Wenjing Qi

With increasing emphasis on food safety, there is a growing need for simple, effective, and instrument-free methods to monitor food freshness.

Ce( iv )-CdSe/ZnS QDs exhibit phosphatase-like catalytic activity and were applied for time-dependent ratiometric fluorescence detection of Pi based on two fluorescence wavelengths.

A fast fluorescent dual-emission platform for sensitive detection of sodium dehydroacetate (SDHA) in food is established utilizing bimetallic organic frameworks (Eu@Zr-MOFs). Eu@Zr-MOFs show two fluorescent emissions at 430 nm and 616 nm under single excitation wavelength of 290 nm. Two peaks separated by 180 nm help to eliminate environmental interference and improve the accuracy. In the presence of SDHA, fluorescent intensity at 430 nm and 616 nm shows fluorescent quenching within 1 min. Fluorescent lifetime results show that fluorescent quenching is a static quenching mode. Fluorescent quenching may be ascribed to the diketone structure of SDHA coordinated with Eu³⁺ and internal filtering effect. The logarithm of fluorescent intensity (lgI_{430 nm} * I_{616 nm}) has linear relationship with the concentration of SDHA from 0.1 µM to 200 µM with a limit of detection of 31.6 nM. More conveniently, it also achieves visual detection of SDHA through fluorescent color by portable UV lamp and smartphone “color capture” mode. The platform is applied to detect SDHA in fermented and baked food samples. Thus it is an efficient and sensitive fluorescent ratio method for SDHA detection with fast response, high selectivity and accuracy. Graphical Abstract

A novel electrochemiluminescence (ECL) enhanced method for sensitive, selective and accurate ECL detection of ascorbic acid (AA) is developed using tris (2,2′-bipyridine) ruthenium (II) (Ru(bpy)₃²⁺) embedded into zirconium-based metal-organic frameworks (Ru(bpy)₃²⁺@UiO-67 MOFs). AA is oxidized by cerium ion (Ce⁴⁺) into dehydroascorbic acid (DHA) and hydrolyzed into 2,3-diketogulonic acid (DKG). The oxidation product DKG has α-keto acid structure and can form acyl radical, which enhances the ECL of Ru(bpy)₃²⁺@UiO-67 MOFs nearly 220 times. Therefore, AA is used as an efficient ECL co-reactant of Ru(bpy)₃²⁺@UiO-67 MOFs and applied in highly sensitive ECL enhanced detection of AA from 0.1 μM to 100 μM with a limit of detection of 29 nM. More importantly, this method also has high selectivity in AA detection toward other common ions, substances with similar structure to AA and some reducing substances owing to specific α-keto acid structure of the oxidation product DKG of AA. It achieves ECL enhanced detection of AA in tablets, chewable tablets and beverages. Graphical Abstract

Novel cathodic and anodic dual-emitting electrochemiluminescence (ECL) of Ru(bpy)₃²⁺ and α-keto acids system are studied for the first time. Based on their cathodic and anodic ECL intensity, α-keto acids including oxalate, glyoxylic acid, pyruvic acid, and phenylglyoxylic acid can be directly sensitively detected. The limits of detection (LOD) of oxalate, glyoxylic acid, pyruvic acid, and phenylglyoxylic acid are 31.25 nM, 23.26 µM, 36.36 µM, and 18.52 µM, respectively. Possible mechanism of ECL produced is also proposed. Electrochemical results show that the reduction of oxygen at the cathode to produce ·OH is a vital step for cathodic and anodic dual-emitting ECL. Furthermore, using the enhancement strategy of S₂O₈²⁻/Ag⁺ as coreactant accelerators is proposed considering that decarboxylation of α-keto acids to produce acyl radical can be achieved via S₂O₈²⁻ or Ag⁺. Using the S₂O₈²⁻/Ag⁺ enhancement strategy, the LOD of oxalate, glyoxylic acid, pyruvic acid, and phenylglyoxylic acid are improved and are 2.12 nM, 0.37 µM, 3.23 µM, and 0.28 µM, respectively. Coreactants of Ru(bpy)₃²⁺ with dual-emitting ECL are expanded, which includes additional substances with organic carboxylic acid characterized by the keto group in α-position. It also provides an effective way to enhance ECL and improve sensitivity. More importantly, cathodic and anodic dual-emitting ECL greatly improves the selectivity. Graphical Abstract

A Eu³⁺ functionalized zinc metal–organic framework (Eu@Zn-MOF) has been prepared by the post-synthetic modification method and innovatively used to construct a ratiometric fluorescent probe for tetracycline detection.

Fluorescent silver coordination polymer nanoparticles (Ag-TPA CPNs) were synthesized using a combination of terephthalic acid (TPA) and silver nitrate via an ultrarapid microwave-assisted strategy within 15 min. The Ag-TPA CPNs displayed a high fluorescent quantum yield (QY = 20.19%) and large Stokes shift (~200 nm), with two emission peaks at 490 nm and 520 nm under an excitation wavelength of 320 nm. A fluorescent “turn-off” method using fluorescent Ag-TPA CPNs was applied to detect the alkaline phosphatase (ALP) activity on the basis of the ALP-catalyzed hydrolysis of ascorbic acid 2-phosphate (AA2P) to ascorbic acid (AA), and the AA product triggered the reduction of Ag⁺ ions into silver nanoparticles. The fluorescent lifetime of Ag-TPA CPNs decreased from 3.93 ms to 3.80 ms after the addition of ALP, which suggests that this fluorescent “turn-off” detection of ALP activity is a dynamic quenching process. The fluorescent intensity had a linear relationship with the concentration of ALP in the range of 0.2–12 mU/mL (r = 0.991) and with a limit of detection (LOD) of 0.07 mU/mL. It showed high selectivity in ALP detection towards metal ions and amino acids, as well as other enzymes such as horseradish peroxidase, glucose oxidase, tyrosinase, trypsin, lysozyme, and superoxides. When it was applied for the fluorescent “turn-off” detection of ALP activity in serum samples, mean recovery levels ranging from 99.5% to 101.2% were obtained, with relative standard deviations (RSDs) lower than 4% accuracy. Therefore, it is an efficient and accurate tool for analyzing ALP levels in biosamples.