Highly sensitive furazolidone monitoring in milk by a signal amplified lateral flow assay based on magnetite nanoparticles labeled dual-probe

Nano-immuno-conjugates inspired by hydrophilic perovskite fluorescent spheres and magnetic assisted for detection of hepatitis B surface antigen

The rampant hepatitis B virus (HBV) seriously endangers human health, and hepatitis B surface antigen (HBsAg) is its early diagnostic marker. Therefore, it is crucial to construct a fast and highly sensitive HBsAg detection method. Based on high-efficiency magnetic separation technology and fluorescent composite material labelling technology, an accurate, fast and sensitive fluorescent immunosensing system for HBsAg detection was developed. Immunomagnetic beads constructed from carboxyl-functionalized Fe3O4 nanoparticles (Fe3O4-COOH) with excellent magnetic response performance were used as efficient capture carriers for HBsAg. Immunofluorescence composite microspheres constructed based on ultra-stable polystyrene-coated CsPbBr3 perovskite nanocrystals (CPB@PSAA) with high hydrophilic properties, were excellent fluorescent markers for HBsAg. Using this sensitive sandwich fluorescence sensing system a good linear relationship within the range of 0.2-15 ng/mL was established between HBsAg concentration and fluorescence intensity with a limit of detection (LOD) of  0.05 ng/mL. The system obtained satisfactory results when tested on real human serum samples. The magnetic-assisted fluorescence immune-sandwich sensor system has broad application prospects in biomedicine such as rapid and early diagnosis and effective prevention of infectious diseases.

Citizen science in action: Time-resolved immunofluorescence-based field detection of antibiotics with portable analytical kit

Citizen scientist-based environmental monitoring and public education are becoming increasingly popular. However, current technologies for antibiotic-based novel contaminant identification are still restricted to laboratory sample collection and analysis due to detection methodologies and apparatus limitations. This study developed a time-resolved immunofluorescence-based simultaneous field-based assay for ciprofloxacin (CIP) and enrofloxacin (ENR) that matches test results to geographic locations. The assay helps the public understand the potential levels of antibiotic exposures in their environments and helps them take appropriate action to reduce risk. The assay was developed using smartphones and social software in addition to rapid testing. The method uses a portable, low-cost analytical kit with a smartphone app to build a field-based detection platform for the detection and analysis of ENR and CIP in water and aquatic products. The methodological evaluation was good, with detection limits of 0.4 ng/mL and 0.5 ng/g for ENR in water and fish, and quantification limits of 1.2 ng/mL and 1.4 ng/g, with recoveries of 89.0 %-101.0 % and 78.0 %-97.0 %. For CIP in water and fish, the limits of detection were 0.3 ng/mL and 0.4 ng/g, the limits of quantification were 0.9 ng/mL and 1.2 ng/g, and the recoveries were 75.0 %-91.0 % and 72.0 %-89.0 %, both with coefficients of variation <15 %. These limits were sufficient to prevent the two antibiotics from crossing over during simultaneous detection. The assay was validated using real samples to assess the effectiveness of the assay platform in field deployments, and the results were consistent with those obtained through liquid chromatography-tandem mass spectrometry (LC-MS) and enzyme-linked immunoassay (ELISA) techniques. In addition, the TRFIA assay process requires less time, uses more portable instruments, and is less complex than traditional methods. This study provides a new scientific, accurate, and rapid detection method for antibiotic detection by citizen scientists, helping scientists to obtain a wider range of data and providing more opportunities to solve scientific problems.

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.

Simultaneous detection of three nitrofuran antibiotics by the lateral flow immunoassay based on europium nanoparticles in aquatic products

Nitrofuran (NF) antibiotics have been banned worldwide in aquaculture due to their potential carcinogenicity and mutagenicity. Because of the short half-life of NF antibiotics, an easy and sensitive multiple lateral flow immunoassay (mLFIA) based on europium nanoparticles (EuNPs) has been successfully established to simultaneously and quantitatively detect 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ), 3-amino-2-oxazolidinone (AOZ) and sodium nifurstylenate (NFS) in aquatic products. The EuNP-mLFIA assay was accomplished within 10 min. The limits of detection (LODs) for AOZ, AMOZ and NFS were 0.013, 0.019 and 0.023 ng/mL, respectively. The average recoveries of AOZ, AMOZ and NFS were 98.0-104.4%, 96.0-102.6% and 98.0-102.8%, respectively. It showed satisfactory consistency, and the feasibility was validated by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Briefly, this method will become a powerful tool for monitoring multiple NF antibiotics and provide promising applications in the field of food safety and environmental testing.

