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Nitrogen-vacancy (NV-) centers in nanodiamonds have emerged as a versatile platform for a wide range of applications, including bioimaging, photonics, and quantum sensing. However, the widespread adoption of nanodiamonds in practical applications has been hindered by the challenges associated with patterning them into high-resolution features with sufficient throughput. In this work, we overcome these limitations by introducing a direct laser-writing bubble printing technique that enables the precise fabrication of two-dimensional nanodiamond patterns. The printed nanodiamonds exhibit a high packing density and strong photoluminescence emission, as well as robust optically detected magnetic resonance (ODMR) signals. We further harness the spatially resolved ODMR of the nanodiamond patterns to demonstrate the mapping of two-dimensional temperature gradients using high frame rate widefield lock-in fluorescence imaging. This capability paves the way for integrating nanodiamond-based quantum sensors into practical devices and systems, opening new possibilities for applications involving high-resolution thermal imaging and biosensing.

Since wound healing requires cells to repopulate a damaged area, cell migration is essential. In addition, migration plays a crucial role in cancer metastasis. Whether tumour cells can invade tissue and metastasize is a crucial factor determining their malignancy or in other words a hallmark of cancer (Lazebnik in Nat Rev Cancer 10: 232–233, 2010, https://doi.org/10.1038/nrc2827). Nanodiamonds potentially offer a powerful tool to investigate these migration processes. Due to their unprecedented photostability, they can function as long-term fluorescent labels. Besides, nanodiamonds are robust quantum sensors that can reveal, for instance, the temperature or the concentration of certain chemicals with nanoscale resolution. However, to utilise nanodiamonds to study cell migration, it is essential to understand if and how the presence of nanodiamonds influences cell migration. Here, we investigate this process for the first time. We found that nanodiamonds do not alter the speed at which HeLa cells populate a scratch at any tested concentrations. Furthermore, we tested cell attachment by quantifying focal adhesion points. Oxygen-terminated fluorescent nanodiamonds influence the cell spreading, the number of focal adhesions and the size of focal adhesion points. Interestingly, this is different for other types of nanodiamonds in the literature. For these particles, it has been described in the literature that they hinder cell migration. Our results support that fluorescent nanodiamonds do not influence cell migration strongly and thus can be used in labelling and sensing migrating cells. [ABSTRACT FROM AUTHOR]

Abstract Since wound healing requires cells to repopulate a damaged area, cell migration is essential. In addition, migration plays a crucial role in cancer metastasis. Whether tumour cells can invade tissue and metastasize is a crucial factor determining their malignancy or in other words a hallmark of cancer (Lazebnik in Nat Rev Cancer 10: 232–233, 2010, https://doi.org/10.1038/nrc2827 ). Nanodiamonds potentially offer a powerful tool to investigate these migration processes. Due to their unprecedented photostability, they can function as long-term fluorescent labels. Besides, nanodiamonds are robust quantum sensors that can reveal, for instance, the temperature or the concentration of certain chemicals with nanoscale resolution. However, to utilise nanodiamonds to study cell migration, it is essential to understand if and how the presence of nanodiamonds influences cell migration. Here, we investigate this process for the first time. We found that nanodiamonds do not alter the speed at which HeLa cells populate a scratch at any tested concentrations. Furthermore, we tested cell attachment by quantifying focal adhesion points. Oxygen-terminated fluorescent nanodiamonds influence the cell spreading, the number of focal adhesions and the size of focal adhesion points. Interestingly, this is different for other types of nanodiamonds in the literature. For these particles, it has been described in the literature that they hinder cell migration. Our results support that fluorescent nanodiamonds do not influence cell migration strongly and thus can be used in labelling and sensing migrating cells. Graphical Abstract

Alina Sigaeva,* Runrun Li,* Jan Jelle van Laar, Leon Wierenga, Romana Schirhagl Department of Biomaterials and Biotechnology, Groningen University, University Medical Center Groningen, Groningen, the Netherlands*These authors contributed equally to this workCorrespondence: Romana Schirhagl, Email romana.schirhagl@gmail.comIntroduction: As nanodiamonds become more and more widely used for intracellular labelling and measurements, the task of delivering these nanoparticles inside cells becomes more and more important. Certain cell types easily take up nanodiamonds, while others require special procedures.Methods: In previous research, we found that HT-29 cells (a colon cancer cell line), which are notoriously difficult in the context of nanodiamond internalization, show increased uptake rates, when pre-treated with trypsin- ethylenediaminetetraacetic acid (trypsin-EDTA). However, the uptake mechanism has not been studied before. This article focuses on a more detailed investigation of the reasons underlying this phenomenon. We start by identifying the timing of fluorescent nanodiamond (FND) uptake in trypsin-EDTA pre-treated cells. We then use a combination of chemical inhibitors and Immunocytochemistry to identify the main pathways employed by HT-29 cells in the internalization process.Results and Discussion: We investigate how these pathways are affected by the trypsin-EDTA pre-treatment and conclude by offering possible explanations for this phenomenon. We found that nanodiamonds are internalized via different pathways. Clathrin-mediated endocytosis proves to be the dominating mechanism. Trypsin-EDTA treatment increases particle uptake and affects the uptake mechanism.Keywords: nanodiamonds, cell uptake, cancer cells, HT29 cells, NV centers, imaging

