Label-free detection of creatinine using a disposable poly-N-Isopropylacrylamide as an encapsulating creatinine deiminase based Eu ₂Ti ₂O ₇ electrolyte-insulator-semiconductors

In this study, we propose an electrolyte-insulator-semiconductor (EIS) device fabricating from high-k Eu ₂O ₃ and Eu ₂Ti ₂O ₇ sensing membranes deposited on Si substrates through reactive radio frequency sputtering for biomedical engineering applications. We used x-ray diffraction, x-ray photoelectron spectroscopy, and atomic force microscopy to explore the structural and morphological features of these films with annealing at various temperatures. Compared with Eu ₂O ₃ film, Eu ₂Ti ₂O ₇ electrolyte-insulator-semiconductor devices annealed at 900 °C exhibited a higher sensitivity (59.03 mV/pH in the solutions from pH 2 to 12), a smaller hysteresis voltage (2.8 mV in the pH loop 7→4→7→10→7), and a lower drift rate (0.616 mV/h in the pH 7 buffer solution), presumably because of its higher surface roughness and its thinner low-k interfacial layer at the oxide/Si interface. In addition, a disposable poly-N-isopropylacrylamide (PNIPAAm) was used as an encapsulating creatinine deiminase, making easily the loading and removal of a biological recognition element on a biosensor. PNIPAAm film has reversible solubility to become a solution-gelatin state change in response to thermal condition (~32 °C). The high-κ Eu ₂Ti ₂O ₇ creatinine biosensor annealed at 900 °C allowed the potentiometric analysis of creatinine, at concentrations ranging from 10 ^-1 to 10 ^-6 M, with a sensitivity of 42.22 mV/pC _creatinine.