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Norovirus is one of the main pathogens causing acute gastroenteritis worldwide, and possesses rich genetic diversity. We established a simple, fast, and suitable colloidal gold immunochromatographic detection method for common epidemic strains of Norovirus. A pair of monoclonal antibodies that are sensitive to recognizing Norovirus was successfully screened and used as gold-labeled antibody and capture antibody, respectively. The assembly conditions of the test strip were optimized to determine the labeling pH, the concentration of capture antibody and concentration of AuNP-labeled antibody, then the performance of the strips, including sensitivity testing and specificity testing, was evaluated. The minimum detection concentration of the established Norovirus colloidal gold test strip detection method is 10 ng mL−1. This antibody has no cross-reactivity with HCoV-NL63, HCoV-OC43, Influenza A (H1N1), Influenza A (H9N2), respiratory syncytial virus or Varicella zoster virus. The established colloidal gold detection method was used to analyze 11 fecal samples, and the results showed that only two samples were positive and the rest were negative, in agreement with the RT-PCR result. The whole colloidal gold test strip detection method process took 15 min, and could be used for on-site detection. The established colloidal gold test strip detection method has good specificity and stability, and can be used for the detection of common Norovirus strains and in large-scale epidemiological investigations. [ABSTRACT FROM AUTHOR]

Anesthetic residues in fish represent a potential risk to human health. Therefore, it is important to develop a sensitive and broad-specific method for the detection of anesthetics. In this study, we developed a colloidal gold-based quadruplex immunochromatographic (Qua-ICS) assay using four highly sensitive monoclonal antibody immunotherapy (mAbs) that simultaneously detected 11 anesthetic residues in fish within 10 min. The colorimetric and cut-off values (COVs) for procaines, eugenols, bupivacaines, and tricaine (TMS) were 0.37–1.1 and 3.3–10, 11–222 and 100–2000, 0.37 and 3.3, and 111 and 10,000 µg/kg, respectively. Quantitative analysis was achieved with a portable strip-reader, and the detection ranges were 0.15–2.6, 6.3–677, 0.13–2.8, and 83–1245 µg/kg for procaines, eugenols, bupivacaines, and tricaine, respectively. Our developed method was reliable and accurate according to the recovery test results and analyses of real samples. Therefore, the strip can be used as an alternative method for the rapid detection of anesthetic residues in fish. [ABSTRACT FROM AUTHOR]

In this study, we synthesized two haptens similar in structure to nitrofen (NIT), and screened out five monoclonal antibodies with the ability to recognize NIT and bifenox (BIF) by competitive ELISA, with the lowest IC50 values of 0.87 ng mL−1 and 0.86 ng mL−1, respectively. The antibody 5G7 was selected to be combined with colloidal gold to establish a lateral flow immunochromatographic assay strip. This method was shown to qualitatively and quantitatively detect the residues of NIT and BIF in fruit samples. The visual limits of detection for qualitative detection were 5 μg kg−1 and 10 μg kg−1 for NIT and BIF, respectively. The calculated limits of detection for quantitative detection were 0.75 μg kg−1, 1.77 μg kg−1 and 2.55 μg kg−1 respectively, for nitrofen in orange, apple and grapes, and 3.54 μg kg−1, 4.96 μg kg−1 and 5.26 μg kg−1, respectively, for bifenox. Thus the strip assay could be used for rapid analysis of fruit samples. [ABSTRACT FROM AUTHOR]

In this study, we developed a monoclonal antibody (mAb)-based colloidal gold immunochromatography assay (CG-ICA) strip for the rapid and sensitive detection of flubendiamide (FBD) in food samples. Our anti-FBD mAb 2B1 was highly specific and had a half-maximal inhibitory concentration (IC50) of 1.55 ng/mL under optimal conditions. It belongs to the IgG2a isotype and has a Kaff value of 1.52 × 109 mol/L. The strip provided a visual detection limit of 50 ng/g for both grapes and tomatoes, with a cut-off value of 1,000 ng/g and these qualitative results were observed within 15 min. For quantitative analysis, the calculated detection limits were 6 ng/g and 5 ng/g in grapes and tomatoes, respectively. The average recoveries of FBD ranged from 88.8% to 111.8% in grapes and 94.5% to 110.6% in tomatoes. The proposed strip assay is highly practical for screening FDB in food samples. [ABSTRACT FROM AUTHOR]

