Mass production and dynamic imaging of fluorescent nanodiamonds

Disposable biosensor based on nanodiamond particles, ionic liquid and poly-l-lysine for determination of phenolic compounds

This study describes the development of a highly sensitive amperometric biosensor for the analysis of phenolic compounds such as catechol. The biosensor architecture is based on the immobilization of tyrosinase (Tyr) on a screen-printed carbon electrode (SPE) modified with nanodiamond particles (ND), 1-butyl-3-methylimidazolium hexafluorophosphate (IL) and poly-l-lysine (PLL). Surface morphologies of the electrodes during the modification process were evaluated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical characteristics of the modified electrodes. Owing to the synergistic effect of the modification materials, the Tyr/PLL/ND-IL/SPE exhibited high sensitivity (328.2 μA mM-1) towards catechol with a wide linear range (5.0 × 10-8 - 1.2 × 10-5 M) and low detection limit (1.1 × 10-8 M). Furthermore, the method demonstrated good reproducibility and stability. The amperometric response of the biosensor towards other phenolic compounds such as bisphenol A, phenol, p-nitrophenol, m-cresol, p-cresol and o-cresol was also investigated. The analytical applicability of the biosensor was tested by the analysis of catechol in tap water. The results of the tap water analysis showed that the Tyr/PLL/ND-IL/SPE can be used as a practical and effective method for catechol determination.

Surface engineered nanodiamonds: mechanistic intervention in biomedical applications for diagnosis and treatment of cancer

In terms of biomedical tools, nanodiamonds (ND) are a more recent innovation. Their size typically ranges between 4 to 100 nm. ND are produced via a variety of methods and are known for their physical toughness, durability, and chemical stability. Studies have revealed that surface modifications and functionalization have a significant influence on the optical and electrical properties of the nanomaterial. Consequently, surface functional groups of NDs have applications in a variety of domains, including drug administration, gene delivery, immunotherapy for cancer treatment, and bio-imaging to diagnose cancer. Additionally, their biocompatibility is a critical requisite for theirin vivoandin vitrointerventions. This review delves into these aspects and focuses on the recent advances in surface modification strategies of NDs for various biomedical applications surrounding cancer diagnosis and treatment. Furthermore, the prognosis of its clinical translation has also been discussed.

Nanodiamonds: Next generation nano-theranostics for cancer therapy

Cancer remains a leading global cause of mortality, demanding early diagnosis and effective treatment. Traditional therapeutic methods often fall short due to their need for more specificity and systemic toxicity. In this challenging landscape, nanodiamonds (ND) emerge as a potential solution, mitigating the limitations of conventional approaches. ND are tiny carbon particles that mimic traditional diamonds chemical stability and hardness and harness nanomaterials' advantages. ND stands out for the unique properties that make them promising nanotheranostics candidates, combining therapeutic and imaging capabilities in one platform. Many of these applications depend on the design of the particle's surface, as the surface's role is crucial in transporting bioactive molecules, preventing aggregation, and building composite materials. This review delves into ND's distinctive features, structural and optical characteristics, and their profound relevance in advancing cancer diagnosis and treatment methods. The report delves into how these exceptional ND properties drive the development of state-of-the-art techniques for precise tumor targeting, boosting the effectiveness of chemotherapy as a chemosensitizer, harnessing immunotherapy strategies, facilitating precision medicine, and creating localized microfilm devices for targeted therapies.

Fluorescent nanodiamond immunosensors for clinical diagnostics of tuberculosis

Fluorescent nanodiamonds (FNDs) are carbon nanoparticles containing a dense ensemble of nitrogen-vacancy defects as color centers. These centers have exceptional photostability and unique quantum properties, making them useful for ultrasensitive biosensing applications. This work employed FNDs conjugated with antibodies as magneto-optical immunosensors for tuberculosis (TB) diagnostics using competitive spin-enhanced lateral flow immunoassay (SELFIA). ESAT6 (6-kDa early secretory antigenic target) of Mycobacterium tuberculosis is a clinical marker of TB. We evaluated the assay's performance using the recombinant ESAT6 antigen and its antibodies noncovalently coated on FNDs. A detection limit of ∼0.02 ng mL-1 was achieved with the lateral flow membrane strip pre-structured with a narrow channel of 1 mm width. Adopting a cut-off value of 24.0 ng mm-1 for 100-nm FNDs on the strips, the method detected 49 out of 50 clinical samples with Mycobacterium tuberculosis complexes. In contrast, none of the assays for 10 clinical samples with non-tuberculous mycobacteria (NTM) isolates exhibited the presence of ESAT6. These results suggest that the SELFIA platform is applicable for TB detection and can differentiate TB from NTM infections, which also affect the human respiratory system. The FND-enabled immunosensing techniques are versatile and promising for early detection of TB and other diseases, opening a new avenue for biomedical applications of carbon-based nanomaterials.

Nanodiamond Effects on Cancer Cell Radiosensitivity: The Interplay between Their Chemical/Physical Characteristics and the Irradiation Energy

Nanoparticles are being increasingly studied to enhance radiation effects. Among them, nanodiamonds (NDs) are taken into great consideration due to their low toxicity, inertness, chemical stability, and the possibility of surface functionalization. The objective of this study is to explore the influence of the chemical/physical properties of NDs on cellular radiosensitivity to combined treatments with radiation beams of different energies. DAOY, a human radioresistant medulloblastoma cell line was treated with NDs-differing for surface modifications [hydrogenated (H-NDs) and oxidized (OX-NDs)], size, and concentration-and analysed for (i) ND internalization and intracellular localization, (ii) clonogenic survival after combined treatment with different radiation beam energies and (iii) DNA damage and apoptosis, to explore the nature of ND-radiation biological interactions. Results show that chemical/physical characteristics of NDs are crucial in determining cell toxicity, with hydrogenated NDs (H-NDs) decreasing either cellular viability when administered alone, or cell survival when combined with radiation, depending on ND size and concentration, while OX-NDs do not. Also, irradiation at high energy (γ-rays at 1.25 MeV), in combination with H-NDs, is more efficient in eliciting radiosensitisation when compared to irradiation at lower energy (X-rays at 250 kVp). Finally, the molecular mechanisms of ND radiosensitisation was addressed, demonstrating that cell killing is mediated by the induction of Caspase-3-dependent apoptosis that is independent to DNA damage. Identifying the optimal combination of ND characteristics and radiation energy has the potential to offer a promising therapeutic strategy for tackling radioresistant cancers using H-NDs in conjunction with high-energy radiation.

