Spin-manipulated nanoscopy for single nitrogen-vacancy center localizations in nanodiamonds

Wide-field tomography imaging of a double circuit using NV center ensembles in a diamond

The wide-field (2.42 mm × 1.36 mm, resolution: 5.04 µm) tomography imaging of double circuits is performed using nitrogen-vacancy (NV) center ensembles in a diamond. The magnetic-field distribution on the surface of the circuit produced by the lower layer is obtained. Vector magnetic superposition is used to separate the magnetic-field distribution produced by the lower layer from the magnetic-field distribution produced by two layers. An inversion model is used to perform the tomography imaging of the magnetic-field distribution on the lower layer surface. Compared with the measurements of the upper layer, the difference in the maximum magnetic-field intensity of inversion is approximately 0.4%, and the difference in the magnetic-field distribution of inversion is approximately 8%, where the depth of the lower layer is 0.32 mm. Simulations are conducted to prove the reliability of the imaging. These results provide a simple and highly accurate reference for the detection and fault diagnosis of multilayer and integrated circuits.

Self-Assembly of Nanodiamonds and Plasmonic Nanoparticles for Nanoscopy

Nanodiamonds have emerged as promising agents for sensing and imaging due to their exceptional photostability and sensitivity to the local nanoscale environment. Here, we introduce a hybrid system composed of a nanodiamond containing nitrogen-vacancy center that is paired to a gold nanoparticle via DNA hybridization. Using multiphoton optical studies, we demonstrate that the harmonic mode emission generated in gold nanoparticles induces a coupled fluorescence emission in nanodiamonds. We show that the flickering of harmonic emission in gold nanoparticles directly influences the nanodiamonds' emissions, resulting in stochastic blinking. By utilizing the stochastic emission fluctuations, we present a proof-of-principle experiment to demonstrate the potential application of the hybrid system for super-resolution microscopy. The introduced system may find applications in intracellular biosensing and bioimaging due to the DNA-based coupling mechanism and also the attractive characteristics of harmonic generation, such as low power, low background and tissue transparency.

Charge state depletion nanoscopy with a nitrogen-vacancy center in nanodiamonds

The development of super-resolution imaging has driven research into biological labeling, new materials' characterization, and nanoscale sensing. Here, we studied the photoinduced charge state conversion of nitrogen-vacancy (NV) centers in nanodiamonds (NDs), which show the potential for multifunction sensing and labeling at the nanoscale. Charge state depletion (CSD) nanoscopy is subsequently demonstrated for the diffraction-unlimited imaging of NDs in biological cells. A resolution of 77 nm is obtained with 50 nm NDs. The depletion laser power of CSD nanoscopy is approximately 1/16 of stimulated emission depletion (STED) microscopy with the same resolution. The results can be used to improve the spatial resolution of biological labeling and sensing with NDs and other nanoparticles.

Quantum nanodiamonds for sensing of biological quantities: Angle, temperature, and thermal conductivity

Measuring physical quantities in the nanometric region inside single cells is of great importance for understanding cellular activity. Thus, the development of biocompatible, sensitive, and reliable nanobiosensors is essential for progress in biological research. Diamond nanoparticles containing nitrogen-vacancy centers (NVCs), referred to as fluorescent nanodiamonds (FNDs), have recently emerged as the sensors that show great promise for ultrasensitive nanosensing of physical quantities. FNDs emit stable fluorescence without photobleaching. Additionally, their distinctive magneto-optical properties enable an optical readout of the quantum states of the electron spin in NVC under ambient conditions. These properties enable the quantitative sensing of physical parameters (temperature, magnetic field, electric field, pH, etc.) in the vicinity of an FND; hence, FNDs are often described as “quantum sensors”. In this review, recent advancements in biosensing applications of FNDs are summarized. First, the principles of orientation and temperature sensing using FND quantum sensors are explained. Next, we introduce surface coating techniques indispensable for controlling the physicochemical properties of FNDs. The achievements of practical biological sensing using surface-coated FNDs, including orientation, temperature, and thermal conductivity, are then highlighted. Finally, the advantages, challenges, and perspectives of the quantum sensing of FND are discussed. This review article is an extended version of the Japanese article, In Situ Measurement of Intracellular Thermal Conductivity Using Diamond Nanoparticle, published in SEIBUTSU BUTSURI Vol. 62, p. 122–124 (2022).

