Visual Detection Limit Research Articles

Lateral Flow Immunoassay for the Rapid Detection of Thiamethoxam in Tea Based on a SERS Tag Constructed by Phenolic-Mediated Coating Engineering.

Sensitive and accurate detection of thiamethoxam in tea is significant to ensuring consumer health. In this study, surface-enhanced Raman scattering (SERS) tags were prepared by using a polyphenol-mediated coating engineering strategy. This approach involved the self-assembly of tannic acid (TA) and self-polymerization of benzene-1,4-dithiol (BDT) on the surface of gold nanoparticles, resulting in the formation of Au@pBDT-TA. The SERS tags possess high Raman signals and antibody adsorption properties, avoiding the complex decoration or label steps of SERS reporters. We discovered that Au@pBDT-TA, composed of gold nanoparticles at 40 nm and a pBDT-TA thickness of 10 nm, was optimal for the development of the SERS lateral flow immunoassay (LFIA). In comparison to the gold nanoparticle-based LFIA, the SERS-LFIA demonstrated 4-fold and 720-fold enhancements in visual and quantitative limits of detection in buffer solution. The SERS-LFIA demonstrated quantitative limits of detection of 0.06 and 0.1 ng/g for black and green tea, respectively, with a broader linear range spanning over 2 orders of magnitude and a short detection time of 20 min. The proposed SERS-LFIA not only offers a sensitive and reliable method for monitoring thiamethoxam in tea but also possesses a versatile potential that can be easily adapted for the trace detection of various other targets.

Nanobody-Induced Aggregation of Gold Nanoparticles: A Mix-and-Read Strategy for the Rapid Detection of Cronobacter sakazakii.

Protein-nanoparticle interactions play a crucial role in both biomedical applications and the biosafety assessment of nanomaterials. Here, we found that nanobodies can induce citrate-capped gold nanoparticles (AuNPs) to aggregate into large clusters. Subsequently, we explored the mechanism behind this aggregation and proposed the "gold nucleation mechanism" to explain this phenomenon. Building on this observation, we developed a one-step label-free colorimetric method based on nanobody-induced AuNP aggregation. When nanobodies bind to target bacteria, spatial hindrance occurs, preventing further AuNPs aggregation. This alteration in surface plasmon resonance properties results in visible color changes. As an example, we present a simple and sensitive "mix-and-read" chromogenic immunosensor for Cronobacter sakazakii (C. sakazakii). The experiment can be completed within 20 min, with a visual detection limit of 103 CFU/mL and a quantitative detection limit of 136 CFU/mL. Importantly, our method exhibits no cross-reactivity with other bacterial species. This strategy harnesses the excellent properties of nanobodies and the optical characteristics of AuNPs for direct and rapid detection of foodborne pathogen.

On-site detection of OTA and AFB1 based on branched hybridization chain reaction coupled with lateral flow assay

Mycotoxins are widely prevalent in various agricultural commodities, whose excessive consumption can pose significant risks to human health. In this study, we developed a facile mycotoxin detection platform based on branched hybridization chain reaction coupled with lateral flow assay. Ochratoxin A/Aflatoxin B1 bind to aptamers triggering the release of initiators, which leads to bHCR amplification and forms three-dimensional dendritic DNA nanostructures. Using the functionalized quantum dots as a fluorescent label, by leveraging smartphones and handheld ultraviolet lamps, the qualitative and quantitative detection of OTA and AFB1 can be achieved with a significantly enhanced sensitivity level, surpassing that of commercial test strips by 2–3 orders of magnitude. The visual detection limits for OTA and AFB1 were 30 pg/mL and 4 pg/mL, respectively. This approach eliminates the necessity for enzyme catalysis or the preparation and purification of antibodies and/or hapten, thereby reducing testing expenses and streamlining operational procedures. Moreover, substituting aptamer and nucleic acid sequences can effectively expand the scope of detection targets. Consequently, the as-proposed strategy exhibits great potential as a versatile technique, suitable for various analytical scenarios due to its sensitivity, accuracy, simplicity, and portability.

