Bright Fluorescent Nanodiamonds: No Photobleaching and Low Cytotoxicity

Dynamic Quantum Sensing of Paramagnetic Species Using Nitrogen-Vacancy Centers in Diamond

Naturally occurring paramagnetic species (PS), such as free radicals and paramagnetic metalloproteins, play an essential role in a multitude of critical physiological processes including metabolism, cell signaling, and immune response. These highly dynamic species can also act as intrinsic biomarkers for a variety of disease states, while synthetic paramagnetic probes targeted to specific sites on biomolecules enable the study of functional information such as tissue oxygenation and redox status in living systems. The work presented herein describes a new sensing method that exploits the spin-dependent emission of photoluminescence (PL) from an ensemble of nitrogen-vacancy centers in diamond for rapid, nondestructive detection of PS in living systems. Uniquely this approach involves simple measurement protocols that assess PL contrast with and without the application of microwaves. The method is demonstrated to detect concentrations of paramagnetic salts in solution and the widely used magnetic resonance imaging contrast agent gadobutrol with a limit of detection of less than 10 attomol over a 100 μm × 100 μm field of view. Real-time monitoring of changes in the concentration of paramagnetic salts is demonstrated with image exposure times of 20 ms. Further, dynamic tracking of chemical reactions is demonstrated via the conversion of low-spin cyanide-coordinated Fe3+ to hexaaqua Fe3+ under acidic conditions. Finally, the capability to map paramagnetic species in model cells with subcellular resolution is demonstrated using lipid membranes containing gadolinium-labeled phospholipids under ambient conditions in the order of minutes. Overall, this work introduces a new sensing approach for the realization of fast, sensitive imaging of PS in a widefield format that is readily deployable in biomedical settings. Ultimately, this new approach to nitrogen vacancy-based quantum sensing paves the way toward minimally invasive real-time mapping and observation of free radicals in in vitro cellular environments.

Biocompatible Fluorescent Nanodiamonds as Multifunctional Optical Probes for Latent Fingerprint Detection

There is an immense literature on detection of latent fingerprints (LFPs) with fluorescent nanomaterials because fluorescence is one of the most sensitive detection methods. Although many fluorescent probes have been developed for latent fingerprint detection, many challenges remain, including the low selectivity, complicated processing, high background, and toxicity of nanoparticles used to visualize LFPs. In this study, we demonstrate biocompatible, efficient, and low background LFP detection with poly(vinylpyrrolidone) (PVP) coated fluorescent nanodiamonds (FNDs). PVP-coated FND (FND@PVP) is biocompatible at the cellular level. They neither inhibit cellar proliferation nor induce cell death via apoptosis or other cell killing pathways. Moreover, they do not elicit an immune response in cells. PVP coating enhances the physical adhesion of FND to diverse substrates and in particular results in efficient binding of FND@PVP to fingerprint ridges due to the intrinsic amphiphilicity of PVP. Clear, well-defined ridge structures with first, second, and third-level of LFP details are revealed within minutes by FND@PVP. The combination of this binding specificity and the remarkable optical properties of FND@PVP permits the detection of LPFs with high contrast, efficiency, selectivity, sensitivity, and reduced background interference. Our results demonstrate that background-free imaging via multicolor emission and dual-modal imaging of FND@PVP nanoparticles have great potential for high-resolution imaging of LFPs.

Nanodiamonds with powerful ability for drug delivery and biomedical applications: Recent updates on in vivo study and patents

Nanodiamonds are novel nanosized carbon building blocks possessing varied fascinating mechanical, chemical, optical and biological properties, making them significant active moiety carriers for biomedical application. These are known as the most 'captivating' crystals attributed to their chemical inertness and unique properties posing them useful for variety of applications in biomedical era. Alongside, it becomes increasingly important to find, ascertain and circumvent the negative aspects associated with nanodiamonds. Surface modification or functionalization with biological molecules plays a significant role in managing the toxic behavior since nanodiamonds have tailorable surface chemistry. To take advantage of nanodiamond potential in drug delivery, focus has to be laid on its purity, surface chemistry and other considerations which may directly or indirectly affect drug adsorption on nanodiamond and drug release in biological environment. This review emphasizes on the basic properties, synthesis techniques, surface modification techniques, toxicity issues and biomedical applications of nanodiamonds. For the development of nanodiamonds as an effective dosage form, researchers are still engaged in the in-depth study of nanodiamonds and their effect on life interfaces.

Room temperature "optical nanodiamond hyperpolarizer": Physics, design, and operation

Dynamic Nuclear Polarization (DNP) is a powerful suite of techniques that deliver multifold signal enhancements in nuclear magnetic resonance (NMR) and MRI. The generated athermal spin states can also be exploited for quantum sensing and as probes for many-body physics. Typical DNP methods require the use of cryogens, large magnetic fields, and high power microwave excitation, which are expensive and unwieldy. Nanodiamond particles, rich in Nitrogen-Vacancy (NV) centers, have attracted attention as alternative DNP agents because they can potentially be optically hyperpolarized at room temperature. Here, unraveling new physics underlying an optical DNP mechanism first introduced by Ajoy et al. [Sci. Adv. 4, eaar5492 (2018)], we report the realization of a miniature "optical nanodiamond hyperpolarizer," where ¹³C nuclei within the diamond particles are hyperpolarized via the NV centers. The device occupies a compact footprint and operates at room temperature. Instrumental requirements are very modest: low polarizing fields, low optical and microwave irradiation powers, and convenient frequency ranges that enable miniaturization. We obtain the best reported optical ¹³C hyperpolarization in diamond particles exceeding 720 times of the thermal 7 T value (0.86% bulk polarization), corresponding to a ten-million-fold gain in averaging time to detect them by NMR. In addition, the hyperpolarization signal can be background-suppressed by over two-orders of magnitude, retained for multiple-minute long periods at low fields, and deployed efficiently even to ¹³C enriched particles. Besides applications in quantum sensing and bright-contrast MRI imaging, this work opens possibilities for low-cost room-temperature DNP platforms that relay the ¹³C polarization to liquids in contact with the high surface-area particles.

