Development of a competitive immunochromatographic assay for the sensitive detection of amantadine in chicken muscle

Quantification of water-soluble moroxydine hydrochloride residue using UPLC-MS/MS: Development and validation in 22 different complex plant-based food samples

In order to overcome the challenge of determining water-soluble moroxydine hydrochloride (MH) from 22 plant-based food matrices with different properties, an extraction pretreatment method was developed in this study using trifluoroacetic acid solutions for high-water-content samples and formic acid solutions for low-water, high-oil-content samples. Moreover, the pH was adjusted to 8.5 ± 0.1 during extraction for high-oil-content samples. An ultra-high performance liquid chromatography - tandem mass spectrometry method was developed to determine MH residues in 22 different foods. The method showed excellent linearity (R2 ≥ 0.99) with limits of quantification (LOQ) and limits of detection (LOD) for tea at 0.1 mg kg-1 and 0.03 mg kg-1, respectively, and 0.05 mg kg-1 and 0.015 mg kg-1 for other foods. Recoveries ranged from 71 % to 108 %, indicating high precision and applicability for MH residue analysis in plant-based foods.

Method development and validation for the simultaneous determination of 21 antiviral drugs by ultra-high performance liquid chromatography-tandem mass spectrometry in chicken muscle and liver

The recent unauthorization of antiviral drugs in food-producing animals according to Commission Delegated Regulation (EU) 2022/1644 have increased the need for food control laboratories to develop analytical methods and perform official controls. In this work, a simple and fast analytical methodology was developed for the simultaneous determination of 21 antiviral drugs in chicken muscle and liver by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Chromatographic separation was achieved by an HILIC BEH amide column; followed by detection with a electrospray ionization source in positive and negative modes. Based on extraction efficiencies, critical parameters affecting sample treatment were optimized including the evaporation and clean up steps to extract the largest number of antiviral drugs and reduce interferences. The method was validated according to Commission Implementing Regulation (EU) 2021/808 in chicken muscle and liver. Most compounds showed a linearity of R2>0.9800, while decision limits were between 0.18 and 7.05 μg kg-1 and 0.19 and 36 μg kg-1 for chicken muscle and liver, respectively. Trueness and within-lab reproducibility were determined at three levels (n = 7) and the results showed values ranging from 81 to 133 % and 4.2-57 % for chicken muscle, and 71-136 % and 4.6-106 % for chicken liver, respectively. The applicability of the developed method was demonstrated by the analysis real samples. 20 samples from the National Residue Control Plan in the Netherlands were analyzed and although none of targeted compounds were detected it is important to continue the analysis of larger set of samples to address any possible food safety risks.

Development of Highly Sensitive Immunochromatography Using Time-Resolved Fluorescence Microspheres for Amantadine Detection

Amantadine (AMA), commonly used to treat viral infections in livestock and poultry, has been banned owing to its potential hazards to human well-being. To detect unauthorized AMA usage in livestock, we developed a polyclonal antibody with a high affinity for the specific recognition of AMA through a rational design based on a structure similar to AMA and revealed the availability of the hapten design by computational chemistry analysis. Using this antibody, we established a highly responsive time-resolved fluorescence immunochromatographic assay (TRFICA). The visual detection limit of the assay is 0.6 μg/kg, and the quantitative detection limit is 0.05 μg/kg. The TRFICA also showed good recovery rates ranging from 94.5 to 109.9%, with variability coefficients not exceeding 10%. The outcomes of undisclosed sample examinations aligned with those of HPLC-MS/MS analyses, indicating that this approach can function as an ideal screening and monitoring tool for detecting illegal AMA in chicken muscle.

Ultrasensitive SERS aptasensor using Au@Ag bimetallic nanorod SERS tags for the selective detection of amantadine in foods

Herein, a novel surface enhanced Raman spectroscopy (SERS) aptasensor was developed for amantadine (AMD) detection, based on magnetite nanoparticles coated with polyethylenimine, silver nanoclusters and aptamers (Fe3O4@PEI@AgNC-apt) as the capture probe and complementary DNA-modified gold nanorods (AuNRs@4-MPBA@Ag-c-DNA containing 4-mercaptophenylboric acid molecules) as the reporter probe. In the presence of AMD, the AMD and the reporter probe competed for the aptamer on the surface of the capture probe, resulting in the reporter probe detaching from the capture probe leading to a decrease in intensity of the SERS signal at 1067 cm-1 for 4-MPBA. Under optimal conditions, a good linear relationship was established between the SERS intensity at 1067 cm-1 and the logarithm of the AMD concentration over the range 10-6-102 mg L-1, with a LOD of 0.50 × 10-6 mg L-1. The AMD levels in spiked samples were evaluated using the SERS aptasensor, with good recoveries ranging from 90.57% to 113.49% being obtained.

