Turning waste into wealth: nitrogen-doped carbon quantum dots derived from fruits wastes for sensing.

Hydrothermal treatment of m-phenylenediamine and grape seed powder has been adopted to synthesize nitrogen-doped carbon quantum dots (N-CQDs). The prepared N-CQDs possessed outstanding optical properties and high quantum yield. Based on the combined effect of static quenching effect and inner filter effect of permanganate (MnO4 - ) to N-CQDs and the redox reaction that occurred between MnO4 - and l-ascorbic acid (l-AA), an 'off-on' fluorescence strategy with N-CQDs has been proposed for the detection of MnO4 - and l-AA. The proposed fluorescent probe was fast, sensitive and selective to MnO4 - and l-AA under mild conditions. In addition, the satisfactory results of the proposed strategy for the detection of MnO4 - and l-AA in real samples indicated its practicability.

Dual-emissive metal-organic framework: a novel turn-on and ratiometric fluorescent sensor for highly efficient and specific detection of hypochlorite.

Hypochlorite (ClO-) is widely used as a disinfectant, whose residue content in water should be strictly controlled due to the potential threat to human health in an inappropriate concentration. Herein, dual-emissive metal-organic frameworks with a UiO-66 prototype structure, PDA/Eu/PDA-UiO-66-NH2(x), were elegantly designed and prepared by a mixed ligand assembly and sequential post-synthesis strategy. Since blue emission is sensitive to ClO-, PDA/Eu/PDA-UiO-66-NH2(40) was selected as a model nanosensor for ratiometric and turn-on sensing of ClO- while red emission acts as a reference signal. Remarkably, PDA/Eu/PDA-UiO-66-NH2(40) shows high efficiency and specificity toward ClO- detection, as verified by a very short response time of 15 s, a wide linear range of 0.1-60 µM, a low detection limit of 0.10 µM, and excellent selectivity toward common competing ions. The recovery experiments show that the recoveries of spiking ClO- in tap water range from 96 to 103%. The rigidification of the coordinated H2N-BDC2- ligands should be responsible for the turn-on fluorescence of PDA/Eu/PDA-UiO-66-NH2(40). This work not only shows a highly efficient and specific fluorescent nanosensor for ClO- detection but also presents the first MOF-based fluorescent probe for turn-on and ratiometric sensing of ClO-.

Enhancement of the thermostability of halohydrin dehalogenase from Agrobacterium radiobacter AD1 by constructing a combinatorial smart library.

Halohydrin dehalogenase from Agrobacterium radiobacter AD1 (HheC) is a key enzyme in preparing ß-substituted alcohols and optically pure epoxides. However, the weak thermostability of HheC greatly limits its industrial application and needs to be improved. In this study, a combinatorial smart library was constructed and screened for enhancing the thermostability of HheC. Mutation sites Lys203 and Lys204 located at the protein surface were selected and simultaneously randomized with charged amino acids (Arg, Asp, Glu, Lys), resulting in a combinatorial smart library. After screening a total of only 48 clones, three positive variants CSL1 (Lys203Arg), CSL2 (Lys204Arg) and CSL3 (Lys203Arg/Lys204Arg) were obtained. Compared to the wild type HheC, variant CSL2 exhibited an increase in thermal stability with a nearly 6.9-fold improvement of half-life (τ1/2, 55°C) at 55 °C without compromising catalytic activity. In addition, the double mutant CSL3 displayed approximately 3.4-fold higher τ1/2, 55°C value and 1.8-fold higher kcat value toward 1,3-dicholoro-2-propanol (1,3-DCP) than that of the wild-type HheC. Homology modeling analysis highlights that the newly gained hydrogen bonds and optimizing charge-charge interactions at the protein surface might contribute to the overall conformational stabilization, leading to improving the thermostability of HheC.