The recent breakthrough in integrating single quantum emitters to dielectric metasurfaces opens up avenues in quantum technologies with the possibility to obtain on‐demand single photon sources and efficient spin–photon interface. All‐dielectric metasurfaces with unprecedented possibilities of generating directional light scattering instigated a novel concept of the Kerker effect that led to applications in nanophotonics. Here, an all‐dielectric metasurface consisting of silicon‐like nanodisks with square lattice symmetry that exhibits Kerker condition governed by constructive interference of multipoles optimized for the zero‐phonon line (ZPL) of negatively charged nitrogen‐vacancy (NV‐) center at a wavelength of 640 nm is discussed. The phase and amplitude of excited multipolar moments are manipulated by varying the geometrical parameters of the metasurfaces. The constructive interference between multipolar moments generates a Kerker condition, which is tunable by varying the diameter, thickness, refractive index of nanodisks, and substrate refractive index. The Kerker condition is further used to control the emission from a single NV‐ center and a Purcell enhancement of 300 times is achieved at 640 nm. The study profoundly explores new insights into quantum metasurfaces and paves a new way to utilize dielectric resonators with emitters as on‐chip quantum light sources at Kerker condition. [ABSTRACT FROM AUTHOR]

It is well known that the basis of diffraction analysis of matter is scattering, including the scattering of ultrashort laser pulses. In the theory of scattering of ultrashort pulses, the pulse duration parameter is usually not taken into account, which leads to some error. This error may be more significant than the considered effects in the scattering of the pulse on the studied structure. In this paper, it is shown that the pulse duration parameter should be taken into account when scattering X-ray pulses on oriented diamonds with NV centers. It is shown that the scattering spectra can be used to judge the orientation of NV centers in the diamond structure. The obtained results may be very different from the widely used theory of diffraction analysis, which confirms the necessity of taking into account the pulse duration parameter in the diagnosis of complex structures. [ABSTRACT FROM AUTHOR]

Developing practical quantum technologies will require the exquisite manipulation of fragile systems in a robust and repeatable way. As quantum technologies move toward real world applications, from biological sensing to communication in space, increasing experimental complexity introduces constraints that can be alleviated by the introduction of new technologies. Robotics has shown tremendous progress in realizing increasingly smart, autonomous, and highly dexterous machines. Here, a robotic arm equipped with a magnet is demonstrated to sensitize an NV center quantum magnetometer in challenging conditions unachievable with standard techniques. Vector magnetic fields are generated with 1° angular and 0.1 mT amplitude accuracy and determine the orientation of a single stochastically‐aligned spin‐based sensor in a constrained physical environment. This work opens up the prospect of integrating robotics across many quantum degrees of freedom in constrained settings, allowing for increased prototyping speed, control, and robustness in quantum technology applications. [ABSTRACT FROM AUTHOR]

Introduction: Diffusion weighting in optically detected magnetic resonance experiments involving diamond nitrogen-vacancy (NV) centers can provide valuable microstructural information. Bi-planar gradient coils employed for diffusion weighting afford excellent spatial access, essential for integrating the NV-NMR components. Nevertheless, owing to the polar tilt of roughly 55 ∘ of the diamond NV center, the primary magnetic field direction must be taken into account accordingly. Methods: To determine the most effective bi-planar gradient coil configurations, we conducted an investigation into the impact of various factors, including the square side length, surface separation, and surface orientation. This was accomplished by generating over 500 bi-planar surface configurations using automated methods. Results: We successfully generated and evaluated coil layouts in terms of sensitivity and field accuracy. Interestingly, inclined bi-planar orientations close to the NV–NMR setup's requirement, showed higher sensitivity for the transverse gradient channels than horizontal or vertical orientations. We fabricated a suitable solution as a three-channel bi-planar double-layered PCB system and experimentally validated the sensitivities at 28.7 m T / m / A and 26.8 m T / m / A for the transverse G x and G y gradients, and 26 m T / m / A for the G z gradient. Discussion: We found that the chosen relative bi-planar tilt of 35 ∘ represents a reasonable compromise in terms of overall performance and allows for easier coil implementation with a straight, horizontal alignment within the overall experimental setup. [ABSTRACT FROM AUTHOR]

Oxidative stress originating from the overproduction of free radicals poses a major threat to cell fate, therefore it is of great importance to address the formation of free radicals in cells subjected to various pathological stimuli. Here we investigate the free radical response of endothelial cells to biodegradable zinc. In addition to the standard free radical assays, relaxometry was used for determining the production of free radicals in cells exposed to non‐physiological concentrations of zinc ions. The cellular morphology, intracellular zinc accumulation, as well as the levels of reactive oxygen/nitrogen species, are determined using standard fluorescent methods. For endothelial cells subjected to 50% zinc extracts, deviations from the normal cell shape and cell agglomeration tendency are observed. The culture medium containing the highest amount of zinc ions caused nuclei fragmentation, blebbing, and cell shrinkage, indicating cell death. A potential explanation for the observed phenomena is an overproduction of free radicals. In the case of 1% and 10% zinc extracts, the formation of free radicals is clearly confirmed by relaxometry, while the results obtained by using fluorescent techniques are unambiguous. It is revealed that high concentrations of zinc ions released from biodegradable samples induce a deleterious effect on endothelial cells. [ABSTRACT FROM AUTHOR]

Abstract Developing practical quantum technologies will require the exquisite manipulation of fragile systems in a robust and repeatable way. As quantum technologies move toward real world applications, from biological sensing to communication in space, increasing experimental complexity introduces constraints that can be alleviated by the introduction of new technologies. Robotics has shown tremendous progress in realizing increasingly smart, autonomous, and highly dexterous machines. Here, a robotic arm equipped with a magnet is demonstrated to sensitize an NV center quantum magnetometer in challenging conditions unachievable with standard techniques. Vector magnetic fields are generated with 1° angular and 0.1 mT amplitude accuracy and determine the orientation of a single stochastically‐aligned spin‐based sensor in a constrained physical environment. This work opens up the prospect of integrating robotics across many quantum degrees of freedom in constrained settings, allowing for increased prototyping speed, control, and robustness in quantum technology applications.

