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.

Fabrication of carbon dots@restricted access molecularly imprinted polymers for selective detection of metronidazole in serum.

A custom-tailored design was proposed for the fabrication of carbon dots coupled with restricted access materials and molecularly imprinted polymers (CDs@RAM-MIPs) to detect metronidazole (MNZ). Biomass carbon dots (CDs) were derived from longan peels assisted with high pressure microwave, and had the merits of eco-friendly, excellent photostability and low toxicity. In this work, glycidyl methacrylate was used as a co-polymeric monomer to increase hydroxyl groups on the surface of synthetic materials, which eliminated the interference of biological macromolecules. The specific binding cavities of CDs@RAM-MIPs were formed after removing the template molecule (MNZ). The obtained CDs@RAM-MIPs can selectively capture MNZ through the specific interaction between recognition sites and MNZ, and obey photoinduced electron transfer fluorescence quenching mechanism. The highly sensitive and selective fluorescent sensor based CDs@RAM-MIPs had a wide linear range (50-1200 ng mL-1) and a low detection limit (17.4 ng mL-1) for MNZ. It has been utilized to detect MNZ in serum with recoveries of 93.5%-102.7%, and the relative standards (RSDs) were 1.9%-3.6%, respectively. This work provides a thoughtful strategy for preparation and application of CDs@RAM-MIPs, which presages its great potential for detecting trace compounds in real samples.

Microwave-assisted facile synthesis of polymer dots as a fluorescent probe for detection of cobalt(II) and manganese(II).

Polymer dots (PDs) were synthesized at 200 °C for 90 min via a microwave-assisted method. The PDs were characterized by fluorescence spectroscopy, UV-vis absorbance spectra, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The PDs display blue fluorescence under 320 nm excitation with a fluorescent quantum yield of 13.48%. The PDs show stable fluorescence against ion strength and light bleaching, especially extreme pH. Significant pH-independent behavior may relate to -OH of polyvinyl alcohol (PVA) retained on the surface of PDs. The bright fluorescence of PD solution can be distinctly quenched by cobalt ion (Co2+) and manganese ion (Mn2+) in PD solution. For Co2+, the linear was from 3.4 to 50.0 µmol L-1 and 46.7 to 600.0 µmol L-1 with the limit of detection (LOD) of 1.0 µmol L-1. The LOD of Mn2+ was 0.4 µmol L-1 in the range from 1.5 to 100.0 µmol L-1. Self-film-forming PDs (FPDs) were obtained via dropping PD solution on quartz glass. The bright blue fluorescence of FPDs can be obviously quenched by Co2+ and Mn2+. This paper may provide an efficient and flexible approach to the application of on-site detection. Graphical abstract Graphical abstract.

Microwave-assisted preparation of boron acid modified expanded graphite for the determination of chloramphenicol in egg samples.

A rapid and simple method for the synthesis of boron acid modified expanded graphite (B-EG) with the assist of microwave irradiation was developed. The synthesis process can be completed in one-step, where H2SO4 and H3BO3 were used as intercalating agent and KMnO4 was used as oxidizing agent. The obtained B-EG was worm-like and lamellar structure with plenty of small dispersed particles. The B-EG was successfully used as solid phase extraction absorbent for the enrichment and separation of chloramphenicol in egg samples, followed by liquid chromatography tandem mass spectrometry analysis. The predominant conditions affecting extraction efficiency were optimized. Under optimal conditions, the detection limit of the method was 0.27 ng g-1. The relative standard deviations of within-day and between-day were in the range of 2-6% and 2-8%, respectively. The method was successfully used to detect chloramphenicol in five egg samples. At the spiked concentration of 50 ng g-1, the satisfactory recoveries (87-94%) were obtained.

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.

Single-hole hollow molecularly imprinted polymer embedded carbon dot for fast detection of tetracycline in honey.

It is difficult to detect tetracycline (TC) in honey sample by using carbon dots (CDs) because the autofluorescence of the matrix of honey sample overlaps with the fluorescence emission spectrum of the large majority of CDs. Herein, single-hole hollow molecularly imprinted polymers embedded carbon dots (HMIP@CD) was prepared via microwave-assisted method. TC in diluted honey sample was adsorbed by the HMIP@CD within 3 min, after which the HMIP@CD absorbed with TC was separated by centrifugation from honey sample and redispersed into phosphate buffer solution. The autofluorescence of honey that interferes with the fluorescence signal of HMIP@CD was avoided. The method exhibited an excellent linearity within 10-200 µg L-1 and a low detection limit of 3.1 µg L-1. At three spiking levels of TC, the recoveries ranged from 93% to 105% with precisions below 1.6%. This method provides an effective strategy for detecting analyte in complex matrix with autofluorescence interference.

Selective detection of copper ion in complex real samples based on nitrogen-doped carbon quantum dots.

Highly selective nitrogen-doped carbon quantum dots (ND-CQDs) for copper ion (Cu2+) determination were synthesized by a solvent-free pyrolysis of citric acid and histidine. The resultant ND-CQDs display a stable bright blue fluorescence with a satisfactory product yield of 56% and quantum yield of 16%. The ND-CQDs not only show good photostability under continuous UV irradiation, but are also dramatically stable against extreme ionic strengths. The solid powders of the ND-CQDs re-dispersed in water still maintain a strong blue fluorescence after storing at room temperature for 6 months. The ND-CQDs can be employed to selectively detect Cu2+ in a wide linear range of 0.6-30 µM. The detection limit is as low as 0.19 µM. The ND-CQDs were applied for Cu2+ detection in environmental water samples, fruit juice samples, and urine sample. Satisfactory recoveries of 96-102% with relative standard deviations below 3% were obtained. The research provided a promising prospect for selective detection of Cu2+ in the complex matrix. Graphical abstract Schematic illustration of the preparation of the ND-CQDs and its detection mechanism to Cu2.

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).