Competitive capacitive biosensing technique (CCBT): A novel technique for monitoring low molecular mass analytes using glucose assay as a model study

A novel technique for monitoring of low molecular mass analytes using a flow-injection capacitive biosensor is presented. The method is based on the ability of a small molecular mass analyte to displace a large analyte-carrier conjugate from the binding sites of an immobilized biorecognition element with weak affinity to both compounds. A model study was performed on glucose as the small molecular mass analyte. In the absence of glucose, binding of a glucose polymer or a glycoconjugate to concanavalin A results in a capacitance decrease. Upon introduction of glucose, it displaces a part of the bound glucose polymer or glycoconjugate leading to a partial restoration of capacitance. Experimental results show that the change in capacitance depends linearly on glucose concentration within the range from 1.0×10^-5 to 1.0×10^-1 M, corresponding to 1.8 μg ml^-1 to 18 mg ml^-1 in a logarithmic plot, with a detection limit of 1.0×10^-6 (0.18 μg ml^-1) under optimized conditions. In addition, by modifying the molecular mass of the glucose polymer, amount of biorecognition element, and buffer composition, we were able to tune the analyte-sensing range. The developed technique has the benefits of expanded dynamic range, high sensitivity, and excellent reusability.