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A vanadium and tungsten mixed oxide was deposited onto glassy carbon substrates and used as pH sensor in extended gate field effect transistor (EGFET) devices. WO 3 at a molar ratio of about 5% was mixed with V 2 O 5 by means of the sol-gel method. The main focus of this investigation was to determine the operation conditions for the best response of the device and to propose the mechanism involved in the sensor response. The use of either original or reused films were employed and the importance of the total volume of the starting solution was also examined. The time response of the V 2 O 5 /WO 3 -pH-EGFET sensor is due to a deprotonation mechanism of vanadium and tungsten oxide, similarly to a discharging capacitor. The loss of protons by the oxide film depends on the time it remains immersed in the buffer solution and this process is accelerated upon raising the pH value. The increase of the films fabrication volume reduces the importance of the changes of the surface charges compared to the charges of the bulk, leading to less sensitive and less stable sensor response. Therefore, the smaller the amount of material used, the better the sensing properties of the device.The ion sensitive field effect transistor (ISFET) is fabricated by using a standard MOSFET configuration where the gate is replaced by a sensing material that is directly exposed to the target solution. 1 Several papers have demonstrated that this device aids biosensing studies in the medical and biological areas. [2][3][4] An improvement in the configuration of this device has led to the EGFET (extended gate field effect transistor), which was introduced by J. Van Der Spiegel et al. 5 Basically, the sensing membrane is externally connected to the gate of the commercial MOSFET, so that only the sensing membrane is inserted into the desired solution, while the MOSFET is preserved for future reutilization. In the case of pH sensing, a protonation/deprotonation reaction at the membrane controls the surface potential. 6 The measurement occurs when a change in the surface potential between the gate insulator and the electrolyte produces an electric field at the insulator semiconductor interface, thereby modifying the FET channel conductance, and affecting the source-drain current.A wide range of materials has shown to be sensitive membranes for pH sensors. 7-14 Among them, vanadium pentoxide prepared by the solgel method presented good results, because of its lamellar structure, which allows for a large amount of organic and inorganic species to be intercalated. 11,14 This generates an array of electronic properties due to the presence of mixed valences and ionic species related to the diffusion of protons in the aqueous phase. The sensitivity achieved for V 2 O 5 was about 58.1 mV/pH. 14 Nevertheless, the response of the system was limited to pH values up to 10, and above this value the material deteriorated. 14 In order to overcome this problem, V 2 O 5 was mixed with either hexadecylamine 11 or WO 3 , 15 and a better outcome was observed in the la...

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The first synthesis of pentoxide vanadium (V2O5) as gel completed 135 years in 2020. Since its first synthesis, the V2O5 has attracted attention over the years in different areas in science and technology. There are several possibilities to obtain V2O5 resulting in different structures. Among these methods, it is possible to mention the sol–gel, hydrothermal/solvothermal synthesis, electrospinning, chemical vapor deposition (CVD), physical vapor deposition (PVD), template-based methods, reverse micelle techniques, Pechini method and electrochemical deposition that can be considered as the great asset for its varied structures and properties. Progress towards obtaining of different structures of V2O5, and phases have been resulted in lamellar structure with wide interlayer spacing, good chemical and thermal stability and thermoelectric and electrochromic properties. Throughout this advancement, its performance for industrial applications have made a strong candidate in electrochromic devices, photovoltaic cell, reversible cathode materials for Li batteries, supercapacitor, among others. This chapter will be to assist an updated review since the first synthesis up to current development.