Chloramphenicol Research Articles

Enhancing mediated electron transfer in for efficient chloramphenicol degradation through Cu-modified Co@C catalyst

The degradation of organic pollutants in wastewater, such as the veterinary antibiotic chloramphenicol (CAP), is commonly achieved by increasing the concentration of reactive oxygen species (ROS). However, the contribution of the mediated electron transfer pathway is often overlooked. To address this, a carbon-coated CuCo bimetallic catalyst (CuCo@C) is synthesized by adding Cu into Co@C to activate peroxymonosulfate (PMS) for efficient degradation of CAP. The CuCo@C/PMS system exhibits high degradation activity, relying on the presence of ROS pathway and the enhanced mediated electron transfer pathway. The latter is facilitated by the excellent electron transport ability of the Cu-added Co@C catalyst, which accepts electrons from the CAP to form the active CuCo@C/PMS* complex, allowing further decomposition of CAP. The strong synergy between these two pathways results in a rate constant of first-order reactions (Kobs) of 0.124 min−1, which is 2.2 and 22.9 times higher than those achieved by the single metal systems of Co@C/PMS and Cu@C/PMS, respectively. Intermediate products and toxicity analysis reveal that the toxicity of the CuCo@C/PMS system for the degradation of CAP is substantially reduced. Overall, this work offers a novel perspective on the efficient activation of PMS through enhancing mediated electron transport pathway.

Removal of antibiotics with different charges in water by graphene oxide membranes

Abstract Antibiotics are a large group of emerging organic pollutants with low concentration levels in the water. The presence of antibiotics will affect the ecological environment and human health. The removal of trace organic compounds by graphene oxide (GO) membranes has attracted extensive attention. This study investigated the removal of three differently charged antibiotics by GO membranes and the influence of water quality on the removal of antibiotics. It showed that a crosslinked ethylenediamine-GO (EDA-GO) membrane had better stability and higher antibiotic removal performance than a non-crosslinked GO membrane. Among the three antibiotics, penicillin (PNC) was negatively charged and had the highest removal efficiency due to steric effect and electrostatic repulsion. A low concentration (10 mmol L−1) of Na+ in water could increase the membrane flux but had no significant effect on the removal of antibiotics. Ca2+ could reduce the membrane flux and improve the removal of chloramphenicol (CAP) and PNC. The removal efficiencies of low-concentration antibiotics (500 μg L−1) were higher than those of high-concentration antibiotics (10 mg L−1). Furthermore, the removal of antibiotics under the condition of actual wastewater quality was higher than those in solutions prepared with ultrapure water. The EDA-GO membrane has great potential in the removal of antibiotics in wastewater.

Effectively facilitating the degradation of chloramphenicol by the synergism of Shewanella oneidensis MR-1 and the metal-organic framework

Electroactive bacteria (EAB) and metal oxides are capable of synergistically removing chloramphenicol (CAP). However, the effects of redox-active metal-organic frameworks (MOFs) on CAP degradation with EAB are not yet known. This study investigated the synergism of iron-based MOFs (Fe-MIL-101) and Shewanella oneidensis MR-1 on CAP degradation. 0.5 g/L Fe-MIL-101 with more possible active sites led to a three-fold higher CAP removal rate in the synergistic system with MR-1 (initial bacterial concentration of 0.2 at OD600), and showed a superior catalytic effect than exogenously added Fe(III)/Fe(II) or magnetite. Mass spectrometry revealed that CAP was transformed into smaller molecular weight and less toxic metabolites in cultures. Transcriptomic analysis showed that Fe-MIL-101 enhanced the expression of genes related to nitro and chlorinated contaminants degradation. Additionally, genes encoding hydrogenases and c-type cytochromes associated with extracellular electron transfer were significantly upregulated, which may contribute to the simultaneous bioreduction of CAP both intracellularly and extracellularly. These results indicated that Fe-MIL-101 can be used as a catalyst to synergize with EAB to effectively facilitate CAP degradation, which might shed new light on the application in the in situ bioremediation of antibiotic-contaminated environments.

Chloramphenicol Derivatization in Its Primary Hydroxyl Group with Basic Amino Acids Leads to New Pharmacophores with High Antimicrobial Activity.

