Two haptens were synthesized by introducing spacer arms of different lengths and structures on the free amino of amantadine (AMA). 4-(chlorosulfonyl) benzoic acid (CSBA) was reacted with AMA to produce hapten AMA-CSBA, and succinic anhydride was reacted with AMA to produce hapten AMA-HS. And then, the two haptens coupled with bovine serum albumin (BSA) were prepared as immunogens for the production of monoclonal antibody (mAb). High-sensitive mAbs were obtained and characterized by using indirect competitive enzyme-linked immnunosorbent assay (icELISA). The best antibody was obtained in a heterologous icELISA with an IC50 value of 0.84 and 0.41 ng/mL for AMA and rimantadine, respectively, and negligible cross-reactivity (CR) with memantine and ribavirin. An icELISA was developed to detect AMA residue in chicken muscle. The limit of detection (LOD) was 1 mu g/kg in spiked chicken muscle and the recoveries ranged from 93.6 to 116.9% with the coefficient of variations (CVs) below 9.5%. Good correlation between icELISA and HPLC-MS/MS results in the incurred tissues demonstrated the reliability of the developed icELISA. These results indicated that the new antibody was sufficiently sensitive and specific for the detection of AMA in real samples.
In this work, a novel fiber coating was prepared by using a hybrid material of silica-based ionogels and ionic liquid 1-hexadecyl-3-methylimidazolium bis(trifuluoromethylsulfonyl)imide ([C16MIM][NTf2]). Instead of chemical bonding to sol-gel matrix, high loadings of [C16MIM][NTf2] was confined into the network of silica-based ionogels and thus, the extraction efficiency was significantly improved. The prepared fiber was used for solid-phase microextraction (SPME) of four organophosphorus pesticides (OPPs) from wine and juice samples prior to gas chromatography coupled with flame photometric detection. Under the optimized conditions, the proposed method results in good linearity (R (2) > 0.9991), with low method detection limits (MDLs, S/N = 3) and method quantification limits (MQLs, S/N = 10) in the range of 0.57-4.13 and 1.89-13.76 ng L-1, respectively. The precisions of the method were assessed with repeatability and reproducibility of RSD% E,28 and E,23%, respectively. The spiked recoveries of OPPs from wine and juice samples were in the range of 54 +/- 5-118 +/- 20 and 56 +/- 14-109 +/- 12%, at two different concentration levels. The expanded uncertainties at 1 mu g L-1 were below 20% for target OPPs in all selected samples.
A simple, quick, and efficient method based on dispersive solid phase extraction combined with ultra-high-performance liquid chromatography tandem mass spectrometry has been constructed for the detection of alpha-, beta-, and gamma- hexabromocyclododecane isomer and their hydroxylated metabolites in poultry tissues. Four different samples including poultry muscle, heart, fat, and liver were extracted with acetonitrile and cleaned up through dispersive solid phased extraction using enhanced lipid-removing material or the combination of primary secondary amine +C-18+Z-sep. By analysis with UPLC mass spectrometry in full scan mode, it was shown that more co-eluting interference was removed by the former material than by the latter in four matrices. For alpha-, beta-, and gamma-hexabromocyclododecane isomer in poultry tissues analyzed by constructed method, they were quantitated using internal standards and validated at the fortification levels of 1, 10, and 50 mu g kg(-1). Satisfied recoveries ranging in 80.2-99.6% were obtained for three isomers with relative standard deviation ranging in 3.1-13.7%. Good recoveries were also obtained for monohydroxyl-hexabromocyclododecane, dihydroxyl-hexabromocyclododecane, monohydroxyl-pentabromocyclododecene, and monohydroxyl-tetrabromocyclododecadiene in spiked poultry liver samples.
A simple hyphenated ultrahigh-performance liquid chromatography-ion chromatography (UHPLC-IC) column-switching analytical method was developed for the simultaneous determination of vanillin, ethyl vanillin, and six inorganic anions (i.e., BrO3 (-), Cl-, NO2 (-), ClO3 (-), NO3 (-), and SO4 (2-)) in food samples. A fast ultrasound-assisted extraction method with a solvent of acetonitrile/water (3:2, v/v) was utilized. Methanol/water (30:70, v/v) and 13 mmol/L KOH were used as eluents for separation. An IonPac AG19 column was applied as the concentration column for the online pre-concentration of anions. The C18 column functioned as the analytical column for the separation of organic compounds and as the online matrix elimination column for inorganic anions. The effects of the analytical variables were systematically studied and optimized. Under optimal experimental conditions, the limits of detection for vanillin, ethyl vanillin, and inorganic anions ranged from 6.2 to 27 mu g/L. The relative standard deviations of the retention time and peak area were less than 1.36 and 3.05%, respectively. The spiked recoveries were 95.73-107.3%. Experimental results demonstrated that the hyphenated UHPLC-IC column-switching analytical method could be successfully applied for the analysis of vanillin, ethyl vanillin, and inorganic anions in food samples.
