Abstract
The difference in gold nanoparticle (AuNPs) aggregation caused by different mixing orders of AuNPs, 4-mercaptophenylboronic acid (4-MPBA), and hydrogen peroxide (H2O2) has been scarcely reported. We have found that the color change of a ((4-MPBA + AuNPs) + H2O2) mixture caused by H2O2 is more sensitive than that of a ((4-MPBA + H2O2) + AuNPs) mixture. For the former mixture, the color changes obviously with H2O2 concentrations in the range of 0~0.025%. However, for the latter mixture, the corresponding H2O2 concentration is in the range of 0~1.93%. The mechanisms on the color change originating from the aggregation of AuNPs occurring in the two mixtures were investigated in detail. For the ((4-MPBA + H2O2) + AuNPs) mixture, free 4-MPBA is oxidized by H2O2 to form bis(4-hydroxyphenyl) disulfide (BHPD) and peroxoboric acid. However, for the ((4-MPBA+AuNPs) + H2O2) mixture, immobilized 4-MPBA is oxidized by H2O2 to form 4-hydroxythiophenol (4-HTP) and boric acid. The decrease in charge on the surface of AuNPs caused by BHPD, which has alarger steric hindrance, is poorer than that caused by -4-HTP, and this is mainly responsible for the difference in the aggregation of AuNPs in the two mixtures. The formation of boric acid and peroxoboric acid in the reaction between 4-MPBA and H2O2 can alter the pH of the medium, and the effect of the pH change on the aggregation of AuNPs should not be ignored. These findings not only offer a new strategy in colorimetric assays to expand the detection range of hydrogen peroxide concentrations but also assist in deepening the understanding of the aggregation of citrate-capped AuNPs involved in 4-MPBA and H2O2, as well as in developing other probes.
Highlights
Gold nanoparticle (AuNP) probes based on colorimetric strategy have drawn increasing attention due to their simplicity, high sensitivity, and low cost [1]
These findings offer a new strategy in colorimetric assays to expand the detection range of hydrogen peroxide concentrations and assist in deepening the understanding of the aggregation of citrate-capped AuNPs involved in 4-mercaptophenylboronic acid (4-MPBA) and H2 O2, as well as in developing other probes
523 nm,a new absorbance peak gradually appears between 600 to 900 nm, and the solution color visibly changes from ruby red to blue. These results suggest that the aggregation of AuNPs enhances with the increase of H2O2, which is further proved by Transmission electron microscopy (TEM) images
Summary
Gold nanoparticle (AuNP) probes based on colorimetric strategy have drawn increasing attention due to their simplicity, high sensitivity, and low cost [1]. 4-MPBA-modified AuNPs (4-MPBA/AuNPs), various AuNP-based colorimetric assays have been constructed For these methods, the selective reactions of the thiol group or boronic acid group on the surface of 4-MPBA-modified AuNPs with the target analytes can trigger the aggregation or dis-aggregation of AuNPs with an accompanying color change. The selective reactions of the thiol group or boronic acid group on the surface of 4-MPBA-modified AuNPs with the target analytes can trigger the aggregation or dis-aggregation of AuNPs with an accompanying color change Based on this analytic platform, the colorimetric methods have been developed to detect target analytes including sugars [7], sialic acid [8], catechol [9], Hg2+ [10,11], ATP [12], and dopamine [13]. The revealed mechanisms should assistin deepening the understanding of the physical and chemical behavior of the system containing AuNPs, 4-MPBA, and H2 O2 , and have a significant positive effect on developing new AuNP-based probes
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