LAUSR

This note is in response to the criticism vis-à-vis our paper “Comparative evaluation of commercial colloidal silver products” conveyed by Nan Qin, Paul Hemmes, and Kay Mitchen in their “Letter to the Editor”. We are addressing below their comments and provide additional arguments reinforcing the validity of our findings. The objective of our paper was to verify if the term “colloidal silver” was justifiably used in the case of 14 commercial products evaluated. The UV-Vis spectrophotometry, light scattering, and electron microscopy evaluations attested that Sovereign Silver, Argentyn 23, and seven other products did not contain silver nanoparticles and were improperly labeled “colloidal silver”. The conclusion was strongly supported by the absence of a plasmon band, a convincing and widely accepted scientific argument the authors of the letter are dismissing. The use of optical properties for detecting and characterizing plasmonic nanoparticles has been an integral and valuable part of colloid science for more than a century. In 1857, long before electron microscopy was discovered, Michael Faraday postulated that the ruby color of gold sols was caused by the presence of small dispersed metal particles. 1 In 1889, Carey Lea followed the same approach in studying colloidal silver. 2 Decades later, their findings based solely on the optical properties of the samples were confirmed by electron microscopy. As it provides simulta-neously information about the size, uniformity , and dispersion of silver nanoparticles, UV-Vis has been recognized for long as the most versatile technique for evaluating silver sols. Since billions of particles in the light beam path are “interrogated” during the analysis, the information provided is far more representative for the sample than electron microscopy. Despite the vast scientific evidence in favor or UV-Vis, the authors assert that it is unreliable because the SPR