Degradation and detection of organophosphorus pesticides based on peptides and MXene-peptide composite materials.

Safety problems caused by organophosphorus pesticide (OP) residues are constantly occurring, so the development of new methods for the degradation and detection of OPs is of great scientific significance. In the present study, ß-sheet peptides and ß-hairpin peptides for catalyzing the hydrolysis of OPs were designed and synthesized. The peptide sequences with the highest hydrolytic activity (EHSGGVTVDPPLTVEHSAG) were screened by investigating the effect of the location of the active sites of the peptide and the peptide's structure on the degradation of OPs. In addition, the relationship between the peptides' conformation and hydrolytic activity was further analyzed based on density functional theory calculations. The noncovalent interactions of the peptides with the OPs and the electrostatic potential on the molecular surface and molecular docking properties were also investigated. It was found that peptides with approximate active amino acids consisting of the catalytic triad and with the hairpin structure had enhanced hydrolytic activity toward the hydrolysis of OPs. To develop an electrochemical sensor technique to detect OPs, the conductive MXene (Ti3C2) material was first immobilized with a caffeic acid monolayer via enediol-metal complex chemistry and then bound with the ß-hairpin peptide (EHSGGVTVDPPLTVEHSAG) via carboxy-amine condensation chemistry between the -COOH of caffeic acid and the -NH2 of the peptide to prepare a MXene-peptide composite. Then, the prepared composite was modified on the surface of a glassy carbon electrode to construct an electrochemical sensor for the detection of OPs. The developed technique could be used to monitor OPs within 15 min with a two orders of linear working range and with a detection limit of 0.15 µM. Meanwhile, the sensor showed good reliability for the detection of OPs in real vegetables.

Degradation of Di (2-ethylhexyl) phthalic acid plasticizer in baijiu by a foam titanium flow reactor attached with hairpin-like structured peptide enzyme mimics.

Because of the significant environmental and health hazards imposed by di(2-ethylhexyl) phthalate (DEHP), a common plasticizer, developing safe and green techniques to degrade DEHP plasticizer is of huge scientific significance. It has been observed that environmental contamination of DEHP may also induce serious food safety problems because crops raised in plasticizers contaminated soils would transfer the plasticizer into foods, such as Baijiu. Additionally, when plastic packaging or vessels are used during Baijiu fermentation and processing, plasticizer compounds frequently migrate and contaminate the product. In this study, hairpin-like structured peptides with catalytically active sites containing serine, histidine and aspartic acid were found to degrade DEHP. Furthermore, after incorporating caffeic acid molecules at the N-terminus, the peptides could be attached onto foam titanium (Ti) surfaces via enediol-metal interactions to create an enzyme-mimicking flow reactor for the degradation of DEHP in Baijiu. The structure and catalytic activity of peptides, their interaction with DEHP substrate and the hydrolysis mechanism of DEHP were discussed in this work. The stability and reusability of the peptide-modified foam Ti flow reactor were also investigated. This approach provides an effective technique for the degradation of plasticizer compounds.

Smartphone-integrated dual-emission fluorescence sensing platform based on carbon dots and aluminum ions-triggered aggregation-induced emission of copper nanoclusters for on-site visual detecting sulfur ions.

A ratiometric fluorescence strategy was proposed based on carbon dots (CDs) and self-assembled copper nanoclusters (CuNCs) driven by Al3+ ions for S2- detection. Si-CDs/CuNCs@Al3+ exhibits blue and red emission under single excitation. Interestingly, the red emission of the CuNCs was regularly quenched while the blue fluorescence emission of the CDs was preserved after continuous addition of S2-. The fluorescence spectrometer-based S2- linear range is from 0.5 to 40 µM, with a low detection limit (LOD) of 0.16 µM. The fluorescence response of Si-CDs/CuNCs@Al3+ to S2- exhibits a distinct color change process (red to pink to blue), implying feasibility of visual analysis. A portable fluorescence sensing platform was established using the color-to-value conversion function of a smartphone for accurate visualization and quantitative identification of S2- without spectrometer. The fluorescent test strips prepared with Si-CDs/CuNCs@Al3+ can conduct on-site visual analysis of S2- in the water environment more conveniently and quickly. The linear range of S2- detection based on the smartphone-integrated test strip sensing platform is 1-40 µM, and the LOD is 0.42 µM. This work provides a new horizon for target on-site analysis in environmental samples.

Molecularly imprinted polymers combined with membrane-protected solid-phase extraction to detect triazines in tea samples.

Spherical molecularly imprinted polymers (MIPs) were prepared by emulsion polymerization. The isothermal adsorption and selective adsorption indicated that the MIPs obtained exhibit excellent specific recognition for the template (atrazine) and its analogues. The MIPs were encapsulated in a polypropylene microporous membrane to fabricate MIP adsorption packages for the direct extraction of triazines in uncentrifuged and unfiltered tea extracts. The extraction conditions affecting the extraction efficiency, including the type and volume of extraction solvent, the number of MIP adsorption packages, the surface area of the MIP adsorption packages, the mass of MIPs in the MIP adsorption packages, the extraction time, the eluting solvent, and the eluting volume, were optimized. Under the optimal extraction and high-performance liquid chromatography-tandem mass spectrometry conditions, the method exhibited excellent linearity in the range from 0.5 to 250 ng g-1, with R2 ≥ 0.9992. The detection limit of the method was 0.09-0.18 ng g-1. The intraday and interday relative standard deviations ranged from 3.1% to 7.5% and from 3.1% to 7.9%, respectively. The method was successfully used to detect triazines in five tea samples. At a spiking concentration of 2 ng g-1, satisfactory recoveries ranging from (81 ± 3)% to (104 ± 7)% were obtained. The membrane-protected solid-phase extraction method based on molecularly imprinted material is expected to be widely used to enrich triazines in complex samples. Graphical Abstract Schematic illustration of the MIPs combined with membrane-protected solid-phase extraction of triazines in tea sample.

Microwave-assisted synthesis of carbon dots for "turn-on" fluorometric determination of Hg(II) via aggregation-induced emission.

A fluorescent probe is presented for sensitive determination of Hg(II). It is based on aggregation induced enhancement effect (AIEE) of carbon dots co-doped with nitrogen and sulfur (N,S-CDs). The N,S-CDs were prepared by a one-pot microwave-assisted method using glycerol as the reaction solvent, and cystine as the source for C, N and S. The resulting CDs are well soluble in water and have a turn-on fluorescence response to Hg(II). The incubation time and ratio of raw materials were optimized. Fluorescence, best measured at excitation/emission wavelengths of 325/385 nm, increases linearly in the 1-75 µM Hg(II) concentration range, and the detection limit is 0.5 µM. The method performed successfully when detecting Hg(II) in spiked tap and lake waters, with recoveries between 92 and 106%. Graphical abstract Schematic presentation of the aggregation induced enhancement of the fluorescence of carbon dots co-doped with nitrogen and sulfur after addition of Hg(II).