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The preparation of high quantum yield, stable, and multifunctional fluorescent probes is of great significance in the fields of biomedicine and photoelectric sensing. Here, a triphenylamine-based D-π-A fluorescent molecule (TPA-CN) was designed and prepared, demonstrating a fluorescence quantum yield of 88.84%. With a polystyrene nanosphere as the carrier, TPA-CN was encapsulated inside the nanosphere to form intra-nanosphere confining domains. These nanodomain-enhanced fluorescent nanospheres exhibited a fluorescence quantum yield of 98.21%. Using antigen-antibody specificity and the selective catalytic activity of a bioenzyme, with chloramphenicol as a model target, a dual-signal readout biosensor (in fluorescence and colorimetric modes) was designed for ultrasensitive and instrument-free determination. The detection limit was 24 pg/mL within 30 min in fluorescence mode, 38-fold more sensitive and 10-fold faster than that of enzyme linked immunosorbent assays. The nanodomain-enhanced fluorescent probes and dynamic biosensor provide a robust and versatile solution for public health and environmental monitoring needs.

Excessive use of antibiotics in aquaculture severely endangers human health and ecosystems, which has raised significant concerns in recent years. However, conventional laboratory-based approaches regularly required time or skilled manpower. Herein, we propose a point-of-care-testing (POCT) biosensor detection device for the simultaneous determination of multiantibiotics without complex equipment or professional operators. A laser-printed paper-based microfluidic chip loaded with multicolor fluorescence nanoprobes (mCD-μPAD) was developed to rapidly detect sulfamethazine (SMZ), oxytetracycline (OTC), and chloramphenicol (CAP) on-site. These "fluorescence off" detection probes composed of carbon dots (CDs) conjugated with aptamers (donor) and MoS 2 nanosheets (acceptor) (CD-apt-MoS 2 ) were based on Förster resonance energy transfer. Upon the addition of target antibiotics, the significantly recovered fluorescence signal on the μPAD can be sensitively perceived by employing a 3D-printed portable detection box through a smartphone. Under optimal conditions, this μPAD allowed for a rapid response of 15 min toward SMZ, OTC, and CAP with considerable sensitivities of 0.47, 0.48, and 0.34 ng/mL, respectively. In shrimp samples, the recoveries were 95.2-101.2, 96.4-105, and 96.7-106.1% with RSD below 6%. This paper-based sensor opens an avenue for on-site, high-throughput, and rapid detection methods and can be widely used in POCT in food safety.

This study conducted the first extensive and comprehensive investigation of the whole-scale sedimentary antibiotic concentration, possible drivers, environmental fate, and potential ecological risks in the Yangtze River. Totally, 20 antibiotics were detected in the sediments. Results revealed that the order of antibiotic abundance in sediment was fluoroquinolones > tetracyclines > macrolides > sulfonamides > amphenicols. The total antibiotic concentrations were 0.10-134.4 ng/g (mean: 11.88 ng/g). Of these, fluoroquinolones and tetracyclines were the two dominant antibiotic categories. The dominant occurrence of fluoroquinolones and tetracyclines in sediments suggested that the distribution coefficient ( K d ) was one of the important factors to determine their fate. Correlation analysis demonstrated that antibiotic contamination was largely influenced by the local scale of animal husbandry, and the positive correlation between antibiotics and heavy metals was likely driven by their common source of contamination and the complexation. Environmental risk assessment showed that tetracycline and chlortetracycline exhibited potential risks from medium to high in the Yangtze River, although most of the compounds posed minimal and low risks. This work provided a valuable large-scale data set across the whole Yangtze River and revealed the contamination profile of antibiotics. Mitigation and management measures to reduce antibiotic inputs are needed for the Yangtze River basin.