Imaging Extreme Ultraviolet Radiation Using Nanodiamonds with Nitrogen-Vacancy Centers

Extreme ultraviolet (EUV) radiation with wavelengths of 10-121 nm has drawn considerable attention recently for its use in photolithography to fabricate nanoelectronic chips. This study demonstrates, for the first time, fluorescent nanodiamonds (FNDs) with nitrogen-vacancy (NV) centers as scintillators to image and characterize EUV radiations. The FNDs employed are ∼100 nm in size; they form a uniform and stable thin film on an indium-tin-oxide-coated slide by electrospray deposition. The film is nonhygroscopic and photostable and can emit bright red fluorescence from NV0 centers when excited by EUV light. An FND-based imaging device has been developed and applied for beam diagnostics of 50 nm and 13.5 nm synchrotron radiations, achieving a spatial resolution of 30 μm using a film of ∼1 μm thickness. The noise equivalent power density is 29 μW/(cm2 Hz1/2) for the 13.5 nm radiation. The method is generally applicable to imaging EUV radiation from different sources.

Production, surface modification, physicochemical properties, biocompatibility, and bioimaging applications of nanodiamonds

Nanodiamonds (ND) are chemically inert and stable owing to their sp3 covalent bonding structure, but their surface sp2 graphitic carbons can be easily homogenized with diverse functional groups via oxidation, reduction, hydrogenation, amination, and halogenation. Further surface conjugation of NDs with hydrophilic ligands can boost their colloidal stability and functionality. In addition, NDs are non-toxic as they are made of carbons. They exhibit stable fluorescence without photobleaching. They also possess paramagnetic and ferromagnetic properties, making them suitable for use as a new type of fluorescence imaging (FI) and magnetic resonance imaging (MRI) probe. In this review, we focused on recently developed ND production methods, surface homogenization and functionalization methods, biocompatibilities, and biomedical imaging applications as FI and MRI probes. Finally, we discussed future perspectives.

Carbon Nanomaterial-Based Hydrogels as Scaffolds in Tissue Engineering: A Comprehensive Review

Carbon-based nanomaterials (CBNs) are a category of nanomaterials with various systems based on combinations of sp2 and sp3 hybridized carbon bonds, morphologies, and functional groups. CBNs can exhibit distinguished properties such as high mechanical strength, chemical stability, high electrical conductivity, and biocompatibility. These desirable physicochemical properties have triggered their uses in many fields, including biomedical applications. In this review, we specifically focus on applying CBNs as scaffolds in tissue engineering, a therapeutic approach whereby CBNs can act for the regeneration or replacement of damaged tissue. Here, an overview of the structures and properties of different CBNs will first be provided. We will then discuss state-of-the-art advancements of CBNs and hydrogels as scaffolds for regenerating various types of human tissues. Finally, a perspective of future potentials and challenges in this field will be presented. Since this is a very rapidly growing field, we expect that this review will promote interdisciplinary efforts in developing effective tissue regeneration scaffolds for clinical applications.

Simultaneous Nanorheometry and Nanothermometry Using Intracellular Diamond Quantum Sensors

The viscoelasticity of the cytoplasm plays a critical role in cell morphology, cell division, and intracellular transport. Viscoelasticity is also interconnected with other biophysical properties, such as temperature, which is known to influence cellular bioenergetics. Probing the connections between intracellular temperature and cytoplasmic viscoelasticity provides an exciting opportunity for the study of biological phenomena, such as metabolism and disease progression. The small length scales and transient nature of changes in these parameters combined with their complex interdependencies pose a challenge for biosensing tools, which are often limited to a single readout modality. Here, we present a dual-mode quantum sensor capable of performing simultaneous nanoscale thermometry and rheometry in dynamic cellular environments. We use nitrogen-vacancy centers in diamond nanocrystals as biocompatible sensors for in vitro measurements. We combine subdiffraction resolution single-particle tracking in a fluidic environment with optically detected magnetic resonance spectroscopy to perform simultaneous sensing of viscoelasticity and temperature. We use our sensor to demonstrate probing of the temperature-dependent viscoelasticity in complex media at the nanoscale. We then investigate the interplay between intracellular forces and the cytoplasmic rheology in live cells. Finally, we identify different rheological regimes and reveal evidence of active trafficking and details of the nanoscale viscoelasticity of the cytoplasm.

Correlative Fluorescence and Transmission Electron Microscopy Assisted by 3D Machine Learning Reveals Thin Nanodiamonds Fluoresce Brighter

Nitrogen vacancy (NV) centers in fluorescent nanodiamonds (FNDs) draw widespread attention as quantum sensors due to their room-temperature luminescence, exceptional photo- and chemical stability, and biocompatibility. For bioscience applications, NV centers in FNDs offer high-spatial-resolution capabilities that are unparalleled by other solid-state nanoparticle emitters. On the other hand, pursuits to further improve the optical properties of FNDs have reached a bottleneck, with intense debate in the literature over which of the many factors are most pertinent. Here, we describe how substantial progress can be achieved using a correlative transmission electron microscopy and photoluminescence (TEMPL) method that we have developed. TEMPL enables a precise correlative analysis of the fluorescence brightness, size, and shape of individual FND particles. Augmented with machine learning, TEMPL can be used to analyze a large, statistically meaningful number of particles. Our results reveal that FND fluorescence is strongly dependent on particle shape, specifically, that thin, flake-shaped particles are up to several times brighter and that fluorescence increases with decreasing particle sphericity. Our theoretical analysis shows that these observations are attributable to the constructive interference of light waves within the FNDs. Our findings have significant implications for state-of-the-art sensing applications, and they offer potential avenues for improving the sensitivity and resolution of quantum sensing devices.

Three-dimensional printing of silica glass with sub-micrometer resolution

Silica glass is a high-performance material used in many applications such as lenses, glassware, and fibers. However, modern additive manufacturing of micro-scale silica glass structures requires sintering of 3D-printed silica-nanoparticle-loaded composites at ~1200 °C, which causes substantial structural shrinkage and limits the choice of substrate materials. Here, 3D printing of solid silica glass with sub-micrometer resolution is demonstrated without the need of a sintering step. This is achieved by locally crosslinking hydrogen silsesquioxane to silica glass using nonlinear absorption of sub-picosecond laser pulses. The as-printed glass is optically transparent but shows a high ratio of 4-membered silicon-oxygen rings and photoluminescence. Optional annealing at 900 °C makes the glass indistinguishable from fused silica. The utility of the approach is demonstrated by 3D printing an optical microtoroid resonator, a luminescence source, and a suspended plate on an optical-fiber tip. This approach enables promising applications in fields such as photonics, medicine, and quantum-optics.

