Photocatalytic antibacterial activity
E. coli XL1-blue (Invitrogen Life Technologies, USA) was used as
the model bacterium in the study. LB agar and broth were used as
solid and liquid media, respectively. Cultivations were performed
by using shaker (170 rpm) and incubator at 35 ◦C. Stock cultures
containing glycerol were stored in a deep-freezer at −80 ◦C and
working cultures were maintained on slants and stored at 4 ◦C.
After cultivation of E. coli in liquid medium, cells were separated
by using a centrifuge (5000 × g) for 10 min and the harvested cells
were washed twice with sterilized phosphate buffer solution (0.2 M
PBS) at pH 7.2. Cells were then re-suspended in PBS, and the number
of cells was adjusted as 106–108 per ml liquid which is used in
photocatalytic cell inactivation experiments. The number of cells in
cell suspensions was determined by using viable cell count method.
For this purpose, 100 l sample was diluted serially between 10−1
and 10−6 dilution in phosphate buffer solutions (pH 7.2) and pipetted
onto Luria Bertani (LB) agar plates. The numbers of colonies on
plates were counted after overnight incubation at 35 ◦C.
The antibacterial activity of the thin film samples for suspended
cells was determined by exposing 200 l of cell suspension over
sample surface to artificial solar radiation (Suntest Atlas CPS+
equipped with Special window glass filter) with a power flux of
300W/m2 between 310 and 800 nm at 35 ◦C. The flux was measured
and controlled by built in radiometer of solar simulator. Each
thin film compositions were tested by at least 6 different parallel
thin film samples, initially and the time course of number of viable
cells was determined by removing one plate out of test chamber.
100 l samples were collected from thin film surfaces and the time
course of number of viable cells was determined;
Antimicrobial activity
= initial number of microorganisms − final number of microorganisms
initial number of microorganisms × 100 (2