Signal amplification of SiO2 nanoparticle loaded horseradish peroxidase for colorimetric detection of lead ions in water

Abstract

In this work, we developed an aptamer-based optical assay for the analysis of Pb2+, a hazardous heavy metal that may be present in the food chain and harmful to human health. An aptamer targeted against Pb2+ was immobilized onto the microplate as the capture probe. SiO2 nanoparticles (NPs) were synthesized and used as carriers of the signaling horseradish peroxidase (HRP) to achieve amplification of the optical signal. Complementary DNA (cDNA) of the aptamer was also linked to the above mentioned SiO2 nanoparticle (NPs) as the signal probe. The aptamers were found to be able to capture Pb2+, and the unbound aptamers were subsequently hybridized with cDNA-HRP-SiO2 conjugates. As a result, the addition of TMB-H2O2 promoted the formation of blue products in the catalytic system. The assay adopting SiO2 NPs as an enhancer resulted in higher sensitivity with an LOD of 2.5 nM compared to normal procedures. The feasibility of the aptamer-based colorimetric assay was verified by successful detection of Pb2+ in water samples with recoveries in the range of 97.4–103.52%.