An improved clenbuterol detection by immunochromatographic assay with bacteria@Au composite as signal amplifier

Multifunctional magnetic tags with photocatalytic and enzyme-mimicking properties for constructing a sensitive dual-readout ELISA

ELISA has become the gold standard for detecting harmful substances due to its specific antibody recognition and sensitive enzyme-catalyzed reactions. In this study, multifunctional magnetic Prussian blue nanolabels (MPBNs) were synthesized using a simple gentle two-step method to achieve a dual-readout mode. The MPBNs provide a sensitive colorimetric signal by efficiently catalyzing the oxidation of TMB and exhibit prominent photocatalytic degradation activity towards Rhodamine B (RhB). Supplemented by the quenching effect of oxTMB, the fluorescence was enabled to serve as a sensitive second signal. The magnetic property of the labels facilitates the separation and enrichment of the target, thereby improving sensitivity. Utilizing the versatile MPBNs, the visual limit of detection (vLOD) for Staphylococcus aureus is as low as 100 CFU/mL, with a quantitative analysis range of 102-108 CFU/mL. The introduction of photocatalytic reactions into immunoassay has opened up a new signal response system with strong momentum for development and application.

Microfabrication of engineered Lactococcus lactis biocarriers with genetically programmed immunorecognition probes for sensitive lateral flow immunoassay of antibiotic in milk and lake water

Micro/nanomaterials display considerable potential for increasing the sensitivity of lateral flow immunoassay (LFIA) by acting as 3D carriers for both antibodies and signals. The key to achieving high detection sensitivity depends on the probe's orientation on the material surface and its multivalent biomolecular interactions with targets. Here, we engineer Lactococcus lactis as the bacterial microcarrier (BMC) for a multivalent immunorecognition probe that was genetically programmed to display multifunctional components including a phage-screened single-chain variable fragment (scFv), an enhanced green fluorescent protein (eGFP), and a C-terminal peptidoglycan-binding domain (AcmA) anchored on BMC through the cell wall peptidoglycan. The innovative design of this biocarrier system, which incorporates a lab-on-a-chip microfluidic device, allows for the rapid and non-destructive self-assembly of the multivalent scFv-eGFP-AcmA@BMC probe, in which the 3D structure of BMC with a large peptidoglycan surface area facilitates the precisely orientated attachment and immobilization of scFv-eGFP-AcmA. This leads to a remarkable fluorescence aggregation amplification effect in LFIA, outperforming a monovalent 2D scFv-eGFP-AcmA probe for florfenicol detection. By designing a portable sensing device, we achieved an exceptionally low detection limit of 0.28 pg/mL and 0.21 pg/mL for florfenicol in lake water and milk sample, respectively. The successful microfabrication of this biocarrier holds potential to inspire innovative biohybrid designs for environment and food safety biosensing applications.

Sensitization Strategies of Lateral Flow Immunochromatography for Gold Modified Nanomaterials in Biosensor Development

Gold nanomaterials have become very attractive nanomaterials for biomedical research due to their unique physical and chemical properties, including size dependent optical, magnetic and catalytic properties, surface plasmon resonance (SPR), biological affinity and structural suitability. The performance of biosensing and biodiagnosis can be significantly improved in sensitivity, specificity, speed, contrast, resolution and so on by utilizing multiple optical properties of different gold nanostructures. Lateral flow immunochromatographic assay (LFIA) based on gold nanoparticles (GNPs) has the advantages of simple, fast operation, stable technology, and low cost, making it one of the most widely used in vitro diagnostics (IVDs). However, the traditional colloidal gold (CG)-based LFIA can only achieve qualitative or semi-quantitative detection, and its low detection sensitivity cannot meet the current detection needs. Due to the strong dependence of the optical properties of gold nanomaterials on their shape and surface properties, gold-based nanomaterial modification has brought new possibilities to the IVDs: people have attempted to change the morphology and size of gold nanomaterials themselves or hybrid with other elements for application in LFIA. In this paper, many well-designed plasmonic gold nanostructures for further improving the sensitivity and signal output stability of LFIA have been summarized. In addition, some opportunities and challenges that gold-based LFIA may encounter at present or in the future are also mentioned in this paper. In summary, this paper will demonstrate some feasible strategies for the manufacture of potential gold-based nanobiosensors of post of care testing (POCT) for faster detection and more accurate disease diagnosis.