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.

Stepwise Au decoration-assisted double signal amplified lateral flow strip for ultrasensitive detection of morphine in fingerprint sweat

Point-of-care testing (POCT) of morphine (MOP) without invasion of privacy is of critical importance for law-enforcement departments to realize on-site rapid screening. In this study, ultrasensitive and non-invasive screening of MOP residues in the fingerprint sweat was easily realized by stepwise Au decoration-assisted double signal amplification and antibody-saving strategies on lateral flow strip (LFS). The construction of LFS was not intrinsically changed compared with traditional LFS except the labeling material on conjugation pad for enhanced signal reporting. The gold nanoparticle-seeded SiO2 was adopted as the labeling materials in place of traditional gold nanoparticles, which acted as the first-round signal amplification and ready for second-round gold deposition-assisted amplification. And the second-round amplification could be completed in just 10 s, which did not alter the intrinsic simplicity of LFS for rapid and on-site screening. With the designed signal amplification principle of LFS, target MOP in the fingerprint sweat can be effectively transferred to the LFS for analysis without invasion of privacy. As low as 0.5 pg MOP in fingerprint sweat can be visually judged with this double signal amplified LFS, the sensitivity of which has been improved at least 10-fold compared with traditional Au-labeled LFS, guaranteeing accurate screening of trace MOP in the fingerprint sweat. Of great importance, the consumption of valuable antibody can be reduced to just 1/20, which greatly reduces the cost of high-throughput screening. This stepwise Au decoration-assisted double signal amplified LFS holds great potential in the ultrasensitive screening of trace analytes in various fields and further widens the application scope of lateral flow strips.

Paper-based biosensors relying on core biological immune scaffolds for the detection of procymidone in vegetables

In order to achieve a highly sensitive detection of procymidone in vegetables, three paper-based biosensors based on a core biological immune scaffold (CBIS) were developed, which were time-resolved fluorescence immunochromatography strips with Europium (III) oxide (Eu-TRFICS). Goat anti-mouse IgG and europium oxide time-resolved fluorescent microspheres formed secondary fluorescent probes. CBIS was formed by secondary fluorescent probes and procymidone monoclonal antibody (PCM-Ab). The first type of Eu-TRFICS (Eu-TRFICS-(1)) fixed secondary fluorescent probes on a conjugate pad, and PCM-Ab was mixed with a sample solution. The second type of Eu-TRFICS (Eu-TRFICS-(2)) fixed CBIS on the conjugate pad. The third type of Eu-TRFICS (Eu-TRFICS-(3)) was directly mixed CBIS with the sample solution. They solved the problems of steric hindrance of antibody labeling, insufficient exposure of antigen recognition region and easy loss of activity in traditional methods. They realized multi-dimensional labeling and directional coupling. They replaced the loss of antibody activity. And the three types of Eu-TRFICS were compared, among which Eu-TRFICS-(1) was the best detection choice. Antibody usage was reduced by 25% and sensitivity was increased by 3 times. Its detection range was 1-800 ng/mL, the limit of detection (LOD) was 0.12 ng/mL with the visible LOD (vLOD) of 5 ng/mL.

Ultrasensitive lateral flow biosensor based on PtAu@CNTs nanocomposite catalytic chromogenic signal amplification strategy for the detection of nucleic acid

A rapid and ultrasensitive lateral flow biosensor was developed, which based on gold and platinum nanoparticles-decorated carbon nanotubes (PtAu@CNTs) nanocomposite catalytic chromogenic signal amplification strategy for the detection of nucleic acid. Independent platinum and gold nanoparticles modified functional carbon nanotubes (PtAu@CNTs) were prepared by in-situ reduction. Sandwich-type hybridization reaction occurred between PtAu@CNTs-labeled DNA probe, target DNA and Biotin-modified DNA probes, which was captured on test zone of the strip. Accumulation of PtAu@CNTs nano-labels formed a characteristic colored band. After systematic optimization and catalytic chromogen, the naked eye detection limit of PtAu@CNTs-LFA was about 2 pM, and the theoretical detection limit of target DNA is calculated to be 0.43 pM according to the standard curve. The results indicates a rapid, sensitive and specific methods for DNA detection in biological samples, showing great promise for biomedical diagnosis in some malignant diseases in clinical application.