Homocysteine (Hcy) is an amino acid found in the human body and has the potential to predict cardiovascular risk where timely detection and treatment are very important. In this study, we established a method to combine enzymatic hydrolysis with a colloidal gold lateral flow immunoassay (LFIA) for the detection of total Hcy (tHcy) based on the monoclonal antibody (mAb) 3B3 against S-adenosyl- L -homocysteine (SAH). The 50% inhibitory concentration (IC50) for this mAb against SAH was 2.94 nM with a linear range of 0.73–11.75 nM. The developed LFIA could detect SAH with a vLOD and cLOD of 10 nM and 2.07 nM, respectively. For tHcy detection in serum samples, the LFIA strip was able to detect tHcy after enzymatic hydrolysis, and the results correlated well with that of an enzymatic cycling test kit. [ABSTRACT FROM AUTHOR]

In this study, an excellent monoclonal antibody (mAb) was produced that could sensitively and specifically recognize Flu in fruit samples. The mAb belonged to the IgG2 subclass and had a half‐inhibitory concentration (IC50) of 0.59 ng/ml and a limit of detection (LOD) of 0.13 ng/ml. A cross‐reactivity test revealed that the mAb had good specificity for Flu. A gold nanoparticle‐based lateral‐flow immunochromatographic (ICA) strip was used for the rapid screening of Flu in fruit samples. The method had a visual cut‐off value of 10 µg/kg for Flu in three different fruit samples when evaluated with the naked eye. The LODs were 5.25, 3.13, and 4.64 µg/kg for Flu in apples, grapes, and oranges, respectively, as obtained with the aid of a strip scan reader. Therefore, this ICA strip assay represented a potential tool for the detection of Flu in fruit samples. [ABSTRACT FROM AUTHOR]

In this study, a highly specific and sensitive monoclonal antibody against dicofol (DIC) was prepared and used to create a colloidal gold immunochromatographic strip (ICS) for the quantitative analysis of DIC in liquorice and Angelica sinensis samples. We found that for both the liquorice and Angelica sinensis samples, the cut-off value for the ICS was 500 ng g−1, respectively, and using a colloidal gold test strip reader, the half-maximal inhibitory concentrations (IC50) were found to be 35 ng g−1 and 88 ng g−1, the limits of detection were 2 ng g−1 and 3 ng g−1, and the linear detection scopes (IC20–IC80) were from 6 to 201 ng g−1 and from 10 to 819 ng g−1, respectively. In the recovery test, we found that recoveries were within the range of 90.6% to 97.2% and the coefficients of variation were less than 8.6% in the intra-assay and inter-assay for the liquorice samples and the recoveries ranged from 90.8% to 97.3% and the coefficients of variation were less than 9.1% in the intra-assay and inter-assay for the Angelica sinensis samples. The established ICS assay could be used for the rapid quantitative screening of chemicals in Chinese traditional medicinal materials. [ABSTRACT FROM AUTHOR]

In this study, a monoclonal antibody (mAb) 1G5 against novobiocin with high sensitivity and specificity was prepared from a newly-designed hapten. According to the results of an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA), the 50%-inhibitory concentration of the anti-novobiocin mAb was 6.9 ng/mL and the cross-reactivity was less than 0.1% to its analogues. Furthermore, a rapid colloidal gold immunochromatographic assay (ICA) was successfully developed for the determination of novobiocin in spiked samples. Two calibration curves were established respectively, for beef and chicken samples. The ICA results showed a visual colorimetric value of 50 ng/mL and a cut-off value of 300 ng/mL in beef samples. The ICA results of chicken samples were almost the same as that of beef. When quantitative detection was performed using a strip reader, the detection ranges for quantitative analysis in beef and chicken were 23.7–287.5 and 19.7–263.8 µg/kg respectively. Recoveries were between 82.7 and 95.3% for beef samples with the coefficient of variation (CV) ranging from 2.5 to 5.1%. Recoveries were in the range of 89.6–105.5% with the CV ranging from 2.9% to 6.3% for chicken samples. Importantly, these results from the ICA were highly consistent with the results obtained by LC-MS/MS. Therefore, this ICA could be used as an alternative means for the rapid determination of NOV in a large number of beef and chicken samples. [ABSTRACT FROM AUTHOR]

Shigella is the most common foodborne pathogen and can cause bacillary dysentery. Therefore, it is necessary to detect Shigella rapidly and accurately, but it is difficult for traditional methods to meet these requirements. In this study, monoclonal antibodies (mAbs) were prepared using a recombinant invasive plasmid antigen C (IpaC) protein, which is specifically located on the outer membrane of Shigella. Based on our mAbs 2G11 and 5A11, a colloidal gold lateral flow immunochromatographic (LFIA) test strip method for the detection of several serotypes of Shigella was produced. The sensitivity of the LFIA strip was 1 × 105 CFU mL−1 for four groups, and seven serotypes of Shigella. The applicability of the strip was tested using spiked milk and meat samples and the results showed that Shigella could be detected in these matrices. [ABSTRACT FROM AUTHOR]

