C-reactive Protein Detection Using an Ion-sensitive Field-effect Transistor (ISFET)-based Aptasensor with a Chemically Modified Gate Surface for Improved Sensitivity

C-reactive protein (CRP) is an inflammation biomarker that requires simple and real-time monitoring for accurate diagnosis. Conventional CRP tests are complicated, expensive, and time-consuming. Field-effect transistor (FET)-based affinity sensors are seen as the ideal solution but it is difficult to obtain FET with sensitive gate structures. In this work, we propose a simple method of chemically modifying the gate surface of a commercial ion-sensitive FET (ISFET) with (3-glycidyloxypropyl)trimethoxysilane (GPTMS) to lower the background noise signal and then immobilize aptamers that provide significant surface potential change when they bind to CRP. The FET aptasensor was able to measure 0.002-20 mu g/mL CRP in 1 x phosphate-buffered saline (PBS) with a higher sensitivity than the nonmodified ISFET sensors with their original pH sensitivity and was on par with other FET sensors without needing expensive nanomaterial or complicated nanofabrication.