44 research outputs found
High Temperature Treatment of Diamond Particles Toward Enhancement of Their Quantum Properties
Fluorescence of the negatively charged nitrogen-vacancy (NV-) center of diamond is sensitive to external electromagnetic fields, lattice strain, and temperature due to the unique triplet configuration of its spin states. Their use in particulate diamond allows for the possibility of localized sensing and magnetic-contrast-based differential imaging in complex environments with high fluorescent background. However, current methods of NV(-)production in diamond particles are accompanied by the formation of a large number of parasitic defects and lattice distortions resulting in deterioration of the NV(-)performance. Therefore, there are significant efforts to improve the quantum properties of diamond particles to advance the field. Recently it was shown that rapid thermal annealing (RTA) at temperatures much exceeding the standard temperatures used for NV(-)production can efficiently eliminate parasitic paramagnetic impurities and, as a result, by an order of magnitude improve the degree of hyperpolarization of(13)C via polarization transfer from optically polarized NV(-)centers in micron-sized particles. Here, we demonstrate that RTA also improves the maximum achievable magnetic modulation of NV(-)fluorescence in micron-sized diamond by about 4x over conventionally produced diamond particles endowed with NV-. This advancement can continue to bridge the pathway toward developing nano-sized diamond with improved qualities for quantum sensing and imaging
A 50Â l CYGNO prototype overground characterization
The nature of dark matter is still unknown and an experimental program to look for dark matter particles in our Galaxy should extend its sensitivity to light particles in the GeV mass range and exploit the directional information of the DM particle motion (Vahsen et al. in CYGNUS: feasibility of a nuclear recoil observatory with directional sensitivity to dark matter and neutrinos, arXiv:2008.12587, 2020). The CYGNO project is studying a gaseous time projection chamber operated at atmospheric pressure with a Gas Electron Multiplier (Sauli in Nucl Instrum Meth A 386:531, https://doi.org/10.1016/S0168-9002(96)01172-2, 1997) amplification and with an optical readout as a promising technology for light dark matter and directional searches. In this paper we describe the operation of a 50 l prototype named LIME (Long Imaging ModulE) in an overground location at Laboratori Nazionali di Frascati (LNF) of INFN. This prototype employs the technology under study for the 1 cubic meter CYGNO demonstrator to be installed at the Laboratori Nazionali del Gran Sasso (LNGS) (Amaro et al. in Instruments 2022, 6(1), https://www.mdpi.com/2410-390X/6/1/6, 2022). We report the characterization of LIME with photon sources in the energy range from few keV to several tens of keV to understand the performance of the energy reconstruction of the emitted electron. We achieved a low energy threshold of few keV and an energy resolution over the whole energy range of 10–20%, while operating the detector for several weeks continuously with very high operational efficiency. The energy spectrum of the reconstructed electrons is then reported and will be the basis to identify radio-contaminants of the LIME materials to be removed for future CYGNO detectors
Explosive Fragmentation of Luminescent Diamond Particles
Development of efficient and cost-effective mass-production techniques for size reduction of high-pressure, high-temperature (HPHT) diamonds with sizes from tens to hundreds of micrometers remains one of the primary goals towards commercial production of fluorescent submicron and nanodiamond (fND). fNDs offer great advantages for many applications, especially in labelling, tracing, and biomedical imaging, owing to their brightness, exceptional photostability, mechanical robustness and intrinsic biocompatibility. This study proposes a novel processing method utilizing explosive fragmentation that can potentially be used for the fabrication of submicron to nanoscale size fluorescent diamond particles. In the proposed method, synthetic HPHT 20 µm and 150 µm microcystalline diamond particles containing color centers are rapidly fragmented in conditions of high explosive detonation. X-ray diffraction and Raman spectroscopy show that the detonation fragmented diamond particles consist of good quality submicron diamonds of ~420-800 nm in size, while fluorescence spectroscopy shows photoluminescence spectra with noticeable changes for large (150 µm) starting microcrystalline diamond particles, and no significant changes in photoluminescence properties for smaller (20 µm) starting microcrystalline diamond particles. The proposed detonation method shows potential as an efficient, cost effective, and industrially scalable alternative to milling for the fragmentation of fluorescent diamond microcrystals into submicron-to-nano-size domain
Quantitative Determination of Ligand Densities on Nanomaterials by X‑ray Photoelectron Spectroscopy
X-ray
photoelectron spectroscopy (XPS) is a nearly universal method
for quantitative characterization of both organic and inorganic layers
on surfaces. When applied to nanoparticles, the analysis is complicated
by the strong curvature of the surface and by the fact that the electron
attenuation length can be comparable to the diameter of the nanoparticles,
making it necessary to explicitly include the shape of the nanoparticle
to achieve quantitative analysis. We describe a combined experimental
and computational analysis of XPS data for molecular ligands on gold
nanoparticles. The analysis includes scattering in both Au core and
organic shells and is valid even for nanoparticles having diameters
comparable to the electron attenuation length (EAL). To test this
model, we show experimentally how varying particle diameter from 1.3
to 6.3 nm leads to a change in the measured <i>A</i><sub>C</sub>/<i>A</i><sub>Au</sub> peak area ratio, changing
by a factor of 15. By analyzing the data in a simple computational
model, we demonstrate that ligand densities can be obtained, and,
moreover, that the actual ligand densities for these nanoparticles
are a constant value of 3.9 ± 0.2 molecules nm<sup>–2</sup>. This model can be easily extended to a wide range of core–shell
nanoparticles, providing a simple pathway to extend XPS quantitative
analysis to a broader range of nanomaterials
Natural Organic Matter Concentration Impacts the Interaction of Functionalized Diamond Nanoparticles with Model and Actual Bacterial Membranes
Changes to nanoparticle surface charge,
colloidal stability, and
hydrodynamic properties induced by interaction with natural organic
matter (NOM) warrant consideration in assessing the potential for
these materials to adversely impact organisms in the environment.