In this study, thin layer chromatography (TLC) coupled with visible (Vis) spectrophotometry was established as a simple method of determining diacylglycerols (DGs). Samples were analyzed on TLC plates, developed, and then eluted to prepare the test solution. This solution was scanned on an ultraviolet spectrophotometer to ensure that the maximum absorbance of DGs was at 700 nm. Afterward, the relationship between the absorbance and the DG solution was investigated at different concentrations. The linearity of the calibration was within 10-90 mg/mL. The method was highly accurate, as evidenced by its percent recovery of 98.66%. Its slightly low precision can meet the measurement requirements through repeated determination. Moreover, color development was stable enough within 1 h, and the detection limit was 0.51 mg/mL. Therefore, TLC coupled with Vis spectrophotometry could be used to determine DG contents within a certain range.
Listeria monocytogenes (LM) is recognized as an opportunistic, foodborne pathogen that leads to the disease listeriosis. Although the incidence of listeriosis is low, listeriosis has a high mortality rate. LM can survive the most common stresses present during food processing steps, and it causes contamination in many food products. Consequently, most countries have endorsed strong restrictions on LM in food products, especially in ready-to-eat products. Conventional culture-based methods are currently the gold standard for testing, but their inefficiency can no longer meet the needs of batch inspection. As a result, a sensitive, fast, and reliable method for LM detection is required. There are many rapid detection methods for LM that are based on different principles, and an overview of the methods of LM detection is addressed here, with an emphasis on chromatographic, immunological, and aptamer-based techniques. Additionally, the prospect of developing novel LM detection methods is discussed.
An indirect, competitive enzyme-linked immunosorbent assay (ic-ELISA) for the detection of difenoconazole was developed. Two haptens were designed and successfully synthesized. Hapten 1 had a particular moiety of difenoconazole, while hapten 2 had its full structure. The polyclonal antibodies against hapten-protein conjugates were prepared by immunizing rabbits. After optimization of the conditions, the detection limit (IC15) and sensitivity (IC50) were 4.58 and 29.10 mu g L-1, respectively. The cross-reactivities of the antibody with 11 triazole fungicides were all less than 0.1%, which showed that the antibody had excellent specificity. The recoveries of difenoconazole from the spiked samples ranged from 89.70 to 102.31% with good accuracy. The matrix effect was easily removed using a simple, rapid, and efficient extraction method on fruits and vegetables. The detection limit was all 229 mu g kg(-1) in fruits and vegetables. To validate the ic-ELISA, samples were spiked with difenoconazole at three different concentrations and simultaneously analyzed using high-performance liquid chromatography (HPLC). The results showed a good correlation between the ic-ELISA and HPLC data (R (2) = 0.9970). As a result, the developed immunosorbent assay is suitable for the quantitative determination of difenoconazole in fruits and vegetables.
Vibrio cholerae is an important foodborne pathogen causing severe intestinal infectious diseases that have high incidence and mortality. Almost all of rapid testing methods including immunological and molecular assays for V. cholerae are incapable of distinguishing live cells from dead ones, which may overestimate the number of bacteria and result in many false positive results. To address the problems, live cell-specific dye such as propidium monoazide (PMA) is employed. The loop-mediated isothermal amplification (LAMP) assay is a nucleic acid amplification method that is fast, specific, and sensitive. In this study, we developed a real-time visual LAMP assay using PMA dye to detect thyA gene, thereby identifying viable V. cholerae cells. The results showed that only V. cholarae strains could be detected, and there was no cross-reaction with non-V. cholarae strains. Besides, the sensitivity of the PMA-LAMP assay was 1.1 x 10(2) CFU/mL and the entire reaction could be accomplished within 1 h. The sensitivity was on par with that of the PMA-qPCR assay. The detection limit in different artificially inoculated samples was 5 CFU/25 g materials for the tested pathogens. In the practical test, the PMA-LAMP assay performed well in comparison with PMA-qPCR and the culture method. Hence, PMA-LAMP assay can provide a highly effective and rapid approach for detecting viable V. cholerae.
