Investigation of the Photoinduced Antimicrobial Properties of N-Doped TiO\({}_{2}\) Nanoparticles under Visible-Light Irradiation on _Salmonella_ Typhimurium Biofilm  
[PERSON]  
1 Laboratory of General Chemistry, School of Chemical Engineering, National Technical University of Athens (NTUA), 15780 Athens, Greece 1  
[PERSON]  
2 Laboratory of Microbiology and Biotechnology of Foods, Department of Food Science and Human Nutrition, Faculty of Foods, Biotechnology and Development, Agricultural University of Athens (AUA), 11855 Athens, Greece; [EMAIL_ADDRESS] (N.C.); [EMAIL_ADDRESS] (G.-J.N.) 2  
[PERSON]  
2 Laboratory of Microbiology and Biotechnology of Foods, Department of Food Science and Human Nutrition, Faculty of Foods, Biotechnology and Development, Agricultural University of Athens (AUA), 11855 Athens, Greece; [EMAIL_ADDRESS] (N.C.); [EMAIL_ADDRESS] (G.-J.N.) 2  
[PERSON]  
1 Laboratory of General Chemistry, School of Chemical Engineering, National Technical University of Athens (NTUA), 15780 Athens, Greece 1  
Footnote 12  
properties [6; 7]. It is found in three crystalline phases that have differences in stability and catalytic performance. Brookite is orthorhombic and more unstable, whereas rutile and anatase are tetragonal and are more effective catalytically [8]. A TiO\({}_{2}\) catalyst can exhibit different physicochemical properties, depending on the shape or size of the NPs and the dominant crystalline phase present [9]. The energy gap between the valence and conduction bands (Eg) is -3.2 eV for anatase, which makes it easy to sensitize via ultraviolet (UV) irradiation and, consequently, imparts it with self-cleaning and antibacterial behavior [10]. In order to extend these features under visible-light irradiation, TiO\({}_{2}\) can be chemically modified or doped with non-metal or metal elements [11; 12]. Regarding the antimicrobial properties of doped TiO\({}_{2}\), there has been extensive scientific research testing TiO\({}_{2}\) doped with metals such as Cu [13], Zn, Ag [14], Fe [15], and Ni [16]. However, it has been observed that metal doping leads to biological and environmental issues due to their toxicity and low biocompatibility [17]. Consequently, a more eco-friendly choice needs to be found [18]. A low-cytotoxicity solution is the syncrisent of TiO\({}_{2}\) with carbon (quantum dots) [19] or other non-metal elements. The non-metal doping approach, especially with elemental N, is an effective, low-cost, and environmentally safe way to deal with bacterial spreading. Another biocompatible approach is the combination of TiO\({}_{2}\) with organic polymers such as chitosan [20]. The antimicrobial properties of N-TiO\({}_{2}\) have always attracted the interest of the scientific community due to its easy use, testing, and low cost [21]. A recent study focused on the investigation of nitrogen and bismuth co-doping for implant-biofilm-related diseases [22]. The form of N-TiO\({}_{2}\) tested is either a film [23] or a powder [24]. However, most of these studies tested the antimicrobial properties of TiO\({}_{2}\) on single-standing bacteria and not on biofilms, which are the natural form of surface arrangement for microbes in nature [25; 26]. Salmonella is recognized as one of the most significant enteric foodborne bacterial pathogens. Salmonella is a Gram-negative bacterium that can form biofilms on many biotic (e.g., human or animal tissues) and abiotic (e.g., glass or stainless steel) surfaces [27; 28]. In recent years, the resistance of pathogens to biocides and other environmental stresses--especially when they are embedded in biofilm structures--has led to the search for and development of novel antimicrobial strategies capable of displaying both high efficiency and high safety [29]. Different parameters affecting the biofilm formation--such as temperature, pH, and quorum-sensing compounds--have been widely explored in previous studies; thus, the optimal conditions for Salmonella biofilm formation are well known and can be selected for testing [30; 31].