Flower-Shaped PCR Scaffold-Based Lateral Flow Bioassay for Bacillus cereus Endospores Detection

Bacillus cereus, a foodborne pathogen, produces resilient endospores that are challenging to detect with conventional methods. This study presents a novel Flower-Shaped PCR Scaffold-based Lateral Flow Biosensor (FSPCRS-LFB), which employs an aptamer-integrated PCR scaffold as capture probes, replacing the traditional streptavidin-biotin (SA-Bio) approach. The FSPCRS-LFB demonstrates high sensitivity and cost-efficiency in detecting B. cereus endospores, with a limit of detection (LOD) of 4.57 endospores/mL a visual LOD of 102 endospores/mL, and a LOD of 6.78 CFU/mL for endospore-cell mixtures. In chicken and tea samples, the platform achieved LODs of 74.5 and 52.8 endospores/mL, respectively, with recovery rates of 82.19% to 97.88%. Compared to existing methods, the FSPCRS-LFB offers a 3.7-fold increase in sensitivity while reducing costs by 26% over the SA-Bio strategy and 87.5% over rolling circle amplification (RCA). This biosensor provides a rapid, sensitive and cost-effective solution for point-of-care testing (POCT) of B. cereus endospores, expanding detection capabilities and offering novel approaches for pathogen detection.

Portable paper-based multicolor sensor for sensitive on-site detection of organophosphorus pesticides using a high-efficiency Au+-induced gold nanobipyramids aspect ratio regulation strategy

On-site visual detection of organophosphorus pesticides (OPs) is crucial for safeguarding environmental and food safety. This study presents a robust, sensitive, and portable paper-based multicolor sensor (PMS) for the on-site detection of OPs. The PMS involves a novel Au+-induced gold nanobipyramids (AuNBPs) morphology transformation reaction within a paper-based analytical device (PAD) coupled with a bienzymatic hydrolysis system. The Au+-induced reaction sensitively regulates the aspect ratio of AuNBPs through Au+ disproportionation, which decreases the length of AuNBPs and simultaneously increases the width, accompanied by distinct multicolor changes. Upon performing in the PAD incorporating easily-prepared AuNBPs-deposited nylon membranes, a metal heater, and an oscillator, the Au+-induced reaction exhibits excellent reaction sensitivity, efficiency, reproducibility, AuNBPs stability, and color uniformity. In the bienzymatic hydrolysis system, acetylcholinesterase (AChE) and choline oxidase hydrolyze acetylcholine to product H2O2, which consumes tris(2-carboxyethyl)phosphine hydrochloride (TCEP), maintaining free Au+ for the disproportionation in the Au+-induced system, while the presence of OPs inhibits AChE activity, preserving TCEP to chelate Au+ and hindering the disproportionation. Under optimized conditions, the PMS exhibited eight dichlorvos concentration-corresponding color changes with a visual detection limit of 30 μg/L and a spectrometry detection limit of 8.1 μg/L. It achieved recoveries of 85.4–101.9 % in river water, drinking water, rice, and Chinese cabbage samples with relative standard deviations (n = 5) < 6 %. Thus, this study offers a portable, sensitive, reliable, and practical on-site detection method for OPs. Additionally, the proposed Au+-induced AuNBPs morphology transformation system within the PAD offers promising alternative strategies for developing other AuNBPs-based colorimetric sensors.

“Blue-red-purple” multicolored lateral flow immunoassay for simultaneous detection of GM crops utilizing RPA and CRISPR/Cas12a

Advanced multiplexed testing techniques should be designed and developed to ensure an accurate and reliable evaluation for unknown samples. In this study, an efficient platform coupled with the “Blue-Red-Purple” strategy based on recombinant polymerase amplification (RPA), CRISPR/Cas12a and lateral flow strip was established, which could realize the dual-target detection of CP4-EPSPS and Cry1Ab/Ac in genetically modified crops. The lateral flow immunoassay was developed using different colored microspheres to label the antibodies to realize the visualization of results and avoid cross-reactions. The proposed method exhibits high specificity, sensitivity and stability. The visual detection limits of standard plasmids and real samples reached 10 copies/μL and 0.5 %, respectively, which could be stored at 4 °C for 12 months with high detection ability. Moreover, the entire detection process could be completed within 50 min without any complex instruments or professional operators. These findings indicated that a sensitive, specific, rapid and accurate method was established for on-site detection of GM crops.

