Development of a Sensitive Enzyme-Linked Immunosorbent Assay and Rapid Gold Nanoparticle Immunochromatographic Strip for Detecting Citrinin in Monascus Fermented Food

Novel antibody- and aptamer-based approaches for sensitive detection of mycotoxin fusaric acid in cereal

This study presents the first successful generation of polyclonal antibodies (pAbs) and oligonucleotide aptamers specifically targeting fusaric acid (FA). Utilizing these pAbs and aptamers, three highly sensitive and specific assays were developed for the detection of FA in cereals with limits of detection (LOD) ranging from 5 to 50 ng/g: an antibody-based enzyme-linked immunosorbent assay (ELISA), an aptamer-based enzyme-linked aptamer-sorbent assay (ELASA), and a hybrid enzyme-linked aptamer-antibody sandwich assay (ELAAA). The recovery rates of FA in spiked cereal samples ranged from 87 % to 112 % across all assays. Analysis of 15 cereal feed samples revealed FA contamination levels of 459 to 1743 ng/g (ELISA), 427 to 1960 ng/g (ELASA), and 381 to 1987 ng/g (ELAAA). These results were further validated by HPLC analysis, confirming high consistency within developed assays. Overall, the ELISA, ELASA, and ELAAA are promising tools for the rapid detection of FA, significantly contributing to food safety monitoring.

A label-free electrochemical aptasensor based on NH2-MIL-235(Fe) for the sensitive detection of citrinin

This study successfully developed a simple, specific, and ultrasensitive electrochemical aptasensor based on a label-free strategy for detecting citrinin (CIT). The NH₂-Fe-MOF nanomaterial has a large specific surface area, good biocompatibility, a simple preparation method, and low synthesis cost, so it was chosen as the aptamer's loading platform to improve the detection performance of the sensor. When CIT is present, the aptamer will specifically bind to it with a conformational change that prevents electron transfer to the electrode surface. Based on this, CIT could be quantitatively detected by measuring the change of differential pulse voltammetric (DPV) responses of the [Fe(CN)₆]^3-/4- peak current. Under optimized experimental conditions, the proposed aptasensor showed a low detection limit of 4.52 × 10^-11 g mL^-1 and a wide linear range of 0.1 to 1 × 10⁴ ng mL^-1. Furthermore, the proposed aptasensor shows excellent selectivity, reliable stability, and significant potential for the ultrasensitive detection of CIT in practical applications.

Pilot production of a sensitive ELISA kit and an immunochromatographic strip for rapid detecting citrinin in fermented rice

Citrinin (CTN) is a mycotoxin primarily produced by Monascus species. Excess consumption of CTN may lead to nephrotoxicity and hepatotoxicity. A pilot study for commercial production of competitive direct enzyme-linked immunosorbent assay (cdELISA) kit and an immunochromatographic strip (immunostrip) for screening CTN in red yeast rice is established in this study. The coating antibody and the CTN-horse radish peroxidase (HRP) concentrations were optimized to increase the sensitivity and specificity of cdELISA kit. The conjugation methods/ratios of CTN to HRP as well as the long-term stability of kit components were also evaluated. The IC50 and detection limit of the ELISA kit were determined to be 4.1 and 0.2 ng mL-1, respectively. Analysis of 20 red yeast rice samples using ELISA kits revealed the contamination levels of CTN from 64 to 29 404 ng g-1. The on-site rapid detection of CTN with the immunostrip showed that CTN levels in seven samples exceeded the regulatory limit of 5 ppm. Additionally, the coefficient correlation between the results of HPLC and ELISA kits of 20 samples was 0.96. Sensitive and convenient tools at commercial levels for detection of CTN contamination in food are established herein to protect the health of the public.

