatios, iludig DNA seeig [5], sigle moleule detetio [6] ad image ehaemet [7]. Cosequetly, desigig ad developig ad metalli opatile hyids to ehae moleula fluoesee is of oad iteest ad applied impotae. Thee is osideale iteest to study hyid systems made of ioompatile fluoeset moleules ad metalli doule oshells 1

2 (Ds) fo iomedial imagig ad fo the detetio of disease makes i the ea-ifaed wavelegth egio [8]. The peetatio depth of ea-ifaed light is lage i most iologial media. It is foud that these hyids have lage asoptio oeffiiets ad high quatum yields i the fa-ifaed egio [9, 10]. Theefoe, these hyids a e used potetially fo imagig deeply ito the ogas ad soft tissues of livig systems. They a also e used as agets fo otast ehaemet ad i physiologial eviomets [11]. Reetly Badha et al. [9] have faiated a -D hyid system to study the ea-ifaed fluoesee (FL). As they used Idoyaie Gee (ICG), whih is a fluoeset moleule. Cuetly it is the oly FDA-appoved ad ommeially availale ea-ifaed-emittig dye. It is also used extesively as a fluoeset make i liial imagig appliatios [1] suh as the diagosis of adia ad hepati futio [1], measuemet of plasma volume ad optial tomogaphy [14]. Howeve, ICG is a elatively weak fluoophoe with a quatum yield of oly 1.% [15] ad its toxiity limits the maximum oetatio admissile fo liial uses. The D is faiated fom a silia oe, a fist Au oshell ad a seod silia oshell elosig Au oshell. The seod oshell is alled the spae laye. We deote this D as SiO Au SiO. Susequetly ICG moleules ae deposited oto the spae laye to omplete the ICG-D hyid. I this aagemet fluoesee ehaemet of ICG moleules is oseved as a futio of the distae fom the sufae of the D hyid. The distae etwee ICG moleules ad the D sufae is otolled y vayig the thikess of the spae laye. The ehaemet of the asoptio ad FL emissio of s will lead to sigifiat impovemets i the detetio limits of the ea ifa-ed fluoesee ased imagig. Fo example, oe a use these hyids fo detetio of sigifiatly smalle tumo volumes tha it is uetly possile. Badha et al. [10] have also ivestigated the FL emissio i IR800 moleules whe they ae plaed o the spae laye of a D. Hee the D osists of a silia oe, Au oshell ad o oute spae laye. I this ase the spae laye is faiated fom huma seum alumi (HSA) ad its thikess vaies fom 5 m to 11 m. We deote this D as HSA Au SiO. IR800 moleules, whih at as s, ae deposited o the HAS laye to faiate the IR800-D hyid. HSA is a lage multidomai potei elevat to may physiologial futios ad has ee ojugated to Au opatiles extesively fo ell-tagetig appliatios [16, 17]. It ids to Au y eletostati attatio etwee the amie goups of HSA ad the egative hage o the gold sufae. The HSA ats as oth a spae laye as well as a like fo IR800 moleules. Badha et. al have measued the fluoesee ehaemet of IR800 moleules. They foud that the quatum yield of IR800 is ehaed as the thikess of the HSA laye is deeased. I this pape, we study the fluoesee emissio fom -D systems i whih s at as loal soues ad tasmit thei light effiietly i the pesee of the D. The D exhiits uique ad emakaly useful optial popeties duig exitatio of sufae plasmo polaitos (SPPs). SPP exitatios emit sigifiatly ehaed loal fields ea the sufae of the metalli shell. This field iteats with the exitos of s ad gives ise to fudametally iteestig physial pheome fo sesig ad swithig of the fluoesee emissio. We have alulated SPPs fo SiO -Au-SiO ad HAS-Au-SiO doule oshells usig Maxwell s equatios i the quasi-stati appoximatio. We have foud two SPP esoe eegies due to the two itefaes peset i these hyids. It is foud that the loatios of SPP esoes i these hyids a e maipulated y hagig the size ad shape of the metalli shell. We have also alulated the FL emissio i -D hyids usig the desity matix method. The iteatio etwee exitos