Target-inhibited MCOF-Apt-AuNPs self-assembly for multicolor colorimetric detection of Salmonella Typhimurium

Pathogens detection is a crucial measure in the prevention of foodborne diseases. This study developed a novel multicolor colorimetric assay to visually detect Salmonella Typhimurium (S. Typhimurium), by utilizing the etching process of gold nanorods (AuNRs) with TMB2+. The strategy involved the construction of nanozyme by assembling magnetic covalent organic framework (MCOF) with aptamer-conjugated AuNPs (Apt-AuNPs), exhibiting remarkable peroxidase-like activity to catalyze the oxidation of TMB/H2O2 and inducing the etching of AuNRs. The presence of S. Typhimurium could inhibit this process, resulting in the generation of vivid colors. The multicolor colorimetric assay could specifically determine S. Typhimurium from 102 to 108 CFU mL−1 in 60 min with visual detection limit of 102 CFU mL−1, and instrumental detection limit of 2.3 CFU mL−1. Moreover, detecting S. Typhimurium in chicken, milk, pork and lettuce samples has shown promise in practical applications.

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.

Low-cost signal enhanced colorimetric and SERS dual-mode paper sensor for rapid and ultrasensitive screening of mercury ions in tea

Mercury ions (Hg2+) are highly toxic heavy metals that are commonly found in natural environments. Owning to their non-biodegradability and accumulation in the food chain, the precise detection of trace amounts of Hg2+ is essential for preventing chronic accumulation and ensuring food safety. In this study, we present a dual-mode paper sensor for simultaneous colorimetric and Surface-Enhanced Raman Spectroscopy (SERS) detection of Hg2+ in tea, achieving ultrasensitive, rapid, and on-site screening. 4-Mercaptopyridine (4-MPY) was effectively chemisorbed onto the gold nanoparticles (AuNPs), acting as a signal probe for colorimetric methods. Moreover, it can produce plasmonic hot spots for SERS by interacting with the pyridine ring. To enhance the signal intensity of both colorimetry and SERS, a silver shell is in-situ grown on the surface of AuNPs captured on the paper sensor by reduction of Ag+, achieving signal amplification. The visual limit of detection (LOD) for the colorimetric biosensor is 2.5 pM, while the LOD of SERS is 0.48 pM with this dual-mode paper sensor. The sensitivity of both the colorimetric method and SERS was improved by approximately 200 and 500 times, respectively, with the designed signal amplification strategy. The system allows for multiple parallel screening of the same sample, ensuring accurate results without any false-positive or false-negative. This study provides a valuable platform for the accurate detection of various other heavy metal ions and provides effective strategies for improving the performance of colorimetric methods.

Modulating of d-band center in Cu single-atom anchored Co3O4 nanozyme for sensitive immunochromatographic test strip

Immunochromatographic test strip (ITS) has been widely employed for point-of-care diagnoses. However, how to significantly enhance the analytical sensitivity of device-free ITS remains a challenge. Here, we synthesized a Cu single-atom anchored Co3O4 (CuSA/Co3O4) nanozyme that possesses ultrahigh peroxidase-mimicking catalytic activity owing to d-band center upshift mediated by Cu single-atom. Molecular orbital analysis demonstrated that d orbitals in CuSA/Co3O4 have stronger orbital hybridization affinity than Co3O4 to H2O2′s π* orbitals. This reinforces hydroxyl radical (OH) production and provides a stronger catalytic colorimetric signal, which is beneficial for improving the sensitivity of ITS. Moreover, we applied the CuSA/Co3O4 to ITS as a signal reporter for monitoring Xanthomonas oryzae pv. oryzicola (Xoc), the pathogen of rice bacterial leaf streak. The visual limit of detection (LOD) of the developed CuSA/Co3O4-based ITS was as low as 6.4 × 102 CFU mL−1, which is 25-fold more sensitive than the traditional Au nanoparticles (AuNP)-based ITS. Taken together, this work demonstrates the great potential of CuSA/Co3O4 nanocomposite as a signal reporter to improve the sensitivity of ITS for on-site Xoc detection.

Lateral flow immunoassay device to detect staphylococcal enterotoxin B (SEB) in durian candy.

Staphylococcal enterotoxin B (SEB), a potent enterotoxin produced by Staphylococcus aureus, has been implicated in incidences of Staphylococcal food poisoning in the Philippines. The use of lateral flow immunoassay devices to detect this toxin in solid food samples, like durian candy, at the point of sampling is constrained by the requirement for sample purification (e.g. centrifugation). This problem is also true with the other applications of LFIA devices on food samples. To overcome this challenge, a lateral flow immunoassay (LFIA) device capable of detecting SEB in unpurified durian candy sample was developed in this study. A modified LFIA device was assembled with three layers of glass fiber pads functioning as sample pads instead of a conventional cellulose fiber pad. Unlike with the cellulose fiber pad, the glass fiber sample pads acted as filter and allowed the flow of a 1:5 dilution of durian candy. The LFIA device applied to spiked 1:5 diluted durian candy samples achieved a visual limit of detection of 5ng/mL for SEB, which is twofold lower than reported for previous LFIA devices designed to detect SEB in food samples.

