**1. Introduction**

Biofilms are defined as communities of microorganisms that are developed on material surfaces. Prevention of microbial biofilm formation over the surface of materials is a technological imperative in health care. Many bacteria capable of forming biofilms on abiotic surfaces are menacing problems in medical and industrial systems. The biofilm forming ability of the opportunistic human pathogens *Staphylococcus aureus* and *Escherichia coli*, is a crucial step for sustenance and growth in above said environments [1]. Biofilms are a major source of biofouling in industrial water systems, and biofilm based industrial slimes also pose major problems for various industrial processes. Biofilm forming microbial cells attached to any surface in a moist environment can survive and proliferate. Pathogenic and resilient biofilms are difficult to eradicate with conventional disinfectants [2]. The interest in inorganic disinfectants such as metal oxide nanoparticles (NPs) is increasing. In the last decade, many studies describing the photocatalytic inactivation of bacteria using doped and undoped TiO2 coated on different substrates have been reported, including silver doped TiO2 [3–6]. A majority of these articles is focused on powder materials and thin films of TiO2 or doped TiO2. Unfortunately, most bare TiO2 coated films lose their efficiency of photocatalysis due to mass transfer [7,8]. However, only a fraction of studies deal with stemming of mass transfer of immobilized TiO2 or doped-TiO2 photocatalyst films. The most promising approach to overcome this disadvantage is by immobilization of TiO2 in the porous polymer matrix such as epoxides, the most important classes of compounds used in the coating industry. These epoxy composites provide thin-layer durable coatings having mechanical strength and good adhesion to a variety of substrates [9]. Antimicrobial epoxy based surface coatings of walls and floors can fight the nosocomial menace [10] in hospitals.

The antibacterial function of a TiO2 photocatalyst is markedly enhanced even with weak UV light, such as fluorescent lamps and with the aid of either silver or copper, which is harmless to the human body [11]. TiO2 nano-fillers improve mechanical properties like crack resistance, surface characteristics and can also contribute to the photostability of the host material. The photostability and photocatalytic activity of epoxy/nano-TiO2 coatings under UV irradiation has been reported by Calza *et al.* [12]. While doping TiO2 with silver can synergistically enhance photobactericidal acitivity of TiO2, a considerable improvement in mechanical properties can also be achieved by introducing very low amount of nano-fillers into resin system [13]. In addition, photo-stability of epoxy resin can be improved by the presence of nano-TiO2 by its UV absorption properties [14]. Thus, modification of polymers with TiO2 and subsequent coupling with Ag<sup>+</sup> /Ag NP enhance the photocatalytic and antimicrobial property of the material. Nanoparticles are generally introduced into epoxy matrix using various approaches like, *in situ* synthesis by reacting the precursors or physical dispersion of pretreated nano-fillers by mechanical stirring and subsequently processed by ultrasonication [15,16]. Successful dispersion of nanoparticles within the polymer matrix is determined by factors like particle size, particle modifications, specific surface area, particle load and the particle morphology.

Broadly there are two methods to impregnate a biocidal agent in order to achieve antibacterial polymeric materials. That is, either by introduction of aleaching biocidal agent into the polymer to form a composite or by covalent functionalization of the polymer with the pendent groups that confer antimicrobial activity. Such materials have displayed potent and broad spectrum antimicrobial activity [17]. The polycaprolactone-titania nanocomposites have been shown to decrease surface colonization of *Escherichia coli* and *Staphylococcus aureus* [18]. Similarly, introduction of (+)usnic acid, a natural antimicrobial agent into modified polyurethane prevented biofilm formation on the polymer surface by *Staphylococcus aureus* and *Pseudomonas aeruginosa* [19]. The poly(ethylene terephthalate) (PET) was surface functionalized with pyridinium groups possessing antibacterial properties, as shown by their effect on *Escherichia coli* [20]. Highly potent antibacterial activity toward both Gram-positive and Gram-negative bacteria was demonstrated by composites consisting of a cationic polymer matrix and embedded silver bromide nanoparticles [21].

There are very few empirical reports that quantitatively assess inhibition of biofilm formation on polymer surfaces by employing indicator dyes (crystal violet/fluorescent dye). Crystal violet (hexamethyl pararosaniline chloride) is such a dye, which binds proportionately to the peptidogly and can be a component of bacterial cell walls. It has been used by Kwasny and Opperman [22] to evaluate the amount of biofilm formed by staining the thick peptidoglycan layer of Gram-positive bacteria, the thin peptidoglycan layer of Gram-negative bacteria. In this study, anti-biofilm activity of polymeric surfaces was measured by protocol adoption as described by Kwasny and Opperman with minor modifications. The optical density of destaining solution after washing crystal violet adsorbed onto biofilm was measured with a multi-well plate spectrophotometer (using a 96 well titer plate). The color intensity of destaining solution after washing has been shown to be proportional to the quantity of biofilm formed. This method makes more practical high-throughput screening of polymer surfaces for their antibiofilm activity.

Metallic silver/TiO2 and silver ion doped TiO2 system in the form of films, deposition and its antibacterial performance in visible/UV light have been reported frequently [23–25]. To the best of our knowledge, there have been limited reports on the synthesis of polymers loaded with silver doped titania, for durable photobactericidal coatings that is compatible with many substrates to fight biofilms. In this work, composite materials suitable for coating was obtained by the addition of Ag-TiO2 nanoparticles into epoxy resin system, with the aim to achieve "*in situ*" formation of silver species by photoreduction. The antibiofilm activity of this composite system is exhibited by the actions of photokilling and release of biocide (Ag+/Ag0 ) upon contact with aqueous environment.
