Influence of Eddition Buffer Layer on CRP Sensor Sensitivity Based on ISFET

Abstract

The properties of sensor structure based on ion selectivity field effect transistor for electrical detection of C-reactive protein (CRP) were described and investigated in this paper. This protein is an acute phase biomarker that allows identification of inflammation in human body and also the CRP blood level is known to be associated with probability of cardio-vascular diseases. The physico-technlogical and topological characteristics of sensor based on ISFET with СеО₂ gate dielectric were studied and described in this paper. Cerium dioxide is a promising material for utilization as a gate oxide for FET fabrication and has a number of advantages compared to SiO₂, In particular, it characterized by higher density of surface sensitive centers, better dielectric structure isolation, less current leakage through the dielectric, higher thermal and chemical stability, biocompatibility, as well as effective immobilization of biochemical elements using membranes to create biosensors. Silicon and cerium materials also have close value soflattice constants, ensuring their better adhesion in the structure of the ISFET. The experimental characteristics for both modification of sensors with and without addition buffer layer (melanin) were compared. Surfaces of both structures are almost the same in optical microscope, except surface with melanin has more branched structure. Based on this it was assumed that more streptavidin can be deposited on the surface and, as a result, a greater number of pairs of antigen-antibodies as one of the main working reactions of the biosensors. According to the measurements, sensitivity for both types of sensors was determined and it was established that the sensor sensitivity without melanin was 92 mV/(mg/L), and with addition buffer layer — 204,4 mV/(mg/L). Therefore the additional layer of melanin increases the sensor sensitivity more than 2 folds and this type of sensor is valuable to detect inflammation in human body at the early stage and predict the probability to appear the cardiovascular diseases and also decrease the number of deaths.