In a previous study published by our group, successful modification of the antibiotic chloramphenicol (CHL) was reported, which was achieved by replacing the dichloroacetyl tail with alpha and beta amino acids, resulting in promising new antibacterial pharmacophores. In this study, CHL was further modified by linking the basic amino acids lysine, ornithine, and histidine to the primary hydroxyl group of CHL via triazole, carbamate, or amide bonding. Our results showed that while linking the basic amino acids retained antibacterial activity, it was somewhat reduced compared to CHL. However, in vitro testing demonstrated that all derivatives were comparable in activity to CHL and competed for the same ribosomal binding site with radioactive chloramphenicol. The amino acid-CHL tethering modes were evaluated either with carbamate (7, 8) derivatives, which exhibited higher activity, or with amide- (4-6) or triazole-bridged compounds (1-3), which were equally potent. Our findings suggest that these new pharmacophores have potential as antimicrobial agents, though further optimization is needed.

A Highly Selective Electrochemical Sensor Based on Molecularly Imprinted Copolymer Functionalized with Arginine for the Detection of Chloramphenicol in Honey.

Developing an efficient method for chloramphenicol (CAP) detection is of great significance for food safety. Arginine (Arg) was selected as a functional monomer. Benefiting from its excellent electrochemical performance, which is different from traditional functional monomers, it can be combined with CAP to form a highly selective molecularly imprinted polymer (MIP) material. It overcomes the shortcoming of poor MIP sensitivity faced by traditional functional monomers, and achieves high sensitivity detection without compounding other nanomaterials, greatly reducing the preparation difficulty and cost investment of the sensor. The possible binding sites between CAP and Arg molecules were calculated by molecular electrostatic potential (MEP). A low-cost, non-modified MIP electrochemical sensor was developed for the high-performance detection of CAP. The prepared sensor has a wide linear range from 1 × 10-12 mol L-1 to 5 × 10-4 mol L-1, achieves a very low concentration CAP detection, and the detection limit is 1.36 × 10-13 mol L-1. It also exhibits excellent selectivity, anti-interference, repeatability, and reproducibility. The detection of CAP in actual honey samples was achieved, which has important practical value in food safety.

Co-Application of Sewage Sludge, Chinese Medicinal Herbal Residue and Biochar Attenuated Accumulation and Translocation of Antibiotics in Soils and Crops

Sewage sludge (SL), Chinese medicinal herbal residues (CMHRs) and the raw materials of biochar (BC) are normally treated as wastes. However, SL, CMHRs and BC are potential candidates for soil amendments. The performances of soils amended with three different proportions (5%, 10% and 20% on a dry-weight basis) of SL-BC and SL-CMHR-BC in terms of ameliorating soil properties and attenuating antibiotics in soil–plant systems were investigated with two common crop species: carrot and lettuce. The amended soils in general showed higher nutrient levels than the control soils, and particularly for the 20% SL-CMHR-BC. The soils with 10% or 20% SL-BC or SL-CMHR-BC apparently retarded the germination performances of the two crop species, but the negative effects were not noticeable after a growing period. Six target antibiotics, amoxicillin (AMX), tetracycline (TC), sulfamethazine (SMX), norfloxacin (NOR), erythromycin (ERY) and chloramphenicol (CAP), were applied for growing the crops by using irrigation water with 3 μg L−1 (IW3) and 30 μg L−1 (IW30) of each antibiotic. The amended soils led to lower levels of antibiotics in the soils and crop tissues as compared with the control, with the 20% SL-CMHR-BC soils showing the most pronounced effect. The effects of the soil amendments on the bioconcentration factor (BCF) varied, but generally with lower values in the amended soils. Both SL-BC and SL-CMHR-BC were proven in the study as potential soil amendments for alleviating the environmental dispersal and human exposure risks of different antibiotics, and specifically 20% SL-CMHR-BC.