In this study, a highly specific and sensitive monoclonal antibody (mAb) against azoxystrobin (AZX) was prepared. Based on this mAb and the use of colloidal gold, an immunochromatographic strip (ICS) was developed to specifically detect AZX in cucumber, tomato, and cabbage samples. For qualitative detection, the cut off value using the ICS was 100 ng mL−1 using the naked eye and results could be seen within 10 min. For quantitative detection, the linear regression equations were obtained using a strip reader and the half maximal inhibitory concentrations (IC50) were found to be 4.16, 10.64, and 8.90 ng mL−1 in cucumber, tomato, and cabbage samples, the limit of detections (LODs) were 0.36, 1.03, and 0.92 ng mL−1, and the linear detection ranges (IC20–IC80) were respectively 0.64–21.77, 1.86–65.15, and 1.62–49.26 ng mL−1. The intra-assay recoveries range from 82.5% to 91.4%, with a coefficient of variation of less than 8.2%, and the inter-assay recoveries range from 81.7% to 92.5%, with the coefficient of variation less than 10.2%. The results demonstrated that the ICS could be used as a rapid tool for the qualitative and quantitative detection of AZX in vegetable samples. [ABSTRACT FROM AUTHOR]

As a common class of growth regulators, gibberellins (GAs) are widely used in agricultural production. However, the abuse and misuse of GAs have led to the problem of high residues in crops. The existing detection methods are still mainly instrumental, and rapid and sensitive detection of GAs remains a challenge. In this study, we designed a novel hapten scheme by analyzing the structure of GAs, which enabled the prepared mAb to simultaneously detect common GAs (GA 3 , GA 1 , GA 4 and GA 7) with high sensitivity and homogeneity. Subsequently, a colloidal gold immunochromatographic assay (GICA) for GAs detection was established by combining mAb with synthetic gold nanoparticles, which could simplify the sample pre-treatment step and the calculated limit of detection, visual limit of detection, cut-off values and linear ranges were 0.09 mg/kg, 0.2 mg/kg, 8 mg/kg, 0.13–1.36 mg/kg for rice and 0.11 mg/kg, 0.2 mg/kg, greater than 8 mg/kg, 0.13–2.45 mg/kg for tomatoes. The recovery assays of GA 3 -spiked samples ranged between 95.1% and 105.1%. The results indicate that our developed method can be used for the rapid, sensitive and efficient on-site detection of GAs in food. • A GA 3 -hapten was designed to produce a highly sensitive and versatile mAb. • A visual immuno-sensing platform was developed. • The results showed a visual LOD of 0.2 mg/kg in rice and tomato samples. • No significant difference in recovery rates were seen between GICA and ic-ELISA. [ABSTRACT FROM AUTHOR]

In this study, a monoclonal antibody with selectivity for clopidol was produced based on a new hapten. The 50% inhibition concentration (IC50) for the developed ic-ELISA was 0.275 ng/mL. Cross-reactivity tests showed that the monoclonal antibody had high specificity for clopidol. Using this antibody, a lateral-flow colloidal gold immunoassay (LCGA) was created for the rapid screening of clopidol in raw chicken samples. With the naked eye, the cut-off value of the strip assay was 5 μg/kg for clopidol in chicken samples. Therefore, this LCGA provides a sensitive and rapid method for on-site detection of clopidol in chicken samples. [ABSTRACT FROM AUTHOR]

In this study, an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and a gold immunochromatographic assay were developed to detect the furaltadone metabolite, 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ). The detection of AMOZ was based on the AMOZ derivative 3-([2-nitrophenyl] methyleneamino)-5-morpholinomethyl-2-oxazolidinone (2-NPAMOZ). The monoclonal anti-2-NPAMOZ antibody 4G11, was prepared and exhibited a 50%-inhibitory concentration (IC50) of 0.049 ng/mL. Its cross-reactivity with structurally related analogues was less than 3%. This immunochromatographic assay was assembled for the rapid screening of AMOZ in catfish samples. The strip assay had a cut-off value of 0.1 μg/kg and a limit of detection (LOD) of 0.009 μg/kg. Analysis of AMOZ in catfish indicated that the results from the strip assay were highly comparable to results obtained using ic-ELISA and LC-MS/MS. Therefore, the colloidal gold (CG) immunoassay is a sensitive screening method for the detection of AMOZ residues in catfish samples. [ABSTRACT FROM AUTHOR]

