Rapid and simultaneous detection of five mycotoxins and their analogs with a gold nanoparticle-based multiplex immuno-strip sensor

Mycotoxins, as secondary metabolites produced by fungi, have been the focus of researchers in various countries and are considered to be one of the major risk factors in agricultural products. There is an urgent need for a rapid, simple and high-performance method to detect residues of harmful mycotoxins in agricultural foods. We have developed a gold nanoparticle-based multiplexed immunochromatographic strip biosensor that can simultaneously detect fifteen mycotoxins in cereal samples. With this optimized procedure, five representative mycotoxins, deoxynivalenol (DON), zearalenone (ZEN), T-2 toxin (T-2), tenuazonic acid (TEA) and alternariol (AOH) were detected in the range of 0.91-4.77, 0.04-0.56, 0.11-0.68, 0.12-1.02 and 0.09-0.75 ng/mL, respectively. The accuracy and stability of these measurements were demonstrated by analysis of spiked samples with recoveries of 91.8%-115.3% and coefficients of variation <8.7%. In addition, commercially available samples of real cereals were tested using the strips and showed good agreement with the results verified by LC-MS/MS. Therefore, Our assembled ICA strips can be used for the simultaneous detection of 5 mycotoxins and their analogs (15 mycotoxins in total) in grain samples, and the results were consistent between different types of cereal foods, this multiplexed immunochromatographic strip biosensor can be used as an effective tool for the primary screening of mycotoxin residues in agricultural products.

Development and evaluation of time-resolved rapid immunofluorescence test for detection of TSOL18 specific antibody in porcine cysticercosis infections

BACKGROUND

Porcine cysticercosis, a serious zoonotic parasitic disease, is caused by the larvae of Taenia solium and has been acknowledged by the World Organization for Animal Health. The current detection methods of Cysticercus cellulosae cannot meet the needs of large-scale and rapid detection in the field. We hypothesized that the immunofluorescence chromatography test strip (ICS) for detecting Cysticercus cellulosae, according to optimization of a series of reaction systems was conducted, and sensitivity, specificity, and stability testing, and was finally compared with ELISA. This method utilizes Eu3+-labeled time-resolved fluorescent microspheres (TRFM) coupled with TSOL18 antigen to detect TSOL18 antibodies in infected pig sera.

RESULTS

ICS and autopsy have highly consistent diagnostic results (n = 133), as determined by Cohen's κ analysis (κ = 0.925). And the results showed that the proposed ICS are high sensitivity (0.9459) with specificity (0.9792). The ICS was unable to detect positive samples of other parasites. It can be stored for at least six months at 4℃.

CONCLUSIONS

In summary, we established a TRFM-ICS method with higher sensitivity and specificity than indirect ELISA. Results obtained from serum samples can be read within 10 min, indicating a rapid, user-friendly test suitable for large-scale field detection.

On-site rapid detection of perfluorooctanoic acid by visual immunochromatographic strip biosensor in domestic water and real human samples

The International Agency for Research on Cancer (IARC) classifies PFOA as a Class 1 carcinogen. Here, a new naked-eye PFOA immunochromographic strip was developed to recognize PFOA in domestic water and real human samples within 10 min based on a novel custom designed anti-PFOA monoclonal antibody (mAb) 2A3, which was firstly an immune rapid detection method for PFOA has been proposed. Using computer simulation techniques such as quantum computing to assist in designing the structural formula of PFOA semi antigen, which hapten was firstly proposed. The half maximal inhibitory concentration of PFOA monoclonal antibody (mAb) 2A3 was 2.4 μg/mL. Using mAb 2A3, we developed an immunochromatographic strip (ICS) for detecting PFOA in real samples. The developed method generated results in 10 min, with visual detection limits of 20, 20, and 200 μg/mL and limit of detection of 50, 200, and 500 μg/mL for water, blood and urine samples, respectively. The established ICS and indirect competitive enzyme-linked immunosorbent assay were used to analyze the actual samples, and the results were confirmed by LC-MS/MS. Our study findings showed that the ICS and ic-ELISA can quickly detect PFOA in actual samples.

Development of a quantum dots based immunochromatographic strip for rapid and on-site detection of African swine fever virus

African swine fever (ASF) is a lethal disease caused by ASF virus (ASFV), severely impacting the global swine industry. Though nuclear acid-based detection methods are reliable, they are laboratory-dependent. In this study, we developed a device-independent, user friendly and cost-effective quantum dots based immunochromatographic strip (QDs-ICS) with high specificity and sensitivity for the rapid and on-site detection of ASFV antigen. For the preparation of the QDs-ICS, we generated a monoclonal antibody (mAb) mAb-8G8 and polyclonal antibody (pAb) against ASFV-p72 protein. The pAb was labelled with QDs to be used as the detection probe and the mAb-8G8 was coated on the nitrocellulose membrane as the test line. Our results proved that the strip displayed no cross-reactivity with other swine viruses and detection limit of the QDs-ICS was down to 1 ng/mL for the ASFV-p72 protein with great reproducibility. The strip also exhibited high stability with a storage period up to 12 months under room temperature. Twenty blind samples and one hundred clinical samples were examined by the QDs-ICS, conventional PCR and real-time PCR method, respectively. Results showed that the agreement rate between the QDs-ICS and PCR method was 100%, and the agreement rate between the strip and real-time PCR was 94%. The novel QDs-ICS developed here would be an effective tool for on-site detection of ASFV.

Establishment of ultrasensitive immunoassay strip based on colloidal gold-McAb probe for detecting cyproheptadine hydrochloride and six phenothiazines in feed

An ultrasensitive and broad-specific monoclonal antibody recognising cyproheptadine hydrochloride and six phenothiazines was produced. The 50% inhibition concentration against cyproheptadine hydrochloride was 0.036 ng/mL, and the cross-reactivities for six phenothiazines were from 6.33% to 63.16%. Based on the developed monoclonal antibody, an immunochromatographic strip was established, with the visual detection limits (cut-off values) of seven drugs ranging from 5 to 100 ng/g in feedstuffs. With the strip reader, the 50% inhibition concentration of the developed immunochromatographic strip for seven drugs ranged from 0.570 to 7.750 ng/g. The intra-assay recoveries were from 79.8% to 103.4% with the highest coefficient of variation of 11.3%. The inter-assay recoveries were from 79.0% to 96.6% with the highest coefficient of variation of 12.7%. In summary, the proposed immunochromatographic strip was considered suitable for simultaneously monitoring cyproheptadine hydrochloride and phenothiazines in feedstuffs.