Lateral Flow Immunoassay for Proteins

Protein biomarkers are useful for disease diagnosis. Identification thereof using in vitro diagnostics such as lateral flow immunoassays (LFIAs) has attracted considerable attention due to their low cost and ease of use especially in the point of care setting. Current challenges, however, do remain with respect to material selection for each component in the device and the synergistic integration of these components to display detectable signals. This review explores the principle of LFIA for protein biomarkers, device components including biomaterials and labeling methods. Medical applications and commercial status are examined as well. This review highlights critical methodologies in the development of new LFIAs and their role in advancing healthcare worldwide.

Specific lateral flow detection of isothermal nucleic acid amplicons for accurate point-of-care testing

For point-of-care testing (POCT), coupling isothermal nucleic acid amplification schemes (e.g., recombinase polymerase amplification, RPA) with lateral flow assay (LFA) readout is an ideal platform, since such integration offers both high sensitivity and deployability. However, isothermal schemes typically suffers from non-specific amplification, which is difficult to be differentiated by LFA and thus results in false-positives. Here, we proposed an accurate POCT platform by specific recognition of target amplicons with peptide nucleic acid (PNA, assisted by T7 Exonuclease), which could be directly plugged into the existing RPA kits and commercial LFA test strips. With SARS-CoV-2 as the model, the proposed method (RPA-TeaPNA-LFA) efficiently eliminated the false-positives, exhibiting a lowest detection concentration of 6.7 copies/μL of RNA and 90 copies/μL of virus. Using dual-gene (orf1ab and N genes of SARS-CoV-2) as the targets, RPA-TeaPNA-LFA offered a high specificity (100%) and sensitivity (RT-PCR Ct < 31, 100%; Ct < 40, 71.4%), and is valuable for on-site screening or self-testing during isolation. In addition, the dual test lines in the test strips were successfully explored for simultaneous detection of SARS-CoV-2 and H1N1, showing great potential in response to future pathogen-based pandemics.

Enhancing catalytic activity through the construction of praseodymium tungstate decorated on hierarchical three-dimensional porous biocarbon for determination of furazolidone in aquatic samples

Boosting catalytic performance as a vital role for an electrochemical sensor for monitoring various hazardous nitro drugs. Herein, an inexpensive, facile, and eco-friendly construction of praseodymium tungstate decorated on three dimensional porous biocarbon (PrW/3D-PBC) for electrochemical determination of carcinogenic residue furazolidone (FZ). The nanostructured PrW nanoparticles were prepared by solvent evaporation from peroxo-tungstic acid and 3D-PBC was prepared from biomass precursor under the carbonization method. Furthermore, the composite of PrW decorated on 3D-PBC was prepared by an ultrasonic-assisted wet chemical approach. Besides, the composite characterization of crystalline, functional group, degree of carbonization, chemical states, and morphology were utilized by theXRD, FTIR, RAMAN, XPS, and FESEM analysis. These 3D porous carbon decorated PrW nanoparticles facilitate the electrochemical anchoring sites, surface area, and ease of diffusion layers towards the detection of hazardous nitro pollutant FZ by using CV analysis. The low LOD and high sensitivity were achieved by FZ determination through using LSV and DPV techniques. The practical capability of the PrW/3D-PBC/GCE sensor was determined by using aquatic samples to achieve a good recovery result. These results instigate that the PrW/3D-PBC will be an efficient electrocatalytic material for FZ sensor in environmental aquatic samples.

