Development of qualitative and quantitative immunochromatographic strip test assay for rapid and simple detection of leucomalachite green residual in aquatic animals

Hapten prediction, monoclonal antibody preparation, and development of an immunochromatographic assay for the detection of fenamiphos

Fenamiphos (FENA) is an organophosphorus insecticide, and its residues in fruits, vegetables, and the environment have raised concerns. Therefore, it is very important to develop a simple, rapid, and accurate method for FENA detection. In this study, a novel FENA hapten was designed and predicted based on computer-aided simulation technology, and high-performance anti-FENA monoclonal antibodies were screened using a matrix effect-enhanced screening method, with a half-maximal inhibitory concentration of 1.269 ng/mL. Furthermore, a colloidal gold immunochromatographic assay (ICA) was established for the detection of FENA, with calculated limits of detection of 1.030 μg/kg, 0.515 μg/kg, 0.250 ng/mL, and 0.405 μg/kg in oranges, cowpeas, river water, and soil. Spiked recovery experiments and real sample validation showed that the detection results from the ICA and LC-MS/MS were consistent, with a CV < 10 %, indicating that the ICA had good accuracy and stability and shows promise as a rapid screening method for FENA in fruits, vegetables, and the environment.

A Time-Resolved Fluorescent Microsphere Immunochromatographic Assay for Determination of Vitamin B12 in Infant Formula Milk Powder

Vitamin B12 (VB12) is an important nutrient, and its quality control in food is crucial. In this study, based on the principle of specific recognition of target analyte by monoclonal antibodies (mAbs), a time-resolved fluorescent microsphere immunochromatographic assay (TRFM-ICA) was developed to detect the content of VB12 in infant formula milk powder. First, the performance of the anti-VB12 mAb was evaluated, revealing a half-maximal inhibitory concentration of 0.370 ng/mL, an affinity constant of 2.604 × 109 L/mol and no cross-reactivity with other vitamins. Then, a highly sensitive TRFM-ICA was developed, with a visual limit of detection of 10 μg/kg and a cut-off value of 100 μg/kg for qualitative detection and a detection range of 4.125-82.397 μg/kg for quantitative detection. In addition, the test results of real samples were consistent with the results of quantification using microbiological methods, with a coefficient of variation of less than 10%, showing good accuracy and stability, and confirming that the TRFM-ICA is suitable for the analysis of VB12 in real infant formula milk powder samples. In this study, based on the principle of specific recognition of VB12 by monoclonal antibodies (mAbs) against VB12, a time-resolved fluorescence microsphere immunochromatographic assay (TRFM-ICA) was developed to detect the content of VB12 in infant formula by converting biological signals into optical signals.

A label-free colorimetric aptasensor for rapid multiplex detection of leuco-malachite green and leuco-crystal violet

Leuco-malachite green (LMG) and leuco-crystal violet (LCV) are widespread co-pollutants in aquatic products that pose a severe threat to human health. Therefore, it is urgent and challenging to develop rapid multiplex detection of LMG and LCV. Herein, the bispecific aptamer (A5b) for LMG and LCV was characterized. Its dissociation constant (Kd) was 2.03 ± 0.13 μM for LMG and 0.97 ± 0.06 μM for LCV. Then, we used A5b as a sensing probe to develop a label-free colorimetric aptasensor using gold nanoparticles (AuNPs) as an indicator and poly-diallyl dimethylammonium chloride (PDDA) as an aggregation inducer. In the absence of LMG and LCV, PDDA hybridized A5b via electrostatic interaction to form a "duplex" structure, which failed to induce the aggregation of AuNPs. However, in the presence of LMG or LCV, A5b specifically bound to LMG or LCV, releasing PDDA. The free PDDA then induced the aggregation of AuNPs. Consequently, a visible color change from red to blue was observed with increasing LMG/LCV concentration. This sensor exhibited excellent sensitivity and bispecificity, and a limit of detection (LOD) of 77.9 nM for LCV and 123.1 nM for LMG, with a linear concentration range of 1-6 μM for LCV and 1-8 μM for LMG. Additionally, the potential of this sensor for real-world applications was well demonstrated in crucian samples. Overall, this work provided a bispecific affinity probe for LMG and LCV for the first time and reported a label-free colorimetric aptasensor for multiplex detection of LMG and LCV in aquatic products.

