Abstract: Polydopamine (PDA) is a widely employed anchoring layer across various applications. Despite its straightforward preparation, PDA's utility is restricted due to its notable chemical and topological variability. Understanding the formation process and physicochemical characteristics of the formed confluent layers, as well as the present adherent nanoaggregates [1 – 3], on a nanoscale level is essential for expanding the applications of PDA. Through the employment of Scanning Near-Field Infrared Microscopy (SNIM) [2] and nano-FTIR spectroscopy [1], we examined PDA layers on three distinct substrates (Si/SiO2, nitrogendoped TiO2, and Au substrates) at different times of deposition (ToD). The topography was compared with SNIM images obtained at different wavenumbers corresponding to the intermediates and the polymerization products [2].
Moreover, we identified a strong correlation between nano-FTIR and macroscopic FTIR spectra [1, 3], reflecting alterations in the relative abundance of PDA and polymerization intermediates. Furthermore, employing principal component analysis (PCA) allowed for additional insights from loadings spectral curves and data distribution in score plots. Notably, the spectral variability is higher for the ultrathin surface confluent layers than for the nanoaggregates. While nanoaggregate spectra displayed no discernible dependence on ToD or substrate material, layer spectra were significantly influenced by increasing ToD, showcasing the growth of the layers. Additionally, at the lowest ToD, spectral clustering based on substrate material indicated an initial influence of substrate material on PDA's physicochemical properties, which gradually diminished with increasing ToD as the influence of substrate material lessened.
Acknowledgments
This study was financially supported by the Czech Science Foundation (Project No. 20 08679S).