An ultra-sensitive monoclonal antibody-based fluorescent microsphere immunochromatographic test strip assay for detecting aflatoxin M 1 in milk

Hemin as electrochemically regenerable co-reaction accelerator for construction of an ultrasensitive PTCA-based electrochemiluminescent aptasensor

In this work, hemin was firstly used as electrochemically regenerable co-reaction accelerator for signal amplification to develop an ultrasensitive aptasensor for Aflatoxin M1 (AFM1) detection. Initially, the perylenetetracarboxylic acid (PTCA) was directly employed as luminophore to construct the ECL sensing nano-platform by combining Au nanoparticles (Au NPs) for immobilizing thiol-terminated hairpin probe (H1). Then with the help of hairpin H2, H3, the AFM1-catalyzed hairpin assembly (CHA) was executed to produce the H1-H3 duplex, which could further initiate the hybridization chain reaction (HCR) to generate dendritic DNA polymers consisting of G-rich sequence for capturing large quantities of hemin on the electrode surface. Herein, hemin as electrochemically regenerable co-reaction accelerator could interact with the co-reactant (S₂O₈^2-) to obviously improve the luminous efficiency of the PTCA. Therefore, a strong and stable ECL signal was achieved by the employment of hemin as electrochemically regenerable co-reaction accelerator. The proposed aptasensor determined AFM1 down to 0.09pgmL^-1 within a linear range of 0.4pgmL^-1 to 400ngmL^-1. With excellent sensitivity and stability, the strategy provided an efficient and simple method for the trace detection of biomolecules in clinical analysis.

Aptamer-based fluorescence-quenching lateral flow strip for rapid detection of mercury (II) ion in water samples

Divalent mercury ion (Hg²⁺) is one of the most common and stable forms of mercury pollution. In this study, a skillfully designed lateral flow strip (LFS) was developed for sensitive detection of Hg²⁺ in river water samples. Aptamer, a specific oligonucleotide probe, was used to selectively identify and target Hg²⁺ instead of antibody in traditional immunechromatographic strips; and the fluorescence-quenching system was used to generate positive and low background florescence signals in the competitive-likely LFS. The linear detection range of the LFS for Hg²⁺ was 0.13 ng mL^-1 to 4 ng mL^-1 and the limit of detection (LOD) was 0.13 ng mL^-1. This test provided results in 15 min and demonstrated high specificity. For detection of Hg²⁺ in river water, the results were consistent with inductively coupled plasma-mass spectrometry measurements. The aptamer-based fluorescence-quenching LFS was shown to provide a reliable, accurate method for rapid detection of mercury contamination. Graphical Abstract The principle of the aptamer-based fluorescence-quenching LFS.

Fluorescence Polarization Immunoassay Based on a New Monoclonal Antibody for the Detection of the Zearalenone Class of Mycotoxins in Maize

To develop a sensitive fluorescence polarization immunoassay (FPIA) for screening the zearalenone class of mycotoxins in maize, two new monoclonal antibodies with uniform affinity to the zearalenone class and four fluorescein-labeled tracers were prepared. After careful selection of appropriate tracer-antibody pairs in terms of sensitivity and specificity, a FPIA that could simultaneously detect the zearalenone class with similar sensitivity was developed. Under optimum conditions, the half maximal inhibitory concentrations of the FPIA in buffer were 1.89, 1.97, 2.43, 1.99, 2.27, and 2.44 μg/L for zearalenone, α-zearalenol, β-zearalenol, α-zearalanol, β-zearalanol, and zearalanone, respectively. The limit of detection of FPIA for the zearalenone class was around 12 μg/kg in maize, and the recoveries ranged from 84.6 to 113.8%, with coefficients of variation below 15.3% in spiked samples. Finally, the FPIA was applied for screening naturally contaminated maize samples, and the results indicated a good correlation with that of high-performance liquid chromatography-tandem mass spectrometry.

Advantage of Eu3+ -Doped Polystyrene Microspheres Compared with Colloidal Gold Used in Immunochromatographic Assays for the Detection of Melamine in Milk

Colloidal gold and Eu³⁺ -doped fluorescent microspheres were applied as labels to develop the immunochromatographic strips for detecting melamine in milk. Under the optimized condition, the visual detection limit of colloidal gold-immunochromatographic test strip (ICTS) was 150 μg/L of melamine in phosphate-buffered saline (PBS), although the visual detection limit of fluorescent nanoparticles (FN)-ICTS was 75 μg/L in PBS. As thermal acceleration test, FN-ICTS could be stored at 37 °C for at least 11 d before sample testing, but the color of the lines on colloidal gold-ICTS faded away after 7-d storage. The visual result of FN-ICTS was more stable than that of colloidal gold-ICTS, and the fluorescence intensity of the line on FN-ICTS could be maintained up to 30 d at 22 °C after sample testing. Once the immunochromatographic strips were used to detect melamine in milk, no negative effect of milk components on the performance of FN-ICTS was identified, whereas the performance of colloidal gold-ICTS was significantly influenced by milk matrix.