Introducing direct probe electrospray ionization tandem mass spectrometry in apiculture: Comparison with other mass spectrometric methods for the determination of antibiotics in bees and honey

Amphenicols and tetracyclines (TCs) antibiotics use in apiculture is mainly focused on the treatment of bee brood diseases. Despite their efficiency, the serious genotoxic effects that some elicit led to their banning for use in apiculture and for chloramphenicol (CAP) in all food-producing animals. In this work, three tandem mass spectrometric methods were developed and validated for the analysis and quantification of CAP, thiamphenicol (TF), florfenicol (FF), tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) in honey and honeybees. With the first, we have demonstrated the first use of probe electrospray ionization (PESI) in conjunction with tandem mass spectrometry (MS/MS) for antibiotics determination in honey and bees entailing a minimum sample preparation for bees, resulting in rapid chemical analysis for both commodities. The second was a reversed-phase HPLC-ESI-MS/MS method sharing the same scope. With the third chiral HPLC-ESI-MS/MS method, it was attempted to separate CAP stereoisomers in both commodities since reports have shown that only the D-threo isomer displays antimicrobial properties. The analytical methods fulfilled validation criteria demonstrating recoveries in the range of 74–92%, managing to address the minimum required performance limit (MRPL) for CAP, with the exception of PESI-MS/MS. The latter displayed a detection capability (CCβ) for all compounds in proximity to 1 ng/g, and an overall runtime of 1.5 min. In total, 68 samples of honeybees and honey were evaluated for amphenicols and TCs residues. CAP was detected only in two honeybee samples, while one honey sample was positive to TC and OTC was detected in traces in another sample. PESI-MS/MS managed to quantify both TC in honey and CAP in bees in proximity to the values assigned by the conventional HPLC-ESI-MS/MS methods. With regard to the separation of CAP's isomers, the chiral method managed to resolute all isomers and quantify CAP in one bee sample in the form of its L-threo stereoisomer. Overall, ABCs detection in honey and related matrices still constitutes a challenge, considering their prevalence and potential applications in major honey-producing countries.

Interactions of metronidazole and chloramphenicol with myoglobin: Crystal structure of a Mb-acetamide product.

Nitroorganics present a general concern for a safe environment due to their health hazards. However, some nitroorganics such as metronidazole (Mtz) and chloramphenicol (CAM) also possess medicinal value. Mtz and CAM can undergo reductive bioactivation presumably via their nitroso derivatives. We show, using UV-vis spectroscopy, that sperm whale myoglobin (swMb) and its distal pocket mutants retaining H-bonding capacity react with Mtz in the presence of dithionite to generate products with spectra suggestive of the Fe-bound nitroso (Fe-RNO; λmax ~420 nm) forms. We have crystallized and solved the X-ray crystal structure of an H64Q swMb-acetamide compound to 1.76 Å resolution; formation of this compound results from the serendipitous crystallographic trapping, by the heme center, of acetamide from the reductive decomposition of Mtz. Only one of the swMb proteins, namely H64Q swMb with a relatively flexible Gln64 residue, reacted with CAM presumably due to the bulky nature of CAM that generally may restrict its access to the heme site.

Molecular dynamics simulations on interactions of five antibiotics with luciferase of Vibrio Qinghaiensis sp.-Q67

A large number of antibiotics have been used in the medical industry, agriculture, and animal husbandry industry in recent years. It may cause pollution to the aquatic environment and ultimately threaten to human health due to their prolonged exposure to the environment. We aim to study the toxicity mechanism of enrofloxacin (ENR), chlortetracycline hydrochloride (CTC), trimethoprim (TMP), chloramphenicol (CMP), and erythromycin (ETM) to luciferase of Vibrio Qinghaiensis sp.-Q67 (Q67) by using toxicity testing combined with molecular docking, molecular dynamics, and binding free energy analysis. The curve categories for ENR were different from the other four antibiotics, with ENR being J-type and the rest being S-type, and the toxicity of these five antibiotics (pEC50) followed the order of ENR (7.281) > ETM (6.814) > CMP (6.672) > CTC (6.400) > TMP (6.123), the order of toxicity value is consistent with the the magnitude of the binding free energy (ENR (−47.759 kcal/mol), ETM (−46.821 kcal/mol), CMP (−42.905 kcal/mol), CTC (−40.946 kcal/mol), TMP (−28.251 kcal/mol)). The van der Waals force provided the most important contribution to the binding free energy of the five antibiotics in the binding system with Q67 luciferase. Therefore, the dominant factor for the binding of antibiotics to luciferase was shape compensation. The face-to-face π-π stacking interaction between the diazohexane structure outside the active pocket region and the indoles structure of Phe194 and Phe250 in the molecular structure was the main reason for the highest toxicity value of antibiotic ENR. The hormesis effect of ENR has a competitive binding relationship with the α and β subunits of luciferase. Homology modeling, molecular docking, molecular dynamics simulations and binding free energy calculations were used to derive the toxicity magnitude of different antibiotics against Q67, and insights at the molecular level. The conclusion of toxicological experiments verified the correctness of the simulation results. This study contributes to the understanding of toxicity mechanisms of five antibiotics and facilitates risk assessment of antibiotic contaminants in the aquatic environment.

