Time-Dependent Size and Shape Evolution of Gold and Europium Nanoparticles from a Bioproducing Microorganism, a Cyanobacterium: A Digitally Supported High-Resolution Image Analysis

Abstract

Herein, the particle size distributions (PSDs) and shape analysis of in vivo bioproduced particles from aqueous Au3+ and Eu3+ solutions by the cyanobacterium Anabaena sp. are examined in detail at the nanoscale. Generally, biosynthesis is affected by numerous parameters. Therefore, it is challenging to find the key set points for generating tailored nanoparticles (NPs). PSDs and shape analysis of the Au and Eu-NPs were performed with ImageJ using high-resolution transmission electron microscopy (HR-TEM) images. As the HR-TEM image analysis reflects only a fraction of the detected NPs within the cells, additional PSDs of the complete cell were performed to determine the NP count and to evaluate the different accuracies. Furthermore, local PSDs were carried out at five randomly selected locations within a single cell to identify local hotspots or agglomerations. The PSDs show that particle size depends mainly on contact time, while the particle shape is hardly affected. The particles formed are distributed quite evenly within the cells. HR-PSDs for Au-NPs show an average equivalent circular diameter (ECD) of 8.4 nm (24 h) and 7.2 nm (51 h). In contrast, Eu-NPs preferably exhibit an average ECD of 10.6 nm (10 h) and 12.3 nm (244 h). Au-NPs are classified predominantly as “very round” with an average reciprocal aspect ratio (RAR) of ~0.9 and a Feret major axis ratio (FMR) of ~1.17. Eu-NPs mainly belong to the “rounded” class with a smaller RAR of ~0.6 and a FMR of ~1.3. These results show that an increase in contact time is not accompanied by an average particle growth for Au-NPs, but by a doubling of the particle number. Anabaena sp. is capable of biosorbing and bioreducing dissolved Au3+ and Eu3+ ions from aqueous solutions, generating nano-sized Au and Eu particles, respectively. Therefore, it is a low-cost, non-toxic and effective candidate for a rapid recovery of these sought-after metals via the bioproduction of NPs with defined sizes and shapes, providing a high potential for scale-up.

Gold Nanoparticles Bioproduced in Cyanobacteria in the Initial Phase Opened an Avenue for the Discovery of Corresponding Cerium Nanoparticles

“…Finally, it is worth considering a comparison with previous studies [ 23 ] that examined the PSDs for 24 and 51 h. The AuNPs had an average ECD of 8.4 nm for 24 h (160 particles) and 7.2 nm for 51 h (314 particles) in HR. The value obtained here for 10 h is significantly lower at 4.8 nm.…”

“…The biosynthesis experiments of AuNPs and CeNPs were performed according to the previously established methods [ 22 , 23 , 25 ]. Briefly, the stock cultures of the cyanobacteria Anabaena sp.…”

“…The system was operated at 100 kV acceleration voltage. The preparation procedure followed the established protocols and has been described in detail in previous studies [ 22 , 23 , 25 ].…”

“…In the past, bio-based synthesis was disadvantaged compared to the conventional NP production methods due to the difficulty in obtaining size-specific NPs with controlled morphologies. However, recent studies have shown that certain factors can be influenced to affect particle size and shape, demonstrating that control is possible in principle [ 22 , 23 ].…”

“…The formation of CeNPs takes longer, which is further complicated by the fact that the CeNPs formed have no sharp edges compared to their background due to their amorphous structure. This makes it more difficult to detect CeNPs than the other rare earth element NPs used in our previous studies [ 23 , 25 , 26 ]. This paper is dedicated to the previously established tool for the detection of AuNPs in the range down to ~2 nm, and the easy-to-use Anabaena sp.…”