A simple, rapid, and environmentally friendly surface-enhanced Raman scattering (SERS) method was developed for the determination of trace amitraz in milk with the use of silver-coated gold nanoparticles (Au@Ag NPs) as enhancing reagent. The normal Raman and SERS spectra of amitraz were analyzed, and the peaks were assigned by density functional theory. The morphology of Au@Ag NPs was characterized and confirmed by transmission electron microscopy, scanning electron microscopy, and ultraviolet-visible spectroscopy. The SERS effects of Au@Ag NPs were investigated, including the types of solvents for dissolving amitraz, the volume ratio of the Au@Ag NPs and amitraz, and the concentration of aggregating agent (NaCl) for aggregate Au@Ag NPs. Results show that ethanol exerts the least interference on the SERS spectrum of amitraz and is more environmentally sound than methanol. The strongest SERS signal appeared when the volume ratio of Au@Ag NPs and amitraz was 2:1. Moreover, the strongest SERS signals appeared when the concentration of NaCl was 0.025 mol L-1 because of appropriate aggregation. Under the optimum conditions, the concentration of amitraz presents a good linear relationship with Raman intensity (723 cm(-1)) with a linear range of 9.77 x 10(-4)similar to 2.93 x 10(-2) g L-1. The detected recoveries of amitraz in milk were between 81.7 and 100.5% with a relative standard deviation (RSD) of 2.61 similar to 5.51%.
An efficient method for rapid and simple identification of infant formula quality was investigated so as to prevent brand counterfeit of infant formulas. Reversed-phase, high-performance liquid chromatography (RP-HPLC) method combined with chemometric method was developed for fingerprints analysis. To optimize the RP-HPLC conditions, the RP-HPLC analysis was performed on a C-8 column by using gradient elution with 0.1% (v/v) aqueous trifluoroacetic acid (TFA) in water as mobile phase A and 0.1% (v/v) TFA in acetonitrile as mobile phase B, the flow rate was 0.5 mL min(-1), and the detection wavelength was set at 214 nm. Three different stages of infant formulas of two series (R-1 and R-2) of R brand were analyzed to establish infant formula fingerprints of each series at different stages under optimal conditions. Five major common peaks in each chromatogram of the infant formulas were used in fingerprint analysis. The results showed that the RP-HPLC fingerprints and principal component analysis (PCA) method can effectively differentiate the infant formula of different brands, as well as the different series of infant formulas of the same brand, which provide an effective testing method for authenticity identification and brand protection in infant formulas.
A solid-phase extraction (SPE) combined with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed to determine five phenols in grease-rich food (i.e., hotpot seasoning). Sample added with isotope internal standards bisphenol A-d (4) (BPA-d (4)) and 4-n-nonylphenol-d (4) (4-n-NP-d (4)) was dispersedly dissolved in n-hexane. After centrifugation, the supernatant was purified by Carb/PSA SPE. Then, target analytes were separated on a Waters XBridge C18 column, detected under multiple reaction monitoring (MRM) mode. The developed method was validated in terms of linearity, limit of quantitation (LOQ), recovery, and precision. Results found that linear relations were favorable in the selected concentration range of 0.5-100 mu g/L for all phenols, with R (2) greater than 0.995. LOQs were between 1.0 and 2.0 mu g/kg. The mean recoveries for negative sample at three spiked concentration levels were in the range of 83.5-97.1%, and the intra-day and inter-day precision were calculated between 4.7 and 12.5%. This method is accurate and sensitive and has good purifying effect, which can be applied for screening and quantitation of target phenols in grease-rich food.
A simple sensor ordered mesoporous carbon/glassy carbon electrode (OMC/GCE) is developed in this paper for melamine (Mel) detection, which is based on conversion of Mel from non-electroactive Mel to electroactive Cu-Mel complex under presence of copper ions in 0.1 M pH 9.0 borate buffer containing 20% methanol (v/v) as supporting electrolyte at the surface of OMC modified electrode. Fourier transform infrared (FT-IR) spectra demonstrate that Mel interact with copper ions to form a complex through coordinate bond interaction. Surface feature of modified electrode was characterized by cyclic voltammetry (CV). Several important parameters controlling performance of the sensor were investigated and optimized. In optimal conditions, the anodic peak of Cu-Mel complex is linear with concentration of Mel ranging from 1.0 x 10(-8) to 5.0 x 10(-7) M and 5.0 x 10(-7) to 2.0 x 10(-5) M, with limit of detection (LOD) (based on S/N = 3) of 2.0 x 10(-9) M for Mel. This sensor was successfully applied to determination of Mel in milk products.