3 i the ad SPPs i the D was iluded i the FL evaluatio. This iteatio is also alled the dipole-dipole iteatio (DDI). Whe this hyid is ijeted i a aimal o huma ody, it is suouded y iologial ells suh as ae ells. The effet of iologial ells has also ee iluded i the FL ad SPPs evaluatios. Filly, we have ompaed ou theoy with the fluoesee emissio of IGL-D hyid [9]. Hee the D is made fom silia oe, Au-oshell ad the silia spae laye. The IGL moleules ae deposited o the sufae of the Au-D. We have also ompaed ou theoy with the seod hyid IR800-D [10]. I this ase the D is faiated fom a silia oe, Au-oshell ad a HAS spae laye. The IR800 moleules ae deposited o the HSA laye. I ou alulatios, we have osideed that IR800 ad IGL moleules have two degeeate exitos whih ae iteatig with SPPs of the D. Good ageemet etwee ou theoy ad the expeimetal liteatue data is foud whe the distae etwee the ad D is vaied. We have also alulated the fluoesee fo a whih has two o-degeeate exitos. We foud that the FL spetum splits fom oe peak to two peaks i the pesee of exito-spp ouplig (i.e. DDI). These iteestig fidigs may e useful i the faiatio of osesos ad oswithes fo appliatios i mediie. II: Polaizaility ad sufae plasmo polaitos of doule metalli oshells I this setio, we alulate the polaizaility ad SPP esoe fequeies. Fo this we model the D as osistig of a dieleti oe, a metalli oshell ad a oute spae laye oshell. The D has a spheoidal shape. s ae deposited o the spae laye to omplete the -D hyid. We deote the oe, the metalli oshell ad the spae laye as 1, ad, espetively. Dieleti ostats fo the oe, metalli oshell ad the spae laye ae deoted as, ad, espetively. The hyid is assumed to e ijeted ito a huma o aimal ell. This meas that the hyid is suouded y io-ells ad the dieleti ostat of io-ells is deoted as. We deote the volumes of the oe, metalli shell ad oe ad D as V 1, V ad V, espetively. A shemati diagam of the D is depited i fig. 1. At the itefae etwee the metalli shell ad the oe sufae plasmo polaitos (SPPs) ae peset. Similaity, SPPs ae also foud at the itefae etwee the spae laye ad the metalli shell. SPP esoe fequeies ae alulated fom the polaizaility of the D. Hee we alulate the polaizaility of the D as follows. A poe lase light with fequey ω, wavelegth λ ad eleti field is applied to the D. The typial size of the D is less tha oe huded ometes. The wavelegth of light i the visile egio is of the ode of seveal huded ometes. This meas that the size of the D is muh smalle tha the wavelegth of light. Hee, we oside that the amplitude of eleti field is ostat ove the D. This is kow as the quasi-stati appoximatio [18-0]. Solvig Maxwell s equatios i this appoximatio ad usig the tasfe matix method, the polaizaility α of the D is foud as 0 V (1)

4 Fig. 1: (A) Shemati diagam of the doule oshell. The dieleti ostats of the ie oe mateial, metalli oshell ad the spae laye ae deoted as 1, ad espetively. The D is doped ito a io-ell with dieleti ostat. s ae deposited o the sufae of the D. The distae etwee the D ad is deoted as. (B) The eegy levels of the D ad WE ae plotted. The has two exitoi states ω a ad ω a, the D has two loalised SPP states ad. whee 0 is the vauum pemittivity ad ς is alled the polaizaility fato whih has the followig fom Paametes appeaig i eq. () ae alulated as 4 () (a) () (4a)

