2.1. Chemicals and bacterial cultures
AgNO3, HCl, NaOH, and sodium alginate were purchased
from Sigma Aldrich, USA, dihydroethidium (DHE) from Yeasen
Biotechnology, China and both PBS buffer solution (135 mM NaCl, 4.7 mM
KCl, 10 mM Na2HPO4, 2 mM
NaH2PO4, pH=7.3±0.1) and
polydimethylsiloxane (PDMS) were from Beyotime Biotechnology, China. All
these reagents were analytical-grade and used as received. All solutions
were prepared with Milli-Q ultrapure water (18 MΩ·cm, Thermo Fisher).
Deinococcus radiodurans Strain R1 (ATCC 13939) was grown from a
single bacterium aerobically (under atmospheric conditions) at 30°C in
peptone yeast glucose (PYG) broth (containing 2% peptone, 0.5%
glucose, 1% yeast extract, pH 7.2) with agitation at 300 rpm. The pH of
the broth was adjusted to 7 by adding hydrochloric acid or sodium
hydroxide. The bacterial growth was assessed by measuring optical
density (OD) via a microplate reader (see below Section 2.2.3) at
the wavelength of 600 nm of the strain. The OD value stayed stable since
reaching 1.0, and the D.r. strain at this stage was considered to
have a stable population and morphology, and therefore selected to be
used throughout the experiment. For obtaining the bacteria containing
silver particles, the grown culture above was cultivated in a fresh PYG
broth initially containing 2.0 mM AgNO3 with a pH of 7
and at 30 ℃ for another 9 hours. The bacteria after incubation in
AgNO3 solutions were centrifuged at 8000xg to collect
the microbes and washed with PBS for further analysis.