Dual-color immunochromatographic test strip for simultaneous sensitive detection of malachite green and leucomalachite green residues in fish and shrimp meat samples

A sensitive dual immunochromatographic test strip (dual-ICTS) was developed to detect malachite green (MG) and its metabolite, leucomalachite green (LMG), using two types of gold nanoparticles: round-shaped (red) and star-shaped (blue). The detection limits were determined to be 0.221 μg L-1 for MG and 0.214 μg L-1 for LMG, respectively. The dual-ICTS provided a cut-off value of 1.8 μg L-1 for MG and LMG detection. The dual-ICTS successfully detected MG and LMG in food samples, with recovery rates ranging from 86 % to 116 %. The dual-ICTS was evaluated by correlation analysis between the proposed assay and the well-established enzyme-linked immunosorbent assay in the MG and LMG detection. This is the first report on the development of the ICTS that can detect both MG and LMG at the same time within only 5 min, making it a sensitive and rapid tool for on-site detection.

Immunochromatographic strip for rapid and sensitive detection of bupirimate residues in peach, orange, and carrot

Bupirimate (BPM) is a high-efficiency and low-toxicity fungicide used to combat powdery mildew in crops. To mitigate potential health risks to consumers resulting from improper BPM usage, we prepared a monoclonal antibody against BPM based on novel hapten synthesis, which has high sensitivity and strong specificity, and then successfully designed a colloidal gold-based immunochromatographic (ICG) strip. The newly designed ICG strip was then employed for detecting BPM residues in peach, orange, and carrot. The results show that for the peach, orange, and carrot samples, the calculated detection limits of the ICG strip are 9.36, 0.79, and 0.57 ng/g, respectively, and that it is resistant to the matrix effect and meets the maximum residue limit requirements of European Commission for BPM. Therefore, this developed ICG strip is expected to enable swift detection of BPM residues on the spot.

Production of a monoclonal antibody against thiacloprid, resistant to matrix interference, and its application in quantitatively immunochromatographic assay

Thiacloprid (THI) is a neonicotinoid insecticide, and its residues pose potential risks to the ecological environment and human health. In this study, computer simulation technology was applied to analyze THI haptens to ensure the similarity in spatial structure, charge properties, and potential distribution. And anti-THI monoclonal antibodies insensitive to matrix effects were prepared using sample extraction solution to simulate the matrix environment, with the half-maximal inhibitory concentration of 0.070 ng/mL in the matrix environment. Furthermore, a colloidal gold immunochromatographic assay (ICA) was established for the detection of THI residues in fruit and vegetable samples, with a quantitative detection range of 0.880-11.091 μg/kg, 1.669-14.056 μg/kg, 31.570-586.121 μg/kg, and 42.291-778.803 μg/kg in grapes, oranges, cucumbers, and tomatoes, respectively. Real sample testing indicated that this method had good consistency with LC-MS/MS. Therefore, the ICA withstood matrix interference, accurately and effectively determined THI residues in fruit and vegetable samples.

Dual-mode aptasensor based on P-CeO2NR@Mxene and exonuclease I-assisted target recycling for malachite green detection

Malachite green (MG) has been illicitly employed in aquaculture as a parasiticide, however, its teratogenic and carcinogenic effects pose a significant human health threat. Herein, a dual-mode colorimetric and electrochemical aptasensor was fabricated for MG detection, capitalizing on the robust catalytic and peroxidase-like activity of P-CeO2NR@Mxene and good capture efficiency of a tetrahedral DNA nanostructure (TDN) designed with multiple aptamers (m-TDN). P-CeO2NR@Mxene-modified complementary DNA (cDNA) served as both colorimetric and electrochemical probe. m-TDN was attached to AuE to capture MG and P-CeO2NR@Mxene/cDNA. The superior aptamer and MG binding to cDNA regulated signals and enabled precise MG quantification. The further introduced Exo I enabled aptamer hydrolysis, releasing MG for further binding rounds, allowing target recycling amplification. Under the optimal conditions, the aptasensor reached an impressively low detection limit 95.4 pM in colorimetric mode and 83.6 fM in electrochemical mode. We believe this dual-mode approach holds promise for veterinary drug residue detection.