5 (4) with = V / V ad 1 = V 1 / V. Paamete ξ i is alled the depolaizatio fato ad depeds o the shape of the D. Its expessio is otaied as [19] V ds i (5) i 0 1/ s L / 1/ ix s Liy s Liz whee L ix, L iy ad L iz with i =1,, ae the legth, width ad thikess of the i th mateial, espetively. Note that it is a dimesioless quatity. We a also alulate the polaizaility fo the spheially shaped D fom eqs. (1-5). We oside that the adii of the oe, metalli shell ad D ae deoted as, ad, espetively. The expessio of the polaizaility is foud as 4 R (6) 0 whee ς is alulated as 1 R R (7) R R R R 1 R1 R 1 1,, (8) Note that the aove expessio depeds o the adii of the D. Hee the polaizaility depeds o the adii ad the dieleti ostats of the ostituets of the D. We use the Dude model fo the dieleti futio of the metalli shell i the fom: p i m whee is the plasmo fequey of the metal ad is its elative pemittivity at vey lage eegies. is alled the deay ate ad epesets the themal eegy loss i the metalli shell. The sigulaity i the polaizaility gives the loatios of SPP fequeies ad a e foud y equatig the deomito of the polaizaility fato to zeo. The D stutue has two sufae plasmo polaitos popagatig withi the two itefaes. Let us deote the SPP fequey (wavelegth) at the itefae etwee the metalli shell ad the oe as ( ), ad etwee 5

6 the metalli shell ad the spae laye as ( ). Note that the polaizaility fo the spheoidal give i eq. () depeds o, 1 ad ξ i. This meas y adjustig the shape of the D, the SPP esoe wavelegths a e made lage tha the size of the D. These esoes a e vaied fom UV to IR wavelegths of light. III: Fluoesee ad exito-ssp iteatio I this setio, we alulate the FL emissio spetum fo the i the -D hyid usig the desity matix method i the pesee of exito-spp iteatio. The has exitos (eleto-hole pais) ad the D otais SPPs. These iteat with eah othe via dipole-dipole iteatios (DDI). We oside that the has thee-levels deoted as, ad. It has two exitos with fequeies (wavelegths) ω a ( ) ad ω a ( ), whih ae due to the tasitios ad, espetively. A shemati diagam of the is show i fig. 1. We apply a poe field to moito the FL emissio due to the tasitios ad. Due to the poe field a idued polaizatio is eated i the D as PSP αspe P whih i tu podues a SPP dipole eleti field (E SP ) at a distae fom the ete of the D. It is foud that [0, 1] = g P g V E l SP l SP E p (10) The ostat g l is alled the polaizatio paamete ad has the values g l = -1 ad g l = fo ad, espetively. Note that the SPP eleti field depeds o the polaizaility fato. The polaizaility fato has its lagest values at ad, ad they ae deoted as ad, espetively. Fo othe values the polaizaility fato is egleted sie its effet i the alulatio of the FL will e egligile. Theefoe, the SPP eleti field give i eq. (10) a e expessed as = + whee ad oespod to ad, espetively. Note that the SPP eleti field depeds o the distae fom the D. Let us fist alulate the iteatio Hamiltoia etwee the ad the D. The poe ad SSP eleti fields ae fallig o the. Hee the total field see y the a e expessed as E = E P E SP E SP The poe ad SPP fields idue dipoles i the due to exito tasitios ad. Hee these idued dipoles iteat with the applied eleti fields ad this iteatio is alled the exito-spp iteatio. The Hamiltoia fo this iteatio is expessed i the dipole ad otatig wave appoximatio as 6

7 H exspp E,, P,, glv 4,, h.. glv 4 whee h.. stads fo the Hemitia ojugate ad with, is the exito eatio opeato. Hee is alled the Rai fequey whih is assoiated with the tasitio. The fist tem i Eq. (1) is the Hamiltoia of the. The seod tem is the iteatio etwee the exito ad the extel poe field E p. The thid tem is due to the iteatio of dipoles of the with the dipoles of the D (i.e. SPPs). This tem is also alled the DDI eause idued dipoles i ad idued dipoles i the D iteat with eah othe. We oside that the SPP fequey lies lose to exito fequey ω a. Similaly, the SPP fequey lies lose to exito fequey ω a. We oside that exitos i the deay fom exited states ad to the goud state ad lose eegy due spotaeous emissio. This is alled the adiative deay ate. It is also osideed that exitos deay due to the exito-spp iteatio ad lose eegy to the D. This is kow as the odiative deay ate. The deay iteatio Hamiltoia a e witte i the seod quatized otatio usig the otatig wave appoximatio as H it k, V k a k V a h.., whee V ad V ae ouplig ostats fo the adiative ad odiative iteatios, espetively. They ae foud as (1) V V k i 0 V 1/ 1/. e k (14) glv i., ek (15) 0 V 4 whee is the idued dipole momet due to the tasitio, opeato a k is the photo aihilatio opeato, opeato is the SPP aihilatio opeato ad V is the volume of the. Usig the maste equatio fo the desity matix [0-4] ad Eqs. (1, 1) fo the Hamiltoia of the system, we otaied the followig equatios of motio fo the desity matix elemets d dt d dt a i a i (16a) a i a i (16) 7

