AIChE American Institute of Chemical Engineers


2012 Annual Meeting
Biomedical Applications of Chemical Engineering
(104g) The Synthesis of Selenium Nanoparticles On Polycarbonate Via a Simple Fast Reaction and Its Antibacterial Application
Wang, Q., Brown University
Webster, T. J., Brown University
Originally presented on: 10/29/2012 14:45:00 - 15:00:00

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.


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