Unraveling Dynamical and Light Effects on Functionalized Titanium Dioxide Nanoparticles for Bioconjugation

Functionalizing nanoparticles (NPs) with biological molecules is apromising modern strategy in bionanotechnology to build up smart bioinorganicdevices for medical applications. Bifunctional linkers provide an interesting andductile bioconjugation approach especially because they behave not only asanchoring and tethering agents but also as spacers between the NP and thebiomolecules, which helps in maintaining their 3D structural and functionalproperties. In this work, by means of a wide set of density functional theory(DFT) electronic structure calculations and density functional tight binding(DFTB) molecular dynamics simulations, we provide an all-round investigation ofthe functionalization of realistic curved TiO2 NPs (2−3 nm size with∼800atoms) with a catechol derivative, such as dopamine and DOPAC. We span fromsingle-molecule adsorption to the full coverage regime. For the low coverage, weachieve a detailed description of the mechanisms of molecular adsorption, of theinterfacial electronic charge-transfer effects, and of the processes following visiblelight irradiation (exciton formation, trapping, charge carrier diffusion, or recombination). We then consider a growing molecularlayer on the NP and analyze the self-assembling mechanism and the effects on the electronic properties of the complex. Finally,for the maximum coverage (46 molecules per NP) we perform molecular dynamics runs at 300 K to compare the molecularconfiguration and electronic properties of the NP/linker complex interface before and after thermal treatment to better accountfor the competition between molecule/surface and molecule/molecule interactions. The use of curved NP surfaces combinedwith dopamine, with respect to aflat one and DOPAC, respectively, is found to be more effective for bioconjugation