Magnetism-Controllable Catalytic Activity of DNAzyme

Controllable regulation of enzyme activity is an important prerequisite for the in-depth application of enzymes, especially in today's intelligent era. However, irreversible regulation and cumbersome operation make this goal difficult to achieve. Here, by adopting magnetism and a harmless, noncontact, and time- and space-controllable physical element, we developed a system that could conveniently and reversibly regulate the activity of DNAzyme. In this system, the strands of the DNAzyme could be stretched or folded by applying or removing a magnetic field. Thereby, the conformation-dependent endonuclease activity of the DNAzyme could be facilely switched between an "OFF" and "ON" state. This system provides a reusable platform for the control of enzyme catalytic activity through magnetism, which provides guidance for further application in some related scientific research, especially the regulation of the activity of conformation-dependent polymers (DNAzymes, aptamers, and peptides).

Development of a Rapid Gold Nanoparticle Immunochromatographic Strip Based on the Nanobody for Detecting 2,4-DichloRophenoxyacetic Acid

2,4-Dichlorophenoxyacetic acid (2,4-D) is a systemic conductive herbicide widely used across the world. With the large-scale and continuous use of 2,4-D, its possible harm to the environment and non-target organisms has attracted increasing attention, and the construction of a stable rapid on-site detection method is particularly important. In order to achieve on-site rapid detection of 2,4-D, we developed a gold nanoparticle immunochromatographic strip method with the visual elimination value was 50 ng/mL, and a quantitative detection limit of 11 ng/mL based on a nanobody. By combing with the color snap, the immunochromatographic strip could quantitatively analyze the amounts of 2,4-D. Meanwhile, a colorimetric card based on the true color of the test strips was developed for the qualitative analysis of 2,4-D on-site. The samples (water, fruits and vegetables) with and without 2,4-D were detected by the immunochromatographic strips, and the results showed the accuracy and reliability. Thus, this assay is a rapid and simple on-site analytical tool to detect and quantify 2,4-D levels in environmental samples, and the analytical results can be obtained in about ten minutes. In addition, the nanobody technology used in this study provides an inexhaustible supply of a relatively stable antibodies that can be archived as a nanobody, plasmid or even its sequence.

A Sensitive Two-Analyte Immunochromatographic Strip for Simultaneously Detecting Aflatoxin M1 and Chloramphenicol in Milk

A two-analyte immunochromatographic strip (immunostrip) was developed for the simultaneous detection of aflatoxin M1 (AFM1) and chloramphenicol (CAP) in milk. Protein conjugates (AFM1-ovalbumin (OVA) and CAP-OVA) and goat anti-rabbit IgG were respectively drawn on nitrocellulose membrane as two test lines (T₁ and T₂) and a control line (C). The immunostrip was dipped into a well that contained a 200 μL milk sample, 5 μL AFM1 antibody-gold conjugates, and 8 μL CAP antibody-gold conjugates; the whole assay was completed in 15 min and the results could be interpreted visually or using a reader. This immunostrip has cut-off levels of 0.1 ng/mL and 0.5 ng/mL for AFM1 and CAP, respectively. Analysis of CAP and AFM1 in milk samples revealed that data from the immunostrip test agreed closely with those obtained from ELISA. The two-analyte immunostrip is a rapid way for on-site simultaneous detection of AFM1 and CAP in milk.

Recent advances in analytical methods for the determination of citrinin in food matrices

Citrinin is a toxic small organic molecule produced as a secondary metabolite by fungi types Penicillium, Monascus and Aspergillus and is known to contaminate various food commodities during postharvest stages of food production. During the last 10 years, most reported methods for citrinin analysis employed enzyme-linked immunosorbent assays or high-performance liquid chromatography. Over this same time period, liquid extraction, solid-phase extraction, dispersive liquid-liquid microextraction and QuEChERS were the most cited sample preparation and clean-up methods. In this review the advantages and disadvantages of the various sample preparation, separation and detection methods for citrinin analysis over the last decade are evaluated. Furthermore, current trends, emerging technologies and the future prospects of these methods are discussed.

