Semiquantitative and visual detection of ferric ions in real samples using a fluorescent paper-based analytical device constructed with green emitting carbon dots.

A simple and portable paper-based analytical device was developed for visual and semiquantitative detection of ferric ion in real samples using green emitting carbon dots (CDs), which were prepared microwave method using sodium citrate, urea and sodium hydroxide as raw materials and then loaded on the surface of paper substrate. When Fe exists, the green fluorescence of CDs was quenched and significant color change from green to dark blue were observed, resulting the visual detection of Fe with a minimum distinguishable concentration of 100 μM. By analyzing the intensity changes of green channels of test paper with the help of smartphone, the semiquantitative detection was realized within the range of 100 μM to 1200 μM.

An ultrasensitive colorimetric and fluorescence dual-readout assay for glutathione with a carbon dot-MnO nanosheet platform based on the inner filter effect.

An ultrasensitive colorimetric and fluorescence dual-readout assay based on the inner filter effect (IFE) was developed for glutathione (GSH) determination, in which carbon dots (C-dots) were used as a fluorophore and MnO nanosheets as an absorber. Due to the excellent optical absorption properties of MnO nanosheets and the good spectral overlap between the fluorophore and absorber, MnO nanosheets could effectively quench the fluorescence of C-dots the IFE. As the target, GSH could reduce MnO nanosheets to Mn ions, which inhibited the IFE and resulted in the fading of solution color and the recovery of the fluorescence signal.