Resonance energy transfer using biotin-peg/pama stabilized CdS quantum dots

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1 Resonance energy transer using biotin-peg/pm stabilized ds quantum dots Third Research Group, Quantum Nano-Technology Laboratory, Konan Universit 呂威 Wei Lu Semiconductor nanocrystals represent a potential class o labeling probes because o their size dependent optical properties, exceptional photochemical stability, broad excitation spectra and narrow emission bands and have been intensively studied in biological applications. However, the dispersion stability o quantum dots (Qs) in aqueous media decreases with decreasing size in the range o nanometers due to increased surace area. In this regard, polymer-supported stabilization o the Qs is one o the eective methods. In our work, PEG-b-poly(-(N,N dimethylamino)ethyl methacrylate) (PEG/PM) molecule was used as a polymer to stabilize surace o Qs. The biotin-peg/pm stabilized Qs as energy donors in conjunction with dye acceptors were prepared. The dispersion stability in aqueous media was greatly improved. Fluorescent resonance energy transer (FRET) was observed by the speciic interaction between biotin-peg/pm stabilized ds Qs and -labeled streptavidin. lthough PEG/PM improved the dispersion stability in aqueous media, it has a disadvantage or FRET since PEG/PM chains have larger length than those o molecules generally used to stabilize Qs. FRET eiciency will decrease i the distance between Qs and dyes is large. Thereore it is important to investigate energy transer mechanism o present system and urther to improve FRET eiciency and to estimate Q-dye distance. Our results suggest that two excited state energy s (shallow energy and deep energy ) dominate emission process o prepared ds nanocrystal. We propose a our-state model to explain photoluminescence (PL) process o ds Qs and suggest there are two emission processes originated rom shallow and deep trap energy s corresponding to ast and slow components o PL decay, respectively. Energy transer mechanism was discussed based on exter theory and the proposed our-state model. It is ound that the energy transer eiciency o deep energy is higher than that o shallow energy. The calculated distance between Q and with the parameters o shallow energy is the same with that o deep, which indicates that the proposed model is reasonable or explaining the PL dynamics o ds Qs.

2 Resonance energy transer using biotin- PEG/PM stabilized ds quantum dots 呂威, 徳弘雄亮, 梅津郁朗,, 杉村陽,, 長崎幸夫 甲南大量子ナノテク研, 甲南大理工, 筑波大学際セ FRET Requirements To make a FRET measurement, you need to have a select pair o luorescent dyes that: Large overlap between donor luorescence and acceptor absorption Relatively eicient donor and acceptor luorescence Suitable distance between donor and acceptor Introduction Fluorescence resonance energy transer (FRET) is a photophysical process involving a donor molecule and an acceptor molecule The donor molecule is optically excited and transers some o its excitation energy to the acceptor molecule The transer mechanism decreases the luorescence lietime o the donor molecule onor cceptor ħω ħω ω > ω exter theory description[] h c Q a ( E ) F ( E ) = de π R n E 6 Q a : area under absorption band : lietime o donor n: reractive index o medium R: distance between donor and acceptor F ( E ) de = ( E ) de = -nm onor cceptor []. L. exter, J. hem. Phys. (5), 86 (95)

3 Fluorescent resonance energy transer (FRET) Large length o PEG/PM chain? poly(ethylene glycol)-b-poly (-(N,N dimethylamino)ethyl methacrylate) (PEG/PM) molecule chain polymer ispersion stability in aqueous media Traditional organic luorophoresorganic dyes system Bio-sensor Luminescent semiconductor quantum dots (Qs)-organic dyes system Research background and purpose Wavelength (nm) large dot 6. 8 bsorption (a.u.) small dot.5.6nm dse Q nm dse Q FRET pplication pplication to biosensor Measuring interactions between two proteins or between nanocrystal and organic dye 5 7 Overlap integral between ds Qs emission and absorption bsorption (a.u.) absorption ds Q emission Sample structure and FRET process Time (min). Quantum yield ratio o small to large dots Wavelength (nm) min min min 8min min min 6 8

4 PL Intensity (rb. unit) P: excitation rom ground state to absorption S S: shallow trap state S: deep trap state : excited state o r: decay probability Proposed our-state model The transer mechanism decreases the luorescence lietime o the donor molecule The donor molecule is optically excited and transers some o its excitation energy to the acceptor molecule Wave Length (nm) ds PL combined ds ds Qs.. Evidence or FRET rom ds Q to 9 ecomposition results show that the time constants rom decomposition at.77ev and.8ev are consistent with result o time-dependent PL intensity ns PL. Experimental result 5ns 6 8. shallow trap state. eep trap state.8ev.77ev ns ecomposition result Position decision o the two trap states []M. ib, M. hamarro, V. Voliotis, and J. L. Fave, Phys. Stat. Sol (b)., 9 (999). 6 8 PL peak redshit to low energy Peak position variation vs delay time ns. ns.5 ns.6 5ns Peak energy (ev) bsorption (a.u.).5 ds PL emission. PL. 5.5 ds absorption Experimental results o ds Qs

5 . Time constants acquired rom PL peak decomposition and the distances calculated using the parameters o shallow and deep energy s indicate that the proposed model is reasonable.. The FRET rom Qs to was observed.energy transer mechanism was discussed based on exter theory and the proposed our-state model. The energy transer eiciency o deep energy (6%) is higher than that o shallow energy (7%).. our-state model is proposed to explain PL behavior o ds Qs. Two trap state at.8ev and.77ev are suggested to dominate emission process o Qs. onclusion 5 FRET rate or shallow trap state:.6/ns FRET eiciency or shallow trap state: 7% FRET rate or deep trap state :./ns FRET eiciency or deep trap state : 6% eep energy.ns -.7ns Shallow energy.6ns -.ns - PL. decay probability o PEG-dS decay probability o -ds. eep energy 7nsec 7nsec ds Qs combined ds Shallow energy 6nsec.5nsec Time constant o ds Time constant o -ds +T : decay probability o combined ds +T : time constant o combined ds : FRET rate : FRET eiciency : decay probability o ds η + T c : time constants o ds = + T = + + T η = = FRET rate and eiciency Thank you or attention The distances calculated using the parameters o deep energy.7nm The distances calculated using the parameters o shallow energy.9nm PL Shallow trap state PL eep trap state absorption bsorption (a.u.) h c Q a ( E ) F ( E ) = de π R n E 6 istance between ds Q and 6