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We experimentally demonstrate a simple and robust optical fiber based method to achieve simultaneously efficient excitation and fluorescence collection from Nitrogen-Vacancy (NV) defects containing micro-crystalline diamond. We fabricate a suitable micro-concave mirror that focuses scattered excitation laser light into the diamond located at the focal point of the mirror. At the same instance, the mirror also couples the fluorescence light exiting out of the diamond crystal in the opposite direction of the optical fiber back into the optical fiber within its light acceptance cone. This part of fluorescence would have been otherwise lost from reaching the detector. Our proof-of-principle demonstration achieves a 25 times improvement in fluorescence collection compared to the case of not using any mirrors. The increase in light collection favors getting high signal-to-noise ratio optically detected magnetic resonance signals and hence offers a practical advantage in fiber-based NV quantum sensors. Additionally, we compacted the NV sensor system by replacing some bulky optical elements in the optical path with a 1 × 2 fiber optical coupler in our optical system. This reduces the complexity of the system and provides portability and robustness needed for applications like magnetic endoscopy and remote-magnetic sensing. [ABSTRACT FROM AUTHOR]

Highly stable lipid-encapsulated fluorescent nanodiamonds (FNDs) are produced by photo-crosslinking of diacetylene-containing lipids physically attached to the FND surface. Not only is this coating method simple and fast, but also it gives the FND–lipid hybrids favorable properties for bioapplications. The hybrids are useful as fluorescent biolabels as well as fiducial markers for correlative light and electron microscopy. [ABSTRACT FROM AUTHOR]

Measuring temperature at or far from equilibrium at the nanoscale is important in many fields of science and engineering. A variety of luminescent nanothermometers have been developed in the past decade for the measurements. Fluorescent nanodiamonds (FNDs) stand out from the rest in terms of biological use, because the nanomaterials contain negatively charged nitrogen-vacancy (NV−) centers as photostable fluorophores and possess a number of remarkable properties including chemical inertness, negligible toxicity, versatile surface modification ability and, most importantly, exceptional temperature-measurement precision. However, to enable practical applications of FNDs for temperature sensing in biological systems, conjugation of the particles with polymers, biomolecules, and/or other nanomaterials are often required. Gold/diamond nanohybrids are one of these combinations that enhance the temperature measurement versatility of the NV− centers. Here, we provide a review of the recent advances in the research and development of diamond nanothermometry, with special focus on the synthesis, characterization, and applications of gold/diamond nanohybrids. Current challenges and future perspectives of the FND-based nanothermometry are also discussed. [ABSTRACT FROM AUTHOR]

This work demonstrates that the gold tip of an atomic force microscope enhances not only the fluorescence of the nitrogen-vacancy centers in nanodiamonds but also improves the optical resolution of the fluorescence image of the particles down to 40 nm in an apertureless near-field scanning optical microscope. With the tip in close contact with 20-30 nm diamonds, the average fluorescence intensity enhancement is 3. By measuring the fluorescence decay lifetime and the saturation intensity, we confirm that the fluorescence enhancement is contributed predominantly by the increase of the radiative decay rate. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates the intercellular transport of yolk lipoproteins in Caenorhabditis elegans by using fluorescence lifetime imaging microscopy (FLIM) and fluorescent nanodiamonds (FNDs) as photostable labels and tracers. The yolk lipoproteins in the nematode are similar to human serum low-density lipoproteins (LDLs), serving as an intercellular transporter of fat molecules and cholesterol. To study this fundamentally important process, FNDs were first coated with yolk lipoprotein complexes (YLCs) and then microinjected into the intestinal cells of the living organism. Real-time imaging over a time period of more than 50 min with FLIM revealed the process of YLC-FND secretion from the intestine to the pseudocoelomic space, followed by transporting into oocytes and subsequent accumulation in the multi-cellular embryos derived from the oocytes. Colocalization studies of the rme-2 adult hermaphrodites expressing green fluorescent protein (GFP)-tagged YLCs confirmed that the injected YLC-FNDs were taken up by oocytes through endocytosis mediated by the LDL receptor, RME-2, functioning as an YLC receptor. Our results demonstrate that FND is useful as a biomolecular nanocarrier without significantly altering the functionality of the cargos for intercellular transport, cell-specific targeting, and long-term imaging applications in vivo. [Copyright &y& Elsevier]

Abstract: Nanocarbon is a promising type of biomaterial for diagnostic and therapeutic applications. Fluorescent nanodiamond (FND) containing nitrogen-vacancy centers as built-in fluorophores is a new addition to the nanocarbon family. Here, we study the long-term stability and biocompatibility of 100-nm FNDs in rats through intraperitoneal injection over 5 months and develop the potential application of this biomaterial for sentinel lymph node mapping in a mouse model. From both in vivo and ex vivo fluorescence imaging as well as transmission electron microscopy, we found that the intradermally administered FND particles can be drained from the injection sites by macrophages and selectively accumulated in the axillary lymph nodes of the treated mice. Our measurements of water consumption, fodder consumption, body weight, and organ index showed no significant difference between control and FND-treated groups of the rats. Histopathological analysis of various tissues and organs indicated that FNDs are non-toxic even when a large quantity, up to 75 mg/kg body weight, of the particles was administered intraperitoneally to the living animals. With the properties of wide-ranging biocompatibility and perfect chemical and photophysical stability, FND is well suited for use as a contrast agent for long-term in vivo imaging. [Copyright &y& Elsevier]

Abstract: Green fluorescent nanodiamonds (denoted as gFNDs) have been produced and characterized for use as cellular markers and/or labels. The gFND particles, containing a high concentration of N–V–N (or H3) centers, were prepared by radiation damage of type Ia natural diamond nanocrystallites with either a home-built 40-keV He+ beam or a research-grade 3-MeV H+ beam, followed by thermal annealing at 800 °C. Prior to the irradiation treatment, infrared spectroscopy of C–N stretches (at 1282 cm−1) of natural diamond single crystals revealed a nitrogen concentration in the range of 900 ppm. Irradiation and annealing of the specimens led to the emergence of a broad absorption band at ~470 nm, corresponding to the phonon sideband of the electronic transition of the H3 center. Measuring the integrated absorption coefficient of the zero-phonon line (at 503 nm) of this center at liquid nitrogen temperature suggested a H3 density of 1.7×1018 centers/cm3 (or 10 ppm). A similarly high concentration of the defect centers was estimated for natural diamond nanocrystallites treated under the same experimental conditions. The centers emitted green light (λ em =530 nm) upon illumination by a blue laser (λ ex =473 nm or 488 nm). Applications of this novel nanomaterial as fluorescent cellular markers were demonstrated with both confocal fluorescence microscopy and flow cytometry of 70-nm-sized gFND particles uptaken by live HeLa cells through endocytosis. [Copyright &y& Elsevier]