Significantly Enhanced Electrocatalytic Reduction of Chloramphenicol from Water Mediated by Fe–F–N Co-doped Carbon Materials

Chloramphenicol (CAP) is a widely used antibiotic drug and poses a great threat to human health and the ecosystem. In this work, an iron–fluorine–nitrogen (Fe–F–N) co-doped porous carbon material was innovatively prepared and applied for the electrocatalytic reduction of CAP from water, and excellent treatment performance was achieved. For an initial CAP concentration of 10 mg/L, after 60 min operation, almost 100% of CAP was removed. The active Fe(II) sites and the F-doping-induced electronic structure of Fe-FNC facilitated the electrocatalytic reductive degradation of CAP by promoting electron transfer, rather than the H*-mediated indirect reduction process. Therefore, a better treatment performance was obtained by Fe-FNC compared to other catalysts such as Fe-NC and FNC. The reaction pathways for CAP reduction were elucidated, and the ecotoxicity of the reaction products was assessed. The toxicity of the intermediate products was found to be significantly reduced, indicative of the good prospect of this method for CAP-containing wastewater pretreatment.

Unraveling kinetics and mechanism of electrocatalytic hydrodechlorination of chlorinated PPCPs by nickel-cobalt metal organic framework supported palladium composite electrode

In this work, a nickel-cobalt bimetallic organic framework (NiCo-MOF) was introduced as an intermediate layer to synthesize a Pd/NiCo-MOF/Nickel foam composite electrode, which was applied for electrocatalytic hydrodechlorination (ECH) of chlorinated pharmaceuticals and personal care products (PPCPs). The introduction of the NiCo-MOF structure dramatically improved the catalytic activity compared with the common Pd/Nickel foam electrode. Combined with transmission electron microscope and X-ray absorption fine structure analysis, catalyst on Pd/NiCo-MOF/Nickel foam surface had smaller particle size. The removal of the Pd/NiCo-MOF/Nickel foam electrode for chloramphenicol (CAP) reached more than 95 % at 40 min, while the removal of the Pd/Nickel foam electrode was only approximately 55 %. In this study, the active atomic hydrogen (H*) adsorbed on the Pd and NiCo-MOF structures is the critical active species to remove chlorinated PPCPs by Pd/NiCo-MOF/Nickel foam electrode. Density functional theory (DFT) was used to calculate and investigate the adsorption strength of the composite electrode structure for CAP, the product and H*. This work provided a new method to achieve higher catalytic performance and reactivity operability and longevity of catalytic materials through the synergism of a NiCo-MOF interlayer with Pd particles.

An Imine-Based Porous 3D Covalent Organic Polymer as a New Sorbent for the Solid-Phase Extraction of Amphenicols from Water Sample.

In this paper, an imine-based porous 3D covalent organic polymer (COP) was synthesized via solvothermal condensation. The structure of the 3D COP was fully characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and powder X-ray diffractometry, thermogravimetric analysis, and Brunauer-Emmer-Teller (BET) nitrogen adsorption. This porous 3D COP was used as a new sorbent for the solid-phase extraction (SPE) of amphenicol drugs, including chloramphenicol (CAP), thiamphenicol (TAP), and florfenicol (FF) in aqueous solution. Factors were investigated for their effects on the SPE efficiency, including the types and volume of eluent, washing speed, pH, and salinity of water. Under the optimized conditions, this method gave a wide linear range (0.1-200 ng/mL) with a high correlation coefficient value (R2 > 0.99), low limits of detection (LODs, 0.01-0.03 ng/mL), and low limits of quantification (LOQs, 0.04-0.10 ng/mL). The recoveries ranged from 83.98% to 110.7% with RSDs ≤ 7.02%. The good enrichment performance for this porous 3D COP might contribute to the hydrophobic and π-π interactions, the size-matching effect, hydrogen bonding, and the good chemical stability of 3D COP. This 3D COP-SPE method provides a promising approach to selectively extract trace amounts of CAP, TAP, and FF in environmental water samples in ng quantities.