The Road to Unconventional Detections: Paper-Based Microfluidic Chips

Conventional detectors are mostly made up of complicated structures that are hard to use. A paper-based microfluidic chip, however, combines the advantages of being small, efficient, easy to process, and environmentally friendly. The paper-based microfluidic chips for biomedical applications focus on efficiency, accuracy, integration, and innovation. Therefore, continuous progress is observed in the transition from single-channel detection to multi-channel detection and in the shift from qualitative detection to quantitative detection. These developments improved the efficiency and accuracy of single-cell substance detection. Paper-based microfluidic chips can provide insight into a variety of fields, including biomedicine and other related fields. This review looks at how paper-based microfluidic chips are prepared, analyzed, and used to help with both biomedical development and functional integration, ideally at the same time.

Colorimetric nano-beacon and magnetic separation-based rapid and visual assay for gram-negative bacteria

Food-borne diseases caused by pathogenic bacteria are one of the serious factors affecting human health. However, the most commonly used detection methods for pathogenic bacteria not only require expensive instruments, but also take a long time due to the complicated and cumbersome detection process. Therefore, the development of a fast, simple, and low-cost detection method for pathogenic bacteria is crucial for food safety and human health. In this work, based on the high binding ability of antimicrobial peptide (AMP) and polymyxin B (PMB) to bacteria, combined with magnetic separation technology, a new enzyme-free colorimetric strategy was constructed to achieve visual detection of Gram-negative bacteria in complex samples. The sensor system was divided into the following two parts: a colorimetric signal amplification nanoprobe, which was modified with AMP to enable effective binding of the colorimetric probe to the surface of bacteria, and a PMB-modified magnetic nanobead (MNB), which was used as the capture and enrichment unit of Gram-negative bacteria, as a result of which PMB could effectively distinguish Gram-negative bacteria from Gram-positive bacteria. Under optimized conditions, the detection limit of the method for Gram-negative bacteria (e.g. E. coli (G^-)) was as low as 10 CFU/mL, and it was successfully applied to complex real samples. In addition, the developed colorimetric sensor offered advantages, such as fast response, less time consumption, high sensitivity, and low cost. It can be expected to become a new diagnostic tool for on-site detection of pathogenic bacteria in remote areas.

Rapid and sensitive detection of tenuazonic acid in agricultural by-products based on gold nano-flower lateral flow

Tenuazonic acid (TA) is a highly toxic mycotoxin mainly generated by the fungi of Alternaria genus and widely contaminates agricultural by-products. Given the threat of TA to food-security, it is very important to develop rapid and sensitive detection methods for TA monitoring. In this study, gold nano-particles (AuNP) with average diameter near 17.25 nm were prepared, and the developed AuNP-based strip has an assay time of 15 min with visual limit of detection (LOD) of 12.5 ng/ml and threshold of 100 ng/ml. To further improve sensitivity, multi-branched gold nano-flowers (AuNF) with average diameter near 50 nm were prepared and characterized by UV-VIS and TEM, and the established AuNF-based strip has visual LOD of 0.78 ng/ml and threshold of 50 ng/ml within 15 min. Both assays were applied to determine TA in apple juice and tomato ketchup, and the results were consistent with that of UHPLC-MS/MS. Thus, these assays could be applied for rapid determination of trace TA in real samples.

Immunosensor of Nitrofuran Antibiotics and Their Metabolites in Animal-Derived Foods: A Review

Nitrofuran antibiotics have been widely used in the prevention and treatment of animal diseases due to the bactericidal effect. However, the residual and accumulation of their metabolites in vivo can pose serious health hazards to both humans and animals. Although their usage in feeding and process of food-derived animals have been banned in many countries, their metabolic residues are still frequently detected in materials and products of animal-derived food. Many sensitive and effective detection methods have been developed to deal with the problem. In this work, we summarized various immunological methods for the detection of four nitrofuran metabolites based on different types of detection principles and signal molecules. Furthermore, the development trend of detection technology in animal-derived food is prospected.

Expanded detection range of lateral flow immunoassay endowed with a third-stage amplifier indirect probe

Here, a third-stage amplifier indirect probe (TsAIP) based lateral flow immunoassay (LFIA) was proposed to detect furazolidone (FZD) with Prussian blue nanoparticles (PBNPs) as carrier to label the goat anti-mouse antibody-horseradish peroxidase conjugation [GAMA(HRP)]. In this strategy, owing to the fact that one monoclonal antibody (mAb) can combine several GAMA molecules simultaneously, the indirect probe can generate primary signal amplification, then realize second-stage amplification attributing to PBNPs, and finally achieve third-stage amplification because of the conjugated HRP. The TsAIP-based LFIA shows improved performance for FZD metabolite derivative with a detection limit of 1 ng mL^-1. The detection range is expanded about 2-fold compared with the original outcome. Besides, the proposed sensor could be successfully applied in food samples. This method provides a platform for broadening the detection range and application of PBNPs based LFIAs.

