Nitrocellulose membranes in situ grown with Prussian blue nanoparticles as stable nanozyme pads for colorimetric detection of dopamine

Prussian blue (PB) is a typical peroxidase mimic with simple preparation, low cost and high eco-friendliness, but it still has drawbacks of poor stability (e.g., decomposition in aqueous dispersions) and intrinsic optical interference (e.g., high extinction coefficient over a wide wavelength range) in colorimetric assays. Herein, we used nitrocellulose (NC) membranes as synthesis hosts of PB nanoparticles (NPs) to develop a new type of three-dimensional (3D) porous nanozyme pad. By means of an in situ synthesis route, PB NPs were uniformly grown on the surfaces of the fiber scaffolds with desirable stability, which also avoided signal interference from PB NPs owing to the easy handling of the pads in a quantitative solid state. The pads showed significant peroxidase-mimicking activity toward the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with the output of colorimetric signals. Based on the reduction of oxidized TMB (oxTMB) by dopamine (DA), the pads were exploited for simple and quantitative colorimetric detection of DA with a limit of detection (LOD) of 0.59 μM and a satisfactory accuracy for analysis of real human urine samples. This is the first attempt at exploiting NC membranes as the synthesis hosts to develop nanozyme pads, which solves the above drawbacks of traditional PB-based peroxidase mimics and has promise for various colorimetric bioanalyses, given the structural benefits of NC membranes and their broad applications in biosensors.