The influence of H2 partial pressure on biogenic palladium nanoparticle production assessed by single‐cell ICP‐mass spectrometry

Abstract

Abstract The production of biogenic palladium nanoparticles (bio‐Pd NPs) is widely studied due to their high catalytic activity, which depends on the size of nanoparticles (NPs). Smaller NPs (here defined as <100 nm) are more efficient due to their higher surface/volume ratio. In this work, inductively coupled plasma‐mass spectrometry (ICP‐MS), flow cytometry (FCM) and transmission electron microscopy (TEM) were combined to obtain insight into the formation of these bio‐Pd NPs. The precipitation of bio‐Pd NPs was evaluated on a cell‐per‐cell basis using single‐cell ICP‐MS (SC‐ICP‐MS) combined with TEM images to assess how homogenously the particles were distributed over the cells. The results provided by SC‐ICP‐MS were consistent with those provided by “bulk” ICP‐MS analysis and FCM. It was observed that heterogeneity in the distribution of palladium over an entire cell population is strongly dependent on the Pd2+ concentration, biomass and partial H2 pressure. The latter three parameters affected the particle size, ranging from 15.6 to 560 nm, and exerted a significant impact on the production of the bio‐Pd NPs. The TEM combined with SC‐ICP‐MS revealed that the mass distribution for bacteria with high Pd content (144 fg Pd cell−1) indicated the presence of a large number of very small NPs (D50 = 15.6 nm). These results were obtained at high cell density (1 × 105 ± 3 × 104 cells μl−1) and H2 partial pressure (180 ml H2). In contrast, very large particles (D50 = 560 nm) were observed at low cell density (3 × 104 ± 10 × 102 cells μl−1) and H2 partial pressure (10–100 ml H2). The influence of the H2 partial pressure on the nanoparticle size and the possibility of size‐tuned nanoparticles are presented.