Towards a catheter-based impedimetric sensor for the assessment of intestinal histamine levels in IBS patients

In this work, we report on the development of a catheter-based sensor designed for measuring the concentration of histamine in the human duodenum. Certain gut disorders, such as the irritable bowel syndrome (IBS), are associated with elevated levels of intestinal histamine due to chronic immune activation. As it is still impossible to determine histamine concentrations in vivo, a nasointestinal catheter with histamine-sensing capabilities has the potential to become a valuable diagnostic instrument. Regarding the sensing principle, we selected impedance spectroscopy using voltages that are compatible with intra-body applications with molecularly imprinted polymers (MIPs) as recognition elements. MIPs are synthetic receptors that offer the advantages of robustness, high specificity and selectivity for histamine as a target. In this specific case, the MIPs were synthesized from acryclic acid monomers, which guarantees a uniform binding capacity within the pH range of intestinal fluid. We have validated the catheter sensor on human intestinal liquids spiked with histamine in a testing setup that mimics the environment inside the duodenum. The dose-response curves show an analytical range between 5 and 200 nM of histamine, corresponding to physiologically normal conditions while higher concentrations correlate with disease. The key output signal of the sensor is the resistive component of the MIP-functionalized titanium electrodes as derived from the equivalent-circuit modelling of full-range impedance spectra. Future applications could be catheters tailored to cardiovascular, urological, gastrointestinal, and neurovascular applications. This, in combination with the versatility of the MIPs, will make this sensor platform a versatile diagnostic tool.