Does the refractive index sensitivity matter the most? Charge of biological material and performance of label-free biosensors

The work discusses the possible impact of the electric charge of biological material on the properties of label-free biosensors, in particular those operating in dual domains, i.e., optical and electrochemical. Optical fiber lossy-mode resonance (LMR) sensors based on indium tin oxide (ITO) were investigated as label-free biosensors with a model biological receptor-target pair, i.e., biotin-avidin. Each of the used biological materials shows different properties, i.e., size, isoelectric point, and, therefore, also charge. The investigations were performed in two electrolytes with differently charged redox couples to better identify the possible influence of chargé of biological material on the optical readout. The obtained results clearly indicate that in designing label-free biosensing solutions, consideration of a broader range of biological materials properties than just refractive index, such as their charge, is required.