Elimination of background color interference by immobilizing Prussian blue on carbon cloth: A monolithic peroxidase mimic for on-demand photometric sensing

Prussian blue (PB) is widely used as an artificial peroxidase for electrochemical biosensors, yet it is rarely utilized in photometric detection because of its intrinsic color interference. Herein, we proposed a new strategy, growing PB on common carbon cloth (CC), to obtain a monolithic peroxidase mimic with no background interference for colorimetric detection. Through a one-pot two-step electrodeposition procedure, a robust PB film composed of compactly assembled cubes was coated on CC surface. Since the active PB is immobilized on a bulk substrate (not like previous nanozymes that were dispersed in solution), the color interference from PB itself is efficiently avoided. In addition, the obtained monolithic nanozyme can be put into and taken out from reaction systems expediently and promptly with just a tiny pair of tweezers, which makes it possible for on-demand detection. As demonstrated, the PB-based nanozyme exhibited excellent peroxidase-like activity and could trigger the color reaction of 3,3′5,5′-tetramethylbenzidine in the presence of H2O2, leading to a detection limit of as low as 1.7 μM for H2O2 sensing. A uric acid (UA) colorimetric assay was further established by incorporating the PB/CC peroxidase mimic with natural uricase, providing a linear absorbance response in the analyte concentration scope of 10-700 μM. Reliable analysis of UA in human serum and urine verified the practicability of the fabricated assay.