Electrochemical/visual microfluidic detection with a covalent organic framework supported platinum nanozyme-based...

The development of smart, portable, and sensitive devices for the monitoring of circulating tumor cells (CTCs) is essential to diagnose several diseases, including pheochromocytoma (PCC). Therefore, in this study, a dual-mode (electrochemical/visual) microfluidic device was designed for the rapid and sensitive detection of PCC-CTCs using a microfluidic chip for automatic cell sampling and detection and a smartphone-based three-dimensional-printed accessory for signal output analysis. The device was employed to capture and identify PCC-CTCs via specific immunogenic binding to the norepinephrine transporter and somatostatin receptor, which are overexpressed on the surface of PCC cells. Specifically, targeted-modified magnetic particles were used to capture and separate PCC-CTCs from peripheral blood; then, similarly modified covalent organic framework based nanozymes (COF@Pt) were used as peroxidase mimics to amplify the electrochemical response from H₂O₂ reduction and catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine by hydroxyl radicals in the presence of the PCC cells to enable visual quantification. Using the prepared microfluidic device, a low detection limit of 1 cell mL^-1 at a signal-to-noise ratio of 3 and a wide linear range of 2 to 10⁵ cells mL^-1 were achieved. Overall, this work demonstrates a portable, sensitive, and visual platform for PCC diagnostics that meets the requirement for quick and precise point-of-care diagnostics.