Metal Cluster-Based Electrochemical Biosensing System for Detecting Epithelial-to-Mesenchymal Transition.

N-cadherin serves as an important oncobiomarker of epithelial-to-mesenchymal transition (EMT) progression, which identifies invasion and metastasis of malignant tumor cells. Although many efforts have been devoted to quantitative detection of N-cadherin, efforts to analyzing the protein of interest at intact cellular levels are scarce. Herein, a metal cluster-based electrochemical biosensing system is developed to determine the expressing levels of N-cadherin during the EMT process of tumor cells. To be specific, a peptide with a unique sequence and function is designed as a reductant and an anchor to synthesize metal clusters in a precise manner. Consequently, peptide-modified metal clusters possess N-cadherin-targeting, photoluminescence, and electrocatalytic properties. Especially, the redox-active metal clusters function as both an electron-transfer mediator and an electronic conductor for enhanced electrochemical sensing. These favorable features enable them as a rapid, sensitive, and reliable whole-cell biosensor, which integrates the fluorescence and electrochemical signals. This cytosensor can accurately quantify the expression levels of N-cadherin on at least 5000 tumor cells. Further, the current signals of model cancer cells gradually increase with EMT progression, indicating tumor cell-type evolution. Our study represents the advanced bioprobe and analytical methods for accurate quantitation of a biomarker to identify tumor progression.