AVS2015 Session NS-WeM: Nanodiamond for Optical and Biomedical Applications

We have developed FNDs into a nanoscale luminescence thermometer for both temporally and spatially resolved temperature sensing with hosted NV^– centers, time-resolved luminescence nanothermometry was demonstrated with 100-nm FNDs spin-coated on a glass substrate and submerged in gold nanorod solution heated by a near-infrared laser, a pump-probe-type experiment that enables the study of nanoscale heat transfer with a temporal resolution of better than 10 μs. Moreover, we present a three-point sampling method that allows real-time monitoring of the temperature changes over ±100 K, an advantage of this three-point method is that it possesses a built-in ability for self-correction of signal fluctuation. To verify the validity of these measurements and to understand the heat transfer in the nanometer and microsecond scales, we carried out heat transfer numerical simulations. The simulated time constants for single exponential decays are τ = 20 μs at r = 1.0 μm and τ = 25 μs at r = 1.5 μm, compared with our experimental observations of 12 and 18 μs, respectively. Finally, the present study represents the first demonstration of thermometric investigation at the nanometric length scale with microsecond time resolution. It adds an important new dimension to the use of NV^– centers in diamond for quantum sensing applications.

Reference:

(1) Toyli, D. M.; Christle, D. J.; Alkauskas, A.; Buckley, B. B.; Van de Walle, C. G.; Awschalom, D. D. Measurement and control of single nitrogen-vacancy center spins above 600 K. Phys. Rev. X.2012, 2, 031001.

(2) Loza, P.; Kouznetsov, D.; Ortega, R. Temperature distribution in a uniform medium heated by linear absorption of a Gaussian light beam. Appl. Opt.1994, 33, 3831–3836.

Detonation is one of the primary methods to produce nanodiamond. A new small-angle x-ray scattering (SAXS) end station has been developed by LLNL for use at the new Dynamic Compression Sector at the Advanced Photon Source to observe carbon condensation during detonation of high explosives. The beamline and endstation are capable of synchronously initiating detonation and then acquiring up to four SAXS patterns from single x-ray pulses, which in 24-bunch mode at the APS are < 100 ps and arrive every 153.4 ns. Timescales are ideal: detonation investigation and model validation requires data regarding processes occurring at nanometer length scales on time scales ranging from nanoseconds to microseconds. The endstation and beamline have now demonstrated unprecedented fidelity in SAXS data during detonation; for the first time the data contains a clear Guinier knee and high-fidelity power law slope, giving information about the size and morphology of the resultant nanoparticles. We have commenced investigating HNS which is an explosive known to produce copious graphitic soots, RDX/TNT mixutures similar to what is commonly used to produce nanodiamond, and DNTF, a hydrogen-free, nitrogen rich, hot, and high velocity explosive. HNS produces carbon particles with a radius of gyration of 3 nm in less than 400 ns after the detonation front has passed, and this size is constant over the next several microseconds. The power-law slope is about -3, consistent with a disordered, irregular, or folded sp² structure. Comp B, a 60% RDX, 40% TNT mixture, produces 3 nm particles also within a few hundred ns, and has a power law that is around -3.7, consistent with 3D nanodiamond particles. DNTF produces larger, 7 nm particles with a power law that is -4 over the first few hundred ns and then decreases to -3.8, ultimately also consistent with 3D diamond nanoparticles. In all three cases, particles are produced in the first few hundred ns, and then do not appreciably grow over the next several microseconds, which is in direct contradiction to previous pioneering work on RDX/TNT mixtures, TATB, and several other explosives, where observations indicate significant particle growth (50% or more) continues over several microseconds.

High explosive detonation is an exothermic process where CHNO molecules are transformed into, but not limited to, H₂O, CO, CO₂, N₂, and solid carbon (i.e. soot). The type and quantity of carbon allotrope present depends on the explosive formulation and the temperature and pressure of the detonation. The carbon allotropes that form during a detonation include nanodiamond, graphite, and amorphous carbon; however, nanodiamonds are the most interesting. Due to their chemical inertness and biocompatibility, nanodiamonds have garnered interest in biomedical and elec­tronic applications.^₁

The nature of a detonation event produces soot that is contaminated with metals, metal oxides, and other carbon phases (i.e. sp² carbons). Removal of these species is essential to obtaining pristine nanodiamond. Metals and metal oxides are removed using mineral acid treatments; whereas, sp² species are thermally oxidized above 400 ^oC.² Although acid treatment and thermal oxidation generate pristine nanodiamond, these methods damage the characteristic markers that provide information about the processes and conditions that give rise to nanodiamond as a carbon allotrope.

Another benign approach could be surface functionalization of the soot followed by separation of functionalized and non-functionalized components. Carbon nanotubes have been known to de-aggregate and disperse in ionic liquids.³ A similar approach was demonstrated for pristine nanodiamond using an imidazolium based ionic liquid covalently bound to its surface. These functionalized nanodiamonds showed increased dispersibility in polar solvents and formed stable gels in other ionic liquids.⁴

Our efforts to adapt ionic liquids for the surface functionalization of nanocarbons produced by high explosive detonation will be discussed. Specifically, imidazolium based ionic liquids incorporating decyl chains through various coupling strategies will be reviewed. The functionalized nanocarbons could then be dispersed in solvents, allowing for individual component isolation and size fractionation. The isolated products were characterized using a range of techniques including SEM, TEM, powder X-ray diffraction, X-ray scattering, and XPS.

References:

1. Krueger, A.; Lang, D. Adv. Funct. Mater. 2012,22, 890.

2. Pichot, V.; Comet, M.; Fousoon, E.; Baras, C.; Senger, A.; Le Normand, F.; Spitzer, D. Diam. Relat. Mater. 2008,17, 13.

3. Fukushima, T.; Kosaka, A.; Ishimura, Y.; Yamamoto, T.; Takigawa, T.; Ishii, N.; Aida, T. Science 2003,300, 2072.

4. Park, C.; Young, A. Y.; Lee, M.; Lee, S. Chem. Commun. 2009, 5576.

Nanodiamond (ND) particles have recently emerged as a key platform for many sectors of nanoscience and nanotechnology due to their outstanding mechanical performance, biocompatibility and distinctive optical properties, a combination of assets not often met in the nanoworld. Particularly production of ND particles containing nitrogen-vacancy (NV) color centers exhibiting stable luminescence and unique spin properties have brought ND particles to the forefront of materials research. Based on the SBIR award from National Institute of Health (NIH), Adámas Nanotechnologies developed a large scale production of ND containing NV color centers in hundreds of grams batches. While nitrogen is an intrinsic impurity in diamond, vacancies must be created by high energy irradiation. Variety of factors play a role in creation of a high density ensemble of NV centers in NDs including density of substitutional nitrogen, size of starting particles that undergo irradiation, irradiation dose and temperature, post irradiation processing including fragmentation to the smaller sizes. In the paper, role of these factors will be discussed. Production of fractions of NDs with median sizes ranging between 10 and 100 nm was demonstrated, exceeding by an order of magnitude brightness of a relevant typically used organic dye for NDs with sizes exceeding 50nm. The brightness of fluorescent nanodiamonds and an organic dye was compared side-by-side under identical conditions using total internal reflection fluorescence microscopy (TIRFM) measurements at NIH.

Acknowledgment: Contract HHSN268201300030C, NHLBI COAC Services Branch RFP No. PHS 2013-1, Topic 80, “Fluorescent Nanodiamonds for In Vitro and In Vivo Biological Imaging”