Reagentless colorimetric biosensing platform based on nanoceria within an agarose gel matrix

A composite consisting of cerium oxide nanoparticles (nanoceria) and an oxidative enzyme co-entrapped in an agarose gel has been developed for the reagent-free colorimetric detection of biologically important target molecules. The oxidase, immobilized in the agarose matrix, promotes the oxidation of target molecules to generate H₂O₂ that subsequently induces changes in the physicochemical properties of nanoceria exhibiting a color change from white/light-yellow into intense-yellow/light-orange without any requirement for additional colorimetric substrates. By utilizing the unique color-changing property of nanoceria entrapped within the agarose gel, target glucose molecules were very specifically detected over a wide linear range from 0.05 to 2mM, which is suitable to measure the serum glucose level, with excellent operational stability over two weeks at room temperature. The biosensor also exhibited a high degree of precision and reproducibility when employed to detect glucose present in real human serum samples. We expect that this novel nanoceria-based biosensing format could be readily extended to other oxidative enzymes for the convenient detection of various clinically important target molecules.