Nanosensors: A smart remedy for early detection of clenbuterol contamination in food

Veterinary drugs which are primarily meant for livestock treatment have now been categorised under potential food contaminant due to its unregulated usage and abuse. Their over usage by animal workers lead to production of contaminated animal-based food products which contain veterinary drug residues. These drugs are also misused as growth promoters to enhance the muscle to fat ratio in human body. This review highlights the misuse of such a veterinary drug; Clenbuterol. In this review, we have comprehensively discussed the usage of nanosensors to detect clenbuterol in food samples. Colorimetric, fluorescent, electrochemical, SERS and electrochemiluminescence are major categories of nanosensors that have been utilized for this purpose. The mechanism through which these nanosensors detect clenbuterol have been discussed in detail. The limit of detection and recovery percentage values of each nanosensor have been compared. This review will impart significant information on various nanosensors for clenbuterol detection in real samples.

Paper-Based Fluidic Sensing Platforms for β-Adrenergic Agonist Residue Point-of-Care Testing

The illegal use of β-adrenergic agonists during livestock growth poses a threat to public health; the long-term intake of this medication can cause serious physiological side effects and even death. Therefore, rapid detection methods for β-adrenergic agonist residues on-site are required. Traditional detection methods such as liquid chromatography have limitations in terms of expensive instruments and complex operations. In contrast, paper methods are low cost, ubiquitous, and portable, which has led to them becoming the preferred detection method in recent years. Various paper-based fluidic devices have been developed to detect β-adrenergic agonist residues, including lateral flow immunoassays (LFAs) and microfluidic paper-based analytical devices (μPADs). In this review, the application of LFAs for the detection of β-agonists is summarized comprehensively, focusing on the latest advances in novel labeling and detection strategies. The use of μPADs as an analytical platform has attracted interest over the past decade due to their unique advantages and application for detecting β-adrenergic agonists, which are introduced here. Vertical flow immunoassays are also discussed for their shorter assay time and stronger multiplexing capabilities compared with LFAs. Furthermore, the development direction and prospects for the commercialization of paper-based devices are considered, shedding light on the development of point-of-care testing devices for β-adrenergic agonist residue detection.

Research on Rapid Detection Technology for β2-Agonists: Multi-Residue Fluorescence Immunochromatography Based on Dimeric Artificial Antigen

To detect two types of β2-agonist residues at the same time, we coupled two haptens of clenbuterol (CLE) and ractopamine (RAC) to the same carrier protein through diazotization to prepare dimeric artificial antigen, and a fluorescent lateral flow immunoassay method based on europium nanoparticles (EuNP-FLFIA) was established by combining polyclonal antibodies with europium nanoparticles to form probes. Under optimized conditions, the EuNP-FLFIA could simultaneously detect eight aniline-type and one phenol-type β2-agonists, and the limits of detection (LOD) were 0.11−0.19 ng/mL and 0.12 ng/mL, respectively. The recovery rate of this method was 84.00−114.00%. This method was verified by liquid chromatography−tandem mass spectrometry (LC-MS/MS), and the test results were consistent (R2 > 0.98). Therefore, the method established in this study could be used as a high-throughput screening for the efficient and sensitive detection of β2-agonists in food.

Graphene-labeled synthetic antigen as a novel probe for enhancing sensitivity and simplicity in lateral flow immunoassay

Lateral flow immunoassay (LFIA), which combines immune-specific recognition properties with sensitive nano-signaling features, has emerged as an excellent tool for point-of-care testing (POCT) in food safety and clinical diagnosis. Exploring novel probes with a simple preparation process, improved signal intensity and good stability is conducive to the development and application of LFIA. Herein, a potent non-antibody probe, graphene-labeled synthetic antigen (G-Ag), was created for LFIA, in which graphene endowed a naked-eye visual colorimetric signal with high sensitivity, and the synthetic antigen competed with the target for binding to the antibody on the test line. During the G-Ag probe manufacturing process, only one simple mixing step was needed because graphene nanosheets presented a strong adsorption capacity toward the protein (BSA) on the synthetic antigen, significantly saving time, labor and cost. Especially, the synthetic antigen forms a fabulous probe element without the need for antibody, and thus the proposed LFIA avoids the destruction of antibody activity, and exhibits excellent sensitivity and stability. After optimization, LFIA was successfully applied to analyze clenbuterol; the lowest visually detectable concentration was 0.1 ng mL^-1, and the probe could be well-applied in pork, mutton, sausage and bacon samples, demonstrating favorable specificity and repeatability. Owing to the advantages of simplicity, non-antibody probe, sensitivity and reliability, G-Ag probe-based LFIA has application potential for small-molecule target monitoring and rapid detection.