Antiviral drugs in animal-derived matrices: A review

The ban of antiviral drugs in food-producing animals in several parts of the world, latest by Commission Delegated Regulation (EU) 2022/1644, has increased the need for food control laboratories to develop analytical methods and perform official controls. However, little is known about antiviral drugs, their use, and its analysis in food-producing animals in the EU. This review aims to provide insights into relevant viruses, antiviral drugs, and animal-derived matrices for analytical method development and monitoring purposes to implement in food control laboratories. For years, animal viruses, such as African swine fever and avian influenza, have caused many outbreaks. Besides, they led to large economic losses due to the applied control measures and a lack of available treatments. Considering these losses and the known effectiveness of authorized human antiviral drugs in different organisms, medicines such as amantadine in Chinese poultry have been misused. Various analytical methods, including screening assays and sensors (published 2016-2023), and mass spectrometry methods (published 2012-2023) have been outlined in this review for the monitoring of antiviral drugs in animal-derived matrices. However, pharmacokinetics information on metabolite formation and distribution of these substances in different animal-derived matrices is incomplete. Additionally, apart from a few countries, there is a lack of available data on the potential misuse of different antiviral drugs in animal-derived matrices. Although a handful of important antiviral drugs, such as influenza, broad-spectrum, antiretroviral, and herpes drugs, and animal-derived matrices, such as chicken muscle, are identified, the priority of the scope should be further specified by closing the aforementioned gaps.

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.

A CG@MXene nanocomposite-driven E-CRISPR biosensor for the rapid and sensitive detection of Salmonella Typhimurium in food

In this study, we developed a novel electrochemical biosensor based on CRISPR/Cas12a (E-CRISPR) for the rapid and sensitive detection of Salmonella Typhimurium (S. Typhimurium). The CRISPR/Cas12a system was applied to identify S. Typhimurium gene and induce signal changes in electrochemical measurement. The colloidal gold and MXene (CG@MXene) nanocomposites were synthesized and immobilized to improve the performance of the biosensor by decreasing the background noise. The formation process of CG@MXene was well characterized, and experiment conditions were fully optimized. Under the optimal conditions, the proposed E-CRISPR biosensor exhibited excellent sensitivity for S. Typhimurium, with a limit of detection (LOD) of 160 CFU/mL, and great specificity against other common foodborne pathogens. Furthermore, the feasibility of the E-CRISPR biosensor was evaluated by analyzing S. Typhimurium-spiked chicken samples, with a recovery rate ranging from 100.46% to 106.37%. In summary, this research proposed a novel E-CRISPR biosensor from a new perspective to detect S. Typhimurium which can be an alternative approach for bacterial detection in the food supply chain.

Highly Sensitive Magnetic-Nanoparticle-Based Immunochromatography Assay for Rapid Detection of Amantadine in Chicken and Eggs

Amantadine (AMD) is an antiviral drug that is prohibited for use in livestock and poultry. In this study, carboxyl-modified magnetic nanoparticles (MNPs) were synthesized using the solvothermal method in one step with harmless and inexpensive regents, and they were used to label monoclonal antibodies (mAbs) of AMD in microwells with electrostatic adsorption. Then, a magnetic immunochromatography assay (MICA) method was successfully established. Under optimal conditions, the MICA showed a good performance, with a linear range of 0.2~10.0 µg/L. The limit of detection (LOD) was 0.068 µg/L with the instrument, and the visual LOD (vLOD) was 0.5 µg/L. There was no cross-reaction with rimantadine and ribavirin. The vLOD in real samples was 1.0 µg/kg. The developed MICA has the advantages of convenience, speed, and sensitivity, which make it suitable for the on-site rapid detection of AMD residues in chicken tissues and eggs.

