A Configurable Mixed-Signal Architecture for Label-Free Smart Biosensor Applications

The authors present a novel approach to perform the readout of a genetic sensor by using a low-frequency impedance-sensing technique based on phase-shift measurements. The proposed architecture is sufficiently simple to be fit into an off-the-shelf programmable system-on-chip (PSoC) and yet has been demonstrated to be powerful enough to measure a wide range of capacitance values (100 pF-10 muF ) with a relative error smaller than 2% compared with a high-cost laboratory instrumentation. Field measurements on real sensing structures demonstrated the functionality of the system in saline solutions characterized by different molarities. In this case, the sensor model could not be reduced to a simple capacitance, and the acquired phase shifts were fitted by exploiting a constant-phase element (CPE) model of the sensor. The worst-case relative error on the extracted capacitance for a given molar concentration is 16% for the 0.1-M solution and 11% for the 0.5-M solution. Since DNA hybridization should cause a capacitance change on the order of 25%, our conclusion is that, in principle, the proposed measurement procedure is able to discriminate between single-stranded and hybridized DNAs. The measured phase shifts as a function of frequency allowed us to extract the parameters of the CPE model with an error on the phase that is smaller than 0.4^deg .