(104g) The Synthesis of Selenium Nanoparticles On Polycarbonate Via a Simple Fast Reaction and Its Antibacterial Application

Introduction

In
this study,
selenium nanoparticles were synthesized and coated
on
polycarbonate surfaces using a simple fast precipitation method. The
amount, roughness, adhesion and other properties of the nano-sized
coatings were measured. By coating with selenium nanoparticles, the
polymer surface was
introduced
with
antibacterial properties
inhibiting biofilm formation.
The objective of the present study was to coat selenium nanoparticles
on polycarbonate and test their effectiveness preventing biofilm
formation.

Materials and Methods

Selenium
nanoparticles were synthesized through a simple reaction between
glutathione and sodium selenite (4:1 molar mixture) and were
precipitated on the surface of polycarbonate
(McMASTER-CARR,
85585k82,
0.13mm thickness, cut into round films 7.01mm in diameter)
for either
30s
or 60s. Sodium
hydroxide (NaOH) was added to bring the pH of the solution to the
alkaline regimen to start the reaction. As the size of selenium
nanoparticles on the surface is influenced by the concentration of
NaOH and the coating time, two coating conditions were
used in this
study. One was using a 0.5M NaOH solution for 30s and the other one
was using a 1.0M NaOH solution for 60s.
After coating,
tape tests (D3359-09e2: Standard Test Methods for Measuring Adhesion
by Tape Test) were used to test the strength of adhesion of the
selenium nanoparticles on the substrate surfaces.
AAS (Atomic Absorption Spectroscopy) was used to measure the amount
of coated selenium on polycarbonate surfaces. SEM
(Scanning Electron Microscope, HITACHI 2700) images of the substrate
surfaces were taken to determine
the size, the
distribution and coverage of selenium nanoparticles. AFM
(Atomic Force Microscope, MFP3D, Asylum Research, Sharp tipped
cantilever, K = 0.06N/M, Contact Mode) was used to demonstrate that
the coated selenium nanoparticles increased the surface selenium
exposure and surface roughness of polycarbonate.

In
order to test the effectiveness of selenium coatings inhibiting
biofilm formation,
bacteria experiments
were implemented.
A
bacteria cell line of Staphylococcus
aureus was
obtained in freeze-dried form from the American Type Culture
Collection (catalog number 25923). Selenium coated samples were
rinsed with 75% ethanol for 20 minutes for sterilization purposes and
were left in the sterile petri dishes for 30 minutes to completely
dry. Then,
the samples were transferred to a 24-well plate,
treated with the
prepared bacterial solutions (10⁶
bacteria/ml,
Staphylococcus
aureus) and cultured
for either 24, 48 or 72 hours in an incubator (37°, humidified,
5% CO₂).
After the treatment, the samples were rinsed with a PBS (phosphate
buffered saline) solution twice and placed into 1.5ml microfuge tubes
with 1ml of PBS. These tubes were shaken at 3000 rmp for 15 minutes
on a vortex mixer to release the bacteria attached on the surface
into the solution. Solutions with bacteria were spread on agar plates
and bacteria colonies were counted after 18 hours of incubation.
Bacterial tests
were conducted in triplicate and repeated three times. Data were
collected and the significant differences were assessed with the
probability associated with a one-tailed Student's t-test.
Statistical analyses were performed using Microsoft Excel (Redmond,
WA).

Results
and Discussion

Most
of the nanoparticles were approximately 50-100nm
in diameter
and well distributed on the polymer surface.
Nanoparticles coated
with a condition
of 1.0M NaOH for 60s were
larger than those with the
condition of 0.5M
NaOH for 30s.
The
concentration of nanoparticles on the polycarbonate surfaces were on
average 19.34g/m²
and 20.95g/m²
for the 0.5M NaOH for 30s condition and for the 1.0M NaOH for 60s
condition, respectively. Tape
tests removed about 50% and 75% of the selenium nanoparticles for the
0.5M NaOH for 30s condition and for the 1.0M NaOH for 60s condition,
respectively,
according to AAS results.
This result indicated that selenium nanoparticles with larger sizes
might have less adhesion to an underlying substrate than smaller
selenium nanoparticles. The
RMS (root mean square) roughness for the selenium coated surface at a
condition of 0.5M NaOH for 30s and at a condition of 1.0M NaOH for
60s were 45.997nm and 53.084nm, respectively. After the tape test,
the RMS roughness decreased to 21.731nm and 34.925nm for the these
two coating conditions. The RMS roughness of the uncoated surface was
14.898nm, which was much smaller than the selenium coated
polycarbonate samples. So, there was a significant increase in
roughness, therefore surface area, after coating with selenium
nanoparticles.

Experiments
with bacteria (specifically,
Staphylococcus
aureus) showed
high effectiveness
for
the selenium
coated
polycarbonate at
killing bacteria and
preventing bacteria from attaching. All
of the selenium coated samples showed a
higher
effectiveness at inhibiting bacteria growth on the polycarbonate
surface than
the uncoated surface (Figure
1).
Compared to uncoated samples, more than 91%,
15% and 73% of the
bacteria
(compared with uncoated polycarbonate)
died or had been removed after 24,
48 and 72 hours on
the selenium
coated
polycarbonate.
Importantly, this
was accomplished without using antibiotics.

Figure 1. Bacteria (S. aureus) growth on the surface of polycabonate. Polycarbonate samples were treated with bacteria (S. aureus) in 0.03% TSB (Tryptic Soy Broth) and were incubated for 24, 48 or 72 hours. The media was changed with 0.03% TSB every 24 hours for those samples incubated at 48 hours or 72 hours. The control group is uncoated polycarbonate. bf = before tape test; aft = after tape test. Data=Mean ± standard deviation by mean, n=3; *p<0.05 compared with control group (uncoated polycarbonate) after 24 hours; **p<0.004 compared with control group after 48 hours; ***p<0.02 compared with control group after 72 hours.

Conclusions

Selenium
nanoparticles were synthesized and coated on polycarbonate by a
simple
fast reaction
occurring in 60s. The
coating of selenium nanoparticles on polycarbonate introduced
significant and effective anti-bacterial properties to the polymer
surface which
deserves further
investigation.

Acknowledgements

The authors thank Dr.
Justin Seil for help with the bacteria experiments and Dr. Vera
Fonseca for help with the AFM images. Funding from the Hermann
Foundation is also acknowledged.