Electrochemical/visual microfluidic detection with a covalent organic framework supported platinum nanozyme-based device for early diagnosis of pheochromocytoma

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.