The optical properties of point luminescent centers formed in the volume IaA-type natural diamond under the action of ultrashort laser pulses in the visible range (515 nm) with durations of 0.3–2.4 ps were investigated. The analysis using confocal Raman spectroscopy demonstrates the formation of nitrogen vacancy centers (NV) and there are no graphitization traces in processing areas. The luminescence amplitude of NV centers depends linearly on the exposure time at different durations of ultrashort laser pulses. [ABSTRACT FROM AUTHOR]

Solid-state defects are attractive platforms for quantum sensing and simulation, e.g., in exploring many-body physics and quantum hydrodynamics. However, many interesting properties can be revealed only upon changes in the density of defects, which instead is usually fixed in material systems. Increasing the interaction strength by creating denser defect ensembles also brings more decoherence. Ideally one would like to control the spin concentration at will while keeping fixed decoherence effects. Here, we show that by exploiting charge transport, we can take some steps in this direction, while at the same time characterizing charge transport and its capture by defects. By exploiting the cycling process of ionization and recombination of NV centers in diamond, we pump electrons from the valence band to the conduction band. These charges are then transported to modulate the spin concentration by changing the charge state of material defects. By developing a wide-field imaging setup integrated with a fast single photon detector array, we achieve a direct and efficient characterization of the charge redistribution process by measuring the complete spectrum of the spin bath with micrometer-scale spatial resolution. We demonstrate a two-fold concentration increase of the dominant spin defects while keeping the T2 of the NV center relatively unchanged, which also provides a potential experimental demonstration of the suppression of spin flip-flops via hyperfine interactions. Our work paves the way to studying many-body dynamics with temporally and spatially tunable interaction strengths in hybrid charge-spin systems. [ABSTRACT FROM AUTHOR]

Multimodal imaging-the ability to acquire images of an object through more than one imaging mode simultaneously-has opened additional perspectives in areas ranging from astronomy to medicine. In this paper, we report progress toward combining optical and magnetic resonance (MR) imaging in such a "dual" imaging mode. They are attractive in combination because they offer complementary advantages of resolution and speed, especially in the context of imaging in scattering environments. Our approach relies on a specific material platform, microdiamond particles hosting nitrogen vacancy (NV) defect centers that fluoresce brightly under optical excitation and simultaneously "hyperpolarize" lattice [Formula: see text] nuclei, making them bright under MR imaging. We highlight advantages of dual-mode optical and MR imaging in allowing background-free particle imaging and describe regimes in which either mode can enhance the other. Leveraging the fact that the two imaging modes proceed in Fourier-reciprocal domains (real and k-space), we propose a sampling protocol that accelerates image reconstruction in sparse-imaging scenarios. Our work suggests interesting possibilities for the simultaneous optical and low-field MR imaging of targeted diamond nanoparticles.

It is well known that the basis of diffraction analysis of matter is scattering, including the scattering of ultrashort laser pulses. In the theory of scattering of ultrashort pulses, the pulse duration parameter is usually not taken into account, which leads to some error. This error may be more significant than the considered effects in the scattering of the pulse on the studied structure. In this paper, it is shown that the pulse duration parameter should be taken into account when scattering X-ray pulses on oriented diamonds with NV centers. It is shown that the scattering spectra can be used to judge the orientation of NV centers in the diamond structure. The obtained results may be very different from the widely used theory of diffraction analysis, which confirms the necessity of taking into account the pulse duration parameter in the diagnosis of complex structures.

Methods of optical dynamic nuclear polarization open the door to the replenishable hyperpolarization of nuclear spins, boosting their nuclear magnetic resonance/imaging signatures by orders of magnitude. Nanodiamond powder rich in negatively charged nitrogen vacancy defect centers has recently emerged as one such promising platform, wherein 13C nuclei can be hyperpolarized through the optically pumped defects completely at room temperature. Given the compelling possibility of relaying this 13C polarization to nuclei in external liquids, there is an urgent need for the engineered production of highly “hyperpolarizable” diamond particles. Here, a systematic study of various material dimensions affecting optical 13C hyperpolarization in diamond particles is reported on. It is discovered surprisingly that diamond annealing at elevated temperatures ∼1720 °C has remarkable effects on the hyperpolarization levels enhancing them by above an order of magnitude over materials annealed through conventional means. It is demonstrated these gains arise from a simultaneous improvement in NV− electron relaxation/coherence times, as well as the reduction of paramagnetic content, and an increase in 13C relaxation lifetimes. This work suggests methods for the guided materials production of fluorescent, 13C hyperpolarized, nanodiamonds and pathways for their use as multimodal (optical and magnetic resonance) imaging and hyperpolarization agents.

