fabrication of new ion sensitive field effect transistors (isfet) based on modification of junction-fet for analysis of hydronium, potassium and hydrazinium ions

a novel and ultra low cost isfet electrode and measurement system was designed for isfet application and detection of hydronium, hydrazinium and potassium ions. also, a measuring setup containing appropriate circuits, suitable analyzer (advantech board), de noise reduction elements, cooling system and pc was used for controlling the isfet electrode and various characteristic measurements. the total setup was subjected to several tests. the results showed that the device can differentiate between small difference voltage or current that created in the isfet electrode. also, the setup can differentiate various ph solutions after depositing the polypyrrole membrane on the gate of the transistor. this device is compared of a commercialized isfet device. for controlling the isfet-based electrode and data acquisition a homemade visual basic program was written. various characteristics of isfet electrode such as transfer characteristics, isfet characteristics, sampling experiment, calibration curve, drift, temperature characteristics and hysteresis effect can be derived by the software. the acquired data can be saved under online manner after acquiring any point of data in the output file. using this program, any data point can be acquired by averaging a large number of data (up to 200000 data). in the next part, a simple and low cost ph sensor is introduced based on a commercial jfet. the transistor was mechanically treated, isolated and used as an isfet for ph detection, after electrodeposition of the sensing membrane on its surface. polypyrrole, as a suitable sensing membrane, was electrodeposited on the copper metal gate of the transistor from a solution containing pyrrole monomer, hydroquinone monosulfonate as a proper ligand and sodium salicylate for avoiding the substrate oxidation, under a two-step deposition conditions. the prepared sensor showed a near- nernstian response of 52.3 mv ph-1 over a linear ph range of 2.75-12.20, an ultra low hysteresis of 0.56 mv, a very low drift of 0.14 mv h-1 and a low response time of lower than 8 s. the isfet sensor was also used to fabricate a hydrazine sensor. copper hexacyanoferrate nanoparticles (cuhcf-nps), as a suitable sensing membrane, was electrodeposited on the copper metal gate of the transistor from a solution containing only k4fe(cn)6, under cyclic voltammetry electrodeposition. the prepared sensor showed a super-nernstian response of 94.8 mv / -log(hyd) over a concentration range of 1.17×10-5 - 2.15×10-2 m, a very low drift of 0.04 mv h-1and a detection limit of 3.16 µm. the isfet hydrazine sensor was characterized by various isfet characterization. also by scanning electron microscopy (sem) the nanostructured surface was characterized. cuhcf-nps were also electrodeposited on the copper gate of transistor by cyclic voltammetry and used for potassium determination. the prepared sensor showed a sub-nernstian response of 57.2 mv pk-1 over a concentration range of 11.166×10-5 – 5.432×10-3m, a very low drift of 0.23 mv h-1and a detection limit of 7.037×10-6 m. isfet-based potassium sensor was characterized by various isfet characterization. the selectivity order is cs+ > k+ > na+ > li+ that reflects the effective dimension of the hydrated cations.