Letter for the article Comparative Analysis of Commercial Colloidal Si


1Natural Immunogenics Corp, Sarasota, Florida, 34243, USA; 2Paul Hemmes Consulting LLC, Austin, TX, USA

Mr Editor

Sovereign Silver and Argentyn 23 are the brand names of bioactive silver hydrosol manufactured by Natural Immunogenics Corp (NIC). The products contain a mixture of positively charged silver ions and silver nanoparticles. In a 2020 publication by Kumar et al.,1 Sovereign Silver and Argentyn 23 have been included as part of a “comparative evaluation of commercial colloidal silver products”. This post concluded that there were no silver nanoparticles (AgNPs) present in either Sovereign Silver products or Argentyn 23 products. manufacturer’s marketing message regarding the presence of silver nanoparticles in its products, providing a detailed characterization using TEM and AFM.

There are many tools that can potentially be used to characterize nanoparticles.2 Although it is preferable to have several orthogonal characterization techniques, there is an international consensus that transmission electron microscopy (TEM) is the “gold standard” technique for the characterization of nanoparticles. For example, the European Food Safety Authority (EFSA) requires two techniques to characterize the size and particle size distribution of nanomaterials in food, one of which must be TEM and the other of the applicant’s choice.3 Figure 1 shows representative TEM images of Sovereign Silver and Argentyn 23 products, which clearly demonstrate discrete and tightly distributed silver nanoparticles. A particle size distribution histogram, obtained from nine batches of Argentyn 23 and no fewer than five images per batch, is also shown in Figure 1.

Figure 1 Representative TEM images (scale bars = 100 nm) of Sovereign Silver (top left) and Argentyn 23 (top right), and particle size distribution of Argentyn 23 nanoparticles obtained from nine different batches (bottom ).

To corroborate the TEM results, atomic force microscopy (AFM) was also used. The same 9 batches included for TEM analysis were analyzed by AFM and the results corroborate the TEM results. A representative AFM height image and size distribution histogram are shown in Figure 2.

Figure 2 A representative image of the Argentyn 23 AFM height and size distribution histogram. The AFM height image is shown with a red mask superimposed. The height of the particles is represented by the brightness of the spots against the scale bar to the right of the image. The size distribution histogram contains data from nine Argentyn 23 lots. At least three images from each lot were analyzed.

The TEM and AFM data presented in this letter provide a robust analytical data set supporting the presence of AgNPs in Sovereign Silver and Argentyn 23 products, directly contradicting the conclusion drawn by Kumar et al.1 Ultraviolet-Visible (UV-Vis) spectroscopy, the technology on which Kumar et al’s main conclusion is based, relies on the phenomenon of surface plasmon resonance (SPR) of nanoparticles. Although sometimes useful with some colloidal silver samples, UV-Vis is not a reliable method to determine the presence or absence of NPs, as the SPR changes or even disappears depending on the size of the NPs, surface chemistry, state of aggregation, among other factors.4–8 Since Sovereign Silver and Argentyn 23 products contain a mixture of silver ions and AgNPs, they are expected to turn yellow when a sodium borohydride reducing agent is added. This experiment therefore cannot be used as evidence for the absence of AgNPs, as suggested in the article by Kumar et al.

The article also claimed the failure of attempting to visualize silver nanoclusters as small as 0.8 nm in Sovereign Silver and Argentyn 23 products using scanning transmission electron microscopy (STEM). Here we present STEM images obtained using an FEI Themis S/TEM operating at 200 kV in high angle annular dark field STEM mode. Sub-nm silver clusters can be clearly visualized (Figure 3). More importantly, the atomic structure of the nanoparticles or clusters can be clearly seen, as shown in the insert of Figure 3. The d-spacing information can therefore be obtained at 0.24 nm, in agreement with the (111 ) metallic silver plans.

picture 3 Scanning transmission electron microscopy (S/TEM) images of sovereign silver.

In conclusion, this communication provides compelling scientific evidence for the presence of nanoparticles in both products, as well as corroboration of the particle size of AgNPs in Sovereign Silver and Argentyn 23 products. The characterization can be repeated using any which Sovereign Silver and Argentyn 23 product is commercially available. Detailed methods can be provided upon request.

Acknowledgement

The authors thank Dr. Nicholas Rudawski for the operation of the FEI Themis S/TEM. The University of Florida’s Herbert Wertheim College of Engineering Research Service Centers are recognized for the use of transmission electron microscope facilities.

Disclosure

Nan Qin is an employee of Natural Immunogenics Corp. Paul Hemmes is a consultant for Natural Immunogenics Corp. Ms. Kay Mitchen is employed by Natural Immunogenics Corp, maker of Silver Hydrosol products. Her position within the company is that of Director of Regulatory Affairs and Quality. She oversees the company’s overall compliance with international good manufacturing practices, which also includes ensuring that all product claims are supported by scientific evidence. The authors report no other conflicts of interest in this communication.

The references

1. Kumar A, Goia DV. Comparative analysis of commercial colloidal silver products. Int J Nanomed. 2020;15:10425–10434. doi:10.2147/IJN.S287730

2. MacCuspie RI. Chapter 4 – Characterization of nanomaterials for NanoEHS studies. In: Hull MS, Bowman DM, editors. Nanotechnology Environmental Health and Safety. 2nd ed. William Andrew Publishing: Oxford; 2014: 55–76.

3. EFS Authority. Guidance on risk assessment of the application of nanosciences and nanotechnologies in the food and feed chain. EFSA J. 2018;9(5):2140.

4. Ishida R, Yamazoe S, Koyasu K, et al. Repeated appearance and disappearance of localized surface plasmon resonance in 1.2 nm gold clusters induced by adsorption and desorption of hydrogen atoms. At the nanoscale. 2016;8(5):2544–2547. doi:10.1039/C5NR06373F

5. Raza S, Kadkhodazadeh S, Christensen T, et al. Multipolar plasmons and their disappearance in silver nanoparticles of a few nanometers. Nat Common. 2015;6:8788. doi:10.1038/ncomms9788

6. Yang H, Wang Y, Chen X, et al. Plasmonically twinned silver nanoparticles with molecular precision. Nat Common. 2016;7(1):12809. doi:10.1038/ncomms12809

7. Scholl JA, Koh AL, Dionne JA. Quantum plasmon resonances of individual metallic nanoparticles. Nature. 2012;483(7390):421–427. doi:10.1038/nature10904

8. Mendis P, de Silva RM, de Silva KMN, Wijenayaka LA, Jayawardana K, Yan M., Nanosilver rainbow: A quick and easy method for tuning different colors of nanosilver through the controlled synthesis of stable spherical silver nanoparticles. RSC Advances. 2016;6(54):48792-48799.

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