Development of durable nitrate-selective membranes for all-solid state ISE and ISFET sensors based on photocurable compositions

Novel nitrate-sensitive membranes have been developed using an aliphatic urethane diacrylate photocurable polymer. This polymer has been chosen due to its easy and fast deposition procedure compared with PVC membranes and its compatibility with microelectronic techniques. These membranes were obtained after UV irradiation during no more than 60 seconds. To optimize their composition and evaluate the chemical response ion selective electrodes (ISEs) with solid inner reference were used. Studies of different plasticizers for nitrate PVC membranes and compositions increasing the ratio between oligomer and diluting agent were performed. ISEs developed presented a sensitivity of -56 mV/dec and a lifetime up to one year. Membrane compositions containing dibutyl phthalate and trioctyl phosphate as plasticizers were deposited onto ISFETs. Studies to elongate ISFETs lifetime were carried out modifying the encapsulation methodology, by using the same polymer family. ISFETs showed a sensitivity between 65-69 mV/decade, depending on the plasticizer, and a linear range of 2.4 × 10-5-0.06 M. The long-term stability of ISFET sensors with trioctyl phosphate plasticizer was up to 10 months, being superior to that described in the literature for PVC membranes and even for other kind of polymers.