The simultaneous detection of three kinds of small-molecule contaminants (antibiotics, mycotoxins, and hormones) in milk was realized by using an 8-17 DNAzyme-based fluorescent enzyme-linked immunosorbent assay (ELISA), in which 8-17 DNAzyme was utilized as the catalytic enzyme for amplifying the signal. Compared with the conventional ELISA in which horseradish peroxidase is used as the catalyzing factor, this 8-17 DNAzyme-based ELISA could achieve multicolor signal output with lower detection limits. The linearities for chloramphenicol, 17β-estradiol, and aflatoxin M 1 were in the range of 0.3 ng/mL-3 μg/mL, 3 ng/mL-3 μg/mL, and 3 pg/mL-3 ng/mL with quantitation limits of 0.3, 3, and 0.003 ng/mL, respectively. This proposed scheme demonstrated that the 8-17 DNAzyme might be an effective substitute for horseradish peroxidase in ELISA for the development of ultrasensitive and multicolor fluorescence immunoassay, which would stimulate the development of ELISA in a new orientation.

An ultrasensitive and portable colorimetric enzyme-linked immunosorbent assay (ELISA) sensor for antibiotics was fabricated by immobilizing antibodies inside the largely porous and highly hydrophilic nanofibrous membranes. Different from regular electrospun nanofibrous membranes where antibodies may frequently be blocked by the heterogeneous porous structure and sterically crowded loaded on the surface, the controlled microporous structure and increased hydrophilicity of nanofibrous membranes could improve the diffusion properties of antibodies, reduce the sterically crowding effect, and dramatically improve the sensitivity of the membrane-based ELISA. The limitation of detection (LOD) for chloramphenicol (CAP) reached 0.005 ng/mL, around 200 times lower than the conventional paper-based ELISA, making quantitative analysis and portable on-site detection achievable via the use of smartphones. The successful design and fabrication of the nanofibrous membrane-based ELISA with novel features overcome the structural drawbacks of regular electrospun nanofibrous membranes and provide new paths to develop highly sensitive on-site detection of hazardous chemical agents.

Sensitive and precise determination of chloramphenicol (CAP) is of great significance for human health due to its high risk in trace amounts. Solid-state artificial nanochannels are expected to be highly promising sensing devices owing to single-molecule sensitivity, target-specific selectivity, and portability. Herein, we report an aptamer self-assembly-functionalized artificial nanochannel-based sensor for highly sensitive and precise determination of CAP. Aptamer self-assembly (AAs) served as the specific recognition component and were in situ grown on the surface of stable anodic aluminum oxide (AAO) nanochannels to develop an AAs@AAO nanochannel-based sensor. Selective interaction with CAP led to the disassembly of AAs and sensitive current change of AAs@AAO nanochannels, allowing sensitive and precise sensing of CAP in complex food samples. The developed AAs@AAO nanochannel-based sensor showed a wide linear range from 0.32 to 1600 pg. mL -1 , low limit of detection (LOD) of 0.1 pg. mL -1 , high precision with relative standard deviation of 2.9%, and quantitative recoveries of 93.4-102.2% for CAP in milk, milk powder, and honey samples. This work proposes a versatile nanochannel-based platform for facile, sensitive, and precise sensing of hazardous residues in food samples.

Stimuli-responsiveness is an important characteristic that show promising potential in various applications. Herein, a novel ZIF-8-on-Tb-dpn (H 3 dpn = 5-(2',4'-dicarboxylphenyl)nicotic acid) heterostructure is constructed using a heteroepitaxial strategy combining the chemical-responsive (antibiotics) and light-responsive behaviors. The pyridine nitrogen of Tb-dpn acts as an anchor site for Zn 2+ , which helps to overcome the limit of lattice mismatch between two metal-organic frameworks (MOFs) and promotes the growth of ZIF-8 nanocrystals. Based on the synergy effect of two MOFs, ZIF-8-on-Tb-dpn exhibits an efficient turn-off response toward tetracycline and chloramphenicol via competitive absorption, Förster resonance energy transfer, and photoinduced electron transfer processes with limit of detection values of 5.6 and 37.6 nM, respectively, which are three- to -fivefold lower than those of Tb-dpn. Moreover, the nanocage of ZIF-8 is utilized to encapsulate photochromic spiropyran (SP) molecules and realize the reversible conversion between SP and merocyanine (MC) under visible light and ultraviolet light. The MC form is accompanied with strong adsorption at 555 nm, which can erase the emission of Tb 3+ . Therefore, a reversible invisible anticounterfeiting pattern is designed with SP ⊂ ZIF-8-on-Tb-dpn for information anticounterfeiting. The excellent stimuli-responsive ability makes the luminescent platform a potential candidate in luminescence applications.