A combination of electronic nose (EN) and electronic tongue (ET) was used to trace apples according to apple variety and geographical origin by detecting the squeezed juices. A total of 126 apple samples from seven producing regions in China were analyzed. Principal component analysis (PCA) was displayed to get a primary distribution overview of samples. Linear discriminant analysis (LDA), support vector machine (SVM), and partial least squares discriminant analysis (PLS-DA) were carried out to develop discrimination models based on EN dataset, ET dataset, and the fusion dataset. All LDA, SVM, and PLS-DA models achieved satisfactory discrimination performances. The data fusion method made it possible to build a more robust classification model, and the discrimination ability was better than models based on solely EN dataset or ET dataset. The results demonstrated that EN and ET analysis combined with chemometrics was a promising approach for tracing apples and guaranteeing their authenticity.
Shigella spp. are enteric pathogens that pose a serious threat to public health worldwide. A novel saltatory rolling circle amplification (SRCA) assay was developed to detect Shigella spp. in food targeting the ipaH gene. SRCA as an isothermal amplification method requires no expensive thermocycle instrument and could avoid electrophoresis as visualization results was successfully applied for SRCA. In order to confirm the specificity of this assay, 34 strains including 11 strains belonging to different Shigella species and 23 non-Shigella bacteria were detected with pure cultures. The sensitivity of Shigella flexneri by SRCA was evaluated using agarose gel electrophoresis, which was 7.3 x 10(1) fg/mu L. In addition, the amplification results were also determined by adding the fluorochrome, SYBR Green I (1 mu L of 1000x), allowing naked eye visualization of results, and the sensitivity was 7.3 x 10(0) fg/mu L. Moreover, the sensitivity of PCR was 7.3 x 10(2) fg/mu L, showing that the sensitivity of SRCA by electrophoresis and SYBR Green I fluorescence were 10- and 100-fold higher than that of PCR, respectively. The detection limit of SRCA was also evaluated with artificially inoculated vegetable salad without enrichment, and it was 4.7 x 10(2) and 4.7 x 10(1) CFU/g by electrophoresis and fluorescence, respectively. The detection limit by PCR was 4.7 x 10(3) CFU/g, which was 10- and 100-fold higher than that of SRCA. Therefore, SRCA is a potentially reliable tool for rapid and specific detection of Shigella in food and could be useful in underdeveloped countries with limited resources.
This study describes the development of a novel reproducible molecularly imprinted quartz crystal microbalance (QCM) sensor for the accurate and sensitive analysis of the residue of enrofloxacin (ENRO) in animal-derived foods. This proposed sensor was easily fabricated by directly immobilizing molecularly imprinted polymer (MIP) of ENRO on the surface of a QCM Au chip, which combined the advantages of selective recognition from the MIP with the high sensitivity and portability of a QCM sensor. The parameters in the fabrication and measurement process were optimized and discussed in detail. It was verified that the MIP-modified QCM Au chip performed favorably for the detection of ENRO residue in common animal-derived food products and demonstrated acceptable accuracy (recovery: pure milk 77.2-84.2%, egg 77.3-85.6%, chicken muscle 73.5-89.1%, pork 74.7-85.8%), precision (relative standard deviation (RSD, n = 3), pure milk 2.9-8.0%, egg 2.9-6.4%, chicken muscle 3.4-6.8%, pork 2.2-4.7%), and sensitivity (limit of detection, pure milk 0.31 mu g L-1, egg 0.44 mu g kg(-1), chicken muscle 0.54 mu g kg(-1), pork 0.57 mu g kg(-1)). The MIP-modified QCM Au chip for sensing ENRO was portable, could be stored for an extended period of time, and reused for more than 30 analysis cycles with a response attenuation of 7.8%. These results have demonstrated that the proposed MIP QCM sensor presents an accurate, sensitive, rapid, and low-cost methodology for ENRO residue detection in animal foods. This research is very promising for the development of novel effective devices applied to the detection of various contaminants in the field of food safety.