Fluorescent Nanoprobes to Specifically Identify the Deposition of Circulating Cathodic Antigen in Mice Tissue from Experimental Schistosomiasis

Schistosomiasis is a neglected disease still considered a serious public health problem. The circulating cathodic antigen (CCA) is an important schistosomiasis biomarker that can accumulate in the organs due to the infection. Quantum dots (QDs) are versatile fluorescent nanoparticles that hold the potential in boosting the identification of antigens. Hence, in this study, a fluorescent nanoprobe based on the covalent conjugation of QDs to anti-CCA antibodies was developed and applied to locate and quantitatively evaluate the CCA profile in kidney and liver tissue cuts – of pre-patent, acute, and beginning of the chronic phases – obtained from mice infected with schistosomiasis. QDs and the conjugate were optically characterized by UV-Vis absorption and emission spectroscopies. The conjugation was analyzed by the fluorescent microplate assay (FMA) and Zeta potential () measurements. The distribution of the CCA in tissue cuts was observed by fluorescence microscopy and an evaluation of the CCA amount was also conducted. The FMA and  indicated that an effective conjugation was achieved, which was also supported by the lack of labeling in non-infected tissues after incubation with the conjugate since they do not present CCA. The infected liver and kidney tissues were highly stained by the conjugate from the 60th day (acute phase), exhibiting high CCA accumulation in the tissue. According to fluorescence intensity quantification on the microscopy images, the CCA amount in the analyzed tissues increased in the following order of days after infection: 30 < 60 = 120. Therefore, the conjugate showed to be an interesting, sensitive, and versatile fluorescent nanoprobe to specifically identify the CCA profile in tissues or other biological samples, opening new perspectives to the schistosomiasis comprehension and diagnosis.