Colorimetric sensing strategy for β-lactamase inhibitor using generation of 2-amino-3-mercapto-3-methylbutanoic acid via enzyme catalysis and Cu(II)-mediated redox

A colorimetric sensing method has been proposed for the detection of β-lactamase (β-Lac) activity and the screening of the inhibitors in this work. The method is based on the aggregation of AuNPs induced by 2-amino-3-mercapto-3-methylbutanoic acid (AMMBA) through the formation of Au-S bond and electrostatic interaction. Since AMMBA can form through β-Lac catalyzed hydrolysis and Cu(II)-mediated redox with penicillin as enzyme substrate, β-Lac activity is related to the extent of AuNPs aggregation. The enzyme activity can be determined at levels as low as 0.556 U/mL and over a linear detection range as wide as from 0 U/mL to 30 U/mL. Furthermore, the inhibitory effects of clavulanic acid and sulbactam on the activity of β-Lac have also been tested and given IC50 values of 0.92 μM and 0.06 μM, respectively. The proposed method can be not only used for the detection of β-Lac activity but also the screening of the inhibitor.