8 da dt da dt d dt a a ( aa ) i( ) i (16) a a ( aa) i( ) i (16d) a i a i ( ) (16e) Paametes appeaig i eq. (16) ae foud as a a i i i (17) Hee a ad a ae alled poe field detuigs. Physial quatities ad ae deay ates of levels ad, espetively, ad ae foud as, (18) Hee ad with =, ae adiative ad odiative deay ates, espetively. They ae foud as a a 4 0 a a 4 0,, glv 4 glv 4 (19) Note that the adiative deay ate depeds o the SSP fequey ad the distae etwee the ad the sufae of the D. Filly, we alulate the expessio of the FL emitted fom the. The method fo this has ee developed fo opatiles i efeee [1]. Hee we use this method to develop a theoy fo the peset pape. Followig the method of efeee [1] we have evaluated the FL expessio fo the -D hyid system as L Q W 8

9 whee L W Q W a Im a Q a aa E p a E Q is alled the FL effiiey fato ad W is the powe emitted y I the aove equatio the. To solve eq. (0) we eed to evaluate methods. a ad a fom eq. (16) usig umeial Howeve, we a otai a alytial expessio fo a ad a i the steady state. We oside that the goud state populatio of the exitos ( aa ) is muh lage tha the populatio of the exited states (, ). This gives the oditio aa ad aa. These desity matix elemets satisfy the oditio aa 1. Fo simpliity, we also oside that a a. This gives us ad. Solvig eq. (16) fo a ad a i the steady state ad sustitutig i eq. (0), we get whee L L L g l a 4 1 Im / i 1 L 4 1 Im / i /, L / V, g l V a 1 (1) Next, we alulate the FL whe the two exitos have degeeate exitoi states. This meas we have. I this ase the FL expessio give i eq. (1) edues to a a Whee I eq. () L L Im k / i / i / k 1 0 L a / is alled the poe detuig ad is defied as k k a a. Note that the FL depeds o whih i tu is ivesely popotiol to. This meas the FL depeds o the DDI etwee ad D. Fo smalle distaes the DDI tem has lage values. It also depeds o the polaizaility fato whih has lage values at the SPP esoe 9

10 eegies. Fig. : (a)plot of the FL (A.U.) as a futio of wavelegth (m) fo the IR800-Au-D. A.U. meas aitay uits. The oe of the Au-oshell is made of silia (SiO ) with a adius of 6 m ad the Au oshell with a adius of 76 m. The Au-oshell is oated with huma seum alumi (HSA) with thikess 8 m. The ope iles deote the expeimetal data. The solid uve is the theoetial esult whe the exito wavelegth ad SSP wavelegth ae ot i esoe (λ sp λ a ). Similaly, the dashed uve is plotted whe the exito wavelegth ad SSP wavelegth ae i esoe (λ sp =λ a ). Othe paametes ae take as ev ad, γ m = 0. ev. The dieleti ostat fo the silia ad HAS ae take as 1 1. ad 1. 5, espetively. () Thee-dimesiol plot of the FL (A.U.) as a futio of wavelegth (m) ad thikess of the HSA laye. IV: Results ad Disussio We have developed a theoy fo the FL i eq. () fo a -D hyid ad this equatio is used to explai the expeimetal data of the FL emissio peseted i efeees [9, 10] Reetly -D hyids have ee faiated y seveal goups [9, 10] fo medial puposes. Fist, we ompae ou theoy with the wok of Badha et al. [9]. These authos have faiated a IR800-Au-D hyid system. The oe of the Au-oshell is made of silia (SiO) with a adius of 6 m. It is oated with a Au shell to a adius of 76 m. Filly, the Au-oshell is oated with HAS, whih seves as a spae laye to ostut the D. Susequetly the hyid system was faiated y asoig IR800 fluoophoe moleules oto the D eletostatially, to get IR800-D hyid. They have studied the fluoesee ehaemet of the IR800 fluoophoe as a futio of distae fom the sufae of D. They foud FL ehaemet i the ea-ifaed egio i IR800-fluoophoe i the pesee of the D y vayig the thikess of the HAS spae laye. Thei measuemets eveal that the quatum yield of IR800 is ehaed fom 7% as a isolated fluoophoe to 86% i the IR800 i the IR800-D hyid. This damati fluoesee ehaemet a e used fo otast ehaemet i fluoesee-ased ioimagig. 10

