ABSTRACT
Detecting protein markers in extracellular vesicles (EVs) is becoming a useful tool for basic research and clinical diagnoses. Most EV protein assays, however, require lengthy processes-conjugating affinity ligands onto sensing substrates and affixing EVs with additional labels to maximize signal generation. Here, we present an iPEX (impedance profiling of extracellular vesicles) system, an all-electrical strategy toward fast, multiplexed EV profiling. iPEX adopts one-step electropolymerization to rapidly functionalize sensor electrodes with antibodies; it then detects EV proteins in a label-free manner through impedance spectroscopy. The approach streamlines the entire EV assay, from sensor preparation to signal measurements. We achieved (i) fast immobilization of antibodies (<3 min) per electrode; (ii) high sensitivity (500 EVs/mL) without secondary labeling; and (iii) parallel detection (quadruple) in a single chip. A potential clinical utility was demonstrated by directly analyzing plasma samples from glioblastoma multiforme patients.
ABSTRACT
Surface chemistry critically affects the diagnostic performance of biosensors. An ideal sensor surface should be resistant to nonspecific protein adsorption, yet be conducive to analytical responses. Here a new polymeric material, zwitterionic polypyrrole (ZiPPy), is reported to produce optimal surface condition for biosensing electrodes. ZiPPy combines two unique advantages: the zwitterionic function that efficiently hydrates electrode surface, hindering nonspecific binding of hydrophobic proteins; and the pyrrole backbone, which enables rapid (<7 min), controlled deposition of ZiPPy through electropolymerization. ZiPPy-coated electrodes show lower electrochemical impedance and less nonspecific protein adsorption (low fouling), outperforming bare and polypyrrole-coated electrodes. Moreover, affinity ligands for target biomarkers can be immobilized together with ZiPPy in a single-step electropolymerization. ZiPPy-coated electrodes are developed with specificity for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The prepared sensor detects SARS-CoV-2 antibodies in human saliva down to 50 ng mL-1 , without the need for sample purification or secondary labeling.