Diamond quantum thermometry: from foundations to applications

Diamond quantum thermometry exploits the optical and electrical spin properties of colour defect centres in diamonds and, acts as a quantum sensing method exhibiting ultrahigh precision and robustness. Compared to the existing luminescent nanothermometry techniques, a diamond quantum thermometer can be operated over a wide temperature range and a sensor spatial scale ranging from nanometres to micrometres. Further, diamond quantum thermometry is employed in several applications, including electronics and biology, to explore these fields with nanoscale temperature measurements. This review covers the operational principles of diamond quantum thermometry for spin-based and all-optical methods, material development of diamonds with a focus on thermometry, and examples of applications in electrical and biological systems with demand-based technological requirements.

Ground-State Depletion Nanoscopy of Nitrogen-Vacancy Centres in Nanodiamonds

The negatively charged nitrogen-vacancy ([Formula: see text]) centre in nanodiamonds (NDs) has been recently studied for applications in cellular imaging due to its better photo-stability and biocompatibility if compared to other fluorophores. Super-resolution imaging achieving 20-nm resolution of [Formula: see text] in NDs has been proved over the years using sub-diffraction limited imaging approaches such as single molecule stochastic localisation microscopy and stimulated emission depletion microscopy. Here we show the first demonstration of ground-state depletion (GSD) nanoscopy of these centres in NDs using three beams, a probe beam, a depletion beam and a reset beam. The depletion beam at 638 nm forces the [Formula: see text] centres to the metastable dark state everywhere but in the local minimum, while a Gaussian beam at 594 nm probes the [Formula: see text] centres and a 488-nm reset beam is used to repopulate the excited state. Super-resolution imaging of a single [Formula: see text] centre with a full width at half maximum of 36 nm is demonstrated, and two adjacent [Formula: see text] centres separated by 72 nm are resolved. GSD microscopy is here applied to [Formula: see text] in NDs with a much lower optical power compared to bulk diamond. This work demonstrates the need to control the NDs nitrogen concentration to tailor their application in super-resolution imaging methods and paves the way for studies of [Formula: see text] in NDs' nanoscale interactions.

Imaging the magnetic field distribution of a micro-wire with the nitrogen-vacancycolor center ensemble in diamond

Imaging the high-precision magnetic distribution generated by the surface current of chips and chip-like structures is an important way to measure thermal parameters of core components. Based on a high-concentration nitrogen-vacancy color center ensemble in diamond, the imaging magnetic field distribution is performed in a wide-field microscope. The magnetic vector detection and reduction model is verified first with continuous wave optical detection of magnetic resonance technology. By systematically measuring the distribution of the electromagnetic field generated on the surface of the micro-wire under different microwave power and different laser power conditions, the imaging quality of the wide-field imaging system can be optimized by adjusting the experimental parameters. Then, the electromagnetic field distribution imaging on the wire surface under different current intensities is obtained. In this way, accurate measurement and characterization of the magnetic distribution on the surface of the micro-wire is realized. Finally, at the field of view in the range of 480µm×270µm, the magnetic intensity is an accurate characterization in 0.5-10 Gs, and the magnetic detection sensitivity can be increased from 100 to 20µT/Hz^1/2. The results show the accurate magnetic distribution imaging for chips and chip-like structures, which provide a new method for chip function detection and fault diagnosis based on precision quantum measurement technology.