Carboxyl-Functionalized, Europium Nanoparticle-Based Fluorescent Immunochromatographic Assay for Sensitive Detection of Citrinin in Monascus Fermented Food

A fluorescent immunochromatographic test strip (FICTS) based on the use of europium nanoparticles (EuNPs) was developed and applied to detect citrinin (CIT) in Monascus fermented food. The sensitivity of the immunoassay to detect CIT was greatly improved by the use of a specific monoclonal antibody to attach EuNPs to form a probe. Under optimum conditions, the visual detection limit was 2.5 ng/mL, and the detection limit of the instrument was 0.05 ng/mL. According to the results, the IC₅₀ was 0.4 ng/mL. Matrix interference from various Monascus fermented foods was investigated in food sample detection. The immunosensor also demonstrated high recoveries (86.8-113.0%) and low relative standard deviations (RSDs) (1.8-15.3%) when testing spiked Monascus fermented food. The detection results of this method showed a good correlation (R² > 0.98) with high-performance liquid chromatography (HPLC). The results showed that the FICTS method could be used as a rapid, sensitive method to detect CIT in Monascus fermented food.

Development of Real-Time Immuno-PCR Based on Phage Displayed an Anti-Idiotypic Nanobody for Quantitative Determination of Citrinin in Monascus

Citrinin (CIT) is a mycotoxin that has been detected in agricultural products, feedstuff, and Monascus products. At present, research has been performed to develop methods for CIT detection, mainly through TLC, HPLC, biosensor, and immunoassay. The immunoassay method is popular with researchers because of its speed, economy, simplicity, and ease of control. However, mycotoxins are inevitably introduced during the determination. Immunoassays require the use of toxins coupled to carrier proteins or enzymes to make competitive antigens. In this study, anti-idiotypic nanobody X27 as CIT mimetic antigen was used as non-toxic surrogate reagents in immunoassay. Therefore, the X27-based real-time immuno-PCR (rtIPCR) method had been established after optimal experiments of annealing temperature and amplification efficiency of real-time PCR, concentration of coating antibody, phage X27, and methyl alcohol. The IC₅₀ value of the established method in the present study is 9.86 ± 2.52 ng/mL, which is nearly equivalent to the traditional phage ELISA method. However, the linear range is of 0.1-1000 ng/mL, which has been broadened 10-fold compared to the phage ELISA method. Besides, the X27-based rtIPCR method has no cross-reactivity to the common mycotoxins, like aflatoxin B₁ (AFB₁), deoxynivalenol (DON), ochratoxin A (OTA), and zearalenone (ZEN). The method has also been applied to the determination of CIT in rice flour and flour samples, and the recovery was found to be in the range of 90.0-104.6% and 75.8-110.0% respectively. There was no significant difference in the results between the rtIPCR and UPLC-MS. The anti-idiotypic nanobody as a non-toxic surrogate of CIT makes rtIPCR a promising method for actual CIT analysis in Monascus products.

The Effect of Blue Light on the Production of Citrinin in Monascus purpureus M9 by Regulating the mraox Gene through lncRNA AOANCR

Blue light, as an important environmental factor, can regulate the production of various secondary metabolites of Monascus purpureus M9, including mycotoxin-citrinin, pigments, and monacolin K. The analysis of citrinin in Monascus M9 exposed to blue light for 0 min./d, 15 min./d, and 60 min./d showed that 15 min./d of blue light illumination could significantly increase citrinin production, while 60 min./d of blue light illumination decreased citrinin production. Analysis of long non-coding RNA (LncRNA) was performed on the transcripts of Monascus M9 under three culture conditions, and this analysis identified an lncRNA named AOANCR that can negatively regulate the mraox gene. Fermentation studies suggested that alternate respiratory pathways could be among the pathways that are involved in the regulation of the synthesis of citrinin by environmental factors. Aminophylline and citric acid were added to the culture medium to simulate the process of generating cyclic adenosine monophosphate (cAMP) in cells under illumination conditions. The results of the fermentation showed that aminophylline and citric acid could increase the expression of the mraox gene, decrease the expression of lncRNA AOANCR, and reduce the yield of citrinin. This result also indicates a reverse regulation relationship between lncRNA AOANCR and the mraox gene. A blue light signal might regulate the mraox gene at least partially through lncRNA AOANCR, thereby regulating citrinin production. Citrinin has severe nephrotoxicity in mammals, and it is important to control the residual amout of citrinin in red yeast products during fermentation. LncRNA AOANCR and mraox can potentially be used as new targets for the control of citrinin production.