Impedimetric detection of histamine in bowel fluids using synthetic receptors with pH-optimized binding characteristics.

Histamine is a biogenic amine that is indispensable in the efficient functioning of various physiological systems. In previous work, a molecularly imprinted polymer (MIP) based sensor platform with impedimetric read-out was presented which could rapidly and at low cost determine histamine concentrations in buffer solutions within pH 7-9. For diagnostic applications, histamine should be detectable in a wider pH range as it mostly occurs in mildly acidic environments. To understand this pH-dependent response of the MIP sensor, we propose a statistical binding analysis model. Within this model, we predict the theoretical performance of MIP based on acrylic acid in the required pH range and verify these results experimentally by UV-vis spectroscopy, microgravimetry, and impedance spectroscopy. Using impedimetric read-out, specific and selective detection of histamine in the physiologically relevant nanomolar concentration range is possible in neutral and mildly acidic phosphate buffer. Finally, this sensor platform was used to analyze the histamine concentration of mildly acidic bowel fluid samples of several test persons. We show that this sensor provides reliable data in the relevant concentration regime, which was validated independently by enzyme-linked immuno sorbent assay (ELISA) tests.