Enhanced oxidase-like activity of selenium nanoparticles stabilized by chitosan and application in a facile colorimetric assay for mercury (II)

Nanozymes, nanomaterials with intrinsic enzyme-like activity, have gained tremendous attention due to their advantages. Our previous study found that selenium nanoparticles (SeNPs) synthesized with bovine serum albumin (BSA) as a stabilizer had intrinsic oxidase-like activity, which could catalyze the oxidation of oxidase substrate 3,3′,5,5′-tetramethylbenzidine by oxygen. However, the catalytic activity of as-synthesized SeNPs was not very high, which greatly limits their applications. Herein, to improve the oxidase-like activity of SeNPs, SeNPs were synthesized using three types of stabilizers (BSA, chitosan (CS) and sodium alginate (SA)). The catalytic activity of CS-stabilized SeNPs (CS-SeNPs) with the most positive surface charge was 4-fold of BSA-stabilized SeNPs (BSA-SeNPs), but that of SA-stabilized SeNPs with negative surface charge was the weakest. Subsequent reactive oxygen capture experiments and electron spin resonance detection showed that superoxide anion and hydroxyl radical might be involved in the catalytic mechanism of CS-SeNPs. Finally, on the basis of the inhibition of Hg2+ on the oxidase-like activity of CS-SeNPs, a simple and economical colorimetric method for Hg2+ detection was achieved with a detection limit of 0.12 μM. The results provide a new clue for improving oxidase-like activity of nanomaterials and broaden the potential application of SeNPs in chemical sensor.