Figure 1.
Representation of passive uptake of Cr-AuNPs by S. oneidensis MR-1 and subsequent Raman Chemical imaging of cells to reveal the intracellular localization of reduced Cr(III) and unreacted Cr(VI).
Figure 2.
Effect of Cr-AuNPs on the growth of Shewanella oneidensis MR-1.
Either 3.5 nm (closed symbols) or 13 nm (open symbols) Cr-AuNPs were added to wells at volumes of 0, 5, 10, and 50 µl. Error bars represent the standard error from three independent cultures.
Figure 3.
Effect of Cr-AuNPs on chromate reduction by S. oneidensis MR-1.
Abiotic controls were included to rule out the reduction of chromate by media components and the Cr-AuNPs (open symbols). There was no adverse effect on chromate reduction ability induced by the nanoparticles (closed symbols). In addition, the nanoparticles did not directly reduce the chromate in the medium in the absence of cells (open symbols). Error bars represent the standard error from three independent cultures.
Figure 4.
Thin-section TEM Images of S. oneidensis MR-1.
A. without particles, B. plain 13 nm gold Nanoparticles, Fig. 4C–4D. Chromate coated gold nanoparticles, Cr-AuNp:13 nm, (Fig. 4E–4F) 3.5 nm Cr-AuNp. Red arrows indicate extracellularly bound Cr-AuNp and green arrows/circle indicate internalized particles. (Fig. 4G–4H) show 3.5 nm and 13 nm probes used in Cr-AuNp preparation.
Figure 5.
Single cell SERS spectra obtained from S. oneidensis MR-1 incubated with 3.5 nm gold nanoparticles depicting the uptake of gold nanoparticles by this organism. chromium(VI) peaks are highlighted with red and the reduced chromium(III) peaks are marked in green. Chromium(VI) –red and Chromium (III) – green spectra are aligned to show their peak positions in bacteria. Bulk Raman spectrum acquired from a cluster of chromate reducing cells is also shown.
Figure 6.
Raman Intensity Maps averaged over a wide wavenumber region (162–1953 cm−1) covering most of bio-molecular components in cells to obtain a Raman chemical image of the cell (A), Phonon Plasmon peak (207–297 cm−1) originating from gold depicting the presence of Cr-AuNps (B), Cr(VI) - hexavalent chromium (C, 837–873 cm−1), reduced non-toxic trivalent Cr(III) (D, 531–567 cm−1). Raman images in grid format, Fig. 6E and 6F are representations of 6B and 6C respectively. 6-E* and F* represent magnified pixel plots to demonstrate the overlap in signal of Au and Cr(VI) peaks within cells.
Figure 7.
Confocal Fluorescence Lifetime Imaging.
S. oneidensis MR-1 incubated with 3.5 nm (Fig. 7A & 7C) and 13 nm (Fig. 7B & 7D) Cr-AuNp probes show scattered low-lifetime (blue) distribution indicating the presence of gold nanoparticles (both internalized and externally bound) compared to the control incubated with plain gold nanoparticles (inset - 7A).
Figure 8.
Inductively Coupled Mass-Spectrometry.
A. ICP-MS Calibration curve for Cr quantification. B. Intracellularly trapped Cr(VI) and Cr(III) at time t = 0 and t = 12 h after Cr-AuNp treatment.