Authors:Susan Moreno-Molek, Salaam Saleh, Druthiman Reddy Mantheni, Manik Pavan Kumar Maheswaram, Tobili Sam-Yellowe, and Alan T. Riga
Cytokines and soluble cytokine receptors serve as important protein biomarkers for chronic and infectious disease diagnosis. The development of biosensors capable of detecting cytokines or their soluble receptors in patient bodily fluids is a growing area of research. In an ongoing series of studies to understand the thermal analytical behavior of cytokines and their soluble receptors, dielectric thermal analysis (DETA) and thermogravimetry (TG) were used in investigations to determine if differentiations based on dielectric properties (e.g., conductivity) of the proteins could be identified. Permittivity (∊′) and dielectric loss factor (∊″) measurements were performed over a frequency range of 0.1–300,000 Hz. Up to 20 min, water associated with the samples was conductive, interacting with the proteins and affecting the temperature-dependent relaxation spectra of proteins. A trend analysis revealed differences between surface charge at 0.1 Hz and bulk charge at 300,000 Hz. In addition, the greatest change detected among proteins was due to the conductivity (dielectric loss factor). Beyond a 20 min drying time, the observed conductivity was due to intrinsic properties of the proteins with limited dependence on frequency. A 100% water loss was obtained for samples within 20–30 min by TG. Sample drying by TG could serve as a preparatory step in drying protein samples for further DETA and DSC analysis.