To achieve the aim and objectives of ‘Sensor4Diabetes’ project, an in-house built thermal oxidation setup was constructed for synthesising 1D semiconducting metal oxide (SMO) nanostructures. Various 1D SMOs such as TiO2, core-shell TiO2-Al2O3, ZnO and CuO was synthesized by thermal oxidation process on Ti, Ti-6Al-4V, brass and Cu substrates, respectively. The growth of 1D nanostructures were optimised. The residual stress inside the particles was measured by XRD-sin2ψ technique. For hybrid mode of sensing, the nanolayers of metal oxides (TiO2 and WO3) were deposited on grated optical fibre using atomic layer deposition (ALD) procedure. The SMOs were characterized by FESEM, EDX, TEM, XRD, and XPS.
Metal oxides were deposited on Au interdigitated substrates and optical fibres for impedometric and hybrid sensing. The substrates were connected to DAQ system with Au wires for measuring the resistance of the sensor in the presence of specific breath environment. For hybrid mode of sensing (both impedometric and photonic simultaneously), a light source and detector was connected with the grated optical fibre surrounded by SMO. The SMO on optical fibre was connected with DAQ system. The resistance and refractive index of SMOs is changed in the presence of breath biomarkers in impedometric and photonic sensing, respectively.
An in-house built experimental setup was constructed for gas sensing experiments. The response, stability, selectivity, optimum operating temperature, detection limit, response time and recovery time was tested of the sensors.
Results revealed four types of morphological variations such as stacked, ribbon, plateau and lamp-post shaped TiO2 nanostructures on oxidized Ti substrates. The 1D TiO2, ZnO and CuO nanostructures have tetragonal rutile, hexagonal wurtzite, and monoclinic structure, respectively. Residual stress is beneficial for 1D growth during thermal oxidation. The growth of nanolayers of SMOs on grated optical fibres via ALD process was optimised.
The SMOs (TiO2 and ZnO based nanostructures) are capable of detecting acetone and ethanol in synthetic breath. The sensors works at high temperatures in the range of 450 to 650 °C. The response of the sensors varied from 10 to 105 depending on SMOs, sensing temperature and concentration of breath biomarker. The response and recovery time of the sensors are in between 3 to 15 min. Based on the findings, the sensors are capable of detecting diabetic biomarkers in breath.
Finally, the project outcome is disseminated through workshops, raising public awareness, website and blog, conference proceedings, journal papers, seminar and outreach activities directed to industry. So far, three conference proceedings, two journal papers and one book chapter have been published from the outcome of this project. Two more journal papers are under preparation.
