ON-CHIP FLOW BIOSENSING AND SAMPLING

Amperometric biosensors provide several advantages for online measurements, including sensitivity, rapid response, simplicity and low cost. Their small size is particularly attractive due to the possibility to use them in lab-on-a-chip applications. The availability of lab-on-a-chip setup under flow conditions is highly desirable, not only because it simplifies the handling of the process, but also because measurements become more robust and operator-independent. In this work we study the integration of flow amperometric biosensors within a microfluidic platform when analyte concentration is indirectly measured. As a case study, we used a platinum miniaturized glucose biosensor, where glucose is enzymatically converted to H2O2 that is oxidized at the electrode. An experimental study was carried out to investigate the effect of convective flow (ranging from 1 to 1000 uL/min) on the measurements, because in indirect amperometric detection the inlet flow rate affect both analyte-enzyme contact and mediator transport, to and from the electrode. The outcome allowed identifying the optimal flow rate conditions (lower than10 uL/min) for accurate sensing at high time resolution (10s). The extension of the results to other sensing systems has been achieved by means of a model-based theoretical analysis according to fluid dynamic similarity principles. Furthermore, a lab-on-a-chip application for integrated sampling and biosensing that decouples the two flow rates (with sampling volume ranging from 10 to 50 nL), offering a reliable and robust method of detection for online in-flow measurements, has been developed. A linear response was achieved in physiological glucose concentration range (1-5 mM). On the other, we developed an alternative approach based on in situ bottom-up biosensor-fabrication within a microfluidic platform equipped with properly designed electrical micro-patterns. Preliminary results show that an indirect electrochemical detection of glucose at physiological concentration can be obtained. Further improvements are required to enhance the sensitivity of this detection system for lower glucose concentrations.