Label-free detection of rheumatoid factor using YbYxOy electrolyte-insulator-semiconductor devices

In this study, we investigated the effect of yttrium content on the structural properties and sensing characteristics of YbYxOy sensing membranes for electrolyte-insulator-semiconductor (EIS) sensors to detect the rheumatoid factor (RF). The YbYxOy EIS device prepared at the 60 W plasma condition exhibited a higher sensitivity of 65.77 mV/pH, a lower hysteresis voltage of ∼1 mV, and a smaller drift rate of 0.14 mV/h than did those prepared at the other conditions. We attribute this behavior to the optimal yttrium content in the YbYxOy film forming a smooth surface. Furthermore, we used a novel YbTixOy EIS biosensor to measure the RF antigen in human serum because of its rapid and label-free detection. Two different techniques were used for the immobilization of RF antibody onto the surface of an YbTixOy EIS sensor. The RF antibody was directly immobilized on the EIS surface modified with 3-aminopropyltriethoxysilane (APTES) followed by glutaraldehyde (GA). In contrast, a mixture of 1-ethyl-3-(3-dimethylamino-propyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) solution was used to functionalize the carboxyl groups at the tail of RF antibodies. RF antibodies functionalized with the active NHS esters were covalently immobilized on the APTES-modified YbTixOy surface. The immobilized RF antibodies on the EIS that are functionalized with the EDC and NHS exhibit higher (41.11mV/pCRF) for detection of serum RF antigen in the range 10(-7) to 10(-3) M, compared to traditional antibody immobilization technique via APTES and GA linkage. The YbTixOy EIS biosensor is a promising analytical tool for RF antigen monitoring due to its good sensitivity, stability and repeatability.