Discovery and Optimization of an Aptamer and Its Sensing Ability to Amantadine Based on SERS via Binary Metal Nanoparticles

With the growing concern of illegal abuse of amantadine (AMD) and its potential harmful impact on humans, detection of AMD has become an urgent food safety and environmental topic. Biosensing is a promising method for this, but the effective recognition of AMD still remains a challenge. Herein, we isolated an aptamer (Am-20) for AMD through a 14-round iterative selection based on capture-SELEX. The preliminary interaction mechanism between AMD and Am-20 was clarified with the help of docking simulations. Facilitated by a base mutation and truncation strategy, an optimized aptamer Am-20-1 with a short length of 62-mer was obtained, which exhibited competitive affinity with a K_d value of 33.90 ± 5.16 nM. A structure-switching SERS-based aptasensor based on Am-20-1 was then established for AMD quantification via a binary metal nanoparticle-embedded Raman reporter substrate (AuNRs@ATP@AgNPs). The fabricated strategy showed a wide linear range (0.005∼25 ng/mL) and a low limit of detection (0.001 ng/mL) for AMD determination. We envision that the novel aptamer identified in this study will provide a complementary tool for specific recognition and detection of AMD and could assist in the supervision of illegal abuse of AMD.

Comparison of two fluorescence quantitative immunochromatographic assays for the detection of amantadine in chicken muscle

The two sensitive fluorescence quantitative immunochromatographic assays (FQICAs), background fluorescence quenching immunochromatographic assay (bFQICA) and time-resolved fluorescent immunochromatographic assay (TRFICA), play an important role increasingly in rapid detection technology for food safety. Amantadine (AMD), used extensively in virus infections in livestock and poultry, has been prohibited due to hazard concerns over public human health. Therefore, AMD was used as a model molecule in the FQICAs establishment and comparison based on the same bioreagents. The outstanding performance in technical parameters of the two FQICAs indicated that they could provide rapid, precise, reliable technical support for large-scale on-site screening for AMD detection. What's more, the systematic and comprehensive comparison of the two FQICAs would give useful suggestions for scientists and users in monitoring the harmful compounds.

Dual-readout fluorescence quenching immunochromatographic test strips for highly sensitive simultaneous detection of chloramphenicol and amantadine based on gold nanoparticle-triggered photoluminescent nanoswitch control

Herein, a novel fluorescence quenching immunochromatographic test strip (FQICTS) for simultaneous detection of chloramphenicol (CAP) and amantadine (AMD) was developed on the basis of inner filter effect (IFE), with the combination of gold nanoparticles (AuNPs) and highly luminescent green-emitting gold nanoclusters (AuNCs) as the IFE quencher/donor pair. The AuNPs could quench the excitation light and emission light of AuNCs and achieve a high IFE efficiency due to dual spectral overlapping. Under optimal conditions, the "turn-on" mode of the AuNCs-based dual-readout FQICTS showed good linearity for CAP detection in chicken samples from 0.05 ng/g to 10 ng/g, with a limit of detection (LOD) of 0.043 ng/g. The linear range of AMD is 0.5-50 ng/g, with LOD of 0.45 ng/g. The visual LODs of CAP and AMD in "turn-on" mode were 200 and 10 times lower than that in "turn-off" mode, respectively. The "turn-on" mode of FQICTS showed high recovery for detecting CAP (82.5-94.5%) and AMD (81.9-110.7%) spiked into chicken samples. The performance and practicability of the established method were verified with commercial enzyme-immunoassay kits, and good correlations were observed. Overall, the newly developed AuNCs-based dual-readout FQICTS is a promising on-site screening tool for rapid, high-sensitivity detection of multiple food contaminants in practical applications.

Synthesis and characterization of tracers and development of a fluorescence polarization immunoassay for amantadine with high sensitivity in chicken