Rapid detection of varicella-zoster virus based on an immunochromatographic strip

Varicella-zoster virus (VZV) is a highly infectious DNA virus that can cause varicella (chickenpox) and herpes zoster (HZ). A simple, sensitive and specific detection method is desirable for the VZV infection. In this study, VZV gE protein, expressed in CHO cells, was used to immunize BALB/c mice for the generation of monoclonal antibodies (mAbs). For the first time, we developed a colloidal gold-based immunochromatographic strip for rapid detection of VZV using a pair of mAbs against gE protein. The limit of detection (LOD) of the strip was 30 ng mL-1 of purified VZV gE antigen, and it could specifically test VZV without cross-reactivity with Enterovirus 71 (EV-71), Herpes simplex virus 1 (HSV-1) and Herpes simplex virus 2 (HSV-2). The coincidence rate between the strip and commercial real-time PCR diagnostic kit was 100% using vesicle as the clinical sample. Our strip provided a technical support for rapid and specific detection of VZV.

Ultrasensitive and simultaneous monitoring of multiple small-molecule pollutants on an immunochromatographic strip with multilayered film-like fluorescent tags

A wide variety of small-molecule pollutants is harmful to human health, and their highly sensitive universal and rapid detection in complex environments remains a challenge. Herein, a multiplexed and ultrasensitive immunochromatographic strip (ICS) was developed for the universal analysis of three kinds of different pollutants based on multilayered fluorescent nanofilm-guided signal amplification. Flexible three-dimensional nanofilms (GO-MQD) with large surface areas, high quantum dot (QD) loading, superior luminescence, and good stability were synthesized through the electrostatic adsorption-mediated layer-by-layer assembly of three layers of small QDs onto two-dimensional graphene oxide (GO) nanosheets, modified with specific antibodies, and utilized as enhanced fluorescent tags in the ICS method for quantitative target detection. By combining the GO-MQD nanofilms and multiplexed ICS, the proposed assay can rapidly and sensitively detect aflatoxin B1, clenbuterol, and kanamycin in actual samples/environmental samples (pork extract, milk, river water, and lake water) with low detection limit (0.87, 2.04, and 0.81 pg/mL), fast testing time (15 min), good stability and high reproducibility (RSD < 8.71 %). The GO-MQD-ICS method developed here exhibits great potential to meet the demands of the on-site and practical detection of small-molecule pollutants.

Immunochromatographic assay for the point-of-care diagnosis of food borne Salmonella strains using smartphone application

Salmonella strain is a prevalent pathogen, affecting poultry industry and hence human population around the world. Host-specific pathogen infections including fowl typhoid, pullorum disease and typhoid fever affects poultry birds, causing huge economic loss worldwide. This study explored the fabrication of immunochromatographic (ICG) strip by colorimetric method integrated with smartphone ColorGrab application for the detection of Salmonella using in-house generated antibodies (Abs) conjugated with gold nanoparticles. The developed point-of-care diagnostic platform was fabricated in-house and tested to detect the presence of Salmonella in a linear range of 10⁷-10⁰ CFU/mL with the limit of detection (LOD) of 10³, 10² and 10⁴ CFU/mL respectively, for Salmonella gallinarum (S.gal), Salmonella pullorum (S.pul) and Salmonella enteritidis (S.ent), which was further confirmed by smartphone-based ColorGrab application. The fabricated ICG strips were further validated using spiked fecal, meat, and milk samples which provided results in 10 mins with stability at 4 °C and 37 °C up to 28 days. Hence, the fabricated in-house ICG strip can be used as a portable, cost-effective diagnostic device for rapid detection of Salmonella strains in food samples.

A lanthanide-based high-sensitivity fluorescence method for the on-site rapid detection of thermostable direct hemolysin of Vibrio parahaemolyticus

Vibrio parahaemolyticus is a common foodborne pathogen in seafood, which often causes seafood borne bacterial gastroenteritis or food poisoning. Thermostable direct hemolysin (TDH) is considered to be one of the main virulence factors involved in this pathogen. The most clinical V. parahaemolyticus isolates produce TDH. Therefore, high sensitivity and specificity detection of TDH are of great significance for food safety and early diagnosis of diseases caused by V. parahaemolyticus. In this study, we developed a rapid, sensitive immunochromatographic test paper assay for the quantitative detection of TDH in seafood samples using time-resolved fluorescence techniques. First, we completed the preparation of fluorescent detection antibodies by coupling lanthanide fluorescent nanospheres with homemade high-affinity polyclonal antibodies based on the principle of the double-antibody sandwich. The lanthanide fluorescent nanospheres used in this study are characterized by a large stokes shift and a long fluorescence lifetime, which effectively reduces background noise and improves detection sensitivity. In addition, the method can be completed within 15 min for the detection of TDH, has a detection limit below 50 ng/mL and good linearity in the range of 50-5000 ng/mL. Moreover, it has good specificity and no cross-reactivity with Vibrio vulnificus hemolysin (VVH), Clostridium perfringens α toxin (CPA) or C. perfringens ε toxin (ETX). Finally, the sensitivity of this method was unchanged when the three simulated samples of Patinopecten yessoensis, Ruditapes philippinarum, and Scapharca broughtonii tested, indicating that the method is not affected by samples in a complex matrix. In conclusion, this study establishes a practical new method for on-site rapid detection of TDH, which is easy to operate, fast response, easy to carry and can be implemented under the field conditions without expensive equipment and professional person.