Current Advances in Immunoassays for the Detection of β2-Agonists

β2-agonists are a group of synthetic phenylethanolamine compounds which are traditionally used for treating bronchospasm. These compounds can also increase skeletal muscle mass and decrease body fat. The illegal use of β2-agonists in food-producing animals results in residue of β2-agonists in edible tissues and causes adverse health effects in humans. Thus, the detection of β2-agonists at trace level in complex sample matrices is of great importance for monitoring the abuse of β2-agonists. Many methods have been developed to detect β2-agonists. Among them, a variety of antigen–antibody interaction-based techniques have been established to detect β2-agonists in various samples, including animal feed, urine, serum, milk, tissues and hair. In this review, we summarized current achievement in the extraction of β2-agonists from testing samples and detection of β2-agonists using immunological techniques. Future perspectives were briefly discussed.

Tailoring noble metal nanoparticle designs to enable sensitive lateral flow immunoassay

Lateral flow immunoassay (LFIA) with gold nanoparticles (AuNPs) as signal reporters is a popular point-of-care diagnostic technique. However, given the weak absorbance of traditional 20-40 nm spherical AuNPs, their sensitivity is low, which greatly limits the wide application of AuNP-based LFIA. With the rapid advances in materials science and nanotechnology, the synthesis of noble metal nanoparticles (NMNPs) has enhanced physicochemical properties such as optical, plasmonic, catalytic, and multifunctional activity by simply engineering their physical parameters, including the size, shape, composition, and external structure. Using these engineered NMNPs as an alternative to traditional AuNPs, the sensitivity of LFIA has been significantly improved, thereby greatly expanding the working range and application scenarios of LFIA, particularly in trace analysis. Therefore, in this review, we will focus on the design of engineered NMNPs and their demonstration in improving LFIA. We highlight the strategies available for tailoring NMNP designs, the effect of NMNP engineering on their performance, and the working principle of each engineering design for enhancing LFIA. Finally, current challenges and future improvements in this field are briefly discussed.

Simultaneous quantitative analysis of Listeria monocytogenes and Staphylococcus aureus based on antibiotic-introduced lateral flow immunoassay

Food poisoning caused by microorganisms has caused widespread concern. Herein, a highly sensitive on-site screening test strip for the detection of different pathogenic microorganisms (Listeria monocytogenes and Staphylococcus aureus) was designed. In this analysis platform, colloidal gold-coupled vancomycin was used as a signal unit to label Gram-positive bacteria, and highly sensitive polyclonal antibodies were used as recognition molecules to capture these specific strains. Compared with the traditional dual-antibody sandwich model, this new type of antibiotic-pathogen-antibody sandwich model is low-cost and can simultaneously detect multiple microorganisms. Under optimal conditions, this strategy showed satisfactory sensitivity and a wide linear range (L. monocy and S. aure could be directly assayed within linear ranges of 5 × 10⁴ to 10⁷ and 5 × 10² to 10⁷ CFU mL^-1, and the visual detection limits were 10⁵ and 10³ CFU mL^-1, respectively). The analytical performance and practicability of this sensor system have been further studied. This developed biosensor was applied to bacteria-contaminated water, milk and broth with satisfactory results. All of these attractive characteristics make the assay possess potential applications in food safety, medical diagnosis and environmental monitoring.

Highly Sensitive Colorimetric/Surface-Enhanced Raman Spectroscopy Immunoassay Relying on a Metallic Core-Shell Au/Au Nanostar with Clenbuterol as a Target Analyte

