13 research outputs found
Nanobody-Based Immunosensor Detection Enhanced by Photocatalytic-Electrochemical Redox Cycling
peer reviewedDetection of antigenic biomarkers present in trace
amounts is of crucial importance for medical diagnosis. A parasitic
disease, human toxocariasis, lacks an adequate diagnostic method
despite its worldwide occurrence. The currently used serology tests
may stay positive even years after a possibly unnoticed infection,
whereas the direct detection of a re-infection or a still active infection
remains a diagnostic challenge due to the low concentration of
circulating parasitic antigens. We report a time-efficient sandwich
immunosensor using small recombinant single-domain antibodies
(nanobodies) derived from camelid heavy-chain antibodies specific
to Toxocara canis antigens. An enhanced sensitivity to pg/mL levels is achieved by using a redox cycle consisting of a photocatalytic oxidation and electrochemical reduction steps. The photocatalytic oxidation is achieved by a photosensitizer generating singlet oxygen (1O2) that, in turn, readily reacts with p-nitrophenol enzymatically produced under alkaline conditions. The photooxidation produces benzoquinone that is electrochemically reduced to hydroquinone, generating an amperometric response. The light-driven process could be easily separated from the background, thus making amperometric detection more reliable. The proposed method for detection of the toxocariasis antigen marker shows superior performances compared to other detection schemes with the same nanobodies and outperforms by at least two orders of magnitude the assays based on regular antibodies, thus suggesting new opportunities for electrochemical immunoassays of challenging low levels of antigens