Fluorescence polarization immunoassay (FPIA) is a homogeneous and rapid analytical method that is suitable for high-throughput screening of large numbers of samples. However, FPIA typically suffers from lower sensitivity than the well-established enzyme-linked immunosorbent assay (ELISA), limiting its wide application as an analytical tool that can be run with trace levels of an analyte. Herein, a highly sensitive FPIA for detecting amantadine (AMD) in chicken is described. To achieve high sensitivity, nine chemical tracers of AMD that employ different fluoresceins, fluorescein derivatives, and haptens were synthesized and paired with four previously produced monoclonal antibodies (mAbs). The effect of the tracer structure on the sensitivity of FPIA was investigated and discussed. We found that the tracers with a linear and shorter bridge between adamantane and fluorescein generally provided higher sensitivity. After optimization, N'-(1-adamantyl) ethylenediamine (AEDA), an AMD structural analogue labeled with fluorescein isothiocyanate (FITC), achieved the lowest IC₅₀ value (1.0 ng/ml) in the FPIA, which was comparable to that of the heterologous ELISA format that used the same mAb7G2. We also investigated the possible recognition mechanism of mAbs in terms of conformational and electronic aspects. The developed FPIA was applied to chicken to detect AMD residue, demonstrating a limit of detection (LOD) of 0.9 µg/kg with recoveries of 76.5-89.3% and coefficients of variation (CVs) below 14.5%. These results show that the proposed FPIA is an efficient, accurate, and convenient method for the rapid screening of AMD residues in chicken. PRACTICAL APPLICATION: The fluorescence polarization immunoassay (FPIA) was developed to determine and quantify amantadine (AMD) in chicken samples with high sensitivity. This homogeneous method avoids coating and washing steps and may provide high-throughput AMD screening in chicken in 10 min with high accuracy and precision. FPIA can be used as a monitoring tool and contribute significantly to the rapid detection of AMD in chicken.

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.

Nanochannel sensor for sensitive and selective adamantanamine detection based on host-guest competition

The abuse of adamantanamine (ADA) and its derivatives as veterinary drugs in the poultry industry could cause severe health problems for humans. It is of great need to develop a rapid, cheap and ultrasensitive method for ADA detection. In this study, a sensitive conical nanochannel sensor was established for the rapid quantitative detection of ADA with the distinctive design of the host-guest competition. The sensor was constructed by functionalizing the nanochannel surface with p-toluidine and was then assembled with Cucurbit [7]uril (CB [7]). When ADA is added, it could occupy the cavity of CB [7] due to the host-guest competition and makes CB [7] to release from the CB [7]-p-toluidine complex, resulting in a distinct change of hydrophobicity of the nanochannel, which could be determined by the ionic current. Under the optimal conditions, the strategy permitted sensitive detection of ADA in a linear range of 10-1000 nM. The nanochannel based ADA sensing platform showed both high sensitivity and excellent reproducibility and the limit of detection was 4.54 nM. For the first time, the rapid and sensitive recognition of an illegal medicine was realized based on the host-guest competition method with the nanochannel system and the principle and feasibility of this method were described at length. This strategy provides a simple, reliable, and effective way to apply host-guest system in the development of nanochannel sensor for small-molecule drug detection.

Homogeneous fluorescent immunoassay for the simultaneous detection of chloramphenicol and amantadine via the duplex FRET between carbon dots and WS2 nanosheets

Herein, we proposed a duplex and homogeneous fluorescent immunoassay for the simultaneous detection of amantadine (AMD) and chloramphenicol (CAP) residue in chicken breast with both high sensitivity and short assay time. The immunoassay was based on the fluorescence resonance energy transfer (FRET) between hapten-labeled carbon dots (CDs) and antibody-modified WS₂ nanosheets. To achieve the duplex FRET, polyethyleneimine-functionalized blue and green emissive CDs with separated emission were synthesized via a one-pot hydrothermal method and directly coupled with the haptens of AMD and CAP, serving as the energy donors. The antibodies were modified on the surface of WS₂ nanosheets with high quenching efficiency to construct the energy acceptor. The specific immunoreaction could trigger the efficient FRET between the donors and the acceptors, causing the fluorescence quenching of CDs. The developed immunoassay was applied to simultaneously detect AMD and CAP, having the detection limit of 0.10 ng g^-1 and 0.06 ng g^-1, respectively.

Hapten Synthesis and the Development of an Ultrasensitive Indirect Competitive ELISA for the Determination of Diethylstilbestrol in Food Samples

An ultrasensitive indirect competitive enzyme-linked immunosorbent assay (ic ELISA) using monoclonal antibodies (mAbs) was developed for the specific detection of diethylstilbestrol (DES) residues. To establish an ELISA based on mAbs, hapten diethylstilbestrol mono-carboxypropyl-ether (DES-MCPE) was chemically synthetized and then conjugated to bovine serum albumin (BSA) for immunization in mice. This ic ELISA was further optimized for DES determination. The sensitivity of the ic ELISA was found to be 0.49 μg/kg and the limit of detection was 0.075 μg/kg. DES residues in salmon meat and pork were tested with the recovery range from 74.0 to 85.2% and the coefficient of variation (CV) was less than 10%. Parallel analysis of DES samples from salmon meat showed comparable results from the ic ELISA with high-performance liquid chromatography. The ic ELISA provides a useful screening method for the quantitative detection of DES residues in animal-derived food.