Smartphone-integrated tri-color fluorescence sensing platform based on acid-sensitive fluorescence imprinted polymers for dual-mode visual intelligent detection of ibuprofen, chloramphenicol and florfenicol

The abuse of multiple antibiotics and anti-inflammatory drugs can harm the ecological environment and human health. Herein, a smartphone-integrated tri-color fluorescence sensing platform based on acid-sensitive fluorescence imprinted polymers was proposed for dual-mode visual intelligent detection of ibuprofen (IP), chloramphenicol (CAP), and florfenicol (FF). In this research, the dual-mode of tri-color ratiometric fluorescence imprinted sensor (TC-FMIPs) was realized at different pH environments for the detection IP, CAP, and FF. The fluorescence peak at 551 nm of TC-FMIPs was quenched in the presence of IP solution and fluorescence peak at 687 nm was quenched in the presence of CAP phosphate buffer solution (PBS, pH 7.0), while the fluorescence peak at 433 nm kept stable. Interestingly, the TC-FMIPs has a peroxidase-like activity, in which a new fluorescence peak at 561 nm was quenched and the fluorescence peak at 433 nm increased gradually with the addition of FF solution in pH 4.0 PBS. The TC-FMIPs showed a low detection limit of 10 pM, 8.5 pM, and 5.5 nM for IP, CAP, and FF, respectively. Additionally, a smartphone was used to capture of fluorescence colors and read out the RGB values for intelligent detection of IP, CAP, and FF, in which the detection limit was calculated as 15 pM, 12 pM and 7 nM toward IP, CAP and FF, respectively. The smartphone-integrated tri-color fluorescence sensing platform was developed for dual-mode visual intelligent detection of IP, CAP and FF successfully, which provided a new strategy for multi-target detection in the complex environment.

Fabrication of polyglutamic acid-based sensor for electrochemical determination of a phenicol antibiotic in water environment

In this study, a graphite electrode (GrE) modified with polyglutamic acid was used to determine chloramphenicol (CAP), a phenicol antibiotic, in a water environment using adsorptive stripping linear sweep voltammetry. The pGA modification process involved electropolymerization via cyclic voltammetry, resulting in a significantly enlarged electrochemical active area of the pGA/GrE interface (1.5 times greater than that of the unmodified GrE). The highest CAP signal was obtained on the electrode fabricated by scanning 50 cycles in the potential range of -1.2 V to +2.0 V. The CAP signal recorded on the pGA/GrE electrode was nine times higher than that on the GrE, which was due to the larger electrochemical active area of the pGA/GrE and its good adsorption capacity with CAP. Analysis conditions including the pH of electrolyte and accumulation time, were optimized. Under optimal conditions, the calibration curve was built with two linear regions in the concentration ranges of 0.5-20 µmol L-1 (R2 = 0.987) and 20-100 µmol L-1 (R2 = 0.996), and the detection limit for CAP was 0.28 µmol L-1.

Antidepressant exposure as a source of disinfectant resistance in waterborne bacteria

The emergence of disinfectant-resistant pathogens in water is a major threat to public health. However, whether human-consumed pharmaceuticals can induce bacterial resistance to disinfectants remains unclear. Herein, Escherichia coli was exposed to 12 antidepressants, and susceptibility of antidepressant-induced chloramphenicol (CHL)-resistant mutants to disinfectants was tested. Whole genome sequencing, global transcriptomic sequencing, and real-time quantitative polymerase chain reaction were used to elucidate the underlying mechanisms. We observed that duloxetine, fluoxetine, amitriptyline, and sertraline significantly increased the mutation frequency of E. coli against CHL by 15- to 2948-fold. The resultant mutants increased the average MIC50 of sodium hypochlorite, benzalkonium bromide, and triclosan roughly 2- to 8-fold. Consistently, marRAB and acrAB-tolC genes, together with ABC transporter genes (e.g., yddA, yadG, yojI, and mdlA), were triggered to increase the efflux of disinfectants out of the cell, while ompF was inhibited, reducing disinfectant penetration into the cell. Additionally, the occurrence of DNA mutations in marR and acrR in the mutants was observed, potentially resulting in increased synthesis of the AcrAB-TolC pump. This study indicates that pharmaceutical exposure may create disinfectant-resistant bacteria, which may then be released into water systems, providing novel insights into the potential source of water-borne disinfectant-resistant pathogens.

