Electrical modes of Atomic Force Microscopy (AFM) allow the high-resolution mapping of surface charges on a sample with nanometer precision. A particular measurement challenge is to perform such modes on biological samples (tissue extracts, biomolecules, biomembranes, etc). To this end, the project aims to investigate different preparation and measurement approaches and a specific goal is to determine alterations of surface charge of biological fibers caused by the reaction with sugar, which has important implications in medicine and cell biology.