Rapid detection of porcine circovirus type 2 by a red latex microsphere immunochromatographic strip

Abstract

To establish a rapid and specific antigen detection method for porcine circovirus type 2 (PCV2), monoclonal antibodies (mAbs) were produced against the PCV2 epidemic strains and a red latex microsphere immunochromatographic strip was established. A total of eight anti-PCV2b and four anti-PCV2d mAbs were produced, and seven mAbs were confirmed to react with PCV2a, PCV2b, and PCV2d strains using an immunoperoxidase monolayer assay. The results of micro-neutralization tests showed that the mAbs 2C8, 9H4, 10G7, 7B9, and 7C7 had good neutralizing activity, whereas the neutralizing activity of the mAbs 4B3, 4C9, 6H9, and 7E2 was lower than 50%. Three mAbs, 4B3, 7C7, and 9H4, and PCV2 pAb were selected for the establishment of a red latex microsphere immunochromatographic strip, and the combination of mAb 7C7 labeled with red latex microspheres and mAb 9H4 exhibited the greatest detection ability. The immunochromatographic strip had minimum detection limits of 10^2.5 TCID₅₀/0.1 ml, 10^0.7 TCID₅₀/0.1 ml, and 10^1.5 TCID₅₀/0.1 ml for PCV2a/CL, PCV2b/MDJ, and PCV2d/LNHC, respectively. Furthermore, no cross-reactivity was found for African swine fever virus, classical swine fever virus, porcine respiratory and reproductive syndrome virus, porcine parvovirus, porcine pseudorabies virus, porcine circovirus type 1, transmissible gastroenteritis virus, porcine epidemic diarrhea virus, porcine rotavirus, or porcine deltacoronavirus using the immunochromatographic strip. Using PCR as a reference standard, the detection sensitivity, specificity, and overall coincidence rate of the immunochromatographic strip were 81.13%, 100%, and 90.00%. Additionally, the detection ability of the immunochromatographic strip was correlated with that of virus titration. The immunochromatographic strip was used to detect 183 clinical disease samples, and the average positive detection rate was 22.95%. In summary, this method has good sensitivity and specificity and is simple, convenient, and quick to operate. It has high application value for on-site diagnosis of PCV2 and virus quantification.

Key points

• A red latex microsphere immunochromatographic strip for PCV2 detection was developed.

• The method was not only simple to operate, but also takes less time.

• The method had good sensitivity and specificity.

Golf-shaped Bi2Se3 microparticles based-immunochromatographic strip for ultrasensitive detection of Acetamiprid

Rapid and sensitive detection of pesticide is of significance to the field of food safety and human health, but it is still challenging due to interferents from complex food matrices. Herein, a superb golf-shaped Bi₂Se₃ microparticles-based immunochromatographic strip (BS MPs-ICS) was constructed for ultrasensitive detection of acetamiprid (ATM). The novel immune signal tag demonstrated outstanding luminance, excellent biocompatibility, and high affinity with ATM (affinity constant was 3.874 ×10⁷ M^-1), which not only possessed a preeminent labeling efficiency but also significantly improved detection sensitivity. After optimization, the limit of detection (LOD) of the BS MPs-ICS was 8.780 pg/mL with an excellent linear relationship at the range of 0.010-6.000 ng/mL, which was approximately 62-fold lower than that of conventional gold nanoparticles-ICS (0.545 ng/mL), The BS MPs-ICS biosensor was well applied in apple and tomato samples with satisfactory recoveries of 83.823-99.223% (relative standard deviation < 1.739%). Therefore, the BS MPs-ICS could serve as a promising candidate for ATM detection in complicated samples and develop a new method in real-time monitoring.

A multiplex lateral flow immunochromatography assay for the quantitative detection of pyraclostrobin, myclobutanil, and kresoxim-methyl residues in wheat

We produced three monoclonal antibodies with high specificity and sensitivity, and developed a lateral flow immunochromatography assay (LFIA) for the qualitative and quantitative detection of pyraclostrobin (PYR), myclobutanil (MYC), and kresoxim-methyl (KRE) in wheat. In the qualitative analysis, the cut-off values of LFIA were 400, 200, and 800 ng/g for PYR, MYC, and KRE in wheat, respectively. Based on the results obtained from the membrane strip reader, we generated calibration curves for the quantitative analysis. PYR, MYC, and KRE monoclonal antibodies (mAbs) had half maximal inhibitory concentrations (IC₅₀) of 25.4, 17.7, and 94.6 ng/g, respectively, and limit of detection (LOD) of 2.5, 2.0, and 8.8 ng/g, respectively. The linear detection scopes were 5.6-116.5, 4.2-74.4, 23.4-383.3 ng/g for PYR, MYC, and KRE, respectively. The intra-assay recoveries ranged from 89.2% to 101.7%, and the coefficients of variation ranged from 4.6% to 6.5%. The inter-assay recoveries ranged from 88.7% to 102.7%, with the coefficients of variation ranged from 7.2% to 9.1%. Thus, our developed LFIA is suitable for the qualitative and quantitative detection of PYR, MYC, and KRE residues in wheat.

Rose petals-like Bi semimetal embedded on the zeolitic imidazolate frameworks based-immunochromatographic strip to sensitively detect acetamiprid

Ultrasensitive and facile detection of Acetamiprid (ACE) is of exceptional significance to assess the environmental and biological pollution. In this study, an advanced Bi semimetal/Zeolitic imidazolate frameworks hybrid material-based immunochromatographic strip (Bi/ZIF HM-ICS) sensor was developed for the sensitive detection of ACE. The novel Bi/ZIF HM was prepared through one-pot hydrothermal reduction of Bi nanoparticles on ZIF, which was selected as a signal tag taking advantages of its excellent color intensity, strong affinity with monoclonal antibodies (mAbs), and favorable biocompatibility. Bi/ZIF HM could not only improve the utilization efficiency of mAbs but also boost the sensing performance. Under optimal conditions, the limit of detection (LOD) of the Bi/ZIF HM-ICS was 4.68 pg/mL with the linear range from 0.01 ng/mL to 6 ng/mL, which was 98-fold lower than that of traditional gold nanoparticles-based ICS (0.457 ng/mL), and the recoveries of the Bi/ZIF HM-ICS ranged from 80.27% to 118.52% with the relative standard deviation (RSD) below 3.67% in pear, apple, tomato, and cucumber. Overall, the practical application of the Bi/ZIF HM-ICS in complicated samples was realized for detecting pesticide residue, and expanding its application scope in monitoring environment.

