Advancement in continuous lactate determination in untreated human serum: multipolymer-based amperometric biosensor coupled with a low-cost 3D-printed microfluidic cell

Enzyme saturation in biosensing has been established as a main hindrance in lactate monitoring due to the high concentration of this species in biological samples. In this paper, a Sonogel-carbon transducer has been used for the fabrication of an amperometric biosensor for lactate (LA) determination. The sensor was constructed by immobilizing lactate oxidase as the bioreceptor and coating the electrode surface with multipolymer layers to minimize enzyme saturation and improve operational stability. This biosensor shows adequate sensitivity (1.74 µA mM^{- 1} cm^-2) in a linear working range from 0.2 mM to 20 mM, suitable for physiological lactate concentrations in biofluids. The response of the biosensor was studied in physiological medium using several potential interferents (glucose, uric acid, dopamine, ascorbic acid, KCl, NaCl, CaCl₂ and BSA), demonstrating negligible interference from these common electroactive species. A microfluidic cell was designed and fabricated using polyethylene terephthalate glycol (PETG) through a rapid and low-cost 3D printing process. Finally, the prepared microfluidic cell was applied to lactate monitoring in flow regime using the biosensor with both synthetic and real untreated human serum samples, showing excellent correlation with two standard reference techniques and confirming its reliability. These results highlight the potential of the proposed microfluidic amperometric biosensor as a robust, real-time tool for biomedical lactate monitoring.