In this study, carboxyl group functionalized-CdSe/ZnS quantum dots (QDs) and aminofluorescein (AF)-encapsulated polymer particles were synthesized and immobilized to a sol-gel mixture of glycidoxypropyl trimethoxysilane (GPTMS) and aminopropyl trimethoxysilane (APTMS) for the fabrication of a hydrogen peroxide-sensing membrane. CdSe/ZnS QDs were used for the redox reaction of hydrogen peroxide (H2O2) via a reductive pathway by transferring electrons to the acceptor that led to fluorescence quenching of QDs, while AF was used as a reference dye. Herein, the ratiometric fluorescence intensity of CdSe/ZnS QDs and AF was proportional to the concentration of hydrogen peroxide. The fluorescence membrane (i.e., QD-AF membrane) could detect hydrogen peroxide in linear detection ranges from 0.1 to 1.0 mM with a detection limit (LOD) of 0.016 mM and from 1.0 to 10 mM with an LOD of 0.058 mM. The sensitivity of the QD-AF membrane was increased by immobilizing horseradish peroxidase (HRP) over the surface of the QD-AF membrane (i.e., HRP-QD-AF membrane). The HRP-QD-AF membrane had an LOD of 0.011 mM for 0.1-1 mM H2O2 and an LOD of 0.068 mM for 1-10 mM H2O2. It showed higher sensitivity than the QD-AF membrane only, although both membranes had good selectivity. The HRP-QD-AF membrane could be applied to determine the concentration of hydrogen peroxide in wastewater, while the QD-AF membrane could be employed for the detection of α-ketobutyrate.
Keywords: CdSe/ZnS QDs; hydrogen peroxide; ratiometric fluorescence QD membrane; redox reaction; α-ketobutyrate.