Electrochemical oxidation of chloramphenicol by modified Sm-PEG-PbO2 anodes: Performance and mechanism

Chloramphenicol (CAP) is used extensively in industry and daily life, but its abuse has seriously affected the environment and public health. In this paper, a new composite PbO2 electrode was obtained through the modification Sm and polyethylene glycol (PEG), and an electrocatalytic oxidation technology of CAP degradation was investigated. The results showed that the catalytic degradation ability and industrial service life of the PEG-Sm-PbO2 composite electrode were significantly enhanced. Co-doping inhibited the growth of grains, resulting in the formation of refined pyramidal grains on the surface of the electrode, which increased the number of active spots. The industrial service life of the modified electrode was improved by 87.0%. In addition, the degradation effect under different conditions and mechanism of CAP were also explored. The optimal conditions for CAP degradation were explored, at which time the CAP degradation rate reached 99.1%. The degradation process was in accordance with the primary reaction kinetics, and the apparent rate constant of CAP at the PEG-Sm-PbO2 electrode was raised by 57.1% in comparison with the unmodified electrode, indicating that the modification facilitated the degradation of CAP in the electrode. Finally, two possible CAP degradation pathways were deduced. The results will provide technical support and a theoretical basis for the degradation of persistent organic pollutants.

Characterization of resistance genes and plasmids from sick children caused by Salmonella enterica resistance to azithromycin in Shenzhen, China.

Samonella is 1 of 4 key global causes of diarrhoeal diseases, sometimes it can be serious, especially for yong children. Due to the extensive resistance of salmonella serotypes to conventional first-line drugs, macrolides (such as azithromycin) have been designated as the most important antibiotics for the treatment of salmonella. Antimicrobial resistance is a major public health problem in the world, and the mechanism of azithromycin resistance is rarely studied. This study determined the azithromycin resistance and plasmids of Salmonella enterica isolates from children attending the Shenzhen Children's Hospital. The susceptibility of ampicillin (AMP), ciprofloxacin (CIP), ceftriaxone (CRO), sulfamethoxazole (SMZ), chloramphenicol (CL), and azithromycin (AZM) were detected and the genes and plasmids from azithromycin-resistant Salmonella were detected by Illumina hi-seq and Nanopore MinIone whole genome sequencing (WGS) using a map-based method, and the genomic background of these factors was evaluated using various bioinformatics tools. In total, 15 strains of nontyphoid Salmonella strains that were isolated (including S. typhimurium, S.London, S. Goldcoast, and S.Stanley) demonstrated resistance to azithromycin (minimum inhibitory concentration,MIC from 32 to >256 µg/mL), and the resistance rate was 3.08% (15/487). The sensitivity test to other antibiotics demonstrated 100% resistance to AMP, and the resistance to SMZ and CL was 86.7% and 80.0%, respectively. Through WGS analysis, all isolates were positive for a plasmid-encoded mphA gene. Plasmid incompatibility typing identified five IncFIB(K), five IncHI2/HI2A/Q1, two IncC, one IncHI2/HI2A/N, one IncR, one IncFII and one IncHI2/HI2A plasmids. Sequence analyses of plasmids revealed extensive homology to various plasmids or transposons in regions involved in plasmid replication/maintenance functions and/or in antibiotic resistance gene clusters. mphA is the main gene involved in azithromycin, a macrolide, and resistance to Salmonella. It is usually located on plasmids and easily spreads, hence posing a great threat to the current treatment of Salmonella infection. The plasmid sequence similarities suggest that the plasmids acquired resistance genes from a variety of enterica bacteria and underscore the importance of a further understanding of horizontal gene transfer among enterica bacteria.

