Layer by layer construction of ascorbate interference-free amperometric lactate biosensors with lactate oxidase, ascorbate oxidase, and ceria nanoparticles

We report on the design of an ascorbate interference-free lactate biosensor that takes advantage of the redox properties of ceria (CeO₂) nanoparticles that make this material suitable to be used in electrochemical biosensors operating in low oxygen conditions. First, ceria-free lactate biosensors were fabricated using a positively charged polymer, polyethylenimine (PEI), for the immobilization of lactate oxidase (LOx) and ascorbate oxidase (AOx) on Pt electrodes. When AOx was not immobilized on the electrode, the sensor was interfered by ascorbate. Immobilization of AOx on the electrode surface, however, resulted in a loss of interference by ascorbate due to the depletion of oxygen in the enzyme layer. To address this challenge, we exploited the oxygen storage capacity of ceria nanoparticles. Their introduction into the enzyme layer enabled the fabrication of lactate biosensors that are not interfered by ascorbate and yet can be operated under low oxygen conditions. The Pt/CeO₂–3(PEI/LOx)-3(PEI/AOx) biosensors, if operated at a working voltage of 0.6 V (vs. Ag/AgCl) display a wide linear range (20 μM to 1 mM), a low detection limit (0.3 μM) and a sensitivity of 172.9 ± 11.7 μA∙mM⁻¹∙cm⁻². Evidently, the layer-by-layer configuration eliminates interferences by common species such as ascorbic acid, uric acid, and glucose. The practical applicability of the sensors was evaluated by detecting lactate in human serum. [Figure not available: see fulltext.]