EVQ-218: Characterization of high-energy nanoparticles that measure up to NIST standards

This is an accessible summary of the peer-reviewed article, not a replacement for it. Read the source PDF for the complete methods, results, supporting-information references, and publication context.

Publication

Kennon, B. S.; Niedermeyer, W. H. “EVQ-218: Characterization of High-Energy Nanoparticles that Measure up to NIST Standards.” ACS Omega 2024, 9, 7891-7903. https://doi.org/10.1021/acsomega.3c07745

The article is published under a CC BY-NC-ND 4.0 license. This page summarizes its reported methods and findings in a more accessible web format.

Study overview

The study compares EVQ-218, a laser-ablated silver particle produced directly in high-purity water, with a NIST-traceable nanoComposix silver-particle reference. The authors evaluated particle morphology and size distribution, behavior in mineral-containing media, silver dissolution, surface chemistry, and long-term particle stability.

What the researchers tested

Scanning transmission electron microscopy (STEM) for morphology and particle sizing.
Dynamic light scattering (DLS) for particle-size distributions in different media.
ICP-OES and a silver-ion-selective electrode for dissolution and silver measurements.
STEM/EDS and EELS for elemental mapping and surface-chemistry characterization.
Deionized water, moderately hard water, and concentrated artificial alveolar fluid as test media.

Particle morphology and sizing

The authors report that EVQ-218 had a predominantly spherical morphology and a narrow particle-size distribution. Images showed small, regularly spaced groupings on the microscopy grid without the fused agglomeration that would indicate loss of particle identity. The NIST-traceable comparison material also had a narrow distribution, although the paper notes more faceted and nonspherical particles in the reference images.

STEM images showing EVQ-218 particle morphology and spacing — Figure 1 excerpt. STEM images used to compare EVQ-218 morphology, grouping, and particle spacing with the NIST-traceable reference material.

STEM particle-sizing images for EVQ-218 — Particle-sizing image set. EVQ-218 measurements produced a distribution centered near the nominal 8-10 nm range reported in the paper.

Particle statistics reported in the article

Percentile	EVQ-218 diameter	Number density	Specific surface area
d(10)	3.9 nm	3.2 × 10¹³ NP/mL	148.5 m²/g
d(50)	8.0 nm	3.5 × 10¹² NP/mL	71.1 m²/g
d(90)	10.8 nm	1.5 × 10¹² NP/mL	53.1 m²/g

Percentile	NIST-reference diameter	Number density	Specific surface area
d(10)	8.5 nm	3.0 × 10¹² NP/mL	67.5 m²/g
d(50)	11.5 nm	1.2 × 10¹² NP/mL	49.9 m²/g
d(90)	13.7 nm	7.0 × 10¹¹ NP/mL	41.6 m²/g

Particle-size distributions and media comparisons — Particle-size data excerpt. The complete article and supporting information explain the DLS distributions, media conditions, and interpretation.

Dissolution and behavior in test media

The study tracked both total silver and ionic silver after exposure to deionized water, moderately hard water, and concentrated artificial alveolar fluid. Mineral-rich media changed the appearance and dispersion state of the samples, so the authors combined bulk silver measurements with microscopy rather than treating a color change or a single sizing result as proof of dissolution.

ICP-OES measurements and ion-selective-electrode results were interpreted alongside ultracentrifugation and microscopy. The article reports low ion emission for EVQ-218 and emphasizes that mineral association, precipitation, and electrode interference must be distinguished from true particle dissolution.

ICP-OES comparison of EVQ-218 and the NIST-traceable reference in test media — Silver measurement excerpt comparing EVQ-218 and the NIST-traceable reference across the reported media conditions.

Silver-ion-selective-electrode results for EVQ-218 — Ion-selective-electrode results. The authors discuss low readings as well as possible false-positive interactions in moderately hard water.

Surface chemistry and particle fate

STEM/EDS mapping showed how calcium-, carbon-, oxygen-, and phosphorus-containing minerals associated with silver particles after media exposure. These maps let the authors distinguish an elemental silver signal from the surrounding mineral precipitate and compare the morphology retained by each material.

STEM images of EVQ-218 after exposure to moderately hard water — STEM image set of EVQ-218 after moderately hard water exposure; spherical particle features remain visible within the precipitate.

Elemental map of mineral-exposed EVQ-218 — EDS map of mineral-exposed EVQ-218, showing the silver signal in relation to calcium-, carbon-, and oxygen-containing material.

EELS analysis was used to examine the particle surface and compare EVQ-218 with the citrate-containing reference. The authors interpret the EVQ-218 spectra as evidence of a bare silver surface without an added stabilizing shell.

EELS spectrum image map for EVQ-218 — EELS spectrum-image map used to evaluate the EVQ-218 particle surface. See the article for acquisition and processing details.

Long-term stability

The article includes microscopy of EVQ-218 material produced in 2007 and imaged in 2020. The authors report retained particle identity and uniform silver density over that interval. This observation supports long-term material stability in the stored sample; it does not by itself establish shelf life in every formulation, package, or application environment.

Conclusions and boundaries

The paper reports that EVQ-218 was comparable with the NIST-traceable reference in particle morphology and uniformity while differing in surface chemistry and emission behavior. Its central conclusion is that the laser-produced particles combine a narrow size distribution with a stable, surfactant-free silver surface.

These are physicochemical characterization results. Application performance, toxicology, environmental fate, and clinical outcomes require their own studies and should not be inferred from particle characterization alone.