Rapid and label-free detection of the troponin in human serum by a TiN-based extended-gate field-effect transistor biosensor

In this article, the TiN sensitive film as a sensing membrane was deposited onto n⁺-type Si substrate by a DC sputtering technique for extended-gate field-effect transistor (EGFET) pH sensors and detection of cardiac troponin-I (cTn-I) in the patient sera for the first time. The crystal structure, Raman spectrum, element profile, surface roughness, and surface morphology of the TiN sensitive film were characterized by X-ray diffraction, Raman spectroscopy, secondary ion mass spectroscopy, atomic force microscopy, and scanning electron microscopy, respectively. The sensing performance of the TiN sensitive film is correlated with its relative structural feature. A high sensitivity of 57.49 mV/pH, a small hysteresis voltage of ∼1 mV, and a low drift rate of 0.31 mV/h were obtained in the TiN sensitive film. In addition, the pH sensitivity of this TiN EGFET sensor was preserved approximately 57 mV/pH after operation time of 180 days. Subsequently, the cTn-I antibodies with carboxyl groups activated by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) along with N-hydroxysuccinimide (NHS) were immobilized on the TiN sensitive film functionalizing with 3-aminopropyl triethoxysilane (APTES). After obtaining the successful immobilization of cTn-I antibodies on the TiN EGFET biosensor, the cTn-I antigen specifically binds with its relative antibody. The cTn-I EGFET biosensor showed a high sensitivity of 21.88 mV/pC_cTn-I in a wide dynamic range of 0.01–100 ng/mL. Furthermore, the concentrations of cTn-I in patient sera measured by our TiN EGFET biosensors are comparable to those determined by commercial enzyme-linked immuno-sorbent assay kits.