Photoinduced discharge of electrons stored in a TiO2-MWCNT composite to an analyte: application to the fluorometric determination of hydrogen peroxide, glucose and aflatoxin B1.

The authors describe an analytical detection scheme based on the use of multiwalled carbon nanotubes (MWCNTs) that accept and store electrons upon contact with photo-irradiated TiO2 nanoparticles (TiO2-NPs). The Fermi level equilibration with photo-irradiated TiO2-NPs has a storage value of 0.35 mM of electrons per 120 mg·L-1 of MWCNTs. The stored electrons can be discharged on demand upon addition of electron acceptors to the TiO2-NP/MWCNT composite. These findings are applied to detect the quencher hydrogen peroxide. H2O2 also is produced on enzymatic action of glucose oxidase on glucose, and this enables glucose also to be quantified by using the TiO2-NP/MWCNT fluorescent nanoprobe. The wide scope of the method also is demonstrated by an assay for aflatoxin B1 that is making use of an FAM-labeled aptamer where the FAM fluorophore on the aptamer quenches the emission of the nanoprobe. The following analytical linear ranges and limits of detection are found: H2O2: 0.1-100 μM and 15 nM; glucose: 5-200 μM and 0.5 μM; aflatoxin: 0.1-40 ng·mL-1 and 0.02 ng·mL-1. The method was applied to the determination of glucose in human serum. Graphical abstract The assays demonstrated in (b) and (c) are based on the fluorescence quenching ability of MWCNTs-TiO2. In the presence of the target (analyte), the fluorescence is restored and the target concentration is determined from the percentage of fluorescence recovery.