Enzyme-based electrochemical biosensor for antimonite detection in water

Antimonite (SbIII) is a naturally occurring contaminant demanding on-site ultrasensitive detection. The enzyme-based electrochemical (EC) biosensors are promising, but the lack of specific SbIII oxidizing enzymes hindered the past efforts. Herein, we modulated the specificity of arsenite oxidase AioAB toward SbIII by regulating its spatial conformation from tight to loose using the metal-organic framework ZIF-8. The constructed EC biosensor, AioAB@ZIF-8, exhibited the substrate specificity toward SbIII at 12.8 s-1 μM-1, an order of magnitude higher than that of AsIII (1.1 s-1 μM-1). Relaxing AioAB structure in ZIF-8 was evidenced by the break of the S-S bond and the conversion of α helix to the random coil as suggested by Raman spectroscopy. Our AioAB@ZIF-8 EC sensor exhibited a dynamic linear range in 0.041-4.1 μM at a response time of 5 s, and the detection limit at 0.041 μM at a high sensitivity of 1894 nA μM-1. The insights into tuning the specificity of an enzyme shed new light on biosensing metal(loid)s without specific proteins.