In this study, we produced a specific monoclonal antibody (mAb) against triadimefon (TDF) and triadimenol (TDN). The half-maximal inhibitory concentration for TDF and TDN was 5.25 and 9.98 ng/mL, respectively, with a linear detection range (IC20–IC80) of 1.09–25.35 and 2.29–43.61 ng/mL, respectively. Subsequently, we developed a colloidal gold immunochromatography test strip for the analysis of TDF and TDN in tomato. The results obtained from the colloidal gold immunochromatography test strip were in accordance with those obtained from the indirect competitive enzyme-linked immunosorbent assay. The colloidal gold immunochromatography test strip is efficient and suitable for on-site detection of TDF and TDN. [ABSTRACT FROM AUTHOR]

The medicinal properties and toxicity of aconitine in traditional Chinese medicine have caused widespread concern. In this study, we screened a highly specific and sensitive monoclonal antibody with an IC50 of 3.65 ng/mL generated by immunizing mice and cell fusion, and the limits of detection of the ic-ELISA were 1.13 and 11.76 ng/mL. We then developed a colloidal gold test strip based on the antibody. For rapid detection of aconitine in herbs, the visual limit and detection limit of the test strip are 10 and 25 ng/mL, respectively; the results are obtained within 5 min and are visible to the naked eye. Therefore, the colloidal gold test strip is very suitable for on-site detection and quality screening of aconitine in Chinese herbal medicine. [ABSTRACT FROM AUTHOR]

A monoclonal antibody against carazolol (CRZ), 2F5, was generated for the construction of an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and an immunochromatographic strip for detection of CRZ in milk and pig kidney samples. The antibody had a half-maximal inhibitory concentration of 0.29 ng/mL; its limit of detection was 0.068 ng/mL, and its linear range of detection was 0.137–0.638 ng/mL. For CRZ in milk samples and porcine kidney samples, the detection limits for this strip were 0.25 and 2.5 ng/mL, respectively. Analysis of CRZ in milk samples showed that the results obtained by immunochromatographic strip were consistent with those obtained by ic-ELISA. Therefore, the CG immunoassay is a sensitive screening method for semi-quantitative and qualitative detection of residual CRZ in milk and porcine kidney samples. [ABSTRACT FROM AUTHOR]

The label is a significant factor when analyzing the performance of lateral flow immunoassays (LFIAs) in practical applications. In this study, we first produced a broad-specificity monoclonal antibody (mAb) against five antibacterial synergists (ASGs) whose subclass was IgG2b and affinity constant was 1.30 × 1010 L mol−1. Then, time-resolved fluorescent microspheres (TRFMs) and colloidal gold nanoparticles (CGs) were used to label the mAbs, and the two different label-based LFIAs were developed and compared for their ability to quantitatively detect ASGs in chicken samples. Under optimal conditions, the limits of detection (LODs) of the TRFM-based LFIA were 0.001–0.01 μg kg−1 and those of the CG-based LFIA were 0.01–0.11 μg kg−1. The sensitivity of the TRFM-based LFIA was higher than that of the CG-based LFIA. In addition, owing to the visible test zone of the CG-based LFIA, qualitative results can be easily obtained. Analysis of real samples showed that results from the two LFIAs were consistent with that of an ic-ELISA. [ABSTRACT FROM AUTHOR]

In this study, a gold immunochromatographic assay (GICA) based on a penicillin receptor protein (PBP) is proposed to simultaneously detect penicillin, cephalosporin, and carbapenem antibiotics in milk and chicken. A mutant PBP, carboxy-terminal of the β-lactam sensor-transducer protein (BlaR-CTD, I188KS19CG24C) from Bacillus licheniformis ATCC14580 was expressed in E. coli as a soluble His-tag fusion protein. The purified BlaR-CTD mutant was labeled with colloidal gold (CG-BlaR-CTD-M) and applied to develop GICA. The GICA method was performed based on a competitive form, where the binding of the ampicillin-bovine serum albumin conjugate (Amp-BSA) to CG-BlaR-CTD-M was inhibited by free β-lactams in samples. The performance of the assay was confirmed by analysis of milk and chicken samples. The limits of detection of 21 β-lactam antibiotics met the maximum residue limits set by the European Union and China. The GICA gave results within 10 min, thus providing a rapid and reliable method for the on-site detection of multiple β-lactams in milk and chicken samples. [ABSTRACT FROM AUTHOR]

