Thiourea enhanced oxidase-like activity of CeO/CuO nanozyme for fluorescence/colorimetric detection of thiourea and glutathione.

A novel fluorescence/colorimetric dual-mode sensor, based on enhancement of the oxidase-like activity of CeO/CuO nanozyme towards the oxidation of o-phenylenediamine (OPD) induced by thiourea (TU), has been proposed for TU detection. The catalytic activity enhancement on CeO/CuO can be attributed to the strong electron-donation ability of TU, which promoted hydroxyl radical generation and amplified OPD oxidization with enhanced dual-signal readout. By integrating a portable paper-chip and smartphone system, this CeO/CuO-OPD system achieved on-site visual colorimetric analysis of TU. The dual-mode sensor demonstrated high sensitivity and specificity in recognizing TU, with a detection limit (LOD) of 1.90 μM and a linear range (LR) 2.5-80 μM in fluorescent mode; as well as an LOD of 6.69 μM and an LR 10-250 μM in colorimetric mode. Furthermore, the CeO/CuO-TU-OPD system has been designed for dual-mode glutathione (GSH) detection with enhanced sensitivity, achieving an LOD of 0.19 μM and an LR 0.5-10 μM in fluorescent mode; as well as an LOD of 1.24 μM and an LR 1.25-25 μM in colorimetric mode. Additionally, GSH discrimination (fluorescent mode) was successfully achieved in different biological samples, showing good consistency with the standard method. The recoveries ranged from 96.8 % to 116.7 % in serum samples and from 97.3 % to 107.7 % in cell lysates, with RSDs less than 2 %. This work not only introduced a novel approach to enhance oxidase-like activity of nanozymes but also provided an efficient field-suitable tool for enhanced dual-mode response towards TU and GSH.