Herein, a hierarchically porous Zr-MOF-labeled electrochemical aptasensor based on the composite of PtPd@Ni-Co hollow nanoboxes (PtPd@Ni-Co HNBs) and poly (diallyldimethylammonium chloride)-functionalized graphene (PDDA-Gr) was developed for ultrasensitive detection of chloramphenicol (CAP). PtPd@Ni-Co HNBs have excellent conductivity and provide binding sites for aptamers; the functionalized PDDA-Gr improves its dispersibility and conductivity as a substrate material, which can be successfully used to increase the electrode surface area and support more PtPd@Ni-CoHNBs. Besides, hierarchically porous Zr-MOFs (HP-UiO-66) were utilized as signal probes and showed a stronger load capacity for signal molecules than conventional UiO-66. In the presence of CAP, two ingeniously designed Exo III-assisted cyclic amplification strategies further improved the sensitivity of the aptasensor: CAP causes cycle I to release a large amount of trigger DNA (Tr DNA), and then, Tr DNA initiated cycle II, which causes the exposed capture DNA to further bind the signal probes. With these advantages, the constructed aptasensors performed with satisfactory sensitivity in a wide linear range (10 fM-10 nM) and a detection limit of 0.985 fM. Several signal amplification strategies adopted in this study have effectively improved the performance of the sensor, providing a new avenue for the development of ultrasensitive sensors in the food analysis field.

Antibiotic abuse in agricultural products leads to serious food safety issues. To this end, we proposed a mix-and-read and enzyme-free amplified assay for antibiotics based on a dual triple helix-aptamer probe, potentially applicable for on-site monitoring of antibiotic residues. A dual triple helix-aptamer probe can leverage the response toward target molecules without enzyme-based amplification, rendering it sensitive and robust for profiling target molecules. The proposed assay allowed mix-and-read detection of chloramphenicol with a detection limit of 0.18 nM. Besides, it accommodated for specifically resolving chloramphenicol among other antibiotics. Chloramphenicol residual in aquatic products in fish and milk can be precisely determined. Thus, the aptamer probe deems to enrich the toolbox for managing antibiotic use.

Magnetic relaxation switching assays with a broad and tunable detection range can greatly improve current magnetic sensors for biochemical detections, but it remains challenging in terms of the limited detection range and low sensitivity. Herein, we report a methodology that uses click chemistry to assemble different sizes of polystyrene beads and magnetic nanoparticles to prepare versatile magnetic probes for broad-range bioassays with high sensitivity. Small magnetic nanoparticles can be controllably assembled on different sizes of polystyrene beads to form core-satellite structures, acting as broad-range probes that enable the magnetic relaxation switching assays with high sensitivity because different sizes of polystyrene beads can conjugate different numbers of small magnetic nanoparticles. On the basis of click chemistry, we assemble polystyrene beads and magnetic nanoparticles to develop a biosensing technique for analyzing three different antibiotics, with a high sensitivity and a tunable detection range from pg/mL to μg/mL.

We describe herein a newly developed chemiluminescent optical fiber immunosensor (OFIS) with a tunable detection range for multiplexed analysis of veterinary drug residues with vastly different concentrations in milk samples. The optical fiber probe is used as a carrier of biorecognition element as well as a transducer, enabling a low-cost compact design, which makes this system suitable for cost-effective on-site detection of the target analytes. Importantly, the synergy between modulation of the length of the optical fiber sensing region and the number of fibers allows performing multiplexed immunoassays in an easily controllable manner over a tunable detection range from pg/mL to μg/mL analyte concentrations. By combining the optical fiber sensor with a nanocomplex signal amplification system, a highly sensitive chemiluminescent OFIS system is demonstrated for the multiplexed assaying of veterinary drug residues in milk samples with linear ranges of 10-(2 × 10 4 ) pg/mL for chloramphenicol, 0.5-500 ng/mL for sulfadiazine, and 0.1-300 μg/mL for neomycin. This controllable strategy, based on modulation of the fiber probe, provides a versatile platform for multiplexed quantitative detection of both low-abundance and high-abundance targets, which shows great potential for on-site testing in food safety.