The physical properties of diamond crystals, such as color or electrical conductivity, can be controlled via impurities. In particular, when doped with nitrogen, optically active nitrogen-vacancy centers ( N V ), can be induced. The center is an outstanding quantum spin system that enables, under ambient conditions, optical initialization, readout, and coherent microwave control with applications in sensing and quantum information. Under optical and radio frequency excitation, the Zeeman splitting of the degenerate states allows the quantitative measurement of external magnetic fields with high sensitivity. This study provides a pedagogical introduction to the properties of the N V centers as well as a step-by-step process to develop and test a simple magnetic quantum sensor based on color centers with significant potential for the development of highly compact multisensor systems. [ABSTRACT FROM AUTHOR]

Nanodiamonds are increasingly popular in biomedical applications, including optical labelling, drug delivery and nanoscale sensing. Potential new applications are in studying infertility or labelling sperm cells. However, for these applications, it is necessary that nanodiamonds are inert and do not alter sperm properties. In this article, we assessed the biocompatibility of nanodiamonds in detail. We investigated different sizes and concentrations of nanodiamonds and sperm preparation methods. We evaluated if the metabolic activity, membrane integrity, morphology and formation of reactive oxygen species were altered. These parameters were tested for sperm cells in their uncapacitated and capacitated states. Unfortunately, FNDs are not universally biocompatible. Generally, cells in the capacitated state are more prone to stress. Additionally, larger particles and lower concentrations are tolerated better than smaller and higher concentrated particles.

Advances in applications of nitrogen-vacancy (NV) spin centres in diamond for sensing and quantum metrology depend critically on the NV fabrication methods. One such technique combines epitaxial diamond growth and electron or ion irradiation (He, C, etc), where NVs are activated by vacancy trapping at the nitrogen donor atoms upon thermal diffusion. In this work we study the efficiency of such method by analyzing NV depth profiles created by 340 keV and also 4 keV He irradiation in high purity CVD and HPHT diamond crystals and subjected to sequent annealing at 950 °C and 1200 °C temperatures. This analysis is coupled with the measurement of NV density in the bulk of CVD diamonds with nitrogen doping at low-ppb and low-ppm levels, exposed to MeV electrons in a wide range of the doses. For data analysis we developed an atomistic model based on probabilistic atomic jumps in a crystal lattice, which considers competitive trapping between di- $\mathrm{(\textit{V}_{2})}$ or multi-vacancy defects compared to that of NVs. The efficiency of NV formation was defined as a ratio of the corresponding capture cross sections: σ _NV vs. $\sigma_{\textit{V}2}$ . Applying this model to the experimental data, the $\sigma_\textrm{NV}/\sigma_{\textit{V}2}$ ratio was estimated about 0.1–0.5, where the activation energy of vacancy diffusion of about 1.7 eV was evaluated by 3D localization of individual NVs in depth profiles in a confocal microscope and sampling their spin coherence properties ( $\mathrm{T_{2}}$ ). In addition, we noted two subsidiary effects also discussed here: (i) reduction of NV density within the stopping range of the implanted He atoms after $\mathrm{1200^{\circ}}$ annealing and, (ii) partial suppression of NVs at near-surface areas visible only at low-dose electron exposures. The results of this study could be helpful to optimize the NV fabrication process reducing the density of ‘collateral’ lattice damage.

A possibility of laser printing of single diamond nanoparticles with luminescent SiV centers is demonstrated. To provide the transfer, a target consisting of a transparent sapphire plate and an absorbing thin titanium film (600 nm thick) coated with nanoparticles was irradiated with a KrF excimer laser ("lambda"=248 nm, "tau"=20 ns). Optimal values of the laser fluence have been determined and a technique for applying labels for the targeted transfer of nanoparticles has been developed. Luminescence mapping of the donor and the receiving substrates confirmed the transfer of diamond nanoparticles with SiV centers.

We demonstrate a method for thermal detection that is the sensitivity 6.2 mK Hzâˆ'1 2, which uses the frequency lock closed-loop scheme to track Zeeman-split resonance of nitrogen-vacancy (NV) centers in diamond. The NV diamond surface acts as a temperature measurement sensor to transfer the temperature variation as D (T) parameter change to lead to the movement of the energy levels to detect the temperature. By frequency modulation technology and closed-loop feedback locking technology, automatic temperature detection and step signal reading are realized, with a resolution of 7.6 mK. It is found that the closed-loop output is basically unchanged, while the open-loop output has an error signal proportional to the laser fluctuation. The closed-loop feedback technique can improve the stability and resolution of the system and provides a method for measuring the actual temperature detection. Such a demonstration marks a vital advance in transitioning the NV thermometer from a laboratory system to a functional device for detecting temperature fields in a practical environment. [ABSTRACT FROM AUTHOR]

Nitrogen-vacancy (NV) color centers in diamond are excellent quantum sensors possessing high sensitivity and nano-scale spatial resolution. Their integration in photonic structures is often desired, since it leads to an increased photon emission and also allows the realization of solid-state quantum technology architectures. Here, we report the fabrication of diamond nano-pillars with diameters up to 1000 nm by electron beam lithography and inductively coupled plasma reactive ion etching in nitrogen-rich diamonds (type Ib) with [100] and [111] crystal orientations. The NV centers were created by keV-He ion bombardment and subsequent annealing, and we estimate an average number of NVs per pillar to be 4300 ± 300 and 520 ± 120 for the [100] and [111] samples, respectively. Lifetime measurements of the NVs' excited state showed two time constants with average values of τ1 ≈ 2 ns and τ2 ≈ 8 ns, which are shorter as compared to a single color center in a bulk crystal (τ ≈ 10 ns). This is probably due to a coupling between the NVs as well as due to interaction with bombardment-induced defects and substitutional nitrogen (P1 centers). Optically detected magnetic resonance measurements revealed a contrast of about 5% and average coherence and relaxation times of T2 [100] = 420 ± 40 ns, T2 [111] = 560 ± 50 ns, and T1 [100] = 162 ± 11 μs, T1 [111] = 174 ± 24 μs. These pillars could find an application for scanning probe magnetic field imaging. [ABSTRACT FROM AUTHOR]