Rapid and sensitive quantitation of amitraz in orange, tomato, and eggplant samples using immunochromatographic assay

Amitraz (AMT) is a broad-spectrum formamidine insecticide and acaricide. In this study, we produced an anti-AMT monoclonal antibody (mAb) with high performance. The half-maximal inhibitory concentration of the anti-AMT mAb was 4.418 ng/mL, the cross reactivity with other insecticides was negligible, and an affinity constant was 2.06 × 109 mmol/L. Additionally, we developed an immunochromatographic assay for the rapid detection of AMT residues in oranges, tomatoes, and eggplants. The cut-off values were 2000 μg/kg in oranges and tomato samples and 1000 μg/kg in eggplant samples and the calculated limits of detection were 14.521 μg/kg, 6.281 μg/kg, and 3.518 μg/kg in oranges, tomatoes, and eggplants, respectively, meeting the detection requirements for AMT in fruits and vegetables. The recovery rates ranged between 95.8 % and 105.2 %, consistent with the recovery rates obtained via LC-MS/MS. Our developed immunochromatographic assay can effectively, accurately, and rapidly determine AMT residues in oranges, tomatoes, and eggplants.

A Highly Sensitive and Rapid Colloidal Gold Immunoassay for Puerarin Detection

Radix Puerariae is a traditional Chinese medicinal material with a rich history of use in East and Southeast Asia. Puerarin, a unique component of the Pueraria genus, serves as a quality control marker for herbal medicines like Pueraria lobata and Pueraria thomsonii in China, displaying diverse pharmacological properties. This study developed puerarin colloidal gold immunoassay dipsticks utilizing an anti-puerarin monoclonal antibody, resulting in a fast and sensitive detection method with a limit of 500-1000 ng·mL-1. Evaluation using tap water-extracted P. lobata and P. thomsonii samples showed consistent results compared to LC-MS analysis. Cross-reactivity assessments of puerarin analogs revealed minimal interference, affirming the dipstick's reliability for distinguishing between the two species.

Cobalt oxyhydroxide nanosheet-modulated ratiometric fluorescence platform for the selective detection of malachite green in fish

A ratiometric fluorescence platform was developed based on the cobalt oxyhydroxide (CoOOH) nanosheet-modulated fluorescence response of blue emissive copper nanoclusters (Cu NCs) and yellow emissive o-phenylenediamine (OPD). CoOOH nanosheets showed dual function of strong absorption and oxidation ability, which can effectively quench the blue fluorescence of Cu NCs, with an excitation and emission peak maximum at 390 and 450 nm, respectively , and transfer the OPD into yellow fluorescence products, with an excitation and emission peak maximum at 390 and 560 nm, respectively. Upon introducing butyrylcholinesterase (BChE) and its substrates, CoOOH nanosheets were decomposed into Co2+, and malachite green (MG) showed strong inhibition ability to this  process. This resulted in the obvious difference on the ratio of blue and yellow fluorescence recorded on the system in the presence and absence of MG, which was utilized for the quantitative detection of MG, with a limit of detection of 0.140 μM and a coefficient of variation of 3.5%. The fluorescence ratiometric assay showed excellent detection performances in practical sample analysis.

A highly sensitive hyperbranched Au plasmonic blackbody immunochromatographic assay for detection of leucomalachite green in fish and shrimp

A novel immunochromatographic assay (ICA) based on hyperbranched Au plasmonic blackbodies (AuPBs) with a smartphone readout was fabricated for the detection of leucomalachite green (LMG) in fish and shrimp products. The ICA was carried out in a competitive immunoassay format with AuPBs as labels. The developed AuPBs-ICA allowed for the LMG detection with a low detection limit (0.15 μg L-1) within 5 min by the smartphone reader. With the label-AuPBs ICA, the color intensity response was linearly related to the concentrations of the LMG (0.2 -1.7 μg L-1). The test line signal could be clearly distinguished at a 1.7 μg L-1 LMG as a cut-off level by the naked eye, which is lower than the conventional colloidal gold nanoparticle (2 μg L-1) and star-shaped nanoparticles (1.9 μg L-1) labeling. LMG contamination in samples was determined with the proposed AuPBs-ICA and the enzyme-linked immunosorbent (ELISA). The AuPBs-ICA results showed good agreement with those from the ELISA. The proposed AuPBs-ICA has the potential to be used as a rapid, sensitive, and simple device for the analysis of LMG residues in fish and shrimp samples.

