Flexible ITO/PET Electrodes on EGFET for pH and Urea Detection Application

• Main Authors: I Shun Wang, 王義舜
• Other Authors: C. S. Lai
• Format: Others
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/25101887049528301818

碩士 === 長庚大學 === 光電工程研究所 === 100 === In this work, pH and urea sensitivity were investigated by using HfO2 EIS structure, ITO/PET electrode and ITO/PET electrode with graghene and PEDOT/PSS membrane. indium tin oxide (ITO) layers were deposited by radio frequency sputtering on flexible polyethylene terephthalate substrates as pH-sensing electrodes of extended gate field effect transistors (EGFETs). When the pH sensitivity of EGFETs for ITO layers with different sheet resistances was compared, a higher sensitivity was found for samples with a lower sheet resistance (100 Ω/□), and a reliability evaluation was carried out for this condition. The temperatures available for measurement are 25-40°C. Up to this point, the behavior of samples stored in dry conditions has been found to persist for more than180 days. The ammoniated indium tin oxide (ITO) films prepared by different condition of NH3 plasma treatment on flexible polyethylene terephthalate substrates are proposed as sensing electrodes of extended gate field-effect-transistors (EGFETs). pH sensitivity calculated from the output voltage in buffer solution from pH 2.1 to pH 12.1 in the samples with NH3 plasma treatment for 6 min is slightly increased about 2.8 mV/pH. For urea detection, enzyme was immobilized on HfO2 EIS structure and ITO/PET electrode by using cross-linking method by using NH3 plasma. Before the urea detection, the pH sensitivity of both the structures was measured. For EIS structure, the pH sensitivity is no difference comparing with the results before NH3 plasma. However, the ITO/PET electrodes show the lower pH sensitivity because of the damage caused by longer treatment time. The output signal of urea detection increased with increasing plasma power and treatment time. It indicates that more active groups could be produced with longer plasma time and large plasma power is beneficial for nitrogen reaction with HfO2 and ITO films. Low-cost substrate and high-reproducibility surface modification of NH3 plasma treatment are suggested to investigate the lifetime and stability for future urea sensor application. For physical adsorption method, the sensitivity of pure graphene layer showed the highest urea sensitivity than the mixed membrane because the higher pH sensitivity and more urease can be attached onto the membranes.