Recently, the development of new fluorescent probes for the ratiometric detection of target objects inside living cells has received great attention. Normally, the preparation, modification as well as conjugation procedures of these probes are complicated. On this basis, great efforts have been paid to establish convenient method for the preparation of dual emissive nanosensor. In this work, a functional dual emissive carbon dots (dCDs) was prepared by a one-pot hydrothermal carbonization method. The dCDs exhibits two distinctive fluorescence emission peaks at 440 and 624 nm with the excitation at 380 nm. Different from the commonly reported dCDs, this probe exhibited an interesting wavelength dependent dual responsive functionality toward lysine (440 nm) and pH (624 nm), enabling the ratiometric detection of these two targets. The quantitative analysis displayed that a linear range of 0.5–260 μM with a detection limit of 94 nM toward lysine and the differentiation of pH variation from 1.5 to 5.0 could be readily realized in a ratiometric strategy, which was not reported before with other carbon dots (CDs) as the probe. Furthermore, because of the low cytotoxicity, good optical and colloidal stability, and excellent wavelength dependent sensitivity and selectivity toward lysine and pH, this probe was successfully applied to monitor the dynamic variation of lysine and pH in cellular systems, demonstrating the promising applicability for biosensing in the future.

Colorimetric and fluorescent dual mode detection methods have gained much attention in recent years; however, it is still desirable to develop new colorimetric and fluorescent dual mode nanosensors with more simple preparation procedures, low cost, and excellent biocompatibility. Herein, a colorimetric and fluorescent nanosensor based on B, N, S-co-doped carbon dots (BNS-CDs) was synthesized by one-step hydrothermal treatment of 2,5-diaminobenzenesulfonic acid and 4-aminophenylboronic acid hydrochloride. Using this nanosensor, a highly sensitive assay of Fe3+ in the range of 0.3–546 μM with a detection limit of 90 nM was provided by quenching the red emission fluorescence. It is more attractive that Fe3+ can also be visualized by this nanosensor via evident color changes of the solution (from red to blue) under sunlight without the aid of an ultraviolet (UV) lamp. Furthermore, the designed nanosensor can be applied for efficient detection of intracellular Fe3+ with excellent biocompatibility and cellular imaging capability, and it holds great promise in biomedical applications.Keywords: cell imaging; colorimetric and fluorescent; dual mode; Fe3+ detection; red emission carbon dots;

A new facile fluorescence probing strategy, which was based on N-doped carbon dots (NCDs) and methyl parathion hydrolase (MPH), was developed for the determination of parathion-methyl (PM). The fluorescence intensity of NCDs-MPH system was proportional to PM concentration in the range of 2.38–73.78 μmol/L, with a detection limit of 0.338 μmol/L. Moreover, the present simple and facile method could be used to determine methyl parathion in environmental and agricultural samples successfully. Furthermore, the detection mechanism of this system is inner filter effect and molecular interactions between NCDs and p-nitrophenol, which is the hydrolysis product of PM catalyzed by methyl parathion hydrolase.Download high-res image (118KB)Download full-size imageA novel system made up of nitrogen doped carbon dots (NCDs) and methyl parathion hydrolase (MPH) was developed for the detection of parathion-methyl (PM). This method is based on inner filter effect (IFE) and molecular interactions between NCDs and p-nitrophenol, which is the hydrolysis product of PM catalyzed by MPH.