A monoclonal antibody (mAb), 2C9, selective for four eugenol compounds, was developed based on the eugenol derivatives (Eug-1). The semi-inhibitory concentrations (IC50) of this antibody against eugenol, isoeugenol, methyl eugenol, and methyl isoeugenol were 0.043, 0.302, 0.016, and 0.082 μg/mL, respectively, and the detection limits (LOD) were 0.012, 0.070, 0.004 and 0.024 μg/mL. With the exception of isoeugenol, which had cross-reactivity of less than 15%, the cross-reactivity of the other compounds was good, ranging from 52.4% to 269%. In the ic-ELISA recovery test, recovery was between 80% and 94%, indicating that the method was suitable for analysis of eugenol compounds in water. The cut-off values of the immunochromatographic strips for the four compounds in water were 5, 100, 100, and 100 μg/mL, respectively, indicating that the ic-ELISA and immunochromatographic strips we developed can be used to rapidly detect eugenol compounds in water. [ABSTRACT FROM AUTHOR]

A highly sensitive, specific, and rapid immunochromatographic assay for halofuginone (HFG) has been developed. A well-characterized immunogenic conjugate of HFG with bovine serum albumin was produced using the N,N″-Carbonyldiimidazole method. A sensitive monoclonal antibody specific for HFG was then generated by immunizing BALB/c mic with the HFG conjugate. The antigen, HFG-CDI-ovalbumin and goat anti-mouse IgG were attached to a nitrocellulose membrane as the test line and the control line, respectively to produce an immunochromatographic test strip for the rapid detection of HFG in milk. Under optimized conditions, the detection limits of the semi-quantitative test strip for HFG were as low as 50 ng/mL in 0.01 M PBS (pH 7.4) and 100 ng/mL in milk. All the results were obtained within 5 min. The newly developed immunochromatographic assay provides a sensitive, rapid, and specific procedure for on-site screening for HFG. [ABSTRACT FROM AUTHOR]

A lateral flow colloidal gold (CG) immunoassay strip has been developed for detection of dexamethasone (DEX) residues in milk samples. For this purpose, an anti-DEX monoclonal antibody (McAb), based on a DEX succinic anhydride derivative hapten, was prepared and characterized. The McAb showed a high specificity to DEX, the half inhibitory concentration of the antibody was 0.095 ng/mL, its limit of detection (LOD) was 0.017 ng/mL, and its linear range of detection was 0.034–0.265 ng/mL. The developed CG immunoassay had a visual cut-off value of 0.3 ng/mL in phosphate buffered saline (PBS) and 0.5 ng/mL in milk samples. Each test requires 10 min. Analysis of DEX in milk indicated that the results of strip assay had a strong agreement with indirect competitive enzyme-linked immunosorbent assay. Therefore, the CG immunoassay is a sensitive screening method for semi-quantitative and qualitative detection of DEX residues in milk samples. [ABSTRACT FROM PUBLISHER]

Nicotine (NCT) is commonly contained in e-cigarette oils, and long-term nicotine intake can exacerbate cardiovascular disease, neurodegenerative disease, and lung cancer. Therefore, there is a need to develop a fast and sensitive method for detecting NCT in e-cigarette oils. We prepared anti-NCT monoclonal antibodies (mAbs), which belong to the IgG2 subclass. The optimum mAb had a half-maximal inhibitory concentration (IC 50) of 6.81 ng/mL for NCT. We developed a colloidal gold immunochromatographic strip (CG-ICS) to detect NCT content with a visual cut-off and limit of detection of 20 ng/mL and 0.40 ng/mL, respectively. The recovery rates of NCT from spiked samples ranged between 100.36% and 109.96% based on CG-ICS. These results were consistent with those obtained from high performance liquid chromatography (HPLC). We confirmed the reliability of CG-ICS using NCT-positive samples. Therefore, CG-ICS represents an effective and rapid on-site screening tool for the detection of NCT in e-cigarette oils. • Anti-NCT mAbs were prepared, which had a IC 50 of 6.81 ng/mL for NCT. • CG-ICS was developed to detect NCT content with a visual cut-off and LOD of 20 ng/mL and 0.40 ng/mL, respectively. • The recovery rates of NCT from spiked samples ranged between 100.36% and 109.96% based on CG-ICS. • These results were consistent with those obtained from HPLC. [ABSTRACT FROM AUTHOR]