The main issues of imaging ellipsometry-based biosensing for small molecules are the low sensitivity and narrow detection range due to the low molecular weight of small molecules that results in a negligible signal. To meet this challenge, we theoretically investigated the deciding factors of the ellipsometry signal and further applied the theory to guide the design of ellipsometry-based biosensor using metal nanoparticles that have a high dielectric constant. Significant signal amplification effects can be achieved by using nanoparticle labels including magnetic nanoparticles and gold nanoparticles. Guided by the theory, we have developed a sensitive surface-enhanced imaging ellipsometry (SEIE)-biosensor for detecting chloramphenicol in real milk sample with high sensitivity (with a limit of detection of 6 pg/mL) and broaden detection range. This nanoparticles-enabled SEIE not only greatly improves the sensitivity of conventional imaging ellipsometry-based biosensors but also retains the advantages of conventional methods in terms of automated and convenient operation, providing an effective strategy for detection of trace small molecules in complex samples that holds great promise in scientific research, clinical diagnosis, and food safety.

The electronic conductivity and electrocatalytic activity of metal chalcogenides are normally enhanced by following the ideal strategies such as substitution/doping of heterogeneous atoms and hybridization of highly conductive carbon supportive materials. Here, a rare earth element (samarium) was substituted with MoSe 2 using the simple hydrothermal method. The lattice distortion due to the substitution of Sm 3+ with MoSe 2 was clearly observed by using high-resolution transmission electron microscopy analysis. As a consequence, the prepared SmMoSe 2 nanorod was encapsulated with graphene oxide (GO) sheets by using ultrasonication process. Furthermore, the GO-encapsulated SmMoSe 2 nanocomposite modified glassy carbon electrode (GO@SmMoSe 2 /GCE) was used for the sensing of chloramphenicol. The results showed that the GO@SmMoSe 2 /GCE revealed the superior electrocatalytic activity with low detection (5 nM) and sensitivity (20.6 μA μM -1 cm -2 ) to electrochemical detection of proposed analyte. It indicates that the substitution of Sm 3+ and encapsulation of GO significantly increased both the electrical conductivity and electrocatalytic activity of MoSe 2 .

Conventional magnetic relaxation switching (MRS) sensor suffers from its relatively low sensitivity when it comes to the analysis of trace small molecules in complicated samples. To meet this challenge, we develop a cascade reaction-mediated magnetic relaxation switching (CR-MRS) sensor, based on the assembly of silver nanoparticles (Ag NPs) and magnetic nanoparticles (MNPs) to improve the sensitivity of conventional MRS. The cascade reaction triggered by alkaline phosphatase generates ascorbic acid, which reduces Ag + to Ag NPs that can assemble the initially dispersed MNPs to form magnetic/silver nanoassemblies, thus modulating the state of MNPs to result in the change of transverse relaxation time. The formed magnetic/silver nanoassemblies can greatly enhance the state change of MNPs (from dispersed to aggregated) and dramatically improve the sensitivity of traditional MRS sensor, which makes this CR-MRS sensor a promising platform for highly sensitive detection of small molecules in complicated samples.

We developed and validated a method for the extraction, identification, and quantitation of four nitrofuran metabolites, 3-amino-2-oxazolidinone (AOZ), 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ), semicarbazide (SC), and 1-aminohydantoin (AHD), as well as chloramphenicol and florfenicol in a variety of seafood commodities. Samples were extracted by liquid-liquid extraction techniques, analyzed by ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), and quantitated using commercially sourced, derivatized nitrofuran metabolites, with their isotopically labeled internal standards in-solvent. We obtained recoveries of 90-100% at various fortification levels. The limit of detection (LOD) was set at 0.25 ng/g for AMOZ and AOZ, 1 ng/g for AHD and SC, and 0.1 ng/g for the phenicols. Various extraction methods, standard stability, derivatization efficiency, and improvements to conventional quantitation techniques were also investigated. We successfully applied this method to the identification and quantitation of nitrofuran metabolites and phenicols in 102 imported seafood products. Our results revealed that four of the samples contained residues from banned veterinary drugs.