Nano-Diamond-Enhanced Integrated Response of a Surface Plasmon Resonance Biosensor

Surface plasmon resonance (SPR) sensing is a real-time detection technique for measuring biomolecular interactions on gold surfaces. This study presents a novel approach using nano-diamonds (NDs) on a gold nano-slit array to obtain an extraordinary transmission (EOT) spectrum for SPR biosensing. We used anti-bovine serum albumin (anti-BSA) to bind NDs for chemical attachment to a gold nano-slit array. The covalently bound NDs shifted the EOT response depending on their concentration. The number of ND-labeled molecules attached to the gold nano-slit array was quantified from the change in the EOT spectrum. The concentration of anti-BSA in the 35 nm ND solution sample was much lower than that in the anti-BSA-only sample (approximately 1/100). With the help of 35 nm NDs, we were able to use a lower concentration of analyte in this system and obtained better signal responses. The responses of anti-BSA-linked NDs had approximately a 10-fold signal enhancement compared to anti-BSA alone. This approach has the advantage of a simple setup and microscale detection area, which makes it suitable for applications in biochip technology.

Electronic Structures and Spectroscopic Signatures of Noble-Gas-Doped Nanodiamonds

Fluorescent nanodiamonds, that is, those containing optically active defects, have attracted interest for their ability to be used as qubits; for in vivo imaging; and as sensors for spin, stress, and temperature. One of the most commonly studied nanodiamond color centers is the nitrogen vacancy. However, there is strong interest in discovering other impurity centers that provide localized midband gap transitions. Noble gas atoms have garnered attention since they have been discovered within nanodiamonds produced through high-pressure-high-temperature laser-heated diamond anvil cell synthesis methods, where they are commonly used as hydrostatic pressure media. Noble gas atoms that exist in macrosized natural or synthetic diamonds have been shown to be able to form color centers. This research uses ab initio density functional theory and cluster models to systematically study the localized electronic structure for group VIII impurities of nanodiamond, including helium, neon, argon, krypton, and xenon. An in-depth examination of the interaction between the noble gas atom and diamond lattice has been carried out. The changes to the vibrational and UV/vis absorption spectra have been analyzed. It was determined that the energetically preferred geometry is dependent on the atom size. Most noble gas defects are stabilized within the nanodiamond lattice and exist in tetrahedral interstitial positions, except for the largest noble gas studied in this work, Xe, which was determined to prefer a substitutional configuration. Both Kr and Xe are expected to be able to manifest visible/near-IR optical responses when included in the diamond lattice.

Highly Dispersed 3C Silicon Carbide Nanoparticles with a Polydopamine/Polyglycerol Shell for Versatile Functionalization

Silicon carbide (SiC) nanoparticles containing lattice defects are attracting considerable attention as next-generation imaging probes and quantum sensors for visualizing and sensing life activities. However, SiC nanoparticles are not currently used in biomedical applications because of the lack of technology for controlling their physicochemical properties. Therefore, in this study, SiC nanoparticles are deaggregated, surface-coated, functionalized, and selectively labeled to biomolecules of interest. A thermal-oxidation chemical-etching method is developed for deaggregating and producing a high yield of dispersed metal-contaminant-free SiC nanoparticles. We further demonstrated a polydopamine coating with controllable thickness that can be used as a platform for decorating gold nanoparticles on the surface, enabling photothermal application. We also demonstrated a polyglycerol coating, which gives excellent dispersity to SiC nanoparticles. Furthermore, a single-pot method is developed to produce mono/multifunctional polyglycerol-modified SiC nanoparticles. Using this method, CD44 proteins on cell surfaces are selectively labeled through biotin-mediated immunostaining. The methods developed in this study are fundamental for applying SiC nanoparticles to biomedical applications and should considerably accelerate the development of various SiC nanoparticles to exploit their potential applications in bioimaging and biosensing.

Atomically Precise Detection and Manipulation of Nitrogen-Vacancy Centers in Nanodiamonds

Nitrogen-vacancy (NV) centers in nanodiamonds are a promising quantum communication system offering robust and discrete single photon emission, but a more thorough understanding of properties of the NV centers is critical for real world implementation in functional devices. The first step to understanding how factors such as surface, depth, and charge state affect NV center properties is to directly characterize these defects on the atomic scale. Here we use Angstrom-resolution scanning transmission electron microscopy (STEM) to identify a single NV center in a ∼4 nm natural nanodiamond through simultaneous acquisition of electron energy loss and energy dispersive X-ray spectra, which provide a characteristic NV center peak and a nitrogen peak, respectively. In addition, we identify NV centers in larger, ∼15 nm synthetic nanodiamonds, although without the single-defect resolution afforded by the lower background of the smaller natural nanodiamonds. We have further demonstrated the potential to directly position these technologically relevant defects at the atomic scale using the scanning electron beam to "herd" NV centers and nitrogen atoms across their host nanodiamonds.

Multifunctional Carbon-Based Nanoparticles: Theranostic Applications in Cancer Therapy and Diagnosis

Cancer diagnosis and treatment are the most critical challenges in modern medicine. Conventional cancer treatments no longer meet the needs of the health field due to the high rate of mutations and epigenetic factors that have caused drug resistance in tumor cells. Hence, the search for unique methods and factors is quickly expanding. The development of nanotechnology in medicine and the search for a system to integrate treatment and diagnosis to achieve an effective approach to overcome the known limitations of conventional treatment methods have led to the emergence of theranostic nanoparticles and nanosystems based on these nanoparticles. An influential group of these nanoparticles is carbon-based theranostic nanoparticles. These nanoparticles have received significant attention due to their unique properties, such as electrical conductivity, high strength, excellent surface chemistry, and wide range of structural diversity (graphene, nanodiamond, carbon quantum dots, fullerenes, carbon nanotubes, and carbon nanohorns). These nanoparticles were widely used in various fields, such as tissue engineering, drug delivery, imaging, and biosensors. In this review, we discuss in detail the recent features and advances in carbon-based theranostic nanoparticles and the advanced and diverse strategies used to treat diseases with these nanoparticles.