Site-directed mutations of anti-amantadine scFv antibody by molecular dynamics simulation: prediction and validation

A recombinant single-chain variable fragment (scFv) antibody was produced from a hybridoma cell strain secreting the monoclonal antibody for amantadine (AMD), and then its recognition mechanisms for AMD were studied using the molecular docking and molecular dynamics. Complex dockings revealed that three regions are involved in antibody recognition; framework 2 of the VL chain (LFR2) GLU40 and TYR42, complementarity-determining region of the VL chain (LCDR3) TYR116, and framework 2 of the VH chain (HFR2) HIS40 and TRP52 were the key amino acid residues. The results of molecular dynamics show that the most important amino acid residues in the interaction between AMD and scFv are HIS40 and TYR116. On the basis of the results of virtual mutation, the scFv antibody was evolved by directional mutagenesis of amino acid residue GLY107 to PHE. Indirect competitive ELISA (icELISA) results indicated that the scFv mutant had highly increased affinity for AMD with up to 3.9-fold improved sensitivity. Thus, the scFv antibody can be applied for mechanistic studies of intermolecular interactions, and our work offered affinity maturated antibodies by site mutations, which were beneficial for valuable anti-AMD antibody design and preparation in future.

Fabrication and evaluation of a label-free piezoelectric immunosensor for sensitive and selective detection of amantadine in foods of animal origin

A label-free piezoelectric immunosensor was fabricated and applied to the detection of the antiviral drug amantadine (AM) in foods of animal origin. Experimental parameters associated with the fabrication and measurement process were optimized and are discussed here in detail. The proposed piezoelectric sensor is based on an immunosuppression format and uses a portable quartz crystal microbalance (QCM) chip. It was found to provide a good response to AM, with a sensitivity and limit of detection (LOD) of 33.9 and 1.3 ng mL^-1, respectively, as well as low cross-reactivity (CR, < 0.01%) with AM analogues. The immunosensor was further applied to quantify AM at three levels in spiked samples of typical foods of animal origin, and yielded recoveries of 83.2-93.4% and standard deviations (SDs, n = 3) of 2.4-4.5%, which are comparable to the results (recoveries: 82.6-94.3%; SDs: 1.7-4.2%) obtained using a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method. Furthermore, the piezoelectric immunosensing chip can be regenerated multiple (at least 20) times with low signal attenuation (about 10%). A sample analysis can be completed within 50 min (sample pretreatment: about 40 min, QCM measurement: 5 min). These results demonstrate that the developed piezoelectric immunosensor provides a sensitive, accurate, portable, and low-cost analytical strategy for the antiviral drug AM in foods of animal origin, and this label-free detection method could also be applied to analyze other targets in the field of food safety. Graphical abstract.

Quantitative and rapid detection of amantadine and chloramphenicol based on various quantum dots with the same excitations

Herein, we developed a sensitive and quantitative flow assay for simultaneous detection of amantadine (AMD) and chloramphenicol (CAP) in chicken samples based on different CdSe/ZnS quantum dots (QDs). In contrast to other reports, the QDs could be excited by the same excitations that lowered the requirements for the matching instruments. Under the optimal conditions, the strategy permitted sensitive detection of AMD and CAP in a linear range of 0.23 to 1.02 ng/g and 0.02 to 0.66 ng/g. The limits of detection were 0.18 ng/g and 0.016 ng/g, respectively. Moreover, the whole detection process could be completed within 20 min with no additional sophisticated instruments and complicated operations. Spiked samples were analyzed using both QD-based lateral flow immunoassay (QD-LFIA) and commercial ELISA kits with good correlation (R² = 0.96). Moreover, this study laid the foundation and simplified the development of the requisite instrument. Graphical abstract ᅟ.

A Lateral Flow Immunochromato-graphic Strip Test for Rapid Detection of Oseltamivir Phosphate in Egg and Chicken Meat

A lateral flow immunochromatographic strip test (LFIST) based on a competitive format was developed for rapid and sensitive on-site detection of oseltamivir phosphate (OP) residues in poultry product. The sensitivity (half inhibitory concentration, IC₅₀) of the LFIST in the detection of egg and chicken meat samples was confirmed to be 2.56 and 2.63 µg/kg, and the limit detection (LOD) value were 0.43 and 0.42 µg/kg, respectively. For intra-assay and inter-assay reproducibility, recoveries of OP spiked samples ranged between 82.8% and 91.2% with coefficients of variations (CV) less than 5.67% (intra-assay) and 6.52% (inter-assay). The performance of LFIST was comparable to high-performance liquid chromatography (HPLC) in a parallel testing of egg samples and chicken samples. LFIST takes less than 5 minutes, eliminates the dependency on professional personnel, and thus can be used as a surveillance tool for on-site detection of OP residues.