Specific antibodies are essential for the immune detection of small molecule contaminants. In the present study, the heavy and light variable regions (V(H )and V(L)) of the immunoglobulin genes from a hybridoma secreting a chloramphenicol (CAP)-specific monoclonal antibody (mAb) were cloned and sequenced. In addition, the light and heavy chains obtained from the monoclonal antibody were separated using SDS-PAGE and analyzed using Orbitrap mass spectrometry. The results of DNA sequencing and mass spectrometry analysis were compared, and the V(H) and V(L) chains specific for CAP were determined and used to construct a single-chain variable fragment (scFv). This fragment was recombinantly expressed as a soluble scFv-alkaline phosphatase fusion protein and used to develop a direct competitive ELISA. Compared with the parent mAb, scFv exhibits lower sensitivity but better food matrix resistance. This work highlights the application of engineered antibodies for CAP detection.

A novel, label-free folding induced aptamer-based electrochemical biosensor for the detection of chloramphenicol (CAP) in the presence of its analogues has been developed. CAP is a broad-spectrum antibiotic that has lost its favor due to its serious adverse toxic effects on human health. Aptamers are artificial nucleic acid ligands (ssDNA or RNA) able to specifically recognize a target such as CAP. In this article, the aptamers are fixed onto a gold electrode surface by a self-assembly approach. In the presence of CAP, the unfolded ssDNA on the electrode surface changes to a hairpin structure, bringing the target molecules close to the surface and triggering electron transfer. Detection limits were determined to be 1.6 × 10(-9) mol L(-1). In addition, thiamphenicol (TAP) and florfenicol (FF), antibiotics with a structure similar to CAP, did not influence the performance of the aptasensor, suggesting a good selectivity of the CAP-aptasensor. Its simplicity and low detection limit (because of the home-selected aptamers) suggest that the electrochemical aptasensor is suitable for practical use in the detection of CAP in milk samples.

A reliable, rapid, and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous determination of chloramphenicol and aflatoxin M(1) in milk has been developed. This method includes simple extraction of sample with acetonitrile, separation on a MGIII-C(18) column using 5 mM ammonium acetate aqueous solution/methanol (60:40, v/v) as mobile phase, and MS/MS detection using multiple reaction monitoring mode. The method was validated according to Commission Decision 2002/657/EC. The limits of detection (LODs) were 0.05 μg/kg for chloramphenicol and 0.005 μg/kg for aflatoxin M(1.) The limits of quantification (LOQs) were 0.2 μg/kg for chloramphenicol and 0.02 μg/kg for aflatoxin M(1). The recovery values ranged from 88.8% to 100.6%, with relative standard deviation lower than 15% in all cases, when samples were fortified at three different concentrations. The decision limits (CCα) and detection capability (CCβ) of the method were also reported. This method has been successfully applied for simultaneous analysis of chloramphenicol and aflatoxin M(1) residues in milk from local supermarkets in China.

A sensitive biotin-streptavidin amplified enzyme-linked immunosorbent assay (BA-ELISA) method was developed for the determination of chloramphenicol residues in milk. The biotin-streptavidin system was applied to enhance the sensitivity. After optimization, the detection limit of the method was found to be 0.042 +/- 0.006 ng mL(-1), which is 8-fold more sensitive than the traditional competitive ELISA using the same antibody and coating antigen. The amplification mechanism of the biotin-streptavidin system and the major factors affecting the sensitivity of detection are discussed. This method was successfully applied to determine the chloramphenicol residues in milk samples with a simple and rapid extraction procedure, and good recoveries (85.66-109.67%) were obtained. The result indicated that the biotin-streptavidin system may be a valuable tool to improve the specific detection of trace veterinary drug residues and could be widely used for routine monitoring of food samples.