Versatile nanodiamond-based tools for therapeutics and bioimaging

Nanodiamonds (NDs) are a remarkable class of carbon-based nanoparticles in nanomedicine which have recently become a hot topic of research due to their unique features including functionalization versatility, tunable opto-magnetic properties, chemical stability, minimal cytotoxicity, high affinity to biomolecules and biocompatibility. These attractive features make NDs versatile tools for a wide range of biologically relevant applications. In this feature article, we discuss the opto-magnetic properties of negatively charged nitrogen vacancy (NV^-) centres in NDs as fluorescence probes. We further discuss the frequently used chemical methods for surface chemistry modification of NDs which are relevant for biomedical applications. The in vitro and in vivo biocompatibility of modified NDs is also highlighted. Subsequently, we give an overview of recent state-of-the-art biomedical applications of NDs as versatile tools for bioimaging and detection, and as targeting nanocarriers for chemotherapy, photodynamic therapy, gene therapy, antimicrobial and antiviral therapy, and bone tissue engineering. Finally, we pinpoint the main challenges for NDs in biomedical applications which lie ahead and discuss perspectives on future directions in advancing the field for practical applications and clinical translations.

Targeting EGFR and Monitoring Tumorigenesis of Human Lung Cancer Cells In Vitro and In Vivo Using Nanodiamond-Conjugated Specific EGFR Antibody

Nanoprobes provide advantages for real-time monitoring of tumor markers and tumorigenesis during cancer progression and development. Epidermal growth factor receptor (EGFR) is a key protein that plays crucial roles for tumorigenesis and cancer therapy of lung cancers. Here, we show a carbon-based nanoprobe, nanodiamond (ND), which can be applied for targeting EGFR and monitoring tumorigenesis of human lung cancer cells in vitro and in vivo. The optimal fluorescent intensities of ND particles were observed in the human lung cancer cells and nude mice under in vivo imaging system. The fluorescence signal of ND particles can be real-time detected in the xenografted human lung tumor formation of nude mice. Moreover, the ND-conjugated specific EGFR antibody cetuximab (Cet) can track the location and distribution of EGFR proteins of lung cancer cells in vitro and in vivo. ND-Cet treatment increased cellular uptake ability of nanocomposites in the EGFR-expressed cells but not in the EGFR-negative lung cancer cells. Interestingly, single ND-Cet complex can be directly observed on the protein G bead by immunoprecipitation and confocal microscopy. Besides, the EGFR proteins were transported to lysosomes for degradation. Together, this study demonstrates that ND-conjugated Cet can apply for targeting EGFR and monitoring tumorigenesis during lung cancer progression and therapy.

Evaluation of Cytotoxicity and Bioimaging of Nitrogen-Vacancy Nanodiamonds

Nanodiamonds, due to their chemical inertness and biocompatibility, have found extensive uses in drug delivery and biomedical applications. Fluorescent nanodiamonds with fluorescent properties generated by nitrogen-vacancy defects have been intensively investigated for bioimaging, due to their high quantum yield and high photobleaching stability. In addition, the surface properties and particle size of nanodiamonds have significant impacts on cellular uptake and imaging quality. In this study, nitrogen-vacancy nanodiamonds with different particle sizes (40 nm and 90 nm) have been physicochemically characterised and investigated for their cytotoxicity and potential in fluorescence imaging. The nanodiamonds (with concentrations up to 100 µg/mL) showed cell viability >70% with mesenchymal stromal cells. The number of nanodiamonds was observed to have a larger impact on cell viability than the mass of nanodiamonds. Larger nanodiamonds (90 nm) exhibited a lower level of cytotoxicity, higher cellular uptake and fluorescence intensity. The results indicate the potential of using fluorescent nanodiamonds as a nanoprobe for effective bioimaging and cell tracking.

Microgels based on 0D-3D carbon materials: Synthetic techniques, properties, applications, and challenges

Microgels are three-dimensional (3D) colloidal hydrogel particles with outstanding features such as biocompatibility, good mechanical properties, tunable sizes from submicrometer to tens of nanometers, and large surface areas. Because of these unique qualities, microgels have been widely used in various applications. Carbon-based materials (CMs) with various dimensions (0-3D) have recently been investigated as promising candidates for the design and fabrication of microgels because of their large surface area, excellent conductivity, unique chemical stability, and low cost. Here, we provide a critical review of the specific characteristics of CMs that are being incorporated into microgels, as well as the state-of-the art applications of CM-microgels in pollutant adsorption and photodegradation, H₂ evoluation, CO₂ capture, soil conditioners, water retention, drug delivery, cell encapsulation, and tissue engineering. Advanced preparation techniques for CM-microgel systems are also summarized and discussed. Finally, challenges related to the low colloidal stability of CM-microgels and development strategies are examined. This review shows that CM-microgels have the potential to be widely used in various practical applications.

Fluorescent nanodiamond-based spin-enhanced lateral flow immunoassay for detection of SARS-CoV-2 nucleocapsid protein and spike protein from different variants

SARS-CoV-2 viruses, responsible for the COVID-19 pandemic, continues to evolve into new mutations, which poses a significant threat to public health. Current testing methods have some limitations, such as long turnaround times, high costs, and professional laboratory requirements. In this report, the novel Spin-Enhanced Lateral Flow Immunoassay (SELFIA) platform and fluorescent nanodiamond (FND) reporter were utilized for the rapid detection of SARS-CoV-2 nucleocapsid and spike antigens from different variants, including wild-type (Wuhan-1), Alpha (B.1.1.7), Delta (B.1.617.2), and Omicron (B.1.1.529). The SARS-CoV-2 antibodies were conjugated with FND via nonspecific binding, enabling the detection of SARS-CoV-2 antigens via both direct and competitive SELFIA format. Direct SELFIA was performed by directly adding the SARS-CoV-2 antibodies-conjugated FND on the antigens-immobilized nitrocellulose (NC) membrane. Conversely, the SARS-CoV-2 antigen-containing sample was first incubated with the antibodies-conjugated FND, and then dropped on the antigen-immobilized NC membrane to carry out the competitive SELFIA. The results suggested that S44F anti-S IgG antibody can be efficiently used for the detection of wild-type, Alpha, Delta, and Omicron variants spike antigens. Findings were comparable in direct SELFIA, competitive SELFIA, and ELISA. A detection limit of 1.94, 0.77, 1.14, 1.91, and 1.68 ng/mL can be achieved for SARS-CoV-2 N protein, wild-type, Alpha, Delta, and Omicron S proteins, respectively, via competitive SELFIA assay. These results suggest that a direct SELFIA assay can be used for antibody/antigen pair screening in diagnosis development, while the competitive SELFIA assay can serve as an accurate quantitative diagnostic tool. The simplicity and rapidity of the SELFIA platform were demonstrated, which can be leveraged in the detection of other infectious diseases in the near future.