Novel immunochromatographic strip assay based on up-conversion nanoparticles for sensitive detection of imidacloprid in agricultural and environmental samples

Neonicotinoid insecticides are widely used in agriculture for pest control, but the pesticide residues in environmental and agricultural products were a big threat to the health of non-target organisms. In this study, a new immunochromatographic strip test was established for the rapid detection of imidacloprid residue, a neonicotinoid insecticide, based on up-conversion nanoparticles (UCNPs) coupled with the monoclonal antibody against imidacloprid. Under optimal conditions, the half inhibitory concentration (IC₅₀), detection limit, and the linear range of this strip were 8.37 ng/mL, 0.45 ng/mL, and 0.97-250 ng/mL. The strip test could be completed in 30 min. The average recoveries of imidacloprid spiked in water, Chinese cabbages, cucumber, honey, and tea samples were 70.1~101.8%, with coefficient of variations less than 18.9%. The strip was used to test real samples and verified by UPLC-MS/MS method with the good agreement (R² was 0.9825), indicating this novel strip immunoassay is accurate and reliable.

Lateral flow immunogold assay as a rapid detection tool for screening of congenital hypothyroidism

Congenital hypothyroidism (CH) is one of the most common preventable causes of mental retardation. The majority of infants are diagnosed after detection through newborn screening programs using thyroid-stimulating hormone (TSH) test. A rapid immunochromatographic lateral flow assay based on monoclonal antibodies (MAbs) colloidal gold nanoparticles was developed in a sandwich format for the detection of TSH. Two MAbs binding distinct TSH epitopes are used; one is conjugated to the detection reagent while the other is immobilized at the test line on the membrane. The colloidal gold was prepared by the reduction of gold salt coupled with MAbs and this optimal concentration was determined by spectrophotometry method. The sensitivity of our developed lateral flow immunoassay was determined using 5, 10, 15, 25 and 50 μUI/mL of TSH. The color intensity of the test line was directly proportional to the TSH concentration and the visual limit of detection was 10 μUI/mL. Twenty samples of umbilical cord serum were analyzed by the developed strips and the intensity of the signal was in agreement with the results obtained by the conventional radioimmunoassay method. The results suggest that this rapid test can be used in initial screening for congenital hypothyroidism especially in rural areas.

Development of a rapid and sensitive immunochromatographic strip based on EuNPs-ES fluorescent probe for the detection of early Trichinella spiralis-specific IgG antibody in pigs

Trichinellosis, which is caused by nematodes of the genus Trichinella, is one of the most important zoonotic parasite diseases in the world. A rapid and sensitive immunochromatographic strip (ICS) based on Eu (III) nanoparticles (EuNPs) was developed for the detection of Trichinella spiralis (T. spiralis) infection in pigs. T. spiralis muscle larvae excretory secretory or preadult worm excretory secretory (ML-ES or PAW-ES) antigens were conjugated with EuNPs probes to capture T. spiralis-specific antibodies in pig sera, after which the complex bound to mouse anti-pig IgG deposited on the test line (T-line), producing a fluorescent signal. In the pigs infected with 100, 1000 and 10 000 ML, seroconversion was first detectable for the EuNPs-ML-ES ICS at 30, 25 and 21 days post-infection (dpi) and for the EuNPs-PAW-ES ICS at 25, 21 and 17 dpi. These results show that EuNPs-PAW-ES ICS detects anti-Trichinella IgG in pigs 4–5 days earlier that test using ML-ES antigens. Our ICS have no cross reaction with other parasite infection sera. Furthermore, the detection process could be completed in 10 min. This study indicated that our ICS can be used for the detection of the circulating antibodies in early T. spiralis infection and provide a novel method for on-site detection of T. spiralis infection in pigs.

Visual-afterglow dual-mode immunochromatographic strip for 17β-estradiol detection in milk

The continuous intake of 17β-estradiol (E2) residue from animal-derived food may pose a threat to the health of consumers, so the rapid screen and detection of E2 is very necessary. Although visual immunochromatographic strip (ICS) has played a great role in food safety control such as the screen of many food contaminants, it cannot meet the requirements for E2 detection due to the insufficient sensitivity of traditional visual ICS and the low concentration range of estrogen in food. Here, we developed a dual-mode ICS strategy to achieve rapid and highly sensitive detection of E2. Based on the visual detection mode of a competitive ICS, the afterglow detection mode working in fluorescence resonance energy transfer mechanism was introduced by using the afterglow particles (APs) as energy donor and gold nanoparticles (AuNPs) as energy acceptor. In this method, large APs of micron size with superior afterglow were applied as the test zone-fixed fluorescence signal source, thus the contradiction between migration and afterglow characteristics was skillfully resolved. In addition, a 6 W UV lamp was used as the light source to excite APs, and a smartphone was used to capture an image of 0.5 s after the UV light was turned off to effectively remove the autofluorescence from the strips and improve the signal-to-noise ratio. The limit of detection of this afterglow mode was 0.5 ng/mL, twenty times more sensitive than that of visual mode (10 ng/mL). The strategy has been successfully applied to the detection of estradiol in milk and verified by HPLC-FLD.

Development of an immunochromatographic strip for rapid detection of H7 subtype avian influenza viruses

BACKGROUND

H7N9 avian influenza virus (AIV) including highly and low pathogenic viruses have been detected in China since 2013. H7N9 AIV has a high mortality rate after infection in humans, and most human cases have close contacted with poultry in the live poultry market. Therefore, it is necessary to develop a rapid point-of-care testing (POCT) technique for H7N9 AIV detection.

METHODS

The H7N9 AIV was inactivated and purified, and was used as the antigen to immunize BALB/c. Twelve H7-HA specific monoclonal antibodies (McAbs) were produced through the hybridoma technique. The McAb 10A8 was conjugated with colloid gold as detecting antibody; McAb 9B6 was dispensed on the nitrocellulose membran as the capture test line and the Goat-anti mouse IgG antibody was dispensed as control line respectively. The immunochromatographic strip was prepared.