A lateral flow immunochromatographic strip test for rapid detection of hexoestrol in fish samples

A lateral flow immunochromatographic strip test was developed for rapid and sensitive on-site detection of hexoestrol (HES) residues in fish samples with colloidal gold labelling of the anti-HES monoclonal antibody. The strip is composed of a sample pad, a conjugate reagent pad, an absorbent pad and a test membrane containing a control line and a test line. The sensitivity (half inhibitory concentration, IC50) of the strip in the detection of fish extract samples was confirmed to be 1.86 µg kg-1, and the limit of detection value was 0.62 µg kg-1. For intra-assay and inter-assay reproducibility, recoveries of HES-spiked samples ranged from 86.3% to 92.3% and 85.8% to 93.4%, coefficients of variation were 2.91-4.64% and 4.24-5.17%, respectively. High-performance liquid chromatography was employed to confirm the performance of the strip. The strip test takes less than 10 min, and thus provides a repaid method for on-site detection of HES residues.

Highly sensitive visual detection of amantadine residues in poultry at the ppb level: A colorimetric immunoassay based on a Fenton reaction and gold nanoparticles aggregation

Colorimetric biosensors for the on-site visual detection of veterinary drug residues are required for food control in developing countries and other resource-constrained areas, where sophisticated instruments may not be available. In this study, we developed a highly sensitive immunoassay for amantadine residues in poultry. By introducing a novel signal generation strategy into an indirect competitive immunoassay, a highly sensitive assay for amantadine residues in chicken was achieved for naked eye readout at the part per billion (ppb) level. Signal amplification was achieved in the designed immunoassay by combining conventional indirect competitive enzyme-linked immunosorbent assay, Fenton reaction-regulated oxidation of cysteine, and gold nanoparticle aggregation. Therefore, the cascade reaction remarkably enhanced the assay sensitivity and led to a pronounced color change from red to dark purple in the solution, which could be easily distinguished with the naked eye even at approximately 1 μg kg^-1 in poultry muscle. Moreover, the color change can be quantitatively assayed with a classic high-throughput plate reader for contaminated poultry samples. The limit of detection (LOD) was 0.51 nM (0.095 ng mL^-1). The recovery rates for spiked chicken samples ranged from 78% to 84% with relative standard deviations <15%. Therefore, we propose that this immunoassay could be generally applicable for on-site detection in the field of food control.

Sensitive and rapid determination of amantadine without derivatization in human plasma by LC-MS/MS for a bioequivalence study

A highly sensitive, rapid and rugged liquid chromatography-tandem mass spectrometry (LC-ESI-MS/MS) method was developed for reliable estimation of amantadine (AMD), an antiviral drug in human plasma. The analyte and internal standard (IS), amantadine-d6 (AMD-d6), were extracted from 200 µL plasma by solid phase extraction on Phenomenex Strata-X-C 33 µ cartridges. Chromatography was performed on Synergi™ Hydro-RP C₁₈ (150 mm × 4.6 mm, 4 µm) analytical column using a mixture of acetonitrile and 10 mM ammonium formate, pH 3.0 (80:20, v/v) as the mobile phase. Detection and quantitation was done by multiple reaction monitoring in the positive ionization mode for AMD (m/z 152.1 → 135.1) and IS (m/z 158.0 → 141.1) on a triple quadrupole mass spectrometer. The assay was linear in the concentration range of 0.50–500 ng/mL with correlation coefficient (r²) ≥ 0.9969. The limit of detection of the method was 0.18 ng/mL. The intra-batch and inter-batch precisions were ≤ 5.42% and the accuracy varied from 98.47% to 105.72%. The extraction recovery of amantadine was precise and quantitative in the range of 97.89%–100.28%. IS-normalized matrix factors for amantadine varied from 0.981 to 1.012. The stability of AMD in whole blood and plasma was evaluated under different conditions. The developed method was successfully applied for a bioequivalence study with 100 mg of AMD in 32 healthy volunteers. The reproducibility of the assay was determined by reanalysis of 134 subject samples.