All-Optical Modulation of Single Defects in Nanodiamonds: Revealing Rotational and Translational Motions in Cell Traction Force Fields

Measuring the mechanical interplay between cells and their surrounding microenvironment is vital in cell biology and disease diagnosis. Most current methods can only capture the translational motion of fiduciary markers in the deformed matrix, but their rotational motions are normally ignored. Here, by utilizing single nitrogen-vacancy (NV) centers in nanodiamonds (NDs) as fluorescent markers, we propose a linear polarization modulation (LPM) method to monitor in-plane rotational and translational motions of the substrate caused by cell traction forces. Specifically, precise orientation measurement and localization with background suppression were achieved via optical polarization selective excitation of single NV centers with precisions of ∼0.5°/7.5 s and 2 nm/min, respectively. Additionally, we successfully applied this method to monitor the multidimensional movements of NDs attached to the vicinity of cell focal adhesions. The experimental results agreed well with our theoretical calculations, demonstrating the practicability of the NV-based LPM method in studying mechanobiology and cell-material interactions.

Single-Particle Tracking and Trajectory Analysis of Fluorescent Nanodiamonds in Cell-Free Environment and Live Cells

Diamond magnetometry can provide new insights on the production of free radicals inside live cells due to its high sensitivity and spatial resolution. However, the measurements often lack intracellular context for the recorded signal. In this paper, the possible use of single-particle tracking and trajectory analysis of fluorescent nanodiamonds (FNDs) to bridge that gap is explored. It starts with simulating a set of different possible scenarios of a particle's movement, reflecting different modes of motion, degrees of confinement, as well as shapes and sizes of that confinement. Then, the insights from the analysis of the simulated trajectories are applied to describe the movement of FNDs in glycerol solutions. It is shown that the measurements are in good agreement with the previously reported findings and that trajectory analysis yields meaningful results, when FNDs are tracked in a simple environment. Then the much more complex situation of FNDs moving inside a live cell is focused. The behavior of the particles after different incubation times is analyzed, and the possible intracellular localization of FNDs is deducted from their trajectories. Finally, this approach is combined with long-term magnetometry methods to obtain maps of the spin relaxation dynamics (or T1) in live cells, as FNDs move through the cytosol.

Fluorescent Nanoparticles for Super-Resolution Imaging

Super-resolution imaging techniques that overcome the diffraction limit of light have gained wide popularity for visualizing cellular structures with nanometric resolution. Following the pace of hardware developments, the availability of new fluorescent probes with superior properties is becoming ever more important. In this context, fluorescent nanoparticles (NPs) have attracted increasing attention as bright and photostable probes that address many shortcomings of traditional fluorescent probes. The use of NPs for super-resolution imaging is a recent development and this provides the focus for the current review. We give an overview of different super-resolution methods and discuss their demands on the properties of fluorescent NPs. We then review in detail the features, strengths, and weaknesses of each NP class to support these applications and provide examples from their utilization in various biological systems. Moreover, we provide an outlook on the future of the field and opportunities in material science for the development of probes for multiplexed subcellular imaging with nanometric resolution.

Nanodiamonds as Possible Tools for Improved Management of Bladder Cancer and Bacterial Cystitis

Nanodiamonds (NDs) are a class of carbon nanomaterials with sizes ranging from a few nm to micrometres. Due to their excellent physical, chemical and optical properties, they have recently attracted much attention in biomedicine. In addition, their exceptional biocompatibility and the possibility of precise surface functionalisation offer promising opportunities for biological applications such as cell labelling and imaging, as well as targeted drug delivery. However, using NDs for selective targeting of desired biomolecules within a complex biological system remains challenging. Urinary bladder cancer and bacterial cystitis are major diseases of the bladder with high incidence and poor treatment options. In this review, we present: (i) the synthesis, properties and functionalisation of NDs; (ii) recent advances in the study of various NDs used for better treatment of bladder cancer and (iii) bacterial cystitis; and (iv) the use of NDs in theranostics of these diseases.

Applications of Fluorescent Nanodiamond in Biology

Fluorescent nanodiamond (FND) has emerged as a promising material in several multidisciplinary areas, including biology, chemistry, physics, and materials science. Composed of sp 3 ‐carbon atoms, FND offers superior biocompatibility, chemical inertness, a large surface area, tunable surface structure, and excellent mechanical characteristics. The nanoparticle is unique in that it comprises a high‐density ensemble of negatively charged nitrogen‐vacancy (NV − ) centers that act as built‐in fluorophores and exhibit a number of remarkable optical and magnetic properties. These properties make FND particularly well suited for a wide range of applications, including cell labeling, long‐term cell tracking, super‐resolution imaging, nanoscale sensing, and drug delivery. This article discusses recent applications of FND‐enabled developments in biology.

Silicon-Vacancy Nanodiamonds as High Performance Near-Infrared Emitters for Live-Cell Dual-Color Imaging and Thermometry

Nanodiamonds (NDs) with color centers are excellent emitters for various bioimaging and quantum biosensing applications. In our work, we explore new applications of NDs with silicon-vacancy centers (SiV) obtained by high-pressure high-temperature (HPHT) synthesis based on metal-catalyst-free growth. They are coated with a polypeptide biopolymer, which is essential for efficient cellular uptake. The unique optical properties of NDs with SiV are their high photostability and narrow emission in the near-infrared region. Our results demonstrate for the first time that NDs with SiV allow live-cell dual-color imaging and intracellular tracking. Also, intracellular thermometry and challenges associated with SiV atomic defects in NDs are investigated and discussed for the first time. NDs with SiV nanoemitters provide new avenues for live-cell bioimaging, diagnostic (SiV as a nanosized thermometer), and theranostic (nanodiamonds as drug carrier) applications.

Silicon-Vacancy Nanodiamonds as High Performance Near-Infrared Emitters for Live-Cell Dual-Color Imaging and Thermometry

Nanodiamonds (NDs) with color centers are excellent emitters for various bioimaging and quantum biosensing applications. In our work, we explore new applications of NDs with silicon-vacancy centers (SiV) obtained by high-pressure high-temperature (HPHT) synthesis based on metal-catalyst-free growth. They are coated with a polypeptide biopolymer, which is essential for efficient cellular uptake. The unique optical properties of NDs with SiV are their high photostability and narrow emission in the near-infrared region. Our results demonstrate for the first time that NDs with SiV allow live-cell dual-color imaging and intracellular tracking. Also, intracellular thermometry and challenges associated with SiV atomic defects in NDs are investigated and discussed for the first time. NDs with SiV nanoemitters provide new avenues for live-cell bioimaging, diagnostic (SiV as a nanosized thermometer), and theranostic (nanodiamonds as drug carrier) applications.

