Photocatalytic disinfection of Surfaces with Copper Doped TiO2 Nanotube Coatings Illuminated by Ceiling Mounted Fluorescent Light

High economic burden is associated with foodborne illnesses. Different disinfection methods are therefore employed in food processing industry; such as use of ultraviolet light or usage of surfaces with copper-containing alloys. However, all the disinfection methods currently in use have some shortcomings. Here we show that copper doped TiO2 nanotubes deposited on existing surfaces and illuminated with ceiling mounted fluorescent lights or additional low power light emitting diodes can be employed for an economical and permanent disinfection of surfaces. We deposited the nanotubes on various surfaces: polyethylene terephatlate, polystyrene, and aluminum oxide, where they could withstand repeated washings with neutral, alkaline or acidic medium. Here we show that the polymer surfaces coated with the nanotubes and innoculated with 107 bacteria, illuminated with ceiling mounted fluorescent lights retard the growth of Listeria Innocua by up to 99% in seven hours of exposure to the fluorescent lights, compared to a control surface. The disinfection properties of the surfaces depend mainly on the temperature difference of the surface and the dew point, where for maximum effectiveness of the photocatalytic effect the difference should be at least 2.5 degrees celsius. Usage of one dimensional nanomaterials, such as TiO2 nanotubes, offers a promising low cost alternative to current disinfection methods, since illumination of surfaces with common fluorescent lights is sufficient to photo-excite the nanotubes, which sequentially produce microbicidal hydroxyl radicals. Future use of such surfaces with antibacterial nano-coating and resulting sterilizing effect holds promise for such materials to be used in different environments or in better control of critical control points in food production as well as an improved biosecurity during the food manufacturing process.

methods currently in use have some shortcomings. Here we show that copper doped TiO2 23 nanotubes deposited on existing surfaces and illuminated with ceiling mounted fluorescent 24 lights or additional low power light emitting diodes can be employed for an economical and 25 permanent disinfection of surfaces. 26 We deposited the nanotubes on various surfaces: polyethylene terephatlate, polystyrene, 27 and aluminum oxide, where they could withstand repeated washings with neutral, alkaline isolates from poultry abattoir we identified the same serotype (classical 1/2a, molecular IIa) 67 with the exception of one isolate with a different serotype (4b, IVb), mainly found on the 68 surface, but some also in the air 7 .

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Many disinfectants were tested in the prevention of Listeria monocytogenes contamination, 70 however organic burdening and biofilm formation effectively inhibited disinfectants' 71 microbicidal activity 8,9 . Although biofilm formation is common for every environment where 72 microorganisms are close to the surface, its formation is even more problematic in the food 73 industry, where remains of foods in inaccessible places enable survival and the 74 multiplication of Listeria. It was speculated that specific properties of persistence of L. 75 monocytogenes, might be the reason for spreading of persistent strains of L. 76 monocytogenes across the surfaces of food-processing plants, but also by transferring 77 meat products between different plants 10,11 . In addition, some studies report about the 78 possibility of reduced L. monocytogenes susceptibility to some chemical disinfectants 12 .

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Permanent maintenance of hygiene in food processing industry is therefore of utmost 80 importance for the continuous reduction in the number of bacteria. For this reason, regular 81 cleaning and disinfection is mandatory, but it is often performed poorly and irregularly 82 specially when parts of the meat processing equipment are inaccessible 13 . Namely the 83 risk for food contamination arise mainly due to low hygiene of food premises and not from 84 previously contaminated animals as it was shown by Ojeniyi et al. 14 , and by our own work, 85 where we were unable to confirm the transfer of L monocytogenes from broiler farm to the 86 abattoir, since we couldn't prove a positive case of L monocytogenes on broiler farms 87 among the investigated animals 7 . One of the main reasons for spreading of the persistent 88 strains of L. monocytogenes might be its ability of enhanced adherence to surfaces in a 89 relatively short time 15,16 , therefore the continuous antibacterial function of food contact 90 surfaces should be implemented. One of such continuous disinfection methods, suitable 91 for disinfection of the air, liquids and surfaces is the use of ultraviolet light (UV), which is 92 being employed as one of the physical methods of decontamination in the food processing 93 industry 17 . Short-wave ultraviolet light (UVC, 254 nm) was shown to be effective against 94 wide spectrum of bacteria, viruses, protozoa, fungi, yeasts and algae, by altering cell DNA 95 17 . However, UVC has limited applicability in food industry since it can cause sunburn, skin 96 cancer, and eye damage under direct exposure. UVC lights can also produce ozone, 97 which can be harmful to human health, and finally materials exposed to UVC light for 98 longer period age faster, especially plastics and rubber, which break down under UVC 99 exposure. On the other hand, long-wave ultraviolet light (UVA, >320 nm) as a part of a 100 sunlight, not absorbed by the atmosphere ozone layer, thus reaching the earth's ground, 101 and is not harmful to human health, can still cause some oxidative damage, however has 102 much weaker effect on microorganisms than UVC 17 . Since UVA is normally present as a 103 small part of the fluorescent lighting spectrum, one could use ceiling mounted fluorescent 104 lights for permanent surface disinfection provided that the oxidative damage of UVA light 105 at a surface could be enhanced. This can be achieved by illuminating TiO2 deposited on a 106 surface by UVA light. Namely, illuminated TiO2 is known to produce reactive oxygen 107 species, such as hydroxyl or superoxide radicals, which can also be used for disinfection  Using TiO2 surface coatings one should therefore be able to maintain clean surfaces with 119 the use of UV light close to visible spectrum. 120 We have shown previously that Cu 2+ -doped TiO2 nanotubes (Cu-TiO2NTs) coated polymer   of the Cu 2+ was CuSO4·5H2O (Riedel de Haen)) using an ultrasonic bath (30 minutes) and 159 stirred at room temperature for 3 hours. By centrifugation the solid material was separated 160 from the solution, and (iv) finally isolated material was heated in air at 375 °C for 10 hours.

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The powder X-ray diffraction (XRD) pattern was obtained on a Bruker AXS D4 Endeavor 163 diffractometer using Cu K radiation (1.5406 Å; in the 2 range from 10 to 65°).  The amount of deposited material was estimated from EPR signal decrease when rinsing 206 the deposit of 150 L of 1 mg/mL applied to a 2.5  7.5=18.8 cm 2 surface. With EPR signal 207 being decreased to about 1/3, we estimated that the amount of deposited nanomaterial 208 was about 2 g/cm 2 .

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Antimicrobial Activity of nanotube coated PET surface in a meat processing plant 210 Four measurement points were selected in a poultry slaughterhouse with regards to 211 different air microclimate conditions (humidity, temperature, airflow) as well as intensity of 212 UV irradiation. PET slides were innoculated with 10 7 bacteria in 10 µL droplet and placed 213 either vertically or horizontally at different altitudes (0.5 or 2 m) and exposed for 7 hours.          Antimicrobial activity in presence of repeated daily contamination and washing 408 Next we repeatedly inoculated and washed PET surfaces with Listeria innocua daily, in 409 order to mimic daily contamination in food processing industry or surfaces in a household, 410 as shown schematically in Figure 4 A. After application, we left the bacteria on the surface 411 for 7 hours while being exposed to low intensity light from fluorescent lamps on the ceiling 412 (t=7 h, j=2.5 W/m 2 , A= 8 J (total light), A<380nm= 80 mJ). As it can be seen from the 413 measured light intensity spectrum of the fluorescent lamp (Figure 4 B)