A rapid immunochromatographic assay was developed to detect 17β-19-Nortestosterone (19-NT). The 19-NT-OVA conjugate was immobilised to nitrocellulose membrane as a test line and goat anti-rabbit IgG as a control line. Anti-19-NT polyclonal antibody labelled with colloidal gold particles acted as detector reagent. We tested the sensitivity of the strip using spiked swine urine, and analysed the intensity of test line using ImageJ software. The sensitivity by naked eye measurement was determined to be 200 ng/ml and lower limit using ImageJ was distinguished as 5 ng/ml. The total assay time was less than 20 min, suitable for screening and quantifying the residue of 19-NT in swine urine. [ABSTRACT FROM AUTHOR]

Pyriftalid (Pyr) is one of the most commonly used herbicides and due to its widespread and improper use, it has led to serious pollution of groundwater, soil and other ecosystems, threatening human health. A rapid method to detect Pyr was urgently needed. A high specific monoclonal antibody (mAb) against Pyr with IC50 values of 4.7 ng/mL was obtained by mAb screening technique and method with enhanced matrix effect. The study firstly proposed colloidal gold immunochromatographic test strips (CGIA) for Pyr, which enables rapid qualitative and quantitative determination of a large number of samples anytime and anywhere, so as to effectively monitor Pyr in environment and grain samples. Based on the properties of the desired Pyr antibody, the hapten Pyr-hapten-4 with high structural similarity to Pyr molecule, similar electrostatic potential distribution, and the ability to expose Pyr functional groups was screened out from five different Pyr haptens, which was consistent with mouse antiserum test. The CGIA quickly analyze the Pyr content in positive samples such as water samples, soil samples, paddy samples, brown rice samples within 10 min, the LOD for Pyr by CGIA as low as 1.84 ng/g, the v LOD value as low as 6 ng/g, and the extinction value as low as 25 ng/g. The content of positive samples detected by CGIA was consistent with the quantitative results of LC-MS/MS, the relative accuracy was within the range of 97–103 %. The recovery rate range for Pyr by CGIA was 92.0–99.7 %, and the coefficient of variation was between 1.30–8.56 %. It indicated Pyr-targeted CGIA test strip was an efficient and fast detection method to detect real environment and food samples. [Display omitted] • Qualitative and quantitative methods have been developed to monitor Pyr in actual samples. • Five different Pyr haptens were simulated computationally to calculate the functional similarity. • A Pyr CGIA was developed that could detect results by eyes within 10 min. • The CGIA detection results was consistent with that detected by LC-MS/MS. [ABSTRACT FROM AUTHOR]

In this study, we developed highly sensitive and specific monoclonal antibodies (mAbs) against estrone (E 1 ), 17β-estradiol (17β-E 2 ), and estriol (E 3 ). The half-maximal inhibitory concentration values of anti-E 1 , anti-17β-E 2 , and anti-E 3 mAbs were 0.46, 0.36, and 0.39 ng/mL, respectively, based on competitive enzyme-linked immunosorbent assay (ic-ELISA) results. A rapid colloidal gold-based immunoassay strip assay was developed for the determination of E 1, 17β-E 2 , and E 3 residues in milk samples. The assay had a visual cut-off value of 5 ng/mL, and required 10 min to assess with the naked eye. The results obtained from the immunochromatographic strip assay were consistent with those obtained from ic-ELISA and gas chromatography–mass spectrometry. The immunochromatographic strip assay is useful and rapid for the detection of E 1 , 17β-E 2 , and E 3 in milk. [ABSTRACT FROM AUTHOR]

Abstract: A one-step immunochromatographic assay (ICA) was developed for the detection of seven kinds of cephems in milk. Polyclonal antibodies (PcAb) with group-specific to cephems were raised in rabbits after immunization with cephalexin–keyhole limpet hemocyanin (KLH) conjugate. The specificity of anti-sera was determined by indirect competitive enzyme-linked immunosorbent assay (icELISA), and the 50% inhibitions (IC50) of cephalexin and cefadroxil were obtained at 1.5ngmL−1; IC50 of cefatiofur, cefapirin, cefazolin, cefalothin and cefotaxine were 4, 3.7, 3.2, 4.5 and 5ngmL−1, respectively. The PcAb against cephems were conjugated to colloidal gold particles as the detection reagent for ICA strips to test for cephems. This method achieved semi-quantitative detection of cephems in <5min, with high sensitivity to cephalexin and cefadroxil (both 0.5ngmL−1). At the same time, cefatiofur, cefapirin, cefazolin, cefalothin and cefotaxine were detected at <100ngmL−1 in spiked processed-milk samples. This method was compared with an enzyme-linked immunosorbent assay by testing 40 milk samples, and the positive samples were validated by a high-performance liquid chromatographic method, with an agreement rate of 100% for both comparisons. In conclusion, the method was rapid and accurate for the multi-residue detection of cephems in milk. [Copyright &y& Elsevier]