Although viruses are known to modify the free radical concentration in infected cells, the exact location and concentrations of such changes remain unknown. Although this information is important to understand the virus pathogenesis and design better anti-viral drugs or vaccines, obtaining it with the conventional free radical/ROS detection techniques is impossible. Here, we elucidate the utility of diamond magnetometry for studying the free radical response of baby hamster kidney-21 cells upon Semliki Forest virus infection. Specifically, we optically probe the alterations in free radical concentration near infectious viruses via measuring the spin–lattice relaxation (T1) of NV defect ensembles embedded in intracellular nanodiamonds. We performed measurements both at random locations as well as close to the virus entry by conjugating viruses to nanodiamond sensors. We observed alterations of T1, which represent the intracellular free radical concentration during the viral replication process. Moreover, relaxometry is also used to monitor real-time free radical variation during the early infectious process.

In the past decade, a great effort has been devoted to develop new biosensor platforms for the detection of a wide range of analytes. Among the various approaches, magneto-DNA assay platforms have received extended interest for high sensitive and specific detection of targets with a simultaneous manipulation capacity. Here, using nitrogen-vacancy quantum centers in diamond as transducers for magnetic nanotags (MNTs), a hydrogel-based, multiplexed magneto-DNA assay is presented. Near-background-free sensing with diamond-based imaging combined with noninvasive control of chemically robust nanotags renders it a promising platform for applications in medical diagnostics, life science, and pharmaceutical drug research. To demonstrate its potential for practical applications, we employed the sensor platform in the sandwich DNA hybridization process and achieved a limit of detection in the attomolar range with single-base mismatch differentiation. [ABSTRACT FROM AUTHOR]

Spin waves in magnetic insulators are low‐damping signal carriers that can enable a new generation of spintronic devices. The excitation, control, and detection of spin waves by metal electrodes is crucial for interfacing these devices to electrical circuits. As such, it is important to understand metal‐induced damping of spin‐wave transport, but characterizing this process requires access to the underlying magnetic films. Here it is shown that electronic sensor spins in diamond enable imaging of spin waves that propagate underneath metals in magnetic insulators. This capability is then used to reveal a 100‐fold metal‐induced increase in spin‐wave damping. The damping enhancement is attributed to spin‐wave‐induced electrical currents as well as, above a certain frequency, three‐magnon scattering processes. This interpretation is supported by deriving expressions for the current‐induced damping and the three‐magnon threshold from the Landau–Lifshitz–Gilbert equation that agree well with the observations. The detection of buried scattering centers further highlights the technique's power for assessing spintronic device quality. These results open new avenues for studying metal – spin‐wave interactions and provide access to interfacial processes such as spin‐wave injection via the spin‐Hall effect. [ABSTRACT FROM AUTHOR]

The physical properties of diamond crystals, such as color or electrical conductivity, can be controlled via impurities. In particular, when doped with nitrogen, optically active nitrogen-vacancy centers (NV), can be induced. The center is an outstanding quantum spin system that enables, under ambient conditions, optical initialization, readout, and coherent microwave control with applications in sensing and quantum information. Under optical and radio frequency excitation, the Zeeman splitting of the degenerate states allows the quantitative measurement of external magnetic fields with high sensitivity. This study provides a pedagogical introduction to the properties of the NV centers as well as a step-by-step process to develop and test a simple magnetic quantum sensor based on color centers with significant potential for the development of highly compact multisensor systems.

Effective methods to generate colour centres in diamond and other wide band-gap materials are essential to the realisation of solid state quantum technologies based on such systems. Such methods have been the subject of intensive research effort in recent years. In this review, we bring together the various techniques used in the generation and positioning of colour centres in diamond: ion implantation, delta-doping, electron irradiation, laser writing and thermal annealing. We assess the roles and merits of each of these techniques in the formation of colour centres for different quantum technologies and consider future combinations of the techniques to meet the requirements of the most demanding applications.

Thanks to its low or negative surface electron affinity and chemical inertness, diamond is attracting broad attention as a source material of solvated electrons produced by optical excitation of the solid-liquid interface. Unfortunately, its wide bandgap typically imposes the use of wavelengths in the ultraviolet range, hence complicating practical applications. Here, we probe the photocurrent response of water surrounded by single-crystal diamond surfaces engineered to host shallow nitrogen-vacancy (NV) centers. We observe clear signatures of diamond-induced photocurrent generation throughout the visible range and for wavelengths reaching up to 594 nm. Experiments as a function of laser power suggest that NV centers and other coexisting defects─likely in the form of surface traps─contribute to carrier injection, though we find that NVs dominate the system response in the limit of high illumination intensities. Given our growing understanding of near-surface NV centers and adjacent point defects, these results open new perspectives in the application of diamond-liquid interfaces to photocarrier-initiated chemical and spin processes in fluids.

