Development of a Novel Q-body Using an In Vivo Site-Specific Unnatural Amino Acid Incorporation System

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 Q-bead against bone Gla protein with simplified preparation steps

Quenchbody (Q-body)-based immunoassays enable the detection of antigen within a few minutes with high sensitivity and specificity, thereby revealing their applicability as biosensors for quantifying several biomolecules of interest; however, while producing a Q-body, it is necessary to eliminate the unconjugated dye after labeling to separate the Q-body from the capturing bead and to change the buffer using ultrafiltration, which is time-consuming and leads to yield reduction. In this study, we generated a recombinant single chain variable fragment against bone Gla protein as a model antibody. We labeled the antibody with a dye to generate a Q-body and subsequently added affinity beads to the Q-body mixture. After washing, we directly added antigen without extracting the Q-body from the bead and then measured the fluorescence intensity. As a result, the antigen-dependent fluorescence response was obtained from "Q-bead", which was almost the same as that of the Q-body generated according to the conventional method. The Q-bead was generated within only 2.5 h, thus requiring an hour and two steps less than those required for the generation of the traditional Q-body. No expensive Flag peptide was required to recover the total antibody from beads. Moreover, the ultra-filtration step was eliminated in this bead-based method, leading to improved convenience and cost- and time-saving attributes. The Q-bead-based assay can be used as a standard protocol for simple and rapid analysis of antibody-based molecular detection.

Recent Advances in Quenchbody, a Fluorescent Immunosensor

The detection of viruses, disease biomarkers, physiologically active substances, drugs, and chemicals is of great significance in many areas of our lives. Immunodetection technology is based on the specificity and affinity of antigen–antibody reactions. Compared with other analytical methods such as liquid chromatography coupled with mass spectrometry, which requires a large and expensive instrument, immunodetection has the advantages of simplicity and good selectivity and is thus widely used in disease diagnosis and food/environmental monitoring. Quenchbody (Q-body), a new type of fluorescent immunosensor, is an antibody fragment labeled with fluorescent dyes. When the Q-body binds to its antigen, the fluorescence intensity increases. The detection of antigens by changes in fluorescence intensity is simple, easy to operate, and highly sensitive. This review comprehensively discusses the principle, construction, application, and current progress related to Q-bodies.