11 Fig. : Plot of the FL (A.U.) as a futio of wavelegth (m). A.U. stads fo aitay uits. The ope iles ad solid diamods deote the expeimetal data whe the thikess of the silia is 7m ad 1m, espetively. The solid ad dashed uves ae theoetial esults whe the thikess of the silia is 7m ad 1m, espetively. The adii of the oe ad metalli shell ae take as 60 m ad 7 m, espetively. Othe paametes ae take as ev ad, γ m = 0.7 ev. The dieleti ostat fo the silia is take as Now we ompae ou theoy with aove expeimetal data [9]. We oside that the IR800 fluoophoe moleules ats as ad have two exitoi states with wavelegth λ a ad λ a ad oth states ae degeeate (λ a = λ a ). The SPP wavelegth of the Au-D is alulated as λ sp = 805 m to agee with the expeimetal value. The FL theoetial ad expeimetal data ae plotted as a futio of the wavelegth (m) i fig.. The ope iles deote the expeimetal data whe thikess of the HSA is 8 m. The solid uve is plotted whe the exito wavelegth ad SSP wavelegth ae ot i esoe (λ sp λ a ). The dotted uve is the theoetial esult whe the exito wavelegth ad the SSP wavelegth ae i esoe with the exito wavelegth (λ sp = λ a ). Thee is a damati ehaemet i the FL emissio whe the exito wavelegth ad the SPP wavelegth ae i esoe. Note that a good ageemet etwee theoy ad expeimet is foud. We have also plotted a thee-dimesiol figue fo the FL spetum as a futio of the thikess of the HAS laye ad the wavelegth. Oe a see that the FL ehaemet is ieased as the thikess of the HAS laye is deeased. This is osistet with the expeimetal esults of efeee [9]. Futhe we ivestigate expeimetal wok of Badha et al. [10] whee the authos have faiated the ICG-D hyid. Hee ICG moleules at as a. The oe of the D is made of silia (SiO) with a adius of 60m. The oe is oated with a Au shell ad its adius is 7m. The the Au-shell is oated with vayig thikesses of silia spae layes to omplete the D. Cosequetly, the hyid system was faiated y asoig ICG moleules oto the spae laye eletostatially to omplete ICG-D hyid. The silia spae laye a e maipulated to hage the distae etwee the ICG ad Au-oshell. Authos have ivestigated the FL ehaemet of ICG moleules as a futio of distae fom the sufae of the Au-oshell. The distae etwee ICG moleules ad the Au-oshell sufae is otolled y vayig the thikess of the oute silia shell. A fluoesee ehaemet is

