Apostolos Vagias: Complex diffusion dynamics of various tracers in polymer networks by Fluorescence Correlation Spectroscopy

Fluorescence Correlation Spectroscopy (FCS), a well-established single molecule characterization technique for studying diffusion and reaction in biological systems with broad temporal resolution [1,2], has been recently implemented in various polymer systems as well [3]. In this talk, I shall be presenting how FCS can be successfully utilized to probe the translational diffusion and partitioning of various nanometer-sized tracers in grafted poly-N-isopropylacrylamide (PNiPAAm) hydrogel layers. Due to their thermoresponsivity in water at temperatures close to the one of the human body, such gels have been typically utilized as basis materials for biosensor applications [4]. Information on the “gel structure-tracer dynamics” interplay is critical in order to optimize the design of theranostic devices. The first part of my presentation focuses on three different molecular tracers with varying affinity to the polymer network [5], while in the second part of my talk I will discuss findings on the diffusion dynamics of a fluorescently labeled antibody [6], Immunoglobulin G (IgG), in identical gels. The common multivariable investigation for either examined case involved assessing the impact on tracer diffusion dynamics stemming from variation in/of external stimuli, including solvency conditions, polymer volume fraction, pH and/or ionic strength, as well as hydrogel crosslink density. There is a distinct signature between tracer dynamics and given pre-selected external stimuli. Conditions under which a predictive relation (master curve) between the polymer volume fraction and diffusion slowdown of various tracers can be obtained shall be demonstrated. The investigated systems pertain tunable complexity, where several coexisting tracer-matrix interactions are found to bias tracer dynamics but both tracer partitioning and dynamics can be engineered. The presented findings suggest a model approach to explore the synergy between crowding and thermodynamics with respect to the controlled protein transport in PNiPAAm-based hydrogels.