Helios zeta spectrophotometer

The spectra of pure Au and PEG-Au (~17.4, ~43.5, ~174 ppm) were measured using a Helios Zeta spectrophotometer (ThermoFisher, Pittsfield, MA, USA), with the wave range being from 200 to 800 nm. A peak of 520 nm was the absorption wavelength of the Au nanoparticles. To measure the sample, a quartz colorimetric tube was first cleaned with deionized water and wiped dry with mirror paper before having deionized water added. It was then measured for background absorption. Afterwards, each sample was measured sequentially. To avoid any possible factors which would affect the precision of the results, the quartz tube had to be repeatedly cleaned with deionized water in order to remove any residuals from the previous sample. Origin Pro 8 (Originlab Corporation, Northampton, MA, USA) software was applied to measure and quantify the results.

The UV-Vis spectra of pure PEG, pure Au, and PEG–Au 43.5 ppm were measured by a Helios Zeta spectrophotometer (ThermoFisher, Pittsfield, MA, USA), with the wave ranging from 200 to 800 nm. The typical peak of 520 nm was for the Au nanoparticles. The measurement was described in our previous report [23 (link)]. Origin Pro 8 (Originlab Corporation, Northampton, MA, USA) software was used to analyze and quantify the data.
Transmission Fourier transform infrared (FTIR) spectra were obtained through an FTIR spectrometer (Shimadzu Pretige-21, Kyoto, Japan). A solution containing 0.06 g potassium bromide (KBr, Sigma-Aldrich, Burlington, MA, USA) was mixed with 200 mg of pure PEG and PEG–Au 43.5 ppm. The samples were scanned eight times in the scanning range of 500–4000 cm⁻¹ with a 2 cm⁻¹ resolution to obtain the spectrum [31 (link)].
The surface morphology of the pure PEG and PEG–Au 43.5 ppm dry coating was observed through a MFP-3D atomic force microscope (Asylum Research, Santa Barbara, CA, USA). A silicon cantilever with a 2.0 N/m condition was used to obtain topography images, which were captured in AC mode at 512 × 512 pixels.

Bacterial hosts and phages used in this study are listed in Table 1. All experiments were performed with S 39006. Bacteria were cultured at 30°C in Luria-Broth (LB) (10 g liter⁻¹ tryptone, 5 g liter⁻¹ yeast extract, 5 g liter⁻¹ NaCl) or on LB agar (LBA) containing 1.5% w v⁻¹ or 0.35% w v⁻¹ agar to make LBA or top-LBA plates respectively. Bacterial growth was monitored by measuring optical density at 600 nm (OD₆₀₀) using a Thermo Scientific Helios Zeta spectrophotometer. Where required, media were supplemented with ampicillin at 100 μg mL⁻¹. Bacteriophages ΦCHI14, ΦX20, and ΦCBH8 were isolated from treated effluent collected from a sewage treatment plant in Cambridge, United Kingdom. The bacteriophages were selected from a library of S 39006-specific phages isolated using an enrichment procedure detailed previously (Evans et al., 2010 (link)). Phage lysates were generated as described previously (Petty et al., 2006 (link)). Spot tests were performed as described previously (Evans et al., 2010 (link)). Phages were stored at 4°C in phage buffer containing 10 mM MgSO₄, 10 mM Tris-HCl, 0.01% w v⁻¹ gelatin and a few drops of chloroform. Efficiency of Plating (E.O.P.) was calculated after incubating serial dilutions of phage lysates overnight on bacterial lawns on LBA and dividing the titer of the phage on the test host by the titer of the phage on the control host (Kutter, 2009 ).