Application of Nanodiamonds in Modelled Bioremediation of Phenol Pollution in River Sediments

The pollution of aquatic ecosystems is a big problem that has its impact on river sediments. In recent decades, an effective solution to this problem has been the application of bioremediation technologies. Nanoremediation is an innovative part of these technologies. We still know little about the efficiency of nanoparticles, especially nanodiamonds, in modelled conditions. The aim of the present study is to investigate the effect of nanodiamonds on the key parameters of modelled bioremediation of river sediments that are polluted with phenol, as well their effect on the structures and functions of microbial communities. An important indicative mechanism that was used is the application of fluorescent in situ hybridization for sediment microbial communities. The results of this study revealed the positive role of nanodiamonds that is associated with their intoxication with high concentrations of phenol. Readaptation was also found, in which the xenobiotic biodegradation potential evolved by increasing the relative proportions of non-culturable bacteria, namely Acinetobacter (at the 144th hour) and Pseudomonas (at the 214th hour). The results can help to find an effective solution to the question of how information from such precise molecular methods and the application of nanodiamonds can be translated into the accessible language of management and bioremediation technologies.

Chemistry-mediated Ostwald ripening in carbon-rich C/O systems at extreme conditions

There is significant interest in establishing a capability for tailored synthesis of next-generation carbon-based nanomaterials due to their broad range of applications and high degree of tunability. High pressure (e.g., shockwave-driven) synthesis holds promise as an effective discovery method, but experimental challenges preclude elucidating the processes governing nanocarbon production from carbon-rich precursors that could otherwise guide efforts through the prohibitively expansive design space. Here we report findings from large scale atomistically-resolved simulations of carbon condensation from C/O mixtures subjected to extreme pressures and temperatures, made possible by machine-learned reactive interatomic potentials. We find that liquid nanocarbon formation follows classical growth kinetics driven by Ostwald ripening (i.e., growth of large clusters at the expense of shrinking small ones) and obeys dynamical scaling in a process mediated by carbon chemistry in the surrounding reactive fluid. The results provide direct insight into carbon condensation in a representative system and pave the way for its exploration in higher complexity organic materials. They also suggest that simulations using machine-learned interatomic potentials could eventually be employed as in-silico design tools for new nanomaterials.

Modelling the growth of carbon nanoclusters in shock experiments is computationally demanding. Here the authors employ a machine-learned reactive interatomic model to perform large-scale simulations of nanocarbon formation from prototypical shocked C/O-containing precursor.

Synthesis, Characterization, Properties, and Novel Applications of Fluorescent Nanodiamonds

In the last few years, fluorescent nanodiamonds (FNDs)  have been developed significantly as a new member in the nanocarbon family. The surface of FNDs is embedded with some crystallographic defects containing color centres which surmount the properties of other fluorochromes including up conversion and down conversion nanoparticles, quantum dots, nano tubes, fullerenes, organic dyes, silica etc. Some of the intriguing properties like inevitable photostability, inherent bio-compatibility, outstanding optical and robust mechanical properties, excellent magnetic field, and electric field sensing potentiality make FNDs appealing to some benevolent applications in numerous fields like bio-imaging, delivering drugs, fighting cancer, spin electronics, imaging of magnetic structure at nanoscale and as promising nanometric temperature sensor. The structure of FNDs has certain point defects on the surface among which negatively charged nitrogen vacancy centre (NV^-) is the most investigated color centre. The production of NV^- fluorescence nanodiamonds is the most challenging task as substitution of carbon atoms is required to create vacancies by causing irradiation from an electron beam which is followed by high temperature annealing. Thus, this review points out the relative advantages of FNDs containing negatively charged nitrogen vacancy centres produced from HPHT method or CVD method with those nanodiamonds produced through detonation process or pulsed laser ablation (PLA) method. The steps involved in the fabrication of FNDs are described along with the major challenges and struggles underwent during the process in this review. This review also summarizes the recent developments made in the functionalization and applications predominantly made in the field of biological science and it is understood that depending on the defect color centres they can exhibit different emitted wavelengths ranging from UV-visible to near infrared with broad or narrow bandwidths. This review also highlights some of the fluorescent NDs that emit stable and strong red or green photoluminescence from the defect centers of NV^- which are implanted in the crystal lattice. This critical and extensive review will be useful for the further progress in this futuristic field of FNDs.

Bleaching-Resistant Super-Resolution Fluorescence Microscopy

Photobleaching is the permanent loss of fluorescence after extended exposure to light and is a major limiting factor in super-resolution microscopy (SRM) that restricts spatiotemporal resolution and observation time. Strategies for preventing or overcoming photobleaching in SRM are reviewed developing new probes and chemical environments. Photostabilization strategies are introduced first, which are borrowed from conventional fluorescence microscopy, that are employed in SRM. SRM-specific strategies are then highlighted that exploit the on-off transitions of fluorescence, which is the key mechanism for achieving super-resolution, which are becoming new routes to address photobleaching in SRM. Off states can serve as a shelter from excitation by light or an exit to release a damaged probe and replace it with a fresh one. Such efforts in overcoming the photobleaching limits are anticipated to enhance resolution to molecular scales and to extend the observation time to physiological lifespans.

Metastable Brominated Nanodiamond Surface Enables Room Temperature and Catalysis-Free Amine Chemistry

Bromination of high-pressure, high-temperature (HPHT) nanodiamond (ND) surfaces has not been explored and can open new avenues for increased chemical reactivity and diamond lattice covalent bond formation. The large bond dissociation energy of the diamond lattice-oxygen bond is a challenge that prevents new bonds from forming, and most researchers simply use oxygen-terminated NDs (alcohols and acids) as reactive species. In this work, we transformed a tertiary-alcohol-rich ND surface to an amine surface with ∼50% surface coverage and was limited by the initial rate of bromination. We observed that alkyl bromide moieties are highly labile on HPHT NDs and are metastable as previously found using density functional theory. The strong leaving group properties of the alkyl bromide intermediate were found to form diamond-nitrogen bonds at room temperature and without catalysts. This robust pathway to activate a chemically inert ND surface broadens the modalities for surface termination, and the unique surface properties of brominated and aminated NDs are impactful to researchers for chemically tuning diamond for quantum sensing or biolabeling applications.