RESULTS

The analysis of ELISA and virus neutralization test showed that the obtained McAbs specifically recognized H7 HA. Based on the prepared strip, the detection of H7 AIV was achieved within 10 min. No cross-reaction occurred between H7 AIVs and other tested viruses. The detection limit of the strip for H7 was 2.4 log10EID50/0.1 mL for chicken swab samples.

CONCLUSION

The McAbs were specific for H7 and the immunochromatographic strip developed in this study was convenient, rapid and reliable for the detection of H7 AIV. The strip could provide an effective method for the rapid and early detection of H7 AIV.

Development and evaluation of a convenient immunochromatographic strip test for rapid detection of cyprinid herpesvirus 2 (CyHV-2)

Cyprinid herpesvirus 2 (CyHV-2) has become a serious threat to the gibel carp Carassius auratus gibelio industry and has led to enormous losses worldwide. We have therefore developed an immunochromatographic strip (ICS) to enable rapid on-site detection of CyHV-2 by aquaculture facility staff. The ICS employs 2 monoclonal antibodies (MAbs 2C3-1E6 and 3H2-1G5) against the ORF25 protein, a CyHV-2 membrane protein, as the capture and detection antibodies, respectively. Indirect immunofluorescence assay (IIFA) and Western blotting of CyHV-2-infected fathead minnow cells indicated that the 2 MAbs could specifically bind CyHV-2 by recognizing ORF25 antigen. Sandwich ELISA showed that the detection limit of ORF25 protein halved when MAb 2C3-1E6 served as the capture antibody compared to MAb 3H2-1G5. The test for detecting purified CyHV-2 using the ICS could be completed in 10 min and the sensitivity was 1 µg ml-1. Sensitivity of the ICS remained stable following storage at 4, 25 and 37°C for 6 mo. Tissue homogenate from gibel carp with and without obvious gill hemorrhages was subjected to CyHV-2 detection using the ICS: the results were in good accordance with conventional PCR. Our ICS does not require highly trained technicians or specialized equipment, making it suitable for rapid diagnosis of CyHV-2 infection both in the laboratory and in the field.

[Preparation of an anti-cotinine monoclonal antibody and its application in immunological detection]

OBJECTIVE

To prepare monoclonal antibody against cotinine (COT) and to establish immunoassay for detecting COT in human urinary samples.

METHODS

BALB/c mice were immunized with synthesized cotinine-bovine serum albumin (COT-BSA) to screen monoclonal antibody with technique of cell fusion. The monoclonal antibody was used for the indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and colloidal gold immunochromatographic strip assay for the detection of COT in human urine.

RESULTS

The monoclonal antibody against COT was identified by ic-ELISA with a 50%inhibitive concentration (IC50) value of 21 ng/mL; and it was also identified by colloidal gold immunochromatographic strip assay with a cut-off value of 100 ng/mL. For ic-ELISA, the range of detection was 0-100 ng/mL with a minimal limit of 0.1 ng/mL; the recovery of assay was 99.41%-117.98%, and the intra-assay and inter-assay coefficient variations were not higher than 15.31%and 15.07%, respectively. For colloidal gold immunochromatographic strip assay, the accuracy of stability and repeatability both were 100%.

CONCLUSIONS

The ic-ELISA and colloidal gold immunochromatographic strip assay using the prepared monoclonal antibody against COT have been proved to be reliable for the rapid detection of COT in human urines, which may be used for monitoring of environmental tobacco smoke.

Ultrasensitive label-free immunochromatographic strip sensor for Salmonella determination based on salt-induced aggregated gold nanoparticles

Here we present an innovative label-free immunochromatographic strip (ICTS) sensor, in which salt-induced aggregated gold nanoparticles (SIA-AuNPs) act as the signal probe, allowing in 14 min the identification and sensitive quantification of Salmonella as model targets. It has been evidenced that SIA-AuNPs could be absorbed on the surface of bacteria based on van der Waals forces. The SIA-AuNPs@Salmonella complex was captured by anti-Salmonella polyclonal antibody deposited on the test zone. With the label-free ICTS sensor, we successfully detected Salmonella in a concentration range of 10³-10⁸ CFU/mL and a visual detection limit of 1 × 10³ CFU/mL. The band of test zone could be distinguished at a concentration of 10³ CFU/mL by naked eye, which is 100-fold lower than the cationic AuNPs based method. The strip sensor was further validated with real samples including cabbage and drinking water with excellent precision and showed to provide excellent recovery.

Colloidal gold-based immunochromatographic strip assay for the rapid detection of bacitracin zinc in milk

In this study, a murine monoclonal antibody (mAb) of 6D2-G10 against bacitracin zinc (BAC) was produced and applied to an immunochromatographic strip (ICS) for the initial detection of BAC in milk. The ICS with a cut-off value of 25 ng/mL could be perceived by the naked eye within 10 min. With the assist of the strip reader, the limit of detection (LOD) was measured as 0.82 ng/mL, the half-maximal inhibitory concentration (IC₅₀) was recorded as 3.16 ng/mL, and the linear detection range was from 0.97 to 10.30 ng/mL. The recoveries ranged from 87.7% to 96.0% with the highest coefficient of variation (CV) of 9.1% in the intra-assay and from 84.3% to 90.2% with the highest CV of 10.7% in the inter-assay. In short, the established ICS provided a serviceable analytical tool for qualitatively and quantitatively monitoring BAC in milk.

Serological immunochromatographic approach in diagnosis with SARS-CoV-2 infected COVID-19 patients

An outbreak of new coronavirus SARS-CoV-2 was occurred in Wuhan, China and rapidly spread to other cities and nations. The standard diagnostic approach that widely adopted in the clinic is nucleic acid detection by real-time RT-PCR. However, the false-negative rate of the technique is unneglectable and serological methods are urgently warranted. Here, we presented the colloidal gold-based immunochromatographic (ICG) strip targeting viral IgM or IgG antibody and compared it with real-time RT-PCR. The sensitivity of ICG assay with IgM and IgG combinatorial detection in nucleic acid confirmed cases were 11.1%, 92.9% and 96.8% at the early stage (1–7 days after onset), intermediate stage (8–14 days after onset), and late stage (more than 15 days), respectively. The ICG detection capacity in nucleic acid-negative suspected cases was 43.6%. In addition, the concordance of whole blood samples and plasma showed Cohen's kappa value of 0.93, which represented the almost perfect agreement between two types of samples. In conclusion, serological ICG strip assay in detecting SARS-CoV-2 infection is both sensitive and consistent, which is considered as an excellent supplementary approach in clinical application.

