Nickel Cobalt Oxide Nanoneedles for Electrochromic Glucose Sensors

Uniform nanoneedles of binary oxide (Ni and Co) were synthesized on appropriate conducting substrates [fluorine-doped tin oxide (FTO) coated glass and carbon cloth (CC)] and investigated for dual application in electrochromism and glucose sensing. The prepared samples were characterized using electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy to reveal the presence of a NiCo2O4 phase. Porosity analysis was carried to assign the microporous nature of the prepared sample. Detailed electrochemical and in situ bias-dependent optical spectroscopy studies were carried out to understand various aspects related to electrochromism and glucose sensing. A low-operating-voltage (∼2 V) color modulation with 50% contrast between the whitish translucent and dark-brown colors was achieved from the nanoneedle grown on a transparent FTO substrate. Furthermore, additionally, NiCo2O4 nanoneedles grown on a CC substrate, with an enhanced exposed surface area, showed selective glucose-sensing properties with a very high sensitivity of 3000 μA/mM/cm2, as revealed using detailed electrochemical and impedance spectroscopic measurements.