Which one of the two common reporter systems is more suitable for chemiluminescent enzyme immunoassay: alkaline phosphatase or horseradish peroxidase?

Advances in immunoassay-based strategies for mycotoxin detection in food: From single-mode immunosensors to dual-mode immunosensors

Mycotoxin contamination in foods and other goods has become a broad issue owing to serious toxicity, tremendous threat to public safety, and terrible loss of resources. Herein, it is necessary to develop simple, sensitive, inexpensive, and rapid platforms for the detection of mycotoxins. Currently, the limitation of instrumental and chemical methods cannot be massively applied in practice. Immunoassays are considered one of the best candidates for toxin detection due to their simplicity, rapidness, and cost-effectiveness. Especially, the field of dual-mode immunosensors and corresponding assays is rapidly developing as an advanced and intersected technology. So, this review summarized the types and detection principles of single-mode immunosensors including optical and electrical immunosensors in recent years, then focused on developing dual-mode immunosensors including integrated immunosensors and combined immunosensors to detect mycotoxins, as well as the combination of dual-mode immunosensors with a portable device for point-of-care test. The remaining challenges were discussed with the aim of stimulating future development of dual-mode immunosensors to accelerate the transformation of scientific laboratory technologies into easy-to-operate and rapid detection platforms.

Immunoassay technology: Research progress in microcystin-LR detection in water samples

Increasing global warming and eutrophication have led to frequent outbreaks of cyanobacteria blooms in freshwater. Cyanobacteria blooms cause the death of aquatic and terrestrial organisms and have attracted considerable attention since the 19th century. Microcystin-LR (MC-LR) is one of the most typical cyanobacterial toxins. Therefore, the fast, sensitive, and accurate determination of MC-LR plays an important role in the health of humans and animals. Immunoassay refers to a method that uses the principle of immunology to determine the content of the tested substance in a sample using the tested substance as an antigen or antibody. In analytical applications, the immunoassay technology could use the specific recognition of antibodies for MC-LR detection. In this review, we firstly highlight the immunoassay detection of MC-LR over the past two decades, including classical enzyme-link immunosorbent assay (ELISA), modern immunoassay with optical signal, and modern immunoassay with electrical signal. Among these detection methods, the water environment was used as the main detection system. The advantages and disadvantages of the different detection methods were compared and analyzed, and the principles and applications of immunoassays in water samples were elaborated. Furthermore, the current challenges and developmental trends in immunoassay were systematically introduced to enhance MC-LR detection performance, and some critical points were given to deal with current challenges. This review provides novel insight into MC-LR detection based on immunoassay method.

Mycotoxins in Pistachios (Pistacia vera L.): Methods for Determination, Occurrence, Decontamination

The consumption of pistachios (Pistacia vera L.) has been increasing, given their important benefit to human health. In addition to being an excellent nutritional source, they have been associated with chemical hazards, such as mycotoxins, resulting in fungal contamination and its secondary metabolism. Aflatoxins (AFs) are the most common mycotoxins in pistachio and the most toxic to humans, with hepatotoxic effects. More mycotoxins such as ochratoxin A (OTA), fumonisins (FBs), zearalenone (ZEA) and trichothecenes (T2, HT2 and DON) and emerging mycotoxins have been involved in nuts. Because of the low levels of concentration and the complexity of the matrix, the determination techniques must be very sensitive. The present paper carries out an extensive review of the state of the art of the determination of mycotoxins in pistachios, concerning the trends in analytical methodologies for their determination and the levels detected as a result of its contamination. Screening methods based on immunoassays are useful due to their simplicity and rapid response. Liquid chromatography (LC) is the gold standard with new improvements to enhance accuracy, precision and sensitivity and a lower detection limit. The reduction of Aspergillus' and aflatoxins' contamination is important to minimize the public health risks. While prevention, mostly in pre-harvest, is the most effective and preferable measure to avoid mycotoxin contamination, there is an increased number of decontamination processes which will also be addressed in this review.

