Stereoselective recognition of amino acids is extremely important due to its high chirality-dependent interactions and physiological activities in life activities. We herein report a novel functionalized chiral fluorescent nanosensor prepared from surface modification of CdSe/ZnS quantum dots (QDs) with pyroglutamic acid derivatives, which could serve as a chiral recognition module for fluorescence detection of chiral molecules. The sensor exhibited a unique stereoselective fluorescence response to histidine (His), glutamate (Glu), and dihydroxyphenylalanine (Dopa) and had preferable response performance to l-enantiomers. The enantiomeric fluorescence difference ratios of His, Glu, and Dopa enantiomers were 3.90, 3.40, and 2.49, respectively. The mechanism for the enantiomeric fluorescence recognition was systematically studied through a fluorescence spectrum, fluorescence life, and density functional theory (DFT) calculation. Presumably, the different hydrogen bonding capacity of the chiral recognition module with two enantiomers mainly contributed to the difference in fluorescence signals. As a result, a broader application of the pyroglutamic acid derivative-coated QDs as a fluorescence-responsive chiral sensing platform for enantiomeric detection would be expected.

A series of LMOFs with AIE and ESIPT properties, tunable emissions and large Stokes shifts has been facilely synthesized by binding AIEgens with nanoscale ZIF-8 to realize sensitive sensing of copper(ii) and visual fluorescence detection of glucose.

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A hyphenated strategy by off-line coupling of 1,1 ′ -diphenyl-2-picrylhydrazyl-highperformance liquid chromatography, high-speed countercurrent chromatography, and preparative high-performance liquid chromatography was established to screen and separate antioxidants from ethyl acetate fraction of the roots of Polygonum multiflorum. Under the targeted guidance of 1,1 ′ -diphenyl-2-picrylhydrazyl-highperformance liquid chromatography experiment, 12 compounds were identified as potential antioxidants and readily isolated by high-speed counter-current chromatography and preparative high-performance liquid chromatography. Ultraviolet spectroscopy, mass spectrometry, and 1 H NMR spectroscopy were employed to identify their structures, which were assigned as gallic acid (1, 6.2 mg, 98.28%), catechin (2, 8.8 mg, 90.69%), epicatechin (3, 4.1 mg, 96.71%), polydatin (4, 5.3 mg, 94.91%), 2,3,5,4 ′ -tetrahydroxy stilbene-2-O-β-D-glucoside (5, 20.2 mg, 95.23%), piceatannol (6, 5.3 mg, 96.85%), rutin (7, 5.4 mg, 97.92%), resveratrol (8, 5.2 mg, 96.94%), isorhapontigenin (9, 11.4 mg, 94.81%), hyperoside (10, 9.7 mg, 98.52%), rhein (11, 4.9 mg, 97.46%), and emodin (12, 8.2 mg, 95.74%). Notably, compounds 6 and 9 were isolated from Polygonum multiflorum for the first time. In addition, antioxidant activity of compounds 1-12 were evaluated, and compounds 1-8 and 10 exhibited stronger antioxidant activity than ascorbic acid (positive control). These results indicated that the proposed method is a highly efficient strategy to screen and isolate antioxidants from complex natural products. K E Y W O R D Santioxidants, high-speed countercurrent chromatography, preparative high-performance liquid chromatography, traditional Chinese medicine Article Related Abbreviations: DAD, diode array detector; DPPH, 1,1 ′ -diphenyl-2-picrylhydrazyl; HSCCC, high-speed countercurrent chromatography; PEMW, petroleum ether/ethyl acetate/methanol/water; PM, Polygonum multiflorum Thunb.; prep-HPLC, preparative high-performance liquid chromatography.

A facile, green, and high-output hydrothermal synthesis was proposed for the fabrication of highly fluorescent nitrogen-doped carbon quantum dots (N-doped CDs). The nitrogen content in N-doped CDs reached 19.2% and demonstrated strong blue fluorescence emission was obtained with fluorescence quantum yield (QY) of up to 32.9%, which exhibit high fluorescence quantum yield, high photostability, and excellent biocompatibility. The N-doped CDs possess high photostability, low toxicity, and excellent biocompatibility, based on which the N-doped CDs were successfully applied as a fluorescence probe for cell imaging. Moreover, it was then successfully demonstrated for sensitive and selective detection of Fe3+ in serum.

A digital fluorescence detector (DFD), a handheld fluorescence detection device, can convert the fluorescence signal of samples into the corresponding fluorescer concentration. Herein, by adopting a DFD as the readout, a novel intelligent platform was developed based on a ratiometric paper-based device (RPD) for multiple aminoglycoside detection. There are five layers and four parallel channels contained in the designed RPD, functioning as reagent storage, fluidic path control and signal processing, respectively. The rationale of this design lies in the fact that aptamer/graphitic carbon nitride nanosheet (Apt/g-C 3 N 4 NS) modified layers can catalyze o-phenylenediamine to fluorescent 2,3-diaminophenazine (DAP) in the presence of H 2 O 2 . When Apt was removed from nanosheets via the Apt-target reaction, the peroxidase-like activity would be decreased, thus decreasing the production of DAP. All the changes of the fluorescence DAP signal can be read out using a portable DFD. Based on the DFD signal change related to the concentration of the target, a quantitative reaction platform was established. Furthermore, the sample flow and Apt-target reaction time can be reasonably regulated using the H 2 O 2 -cleavable hydrophobic compound modified layer placed between the target recognition region and detection region. Then, the practicality of this platform was verified through realizing sensitive analysis of streptomycin, tobramycin, and kanamycin simultaneously. Overall, with merits including portability and ease of operation, the platform shows great potential in on-site simultaneous detection of multiple targets, especially in resource-limited settings.