Development of microcantilever biosensors for small molecules was exemplified with the beta-adrenergic agonist clenbuterol and the antibiotic chloramphenicol. In this paper, antibody sulfhydrylation and protein A were used to modify the microcantilever Au surface, and the antibody activities on the microcantilever were evaluated with direct competitive enzyme-linked immunosorbent assay (dcELISA). The activity of the antibodies immobilized on the microcantilever via protein A was 1.7-fold of that via the sulfhydrylation reagent 2-iminothiolane hydrochloride. A microcantilever immunosensor method with protein A as the functionalization reagent was established to detect the residues of clenbuterol and chloramphenicol at limits of detection (LOD) of approximately 0.1 and 0.2 ng/mL, respectively. Such LODs were better than that of the corresponding dcELISAs. The concentration of clenbuterol in a fortified feed sample detected with the microcantilever immunosensor after thorough extraction and purification agreed well with that detected with the dcELISA. Protein A showed to be simple and reproducible for functionalization of the antibodies on the Au surface and, thus, has common application values in microcantilever immunosensor development. The results suggest that microcantilever immunosensors be suitable for detection of small molecules, and the assay sensitivity is mainly related to the quality and activities of the antibodies.

A highly selective and sensitive mesofluidic immunoassay system based on competitive immunoassay in polydimethylsiloxane (PDMS) channels was developed. This immunoassay system was successfully applied to quantificationally detect chloramphenicol (CAP) in animal foods. The glass beads (Ø 250 microm) were amino-silane modified, covalently precoated with chloramphenicol succinate, and then infused into the microchannels (Ø 300 microm); the CAP molecules of samples or standards in flow solution competed for CAP antibody with the CAP immobilized on the beads. The CAP antigen-antibody complex anchored on the beads was probed by Cy5-labeled secondary antibody, and the fluorescence intensities of beads were employed to determine the concentration of CAP. In this system, the detection limit of CAP is 0.008 microg/L. The method reveals good recovery rates from 90 to 108% and coefficients of variance (CV) from 4.72 to 6.52%. The experimental results demonstrate that the bead-based mesofluidic system has high sensitivity and excellent performance. Indeed, this system can readily be operated automatically and expanded for multicomponent analysis. It is therefore an attractive alternative to conventional immunoassays in routine supervised domain application for contamination in foods or the environment.

We report a rapid and ultrasensitive surface plasmon resonance (SPR) assay of chloramphenicol (CAP) by using large gold nanoparticles (40 nm) for signal enhancement on a mixed self-assembled monolayer (mSAM) sensor surface. After immobilization of the target antibiotic CAP through its ovalbumin (OVA) conjugates with an oligoethylene glycol (OEG) linker on the mSAM surface, sequential binding of anti-CAP antibody and IgG/nanogold (40 nm) onto the sensor surface afforded a rapid (<10 min) and ultrasensitive assay format for CAP. A limit of detection (LOD) for CAP as low as 0.74 fg/mL was achieved in aqueous buffer, and the linear working range was between 1-1000 fg/mL. While the LOD of CAP in a honey spiked-specimen is 17.5 fg/mL, the detection range is 80-5000 fg/mL. The mSAM sensor surface was also shown to be highly stable with over 400 binding/regeneration cycles performed.

A method was developed for the analysis of 14 sulfonamide antibiotics and chloramphenicol in honey. These antibiotics have been banned for use in food-producing animals; yet, their residues were found in many samples, illustrating the need for a multiresidue analysis for these antibiotics in honey. The method described here uses an acid hydrolysis step to liberate the sugar-bound sulfonamides followed by a solid-phase extraction to remove potential interferences. Analysis was by liquid chromatography--electrospray ionization--tandem mass spectrometry in negative mode for all 15 analytes. This MRM method generated two structurally significant transitions per compound, and it was designed to conform to U.S. Food and Drug Administration MS confirmation guidelines. It also provides 4-EU identification points. One hundred sixteen samples from 25 countries were analyzed, and 38% were found to contain at least one target antimicrobial. Five different target compounds were found in honey from 13 different countries.

