Novel nanostructured indium tin oxide electrode for electrochemical immunosensors: Suitability for the detection of TNF-α

The need for new and innovative point of care (POC) systems providing a feasible alternative to costly and time consuming standard laboratory techniques is becoming more evident every day, particularly in the case of cardiovascular diseases. Coupling optical and electrochemical principles for highly specific and sensitive detection of biomarkers could boost the successful implementation of POC systems in biomedical environments. We suggest indium tin oxide (ITO) as a promising material for working electrodes in optoelectrochemical sensors, owing to the rare combination of high electrical conductivity and optical transparency it presents. Moreover, the nanostructured nature of the electrodes' surface is crucial for an eventual miniaturization of the POC system. In this work, we describe the construction and characterization of a nanostructured ITO electrode modified with aryl diazonium salt as transparent substrate for electrochemical immunosensors. The developed electrode was tested for the detection of tumour necrosis factor α (TNF-α), a cardiac biomarker playing an important role in the prevention of heart failure. Macro and microscopic evidences (gathered from electrochemical and spectral techniques) of covalent bonding and high surface coverage are provided. Specific interaction between antigen (TNF-α) and monoclonal antibody (Ab-TNF-α) was verified by fluorescence patterning, confirming the proper bio-recognition of the cytokine. As a proof-of-concept, results of electrochemical impedance spectroscopy (EIS) show stabilized semi-quantitative label-free detection of TNF-α at several concentrations (from 10 pg/mL to 100 pg/mL). These preliminary results demonstrate the feasibility of using transparent substrates for the detection of cytokines at low concentrations, and the consequent application in POC systems for the monitoring of cardiovascular diseases.