Table 1.
FTIR absorption band ratios with respect to the C-H absorption band between 2950 and 2850 cm−1 and elemental surface compositions derived from XPS spectra for B. breve ATCC 15700 and B-C-dots, E. coli ATCC 25922 and E-C-dots. FTIR absorption band ratios are averages ± standard deviations over triplicate experiments with separately prepared nanoparticles and different bacterial cultures, while XPS was done in single-fold.
| Strain/ C-Dot |
FTIR Absorption Band Ratios * | ||||
| 1660 cm−1/CH | 1540 cm−1/CH | 1590 cm−1/CH | (1260–1245 cm−1)/CH | (1200–950 cm−1)/CH | |
| B. breve | 3.4 ± 0.3 | 0.8 ± 0.1 | - | 0.7 ± 0.1 | 3.7 ± 0.2 |
| B-C-dots | 1.1 ± 0.5 | - | 3.2 ± 0.1 | 0.2 ± 0.1 | 5.3 ± 1.3 |
| E. coli | 4.9 ± 0.1 | 1.7 ± 0.0 | - | 0.8 ± 0.1 | 2.0 ± 0.1 |
| E-C-dots | 0.8 ± 0.1 | - | 1.4 ± 0.5 | 0.1 ± 0.0 | 2.2 ± 0.4 |
| XPS Elemental Surface Composition (at%) ** | |||||
| C1s | N1s | O1s | P2p | ||
| B. breve | 57.6 | 5.5 | 32.8 | 1.1 | |
| B-C-dots | 57.7 | 4.9 | 25.7 | 2.0 | |
| E. coli | 59.7 | 7.8 | 31.1 | 1.2 | |
| E-C-dots | 66.6 | 2.8 | 22.1 | 0.3 | |
| Chemical Functionalities Involving C (at%) *** | |||||
| C-C/C=C | C-N/C-O | O=C | -COOH | ||
| B. breve | 13 | 32 | 12 | 1 | |
| B-C-dots | 37 | 12 | 8 | 1 | |
| E. coli | 20 | 27 | 11 | 1 | |
| E-C-dots | 47 | 11 | 8 | 0 | |
* Absorption band ratios have been determined after baseline adjustment using Spectragryph software. ** Na, S, Cl, Si were not included in Table 1. *** The percentages of carbon involved in C–C/C=C, C–N/C–O, O=C and –COOH were derived from the decomposition of the C1s peak into four components at 284.8, 286.1, 288.0 and 289.3 eV, respectively. See Figure 2 for corresponding electron binding energy spectra over a narrow binding energy range (276–296 eV).