A signal amplification strategy for prostate specific antigen detection via releasing oxidase-mimics from coordination nanoparticles by alkaline phosphatase

A novel signal amplification method for prostate specific antigen (PSA) is developed by freeing fluorescein with photoinduced oxidase-like activity from coordination nanoparticles (CNPs) in the presence of alkaline phosphatase (ALP). CNPs loaded with fluorescein (F@CNPs) are obtained in aqueous solution by self-assembly using Tb³⁺ as metal ion, guanosine monophosphate (5'-GMP) as ligand, and fluorescein as signal molecule. The F@CNPs display outstanding properties of simple synthesis, low cost, good water solubility, negligible leakage and satisfactory load capacity. Fluorescein is quantitatively encapsulated in CNPs with a binding ratio of 92.72%. Meanwhile, ALP can specifically hydrolyze the phosphate group of 5'-GMP ligand, triggering the destruction of F@CNPs and leakage of fluorescein. Fluorescein, a photoinduced oxidase mimic, can catalyze the oxidation of non-fluorescent Amplex UltraRed (AUR) into fluorescent resorufin under LED lamp. This strategy exhibits good sensitivity for ALP detection. In addition, a new immunoassay for PSA is validated by labelling ALP on PSA antibody. The low detection limit of 0.04 ng mL^-1 in detecting PSA is appropriate for PSA detection in real samples. Therefore, the work not only establishes a new strategy for ALP and PSA determination, but also provides a new conception for putting photoinduced oxidase-like fluorescein in practical application.

Comparison of soybean peroxidase with horseradish peroxidase and alkaline phosphatase used in immunoassays

Enzyme labeling of an antigen or an antibody helps to visualize and amplify the signal and is an important reagent used in immunoassays for the detection of a target of interest. In this research, soybean peroxidase (SBP), a less commonly used enzyme reporter, was compared in immunoassays with the two most commonly used reagents, horseradish peroxidase (HRP) and alkaline phosphatase (ALP). The enzyme-antibody conjugates were evaluated by their performance in an indirect competitive enzyme-linked immunosorbent assay (icELISA) and in an indirect competitive chemiluminescent enzyme immunoassay (icCLEIA) for ractopamine (RAC). The results revealed that the more affordable SBP offers a long-lasting chemiluminescent signal, which outperformed ALP and HRP. SBP-antibody conjugate (SBP-Ab) based immunoassays produced lower limits of detection (LODs) and better accuracy in the detection of RAC in animal urine samples. Additionally, SBP-Ab has advantages in being more resistant to heat, acid and organic solvents. These results suggest that SBP could be a potentially excellent alternative to HRP and ALP for the development of immunoassay in food safety field.

Modified Bacteriophage Tail Fiber Proteins for Labeling, Immobilization, Capture, and Detection of Bacteria

A critical component of bacterial detection assays is choosing a suitable affinity molecule that retains sensitivity and specificity for the target pathogen over a wide range of in situ applications. Bacteriophages (phages) are bacterial viruses that bind and infect their host cells with unmatched specificity. Phage host range is often determined by their long tail fibers (LTFs) that mediate adsorption of the virus particle to potential bacterial host cells, by binding to specific cell surface receptors. The inherent specificity of the LTFs for distinct bacterial species makes them ideal candidates for development into recombinant affinity molecules. In this chapter, we describe the development of the Salmonella phage S16 LTF (S16 LTF) into an affinity molecule as part of a novel assay to detect Salmonella cells. The enzyme-linked long tail fiber assay (ELLTA) involves two steps: (1) Immobilization and separation of Salmonella cells using S16 LTF-coated paramagnetic beads (LTF-MBs), and (2) Labeling of bead-captured Salmonella using horseradish peroxidase-conjugated S16 LTF (HRP-LTF). Rapid HRP-mediated conversion of a chromogenic substrate provides visual confirmation for the presence of Salmonella. Overall, the ELLTA assay requires as little as 2 h to detect as few as 10² cfu/ml Salmonella cells from liquid culture. The absorbance of the enzyme-generated color substrate is largely proportional to the present bacterial concentrations between 10² and 10⁷ cfu/ml, providing semiquantitative determination of Salmonella cell counts. The methodology described in this chapter can be adapted for other phage receptor-binding proteins, to develop ELLTAs for the detection of other relevant bacterial pathogens.