Lateral flow immunoassay (LFIA) has emerged as an effective technique in the field of food safety and environmental monitoring. However, sensitive and quantitative detection is still challenging for LFIAs in complex environments. In this work, a dual-model colorimetric/SERS lateral flow immunoassay for ultrasensitive determination of clenbuterol was constructed based on a metallic core-shell Au/Au nanostar acting as a multifunction tag. Raman reporter molecules are located between the core (AuNP) and shell (Au nanostar) to form a sandwich structure, which contributes to eliminate the environmental interference and improve the detection stability. In addition, the Au/Au nanostar provides a much higher Raman enhancement due to the presence of sharp tips and larger surface roughness in comparison with gold nanoparticles (AuNPs). Thus, on the basis of the antibody-antigen interaction, the dual-model immunoassay can produce strong colorimetric and surface-enhanced Raman spectroscopy (SERS) signals for highly sensitive detection of the target analyte, clenbuterol. Under optimal conditions, clenbuterol could be detected by the colorimetric model with a visual detection limit of 5 ng/mL. Meanwhile, the SERS signal of the Au/Au nanostar was accumulated on the test line for the SERS model detection with a quantitative detection limit as low as 0.05 ng/mL, which is at least 200-fold lower than that of the traditional AuNPs-based immunoassay. Furthermore, recovery rates of the proposed method in food samples were 86-110%. This dual-model immunoassay provides an effective tool for antibiotic residues analysis and demonstrates a broad potential for future applications in food safety monitoring.

Diverse Dyes-Embedded Staphylococcus aureus as Potential Biocarriers for Enhancing Sensitivity in Biosensing

Nanomaterials-based immunochromatographic assays (ICAs) have gained great commercial success in real-life point-of-care testing (POCT). Exploring novel carriers of ICAs with improved signaling and sustained activity favors the development of sensitive POCT. Herein a potent signal biotag, colored Staphylococcus aureus (SA), was created for ICA carriers through a mild self-assembly strategy, providing high luminance and abundant specific binding sites for immobilization of monoclonal antibodies (mAbs). The biocompatible SA-dyes (SADs) retained both an intact surface structure for mAbs labeling (Fc portion) and the superior bioactivity of immobilized mAbs (affinity constant was about 10⁹ M^-1), thus waiving the intrinsic limitations of traditional nanomaterials and endowing high sensitivity. Proof-of-concept was demonstrated by employing Congo red- or/and fluorescein isothiocyanate-embedded SA (SACR, SAFITC, and SACR-SAFITC) as ICA carriers to detect zearalenone (ZEN) through colorimetric or/and fluorimetric signals. Furthermore, the ICAs satisfied the clinical requirement perfectly, including limit of detection (0.013 ng/mL, which was at least an 85-fold improvement over that of traditional gold nanoparticles-based ICA), linearity (R² > 0.98), reproducibility (RSD < 8%), selectivity, and stability. Importantly, the proposed biosensors could be well-applied in four real samples for ZEN monitoring with satisfactory recoveries, correlating well with the results from liquid chromatography-tandem mass spectrometry (LC-MS). This work also proved a universal design for tailoring coloration bands for SAD-ICA detection of multiple analytes.

Nanoscale Metal-Organic Frameworks as Fluorescence Sensors for Food Safety

Food safety has attracted attention worldwide, and how to detect various kinds of hazardous substances in an efficient way has always been a focus. Metal-Organic Frameworks (MOFs) are a class of hybrid porous materials formed by organic ligand and metal ions. Nanoscale MOFs (NMOFs) exhibit great potential in serving as fluorescence sensors for food safety due to their superior properties including high accuracy, great stability, fast response, etc. In this review, we focus on the recent development of NMOFs sensing for food safety. Several typical methods of NMOFs synthesis are presented. NMOFs-based fluorescence sensors for contaminants and adulterants, such as antibiotics, food additives, ions and mycotoxin etc. are summarized, and the sensing mechanisms are also presented. We explore these challenges in detail and provide suggestions about how they may be surmounted. This review could help the exploration of NMOFs sensors in food related work.

Graphite-like carbon nitride-laden gold nanoparticles as signal amplification label for highly sensitive lateral flow immunoassay of 17β-estradiol

Conventional gold nanoparticles-based lateral flow immunoassays (AuNPs-LFIA) lack sensitivity. In this work, we developed a graphite-like carbon nitride-laden AuNPs (g-C₃N₄@Au) assisted LFIA to improve sensitivity for 17β-estradiol (E2) in foods. g-C₃N₄ nanosheets were applied as carriers, because of their excellent chemical stability, large surface areas and low-cost, loading large numbers of AuNPs to amplify signals and improve the overall response of g-C₃N₄@Au-based LFIA (g-C₃N₄@Au-LFIA). The lowest visual limit of detection (vLOD) of E2 is 0.5 ng mL^-1 for g-C₃N₄@Au-LFIA, which exhibit a significantly three-fold improved analytical performance compared with that of AuNPs-LFIA. Additionally, this method was successfully used to the detection of E2 in four spiked food samples, offering a great potential of the g-C₃N₄@Au based LFIA for its application in food products.