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.

Freestanding Fe3O4/Ti3C2TxMXene/polyurethane composite film with efficient electromagnetic shielding and ultra-stretchable performance

Electromagnetic pollution seriously affects the human reproductive system, cardiovascular system, people's visual system, and so on. A novel versatile stretchable and biocompatible electromagnetic interference (EMI) shielding film has been developed, which could effectively attenuate electromagnetic radiation. The EMI shielding film was fabricated with a convenient solution casting and steam annealing with 2D MXene, iron oxide nanoparticles, and soluble polyurethane. The EMI shielding effectiveness is about 30.63 dB at 8.2 GHz, based on its discretized interfacial scattering and high energy conversion efficiency. Meanwhile, the excellent tensile elongation is 30.5%, because of the sliding migration and gradient structure of the nanomaterials doped in a polymer matrix. In addition, the film also demonstrated wonderful biocompatibility and did not cause erythema and discomfort even after being attached to the arm skin over 12 h, which shows the great potential for attenuation of electromagnetic irradiation and protection of human health.

A nanomaterial-free and thionine labeling-based lateral flow immunoassay for rapid and visual detection of the transgenic CP4-EPSPS protein

Nanomaterial-based lateral flow immunoassays (LFIAs) have been widely used for the on-site detection of genetically modified components. However, the practical applications are often limited by the complex matrix, such as in red samples. In this study, a thionine (Thi) labeling-based LFIA was developed for the first time to detect CP4-EPSPS protein. The optimal labeling concentration of Thi was 0.5 mg/mL, and the antibody could be rapidly coupled to Thi in 10 min. The visual limit of detection (vLOD) levels for transgenic soybean, sugar beet, and cotton containing the CP4-EPSPS protein reached 0.05%, 0.1%, and 0.1%, respectively, and had no interference from other proteins. After storage at 4 °C for three months, the LFIA sensitivity remained unchanged and showed good stability. This method could be used to screen and detect a variety of transgenic crops containing the CP4-EPSPS protein, and the results were consistent with the current standard assay. This study pioneered the development of an immunochromatographic method using Thi as a marker and applied it to the detection of the CP4-EPSPS protein in herbicide-tolerant transgenic crops. This provides a new method for the rapid immunoassay of Thi as a dye and has good prospects for practical application.

Metal-Organic Framework-Based Composites for the Detection and Monitoring of Pharmaceutical Compounds in Biological and Environmental Matrices

The production of synthetic drugs is considered a huge milestone in the healthcare sector, transforming the overall health, aging, and lifestyle of the general population. Due to the surge in production and consumption, pharmaceutical drugs have emerged as potential environmental pollutants that are toxic with low biodegradability. Traditional chromatographic techniques in practice are time-consuming and expensive, despite good precision. Alternatively, electroanalytical techniques are recently identified to be selective, rapid, sensitive, and easier for drug detection. Metal-organic frameworks (MOFs) are known for their intrinsic porous nature, high surface area, and diversity in structural design that provides credible drug-sensing capacities. Long-term reusability and maintaining chemo-structural integrity are major challenges that are countered by ligand-metal combinations, optimization of synthetic conditions, functionalization, and direct MOFs growth over the electrode surface. Moreover, chemical instability and lower conductivities limited the mass commercialization of MOF-based materials in the fields of biosensing, imaging, drug release, therapeutics, and clinical diagnostics. This review is dedicated to analyzing the various combinations of MOFs used for electrochemical detection of pharmaceutical drugs, comprising antibiotics, analgesics, anticancer, antituberculosis, and veterinary drugs. Furthermore, the relationship between the composition, morphology and structural properties of MOFs with their detection capabilities for each drug species is elucidated.

