Enhanced ultrasensitive detection of Cr(III) using 5-thio-2-nitrobenzoic acid (TNBA) and horseradish peroxidase (HRP) dually modified gold nanoparticles (AuNPs)

In this study, an enhanced ultrasensitive and selective sensor for detection of Cr(III) was constructed based on gold nanoparticles (AuNPs) dually labeled with 5-thio-2-nitrobenzoic acid (TNBA) and horseradish peroxidase (HRP). TNBA was used as an affinity tag for Cr(III) binding and HRP as optical signal amplifier. Following the addition of Cr(III), the aggregation of AuNPs labeled with TNBA occurred, because the nitryl groups of TNBA selectively interacted with Cr(III). After the addition of TMB solution to the aggregation, the optical signals would be generated. The density of the signal is correlated with the concentration of Cr(III), which can be easily discerned by the naked eye or be measured spectrophotometrically. The application results indicated that the dually labeled sensor (TNBA–AuNPs–HRP) was highly sensitive to Cr(III) in the concentration of 0.04 to 210 μM. The limit of detection (LOD) was 0.04 μM, which is 45 times lower than that of the sensor without HRP enhancement.