Searching for a common origin of heat-transfer effects in bio- and chemosensors: A study on thiols as a model system

The heat-transfer method HTM is a bioanalytical technique in which a temperature gradient is established between the backside of a functionalized chip and the supernatant liquid. By combining the measured temperature difference with the power used to generate this gradient, one obtains the thermal resistance R-th. This parameter responds sensitively and in a concentration-dependent way to the binding of bioparticles to receptors as well as to phase transitions in coatings on the chip. The size of particles that can be detected with HTM spans from lowmolecular weight molecules over proteins and DNA fragments up to cells with diameters at the micron scale. In this work, we explore the question whether and why small ligands adsorption can result still in quantifiable R-th changes and whether there is a common origin of the generally observed R-th increase upon binding a wide variety of cells and biomolecules. The data obtained on thiols with different capping groups suggest that the correspondence of molecular vibration frequencies of the ligands and the liquid is decisive for an efficient or impeded heat transfer and hence for the macroscopically determined R-th parameter.