Broad-spectrum detection of zeranol and its analogues by a colloidal gold-based lateral flow immunochromatographic assay in milk

Based on colloidal gold and broad-spectrum monoclonal antibody that binds to zeranol and its five analogues with high sensitivity, a lateral flow immunochromatographic assay (LFIA) in a competitive format was developed to specifically determine residues of zeranol, an illegal growth promoter in livestock. In this study, the assay had high sensitivity and was broad-spectrum only for zeranol and its five analogues, and the results were obtained within 10 min without needing sophisticated procedures. The cutoff values for zeranol and its five analogues were 10 ng/mL, and the IC₅₀ values for zeranol, β-zearalanol, zearalanone, α-zearalenol, β-zearalenol and zearalenone were 1.250, 1.800, 1.775, 1.225, 1.709 and 1.319 ng/mL, respectively. The recovery rates were ranged from 85.6 to 93.9%, with the coefficient of variations less than 12.4%. The results demonstrated that the LFIA could be used for rapid, simultaneous, semi-quantitative and quantitative detection of residues of zeranol and its five analogous in milk.

An integrated strategy for rapid on-site screening and determination of prometryn residues in herbs

We produced a prometryn-specific monoclonal antibody and propose a strategy for convenient on-site detection of prometryn residues in herbs for the first time. This strategy has perfect applicability in a complex herbal medicine matrix. The strategy combines a semiquantitative immunochromatographic strip assay with a heterologous indirect competitive ELISA. When there was no matrix interference, the ELISA had a half-maximal inhibitory concentration of 2.6 ng·mL^-1 and a limit of detection of 0.2 ng·mL^-1. The immunochromatographic strip assay can be completed within 5 min with a visual limit of detection of 1 ng·mL^-1. Although the sample matrix had different effects on the sensitivity of the antibody, excellent repeatability and accuracy were achieved. The method was successfully applied for the screening and determination of prometryn residue in multiple complex herb samples for the first time, and the results were in good agreement with those obtained by liquid chromatography-tandem mass spectrometry. The proposed strategy is rapid, of high-throughput, and of low cost, and may be a promising choice for on-site detection of prometryn in different kinds of herbs. Graphical abstract.

Fluorometric lateral flow immunoassay for simultaneous determination of three mycotoxins (aflatoxin B1, zearalenone and deoxynivalenol) using quantum dot microbeads

A fluorometric lateral flow immunoassay (LFA) is described for the simultaneous determination of the mycotoxins aflatoxin B₁ (AFB₁), zearalenone (ZEN) and deoxynivalenol (DON). The method is based on the use of CdSe/SiO₂ quantum dot microbeads (QBs) with a mean diameter of 106 nm. These have strong red luminescence (with excitation/emission peaks at 365/622 nm) which results in enhanced sensitivity. The QBs binding with monoclonal antibodies (mAbs) as the signal probes can react specifically with AFB₁, ZEN and DON, respectively. There is an inverse correlation between the fluorescence signal intensity of test line and the analyte content, which can realize the quantitative analysis of analytes within 15 min. The limits of detection in solution are 10, 80 and 500 pg mL^-1 for AFB₁, ZEN and DON, respectively. Besides, the average recoveries from spiked feed range from 85.5 to 119.0%, and the relative standard deviations are less than 16.4% for both intra- and inter-day assays. The method was used to analyze naturally contaminated feedstuff, and this resulted in a good agreement with data obtained by LC-MS/MS. Graphical abstractSchematic representation of a fluorometric method for the simultaneous determination of three mycotoxins. Quantum dot microbeads (QBs) binding with monoclonal antibodies (mAbs) are signal probes. There is an inverse correlation between the fluorescence intensity of test line and the analyte concentration.

Fluorometric lateral flow immunochromatographic zearalenone assay by exploiting a quencher system composed of carbon dots and silver nanoparticles

It is found that the fluorescence of carbon dots (CD) with an emission peak at 459 nm is strongly quenched by silver nanoparticles (AgNPs) with their absorption peak at 430 nm. The finding was applied in a fluorescence quenchometric lateral flow immunochromatographic assay for detection of zearalenone (ZEN) with CDs conjugated to ovalbumin (OVA) as donor signal probe and AgNP-Ab as acceptor signal probe. The assay has an LOD of 0.1 μg·L^-1 for ZEN. This is 10 times better than the respective "turn-off" AgNP-based LFIA. In case of cereal samples and their products, the LODs range from 1 to 2.5 μg·kg^-1. Only minor cross reactivity is found for fusarium toxins, and no cross-sensitivity for aflatoxin B1, T-2 mycotoxin, ochratoxin A, deoxynivalenol, and fumonisin B1. The assay represents a simple, sensitive, and rapid tool for determination of ZEN in cereal samples and their products. Graphical abstract Schematic presentation of fluorescence quenching lateral flow immunochromatographic assay (FLFIA) based on carbon dots (CD) and silver nanoparticle (AgNP) fluorescence resonance energy transfer (FRET) system for the rapid high sensitive detection of zearalenone (ZEN) in cereal samples.