Hexagonal boron nitride: a review of the emerging material platform for single-photon sources and the spin-photon interface

Single-photon sources and their optical spin readout are at the core of applications in quantum communication, quantum computation, and quantum sensing. Their integration in photonic structures such as photonic crystals, microdisks, microring resonators, and nanopillars is essential for their deployment in quantum technologies. While there are currently only two material platforms (diamond and silicon carbide) with proven single-photon emission from the visible to infrared, a quantum spin-photon interface, and ancilla qubits, it is expected that other material platforms could emerge with similar characteristics in the near future. These two materials also naturally lead to monolithic integrated photonics as both are good photonic materials. While so far the verification of single-photon sources was based on discovery, assignment and then assessment and control of their quantum properties for applications, a better approach could be to identify applications and then search for the material that could address the requirements of the application in terms of quantum properties of the defects. This approach is quite difficult as it is based mostly on the reliability of modeling and predicting of color center properties in various materials, and their experimental verification is challenging. In this paper, we review some recent advances in an emerging material, low-dimensional (2D, 1D, 0D) hexagonal boron nitride (h-BN), which could lead to establishing such a platform. We highlight the recent achievements of the specific material for the expected applications in quantum technologies, indicating complementary outstanding properties compared to the other 3D bulk materials.

Nanoscale magnetic imaging enabled by nitrogen vacancy centres in nanodiamonds labelled by iron-oxide nanoparticles

Nanodiamonds containing the nitrogen vacancy centre (NV) have a significant role in biosensing, bioimaging, drug delivery, and as biomarkers in fluorescence imaging, due to their photo-stability and biocompatibility. The optical read out of the NV unpaired electron spin has been used in diamond magnetometry to image living cells and magnetically labelled cells. Diamond magnetometry is mostly based on the use of bulk diamond with a large concentration of NV centres in a wide field fluorescence microscope equipped with microwave excitation. It is possible to correlate the fluorescence maps with the magnetic field maps of magnetically labelled cells with diffraction limit resolution. Nanodiamonds have not as yet been implemented to image magnetic fields within complex biological systems at the nanometre scale. Here we demonstrate the suitability of nanodiamonds to correlate the fluorescence map with the magnetic imaging map of magnetically labelled cells. Nanoscale optical images with 17 nm resolution of nanodiamonds labelling fixed cells bound to iron oxide magnetic nanoparticles are demonstrated by using a single molecule localisation microscope. Nanoscale magnetic field images of the magnetised magnetic nanoparticles spatially assigned to individual cells are superresolved by the NV centres within nanodiamonds conjugated with the magnetic nanoparticles with 20 nm resolutions. Our method offers a new platform for the super-resolution of optical magnetic imaging in biological samples conjugated with nanodiamonds and iron-oxide magnetic nanoparticles.

Low power charge state depletion nanoscopy of the defect in diamonds with a pulsed laser excitation

Two-photon charge state conversion has been utilized to improve the spatial resolution of the sensing and imaging with the nitrogen vacancy (NV) center in diamonds. Here, we studied the charge state conversion of the NV center under picosecond pulsed laser excitation. With the same average power, the charge state conversion rate can be improved approximately 24 times by reducing the repetition rate of the laser pulse from 80 to 1 MHz. Subsequently, a pulsed laser with a low repetition rate was applied for the super-resolution charge state depletion microscopy of the NV center. The average power of the depletion laser was reduced approximately 5 times. It can decrease the optical heating, which affects the accuracy and sensitivity of sensing. With the assistance of an additional near-infrared laser, a resolution of 12 nm was obtained with 1 mW depletion laser power. Combined with spin manipulation, we expect our results can be used for the development of a diffraction-unlimited NV center sensing.

Nitrogen-vacancy centers in diamond for nanoscale magnetic resonance imaging applications

The nitrogen-vacancy (NV) center is a point defect in diamond with unique properties for use in ultra-sensitive, high-resolution magnetometry. One of the most interesting and challenging applications is nanoscale magnetic resonance imaging (nano-MRI). While many review papers have covered other NV centers in diamond applications, there is no survey targeting the specific development of nano-MRI devices based on NV centers in diamond. Several different nano-MRI methods based on NV centers have been proposed with the goal of improving the spatial and temporal resolution, but without any coordinated effort. After summarizing the main NV magnetic imaging methods, this review presents a survey of the latest advances in NV center nano-MRI.