Developing a Simple Immunochromatography Assay for Clenbuterol with Sensitivity by One-Step Staining

An innovative lateral flow competition immunoassay (LFCIA) for detecting clenbuterol (CL) was developed by employing the advantages of the coomassie brilliant blue (CBB) staining method. An antibody stained by CBB was used both as a recognition reagent and as a chromogenic probe, enabling the simple but sensitive LFCIA of CL. The CBB-based LFCIA exhibited sensitivity for CL with a detection limit of 2 ng mL^-1. Furthermore, this strategy was preliminarily verified by screening for CL in milk, pork tenderloin, and swine liver with recoveries ranging from 81 to 102%. Compared with conventional LFCIAs, the use of CBB as a signal label not only avoided the complicated material synthesis and surface modification process but also simplified the cross-linking with antibodies, meanwhile reducing the steric hindrance and increasing the possibility of immune recognition reactions, which was propitious for the effective utilization of antibodies. Taking advantages of the simplicity, rapidity, and cost-effectiveness, the CBB-based LFCIA may have potential for on-demand monitoring of general harmful small molecules by changing the kind of the staining antibody.

Extracellular and intracellular zilpaterol and clenbuterol quantification in Hep G2 liver cells by UPLC-PDA and UPLC-MS/MS

Zilpaterol and Clenbuterol are β-adrenergic agonists that have been widely used to feed cattle. Although the use of Zilpaterol has been approved, Clenbuterol is still used illegally at unknown doses. However, the research of both substances has been based mainly on the evaluation of residues. To our knowledge, this is the first time that a cellular model using Hep G2 cells treated with Zilpaterol and Clenbuterol is presented as an alternative approach to quantify both drugs at the cellular level. Thus, a complete analytical methodology has been developed for the accurate quantitation of these β-adrenergic agonists in both cellular compartments. We propose the use of ultra-performance liquid chromatography with photodiode array detector (UPLC-PDA) for extracellular determinations while UPLC coupled to a tandem mass spectrometer (UPLC-MS/MS) for intracellular analysis. The methods were fully validated in terms of selectivity, linearity, accuracy, and precision, limits of detection and quantitation (LOD and LOQ, respectively), stability, carryover, and matrix effect. The method for intracellular content was linear ranging from 0.25 to 8 ng/mL while for extracellular content, the concentration of Zilpaterol and Clenbuterol ranged from 0.125 to 4 μg/mL, with correlation coefficients of R > 0.98 and >0.99, respectively. The combination of the two methodologies in the cellular model showed intracellular concentrations of 0.344 ± 0.06 μg/mL and 2.483 ± 0.36 μg/mL for Zilpaterol and Clenbuterol, respectively. Extracellular concentration was 0.728 ± 0.14 μg/mL and 0.822 ± 0.11 μg/mL for Zilpaterol and Clenbuterol, respectively. This work shows the potential applications of cellular modelling in the study of toxicity for the mentioned drugs.

Gold nanoparticle-decorated metal organic frameworks on immunochromatographic assay for human chorionic gonadotropin detection

Gold nanoparticle-decorated metal organic frameworks (MOF@AuNPs) with significantly enhanced color signal intensity were synthesized through in situ growth of AuNPs on the MOF skeleton. The resultant MOF@AuNP nanocomposites were characterized with 16.7-fold higher absorbance than conventional 40 nm AuNPs (AuNP₄₀). Thus, for the first time, we applied it as a signal amplification label to improve the immunochromatographic assay (ICA) of human chorionic gonadotropin (HCG). The detection limit of our enhanced ICA was 1.69 mIU/mL, which is ca. 10.6-fold improvement in sensitivity compared to traditional AuNP₄₀-ICA. The recoveries of this MOF@AuNPs-ICA ranged from 86.03 to 119.22%, with coefficients of variation of 3.05 to 13.74%. The reliability and practicability were further validated by the clinically used chemiluminescence immunoassay method. Given their excellent signal amplification ability, the proposed MOF@AuNPs could serve as an ideal ICA label for rapid and sensitive detection of disease biomarkers. Graphical abstract.