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 SERS detection of residual nitrofurantoin and 1-amino-hydantoin in aquatic products and feeds

Nitrofurantoin (NFT), a typical highly effective nitrofuran antibiotic drug, has been prohibited but still widely found in animal food products. It can be metabolized in animals to form 1-amino-hydantoin (AHD) that can then form stable and toxic metabolite-protein adducts. Hence, the detection of NFT and AHD in aquatic products and feeds is very important. However, there are limited reports concerning NFT detection and none about AHD by using surface-enhanced Raman spectroscopy (SERS) method. Herein, potassium bromide (KBr) decorated silver (Ag) nanoparticles (Ag-BrNPs)-based SERS approach was proposed for NFT and AHD detection. The limit of detection (LOD) for NFT was 1 μg/L. The detection of NFT residues in sea cucumber and fish feeds was also realized with the LOD of 1 and 50 ng/g, respectively. More importantly, the sensing of AHD was easily realized with the SERS approach for the first time. After the derivatization with 2-nitrobenzaldehyde (2-NBA), Ag-BrNPs were also successfully utilized for AHD detection in sea cucumber with the LOD of 5 ng/g.

MOF-derived hollow NiCo2O4/C composite for simultaneous electrochemical determination of furazolidone and chloramphenicol in milk and honey

Herein, bimetallic Co/Ni-MOF derived hollow NiCo₂O₄@C composite modified glassy carbon electrode (NiCo₂O₄@C/GCE) is constructed and applied to simultaneously detect furazolidone (FZD) and chloramphenicol (CAP) for the first time. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen adsorption-desorption and X-ray photoelectron spectroscopy confirm that NiCo₂O₄@C has hollow and mesoporous structure, abundant carbon matrixes, sufficient oxygen defects and mixed-valence metallic elements. These advantages make NiCo₂O₄@C/GCE show distinguished electrocatalytic performance toward the simultaneous determination of FZD and CAP. The NiCo₂O₄@C/GCE shows wide linear ranges of 0.5-240 µM for FZD and 0.5-320 µM for CAP, low limit of detection of 8.47 nM for FZD and 35 nM for CAP. The mechanism studies show that reductions of FZD and CAP on NiCo₂O₄@C/GCE are both four-electron and four-proton processes. Moreover, the sensor obtains desirable recoveries for the simultaneous determination of FZD (95.85%-103.9%) and CAP (95.72%-104.4%) in milk and honey by standard addition method.

A high sensitive platinum-modified colloidal gold immunoassay for tenuazonic acid detection based on monoclonal IgG

Due to the threat of tenuazonic acid (TA) to public health, it is urgent to establish rapidly effective and sensitive assay methods for TA. In this study, a TA-specific IgG monoclonal antibody (McAb) with high affinity (Kaff was 1.72 × 10¹⁰ L/mol) was screened, and the developed icELISA for TA detection has IC₅₀ of 2.50 ng/mL and LOD of 0.17 ng/mL. Platinum-modified gold nanoparticle (Au@PtNP) was optimized as Au@Pt_0.4NP, and the resulted Au@Pt_0.4NP-McAb probe was designed to catalyze precipitation-type tetramethylbenzidine for visual detection of trace TA with visual LOD of 0.39 ng/mL. The sensitivity of this established Au@Pt_0.4NP-McAb strip was highly increased when compared with the existing colloidal gold strip. The developed strip was used to detect trace TA in apple juice and tomato ketchup which were consistent with the results from UHPLC-MS/MS. Therefore, this developed strip could be used for rapid detection of trace TA in real samples.

Lateral flow immunoassay for furazolidone point-of-care testing: Cater to the call of saving time, labor, and cost by coomassie brilliant blue labeling

Furazolidone (FZD) and its metabolite called 3-amino-2-oxazolidinone (AOZ) would induce carcinogenic and mutagenic effects to human. In this work, to develop a novel, stable, and simple point of care testing (POCT) with a potential to social applied for FZD detection, we utilized the aspect of protein staining of coomassie brilliant blue (CBB) to exploit a new CBB-LFIA strategy free of NPs. Only one mixing step is needed during the probe manufacturing process, which requires just 2 h and is a great time saving strategy compared with other methods (requiring 4-33 h for probe preparation). Besides, the cost of CBB-LFIA is 300 times lesser than other LFIA with respect to obtaining the label. The developed CBB-LFIA was successfully applied to detect AOZ with a detection limit of 2 ng mL^-1, without any influence from other potential interfering compounds. The proposed CBB-LFIA exhibited prominent practical application, and possesses considerable utilization potential in the related field.