Immunochromatographic strip biosensor for the rapid detection of N-glycolylneuraminic acid based on aptamer-conjugated nanoparticle

N-glycolylneuraminic acid (Neu5Gc) is a type of sialic acid that is not typically produced in healthy humans but detective in some visceral cancer cells. As a new carcinoma biomarker, the level change in the serum and urine from the patient could potentially have the relation to the disease progression. So the measurement of the Neu5Gc will help to take a better response to therapeutic schedule for the sufferers. A sensitive and rapid aptamer-nanoparticle immunochromatographic strip for the visual detection of Neu5Gc was developed. The assay is based on the competitive reaction of binding the DNA aptamer targeting the candidate molecule selected by SELEX between Neu5Gc and complementary DNA. The sensing results indicated that the aptamer-based strip was sufficiently sensitive to detect Neu5Gc. The visual limit of detection (LOD) for semi-quantitative detection was 30 ng/mL under the optimal conditions and a quantitative detection limit of 5.38 ng/mL could be obtained using a scanning strip reader. The average recovery of the spiked cancer cell samples was 88.86%, with a coefficient of variation (CV) of 5.27%. The detection could be performed in less than 15 min using a simple procedure without any complicated equipment, demonstrating that this aptamer-nanoparticle biosensor strip has great potential for use to Neu5Gc-related cancer diagnosis.

Fluoroimmunoassays for the detection of zearalenone in maize using CdTe/CdS/ZnS quantum dots

CdTe/CdS/ZnS quantum dots (QDs) were synthesized in aqueous phase and conjugated with a new anti-zearalenone (ZEN) monoclonal antibody. Using this novel fluorescent probe, a fluoroimmunoassay (FLISA) and a rapid immunochromatographic strip (ICTS) were developed for the detection of ZEN in maize. Our proposed FLISA allowed for ZEN determination in the range of 0.038-0.977 ng/mL with an IC₅₀ of 0.162 ng/mL and a limit of detection (LOD) of 0.012 ng/mL occurring in maize. The rapid ICTS had a visual LOD of 1.0 ng/mL in buffer solution and 1.5 ng/mL in maize extract. These two QDs-based immunoassays were all successfully verified by commercial ELISA kits. The results confirmed that: firstly, the FLISA can be used as a robust method for the sensitive detection of ZEN; and secondly, the ICTS is ideally suited for rapidly screening large numbers of samples.

Development of a colloidal gold immunochromatographic strip based on HSP70 for the rapid detection of Echinococcus granulosus in sheep

Echinococcus granulosus is the causative pathogen of cystic echinococcosis, a serious disease endangering human and animal health. In this study, an immunochromatographic strip was developed based on the recombinant protein Heat shock protein 70 (HSP70) for the serological detection of E. granulosus. The protocol completes within 20min requiring no specialized equipment or chemical reagents, while specificity tests confirmed no cross-reactivity with positive serum of Fasciola hepatica, Haemonchus contortus, Peste des petits ruminants virus (PPRV) and Foot-and-mouth disease virus (FMDV). The strips remained stable after storage at 4°C for up to 8 months. Both immunochromatographic strip and ELISA tests were applied to detect E. granulosus antibody in a total of 728 serum samples obtained from slaughter houses in Zhejiang Province. Our data revealed positive rates of 2.61 and 1.65% by immunochromatographic strip and ELISA methods, respectively. The immunochromatographic strip test developed in this study provides a simple, specific and rapid method of E. granulosus antibody detection and infected sheep monitoring.

Development of a colloidal gold immunochromatographic strip for rapid detection of Streptococcus agalactiae in tilapia

A colloidal gold immunochromatographic strip was developed for rapid detection of Streptococcus agalactiae (S. agalactiae) infection in tilapia. The monoclonal antibodies (mAb) 4C12 and 3A9 were used to target S. agalactiae as colloidal gold-mAb conjugate and captured antibody, respectively. The colloidal gold immunochromatographic strip was assembled via routine procedures. Optimal pH and minimum antibody levels in the reaction system for gold colloidal-mAb 4C12 conjugation were pH 7.4 and 18μg/mL, respectively. Optimal concentrations of the captured antibody 3A9 and goat anti-mouse antibody were 0.6mg/mL and 2mg/mL, respectively. The sensitivity of the strip for detecting S. agalactiae was 1.5×10⁵ colony forming units (CFU). No cross-reaction was observed with other commonly encountered bacteria, including Pseudomonas fluorescens, Aeromonas hydrophila, Vibrio anguillarum and Streptococcus iniae. The assay time for S. agalactiae was less than 15min. Tilapia samples artificially infected with S. agalactiae were tested using the newly developed strip. The results indicated that blood, brain, kidney, spleen, metanephros and intestine specimens of infected fish can be used for S. agalactiae detection. The validity of the strip was maintained for 6 months at 4°C. These findings suggested that the immunochromatographic strip was effective for spot and rapid detection of S. agalactiae infected tilapia.

Development and comparison of immunochromatographic strips with three nanomaterial labels: Colloidal gold, nanogold-polyaniline-nanogold microspheres (GPGs) and colloidal carbon for visual detection of salbutamol

In this study, the three nanomaterials: colloidal gold, nanogold-polyaniline-nanogold microspheres (GPGs) and colloidal carbon were respectively labeled with the antibody against salbutamol (SAL). We aimed to develop immunochromatographic strips with these nanomaterial labels and determine their performance in visual detection of SAL. For the colloidal gold-based strip, the detection limit of SAL was 1.0µgL(-1) in standard solution and 5.0µgkg(-1) in meat samples. For the GPG- and colloidal carbon-based strips, the limit of detection was 2.0µgL(-1) in standard solution and 10µgkg(-1) in meat samples. The results obtained using the test strips were found to be highly consistent with those obtained using a commercial kit, indicating the high accuracy of these strips. The three strips were also found to be stable up to 18 weeks under laboratory conditions. In terms of sensitivity, the colloidal gold-based strip was slightly better than the other two. For the GPG- and colloidal carbon-based strips, the difference between the results obtained for different batches was small (high consistency), and the stability was much better than that of the colloidal gold-based one. Our results indicate that colloidal carbon can be used as a label in immunochromatographic tests; it can also help reduce the cost involved and scale-up the production. The use of immunochromatographic test strips labeled with colloidal carbon can be a rapid and inexpensive method for SAL assays in on-site applications.

