Fabrication and Performance of Lactate and Glucose Responsive Hydrogel Biosensors Incorporating Polypyrrole and Carbon Nanotubes

Continual glucose and lactate monitoring is of importance in the measurement of physiological conditions such as hyperlactatemia (>2.0 mM) and hyper- and hypo-glycemia (>5.5 mM and <3.88 mM). Such monitoring can guide patient-specific therapeutic interventions in the management of conditions such as hemorrhaging trauma and diabetes (hyperglycemia). In this study, we have engineered amperometric-enzyme biotransducers for the monitoring of glucose and lactate wherein the enzymes lactate oxidase (LOx) and glucose oxidase (GOx) were hosted within hydrogel membranes consisting of 2-hydroxyethyl methacrylate (HEMA), and other monomers. Enhancements were pursued by forming supramolecular conjugates of the enzymes with Single-Walled Carbon Nanotubes (SWCNT) to promote direct electron transfer and with polypyrrole:poly(styrenesulfonate) (PPy:PSS) nanoparticle inclusions to support redox mediation. Enhancements improved the electronic properties of the responsive hydrogels as characterized by impedance spectroscopy and amperometry. Amperometric dose-response curves (+0.65V vs. Ag/AgCl) were produced for hydrogel-coated, gold-on-polyimide electrodes for 0.0-50.0 mM lithium-L-lactate and D-(+)-glucose (Sigma-Aldrich) in 0.01 M PBS. From the amperometry, CNTs being inherently conductive, show more current when incorporated into the LOx hydrogel. CNTs also serve to facilitate Direct Electron Transfer (DET) to the electrode from the active site of the enzyme. Addition of PPy:PSS, an intrinsically conductive polymer (ICP) further adds to the current response of the hybrid hydrogel containing LOx-CNT and PPy. The most complex hydrogel composed of LOx-CNTs and PPy:PSS showed the highest sensitivity (5.0 x10^-4 A/mM). The sensitivity decreased from the most complex LOx-CNT|PPy:PSS/Gel to the LOx/Gel control which was 2.0x10^-4 A/mM. The sensitivities of the GOx-CNT|PPy:PSS/Gel and GOx/Gel control to glucose were 5.0x10^-4 and 4.0x10^-4 A/mM respectively. Thus, addition of supramolecular complexes based on SWCNTs and PPy:PSS increased the current response and sensitivity from lactate and glucose (not sown) responsive hydrogel biotransducers. These can be extended to sense glucose and lactate of varying concentrations pertinent to various pathologies.