Colloidal gold-based immunochromatographic biosensor for quantitative detection of S100B in serum samples

Traumatic brain injury has become a serious public health problem. Timely detection, diagnosis and treatment of brain injury are closely related to the prognosis of patients, so identification of highly sensitive and specific biochemical markers of brain injury has important clinical value. Currently, the most studied and most promising marker is the protein S100B. In this study, a rapid quantitative biosensor for S100B was established using colloidal gold labeling and double antibody (8C10-6B8) sandwich immunochromatography. The biosensor was capable of quantifying S100B within 15 min, and showed no cross-reactivity with S100A, NSE, GFAP, or PGP9.5. The detection limit was determined to be 4.6 pg mL-1 with a linear range of 0.01-2 ng mL-1. Recovery experiments also indicated that the method had an acceptable accuracy. Moreover, the quantitative colloidal gold assay correlated well with the results of a chemiluminescence immunoassay when testing 40 clinical serum samples. Our developed colloidal gold quantitative immunochromatographic biosensor is a rapid, sensitive, specific and accurate method for the detection of S100B protein in serum, which is useful in the clinic for early diagnosis, as well as assessment of disease progression and prognosis of traumatic brain injury.

Dynamics of the role of LacMeta laccase in the complete degradation and detoxification of malachite green

Laccases highlight for xenobiotic bioremediation, as well as application in the fine chemical, textile, biofuel and food industries. In a previous work, we described the preliminary characterization of laccase LacMeta, a promising enzyme for the bioremediation of dyes, able to decolorization malachite green (MG), trypan blue, methylene blue. Here we demonstrate that LacMeta is indeed suitable for the complete degradation and detoxification of MG dye, not just for its discoloration, since some works show false positives due to the formation of colorless intermediates such as leucomalachite. The optimal pH and temperature parameters of LacMeta were 5.0 and 50 °C, respectively (MG as substrate). LacMeta was tolerant of up to 10 mmol L^- 1 EDTA (82%) and up to 5% (V/V) acetone (91%) and methanol (71%), while SDS promoted severe inhibition. For ions, a high tolerance to cobalt, zinc, manganese, and calcium (10 mmol L^- 1) was also observed (> 90%). Even under high-salinity conditions (1 mol L^- 1 NaCl), the residual bleaching activity of the dye remained at 61%. Furthermore, the bleaching product of MG did not inhibit the germination of sorghum and tomato seeds and was inert to the vegetative structures of the germinated seedlings. Additionally, this treatment effectively reduced the cytotoxic effect of the dye on microorganisms (Escherichia coli and Azospirillum brasilense), which can be explained by H-NMR spectral analysis results since LacMeta completely degraded the peak signals corresponding to the aromatic rings in the dye, demonstrating extreme efficiency in the bioremediation of the xenobiotic at high concentrations (50 mg L^- 1).

Immunochromatographic Assay based on Sc-TCPP 3D MOF for the rapid detection of imidacloprid in food samples

In this work, a highly sensitive immunochromatographic test strip (ITS) based on Scandium-Tetrakis (4-carboxyphenyl) porphyrin (TCPP) metal-organic framework nanocubes (ScTMNs) was developed for ultrasensitive and facile visual determination of imidacloprid (IDP). TCPP as the porphyrin-based planar ligand and Sc³⁺ as the metal center were applied to form the ScTMNs via coordination chelation. Giving the credit to its excellent optical characteristics, strong affinity with monoclonal antibodies, and favorable biocompatibility, the ScTMNs was selected as a signal tag. Under optimized conditions, the ITS exhibited a great liner relationship in the range of 0.04-3 ng/mL and the detection limit was 0.04 ng/mL for the IDP detection. Additionally, IDP was successfully detected in tomatoes, millet, corn and carrot samples with satisfied recoveries. To the best of our knowledge, this is the first time that ScTMNs have been used in immunochromatography which are expected to have potential applications in detection of other substances.

