Label-free detection of serum uric acid using novel high-k Sm₂TiO₅ membrane-based electrolyte-insulator-semiconductor

In this study, we constructed a highly pH sensitive electrolyte-insulator-semiconductor (EIS) sensor with a layer of novel rare-earth metal-oxide, Sm₂TiO₅. This high-k membrane with a thickness of 40 nm was deposited on the Si substrate by using reactive cosputtering technique. The effect of annealing temperature on the structural properties and surface roughness of Sm₂TiO₅ membrane was investigated. Based on X-ray diffraction and atomic force microscopy data, it was found that high temperature annealing (900 °C) leads to the formation of crystalline oxide thin film with a rough surface. The pH sensing experiments of EIS with Sm₂TiO₅ membrane annealed at 900 °C shows that reference voltage is linearly dependent on solution pH and an average sensitivity of 60.5 mV/pH. This outstanding pH sensitivity may be attributed to the high surface roughness of oxide membrane. Furthermore, the EIS sensor with Sm₂TiO₅ membrane showed the great stability and no sign of sensitivity degradation within an operation time of 140 days. Finally, we successfully demonstrated the first example of the use of EIS with uricase-immobilized alginate film for the detection of uric acid in serum. The concentration of serum uric acid measured by EIS biosensor is comparable to that determined by commercial assay kit. This sensitive EIS based biosensor can potentially be served as the diagnosis tool for general clinical examinations.