Selective, sensitive and reliable colorimetric sensor for catechol detection based on anti-aggregation of unmodified gold nanoparticles utilizing boronic acid-diol reaction: optimization by experimental design methodology

A sensitive and selective colorimetric method is presented for quantitative analysis of catechol based on the unmodified gold nanoparticles (AuNPs). In the absence of catechol, the addition of 4-mercaptophenyl boronic acid (MPBA) instigates the aggregation of AuNPs by Au-S covalent binding via self-dehydration condensation of boronic acid groups and causes a noticeable color alteration of AuNPs from wine red to blue. In the presence of catechol, boronic acid-diol binding is preferred than to the self-dehydration condensation. An increase in catechol concentration alleviates AuNPs aggregation by decreasing the amount of free MPBA, and solution color changes from blue to red. Therefore, the concentration of catechol can be detected with the naked eye or by an ultraviolet-visible spectrophotometer. Central composite design and response surface methodology were executed to evaluate interactions among variables. Due to the preference for the binding of 1,2-diol to boronic acid, this method showed high selectivity for catechol determination compared to dihydroxybenzene isomers with a linear response range of 0.87-56 A mu mol L-1 with a detection limit of 0.41 A mu mol L-1. The proposed colorimetric sensing method exhibits the advantage of no necessity for surface modification of AuNPs, avoids tedious separation processes and enables rapid assays. A highly sensitive sensing platform for catechol was established based on the anti-aggregation of AuNPs without prior modification through a competition reaction of boronic acid-diol binding between 4-mercaptophenyl boronic acid (MPBA) and catechol against the self-dehydration condensation of MPBA. [GRAPHICS] .