Novel ractopamine-protein carrier conjugation and its application to the lateral flow strip test for ractopamine detection in animal feed

Integration of a hamper pad on test strips for improved sensitivity of carbendazim detection

Lateral flow immunoassays (LFIAs) are widely used to determine carbendazim (CBZ) residues in food products due to their advantages of low cost, ease and rapid use, on-site detection capability. However, conventional LFIAs have low detection sensitivity. Although improvements have been made to increase the sensitivity, it is not sufficient. Here, a hamper pad, polyvinyl alcohol coated on a nitrocellulose membrane, was integrated to enhance the sensitivity of LFIA for CBZ detection. The hamper pad was inserted between the conjugated and nitrocellulose pads to delay the flow rate, thereby increasing the possibility of the antibody and target analyte binding. This platform exhibited a fourfold sensitivity increase in CBZ detection compared with the conventional LFIA, and its limit of detection was 1.6 ng/mL. In addition, a single-step operation was successfully applied to detect CBZ in rice (white rice, brown rice, sticky rice, and paddy) and soybean samples, with acceptable recoveries of 93.6%-120.0%. This novel device was compared to the standard high-performance liquid chromatography method, which shows high accuracy with a Kappa coefficient of 0.91. Therefore, improved sensitivity with a rapid, simple, and inexpensive device could facilitate the detection of CBZ residues in agricultural products for on-field screening and improved user-friendliness.

Microfluidic Paper-Based Device for Medicinal Diagnosis

BACKGROUND

The demand for point-of-care testing (POCT) devices has rapidly grown since they offer immediate test results with ease of use, makingthem suitable for home self-testing patients and caretakers. However, the POCT development has faced the challenges of increased cost and limited resources. Therefore, the paper substrate as a low-cost material has been employed to develop a cost-effective POCT device, known as "Microfluidic paper-based analytical devices (μPADs)". This device is gaining attention as a promising tool for medicinal diagnostic applications owing to its unique features of simple fabrication, low cost, enabling manipulation flow (capillarydriven flow), the ability to store reagents, and accommodating multistep assay requirements.

OBJECTIVE

This review comprehensively examines the fabrication methods and device designs (2D/3D configuration) and their advantages and disadvantages, focusing on updated μPADs applications for motif identification.

METHODS

The evolution of paper-based devices, starting from the traditional devices of dipstick and lateral flow assay (LFA) with μPADs, has been described. Patterned structure fabrication of each technique has been compared among the equipment used, benefits, and drawbacks. Microfluidic device designs, including 2D and 3D configurations, have been introduced as well as their modifications. Various designs of μPADs have been integrated with many powerful detection methods such as colorimetry, electrochemistry, fluorescence, chemiluminescence, electrochemiluminescence, and SER-based sensors for medicinal diagnosis applications.

CONCLUSION

The μPADs potential to deal with commercialization in terms of the state-of-the-art of μPADs in medicinal diagnosis has been discussed. A great prototype, which is currently in a reallife application breakthrough, has been updated.

Magnetic Nanotag-Based Colorimetric/SERS Dual-Readout Immunochromatography for Ultrasensitive Detection of Clenbuterol Hydrochloride and Ractopamine in Food Samples

Direct and sensitive detection of multiple illegal additives in complex food samples is still a challenge in on-site detection. In this study, an ultrasensitive immunochromatographic assay (ICA) using magnetic Fe₃O₄@Au nanotags as a capture/detection difunctional tool was developed for the direct detection of β2-adrenoceptor agonists in real samples. The Fe₃O₄@Au tag is composed of a large magnetic core (~160 nm), a rough Au nanoshell, dense surface-modified Raman molecules, and antibodies, which cannot only effectively enrich targets from complex solutions to reduce the matrix effects of food samples and improve detection sensitivity, but also provide strong colorimetric/surface-enhanced Raman scattering (SERS) dual signals for ICA testing. The dual readout signals of the proposed ICA can meet the detection requirements in different environments. Specifically, the colorimetric signal allows for rapid visual detection of the analyte, and the SERS signal is used for the sensitive and quantitative detection modes. The proposed dual-signal ICA can achieve the simultaneous determination of two illegal additives, namely, clenbuterol hydrochloride and ractopamine. The detection limits for the two targets via colorimetric and SERS signals were down to ng mL⁻¹ and pg mL⁻¹ levels, respectively. Moreover, the proposed assay has demonstrated high accuracy and stability in real food 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.

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.

Ultramarine blue nanoparticles as a label for immunochromatographic on-site determination of ractopamine

A competitive immunochromatographic assay (ICA) is presented and used for on-site determination of ractopamine (RAC). Ultramarine blue nanoparticles were directly separated from ultramarine blue industrial products by centrifugation (< 10,000 rpm and > 4000 rpm) and used as visible labels in ICAs. The ultramarine blue nanoparticles were coated by polyacrylic acid (PAA), which provides carboxyl groups on the surface of ultramarine blue nanoparticles. An anti-RAC monoclonal antibody (mAb) was covalently immobilized on the carboxyl-modified ultramarine blue nanoparticle surface via diimide-activated conjugation between the carboxyl groups on the ultramarine blue nanoparticle surface and the amino groups of the antibodies. RAC and BSA-modified RAC competitively bind to the anti-RAC mAb on the ultramarine blue nanoparticles. The blue band in the test line is generated by the accumulation of ultramarine blue nanoparticles and is negatively associated with the RAC content. Under optimal conditions, the visual limit of detection (vLOD) of this ICA for RAC is 2.0 ng mL^-1, 2.0 ng mL^-1, and 1.0 ng mL^-1 in phosphate-buffered saline (PBS), feed samples, and pork samples, respectively. The ultramarine blue nanoparticle-based ICA also shows no cross activity with salbutamol, clorprenaline, clenbuterol, or terbutaline. Graphical abstract Schematic representation of the ultramarine blue nanoparticles immunochromatographic assay for detection of ractopamine (RAC) based on competitive method. The ultramarine blue nanoparticles were screened from commercial ultramarine pigments for the first time and used to detect ractopamine.