## 3 Results and Discussion
### Metallic Nanoparticle Synthesis by M. magnetotacticum Using Either Fe, Ag, Au or Zn
#### 3.2.2 DLS Analysis
The size range for the iron-containing nanoparticles obtained using MSGM 6 (sodium nitrate) was 149-199 nm (Figure S16 in Supplementary Material). Use of MSGM 9 (sodium nitrate and Isogro(tm)) resulted in nanoparticles with a size range of 74-239 nm; however, there were two other peaks shown on the graph with size ranges of 255-825 nm and 4145-6439 nm, respectively, and this could also be attributed to the high degree of agglomeration (Figure 7). The size ranges obtained for gold using DLS were 66-195 nm for MSGM original (Figure S18 in Supplementary Material), 599-705 nm for MSGM 6 (sodium nitrate) (Figure S20 in Supplementary Material) and 270-284 nm for MSGM 9 (sodium nitrate and Isogro(tm)) (Figure S21 in Supplementary Material). However, sizing using DLS could not be performed for silver using MSGM original and MSGM 6 (sodium nitrate) due to lack of verification via EDX analysis however the size range for silver obtained using MSGM 9 (sodium nitrate and Isogro(tm)) was 12-342 nm (Figure 8). The zeta potential values for iron nanoparticles showed an increase in stability when using medium modifications MSGM 6 (Figure S17 in Supplementary Material) and MSGM 9 (Figure 9) with values of \(-40\) mV and \(-44\) mV, respectively, as compared to the value of \(-26\) mV which was obtained for iron nanoparticles produced in MSGM original (Figure 10). This indicates that the addition of a higher concentration of sodium nitrate allowed for better stability. Silver nanoparticles were only produced using MSGM 9 (sodium nitrate and Isogro(tm)) and showed good stability with a zeta potential value of \(-40\) mV (Figure 11). However, gold nanoparticles showed decreasing stability with the addition of sodium nitrate and Isogro(tm) (Figure S22 in Supplementary Material). Gold nanoparticles produced in MSGM original, MSGM 6 (sodium nitrate) and MSGM 9 (sodium nitrate and Isogro(tm)) had zeta potential values of \(-35\) mV, \(-23\) mV and \(-15\) mV, respectively (Figures S19 and S22 in Supplementary Material), and thus sodium nitrate and Isogro(tm) could have a role in van der Waals forces acting upon the nanoparticles thereby facilitating their aggregation [47]. According to the graphs obtained for size and zeta potential distribution it could be noted that the nanoparticles were highly polydisperse as there was more than one peak obtained for the size distribution. The high degree of polydispersity is due to the highly agglomerated nanoparticles obtained and as seen using TEM. Figure 7: Size distribution intensity from DLS analysis of iron-containing magnetosomes formed by _M. magnetotacticum_ after incubation at 30\({}^{\circ}\) for 48 h in MSGM 9 (sodium nitrate and Isogro(tm)) containing iron (10 mM). Figure 8: Size distribution intensity from DLS analysis of silver-containing magnetosomes formed by \(M\). _magnetotacticum_ after incubation at 30\({}^{\circ}\) for 48 h in MSGM 9 (sodium nitrate and Isogro(tm)) containing silver (10 mM). Figure 9: Zeta potential data of iron-containing magnetosomes formed by \(M\). _magnetotacticum_ after incubation at 30\({}^{\circ}\) for 48 h in MSGM 9 (sodium nitrate and Isogro(tm)) containing iron (10 mM). This study has thus demonstrated improved yield of green synthesized Fe, Ag and Au nanoparticles using the MTB strain _M. magnetotacticum_. However, further optimization to obtain non-aggregated particles especially in the case of Au needs to be investigated for downstream application. Metallic nanoparticles have a wide range of biotechnological application and a recent review by [PERSON] et al. (2023) clearly outlines the versatility of plasmonics in biosensors [48]. This review explains the properties and structure of photon crystals and how they can be enhanced so that they can be used to improve detection for use in a myriad of applications. Notably, AuNps coupled with quantum dots can be used to improve detection of the surface plasmonics in biosensors. Figure 11: Zeta potential data of silver-containing magnetosomes formed by _M.