Label-Free Capacitive Biosensor for Detection of Cryptosporidium

Abstract

<i>Cryptosporidium</i>, an intestinal protozoan pathogen, is one of the leading causes of diarrhea in healthy adults and death in children. Detection of <i>Cryptosporidium</i> oocysts has become a high priority to prevent potential outbreaks. In this paper, a label-free interdigitated-based capacitive biosensor has been introduced for the detection of <i>Cryptosporidium</i> oocysts in water samples. Specific anti-<i>Cryptosporidium</i> monoclonal antibodies (IgG3) were covalently immobilized onto interdigitated gold electrodes as the capture probes, and bovine serum albumin was used to avoid non-specific adsorption. The immobilization of the antibodies was confirmed by measuring the change in the contact angle. The detection was achieved by measuring the relative change in the capacitive/dielectric properties due to the formation of <i>Cryptosporidium</i>-antibody complex. The biosensor has been tested for different concentrations of <i>Cryptosporidium</i>. The results show that the biosensor developed can accurately distinguish different numbers of captured cells and densities on the surface of the biosensor. The number of <i>Cryptosporidium</i> oocysts captured on the electrode surface was confirmed using a fluorescein isothiocyanate (FITC) immunofluorescence assay. The response from the developed biosensor has been mainly dependent on the concentration of <i>Cryptosporidium</i> under optimized conditions. The biosensor showed a linear detection range between 15 and 153 cells/mm² and a detection limit of 40 cells/mm². The label-free capacitive biosensor developed has a great potential for detecting <i>Cryptosporidium</i> in environmental water samples. Furthermore, under optimized conditions, this label-free biosensor can be extended for detection of other biomarkers for biomedical and environmental analyses.