Facile synthesis of Co(ii)-doped cobalt oxide nanostructures: their application in the sensitive determination of the prophylactic drug furazolidone

Electrochemical detection of prophylactic drug furazolidone through Co–Co₂O₄ modified GCE.

A Comparative Study of Approaches to Improve the Sensitivity of Lateral Flow Immunoassay of the Antibiotic Lincomycin

This study provides a comparative assessment of the various nanodispersed markers and related detection techniques used in the immunochromatographic detection of an antibiotic lincomycin (LIN). Improving the sensitivity of the competitive lateral flow immunoassay is important, given the increasing demands for the monitoring of chemical contaminants in food. Gold nanoparticles (AuNPs) and CdSe/ZnS quantum dots (QDs) were used for the development and comparison of three approaches for the lateral flow immunoassay (LFIA) of LIN, namely, colorimetric, fluorescence, and surface-enhanced Raman spectroscopy (SERS)-based LFIAs. It was demonstrated that, for colorimetric and fluorescence analysis, the detection limits were comparable at 0.4 and 0.2 ng/mL, respectively. A SERS-based method allowed achieving the gain of five orders of magnitude in the assay sensitivity (1.4 fg/mL) compared to conventional LFIAs. Therefore, an integration of a SERS reporter into the LFIA is a promising tool for extremely sensitive quantitative detection of target analytes. However, implementation of this time-consuming technique requires expensive equipment and skilled personnel. In contrast, conventional AuNP- and QD-based LFIAs can provide simple, rapid, and inexpensive point-of-care testing for practical use.

Rapid and Quantitative Detection of Aflatoxin B1 in Grain by Portable Raman Spectrometer

Many foodstuffs are extremely susceptible to contamination with aflatoxins, in which aflatoxin B₁ is highly toxic and carcinogenic. Therefore, it is crucial to develop a rapid and effective analytical method for detecting and monitoring aflatoxin B₁ in food. Herein, a surface-enhanced Raman spectroscopic (SERS) method combined with QuEChERS (quick, easy, cheap-effective, rugged, safe) sample pretreatment technique was used to detect aflatoxin B₁. Sample preparation was optimized into a one-step extraction method using an Au nanoparticle-based solution (Au sol) as the SERS detection substrate. An affordable portable Raman spectrometer was then used for rapid, label-free, quantitative detection of aflatoxin B₁ levels in foodstuffs. This method showed a good linear log relationship between the Raman signal intensity of aflatoxin B₁ in the 1-1000 µg L^-1 concentration range with a limit of detection of 0.85 µg kg^-1 and a correlation coefficient of 0.9836. Rapid aflatoxin B₁ detection times of ∼10 min for wheat, corn, and protein feed powder samples were also achieved. This method has high sensitivity, strong specificity, excellent stability, is simple to use, economical, and is suitable for on-site detection, with good prospects for practical application in the field of food safety.

A Rapid Immunochromatographic Method Based on a Secondary Antibody-Labelled Magnetic Nanoprobe for the Detection of Hepatitis B preS2 Surface Antigen

Hepatitis B is a globally prevalent viral infectious disease caused by the hepatitis B virus (HBV). In this study, an immunochromatographic assay (ICA) for the rapid detection of hepatitis B preS2 antigen (preS2Ag) was established. The magnetic nanoparticles (MNPs) indirectly labelled with goat anti-mouse (GAM) secondary antibody were applied as a nanoprobe for free preS2 antibody (preS2Ab) capturing and signal amplification. By employing sample pre-incubation processing as well, preS2Ag-preS2Ab was sufficiently caught by the GAM-MNPs probe in 5 min. A qualitative sensitivity of 625 ng/mL was obtained by naked-eye observation within 15-20 min. A standard curve (0-5000 ng/mL) was established, with a quantitative limit of detection (LOD) of 3.6 ng/mL, based on the stability and penetrability of the magnetic signal characteristics. The proposed method for preS2Ag was rapid (~25 min, cf. ELISA ~4 h) and had a good accuracy, which was verified using an ELISA kit (relative error < 15%). Large equipment and skilled technicians were not required. The sensitivity and specificity of the developed GAM-MNPs-ICA method were 93.3% and 90% in clinical serum samples (n = 25), respectively. A good detection consistency (84%) was observed between the developed ICA method and 2 types of commercial ELISA kits, indicating that the GAM-MNPs-ICA has a potential application in large-scale screening for and point-of-care diagnosis of hepatitis B or other infectious diseases.

