Highly sensitive electrochemical immunosensor based on polythiophene polymer with densely populated carboxyl groups as immobilization matrix for detection of interleukin 1β in human serum and saliva

A new impedimetric immunosensor was fabricated for detection of Interleukin 1β (IL-1β) by using semi-conductive poly(2-thiophen-3-yl-malonic acid) (P3-TMA) as an immobilization matrix material and anti-IL-1β antibody as a biorecognition element for the first time. The polymer P3-TMA bound onto hydroxylated ITO surface via ester bond to form a polymer interface including active carboxyl groups. These reactive carboxyl groups bound to anti-IL-1β antibodies via amide bond under coupling reagent of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride/N-hydroxysuccinimide. The detection of IL-1β antigen was monitored with electrochemical impedance spectroscopy technique (EIS). Apart from EIS technique, cyclic voltammetry (CV), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), SEM-energy dispersive X-ray (EDX) mapping, atomic force microscopy (AFM) were used for characterization of immunosensor. The effect of antibody and antigen incubation durations, and utilized biorecognition element concentrations were investigated to determine the optimum analytical performance of the immunosensor. Under optimized conditions, the relative change in impedance was proportional to the IL-1β concentration in the range of 0.01-3 pg/mL with the detection limit 3 fg/mL. The proposed immunosensor had good specificity, reproducibility and stability. The immunosensor was applicable for detection of IL-1β in human serum and saliva samples with satisfied recoveries (97.4-104.5%).