Establishment of a Real-Time Fluorescence Isothermal Recombinase-Aided Amplification Method for the Detection of H9 Avian Influenza Virus.

The H9 subtype of avian influenza virus (AIV) has been characterized by its rapid spread, wide range of prevalence, and continuous evolution in recent years, leading to an increasing ability for cross-species transmission. This not only severely impacts the economic benefits of the aquaculture industry, but also poses a significant threat to human health. Therefore, developing a rapid and sensitive detection method is crucial for the timely diagnosis and prevention of H9 AIVs. In this study, a real-time fluorescent reverse transcription recombinase-aided isothermal amplification (RT-RAA) technique targeting the hemagglutinin (HA) of H9 AIVs was established. This technique can be used for detection in just 30 min at a constant temperature of 42 °C, and it exhibits good specificity without cross-reactivity with other viruses. Sensitivity tests revealed that the detection limit of RT-RAA was 163 copies per reaction, and the visual detection limit was 1759 copies per reaction at a 95% confidence interval, both of which are capable of detecting low concentrations of standards. Furthermore, RT-RAA was applied to detect 155 clinical samples, and compared to real-time fluorescent quantitative PCR (RT-qPCR), RT-RAA demonstrated high accuracy, with a specificity of 100% and a kappa value of 0.96, indicating good correlation. Additionally, with the assistance of a portable blue imaging device, we can visually observe the amplification products, greatly facilitating rapid detection in resource-limited environments. The RT-RAA detection method developed in this study does not require expensive equipment or highly skilled staff, making it beneficial for the accurate and low-cost detection of H9 AIVs.

A colorimetric sensor based on multiple elements doped carbon dot nanozyme for rapid detection of 1-naphthol in human urine samples

The residual carbaryl in crops can cause serious damage to the human kidney and nervous system after entering the human body, which may be metabolized to 1-naphthol (1-NAP) and excreted through urine. 1-NAP is often used as the biomarker for carbaryl exposure, so the intake or leakage of carbaryl can be monitored by detecting the concentration of 1-NAP. Herein, Co, N, P ternary co-doped carbon dots (CoNP-CDs) derived from vitamin B12 were synthesized by a facile hydrothermal method. CoNP-CDs exhibited oxidase-like activity and excellent peroxidase-like activity, which was attributed to the Fenton-like reaction of Co2+/Co3+ and the presence of pyrrole N and P elements, which together provided multiple active sites for chromogenic substrates. Due to the dual enzyme-like activity of CoNP-CDs, hydroxyl radicals (OH) and superoxide radicals (O2−) were generated during the catalytic process, which could rapidly oxidize colorless 3,3′,5,5′-tetramethyl benzidine (TMB) to blue oxidation products (oxTMB). The α-carbon in 1-NAP can be attacked by OH, and the catalytic oxidation process of TMB can be inhibited by the consumption of OH, so that the blue color of the solution became lighter. Based on this principle, a smartphone-assisted colorimetric sensing platform was constructed for the detection of 1-NAP, and which resulted in a linear range of 1.07–37.3 μM and a visual detection limit of 0.68 μM. Moreover, the colorimetric sensing system showed satisfactory recoveries in the detection of human urine samples. The colorimetric sensing system owned the advantages of fast response, strong selectivity and simple operation, and provided a potential strategy for the on-site detection of 1-NAP.

Construction of “ant-like tentacle” structure for ultra-sensitive detection of low-concentration ammonia through colorimetric fluorescent dual-signal gas-sensitive cotton fabric

Detection and monitoring of ammonia (NH3) are crucial in various industries, including plant safety management, food freshness testing, and water pollution control. Nevertheless, creating portable, low-cost, highly sensitive, and easily regenerated ppm-level NH3 sensors poses a significant challenge. In this investigation, an innovative “ant-like tentacle” fabrication strategy was proposed, and a colorimetric fluorescent dual-signal gas-sensitive cotton fabric (PAH-fabric) for NH3 detection was successfully prepared by conventional dyeing using suitable molecular-level photoacid (PAH) sensitive units. The visual recognition lower detection limit of the ultra-low is 1.09 ppm-level. PAH-fabric is not only straightforward, convenient, and cost-effective to prepare, but it can also be efficiently regenerated and recycled multiple times (maintaining excellent gas-sensitive performance even after 100 cycles) by strategically leveraging volatile acid fumigation. Detailed molecular reaction mechanisms involved in the NH3 response and PAH-fabric regeneration are elucidated. PAH-fabric, available either as a portable kit or an alarm system, offers a promising approach for ultra-low NH3 detection. The demonstrated “ant-like tentacle” fabrication strategy introduces numerous possibilities for designing and developing sensors with adjustable response thresholds, particularly those requiring high sensitivity.

