Aptamer-Capped Nanocrystal Quantum Dots:  A New Method for Label-Free Protein Detection

Abstract

We demonstrate that aptamer-capped near-infrared PbS quantum dots (QDs) can detect a target protein based on selective charge transfer. The water-soluble QDs are synthesized with the thrombin-binding aptamer, which retains the secondary quadruplex structure necessary for binding to thrombin. These QDs have diameters of 3-6 nm and fluoresce around 1050 nm. When the aptamer-functionalized QD binds to its target, a fluorescence quenching occurs due to charge transfer from amine groups on the protein to the QD. Thrombin is detected within 1 min with a detection limit of approximately 1 nM. This selective detection is observed even in the presence of high background concentrations of interfering negatively or positively charged proteins, suggesting that aptamer-capped QDs could be useful for label-free protein assays.

Semiconductor Quantum Dots for Bioanalysis

“…In a related study, thrombin was detected by the anti-thrombin aptamer conjugated to PbS QDs. [102] Upon binding of thrombin to aptamer-functionalized QDs, selective fluorescence quenching was observed as a result of a charge-transfer process from thrombin to QDs. This method enabled thrombin to be detected at concentrations down to 1 10 À9 m, and it showed high selectivity in the presence of high background concentrations of interfering proteins.…”

Nanomaterial-assisted aptamers for optical sensing

“…The recent advances in the development of various optical NAAs for a wide range of targets have been reviewed, most of which utilize the detection methods of colorimetry, fluorometry (Medley et al, 2008), thrombin (Pavlov et al, 2004), PDGF (Huang et al, 2005), cysteine , ATP (Wang et al, 2007a), adenosine (Liu and Lu, 2004;Zhao et al, 2008), cocaine (Liu and Lu, 2006), Pb 2+ (Liu and Lu, 2003), Hg 2+ (Lee et al, 2007a), Cu 2+ (Liu and Lu, 2007b), UO2 2+ Fluorometry AuNP Fluorescence quenching Thrombin (Wang et al, 2008a), PDGF (Huang et al, 2007), adenosine and cocaine (Liu et al, 2007), Hg 2+ (Liu et al, 2008) Fluorescence emission PDGF (Huang et al, 2008a) AuNW, CNT Fluorescence quenching Thrombin (Huang and Chen, 2008;Yang et al, 2008) MNP Magnetic separation CCRF-CEM, Ramos and Toledo cells (Smith et al, 2007), AMP (Song et al, 2009) QD Fluorescence emission PSMA (Chu et al, 2006;Bagalkot et al, 2007), glioma cells (Chen et al, 2008d), mucin 1 (Cheng et al, 2009), thrombin (Levy et al, 2005;Choi et al, 2006), cocaine and adenosine (Liu et al, 2007 (Farokhzad et al, 2004); PSMA cells Chitosan nanoparticles…”

“…Choi et al (2006) devised simple aptamer-capped PbS QDs ( em = 1050 nm) for thrombin detection. The photoluminescence of this nanostructure gradually decreased with increasing thrombin amount, which was thought to result from the selective aptamer-thrombin interaction and therefore charge transfer between thrombin functional group (e.g., amine) and QD conduction band.…”

Semiconductor quantum dots in chemical sensors and biosensors

“…For example, a DNA aptamer was shown to passivate PbS QDs, rendering them water-soluble and stable against aggregation, while retaining the secondary structure needed to selectively bind to its thrombin target [75]. The selective binding of the target to the aptamerfunctionalized QDs, resulted in a quenching of the photoluminescence that was attributed to charge transfer from functional groups on the protein to the QDs.…”