A simple and fast selective extraction of the antibiotic chloramphenicol (CAP) from milk (raw milk, skimmed milk, and milk powder) using a molecularly imprinted polymer (MIP) sorbent is described. The method entails a single centrifugation step prior to loading the supernatant onto the MIP cartridge and subsequent elution with a mixture of solvents. CAP was further analyzed by isotope dilution liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) operating in negative ionization acquisition mode. The advantages of the MIP approach were assessed by comparing the data generated from a classical solid-phase and liquid-liquid extractions procedure, previously developed in our laboratory. A better recovery of CAP due to an enhanced selectivity and a faster turnaround time (18 samples processed within 3 h compared to 8 h with the classical approach) were evidenced when using the MIP cleanup. The analysis of CAP in raw milk was further validated according to the 2002/657/EC European Union criteria for the analysis of veterinary drug residues at the minimum required performance limit (MRPL) of 0.3 microg/kg, using CAP-d(5) as internal standard. Non-internal-standard corrected recovery values ranged between 50% and 87% over the range of concentrations considered. The decision limit (CCalpha) and detection capability (CCbeta) were calculated to be 0.06 and 0.10 microg/kg, respectively.

A rapid confirmatory method for monitoring chloramphenicol (CAP) residues in honey, whole milk, and eggs is presented. This method is based on the polymer monolith microextraction (PMME) technique and high-performance liquid chromatography (HPLC)-electrospray ionization mass spectrometry (MS). A poly(methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary column was selected as the extraction medium. To obtain optimum extraction efficiency, several parameters related to PMME were investigated. After dissolution in 20 mM phosphate solution at pH 4.0 and centrifugation, honey, eggs, or milk samples were directly passed through the extraction tube. The LC-MS instrument was equipped with an electrospray ion source and a single quadrupole. The eluates were analyzed by LC-MS in the negative-ion mode and by monitoring a pair of isotopic ions for the target compound. The in-source collision-induced dissociation process produced confirmatory ions. The recoveries of CAP from real samples spiked at 0.1-10 ng/g (honey), 0.2-10 ng/mL (milk), and 0.2-10 ng/g (egg) were in the range of 85-102%, with relative standard deviations ranging between 2.1% and 8.9%. The limits of detection (S/N = 3) were 0.02 ng/g, 0.04 ng/mL, and 0.04 ng/g in honey, milk, and eggs, respectively. The proposed method was proved to be robust in monitoring CAP residue in honey, milk, and eggs.

Microarrays have been used as tools for analyzing biological compositions at different levels. In this study, we proposed a small molecule microarray (SMM) method for detection of three veterinary drug residues, chloramphenicol, clenbuterol, and tylosin, in foodstuffs simultaneously and quantitatively. The small drug molecules were immobilized on the surface of the modified glass slides. Then the mixture of drug corresponding antibodies and standards or samples was added to the reaction area. After incubation, the antigen-antibody binding was detected using cy5 labeled secondary antibody. The calibration curves of the residues were drawn, and they indicated the lowest detection limit the linearity range. The detectable concentrations of the three residues are lower than the maximum residue levels (MRLs). No cross reactivity was found among the three residues. The coefficient of variation of the spot intensities was below 5% in a subarray, and below 15% among subarrays. The spike sample test and the comparison of detection results by SMMs and ELISA demonstrated the accuracy of the proposed SMMs method.

An indirect competitive enzyme-linked immunosorbent assay (ELISA) with chemiluminescent (CL) detection for chloramphenicol (CAP) in chicken muscle was developed. CAP-specific polyclonal antibody was raised in rabbit with a CAP-succinate derivative conjugated with bovine serum albumin. Luminol solution was used as the substrate of horseradish peroxidase. The detection limit was 6 ng/L. The CL-ELISA was 10 times more sensitive compared to the colorimetric-ELISA. When CAP was spiked in chicken muscle at levels of 0.05-5 microg/kg, recoveries ranged from 97 to 118% with coefficients of variation of 6-22%. In an actual residue study, the results obtained by CL-ELISA correlated well with those obtained by gas chromatography with microcell electron capture detector. The residue levels of CAP in treated chicken decreased with time and dropped rapidly after the first 6 h from around 50 to 10 microg/kg. After 3 days, CAP was not detected in chicken muscle. The developed method is therefore suitable for screening of CAP in chicken muscle samples.