Label free immunochromatographic sensor based on TCBPE for the detection of Acidovorax citrulli in Cucurbitaceae plants

The presence of Acidovorax citrulli (Ac), the etiological agent responsible for bacterial fruit blotch (BFB), exerts a profound impact on the growth and development of cucurbit plants. Therefore, it is imperative to promptly detect Ac to effectively mitigate the widespread dissemination of this disease among cucurbit crops. The present study describes the development of a novel label-free immunochromatographic strip (ICTS) sensor for the detection of Ac in cucurbit samples. This was achieved by utilizing 4’,4’’’,4’’’’’,4’’’’’’’-(ethene-1,1,2,2-tetrayl) tetrabiphenyl-4-carboxylic acid (TCBPE) carboxyl activation product (CA-TCBPE) as a fluorescent probe. The CA-TCBPE@Ac complex is captured at the detection site through the immobilization of a monoclonal antibody monoclonal antibody (mAb) targeting Ac in this sensor. Under the excitation of 365 nm ultraviolet (UV) light, the detection of Ac in the concentration range of 105-108 CFU/mL was successfully achieved, with a visual detection limit of 105 CFU/mL. The accuracy of the sensor was further validated through experimentation with real samples, including watermelon, cantaloupe, cucumber, and zucchini. This study presents the pioneering development of a label-free ICTS sensor, utilizing TCBPE material markers, for rapid and sensitive detection of Ac. This innovative approach offers a robust solution for the swift detecting of Ac in cucurbits and other samples, thereby holding great promise for future applications.

Development of a Gold Nanoparticle-Based Sensor for Authentication of Organic Milk Based on Differential Levels of miRNA.

Dairy production systems significantly impact environmental sustainability, animal welfare, and human health. Intensive farming maximizes output through high-input practices, raising concerns about environmental degradation, animal welfare, and health risks from antibiotic residues. Conversely, organic farming emphasizes sustainable practices, animal welfare, and minimal synthetic inputs, potentially enhancing biodiversity, soil health, and milk quality. MicroRNAs (miRNAs), non-coding RNAs regulating gene expression, are promising biomarkers due to their response to various conditions. In this study, miRNAs bta-miR-103 and bta-miR-155, which are abundant in milk from pasture-fed cows, were selected. Additionally, bta-miR-215, which is abundant in milk fat from intensive systems, was also studied, in order to differentiate dairy production systems. A novel, cost-effective gold nanoparticle (AuNP)-based sensor was developed for miRNA detection, leveraging the unique plasmonic properties of AuNPs for visual detection. The method involves functionalizing AuNPs with complementary RNA probes and detecting miRNA-induced aggregation through colorimetric changes. This rapid, results in 30 min, and sensitive, visual limit of detection of 200 nM, assay requires minimal instrumentation and can be easily interpreted, offering significant advantages for field implementation in characterizing dairy production systems. This study demonstrates the successful application of this sensor in detecting miRNAs in 350 nM miRNA spiked raw milk, highlighting its potential for in situ dairy industry applications.

Crescent-shaped Janus nanoassemblies of gold nanoparticles and AIEgens: Enhancing plasmonic and fluorescent activities for colorimetric and ratiometric fluorescence lateral flow immunoassay

Herein, crescent-shaped Janus nanoassemblies (Au-AIENPs) with high plasmonic and fluorescent activities are prepared by co-assembling oleylamine-coated gold nanoparticles (OA-AuNPs) and red-emitting aggregation-induced emission luminogens (AIEgens) in separate compartments of polymer nanoparticles. The obtained Au-AIENPs show typical Janus heterostructures, where AIEgens preferentially aggregate to form fluorescent core and OA-AuNPs are distributed in the polymer matrix to form a crescent-shaped plasmonic shell, thus resulting in effective spatial separation of OA-AuNPs and AIEgens to achieve the balance between plasmonic and fluorescent signals and reduce the mutual interference between signals. Taking advantage of the excellent plasmonic and fluorescent activities of Au-AIENPs, we successfully established a colorimetric and ratiometric fluorescence dual-mode lateral flow immunoassay (Au-AIENPs-RLFIA) for the visual and quantitative detection of aflatoxin B1 (AFB1) in corn sample. Under the developed conditions, the visual detection limit (vLOD) of the Au-AIENPs-RLFIA for colorimetric and ratiomentic fluorescence detection was 0.62 ng/mL and 0.02 ng/mL, respectively, while the quantitative LOD (qLOD) for ratiomentic fluorescence mode was as low as 0.0076 ng/mL. The above results indicate that the designed Janus Au-AIENPs are promising as dual-signal output probes and hold great potential for improving flexible dual-mode detection of various targets on the LFIA platform.