• Sensitive and specific monoclonal antibody against tolfenpyrad was produced. • A colloidal gold nanoparticle immunochromatographic test strip (CGN-ICTS) was developed for tolfenpyrad detection. • The results of CGN-ICTS were highly consistent with those of LC-MS. • The CGN-ICTS can be used to quickly screen tolfenpyrad residues in foods. In the study, a hapten was designed to preserve the molecular structure of tolfenpyrad while introducing a carboxyl group and was coupled with a carrier protein to synthesize an immunogen and coating antigen. A monoclonal antibody was fabricated against tolfenpyrad and its performance was assessed by indirect competitive enzyme-linked immunosorbent assay. Finally, we developed a colloidal gold nanoparticle immunochromatographic test strip (CGN-ICTS) for the detection of tolfenpyrad in kale, Chinese cabbage, and eggplant samples. The results shows that CGN-ICTS was sensitive, with calculated detection limits of 0.49 ng/g for kale and Chinese cabbage and 0.99 ng/g for eggplant. Subsequently, CGN-ICTS and LC-MS were used to analyze the tolfenpyrad-spiked samples. The recovery rate of the CGN-ICTS for kale samples was 97.1–103.0%, for Chinese cabbage samples was 93.7–103.4%, and for eggplant samples was 92.7–105.7%. Recovery rates were similar between CGN-ICTS and LC-MS. Therefore, CGN-ICTS can be used to quickly screen tolfenpyrad residues in foods. [ABSTRACT FROM AUTHOR]

• A new hapten of higenamine was synthesized successfully. • An TRFM-ICTS was developed for the determination of HIG residues. • A half-maximal inhibitory concentration is 1.37 ng/mL. • Good correlations of the results verified by TRFM-ICTS and LC-MS/MS. Higenamine (HIG), a benzyltetrahydroisoquinoline alkaloid found naturally in plants, is classified as an S3 Prohibited Substance in the 2020 World Anti-Doping Agency (WADA) report. To avoid problems such as doping violations in competitive events, it is necessary to develop rapid and sensitive detection methods. In this study, a highly-sensitive anti-HIG monoclonal antibody (mAb) was prepared and a time-resolved fluorescent microsphere immunochromatographic test strip (TRFM-ICTS) was established for the rapid quantitative detection of HIG in functional foods. Under optimized conditions, the TRFM-ICTS was compared with colloidal gold immunochromatographic test strip (CG-ICTS), and the half-maximal inhibitory concentration (IC 50) of TRFM-ICTS was 1.37 ng/mL. The spiked recoveries ranged from 86.4% to 105.3%, which was consistent with the results of liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the detection of real functional food. Therefore, TRFM-ICTS can be a candidate method for doping monitoring in functional foods and a powerful tool for HIG quantification. [ABSTRACT FROM AUTHOR]

Gold-based immunochromatographic strip for rapid ketoconazole detection with a visual limit of detection of 0.5 ng/g and a cut-off value of 20 ng/g. [Display omitted] • A novel hapten of ketoconazole was synthesized. • A highly sensitive and specific monoclonal antibody against ketoconazole was developed. • A half-maximal inhibitory concentration is 0.7 ng/mL. • A colloidal gold immunochromatographic strip was developed for monitoring ketoconazole residues in chicken sample. • Good correlations of the results obtained by CGIA and LC-MS/MS. We developed a highly sensitive and specific monoclonal antibody (mAb) for ketoconazole (KCZ) detection in chicken samples. From indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) analysis, the 50% inhibitory concentration of the mAb was 0.7 ng/mL, and the cross-reactivity with fluconazole, imidazole, itraconazole, and voriconazole was <1%. Using indirect competitive enzyme-linked immunosorbent assay, spiked sample recovery was 92.5%–102.7%. Under optimal conditions, we also developed a colloidal gold immunochromatographic assay (CGIA) to detect KCZ residues in chicken samples, with a visual limit of detection of 0.5 ng/g and a cut-off value of 20 ng/g. When data were assessed using liquid chromatography with tandem mass spectrometry, no significant differences were found between assays. Also, strip results were revealed in 10 min. Therefore, our CGIA has great potential for rapidly detecting KCZ residues in chicken samples. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we report on the application of versatile gold nanorods (GNRs) in optical sensors for the detection of antibiotics. The target analyte, Gentamicin (GM) and ovalbumin (OVA) – antigen-modified GNRs together competed with antibody-modified GNRs, then influenced the formation of side-by-side aggregates of the GNRs by antibody–antigen interactions. Accordingly, the UV–vis absorption intensity of the side-by-side aggregates was changed in the presence of the target analyte. This assay allowed the selective determination of GM in the range of 0.1–20ng/mL, and the limit of detection (LOD) of GM was 0.05ng/mL. Furthermore, compared with the traditional plate-based immunoassay, the developed method was easy to perform without washing cycles and the results could be read as soon as the nanoprobe-analyte incubation was complete. Therefore, the developed method could be a promising tool for the detection of antibiotic residues. [Copyright &y& Elsevier]