12 oseved whe ICG moleules ae spaed lose to the Au-oshell sufae. The ehaemet deeases with ieasig distae of the moleule fom the Au-oshell sufae. Fig. 4: (a) Plot of the FL (A.U.) as a futio of wavelegth (m). The solid ad dotted uves ae theoetial esults fo whe = 86 m ad 11 m, espetively. () Thee dimesiol plot of the FL (A.U.) as a futio of wavelegth (m) ad distae etwee the ad the D (). The adius of the oe ad metalli shell ae take as 60 m ad 7 m, espetively. Othe paametes ae take as ev ad, γ m = 0.7 ev. The dieleti ostat fo the silia is take as I fig. we ompae ou theoy with the expeimetal data of the ICG-D hyid [10]. We oside that ICG moleules at as ad have two degeeate exitoi states with wavelegth λ a. The SPP wavelegth of the Au-D is alulated as λ sp = 810m. The theoetial ad expeimetal date ae plotted i fig. a. Ope iles ad solid diamods deote the expeimetal data whe the thikesses of the silia spae laye ae 7m ad 1m, espetively. The solid ad dotted uves ae theoetial esults. I plottig theoetial uves, we have osideed that the exito wavelegth ad SSP wavelegth ae i esoe with eah othe (λ sp = λ a ). Note that a good ageemet etwee theoy ad expeimet is foud whe the exito ad SSP wavelegth ae i esoe. If this oditio wee ot satisfied, the ou theoy would ot agee with expeimets. We have also plotted a thee-dimesiol figue of the FL y vayig the spae thikess. Note that the ehaemet deeases as the distae etwee ICG ad D ieases. This fidig is osistet with expeimetal data of efeee [10]. We also study the FL fo the IR800-D hyid whe the is i the odegeeate state. This meas two exitos fequeies ae diffeet ( ). I plottig theoetial uves, we have osideed that the exito wavelegth λ a ad the SSP wavelegth ( ) ae i esoe with eah othe. Similaly, the seod exito wavelegth λ a ad the seod SSP wavelegth ( ) ae also i esoe. The esults ae plotted i Fig. 4a ad 4. I fig 4a the FL spetum is plotted as a futio of wavelegth. The solid ad dashed uves ae plotted whe the distae etwee IR800 ad D ae = 86 m ad =11 m, espetively. Fig 4 otais the thee-dimesiol plot of the FL as a futio of wavelegth ad distae etwee the ad D. It is foud that the FL spetum has two peaks. The peak elated to λ a is weake tha that 1

13 of λ a. This is eause the exito-ddi ouplig is weake fo the λ a -peak ompaed to that of the λ a -peak. Note that ehaemet of the FL itesity ieases as the distae etwee the ad D deeases. This fidig is osistet with expeimetal esults of efeees [9, 10]. Simila esults ae also foud fo the IR800-D hyid. Note that the FL ehaemet i the seod peak is huge ompaed to the fist peak. Ou theoy is valid fo ay dieleti mateial used as oe o spae laye fo the faiatio of D suh as Silia, Y O ad YPO 4. The effet of these mateials i ou theoy is epeseted y thei oespodig dieleti ostats (i.e. see eqs. (1-9)). The dieleti ostat of these mateials plays a impotat ole i ou theoy. Aodig to ou theoy, the loatios of the SPP esoe fequeies ad the itesity of the SPPs eleti field deped o the dieleti ostat of the mateials used i the D faiatio (see eqs. (6, 10)). Let us oside that s (ICG/IR800) ae plaed o the metal sufae istead of the spae laye of the D. This meas we have a sigle oshell whih is made of a metalli shell ad a silia oe. The itesity of the FL emitted fom s will e stoge tha whe s ae apped o the sufae of the D. This is eause sufae plasmos polaitos ae eated at the metalli sufae whee the eleti field itesity has the lagest value. The dipole-dipole iteatio etwee s ad a sigle metalli shell will also e ehaed sie the distae etwee the ad the metalli sufae is smalle i the asee of the spae laye. We have show that DDI depeds o the distae fom the metal sufae to the. We have also foud that the DDI is esposile fo the ehaemet of the FL i s. I summay, ou theoy explais the ehaemet of the FL speta fo IR800-D ad ICG-D hyids. We showed that the ehaemet i the FL is deeased as the thikess of the spae laye is ieased. The ehaemet i the FL emissio depeds o the type of the, spae laye ad the D. We also foud that the peak of the FL a e shifted y hagig the shape ad size of the D. It is foud that the FL speta a e swithed fom oe peak to two peaks y emovig the degeeay of exitoi states i the. Hee usig these popeties oe a use these hyids as sesig ad swithig devies fo appliatios i mediie. V: Colusios Light emissio fom -D hyids was studied. The D is made of a dieleti oe oated with a thi laye of metal ad the futhe oated y a spae laye of dieleti mateial. Susequetly s ae deposited o the sufae of the spae laye to faiate the -D hyid. Whe this hyid is ijeted i aimal o huma tissue it is suouded y iologial ells suh as ae ells. Sufae plasmo polaito esoes i the D ae alulated usig Maxwell s equatios i the quasi-stati appoximatio ad the FL is evaluated usig the desity matix method i the pesee of the DDI. It is foud that loatios of SPP esoes i D a e maipulated y hagig the size ad shape of the metalli shell, oe ad spae laye. We have ompaed ou theoy of the FL emissio with expeimetal esults fo the IGL-D hyid whee the D is made of a silia oe, Au shell ad the silia spae laye. We have also ompaed ou theoy with expeimetal esults fo the IR800-D hyid. I this ase, the D osists of a silia oe, Au shell ad a HSA spae laye. Good ageemet etwee theoy ad 1

