Design of fluorescent assays for cyanide and hydrogen peroxide based on the inner filter effect of metal nanoparticles

We have demonstrated the design of a new type fluorescent assay based on the inner filter effect (IFE) of metal nanoparticles (NPs), which is conceptually different from the previously reported metal NPs-based fluorescent assays. With a high extinction coefficient and tunable plasmon absorption feature, metal NPs are expected to be capable of functioning as a powerful absorber to tune the emission of the fluorophore in the IFE-based fluorescent assays. In this work, we presented two proof-of-concept examples based on the IFE of Au NPs by choosing MDMO-PPV as a model fluorophore, whose fluorescence could be tuned by the absorbance of Au NPs with a much higher sensitivity than the corresponding absorbance approach. While the first assay worked in a turn-on mode upon the etching of Au NPs by the analyte, CN^-, the second one functioned in a turn-off mode upon the catalytic growth of Au NPs by the analyte, H₂O₂. As a result, the present IFE-based approach can detect cyanide ranging from 1.0 × 10^-6 to 6.0 × 10^-4 M with a detection limit of 6.0 × 10^-7 M and H₂O₂ ranging from 1.5 × 10^-7 to 2.2 × 10^-5 M with a detection limit of 8.5 × 10^-8 M, respectively. Notably, the present IFE-based approach allows the design of fluorescent assays in a more simple, time-saving, and economical approach when compared with conventional metal NPs-based fluorescent assays, since no modification step of the fluorophore was needed any more.