Nitrogen- and sulfur-doped carbon dots as peroxidase mimetics: colorimetric determination of hydrogen peroxide and glutathione, and fluorimetric determination of lead(II).

Fluorescent carbon dots co-doped with nitrogen and sulfur (N/S CDs) were prepared and found to display viable peroxidase mimicking activity. They have a blue fluorescence (with excitation/emission maxima at 340/456 nm) with a quantum yield of 35%. The N/S CDs catalyze the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2, and this leads to the appearance of a blue solution with a absorption maximum at 654 nm. A colorimetric method was developed for the determination of H2O2 that has a 1.75 µM detection limit and a linear response in the 10-5 to 10-4 M concentration range. The method can be extended to the enzymatic determination of glutathione with a 0.26 µM detection limit and a working range from 0.20 to 100 µM. In addition, the CDs respond to lead(II) which is a quencher of the blue fluorescence at 456 nm, with a detection limit of 11 µM and a working range up to 100 µM. Simultaneously, the color changes can be visually detected with absorbance signal changes from 10 to 100 µM with limit of 3.9 µM. A multiple detection system was worked out that allows monitoring of H2O2 and glutathione successively, and of lead(II). Graphical abstract (A) Schematic representation of the nitrogen & sulphur doped carbon dots with blue fluorescence, (B) the peroxidase-like activity in colorimetric detecting of H2O2 and GSH and (C) the illustration for the application of Pb2+ detection with fluorescence and colorimetric method.

Fluorescent silicon nanoparticles as dually emissive probes for copper(II) and for visualization of latent fingerprints.

The work describes dually-emissive silicon nanoparticles (Si NPs) in aqueous dispersion with two emissions. The Si NPs respond to different solvents independently with various wavelength fluorescence emissions (red to green). The fluorescence emission wavelengths and emissive color of Si NPs can be regulated by adjustment of the solvents. Based on the effect of the solvent, a series different emission color Si NPs is obtained (Si NPs A, B, C and D), which exhibit different fluorescence emission in various solvents. Notably, the Si NP-A (dispersed in water) exhibited excellent analytical performance in sensing Cu2+ ions with amazing fluorescent response from green to brilliant blue light. The much more enhancement at 436 nm than at 500 nm was due to the changing surface chemistry of Si NPs by Cu2+, which was dependent to the concentration of Cu2+ tightly. The excellent sensitivity of Si NP-A towards Cu2+ has been testified with the detection limit as low as 0.91 µM by good linear relationship between ratio of fluorescence intensity (I436/I500) and concentration of Cu2+ (2-30 µM). The Si NP-A can be exploited as a dual-fluorescence visualization agent for latent fingerprints imaging due to the feature of dual emission. The images exhibited green emission under excited at 254 nm, and emerged green light under 365 nm, which allowed the Si NP-A applying in development of latent finger prints at complex background. These acquired fingerprints revealed the particular second-level characteristics. Graphical abstractIllustration of the method for preparation of safranine-dyes silica nanoparticle (Si NPs), the evolution of Si NP-A (VSi NPs/Vwate = 1:2). Si NP-B (VSi NPs/Vdichloromethane = 1:1), Si NP-C (VSi NPs/Vethyl acetate = 1:1) and Si NP-D (VSi NPs/Vacetone = 1:1), and the application of water-dispersed silica nanoparticles (Si NP-A) to the detection and visualization of latent fingerprints (LFPs).

Orange emissive carbon dots for colorimetric and fluorescent sensing of 2,4,6-trinitrophenol by fluorescence conversion.

In this study, infrequent orange carbon nanodots (CNDs) were applied as a dual-readout probe for the effective colorimetric and fluorescent detection of 2,4,6-trinitrophenol (TNP). The orange fluorescence could be rapidly and selectively quenched by TNP, and the colorimetric response from the original pink color to blue could also be captured immediately by the naked eye. A limit of detection of 0.127 µM for TNP was estimated by the fluorescent method and 5 × 10-5 M by visualized detection. Interestingly, the fluorescence of the CNDs with TNP gradually transitioned from orange to green upon irradiation by a UV lamp, and the colorimetric response transitioned from pink to blue to colorless, which ensured effective multi-response detection of TNP. In addition, the CNDs exhibited bright fluorescence, excellent biocompatibility and low toxicity, making them high-quality fluorescent probes for cellular imaging.