Lateral flow immunoassay based on dual spectral-overlapped fluorescence quenching of polydopamine nanospheres for sensitive detection of sulfamethazine

Herein, we propose a lateral flow immunoassay (LFIA) based on the dual spectral-overlapped fluorescence quenching of polydopamine nanospheres (PDANs) caused by the inner filter effect to sensitively detect sulfamethazine (SMZ). The fluorescence quenching LFIA device consists of four parts: absorbent pad, polyvinyl chloride pad, sample pad, and nitrocellulose membrane. Compared with traditional quenchers such as gold nanoparticles (AuNPs) with single spectral-overlapped quenching ability, PDANs can quench the excitation light and emission light of three fluorescence donors (aggregation-induced emission fluorescent microsphere, AIEFM; fluorescent microsphere, FM; and quantum dot bead, QB). The fluorescence intensity changes (ΔF) are numerically larger for PDANs-LFIA (ΔF_AIEFM = 2315, ΔF_FM = 979, ΔF_QB = 910) than those for AuNPs-LFIA (ΔF_AIEFM = 1722, ΔF_FM = 833, ΔF_QB =;520). AIEFM-based PDANs-LFIA exhibits a large ΔF (2315) in response to the changes in the SMZ concentration, and produces a high signal-to-noise ratio. The limit of detection (LOD) and visual LOD of LFIA based on PDANs quenching AIEFM for the detection of SMZ in chicken are 0.043 and 0.5 ng/mL, respectively. The results confirm that the proposed method can be used for the detection of hazardous materials in practical applications.

Spot tests: past and present

Microchemistry, i.e., the chemistry performed at the scale of a microgram or less, has its roots in the late eighteenth and early nineteenth centuries. In the first half of the twentieth century a wide range of spot tests have been developed. For didactic reasons, they are still part of the curriculum of chemistry students. However, they are even highly important for applied analyses in conservation of cultural heritage, food science, forensic science, clinical and pharmacological sciences, geochemistry, and environmental sciences. Modern pregnancy tests, virus tests, etc. are the most recent examples of sophisticated spot tests. The present ChemTexts contribution aims to provide an overview of the past and present of this analytical methodology.

Sensitive Lateral Flow Immunoassay for the Residues of Imidocarb in Milk and Beef Samples

Based on the successful derivation of a hapten, we prepared and optimized a murine monoclonal antibody against imidocarb, with an IC₅₀ of 2.22 ng/mL and a limit of detection (LOD) of 0.45 ng/mL. Cross-experiment results showed that the cross-over rate for 4,4'-dinitrocarbanilide was 18.12%, and the cross-reactivity with other analogues when using the ic ELISA was less than 0.1%. We used the developed ic-ELISA to detect the addition and recovery of imidocarb in milk and beef samples, and values were 86.0-93.5 and 84.5-101.2%, respectively. The preparation of an immunochromatographic test strip based on gold nanoparticles was used for the rapid identification of imidocarb in milk and beef samples. When assessed by the naked eye, the visual LOD for imidocarb in milk and beef samples was 5 and 10 ng/mL, and the cut-off values were 20 and 50 ng/mL, respectively. Because of its high sensitivity, specificity, and simplicity, the test strip can be used for on-site testing and rapid screening of imidocarb in food samples.

Development of a fast and ultrasensitive black phosphorus-based colorimetric/photothermal dual-readout immunochromatography for determination of norfloxacin in tap water and river water

A rapid and ultrasensitive method for colourimetric/photothermal dual-readout detection was developed using an 808 nm NIR laser and a thermal imaging app on mobile phone. Norfloxacin was used as a model contaminant to demonstrate this universal rapid detection method. It is innovatively, to use the advanced two-dimensional material black phosphorus as a colourimetric/photothermal reagent for the first time. The samples were added to the strip, and the analytes were selectively captured on the conjugate pad by monoclonal antibody-modified magnetic/upconversion nanocomposites. The samples flowed through the strips by capillary action until reaching the control line, where immune complex formation occurred due to the presence of secondary antibody. The added black phosphorus could be captured by the the antigens which were directly exposed to the test line and a brown band could be observed by naked eye. Upon illumination by NIR light for 1 min, the real-time temperature is obtained for quantitative analysis through the thermal imaging performed by mobile phone camera. This method can achieve the detection of norfloxacin in water samples within 20 min, and the detection limits of colorimetric and photothermal readout can reach 45 pg mL^-1. Compared with conventional strips, this method provided an increased sensitivity by about two orders of magnitude, with a integrated portable laser and a mobile phone. It is a valuable method for rapid detection and can be applied to other environmental contaminants as well.

An ultrasensitive fluorescent paper sensor for fast screening of berberine

Berberine (BBR) is a highly effective animal feed additive, but it also has adverse side effects on animals and causes potential food safety issues. Based on BBR antibody preparation, fluorescent immunochromatography assay was established for quantitative detection of BBR in feed samples.