Recent progress in homogeneous immunosensors based on fluorescence or bioluminescence using antibody engineering

A triple read-out visible biosensing platform based on multifunctional nanozyme and bipolar electrode for multi-mode detection and imaging of CEA

In this paper, a proposal of closed bipolar electrode (BPE) and nanozyme based multi-mode biosensing platform is first presented. As a novel integrated chip, multi-mode-BPE (MMBPE) combines enzyme-linked immunoassay (ELISA), electrochemiluminescence (ECL), ECL imaging and light emitting diode (LED) imaging, enabling highly sensitive triple read-out visible detection of cancer embryonic antigen (CEA). The ECL probe Ab2@Au@Co3O4/CoFe2O4 hollow nanocubes (HNCs) with excellent peroxidase (POD) activity is introduced into the BPE cathode through immune adsorption. The Au@Co3O4/CoFe2O4 HNCs can increase the rate of hydrogen peroxide oxidation of TMB, thus promoting the reaction, and can be used for ELISA detection of CEA at different concentrations. The modification of the BPE sensing interface and reporting interface involved the introduction of the luminescent reagent Ru(bpy)32+ to the BPE anode. The decomposition rate of H2O2 increased under the catalytic action of Au@Co3O4/CoFe2O4 HNCs nanozyme, leading to an accelerated electron transfer rate in the MMBPE system and an enhanced ECL signal from Ru(bpy)32+. The LED imaging technology further provides a convenient and visible approach for CEA imaging in which no additional chemicals are needed. The integration of nanoenzymes as the catalytic core in MMBPE system provides impetus, while the combination of nanozymes with BPE expands the application of nanoenzymes in the field of biological analysis. The integration of intelligent chips with multiple modes of detection shows portable, miniaturized, and integrated excellent properties which meets the requirements of modern detection devices and thus offers a flexible approach for determination of nucleic acids, proteins, and cells.

Aptamer-enhanced particle aggregation inhibition assay for simple homogeneous protein detection using DNA aptamer and thermo-responsive magnetic nanoparticles

A simple and sensitive homogeneous protein detection system is required for the early detection of biomarkers. Thermo-responsive magnetic particles (TM) have already been developed to achieve easy bound/free separation at the homogeneous protein detection system, but they are still limited owing to the requirement of secondary antibodies and negatively charged polymers, and it is challenging to control the TM aggregation behavior because of the size of the TM. Therefore, at new method to control TM aggregation behavior that is simple, easy, and highly sensitive is required. In this study, we developed a DNA aptamer-based TM assay as a simple protein detection system without additional secondary molecular recognition elements or negatively charged polymer. In the first attempt, a DNA aptamer was modified on the TM surface, and its aggregation behavior was monitored depending on the target molecule concentration. The TM aggregation rate during the heating process decreased depending on the amount of the DNA aptamer and increased depending on the target protein level. This suggests that the DNA aptamer prevented TM aggregation owing to its negative charge and achieved target protein detection owing to the cancellation of repulsion. Capturable aptamers were used in the TM assay to improve the sensitivity and limit of detection. The designed Capture DNA was modified on the TM surface, and the aptamer was captured in the presence of the target protein through a conformational change. Eventually, Capturable aptamer-based TM assay achieved a sub-nanomolar limit of detection and higher sensitivity than that of our initial investigation. Through this study and the ease of the DNA aptamer design, it was shown that the DNA aptamer-modified TM assay enabled the development of a simple and sensitive homogeneous protein detection system.

Special Issue "Immunoanalytical and Bioinformatics Methods in Immunology Research"

To effectively control and prevent diseases on a global scale, it is essential to employ precise, sensitive, selective, and rapid immunoanalytical methods [...].

Quenchbodies That Enable One-Pot Detection of Antigens: A Structural Perspective

Quenchbody (Q-body) is a unique, reagentless, fluorescent antibody whose fluorescent intensity increases in an antigen-concentration-dependent manner. Q-body-based homogeneous immunoassay is superior to conventional immunoassays as it does not require multiple immobilization, reaction, and washing steps. In fact, simply mixing the Q-body and the sample containing the antigen enables the detection of the target antigen. To date, various Q-bodies have been developed to detect biomarkers of interest, including haptens, peptides, proteins, and cells. This review sought to describe the principle of Q-body-based immunoassay and the use of Q-body for various immunoassays. In particular, the Q-bodies were classified from a structural perspective to provide useful information for designing Q-bodies with an appropriate objective.

Generation of a Recombinant scFv against Deoxycholic Acid and Its Conversion to a Quenchbody for One-Step Immunoassay

Development of a rapid detection method for deoxycholic acid (DCA) is crucial for its diagnosis in the early stages of inflammation and cancer. In this study, we expressed a soluble recombinant anti-DCA single-chain variable fragment (scFv) in Escherichia coli. To convert scFv into a Quenchbody (Q-body), we labeled scFv using commercially available maleimide-linked fluorophores. The TAMRA-C5-maleimide-conjugated Q-body showed the highest response within a few minutes of DCA addition, indicating its applicability as a wash-free immunoassay probe for onsite DCA detection.