Surface charge mapping by AC-KFM in water

In this project, we aim to develop a novel method to detect and investigate electrical charges on the surface of biological tissues on the microscopic scale. Such charges are highly significant in many biological processes and govern the properties of a multitude of biomolecular structures such as protein fibrils. There is a long-standing hypothesis that surface charges on protein fibrils are altered when they are exposed to sugars for prolonged periods of time. This is often occurring at an advanced age or in conditions such as diabetes. We will, therefore, first develop and test a new method for charge-mapping on the microscopic scale under natural conditions and, then, apply this method to test the charge alteration hypothesis and investigate possible influencing factors such as duration of sugar exposure, sugar concentration, temperature, etc. We expect to obtain enough fundamental data, which can then underpin future, medical research into the development of new drugs or treatments of many age- or sugar-related conditions, which are highly significant to a large part of the population in Western societies.

The project "Surface charge mapping by AC-KFM in water" demonstrates the measurement of electric surface charges distributions at the nanoscale in water within the field of Atomic Force Microscopy (AFM). Electrostatic charges of biomolecules such as protein fibers are of great significance in various biological phenomena. Mapping these charges at high spatial resolution at ambient conditions (air) is routinely done by conventional methods, such as Kelvin-probe Force Microscopy (KFM). However, its inability to operate in water - the natural environment of biological matter - states limitations to its scientific applicability and usefulness. AC-KFM bypasses the drawbacks of standard KFM by a novel AFM cantilever excitation mechanism. Its dc-bias free operation permits its use in polar liquids (i.e. water) and thus the investigation of biomolecules in their natural environent, which is of great scientific value. Major parts of the project dealt with the evalution of the AC-KFM principle and formation of possible limitations in its use for the investigation of samples in polar ionic liquids. Several derivatives of AC-KFM are developed, to enable quantitative surface charge measurements of nanoscale objects at physiologically relevant ionic concentrations. To this end, the surface charge distribution of collagen fibrils (the most abundant protein in mammals) could succesfully be mapped in aqueous environment. Furthermore, investigations on the pH-dependent charge of various thiols (termianted with carboxy-, methyl-, amino-groups) and charge injection/dissipation of a thin poly-(methyl metacrylate) (PMMA) surface demonstrate its useful application to a wide spectrum of scientifically intriguing phenomena. With the gained knowledge within this project, many use-cases in biology or related fields, such as the glycation of collagen fibrils or histone acetylation are conceivable.