Ultraviolet (UV) radiation is known to cause skin issues, such as dryness, aging, and even cancer. Among UV rays, UVB stands out for its ability to trigger problems within cells, including mitochondrial dysfunction, oxidative stress, and DNA damage. Free radicals are implicated in these cellular responses, but they are challenging to measure due to their short lifetime and limited diffusion range. In our study, we used a quantum sensing technique (T1 relaxometry) involving fluorescent nanodiamonds (FNDs) that change their optical properties in response to magnetic noise. This allowed us to monitor the free radical presence in real time. To measure radicals near mitochondria, we coated FNDs with antibodies, targeting mitochondrial protein voltage-dependent anion channel 2 (anti-VDAC2). Our findings revealed a dynamic rise in radical levels on the mitochondrial membrane as cells were exposed to UVB (3 J/cm 2 ), with a significant increase observed after 17 min.

Two-dimensional (2D) Fe n GeTe 2 , with n = 3, 4, and 5, has been realized in experiments, showing strong magnetic anisotropy with enhanced critical temperature ( T c ). The understanding of its magnetic anisotropy is crucial for the exploration of more stable 2D magnets and its spintronic applications. Here, we report a quantitative reconstruction of the magnetization magnitude and its direction in ultrathin Fe 4 GeTe 2 using nitrogen vacancy centers. Through imaging stray magnetic fields, we identified the spin-flop transition at approximately 80 K, resulting in a change of the easy axis from the out-of-plane direction to the in-plane direction. Moreover, by analyzing the thermally activated escape behavior of the magnetization near T c in terms of the Ginzburg-Landau model, we observed the in-plane magnetic anisotropy effect and the formation capability of magnetic domains at ∼0.4 μm 2 μT -1 . Our findings contribute to the quantitative understanding of the magnetic anisotropy effect in a vast range of 2D van der Waals magnets.

Bio-membranes exhibit complex but unique mechanical properties as communicative regulators in various physiological and pathological processes. Exposed to a dynamic micro-environment, bio-membranes can be seen as an intricate and delicate system. The systematical modeling and detection of their local physical properties are often difficult to achieve, both quantitatively and precisely. The recent emerging diamonds hosting quantum defects (i.e., nitrogen-vacancy (NV) center) demonstrate intriguing optical and spin properties, together with their outstanding photostability and biocompatibility, rendering them ideal candidates for biological applications. Notably, the extraordinary spin-based sensing enable the measurements of localized nanoscale physical quantities such as magnetic fields, electrical fields, temperature, and strain. These nanoscale signals can be optically read out precisely by simple optical microscopy systems. Given these exclusive properties, NV-center-based quantum sensors can be widely applied in exploring bio-membrane-related features and the communicative chemical reaction processes. This review mainly focuses on NV-based quantum sensing in bio-membrane fields. The attempts of applying NV-based quantum sensors in bio-membranes to investigate diverse physical and chemical events such as membrane elasticity, phase change, nanoscale bio-physical signals, and free radical formation are fully overviewed. We also discuss the challenges and future directions of this novel technology to be utilized in bio-membranes.

Magnetometry based on nitrogen-vacancy (NV) centers in diamond is a novel technique capable of measuring magnetic fields with high sensitivity and high spatial resolution. With the further advancements of these sensors, they may open up novel approaches for the 2D imaging of neural signals in vitro. In the present study, we investigate the feasibility of NV-based imaging by numerically simulating the magnetic signal from the auditory pathway of a rodent brainstem slice (ventral cochlear nucleus, VCN, to the medial trapezoid body, MNTB) as stimulated by both electric and optic stimulation. The resulting signal from these two stimulation methods are evaluated and compared. A realistic pathway model was created based on published data of the neural morphologies and channel dynamics of the globular bushy cells in the VCN and their axonal projections to the principal cells in the MNTB. The pathway dynamics in response to optic and electric stimulation and the emitted magnetic fields were estimated using the cable equation. For simulating the optic stimulation, the light distribution in brain tissue was numerically estimated and used to model the optogenetic neural excitation based on a four state channelrhodopsin-2 (ChR2) model. The corresponding heating was also estimated, using the bio-heat equation and was found to be low (

Microwave interactions are an invaluable tool for probing atomic states of matter and are currently being extensively explored for the development of scalable quantum computing. However, many of the available methods for spectroscopic analysis and photonic quantum manipulations are inaccessible for microwaves due to the weak spontaneous emission of quantum emitters. In this work, a mechanism for giant resonant enhancement of spontaneous emission from magnetic dipole emitters is suggested that employs a new phenomenon of near field impedance cancellation via magnetic flux confinement. Enhancements of at least 1011 are theoretically shown for structures with 100 nm features, and much greater potential enhancements are predicted with this method. Subsequently, the realization of integrated systems with enhanced quantum emitters using microwave spoof plasmon waveguides is demonstrated. Taken together, these findings will pave the way for microwave quantum photonics and microwave hybrid quantum computing. [ABSTRACT FROM AUTHOR]