Nanozyme amplification mediated on-demand multiplex lateral flow immunoassay with dual-readout and broadened detection range

Development of sensitive, facile and rapid biosensors is important for widespread applications. Nanozymes can be ideal signal donors for constructing dual-readout lateral flow immunoassays (LFIA) because they are an excellent class of optical reporters. Herein, a magnetic prussian blue nanozyme (MPBN) mediated dual-readout on-demand multiplex lateral flow immunoassay (MLFIA) was established by employing ractopamine (RAC) and clenbuterol (CLE) as the model analytes. The MPBN was synthesized through in-suit shell-growing and introduced as a bifunctional signal tag owing to their darker original color and peroxidase-like activity. Based on the catalytic signal created by catalyzing oxidation of chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) and colorimetric signal generated by tag's original color, improved precision and broadened detection range were acquired by implementing a dual-readout strategy. And a two-fold increase in the detection range could fulfill different limit requirements of the same target in various regions. The obtained recoveries from 84.01% to 119.94% indicating the repeatability and reliability of the proposed method. This method provides an attractive platform for the detection of a same target with different detection limits, which possesses a considerable potential in monitoring of other targets.

Integrated gold superparticles into lateral flow immunoassays for the rapid and sensitive detection of Escherichia coli O157:H7 in milk

Escherichia coli O157:H7 is a common harmful foodborne pathogen that can cause severe diseases at low infectious doses. Traditional lateral flow immunoassay (LFIA) for the rapid screening of E. coli O157:H7 in food suffers from low sensitivity due to its dependence on 20- to 40-nm gold nanoparticles (AuNP) with insufficient brightness as labels. To address this issue, we reported for the first time the successful synthesis of gold superparticles (GSP) by encapsulating numerous small AuNP into a polymer nanobead using an evaporation-induced self-assembly method. Results indicated that the resultant GSP exhibited remarkably enhanced absorbance compared with the most widely used 40 nm AuNP in LFIA. In addition, the absorbance of GSP could be easily tuned by varying GSP sizes. Under optimized conditions, we achieved a rapid and sensitive determination of E. coli O157:H7 in milk with a detection limit of 5.95 × 10² cfu/mL when using the GSP with a size of 342 nm as LFIA signal reporters, exhibiting improvement of approximately 32-fold relative to the conventional 40 nm AuNP-LFIA method. We further demonstrated the selectivity, accuracy, reliability, and practicality of the proposed GSP-LFIA strip. In summary, this work offers a new strategy for improving LFIA sensitivity using assembled GSP as markers and demonstrates huge potential in rapidly and sensitively detecting foodborne pathogens.

Gold Immunochromatographic Assay for Rapid On-Site Detection of Lincosamide Residues in Milk, Egg, Beef, and Honey Samples

Lincosamides (LMs), include clindamycin (CLIN), lincomycin (LIN), and pirlimycin (PIR), that are widely used as veterinary drugs. LM residues in edible animal origin foods endanger human health and are in urgent need of establishing fast, simple, and highly sensitive detection methods. A gold immunochromatographic strip is prepared to detect CLIN, LIN, and PIR residues simultaneously with a single monoclonal antibody. This antibody is obtained with the design of a novel Hapten and can simultaneously recognize CLIN, LIN, and PIR. Under optimized conditions, the strip results can be semi-quantitatively evaluated with the naked eye within 15 min, with cut-off values in phosphate-buffered saline of 1 ng mL^-1 for CLIN, 10 ng mL^-1 for LIN, and 25 ng mL^-1 for PIR, respectively. Besides, the strip can also be quantified using a hand-held strip scanner, and the spiked samples are used for establishing matrix curves. The limits of detection for CLIN, LIN, and PIR in spiked milk, egg, beef, and honey samples can satisfy the detection requirement. The utility of this strip is also confirmed by positive honey sample. In short, this strip should be expected to be a useful tool for the rapid on-site screening of lincosamide residues in milk, egg, beef, and honey samples.

