Transparent and Enzymeless Glucose Sensors
In this study, we explore single source precursors of Ni alkylthiolate, Ni(SR)2 complexes as an active electrode material and coat them on transparent Au mesh network to fabricate a transparent and highly efficient glucose sensor. The metal thiolate complex is electro-oxidized in the alkaline medium by repeated CV measurements to give rise to Ni redox-active centers with sharp anodic and cathodic peaks. Among different chain length metal alkylthiolates, Ni butanethiolate with the shortest carbon chain (C4) is found to be most efficient in retaining sharp oxidation at low potential value and high current density. Electrochemical property of Ni butanethiolate towards glucose oxidation is examined on different electrode surfaces such as Au thin film, Au mesh and FTO. Interestingly, the glucose oxidation takes place most efficiently on Au mesh network as compared to Au film and FTO substrates. The Ni(SC4H9)2/Au mesh exhibited two linear ranges of detection from 0.5 - 2 mM and 2 - 11 mM with the sensitivity value of 675.97 µA.mM-1cm-2 and Limit of Detection (LOD) of 2.2 µM along with excellent selectivity and reproducibility.
(Contributors to this work: Ajay B. Urgunde, Akshay K. and K. P. Shejale)
Humidity based Breathe Rate Sensor for Physiological Monitoring
Humidity sensors have gained immense importance as non-invasive, wearable healthcare devices for personal care as well as disease diagnostics. However, non-specificity, poor stability at extreme conditions, and low sensitivity of the humidity sensor inhibit its usage as a health monitoring device. In the present study, N-F containing organic molecule, Selectfluor (F-TEDA) based humidity sensors with ~1-2 mm long needle-shaped crystals are fabricated on interdigitated electrodes and exhibit excellent performance. The one-dimensional growth of crystals results in the formation of a conduction pathway for water molecules across the crystal, which otherwise are non-conducting. The as-fabricated humidity sensor at an operational voltage of 0.8 V displays a sensitivity of six orders of magnitude, best reported so far. The sensor does not exhibit any response upon exposure to various volatile organic compounds and reactive gases, indicating remarkable specificity. The sensor is tolerant to high moisture of 95% for prolonged hours followed by monitoring over several days and degrades to 50% of its original sensitivity after exposure of several days. Electrochemical impedance spectroscopy (EIS) shows reversal from resistive to capacitive behavior with increasing humidity levels. The fabricated humidity sensor acts as a healthcare device for breath rate monitoring and touch-free examination of skin moisture.
(Contributors to this work: Gaurav Bahuguna and Vinod S. Adhikary)