14 expeimet is foud whe the exito eegy ad the SSP eegy ae i esoe. We have also alulated the FL fo the odegeeate ad foud that the FL spetum splits fom oe peak to two peaks. These iteestig fidigs may e useful i the faiatio of osesos ad oswithes fo appliatios i mediie. Akowledgemet Oe of the authos (MRS) is thakful to the Natual Siees ad Egieeig Reseah Couil of Cada (ERC) fo thei eseah gat ad José M. J. Cid who appeiative to Uivesidad Autóoma del Estado de Méxio fo awadig sholaship. Authos ae thakful to Pofesso M. Zike-Allmag fo editig the pape. Refeees 1. R. D. Atuso, G. W. Byat, Phys. Rev. B8, (010).. S. M. Sadeghi, L. Deg, X. Li, W. P. Huag, Naotehology. 0, (009).. J. D. Cox, M. R. Sigh, G. Gums, M. A. Ato, F. Caeo, Phys. Rev. B86, 1545 (01). 4. M. Sigh, C. Mada, S. Balakish, Naotehology. (sumitted 016). 5. A. C. Pease, D. Solas, E. J. Sulliva, M. T. Coi, C. P. Holmes, S. P. A. Fodo, Po. Natl. Aad. Si. USA. 91, 50 (1994). 6. S. Weiss, Siee. 8, 1676 (1999). 7. A. W. Weiege, B. Kihhof, B. E. Mazii, N. F. Shage, Gaefe s Ah. Cli. Exp. Ophthalmol. 9, 88 (001). 8. K. E. Adams, S. Ke, S. Kwo, F. Liag, Z. Fa, Y. Lu, K. Hishi, M. E. Mawad, M. A. Bay, E. M. Sevik-Muaa, J. Biomed. Opt. 1(), (007). 9. R. Badha, N. K. Gady, J. R. Cole, A. Joshi, N. J. Halas, ACS Nao., 744 (009). 10. R. Badha, N. K. Gady, N. J. Halas, Small. 4, No. 10, 1716 (008). 11. J. P. Housto, S. Ke, W. Wag, C. Li, E. M. Sevik-Muaa, J. Biomed. Opt. 10, (005). 1. T. Tsuoo, S. Todo, N. Jaou, A. Mizoe, V. Waty, A. J. Demetis, T. E. Stazyl, Hepatology. 4, 1165 (1996). 1. S. G. Sakka, K. Reihat, K. Wegsheide, A. Meie-Hellma, Chest. 11, 559 (00). 14. V. Ntziahistos, A. G. Yodh, M. Shll, B. Chae, Po. Natl. Aad. Si. USA. 97, 767 (000). 15. R. C. Beso, H. A. Kues, Phys. Med. Biol., 159 (1978). 16. A. G. Tkaheko, H. Xie, Y. Liu, D. Colema, J. Rya, W. R. Glomm, M. K. Shipto, S. Faze, D. L. Feldheim, Bioojugate Chem. 15, (004). 17. N. L. Rosi, C. A. Miki. Chem. Rev. 105, (005). 18. B.N. Khletsov, N.G. Khletsov, Joul of Quatitative Spetosopy & Radiative Tasfe. 106, 154 (007). 19. L. Novoty, B. Heht, Piiple of Nao-optis (Camidge Uivesity Pess, 006); D. Said, W. A. Challee, Mode Itodutio to Sufae Plasmos: Theoy, Mathematia Modelig, ad Appliatios (Camidge Uivesity Pess, 010). 0. M. R. Sigh, Eletoi, Photoi, Polaitoi ad plasmoi Mateials. Tooto: Wiley Custom (014). 14

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