Supplementary Information
Effect of Gold Nanoparticles and Ciprofloxacin on Microbial Catabolism: A
Community-based Approach
†Kela P. Weber, ‡Elijah J. Petersen, †Sonja Bissegger, †Iris Koch, †Jun Zhang, †Kenneth J.
Reimer, §Lars Rehmann, ||Robin M. Slawson, #Raymond L. Legge, ††, ‡‡Denis M. O’Carroll
† Department of Chemistry and Chemical Engineering, Royal Military College of Canada, Kingston,
Ontario, K7K 7B4, Canada
‡ National Institute of Standards and Technology, Material Measurement Laboratory, Gaithersburg, MD,
USA
§ Department of Chemical and Biochemical Engineering, University of Western Ontario, London,
Ontario, N6A 3K7, Canada
|| Department of Biology, Wilfrid Laurier University, Waterloo, ON, CANADA, N2L 3C5
# Department of Chemical Engineering, University of Waterloo, Waterloo, ON,
CANADA, N2L 3G1
†† Department of Civil and Environmental Engineering, University of Western Ontario, London,
Ontario, N6A 3K7, Canada
‡‡ Water Research Laboratory, School of Civil and Environmental Engineering, University of New South
Wales, Manly Vale, NSW, 2093, Australia
Four pages.
S1.0
Dynamic Light Scattering Methodology Details and Results
The phosphate buffer was filtered using 0.45 µm a disposable filter (Nalgene) and a syringe with a 0.2
µm nylon filter (Daigger) to remove dust. Additionally, all glassware was cleaned beforehand using
pressurized air to remove dust particles. Because testing the samples at a nominal concentration of ~ 5
µg/mL (10:1 dilution of RM solution) did not yield sufficiently high counts, a concentration of ~ 10 µg/mL
(5:1 dilution of RM solution) was used. Three hundred µL was added to glass cuvettes for the
measurement. The samples were centrifuged at 15,558g (Hettich Mikro 120 Microcentrifuge) for 5
minutes to remove dust particles before measurements were taken at 20° C using a 90° scattering angle.
Given the sensitivity of DLS measurements to larger particles and the small size of the particles being
tested challenging the sensitivity of the DLS, centrifugation was necessary; in the report of investigation
for the reference material, the samples were filtered through a 0.1 µm pore size aluminum oxide
membrane for this reason.
The initial value of (14.7 ± 5.5) nm is near the DLS reference size provided by NIST of (13.5 ± 0.1) nm
(https://www-s.nist.gov/srmors/view_report.cfm?srm=8011); this value is close to those measured
using transmission electron microscopy, scanning electron microscopy (SEM), atomic force microscopy,
small-angle x-ray scattering, and differential mobility analysis in the NIST certificate of analysis. The
reason that the DLS values are substantially larger than 9.9 nm (the core size for the AuNPs by SEM
measurement) is that DLS measurements take into account surface coatings in addition to the particle
core and provide the hydrodynamic size of AuNPs. The data was also analyzed using a special NICOMP
program (Particle Sizing Systems (Santa Barbara, CA USA)) which takes into account the potential for
multiple peaks.
However, this program did not present uncertainty estimates for each size
measurement. The average size for the largest (with regards to percentage of the total) peak was (15.7
± 0.1) nm and (15.7 ± 1.2) nm after 0 and 24 h, respectively.
However, the percentage that
corresponded to this peak decreased from (94 ± 2) % to (78 ± 13) % indicating that agglomeration was
occurring.
S2.0
Inductively Coupled Plasma-Mass Spectrometry Methodology Details
Gold standard solutions (1 mg/ml or 1000 mg/L Au(III) in HCl, as HAuCl4), were obtained from two
different sources for the calibration curve (Fisher Scientific Canada) and for a quality control (QC)
calibration check (SCP Science). For ICP-MS daily performance checks, a solution containing 10 μg/L Ba
(barium), and 1 μg/L Be (beryllium), Mg (magnesium), Co (cobalt), Fe (iron), In (indium), Ce (cerium), Pb
(lead), U (uranium) and Th (thorium) was made from a custom stock solution (Inorganic Ventures) in 2%
HNO3 (v/v) (prepared from Optima grade concentrated HNO3 , Fisher Scientific Canada). The Bi (bismuth)
solution used as the internal standard was obtained from SCP Science (Canada). Hydrochloric acid (HCl,
37%, trace metal grade), and nitric acid (HNO3, 70%, trace metal grade) were purchased from Fisher
Scientific Canada and aqua regia consisted of 3:1 (v:v) of HCl: HNO3. The linear calibration curve ranged
from 0.1 to 100 μg/L Au(III) in 2% aqua regia (v/v). A QC solution (18.97 μg/L Au(III) in 2% aqua regia)
was measured every 12 samples to ensure the calibration remained valid throughout the run, and
results were acceptable with recoveries (measured concentration with respect to the known
concentration) between 96 and 110%. Measurements included correction to Bi internal standard to
eliminate signal fluctuations from variations on sample matrix and measurement conditions. Torch
position, nebulizer gas flow and lens voltage were optimized before analysis and operating parameters
are summarized in Table S1.
Table S1. ICP-MS operating conditions.
Instrument
Elan DRC II ICP-MS
Nebulizer gas flow
0.99 L/min
Auxiliary gas flow
1.275 L/min
Plasma gas flow
15 L/min
ICP radiofrequency power
1,400 W
Sample uptake rate
20 rpm
Analysis and detection modes
Standard, peak hopping, pulse counting
Lens voltage
8V
Analog voltage
-1,650 V
Pulse voltage
750 V
Sweeps/reading
50
Readings/replicate
1
Replicates
3
Dwell time
50 ms
Integration time
5,000 ms
Figure S1: Average well colour development (corrected absorbance at 590nm) data (84h), given varying
ciprofloxacin dose, for the different guild groupings for an antibiotic resistant microbial community
(mesocosm wetland 2 – MW2). Data points are the average of triplicate measurements and
uncertainties indicate one standard deviation.