The potential of a nucleic acid-based optical bioprobe for environmental measurements and drug monitoring is described. The sensor employs the long-wavelength intercalating fluorophore TO-PRO-3 (TP3). Compounds that interact with the TP3-DNA complex are indirectly detected by a decrease in the fluorescence intensity. We found that the configuration and length of the DNA dramatically affected the intensity of the fluorescence emitted from the TP3-DNA complex. We compared nucleic acids from different sources and optimized the system for pBR322 plasmid DNA (4363 bp) digested by HindIII restriction endonuclease. This endonuclease has a single recognition site in plasmid pBR322. In the proposed method, we attempt to combine broad-range detection with rapid and simple operation. A fiber-optic capillary fluorescence system was used to analyze toxic aromatic amines, antibiotics, and several kinds of antitumor drugs, using small amounts of sample, down to 10 muL, with a sensitivity comparable to that of current electrochemical methods. The detection limit can be as low as a few ppb or submicromolar. This approach is useful for routine screening in environmental monitoring or for controlling cytotoxic drug administration. The ease of operation and the rapid response allow high-throughput screening.

A method based on liquid chromatography-tandem mass spectrometry was developed and validated for the qualitative and quantitative detection of chloramphenicol (CAP) in seafood samples. The analysis of CAP residues in seafood is important because CAP can cause serious acute reactions in humans, including aplastic anemia and leukemia. The proposed methodology includes a cleanup solid-phase extraction procedure with high recovery efficiency (>90%). Chromatographic separation of CAP and the internal standard (IS) was carried out on a C(18) column, followed by mass spectrometric detection using electrospray ionization in the negative-ion mode. The precursor/product ion transitions 321-->257 (CAP) and 354-->290 (IS) were monitored. Statistical evaluation of this multiple reaction monitoring mass spectrometric procedure reveals good linearity, accuracy, and inter- and intraday precisions. The limit of detection was 0.1 ng/mL, and the limit of quantification for CAP in seafood samples is 0.02 microg/kg. Application in seafood samples allowed the detection of CAP in low parts per billion levels.

A method based on matrix solid-phase dispersion (MSPD) was developed for the gas chromatographic (GC) determination of chloramphenicol (CAP) residues in animal muscle tissue. Muscle tissue was blended with octadecylsilyl-derivatized silica (C(18)). A column made from the C(18)/muscle tissue matrix was washed with n-hexane and acetonitrile/water (5 + 95), after which CAP was eluted with acetonitrile/water (50 + 50) and partitioned into ethyl acetate. The final extract was evaporated, and a trimethylsilyl derivative of CAP was prepared with Sylon HTP and detected by GC with an electron capture detector (ECD) and a mass spectrometer. For quantitation, the internal standard used was the meta isomer of CAP (m-CAP) for GC-ECD. Muscle tissue samples were fortified at three concentration levels. At 5, 10, and 15 microg/kg levels the respective mean recoveries were 93, 96, and 98%, and the repeatabilities were 13, 11, and 3%. The detection and quantitation limits with ECD were 1.6 and 4.0 microg/kg, respectively. No statistically significant difference was observed in the efficiency of CAP extraction from muscle tissue of various animals (bovine, porcine, and poultry) by the MSPD technique.

Circular dichroism spectra of series of chloramphenicol derivatives la-r were measured in water at pH 7. Compounds 1a-o exhibit two positive Cotton effects at 310--340 and 240--260 nm, respectively, and a weaker negative Cotton effect at 280--300 nm. In analogues 1c, 11, and 1m there is only a minimum between the two positive Cotton effects. Derivatives 1p--r possess a strong negative Cotton effect at ca. 280 nm. Compounds 1a--r were examined as inhibitors of the puromycin reaction with Escherichia coli 70S ribosome-poly(U)-N-AcPhe-tRNA complex. Analogues 11, 1n, lo, and lq are potent competitive inhibitors of puromycin comparable to or better than chloramphenicol (1b). Compounds 1k and 1m are less active, whereas 1d--g and 1j are only moderately effective. The rest of the analogues have marginal or no activity. The results are compared with previous biological data and discussed in terms of a retro-inverso relationship of chloramphenicol (1b) to the aminoacyl moiety of puromycin (aminoacyl-tRNA) and to a hypothetical transition state of peptide bond formation.