Kinetic Investigation of Protein Adsorption on Porous Surfaces

Abstract

This work aims to investigate the adsorption of bovine serum albumin (BSA) on different surfaces, namely silicon, germanium, and porous titanium dioxide (TiO2), in order to understand the mechanisms governing protein–surface interactions and to evaluate the effect of porous structures on adsorption behavior. In the theoretical part, the fundamental concepts related to proteins, porous surfaces, and the adsorption phenomenon were reviewed, with particular emphasis on titanium dioxide because of its unique physical, chemical, and biological properties. Fourier Transform Infrared Spectroscopy in Attenuated Total Reflection mode (FTIR-ATR) was also presented as an effective technique for monitoring the adsorption process and analyzing the structural changes occurring in proteins during their interaction with solid surfaces. In addition, classical kinetic models commonly used to describe adsorption kinetics were examined, including the Pseudo-First-Order (PFO), Pseudo-Second-Order (PSO), and Intraparticle Diffusion models. In the experimental part, porous titanium dioxide thin films were prepared on germanium substrates using the drop-casting technique. Adsorption experiments of BSA were then carried out on silicon, germanium, and porous titanium dioxide surfaces. The obtained results were analyzed using both classical kinetic models and a proposed Three-State Kinetic Model developed to describe the complex and multistep nature of protein adsorption. The results showed that the adsorption process is strongly influenced by the nature of the surface and that classical kinetic models are not sufficient to accurately describe all stages of the process. In contrast, the Three-State Model provided the best agreement with the experimental data for all investigated surfaces, confirming that protein adsorption proceeds through several successive stages involving molecular transport in the bulk solution, surface adsorption, molecular rearrangement, and diffusion into the pores. The study also demonstrated that porous titanium dioxide exhibits a higher adsorption capacity than non-porous surfaces such as silicon and germanium. This behavior is attributed to the contribution of the internal pores, which provide additional sites for protein retention and facilitate diffusion within the porous structure. Overall, the proposed model offers a more accurate and realistic description of protein adsorption kinetics and represents an important step toward a better understanding of biological interactions at solid surfaces, thereby contributing to the development of more effective medical and technological applications.