Abstract: An aptamer-based chromatographic strip assay method for rapid toxin detection was developed. The aptamer-based strip assay was based on the competition for the aptamer between ochratoxin A and DNA probes. The sensing results indicated that the sensitivity of the aptamer-based strip was better than that of conventional antibody-based strips. The visual limit of detection of the strip for qualitative detection was 1ng/mL while the LOD for semi-quantitative detection could down to 0.18ng/mL by using scanning reader. The recoveries of test samples were from 96% to 110%. All detections could be achieved in less than 10min, indicating that the aptamer-based strip could be a potential useful tool for rapid on-site detections. [ABSTRACT FROM AUTHOR]

Abstract: Melamine toxicity causing the renal failure and death of animals and humans has recently attracted worldwide attention. Developing an easy, fast, and sensitive method for the routine melamine detection is of great importance. Herein, we report the colorimetric sensing of melamine, based on the 18-crown-6 ether functionalized gold nanoparticles (GNPs) through the formation of cavity complexes with amines. Based on high extinction coefficients and spectral sensitivity of the surface plasmon resonance band of the GNPs, the rapid and sensitive melamine detection was achieved both visually and spectroscopically. Under the optimal conditions, melamine could be selectively detected in a concentration range from 10 to 500ppb with a limit of detection as 6ppb (3σ), which is much lower than the strictest melamine safety requirement of 1ppm. To demonstrate the selectivity and practicality of the method, melamine detection was realized in the real complex samples (dairy) with excellent analyte concentration recovery, indicating its applicability for real-time monitoring of toxins in common products. Crown ether assembly of GNP also opens a new route for the formation of three-dimensional pseudorotaxane-like assemblies of nanoparticles that can be applicable to a variety of amine-bearing ligands. [ABSTRACT FROM AUTHOR]

Abstract: An ultrasensitive and rapid electrochemical platform for the specific detection of ochratoxin A (OTA) was developed. In this method, three single-stranded DNA molecules, including the aptamer, were immobilized on the surface of an electrode. Binding of the OTA target analyte to the aptamer changed the redox current of methylene blue (MB), which was used as the electrochemical probe, in a manner that was dependent on OTA concentration. With signal enhancement from gold nanoparticle-functionalized DNA, the sensitivity of this method for OTA was as low as 30pg/mL, and the effective sensing range was from 0.1 to 20ng/mL. To investigate the sensing process, the conformational switch of the aptamer was studied by circular dichroism (CD), which confirmed the recognition of the aptamer by the target OTA. Given its sensitivity and rapid detection, we believe this approach has the potential to be a main technology for the detection of toxins in the field of food safety, and in other areas. [ABSTRACT FROM AUTHOR]

Abstract: An ultrasensitive and rapid sequential injection analysis (SIA) based on real-time PCR (SIA-rt-PCR) assay was developed by using different nanoparticles for the detection of small molecule chemicals residues. Gold (Au) nanoparticle, conjugated with goat anti-rabbit IgG and duplex strand DNA (dsDNA), was used as a substitute for chemiluminescent probes in an SIA system. By indirect competitive immunoreactions in the SIA system, the gold nanoparticles were attached to antigens which were immobilized by superparamagnetic nanoparticles (SMNPs). The dsDNA on the gold nanoparticles was dehybridized and then the single-stranded DNA (ssDNA) was collected and quantified with rt-PCR, which showed a rather low linearity range from 2.5attomolL−1 (aM) to 250 femtomolL−1 (fM) and the LOD was 1.4aM. This method, which is rapid, automated and capable of high-throughput, was used to detect methyl-3-quinoxaline-2-carboxylic acid (MQCA) residues in real samples. The analytical results had a coefficient of variation of less than 15% and the recovery was 89–108%. [Copyright &y& Elsevier]