Use of Luminescent CdSe-ZnS Nanocrystal Bioconjugates in Quantum Dot-Based Nanosensors

Abstract

Biomolecules labeled with luminescent colloidal semiconductor quantum dots (QDs) have potential for use in numerous applications, including fluoro-immunoassays and biological imaging. QD labels exhibit size-tunable narrow-band luminescent emission and high resistance to photodegradation. They also exhibit efficient Fö rster energy transfer between neighboring QDs of different sizes and their emission is readily quenched by bound fluorescent dyes. In this paper, we describe preliminary results aimed at defining conditions for the design and preparation of nanoscale QD-bioconjugate sensors based on fluorescence quenching. We envision building sensor assemblies that employ quantum dots linked with dye-labeled biological receptors that utilize donor-acceptor energy transfer between QDs and receptors for conducting recognition-based assays. In particular, we report the effects of varying the concentration of energy acceptors bound to nanocrystal surfaces under both soluble and solid phase conditions on quenching phenomena.Introduction Strong quantum confinement of the charge carriers in semiconductor nanocrystals (quantum dots, QDs) increases their effective band gap energy significantly with decreasing particle size, resulting in size dependence of QD light absorption and luminescence spectra [1-3]. Colloidal QDs are approximately spherical nanocrystals with surfaces that can be derivatized with a variety of functional capping groups (surface ligands), allowing their dispersion in a range of solvents, including aqueous environments. Several groups have shown that surface ligands can be used to attach various biological molecules to form QD-bioconjugates [4][5][6][7]. As an alternative to conventional fluorophores, QDs offer a number of attractive features, including high resistance to photodegradation, relatively narrow and symmetric luminescence bands, and simultaneous excitation of several sizes of QDs (thus several colors) over a broad range of wavelengths. Advantages in using luminescent QDs to synthesize bioconjugates with potential use in biological imaging applications and in developing QD-based nanosensors have been elaborated [4][5][6].Our recent work has focused on the design and preparation of aqueous-compatible dithiol-capped CdSe-ZnS QDs having carboxylic acid terminal groups linked with bifunctional asymmetrically charged fusion proteins for QD-bioconjugate formation where conjugation is driven by electrostatic self-assembly [6]. In previous works, we studied the formation of QD-bioconjugates with two proteins, E. coli maltose binding

Aqueous Near‐Infrared Fluorescent Composites Based on Apoferritin‐Encapsulated PbS Quantum Dots

“…cysteine [363][364][365][366], rhodamine [367]) and non fluorescent dyes or quenchers (QSY9, BHQ-10, DABCYL (4-(dimethylaminoazo)benzene-4-carboxylic acid), squaraine) [368][369][370].…”

Bioconjugated quantum dots for in vivo molecular and cellular imaging☆

“…The surfaces of QDs may also be modified with bio-inert, hydrophilic molecules such as polyethylene glycol, to eliminate possible nonspecific binding, or to decrease the rate of clearance from the bloodstream following intravenous injection. QDs have also emerged as a new class of sensor, mediated by energy transfer to organic dyes (fluorescence resonance energy transfer, FRET) [52][53][54]. It has also recently been reported that QDs can emit fluorescence without an external source of excitation when conjugated to enzymes that catalyze bioluminescent reactions, due to bioluminescence resonance energy transfer (BRET) [55].…”

A mechanism to signal receptor–substrate interactions with luminescent quantum dots

“…In fact, clever assays for the recognition of various analytes are starting to be designed on the basis of energy transfer processes (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34). Instead, mechanisms based on electron transfer still remain to be explored (35,36).…”