Multimodal imaging--the ability to acquire images of an object through more than one imaging mode simultaneously--has opened additional perspectives in areas ranging from astronomy to medicine. In this paper, we report progress toward combining optical and magnetic resonance (MR) imaging in such a "dual" imaging mode. They are attractive in combination because they offer complementary advantages of resolution and speed, especially in the context of imaging in scattering environments. Our approach relies on a specific material platform, microdiamond particles hosting nitrogen vacancy (NV) defect centers that fluoresce brightly under optical excitation and simultaneously "hyperpolarize" lattice 13C nuclei, making them bright under MR imaging. We highlight advantages of dual-mode optical and MR imaging in allowing background-free particle imaging and describe regimes in which either mode can enhance the other. Leveraging the fact that the two imaging modes proceed in Fourier-reciprocal domains (real and k-space), we propose a sampling protocol that accelerates image reconstruction in sparse-imaging scenarios. Our work suggests interesting possibilities for the simultaneous optical and low-field MR imaging of targeted diamond nanoparticles. [ABSTRACT FROM AUTHOR]

Magnetometry based on nitrogen-vacancy (NV) centers in diamond is a novel technique capable of measuring magnetic fields with high sensitivity and high spatial resolution. With the further advancements of these sensors, they may open up novel approaches for the 2D imaging of neural signals in vitro. In the present study, we investigate the feasibility of NV-based imaging by numerically simulating the magnetic signal from the auditory pathway of a rodent brainstem slice (ventral cochlear nucleus, VCN, to the medial trapezoid body, MNTB) as stimulated by both electric and optic stimulation. The resulting signal from these two stimulation methods are evaluated and compared. A realistic pathway model was created based on published data of the neural morphologies and channel dynamics of the globular bushy cells in the VCN and their axonal projections to the principal cells in the MNTB. The pathway dynamics in response to optic and electric stimulation and the emitted magnetic fields were estimated using the cable equation. For simulating the optic stimulation, the light distribution in brain tissue was numerically estimated and used to model the optogenetic neural excitation based on a four state channelrhodopsin-2 (ChR2) model. The corresponding heating was also estimated, using the bio-heat equation and was found to be low (<2°C) even at excessively strong optic signals. A peak magnetic field strength of ∼0.5 and ∼0.1 nT was calculated from the auditory brainstem pathway after electrical and optical stimulation, respectively. By increasing the stimulating light intensity four-fold (far exceeding commonly used intensities) the peak magnetic signal strength only increased to 0.2 nT. Thus, while optogenetic stimulation would be favorable to avoid artefacts in the recordings, electric stimulation achieves higher peak fields. The present simulation study predicts that high-resolution magnetic imaging of the action potentials traveling along the auditory brainstem pathway will only be possible for next generation NV sensors. However, the existing sensors already have sufficient sensitivity to support the magnetic sensing of cumulated neural signals sampled from larger parts of the pathway, which might be a promising intermediate step toward further maturing this novel technology. [ABSTRACT FROM AUTHOR]

Nitrogen-vacancy (NV) color centers in diamond are excellent quantum sensors possessing high sensitivity and nano-scale spatial resolution. Their integration in photonic structures is often desired, since it leads to an increased photon emission and also allows the realization of solid-state quantum technology architectures. Here, we report the fabrication of diamond nano-pillars with diameters up to 1000 nm by electron beam lithography and inductively coupled plasma reactive ion etching in nitrogen-rich diamonds (type Ib) with [100] and [111] crystal orientations. The NV centers were created by keV-He ion bombardment and subsequent annealing, and we estimate an average number of NVs per pillar to be 4300 ± 300 and 520 ± 120 for the [100] and [111] samples, respectively. Lifetime measurements of the NVs’ excited state showed two time constants with average values of τ1 ≈ 2 ns and τ2 ≈ 8 ns, which are shorter as compared to a single color center in a bulk crystal (τ ≈ 10 ns). This is probably due to a coupling between the NVs as well as due to interaction with bombardment-induced defects and substitutional nitrogen (P1 centers). Optically detected magnetic resonance measurements revealed a contrast of about 5% and average coherence and relaxation times of T2 [100] = 420 ± 40 ns, T2 [111] = 560 ± 50 ns, and T1 [100] = 162 ± 11 μs, T1 [111] = 174 ± 24 μs. These pillars could find an application for scanning probe magnetic field imaging.

Detecting magnetic field is of great importance for many applications, such as magnetoencephalography and underground prospecting. There have been many magnetometers being widely used since the age of Hall magnetometer. One of the magnetometers, the superconducting quantum interference device, is capable of measuring femtotesla magnetic fields at cryogenic temperature. However, a solid-state magnetometer with femtotesla sensitivity under ambient conditions remains elusive. Here we present a hybrid magnetometer based on the ensemble nitrogen-vacancy centers in diamond with the sensitivity of (195 ± 60) fT / Hz 1 / 2 under ambient conditions, which can be further advanced to 11 fT / Hz 1 / 2 at 100 Hz with cutting-edge fabrication technologies. Our method will find potential applications in biomagnetism and geomagnetism. [ABSTRACT FROM AUTHOR]

Understanding the human brain is one of the most significant challenges of the 21st century. As theoretical studies continue to improve the description of the complex mechanisms that regulate biological processes, in parallel numerous experiments are conducted to enrich or verify these theoretical predictions also with the aim of extrapolating more accurate models. In the fields of magnetometry and thermometry, among the various sensors proposed for biological application, nitrogen‐vacancy (NV) centers are emerging as a promising solution due to their perfect biocompatibility and the possibility of being positioned in close proximity to the cell membrane, thus allowing a nanometric spatial resolution down to the nano‐scale. Still many issues must be overcome to obtain either a sensitivity capable of revealing the very weak electromagnetic fields generated by neurons (or other excitable cells) during their firing activity or a spatial resolution sufficient to measure intracellular thermal gradient due to biological processes. However, over the last few years, significant improvements have been achieved in this direction, thanks to the use of innovative techniques. In this review, the new results regarding the application of NV centers will be analyzed and the main challenges that must be afforded for leading to practical applications will be discussed. [ABSTRACT FROM AUTHOR]

