Alloyed AuFeZnSe quantum dots@gold nanorod nanocomposite as an ultrasensitive and selective plasmon-amplified fluorescence OFF-ON aptasensor for arsenic (III)

According to documented reports, more than 200 million people across the globe are exposed to arsenic (As) contamination at levels above the World Health Organization (WHO) guideline limit of 10 μg/L. In this work, a novel fluorescence OFF-ON ultrasensitive aptasensor was developed for As (III). To construct the fluorescence aptasensor, AuFeZnSe alloyed quantum dots (QDs) were newly synthesized and surface-coated with amphiphilic polymers (Amp-P) to render the QDs biocompatible and stable. Thereafter, cationic gold nanorods (AuNRs) were electrostatically bonded to the Amp-P-QDs to form an Amp-P-QDs-AuNR nanocomposite which switched OFF the fluorescence of the bound QDs. Thiolated anti-As (III) DNA aptamer (Apt) was thereafter assembled on the Amp-P-QDs-AuNR surface to form a Amp-P-Apt-QDs-AuNR probe. The affinity binding interaction between the targeted As (III) concentration and the Apt, triggered localized surface plasmon resonance (LSPR) from AuNRs to amplify the fluorescence intensity signal, thereby switching ON the fluorescence of the bound Amp-P-QDs. Comparison of the Amp-P-Apt-QDs and the Amp-P-Apt-QDs-AuNR probes, showed that the presence of AuNR enhanced the fluorescence of the bound Amp-P-QDs for As (III) by as much as 230%, representing an ∼20-fold increase over the Amp-P-Apt-QDs probe without AuNRs. Under optimum conditions, As (III) was selectively and quantitatively detected with ultra-high sensitivity. The linear range was 0.01–100 μg/L, while the obtained detection limit of 0.01 μg/L (69.12 pM) was 1000 times lower than the WHO recommended limit. We successfully applied the Amp-P-Apt-QDs-AuNR probe to detect As (III) in environmental and biological samples with analytical recoveries from ∼93 to 105%.