Magnetic particles-based enzyme immunoassay for rapid determination of secoiridoid glycoside, amarogentin

Bioimprinting as a Receptor for Detection of Kwakhurin

Bioimprinting was performed against ovalbumin (OVA) to confer its binding cavities for kwakhurin (Kwa), an isoflavonoid, produced solely by Pueraria candollei var. mirifica (P. candollei). The characterization of bioimprinted-OVA (biOVA), evaluated by an enzyme-linked immunosorbent assay (ELISA), revealed that it functioned as a specific receptor for Kwa. Using biOVA, two systems, i.e., an indirect competitive ELISA (icELISA) and the even simpler and more rapid competitive enzyme-linked bioimprinted-protein assay (cELBIA), were developed as novel techniques for the quantitative analysis of Kwa in P. candollei and its related products. The two analysis methods were found to have limits of detection (LOD) of 4.0 and 2.5 µg/mL, respectively. The high reliability of the developed icELISA and cELBIA using biOVA was also demonstrated by various validation analyses. Subsequently, bioimprinting was performed using eight other proteins to investigate them as candidate scaffolds for the generation of binding cavities for Kwa. Interestingly, two bioimprinted-IgG monoclonal antibodies (biMAbs) recognized Kwa, but their original binding affinity to hapten was lost. That is, the MAbs obtained a new binding ability to Kwa in exchange for their original binding affinity, raising the possibility that biMAb could be alternatively used as a probe for the quantitative analysis of Kwa as well as biOVA. This is the first report of small molecules recognition by MAbs used as proteins for bioimprinting.

Directional immobilization of antibody onto magnetic nanoparticles by Fc-binding protein-assisted photo-conjugation for high sensitivity detection of antigen

Immobilized antibodies with site-specific, oriented, and covalent pattern are of great significance to improve the sensitivity of solid-phase immunoassay. Here, we developed a novel antibody conjugation strategy that can immobilize antibodies in a directional and covalent manner. In this study, an IgG-Fc binding protein (Z domain) carrying a site-specific photo-crosslinker, p-benzoyl-L-phenylalanine, and a single C-terminal cysteine (Cys) handle was genetically engineered. Upon UV irradiation, the chimeric protein enables the Cys handle to couple with the native antibody in Fc-specific and covalent conjugation pattern, resulting in a novel thiolated antibody. Thus, an approach for the covalent, directional immobilization of antibodies to maleimide-modified magnetic nanoparticles (MNPs) was developed on the basis of the crosslinking between sulfhydryl and maleimide groups. The antibody-conjugated MNPs were applied in MNP-based enzyme-linked immunosorbent assay (ELISA) for the detection of carcinoembryonic antigen. The MNP-based ELISA presented a quantification linear range of 0.1-100 ng mL^-1 and detection limit of 0.02 ng mL^-1, which was approximately 100 times more sensitive than the traditional microplate ELISA (2.0 ng mL^-1). Thus, the proposed antibody immobilization approach can be used in surface functionalization for the sensitive detection of various biomarkers.

Magnetic assisted fluorescence immunoassay for sensitive chloramphenicol detection using carbon dots@CaCO3 nanocomposites

Analytical methods with high sensitivities and short assay times are urgently required for the screening of "zero tolerance" hazardous substances in food. Herein, we propose a fluorescent immunoassay for the highly sensitive and rapid analysis of chloramphenicol (CAP) based on carbon dots (CDs)-encapsulated CaCO₃ nanospheres and magnetic nanoparticles (MNPs). The fluorescent immunoprobes were prepared by coupling the anti-CAP antibodies to carboxymethyl cellulose-functional CDs@CaCO₃ nanospheres. Chitosan-modified MNPs with "core-shell" structures were prepared and then conjugated to the CAP hapten, acting as the nano-carrier and interface for the immunoreaction. With the assistance of MNPs, the established fluorescent immunoassay achieved the sensitive detection of CAP in chicken with a limit of detection of 0.03 μg kg^-1 and recoveries ranging from 83.7%-105.0%. The analysis results of the fluorescent immunoassay were evaluated by the enzyme-linked immunosorbent assay, having a correlation coefficient of 0.981. Our work provides a rapid, facile, and reliable strategy for the highly sensitive analysis of food contaminants based on "green" fluorescent nanoprobes.

