Direct bottom-up high pressure high temperature (BU_HPHT) synthesis of nanodiamonds (NDs) from organic precursors excels in the ability to control the size of the resulting BU_HPHT NDs via the temperature of the synthesis. Here we investigated size-dependent thermal, colloidal, and structural properties of the BU_HPHT NDs and focused on the transition in morphology and properties occurring at around 900 °C (≈2 nm). Using transmission electron microscopy, small angle X-ray scattering and atomic force microscopy we show that the sub-900 °C samples (<2 nm NDs) do not have nanoparticle character but 2D platelet morphology with sub-nm unit thickness. Correspondingly, sub-900 °C samples (<2 nm NDs) have a negative zeta potential and hydrophobic character and should be considered as a form of a molecular diamond. The above-900C (>2 nm NDs) samples have nanocrystalline character, positive zeta potential and are dispersible in water similarly to other types of hydrogenated NDs. By in situ Raman spectroscopy experiments, we show that the transition is also related to the structural instability of the oxidized sub-2 nm BU_HPHT NDs.

• Publication type
• Journal Article MeSH

Temperature is one of the most relevant parameters for the regulation of intracellular processes. Measuring localized subcellular temperature gradients is fundamental for a deeper understanding of cell function, such as the genesis of action potentials, and cell metabolism. Notwithstanding several proposed techniques, at the moment detection of temperature fluctuations at the subcellular level still represents an ongoing challenge. Here, for the first time, temperature variations (1 °C) associated with potentiation and inhibition of neuronal firing is detected, by exploiting a nanoscale thermometer based on optically detected magnetic resonance in nanodiamonds. The results demonstrate that nitrogen-vacancy centers in nanodiamonds provide a tool for assessing various levels of neuronal spiking activity, since they are suitable for monitoring different temperature variations, respectively, associated with the spontaneous firing of hippocampal neurons, the disinhibition of GABAergic transmission and the silencing of the network. Conjugated with the high sensitivity of this technique (in perspective sensitive to < 0.1 °C variations), nanodiamonds pave the way to a systematic study of the generation of localized temperature gradients under physiological and pathological conditions. Furthermore, they prompt further studies explaining in detail the physiological mechanism originating this effect.

• Keywords
• ODMR, intracellular nanoscale sensing, nanodiamonds, nitrogen-vacancy (NV) centers,
• MeSH
• Nitrogen MeSH
• Hippocampus MeSH
• Nanodiamonds * MeSH
• Neurons MeSH
• Temperature MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Nitrogen MeSH
• Nanodiamonds * MeSH

Nitrogen vacancy diamonds have emerged as sensitive solid-state magnetic field sensors capable of producing diffraction limited and sub-diffraction field images. Here, for the first time, to our knowledge, we extend those measurements to high-speed imaging, which can be readily applied to analyze currents and magnetic field dynamics in circuits on a microscopic scale. To overcome detector acquisition rate limitations, we designed an optical streaking nitrogen vacancy microscope to acquire two-dimensional spatiotemporal kymograms. We demonstrate magnetic field wave imaging with micro-scale spatial extent and ~400 μs temporal resolution. In validating this system, we detected magnetic fields down to 10 μT for 40 Hz magnetic fields using single-shot imaging and captured the spatial transit of an electromagnetic needle at streak rates as high as 110 μm/ms. This design has the capability to be readily extended to full 3D video acquisition by utilizing compressed sensing techniques and a potential for further improvement of spatial resolution, acquisition speed, and sensitivity. The device opens opportunities to many potential applications where transient magnetic events can be isolated to a single spatial axis, such as acquiring spatially propagating action potentials for brain imaging and remotely interrogating integrated circuits.

• Publication type
• Journal Article MeSH

Free radicals are crucial indicators for stress and appear in all kinds of pathogenic conditions, including cancer, cardiovascular diseases, and infection. However, they are difficult to detect due to their reactivity and low abundance. We use relaxometry for the detection of radicals with subcellular resolution. This method is based on a fluorescent defect in a diamond, which changes its optical properties on the basis of the magnetic surroundings. This technique allows nanoscale MRI with unprecedented sensitivity and spatial resolution. Recently, this technique was used inside living cells from a cell line. Cell lines differ in terms of endocytic capability and radical production from primary cells derived from patients. Here we provide the first measurements of phagocytic radical production by the NADPH oxidase (NOX2) in primary dendritic cells from healthy donors. The radical production of these cells differs greatly between donors. We investigated the cell response to stimulation or inhibition.

• Keywords
• NV centers, magnetometry, nanodiamonds, relaxometry measurements (T1),
• MeSH
• Dendritic Cells MeSH
• Diamond MeSH
• Humans MeSH
• Magnetics MeSH
• Nanodiamonds * chemistry   MeSH
• Free Radicals MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Diamond MeSH
• Nanodiamonds * MeSH
• Free Radicals MeSH