On-Demand, Direct Printing of Nanodiamonds at the Quantum Level

The quantum defects in nanodiamonds, such as nitrogen-vacancy (NV) centers, are emerging as a promising candidate for nanoscale sensing and imaging, and the controlled placement with respect to target locations is vital to their practical applications. Unfortunately, this prerequisite continues to suffer from coarse positioning accuracy, low throughput, and process complexity. Here, it is reported on direct, on-demand electrohydrodynamic printing of nanodiamonds containing NV centers with high precision control over quantity and position. After thorough characterizations of the printing conditions, it is shown that the number of printed nanodiamonds can be controlled at will, attaining the single-particle level precision. This printing approach, therefore, enables positioning NV center arrays with a controlled number directly on the universal substrate without any lithographic process. The approach is expected to pave the way toward new horizons not only for experimental quantum physics but also for the practical implementation of such quantum systems.

General Method to Increase Carboxylic Acid Content on Nanodiamonds

Carboxylic acid is a commonly utilized functional group for covalent surface conjugation of carbon nanoparticles that is typically generated by acid oxidation. However, acid oxidation generates additional oxygen containing groups, including epoxides, ketones, aldehydes, lactones, and alcohols. We present a method to specifically enrich the carboxylic acid content on fluorescent nanodiamond (FND) surfaces. Lithium aluminum hydride is used to reduce oxygen containing surface groups to alcohols. The alcohols are then converted to carboxylic acids through a rhodium (II) acetate catalyzed carbene insertion reaction with tert–butyl diazoacetate and subsequent ester cleavage with trifluoroacetic acid. This carboxylic acid enrichment process significantly enhanced nanodiamond homogeneity and improved the efficiency of functionalizing the FND surface. Biotin functionalized fluorescent nanodiamonds were demonstrated to be robust and stable single-molecule fluorescence and optical trapping probes.

Steric Interaction of Polyglycerol-Functionalized Detonation Nanodiamonds

Detonation nanodiamonds have found numerous potential applications in a diverse array of fields such as biomedical imaging and drug delivery. Here, we systematically characterized non-functionalized and polyglycerol-functionalized detonation nanodiamond particles (DNPs) dispersed in aqueous suspensions at different ionic strengths (∼1.0 × 10^-7 to 1.0 × 10^-2 M) via dynamic light scattering and cryogenic transmission electron microscopy. For these colloidal suspensions, the total potential energies of interactions between a pair of DNPs were theoretically calculated using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory plus the fitting of the Boltzmann distribution to the interparticle spacing distribution of the colloidal DNPs. These investigations revealed that the non-functionalized DNPs are dispersed in aqueous media through the long-range (>10 nm) and weak (<7 k_BT) electrical double-layer repulsive interaction, while the driving force on dispersion of polyglycerol-functionalized DNPs is mostly derived from the short-range (<2 nm) and strong (∼55 k_BT) steric repulsive potential barrier generated by the polyglycerol. Moreover, our results show that the truly monodispersed and individually dispersed DNP colloids, forming no aggregates in aqueous suspensions, are available by both functionalizing DNPs by polyglycerol and increasing ionic strength of suspending media to ≳1.0 × 10^-2 M.

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).

Ag-Diamond Core-Shell Nanostructures Incorporated with Silicon-Vacancy Centers

Silicon-vacancy (SiV) centers in diamond have attracted attention as highly stable fluorophores for sensing and as possible candidates for quantum information science. While prior studies have shown that the formation of hybrid diamond-metal structures can increase the rates of optical absorption and emission, many practical applications require diamond plasmonic structures that are stable in harsh chemical and thermal environments. Here, we demonstrate that Ag nanospheres, produced both in quasi-random arrays by thermal dewetting and in ordered arrays using electron-beam lithography, can be completely encapsulated with a thin diamond coating containing SiV centers, leading to hybrid core-shell nanostructures exhibiting extraordinary chemical and thermal stability as well as enhanced optical properties. Diamond shells with a thickness on the order of 20-100 nm are sufficient to encapsulate and protect the Ag nanostructures with different sizes ranging from 20 nm to hundreds of nanometers, allowing them to withstand heating to temperatures of 1000 °C and immersion in harsh boiling acid for 24 h. Ultrafast photoluminescence lifetime and super-resolution optical imaging experiments were used to study the SiV properties on and off the core-shell structures, which show that the SiV on core-shell structures have higher brightness and faster decay rate. The stability and optical properties of the hybrid Ag-diamond core-shell structures make them attractive candidates for high-efficiency imaging and quantum-based sensing applications.

All-Optical Wide-Field Selective Imaging of Fluorescent Nanodiamonds in Cells, In Vivo and Ex Vivo

Fluorescence imaging is a critical tool to understand the spatial distribution of biomacromolecules in cells and in vivo, providing information on molecular dynamics and interactions. Numerous valuable insights into biological systems have been provided by the specific detection of various molecular species. However, molecule-selective detection is often hampered by background fluorescence, such as cell autofluorescence and fluorescence leakage from molecules stained by other dyes. Here we describe a method for all-optical selective imaging of fluorescent nanodiamonds containing nitrogen-vacancy centers (NVCs) for wide-field fluorescence bioimaging. The method is based on the fact that the fluorescence intensity of NVCs strictly depends on the configuration of ground-state electron spins, which can be controlled by changing the pulse recurrence intervals of microsecond excitation laser pulses. Therefore, by using regulated laser pulses, we can oscillate the fluorescence from NVCs in a nanodiamond, while oscillating other optical signals in the opposite phase to NVCs. As a result, we can reconstruct a selective image of a nanodiamond by using a series of oscillated fluorescence images. We demonstrate application of the method to the selective imaging of nanodiamonds in live cells, in microanimals, and on a hippocampal slice culture obtained from a rat. Our approach potentially enables us to achieve high-contrast images of nanodiamond-labeled biomolecules with a signal-to-background ratio improved by up to 100-fold over the standard fluorescence image, thereby providing a more powerful tool for the investigation of molecular dynamics in cells and in vivo.

