Colorimetric assay based on NiCo 2 S 4 @N,S-rGO nanozyme for sensitive detection of H 2 O 2 and glucose in serum and urine samples.

Traditional bimetallic sulfide-based nanomaterials often have a small specific surface area (SSA), low dispersion, and poor conductivity, thereby limiting their wide applications in the nanozyme-catalytic field. To address the above issues, we herein integrated NiCo 2 S 4 with N,S-rGO to fabricate a nanocomposite (NiCo 2 S 4 @N,S-rGO), which showed a stronger peroxidase-mimetic activity than its pristine components. The SSA (155.8 m 2 g -1 ) of NiCo 2 S 4 @N,S-rGO increased by ∼2-fold compared to NiCo 2 S 4 with a pore size of 7-9 nm, thus providing more active sites and charge transfer channels. Based on the Michaelis-Menten equation, the affinity of this nanocomposite increased 40% and 1.1∼10.6-fold compared with NiCo 2 S 4 with N,S-rGO, respectively, highlighting the significant enhancement of the peroxidase-like activity. The enhanced activity of this nanocomposite is derived from the joint participation of ˙OH, ˙O 2 - , and photogenerated holes (h + ), and was dominated by h + . To sum up, N,S-codoping, rich S-vacancies, and multi-valence states for this nanocomposite facilitate electron transfer and accelerate reaction processes. The nanocomposite-based colorimetric sensor gave low detection limits for H 2 O 2 (12 μM) and glucose (0.3 μM). In comparison with the results detected by a common glucose meter, this sensor provided the relative recoveries across the range of 97.4-101.8%, demonstrating its high accuracy. Moreover, it exhibited excellent selectivity for glucose assay with little interference from common co-existing macromolecules/ions, as well as high reusability (>6 times). Collectively, the newly developed colorimetric sensor yields a promising methodology for practical applications in H 2 O 2 and glucose detection with advantages of highly visual resolution, simple operation, convenient use, and satisfactory sensitivity.