Competitive immunochromatographic test strips for the rapid semi-quantitative analysis of the biologically active bitter glycoside, amarogentin

Amarogentin (AG), a biologically active secoiridoid glycoside, is responsible for the efficacy of Gentianaceae based medications. Thus, qualitative and quantitative analyses of AG are of significance for batch to batch quality control purposes. By conjugating colloidal gold nanoparticles with the AG-specific monoclonal antibody, MAb 1E9, we were able to develop a single-step competitive immunochromatographic assay (ICA) for simple quantification of the AG content in plant samples. With a limit of detection of 250 ng/mL, the analytical results were obtained after immersing the ICA test strip in the detection mixture for 15 min. This new ICA is superior to conventional ICAs as it is considerably faster due to the speed with which the test strips can be produced and the omission of the time-consuming preparation phase that was previously required to make the fiber pad. Moreover, our ICA only needs a small amount of analyte (20 µL).The reliability of the reported test strip was confirmed by comparing its semi-quantitative results with those obtained via an indirect competitive enzyme-linked immunosorbent assay (icELISA). The positive correlation between these methods (R² = 0.984) indicated that this new ICA could be applied for the semi-quantitative analysis of the AG content in plant samples.

Rapid magnetic particles-based enzyme immunoassay for the quality control of Glycyrrhiza spp. based on glycyrrhizin content

Glycyrrhizin (GC) is a triterpenoid saponin isolated from the roots of Glycyrrhiza spp., a medicinal plant that is present in 70% of Kampo prescriptions. Since the GC content in Glycyrrhiza spp. affects its various pharmacological activities, Glycyrrhiza spp. is prescribed to contain at least 2% of GC in the Japanese pharmacopoeia, and its quality control based on GC content is required. In this study, a magnetic particles-based enzyme immunoassay (MPs-EIA) was developed using specific monoclonal antibody against GC (MAb 2H2) for the detection of GC in Glycyrrhiza spp. In this system, the immunoreaction time using primary and secondary antibodies was reduced by taking advantage of the wide surface area of magnetic particles (MPs) conjugated with GC by N,N'‑carbonyldiimidazole (CDI)-mediated method. Optimization of MPs-EIA revealed that total assay time (~2 h) was reduced to over half of that of conventional indirect competitive enzyme-linked immunosorbent assay (ELISA) (~5 h). In addition, the GC concentration was detectable within the range from 97.7 to 781 ng/mL, with a limit of detection of 71.4 ng/mL. A series of further validation analyses support the reliability and accuracy of the developed MPs-EIA for the detection of GC in Glycyrrhiza spp. Since the present MPs-EIA overcomes the disadvantage of ELISA in terms of rapidity, it provides a useful approach for the effective quality control of Glycyrrhiza spp., especially when handling multiple samples.

Kwakhurin-magnetic particles conjugates enable fast enzyme immunoassay for the detection of kwakhurin in Pueraria candollei

INTRODUCTION

Kwakhurin (Kwa) is one of the unique isoflavonoids produced in Pueraria candollei var. mirifica (P. candollei), which has long been used as folk medicine for rejuvenation in Thailand. Recently, the use of P. candollei-derived products has widely spread among Japanese women for cosmetic purposes. Correspondingly, there has been an increase in the number of reports regarding possible health hazards caused by estrogenic activity inherent to the plant; thus, the need for a detailed evaluation of the phytoestrogen content of P. candollei-derived products has gained a sense of urgency in recent years.

OBJECTIVE

This study aims to develop a rapid enzyme immunoassay that can be applied to the quantitative analysis of Kwa in P. candollei and its derived products.

MATERIAL AND METHOD

A rapid and sensitive immunoassay was developed with a combination of Kwa-specific monoclonal antibody (MAb 11F) and Kwa-magnetic particles (MPs) conjugates, which increased the surface area of the solid phase, resulting in a decrease in the immunoreaction time.

RESULT

This novel MPs-based enzyme immunoassay (MPs-EIA) was used to determine Kwa concentration in the range from 2.44 to 78.1 ng/mL with a limit of detection of 1.90 ng/mL. Validation analyses revealed that the proposed MPs-EIA protocol was sufficiently precise and accurate for effective quantitative analysis of Kwa in P. candollei and its derived products.