Synthesis of magnetic nanoparticles to detect Sudan dye adulteration in chilli powders

Magnetic nanoparticles were synthesised to extract Sudan dyes from chilli powders. The adsorbents used were magnetic ferroferric oxide nanoparticles coated with polystyrene. The extraction procedures for Sudan dyes comprised liquid-solid extraction and magnetic solid phase extraction. The conditions were optimised to achieve efficient magnetic solid phase extraction, including extraction and desorption time, type and volume of the desorption solvent, and the mass of the adsorbents. Repeatability tests showed satisfactory recovery rates of 80.2-115.8%, with a relative standard deviation <3.8%. The results suggested that the proposed extraction method was effective and efficient to extract Sudan dyes from chilli powders. The extraction process was simpler compared with traditional approaches because the adsorbents can be rapidly removed from the sample matrix using a permanent magnet. The use of recyclable adsorbents decreased the cost greatly. Chilli powder samples collected from local markets in Singapore were tested using the proposed method under optimum conditions.

New Functional Tracer-Two-Dimensional Nanosheet-Based Immunochromatographic Assay for Salmonella enteritidis Detection

The rapid monitoring of foodborne pathogens by monoclonal antibody (McAb)-based immunochromatographic tests (ICTs) is desirable but highly challenging as a result of the screening obstacle for a superior performance probe, which will greatly determine the capture efficiency of targets and the sensitivity of the immunoassay. In this work, on the basis of two-dimensional (2D) nanosheets (including MoS₂ and graphene) as the extraordinary capture probe and signal indicator, we fabricated a label-free ICT method for Salmonella enteritidis detection. Especially, without the customarily labeled antibody probe, these 2D versatile probes presented strong capture ability toward bacteria by directly assembling onto the surface of bacteria. An ideal analytical performance with high sensitivity and specificity was achieved by virtue of the novel nanosheet-bacteria-McAb sandwich format. On the basis of MoS₂ 2D nanosheets as a fabulous probe element, the developed ICT exhibited a lowest detectable concentration of 10³ colony-forming units/mL for S. enteritidis and could be well-applied in drinking water and watermelon juice samples. By the smart design, this work removes a series of conditionality issues of traditional double antibody sandwich-based ICTs and can give a new application direction for 2D nanosheet materials in the rapid detection field.

Integrated immunochromatographic assay for qualitative and quantitative detection of clenbuterol

In this study, colloidal gold (CG) and time-resolved fluorescent nanobead (TRFN) probes were used to establish an integrated immunochromatographic assay (ICA) to qualitatively and quantitatively detect clenbuterol (CLE). The best experimental conditions for the two probes in separate ICAs were obtained by optimizing the antibody labeling concentration, the amount of antigen, and the concentration of probe. When the CG and TRFN probes co-existed in the ICA, the latter had no effect on the sensitivity of qualitative detection of the CG probe-based ICA. However, the CG probe optimized the linear range of quantitative detection in the TRFN probe-based ICA. The integrated test strip can be used for qualitative and quantitative detection of CLE in one step. When the amount of antigen reached 0.4 mg/mL, the CG probe concentration reached 1.2 μg/mL, and the TRFN probe concentration reached 0.68 μg/mL. The qualitative sensitivity of the integrated ICA was 0.5 ng/mL and its quantitative limit of detection was 0.04 ng/mL with a detection range of 0.1-2.7 ng/mL. This developed method is of great significance for large-scale samples screening and positive monitoring in the field of food safety testing.

Ultrasensitive quantitative detection of small molecules with rapid lateral-flow assay based on high-affinity bifunctional ligand and magnetic nanolabels

An ultrasensitive lateral-flow assay is developed for rapid quantitative detection of small molecules on-site. The conceptual novelty, which transfers lateral-flow assays to the category of highly sensitive quantitative systems, is due to employment of a bifunctional ligand combined with volumetric registration of magnetic nanolabels. The ligand provides extremely high affinity for trapping the nanolabels and, simultaneously, efficiently competes with the analyzed molecules for the limited quantity of antigen-binding sites on the nanolabels. The developed assay has been demonstrated as the first express method for measuring in human serum of free thyroxine (fT4). The limit of detection is 20 fМ or 16 fg/ml at the assay time <30 min with the dynamic range of 3 orders. Besides, we present the results of first characterization of kinetic parameters of interaction between free thyroxine and monoclonal antibody, as well as of competitive relationship between fT4 and fT4-biotin. The proposed universal platform can be used for ultrasensitive detection of small molecules in human in vitro diagnostics, veterinary, biosafety and counter-terrorism, food quality control, environmental monitoring, etc., as well as for search of new, previously undetectable, diagnostic markers in medicine.