Expedient screening for HIV-1 protease inhibitors using a simplified immunochromatographic assay

A colloidal gold-based immunochromatographic (IC) strip test was developed and validated for the detection of HIV-1 protease (HIV-PR) activity and inhibitory effect of HIV-PR inhibitors (PIs). It is a unique 'two-step' process requiring the combination of proteolysis of HIV-PR and an immunochromatographic reaction. Monoclonal antibodies to the free C-terminus of HIV matrix protein (HIV-MA) conjugated to gold particles and a monoclonal antibody against intact and cleaved forms of the HIV-MA are immobilized on the 'Test'-line of the IC strip. Using lopinavir, a potent HIV protease inhibitor, the IC-strip was optimized to detect inhibitory activity against HIV-protease. At a lopinavir concentration of 1000ng/mL (its suggested minimum effective concentration), a HIV-PRH6 concentration of 6mg/mL and incubation period of 60min were the optimal conditions. A preliminary comparison between a validated high-performance liquid chromatography assay and the IC-strip to semi-quantify HIV protease inhibitor concentrations (lopinavir and atazanavir) demonstrated good agreement. This simplified method is suitable for the rapid screening of novel protease inhibitors for future therapeutic use. Moreover, the IC strip could also be optimized to semi-quantify PIs concentrations in plasma samples.

Development and evaluation of an immunochromatographic strip for rapid detection of capsid protein antigen p27 of avian leukosis virus

A rapid immunochromatographic strip for detecting capsid protein antigen p27 of avian leukosis virus was successfully developed based on two high-affinity monoclonal antibodies. The test strip could detect not only 600pg purified recombinant p27 protein but also quantified avian leukosis virus as low as 70 TCID50, which has comparative sensitivity to the commercial enzyme-linked immunosorbent assay (ELISA) kit. For the evaluation of this test strip, 1100 samples consisting of cloacal swabs, meconium collected from the earliest stool of one day old chicken and virus isolates were assessed both by the strip and by the commercial ELISA kit. The agreement between these two tests was 93.91%, 93.42% and 100%, respectively. The sensitivity and specificity of the strip were also calculated by using the ELISA kit as the standard. This immunochromatographic strip provides advantages of rapid and simple detection of capsid protein antigen p27 of avian leukosis virus, which could be applied as an on-site testing assay and used for control and eradication programs of avian leukosis disease.

Development of a colloidal gold immunochromatographic strip for the rapid detection of soft-shelled turtle systemic septicemia spherical virus

A colloidal gold immunochromatographic strip (ICS) test based on a competitive format was developed for the rapid detection of soft-shelled turtle systemic septicemia spherical virus (STSSSV) in turtle and fecal samples. Specific egg yolk antibodies (IgY) against STSSSV were labeled with colloidal gold and used as probes in the one-step test strip. Antigen (STSSSV) and goat anti-chicken IgY were drawn on the nitrocellulose membrane as the test line and control line, respectively. When STSSSV standard samples (0-100μg/mL) were detected by the strips, the visual limit of detection (LOD) was found to be 50.0μg/mL. The ICS test showed high stability; the strips were stable for at least 3 months at 4°C without significant loss of activity. There was no obvious cross-reactivity with other aquatic pathogens. The assay can be performed within 5-10min. Analysis of STSSSV in turtle samples revealed that data obtained from the ICS test were in a good agreement with those obtained by ELISA. The positive results of fecal samples suggested that this method could be used to detect STSSSV while protecting the animals' welfare. The ICS assay does not need specialized equipment or a technician and can be used as a reliable, rapid, cost-effective and convenient qualitative tool for on-site diagnosis.

Combination of multiplex reverse-transcription loop-mediated isothermal amplification with an immunochromatographic strip for subtyping influenza A virus

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Multiplex RT-LAMP for HA and M genes was developed for subtyping influenza A virus.

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Multiplex RT-LAMP amplicons were simply analyzed by the colorimetric ICS detection.

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Multiplex RT-LAMP (40 min) and ICS detection (15 min) could be complete in 55 min.

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Detection sensitivity for the multiplex RT-LAMP and ICS was 10 copies of viral RNA.

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Our methodology provides simple, rapid genetic analysis platform for viral detection.

Considering the fatal human victims and economic loss by the annual epidemic influenza virus, the development of a rapid and convenient genetic analysis methodology is demanding for timely on-site pathogen detection. In this study, we utilized reverse-transcription loop-mediated isothermal amplification (RT-LAMP) for multiplex target gene amplification, and the resultant amplicons were analyzed on the immunochromatographic strip (ICS) for subtyping influenza A virus. Through the optimized primer design, reaction temperature and time, and concentration of enzymes (Bst DNA polymerase and AMV reverse transcriptase) and dNTP, the HA (H1, H3, and H5 gene) and conserved M gene were amplified. The ICS contains two test lines in addition to a control line in order to detect the presence of the HA and M gene, thereby informing us of influenza virus A type as well as its subtype (H1N1, H3N2, and H5N1). The combination of the multiplex RT-LAMP with the ICS could be complete in 40 min and the pathotyping and subtyping of influenza A virus were performed even with 10 copies of viral RNA templates. Moreover, the subtyping of clinical samples, which were obtained from patients infected by influenza A virus was successfully confirmed using the multiplex RT-LAMP and ICS techniques, showing great feasibility of our methodology for real sample analysis with high speed, simplicity and sensitivity.

A packaged paper fluidic-based microdevice for detecting gene expression of influenza A virus

Pathotyping and subtyping of influenza A virus were performed with a packaged paper fluidic-based analytical microdevice (PFAM) after one-step reverse transcription-polymerase chain reaction (RT-PCR). The PFAM contains two test lines: one for detecting M gene to identify the influenza A virus and another for haemagglutinin subtyping to determine the viral strain among H1N1, H3N2, and H5N1. The M gene and the haemagglutinin gene (H1, H3, and H5 genes) were amplified by using the Digoxigenin and the Texas Red modified primers, respectively, in the multiplex RT-PCR. The amplicon products were loaded in the conjugate pad of the PFAM in which the streptavidin coated gold nanoparticles were linked with the biotin moieties that were incorporated in the middle of the DNA strands, and then captured by the anti-Digoxigenin and anti-Texas Red immobilized on the test lines. Influenza A H1N1, H3N2, and H5N1 could be identified with a limit of detection of 10(2) copies of RNA templates in 10 min. Pathotyping and subtyping of the clinical nasopharyngeal swab samples were also analyzed whose results were confirmed by real-time RT-PCR.