Abstract
An alternative label-free electrochemical immunosensor for the rapid detection of Leishmania braziliensis was developed by immobilizing a peptide-based probe of the promastigote surface antigen (PSA-38S) onto electrospun polyamide-6 (PA6)/chitosan nanofibers. An increase in chitosan content in the spinning solution leads to a decrease in the diameter of the formed fibers, whereas the differential scanning calorimetry (DSC) and X-ray diffraction (XRD) data showed a decrease in crystallinity upon increasing the chitosan content in the formulation. In addition, the incorporation of chitosan into the PA6 nanofibers tends to decrease the resistance to the charge-transfer process at the electrode surface. A 40 wt % chitosan content was used for immobilization of the peptide antigen, which was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The detection was performed by measuring the relative change in impedance before and after the anti-Leishmania braziliensis reaction by EIS. Under the optimized conditions, the relative change in impedance was proportional to the logarithmic value of PSA concentrations in the range of 2.5 to 10 pg·mL–1(r2 = 0.9946) with a detection limit of 0.2 pg·mL–1, which was slightly lower than that of the enzyme-linked immunosorbent assay. Additionally, the sensor was tested against two nonspecific antibodies (T. cruzi and β-actin), whereas multivariate analysis using unsupervised pattern recognition through principal component analysis was successfully applied to identification of the pattern relative to each antibody. Finally, the optimized electrochemical immunoassay can be a favorable approach for Leishmania detection tests, as it is able to differentiate negative and positive visceral leishmaniasis human serum samples.