Toward a comprehensive understanding of effect of cation distribution and M2+ constituent in spinel ferrite nanocrystals MFe2O4 (M = Co, Mn, and Ni) on the electrochemical response in sensitive detection of chloramphenicol

This paper focuses on investigating the effect of the (M2+) cation constituent and the inverse degree within the lattice structure of MFe2O4 (M = Co, Mn, and Ni) nanocrystals on their electrochemical characteristics and sensing performance under the same experimental condition. Using Rietveld refinement of powder X-ray diffraction (XRD), Raman, and scanning electron microscopy (SEM), physical characterizations of CoFe2O4 (CFO), MnFe2O4 (MFO), and NiFe2O4 (NFO) are observed and analyzed. In particular, a detailed study on current response and kinetic parameters for the electron transfer reactions in the presence of K3/K4 probes and chloramphenicol (CAP) analyte is carried out, respectively, highlighting the positive influence of the electrode modification and comparing the electrochemical characteristics and sensing performance. The ordering of their electrochemical performance is listed as follows: CFO/SPE> NFO/SPE> MFO/SPE. The reason for their electrochemical performance difference is discussed in detail. Namely, the CFO sample possessing high crystallization and phase purity, uniform primary particle size, and especially wholly inversed spinel structure possessing multiple valence states (Co2+ and Co3+) on the octahedral sites offered many unique features, which are beneficial for electrical conductivity, charge transferability, surface area, and electrocatalytic active sites. Despite also being the inversed spinel structure, the NFO with the existence of impurity phases and larger grain size, as well as a lower degree of inversion than the CFO sample showed a lower enhancement in electrochemical response. However, its electrochemical signal response still is higher than that of the normal spinel MFO structure, further confirming the critical role of (M2+) cation constituent and the inverse degree to the electrochemical characteristics and sensing performance.

Flexible SERS sensor using AuNTs-assembled PDMS film coupled chemometric algorithms for rapid detection of chloramphenicol in food

The misuse of chloramphenicol (CAP) has led to the development of drug-resistant strains that pose significant threats to public health. Here, we propose a universal flexible surface-enhanced Raman spectroscopy (SERS) sensor utilizing gold nanotriangles (AuNTs) and polydimethylsiloxane (PDMS) film for rapid detection of CAP in food samples. Initially, AuNTs@PDMS with unique optical and plasmonic properties were used to collect spectra of CAP. Afterward, four chemometric algorithms were executed and compared. Accordingly, random frog-partial least squares (RF-PLS) exhibited optimum results with correlation coefficient of prediction (Rp = 0.9802) and the lowest root-mean-square error of prediction (RMSEP = 0.348 µg/mL). Furthermore, the sensor's efficacy to detect CAP in milk samples was confirmed, and the findings were compatible with the conventional HPLC approach (P > 0.05). Therefore, the proposed flexible SERS sensor could effectively be used to monitor milk quality and safety.

Unveiling the Neglected Roles of Chloride and Sulfate in the Removal of Nitro Compounds by Sulfidated Zero-Valent Iron/Ferrous Ion Systems

Ferrous ions (Fe2+) can effectively promote the removal of pollutants by sulfidated zero-valent iron (S-ZVI), but the role of anions coexisting with Fe2+ was often ignored. This study systematically compared the performances of S-ZVI/FeCl2 and S-ZVI/FeSO4 systems for chloramphenicol (CAP) and nitrobenzene (NB) removal. The results showed that FeCl2 and sulfidation had a synergistic promoting effect on the reaction, but FeSO4 could not promote the removal of nitro compounds by S-ZVI. Liquid chromatography/mass spectrometry (LC/MS) and UV–vis analysis showed that only the nitro group was reduced during the removal of CAP and NB. The results of batch experiments showed that both NaCl and Na2SO4 could effectively promote the reaction, but the promotion effect of Na2SO4 weakened with the decrease of pH. X-ray photoelectron spectroscopy (XPS) analysis showed that Fe2+ could promote the adsorption of SO42– on the surface of S-ZVI. A possible mechanism was proposed: Fe2+ could maintain a low pH level because of hydrolysis, which promoted the adsorption of Cl– and SO42– on the surface of S-ZVI. Cl– promoted the reaction because of its pitting corrosion, while SO42– competed with nitro groups for the adsorption sites. Our findings suggest that the coexisting anions are quite essential in the removal of nitro compounds by S-ZVI/Fe2+ systems.