Highly Efficient Intramolecular Electrochemiluminescence Energy Transfer for Ultrasensitive Bioanalysis of Aflatoxin M1

The intermolecular electrochemiluminescence resonance energy transfer (ECL-RET) between luminol and Ru(bpy)₃²⁺ was studied extensively to achieve the sensitive bioanalysis owing to the perfect spectral overlap of the donor and acceptor, but it still suffers from the challenging issue of low energy-transfer efficiency. The intramolecular ECL-RET towards the novel ECL compound containing the donor of luminol and the acceptor of Ru(bpy)₂ (mcpbpy)²⁺ (Lum-Ru) was designed and investigated. With the high-efficient ECL-RET in one molecule, the highly intense ECL signal of Lum-Ru was obtained owing to the short path of energy transmission and less energy loss between luminol and Ru(bpy)₂ (mcpbpy)²⁺ . Lum-Ru was further applied to construct a signal-off electrochemiluminescence (ECL) aptasensor for ultrasensitive detection of a harsh carcinogen of Aflatoxin M1 (AFM1). This sensing platform also provides a significant boost for the trace detection of other biomolecules in clinical analysis.

Fluorescent microsphere immunochromatographic assays for detecting bone alkaline phosphatase based on biolayer interferometry-selected antibody

A convenient, reliable, highly sensitive, and competitive fluorescent microsphere-lateral flow immunochromatographic assay (FM-LFIA) was developed for the quantitative detection of BAP for the first time.

Development of structure switching aptamer assay for detection of aflatoxin M1 in milk sample

The discovery of in-vitro systematic evolution of ligands by exponential enrichment (SELEX) process has considerably broaden the utility of aptamer as bio-recognition element, providing the high binding affinity and specificity against the target analytes. Recent research has focused on the development of structure switching signaling aptamer assay, transducing the aptamer- target recognition event into an easily detectable signal. In this paper, we demonstrate the development of structure switching aptamer assay for determination of aflatoxin M1 (AFM1) employing the quenching-dequenching mechanism. Hybridization of fluorescein labelled anti-AFM1 aptamer (F-aptamer) with TAMRA labelled complementary sequences (Q-aptamer) brings the fluorophore and the quencher into close proximity, which results in maximum fluorescence quenching. On addition of AFM1, the target induced conformational formation of antiparallel G-quadruplex aptamer-AFM1 complex results in fluorescence recovery. Under optimized experimental conditions, the developed method showed the good linearity with limit of detection (LOD) at 5.0ngkg(-1) for AFM1. The specificity of the sensing platform was carefully investigated against aflatoxin B1 (AFB1) and ochratoxin A (OTA). The developed assay platform showed the high specificity towards AFM1. The practical application of the developed aptamer assay was verified for detection of AFM1 in spiked milk samples. Good recoveries were obtained in the range from 94.40% to 95.28% (n=3) from AFM1 spiked milk sample.

Comparison of Fluorescent Microspheres and Colloidal Gold as Labels in Lateral Flow Immunochromatographic Assays for the Detection of T-2 Toxin

A new highly specific and sensitive monoclonal antibody (MAb) to T-2 toxin (T-2) was produced, providing an IC50 value of 1.02 ng/mL and negligible cross-reactivity (CR) to other related mycotoxins. Based on the new MAb, a lateral-flow immunochromatographic assay (LFIA) using colloidal gold (CG) and fluorescent microspheres (FMs) as labels was proposed for T-2. Under the optimized conditions, in rapid qualitative assay, the cut-off values of the CG-LFIA were 400 μg/kg in rice and 50 μg/L in fresh milk, and the cut-off values of the FMs-LFIA were 100 μg/kg in both rice and chicken feed. For the quantitative assay with the FMs-LFIA, the limit of detection (LOD) were 0.23 μg/kg and 0.41 μg/kg in rice and chicken feed, respectively, and the average recoveries ranged from 80.2% to 100.8% with the coefficient of variation (CV) below 10.8%. In addition, we found that the CG-LFIA could tolerate the matrix effect of fresh milk better than the FMs-LFIA, while the FMs-LFIA could tolerate the matrix effect of chicken feed better than CG-LFIA under the same experimental conditions. These results provide a certain reference for the selection of appropriate labels to establish a rapid LFIA in various biological samples.