**Thomas Verdier 1,***∗***, Alexandra Bertron 1, Benjamin Erable <sup>2</sup> and Christine Roques <sup>2</sup>**


Received: 2 February 2018; Accepted: 4 March 2018; Published: 5 March 2018

**Abstract:** Use of photocatalytic paint-like coatings may be a way to protect building materials from microbial colonization. Numerous studies have shown the antimicrobial efficiency of TiO2 photocatalysis on various microorganisms. However, few have focused on easy-to-apply solutions and on photocatalysis under low irradiance. This paper focuses on (a) the antibacterial properties of a semi-transparent coating formulated using TiO2 particles and (b) the microscopic investigations of bacterial biofilm development on TiO2-coated building materials under accelerated growth conditions. Results showed significant antibacterial activity after few hours of testing. The efficiency seemed limited by the confinement of the TiO2 particles inside the coating binder. However, a pre-irradiation with UV light can improve efficiency. In addition, a significant effect against the formation of a bacterial biofilm was also observed. The epifluorescence approach, in which fluorescence is produced by reflect rather than transmitted light, could be applied in further studies of microbial growth on coatings and building materials.

**Keywords:** coating; building materials; bacterial growth; proliferation; biofilm; antibacterial
