Fungal spore adhesion on glycidoxypropyltrimethoxy silane modified silica nanoparticle surfaces as revealed by single cell force spectroscopy.

Thin film coatings prepared from commercially available glycidoxypropyltrimethoxysilane (GPS) modified silica nanoparticles (SiNPs) (Bindzil® CC301 and Bindzil® CC302) have previously shown excellent antifouling performance against a broad range of microbes [Molino et al., "Hydration layer structure of biofouling-resistant nanoparticles," ACS Nano 12, 11610 (2018)]. In this work, single cell force spectroscopy (SCFS) was used to measure the biological interactions between Epicoccum nigrum fungal spores and the same silica nanoparticle-based surfaces used in the aforementioned study, including a: glass coverslip, unmodified SiNP coatings, and both low (Bindzil® CC301) and high density (CC302) GPS functionalized SiNP coatings as a function of NaCl concentration. From the SCFS curves, the spore adhesion to the surface was greatest on the glass coverslip (20-80 nN) followed by the unmodified SiNP (3-5 nN) across all salt concentrations. Upon approach to both surfaces, the spores showed a long-range attraction generally with a profile characteristic of biointeractions and likely those of the outer cell wall structures or biological constituents. The attractive force allowed the spores to initially adhere to the surface and was found to be linearly proportional to the spore adhesion. In comparison, both high and low density GPS-SINP significantly reduced the spore adhesion (0.5-0.9 nN). In addition, the spore adhesion on high density GPS-SiNP occurred in only 14%-27% of SCFS curves (40%-48% for low density GPS-SiNP) compared to 83%-97% for the unmodified SiNP, indicating that in most cases the GPS functionalization completely prevented spore adhesion. The GPS-SiNP surfaces conversely showed a long-range electrostatic repulsion at low 1mM NaCl that was replaced by short-range repulsion at the higher salt concentrations. From the findings, it is proposed that the attractive force is a critical step in initial adhesion processes of the spore. The effective antifouling properties of the GPS are attributed to the ability to negate the attractive forces, either through electrostatic repulsion in low salt conditions and primarily from short-range repulsion correlating to the previously reported combined steric-hydration effect of the GPS functionalization on SiNP coatings.