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.

Advances in immunosensor technology

In recent years, advances in immunosensor device fabrication have significantly expanded the use of this technology in a broad range of applications including clinical diagnosis, food analysis, quality control, environmental studies and industrial monitoring. The most important aspect in fabrication is to obtain a design that provides a low detection limit. The utilization of nanomaterials as a label, catalyst and biosensing transducer is, perhaps, the most popular approach in ultrasensitive devices. This chapter reviews recent advances in immunosensor fabrication and summarizes the most recent studies. Strategies employed to significantly improve sensitivity and specificity of immunosensor technology and the advantages and limitations thereof are explored.

Magnetic Lateral Flow Immunoassays

A new generation of magnetic lateral flow immunoassays is emerging as powerful tool for diagnostics. They rely on the use of magnetic nanoparticles (MNP) as detecting label, replacing conventional gold or latex beads. MNPs can be sensed and quantified by means of external devices, allowing the development of immunochromatographic tests with a quantitative capability. Moreover, they have an added advantage because they can be used for immunomagnetic separation (IMS), with improvements in selectivity and sensitivity. In this paper, we have reviewed the current knowledge on magnetic-lateral flow immunoassay (LFIA), coupled with both research and commercially available instruments. The work in the literature has been classified in two categories: optical and magnetic sensing. We have analysed the type of magnetic nanoparticles used in each case, their size, coating, crystal structure and the functional groups for their conjugation with biomolecules. We have also taken into account the analytical characteristics and the type of transduction. Magnetic LFIA have been used for the determination of biomarkers, pathogens, toxins, allergens and drugs. Nanocomposites have been developed as alternative to MNP with the purpose of sensitivity enhancement. Moreover, IMS in combination with other detection principles could also improve sensitivity and limit of detection. The critical analysis in this review could have an impact for the future development of magnetic LFIA in fields requiring both rapid separation and quantification.

Functional nanomaterials based immunological detection of aflatoxin B1: a review

Aflatoxin B1 (AFB1) is highly carcinogenic, mutagenic and teratogenic. Accordingly, sensitive, rapid and cost-effective techniques for detection of AFB1 is in urgent demand for food safety and the health of consumers. In this review, we report the current state of immunoassay formats and development, mainly based on nanomaterials for determination of AFB1. Following an introduction of the field, the microplate-, membrane- and microelectrode-based immunoassays are described. The relevant mechanisms, sensitivities, superiorities and deficiencies of each format are discussed. Finally, perspectives on the future development of nanomaterials-based immunoassays for AFB1 are provided.

Polydopamine nanospheres as high-affinity signal tag towards lateral flow immunoassay for sensitive furazolidone detection

Currently, the low sensitivity and poor binding stability of detection probe prepared via electrostatic adsorption have become the dilemmas of colloidal gold-based lateral flow immunoassays (Au-LFIAs). In this connection, polydopamine nanospheres (PDA NPs) with an eminent covalent connectivity property were introduced as a promising substitute to improve the stability of probe and sensitivity of LFIA. Whereafter, the PDA NPs-based LFIA was applied for the monitoring of furazolidone (FZD) in food samples because of the potential carcinogenic/mutagenic effects to human of its metabolite (3-amino-2-oxazolidinone, AOZ). Compared with electrostatic adsorption, the binding stability of PDA NPs-based probes was superior. And, as expected, the PDA NPs-based LFIA biosensor exhibited higher sensitivity than that of the Au-LFIA with a detection limit of 3.5 ng mL^-1 for AOZ by naked-eye readout. Based on the significant enhanced binding stability and sensitivity, the PDA NPs-based LFIA is of certain spreading value for detecting other analytes.