Fast and label-free detection of procalcitonin in human serum for sepsis using a WTe_x-based extended-gate field-effect transistor biosensor

In this article, we present the first instance of depositing WTe_x-sensitive films with varying thicknesses (3, 4, and 5 nm) onto flexible polyimide substrates using radio-frequency sputtering. These films were used to create an extended-gate field-effect transistor (EGFET) for pH sensing and detecting procalcitonin (PCT) in the sera of patients with sepsis or bacterial infections. Among the films, the 4 nm WTe_x film exhibited high sensitivity (59.57 mV/pH), minimal hysteresis (∼0.8 mV), and a low drift rate (0.14 mV/h). Additionally, this WTe_x-based EGFET sensor retained a pH sensitivity of 59.2 mV/pH even after 180 days of operation and exhibited excellent mechanical flexibility, enduring 500 bending cycles without degradation. Moreover, PCT antibodies, activated using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide and N-hydroxysuccinimide, were immobilized on the WTe_x film functionalized with 3-aminopropyl triethoxysilane. This effective immobilization enabled the specific binding of PCT antigens. The WTe_x-based EGFET biosensor demonstrated high sensitivity (18.12 mV/pC_PCT) across a wide dynamic range (1 fg/mL to 1 μg/mL). Furthermore, the PCT concentrations in patient sera, whether from individuals with or without sepsis or bacterial infections, measured by our biosensor were comparable to results obtained using clinical enzyme-linked immunosorbent assay kits.