Here, we show that acquisition of a coating, or “corona”,
of NOM alters the hydrodynamic and electrokinetic properties of diamond
nanoparticles (DNPs) functionalized with the polycation polyÂ(allylamine
HCl) in a manner that depends on the NOM-to-DNP concentration ratio.
The NOM-induced changes to DNP properties alter subsequent interactions
with model biological membranes and the Gram-negative bacterium <i>Shewanella oneidensis</i> MR-1. Suwannee River NOM induces changes
to DNP hydrodynamic diameter and apparent ζ-potential in a concentration-dependent
manner. At low NOM-to-DNP ratios, DNPs aggregate to a limited extent
but retain a positive ζ-potential apparently due to nonuniform
adsorption of NOM molecules leading to attractive electrostatic interactions
between oppositely charged regions on adjacent DNP surfaces. Diamond
nanoparticles at low NOM-to-DNP ratios attach to model membranes to
a larger extent than in the absence of NOM (including those incorporating
lipopolysaccharide, a major bacterial outer membrane component) and
induce a comparable degree of membrane damage and toxicity to <i>S. oneidensis</i>. At higher NOM-to-DNP ratios, DNP charge is
reversed, and DNP aggregates remain stable in suspension. This charge
reversal eliminates DNP attachment to model membranes containing the
highest LPS contents studied due to electrostatic repulsion and abolishes
membrane damage to <i>S. oneidensis</i>. Our results demonstrate
that the effects of NOM coronas on nanoparticle properties and interactions
with biological surfaces can depend on the relative amounts of NOM
and nanoparticles
A Citric Acid-Derived Ligand for Modular Functionalization of Metal Oxide Surfaces via “Click” Chemistry
Citric acid is a widely used surface-modifying ligand
for growth
and processing of a variety of nanoparticles; however, the inability
to easily prepare derivatives of this molecule has restricted the
development of versatile chemistries for nanoparticle surface functionalization.
Here, we report the design and synthesis of a citric acid derivative
bearing an alkyne group and demonstrate that this molecule provides
the ability to achieve stable, multidentate carboxylate binding to
metal oxide nanoparticles, while also enabling subsequent multistep
chemistry via the CuÂ(I)-catalyzed azide–alkyne cycloaddition
(CuAAC) reaction. The broad utility of this strategy for the modular
functionalization of metal oxide surfaces was demonstrated by its
application in the CuAAC modification of ZnO, Fe<sub>2</sub>O<sub>3</sub>, TiO<sub>2</sub>, and WO<sub>3</sub> nanoparticles
Quantification of Free Polyelectrolytes Present in Colloidal Suspension, Revealing a Source of Toxic Responses for Polyelectrolyte-Wrapped Gold Nanoparticles
Polyelectrolyte
(PE) wrapping of colloidal nanoparticles (NPs)
is a standard method to control NP surface chemistry and charge. Because
excess polyelectrolytes are usually employed in the surface modification
process, it is critical to evaluate different purification strategies
to obtain a clean final product and thus avoid ambiguities in the
source of effects on biological systems. In this work, 4 nm diameter
gold nanoparticles (AuNPs) were wrapped with 15 kDa polyÂ(allylamine
hydrochloride) (PAH), and three purification strategies were applied:
(a) diafiltration or either (b) one round or (c) two rounds of centrifugation.
The bacterial toxicity of each of these three PAH-AuNP samples was
evaluated for the bacterium <i>Shewanella oneidensis</i> MR-1 and is quantitatively correlated with the amount of unbound
PAH molecules in the AuNP suspensions, as judged by X-ray photoelectron
spectroscopy, nuclear magnetic resonance experiments and quantification
using fluorescent assay. Dialysis experiments show that, for a 15
kDa polyelectrolyte, a 50 kDa dialysis membrane is not sufficient
to remove all PAH polymers. Together, these data showcase the importance
of choosing a proper postsynthesis purification method for polyelectrolyte-wrapped
NPs and reveal that apparent toxicity results may be due to unintended
free wrapping agents such as polyelectrolytes