Quantifying nanodiamonds biodistribution in whole cells with correlative iono-nanoscopy

Correlative imaging and quantification of intracellular nanoparticles with the underlying ultrastructure is crucial for understanding cell-nanoparticle interactions in biological research. However, correlative nanoscale imaging of whole cells still remains a daunting challenge. Here, we report a straightforward nanoscopic approach for whole-cell correlative imaging, by simultaneous ionoluminescence and ultrastructure mapping implemented with a highly focused beam of alpha particles. We demonstrate that fluorescent nanodiamonds exhibit fast, ultrabright and stable emission upon excitation by alpha particles. Thus, by using fluorescent nanodiamonds as imaging probes, our approach enables quantification and correlative localization of single nanodiamonds within a whole cell at sub-30 nm resolution. As an application example, we show that our approach, together with Monte Carlo simulations and radiobiological experiments, can be employed to provide unique insights into the mechanisms of nanodiamond radiosensitization at the single whole-cell level. These findings may benefit clinical studies of radio-enhancement effects by nanoparticles in charged-particle cancer therapy.

The authors demonstrate efficient excitation of nanodiamonds by a focused beam of helium ions, resulting in ionoluminescence. They use this for quantification and correlative localization of single particles within a whole cell at sub-30 nm resolution, and investigate nanodiamond radiosensitisation effects.

Fluorescent nanodiamonds encapsulated by Cowpea Chlorotic Mottle Virus (CCMV) proteins for intracellular 3D-trajectory analysis

Long-term tracking of nanoparticles to resolve intracellular structures and motions is essential to elucidate fundamental parameters as well as transport processes within living cells. Fluorescent nanodiamond (ND) emitters provide cell compatibility and very high photostability. However, high stability, biocompatibility, and cellular uptake of these fluorescent NDs under physiological conditions are required for intracellular applications. Herein, highly stable NDs encapsulated with Cowpea chlorotic mottle virus capsid proteins (ND-CP) are prepared. A thin capsid protein layer is obtained around the NDs, which imparts reactive groups and high colloidal stability, while retaining the opto-magnetic properties of the coated NDs as well as the secondary structure of CPs adsorbed on the surface of NDs. In addition, the ND-CP shows excellent biocompatibility both in vitro and in vivo. Long-term 3D trajectories of the ND-CP with fine spatiotemporal resolutions are recorded; their intracellular motions are analyzed by different models, and the diffusion coefficients are calculated. The ND-CP with its brilliant optical properties and stability under physiological conditions provides us with a new tool to advance the understanding of cell biology, e.g., endocytosis, exocytosis, and active transport processes in living cells as well as intracellular dynamic parameters.

Fluorescent nanodiamond - hyaluronate conjugates for target-specific molecular imaging

Despite wide investigation on molecular imaging contrast agents, there are still strong unmet medical needs to enhance their signal-to background ratio, brightness, photostability, and biocompatibility with multimodal imaging capability. Here, we assessed the feasibility of fluorescent nanodiamonds (FNDs) as carbon based photostable and biocompatible materials for molecular imaging applications. Because FNDs have negatively charged nitrogen vacancy (NV) centers, they can emit bright red light. FNDs were conjugated to hyaluronate (HA) for target-specific molecular imaging. HA is a biocompatible, biodegradable, and linear polysaccharide with abundant HA receptors in the liver, enabling liver targeted molecular imaging. In vitro cell viability tests revealed the biocompatibility of HA-FND conjugates and the competitive cellular uptake test confirmed their target-specific intracellular delivery to HepG2 cells with HA receptors. In addition, in vivo fluorescence lifetime (FLT) assessment revealed the imaging capability of FNDs and HA-FND conjugates. After that, we could confirm the statistically significant liver-targeted delivery of HA-FND conjugates by in vivo imaging system (IVIS) analysis and ex vivo biodistribution tests in various organs. The renal clearance test and histological analysis corroborated the in vivo biocompatibility and safety of HA-FND conjugates. All these results demonstrated the feasibility of HA-FND conjugates for further molecular imaging applications.

Toward Quantitative Bio-sensing with Nitrogen-Vacancy Center in Diamond

The long-dreamed-of capability of monitoring the molecular machinery in living systems has not been realized yet, mainly due to the technical limitations of current sensing technologies. However, recently emerging quantum sensors are showing great promise for molecular detection and imaging. One of such sensing qubits is the nitrogen-vacancy (NV) center, a photoluminescent impurity in a diamond lattice with unique room-temperature optical and spin properties. This atomic-sized quantum emitter has the ability to quantitatively measure nanoscale electromagnetic fields via optical means at ambient conditions. Moreover, the unlimited photostability of NV centers, combined with the excellent diamond biocompatibility and the possibility of diamond nanoparticles internalization into the living cells, makes NV-based sensors one of the most promising and versatile platforms for various life-science applications. In this review, we will summarize the latest developments of NV-based quantum sensing with a focus on biomedical applications, including measurements of magnetic biomaterials, intracellular temperature, localized physiological species, action potentials, and electronic and nuclear spins. We will also outline the main unresolved challenges and provide future perspectives of many promising aspects of NV-based bio-sensing.

Biofilm inhibition in oral pathogens by nanodiamonds

Complex microbial communities, e.g., biofilms residing in our oral cavity, have recognized clinical significance, as they are typically the main cause for infections. Particularly, they show high resistance to conventional antibiotics, and alternatives including nanotechnology are being intensively explored nowadays to provide more efficient therapeutics. Diamond nanoparticles, namely, nanodiamonds (NDs) with many promising physico-chemical properties, have been demonstrated to work as an effective antibacterial agent against planktonic cells (free-floating state). However, little is known about the behaviors of NDs against biofilms (sessile state). In this study, we uncovered their role in inhibiting biofilm formation and their disrupting effect on preformed biofilms in several selected orally and systemically important organisms. The current findings will advance the mechanistic understanding of NDs on oral pathogens and might accelerate corresponding clinical translation.

Nanodiamonds and their potential applications in breast cancer therapy: a narrative review

Breast cancer remains the most commonly diagnosed cancer and the leading cause of cancer-related death among women worldwide. With the projected increase in breast cancer cases in recent years, optimising treatment becomes increasingly important. Current treatment modalities in breast cancer present major limitations, including chemoresistance, dose-limiting adverse effects and lack of selectivity in aggressive subtypes of breast cancers such as triple-negative breast cancer. Nanodiamonds have demonstrated promising outcomes in preclinical models from their unique surface characteristics allowing optimised delivery of various therapeutic agents, overcoming some of the significant hurdles in conventional treatment modalities. This review will present an update on preclinical findings of nanodiamond-based drug delivery systems for breast cancer therapy to date, challenges with the use of nanodiamonds along with considerations for future research.