Development of a Sensitive Monoclonal Antibody-Based Colloidal Gold Immunochromatographic Strip for Lomefloxacin Detection in Meat Products.

Lomefloxacin (LOM), an antibiotic crucial for preventing various animal diseases in animal husbandry, can pose serious health risks when found in excessive amounts in meat products. The development of highly specific and sensitive colloidal gold immunochromatographic test strips is essential for the accurate detection of this class of antibiotics. Our study utilized a monoclonal antibody (mAb) assay and immunochromatographic strips to detect lomefloxacin residues in meat products. The results showed minimal cross-reactivity with other structural analogs, with a maximum half inhibitory concentration (IC50) of 0.93 ng/mL and a linear range of 0.38 to 2.3 ng/mL for the indirect competitive enzyme-linked immunosorbent assay (ic-ELISA). The recovery of LOM was 80% to 120%, with an average coefficient of variation below 5%. The immunochromatographic strip test results showed a visual detection limit of 2.5 ng/g, meeting the market requirements for the test. This study highlights the significance of specific and sensitive testing methods for detecting lomefloxacin, ensuring consumers' safety and health.

Rapid determination of α-lactalbumin in raw cow's milk and recombined milk using an immunochromatographic assay strip analysis method

α-Lactalbumin (α-La) is a common allergenic protein in dairy products, posing a potential hazard to human health. Therefore, there is an urgent need to develop an efficient and sensitive analytical method to assess the α-La content in food. After screening by cell fusion assay, we obtained a pair of monoclonal antibodies (mAbs) (mAb 1 and 9). The calculated limit of detection of the sandwich enzyme-linked immunosorbent assay (ELISA) was 3.99 ng/mL. By labeling mAbs with colloidal gold, we developed a sensitive and rapid immunochromatographic assay (ICA) strip method for the detection of α-La in dairy products. The established ICA strips showed high sensitivity and specificity for the detection of α-La, with a calculated limit of detection and a visual limit of detection of 10.33 and 50 ng/mL, respectively. The average recoveries for the determination of raw cow's milk and recombined milk using ICA strips ranged from 97.60% to 102.96%. The ICA strips showed good correlation with the high-performance liquid chromatography (HPLC) method when analyzing actual samples. The above results indicated that both methods can be used for the determination of α-La in dairy products.

Sensitive dual-channel lateral flow immunoassay tagged with high brightness latex microsphere for simultaneous detection of respiratory viral antigens

Respiratory infectious diseases pose a serious threat to human health worldwide. Timely diagnosis is crucial for effective clinical management and infection control. Herein, we developed a dual-channel lateral flow immunoassay (DC-LFIA) for simultaneous sensitive detection of influenza A virus (IAV) and respiratory syncytial virus (RSV) nucleoprotein (NP) antigens. The high brightness latex microspheres (HB-LMs) exhibiting typical absorption peak at 540 nm with uniform size and excellent optical stability, were prepared by a simple surfactant-free emulsion polymerization by mixing Sudan red, which overcame the complexity and color instability met for traditional synthesis methods. After affinity evaluation, two antibody pairs have good affinity for IAV NP and RSV NP were separately identified. Then, combining antibody pairs as probes and HB-LMs as based signal tag, a DC-LFIA was constructed, by which the visual limit of detection is 25 pg/mL, 100 pg/mL for IAV NP and RSV NP, respectively, 10-fold more sensitive than gold nanoparticles based LFIA. The calculated limit of detection (S/N=3) of IAV NP and RSV NP was improved 22.8- and19.5-fold, respectively, in comparison with gold nanoparticles based LFIA. Additionally, the developed sensor shows excellent specificity and reproducibility. Furthermore, the as-proposed method was validated through the analysis of clinical samples, in good agreement with commercial colloidal gold kits. Thus, the developed DC-LFIA has great potential for clinical application in the multiplex detection of respiratory viral antigens.