Formation of Surface Traps on Quantum Dots by Bidentate Chelation and Their Application in Low-Potential Electrochemiluminescent Biosensing

Bidentate chelation, meso-2,3-dimercaptosuccinic acid (DMSA), was used as a stabilizer for the synthesis of CdTe quantum dots (QDs). The bidentate chelate QDs, characterized with FT-IR. PL, and UV/Vis spectroscopy; element analysis; and high-resolution transmission electron microscope, exhibited surface traps due to the large surface/volume ratio of QD particle and the steric hindrance of the DMSA molecule. The unpassivated surface of the QDs produced a narrower band gap than the core and electrochemiluminescent (ECL) emission at relatively low cathodic potential. In air-saturated pH 7.0 buffer, the QDs immobilized on electrode surface showed an intense ECL emission peak at -0.85 V (vs. Ag/AgCl). H2O2 produced from electrochemical reduction of dissolved oxygen was demonstrated to be the co-reactant, which avoided the need of strong oxidant as the co-reactant and produced a sensitive analytical method for peroxidase-related analytes. Using hydroquinone/horseradish peroxidase/H2O2 as a model system, a new, reagentless, phenolic, ECL biosensor for hydroquinone was constructed, based on the quenching effect of ECL emission of QDs by consumption of co-reactant H2O2. The biosensor showed a linear range of 0.2-10 mu M with acceptable stability and reproducibility. This work opens new avenues in the search for new ECL emitters with excellent analytical performance and makes QDs a more attractive alternative in biosensing.