Methods of optical dynamic nuclear polarization open the door to the replenishable hyperpolarization of nuclear spins, boosting their nuclear magnetic resonance/imaging signatures by orders of magnitude. Nanodiamond powder rich in negatively charged nitrogen vacancy defect centers has recently emerged as one such promising platform, wherein 13C nuclei can be hyperpolarized through the optically pumped defects completely at room temperature. Given the compelling possibility of relaying this 13C polarization to nuclei in external liquids, there is an urgent need for the engineered production of highly "hyperpolarizable" diamond particles. Here, a systematic study of various material dimensions affecting optical 13C hyperpolarization in diamond particles is reported on. It is discovered surprisingly that diamond annealing at elevated temperatures ∼1720 °C has remarkable effects on the hyperpolarization levels enhancing them by above an order of magnitude over materials annealed through conventional means. It is demonstrated these gains arise from a simultaneous improvement in NV− electron relaxation/coherence times, as well as the reduction of paramagnetic content, and an increase in 13C relaxation lifetimes. This work suggests methods for the guided materials production of fluorescent, 13C hyperpolarized, nanodiamonds and pathways for their use as multimodal (optical and magnetic resonance) imaging and hyperpolarization agents. [ABSTRACT FROM AUTHOR]

Here, we discussed the current challenges related with the application of Nitrogen-vacancy (NV)-based magnetometers for biological systems. Major constraints for diamond sensor type as optical illumination, microwave field, bias magnetic field, optics, method of photoluminescence detection and sample preparation have been analyzed. Special attention was paid to the estimation of electromagnetic fields in the nervous system. The mechanism of action potential generation and resultant local current flows was discussed, corresponding magnetic field outside an axon was estimated. It was shown that sensitivity of upcoming generation of NV magnetic field sensors may not be enough for the measurement of single neuron action potential, while monitoring electromagnetic signals in brain slices or cardiac tissues seems very promising. [ABSTRACT FROM AUTHOR]

We report a novel method for synthesis and processing of pure and nitrogen-vacancy (NV)-doped nanodiamonds with sharp NV0 and NV− transitions at ambient temperatures and pressures in air. Carbon films are melted by nanosecond lasers in super undercooled state and quenched rapidly. We can form single-crystal nanodiamonds, microdiamonds, nanoneedles and microneedles, and large-area films. Substitutional nitrogen atoms and vacancies are incorporated into diamond during rapid liquid-phase growth, where dopant concentrations can far exceed thermodynamic solubility limits through solute trapping. These nanodiamonds can be placed deterministically and the transitions between NV− and NV0 can be controlled electrically and optically by laser illumination.

Cells are damaged during hypoxia (blood supply deprivation) and reoxygenation (oxygen return). This damage occurs in conditions such as cardiovascular diseases, cancer, and organ transplantation, potentially harming the tissue and organs. The role of free radicals in cellular metabolic reprogramming under hypoxia is under debate, but their measurement is challenging due to their short lifespan and limited diffusion range. In this study, we employed a quantum sensing technique to measure the real-time production of free radicals at the subcellular level. We utilize fluorescent nanodiamonds (FNDs) that exhibit changes in their optical properties based on the surrounding magnetic noise. This way, we were able to detect the presence of free radicals. To specifically monitor radical generation near mitochondria, we coated the FNDs with an antibody targeting voltage-dependent anion channel 2 (anti-VDAC2), which is located in the outer membrane of mitochondria. We observed a significant increase in the radical load on the mitochondrial membrane when cells were exposed to hypoxia. Subsequently, during reoxygenation, the levels of radicals gradually decreased back to the normoxia state. Overall, by applying a quantum sensing technique, the connections among hypoxia, free radicals, and the cellular redox status has been revealed.

Introduction: Diffusion weighting in optically detected magnetic resonance experiments involving diamond nitrogen-vacancy (NV) centers can provide valuable microstructural information. Bi-planar gradient coils employed for diffusion weighting afford excellent spatial access, essential for integrating the NV-NMR components. Nevertheless, owing to the polar tilt of roughly [Formula: see text] of the diamond NV center, the primary magnetic field direction must be taken into account accordingly., Methods: To determine the most effective bi-planar gradient coil configurations, we conducted an investigation into the impact of various factors, including the square side length, surface separation, and surface orientation. This was accomplished by generating over 500 bi-planar surface configurations using automated methods., Results: We successfully generated and evaluated coil layouts in terms of sensitivity and field accuracy. Interestingly, inclined bi-planar orientations close to the NV-NMR setup's requirement, showed higher sensitivity for the transverse gradient channels than horizontal or vertical orientations. We fabricated a suitable solution as a three-channel bi-planar double-layered PCB system and experimentally validated the sensitivities at [Formula: see text] and [Formula: see text] for the transverse [Formula: see text] and [Formula: see text] gradients, and [Formula: see text] for the [Formula: see text] gradient., Discussion: We found that the chosen relative bi-planar tilt of [Formula: see text] represents a reasonable compromise in terms of overall performance and allows for easier coil implementation with a straight, horizontal alignment within the overall experimental setup., (© 2023. The Author(s).)