Soft Probes for Bio-electrochemical Imaging

Abstract

The aim of bioimaging is to visualize properties and processes of living objects or biological samples and extracts image-related information for revealing important physical structures or map the distribution of specific biomolecules in tissues for clinical purposes. However, current bioimaging methods which mainly rely on optical detection methods can suffer from optical interferences and thus bias the imaging results. Bio-electrochemical imaging with micrometer resolution represents a promising alternative tool since electrochemical signals, e.g., faradaic currents, depend exclusively on the redox reactions occurring at the sample surface and a sensing probe. Scanning electrochemical microscopy (SECM) is a scanning probe technique that is composed of a microor nanoelectrode that can be positioned or scanned in close proximity to an interface. Faradaic current signals can be recorded due to the flux of redox active species between the sample and an amperometric SECM probe. SECM can be used to image the topography and reactivity of biological specimens for mapping localized biochemical activity. Although SECM has been applied to different biological systems, SECM studies of tissues are still under exploration. The reason is due to the shape and high roughness of such real samples and requires overcoming major drawbacks in conventional SECM instrumentation when scanning large, i.e., square centimeter sized, areas with irregular surface keeping a constant working distance. This thesis aims to develop various reliable SECM bioimaging techniques for the study of the antioxidant defense system of fruit peels, distribution of biomarkers and nanomaterials in thin and thick animal samples, as well as human melanoma. Particularly, the last is of major importance, because melanoma is the most lethal form of skin cancer striking thousands of people around the world. The survival rate depends on the stage of cancer when it is diagnosed. Therefore, reliable methodologies for early diagnosis and unequivocal identification of cancer stages are of high relevance. One of the well-known melanoma biomarkers is «tyrosinase» which is the key enzyme involved in the biosynthesis of melanin and fruit maturation. Different tyrosinase SECM detection strategies were developed for the analysis of the spatial distribution of tyrosinase in melanoma as well as in banana