Nitrogen-Vacancy Centers in Diamond for High-Performance Detection of Vacuum Ultraviolet, Extreme Ultraviolet, and X-rays

Fluorescent nanodiamonds (FNDs) containing nitrogen-vacancy (NV) centers as built-in fluorophores exhibit a nearly constant emission profile over 550-750 nm upon excitation by vacuum-ultraviolet (VUV), extreme ultraviolet (EUV), and X-radiations from a synchrotron source over the energy (wavelength) range of 6.2-1450 eV (0.86-200 nm). The photoluminescence (PL) quantum yield of FNDs increases steadily with the increasing excitation energy, attaining a value as great as 1700% at 700 eV (1.77 nm). Notably, the yield curve is continuous, having no gap in the VUV to X-ray region. In addition, no significant PL intensity decreases were observed for hours. Applying the FND sensor to measure the absorption cross-sections of gaseous O₂ over 110-200 nm and comparing the measurements with the sodium-salicylate scintillator, we obtained results in agreement with each other within 5%. The superb photostability and broad applicability of FNDs offer a promising solution for the long-standing problem of lacking a robust and reliable detector for VUV, EUV, and X-radiations.

Carboxylated nanodiamond-mediated CRISPR-Cas9 delivery of human retinoschisis mutation into human iPSCs and mouse retina

Nanodiamonds (NDs) are considered to be relatively safe carbon nanomaterials used for the transmission of DNA, proteins and drugs. The feasibility of utilizing the NDs to deliver CRISPR-Cas9 system for gene editing has not been clearly studied. Therefore, in this study, we aimed to use NDs as the carriers of CRISPR-Cas9 components designed to introduce the mutation in RS1 gene associated with X-linked retinoschisis (XLRS). ND particles with a diameter of 3 nm were functionalized by carboxylation of the surface and covalently conjugated with fluorescent mCherry protein. Two linear DNA constructs were attached to the conjugated mCherry: one encoded Cas9 endonuclease and GFP reporter, another encoded sgRNA and contained insert of HDR template designed to introduce RS1 c.625C>T mutation. Such nanoparticles were successfully delivered and internalized by human iPSCs and mouse retinas, the efficiency of internalization was significantly improved by mixing with BSA. The delivery of ND particles led to introduction of RS1 c.625C>T mutation in both human iPSCs and mouse retinas. Rs1 gene editing in mouse retinas resulted in several pathological features typical for XLRS, such as aberrant photoreceptor structure. To conclude, our ND-based CRISPR-Cas9 delivery system can be utilized as a tool for creating in vitro and in vivo disease models of XLRS. STATEMENT OF SIGNIFICANCE: X-linked retinoschisis (XLRS) is a prevalent hereditary retinal disease, which is caused by mutations in RS1 gene, whose product is important for structural organization of the retina. The recent development of genome editing techniques such as CRISPR-Cas9 significantly improved the prospects for better understanding the pathology and development of treatment for this disease. Firstly, gene editing can allow development of appropriate in vitro and in vivo disease models; secondly, CRISPR-Cas9 can be applied for gene therapy by removing the disease-causative mutation in vivo. The major prerequisite for these approaches is to develop safe and efficient CRISPR-Cas9 delivery system. In this study, we tested specifically modified nanodiamonds for such a delivery system. We were able to introduce Rs1 mutation into the mouse retina and, importantly, observed several XLRS-specific effects.

A lipophilic AIEgen for lipid droplet imaging and evaluation of the efficacy of HIF-1 targeting drugs

A lipid-droplet-specific AIEgen was used to evaluate the inhibitory efficacy of HIF-1-targeting drugs by assessing lipid-droplet levels.

Design, Synthesis, and Targeted Delivery of Fluorescent 1,2,4-Triazole-Peptide Conjugates to Pediatric Brain Tumor Cells

Most of the chemotherapeutics and drug-delivery models pose serious health problems and several undesirable side effects due to nonspecificity, lack of proper targeting system, and their large sizes. The rational design and synthesis of target-specific chemotherapeutics are highly important. This research work is focused on the rational design, synthesis, and anticancer studies of fluorescent 1,2,4-triazole-peptide conjugates for the development of target-specific anticancer drugs. Three novel 1,2,4-triazole derivatives: 4-(4-fluorobenzylidenamino)-3-hydrazino-5-mercapto-1,2,4-triazole (4FBAHMT, 2a), 4-(3,4,5-trimethoxybenzylidenamino)-3-hydrazino-5-mercapto-1,2,4-triazole (TMOBAHMT, 2b), and 4-(4-benzyloxy-2-methyloxbenzylidenamino)-3-hydrazino-5-mercapto-1,2,4-triazole (4BO2MOBAHMT, 2c) were synthesized after screening through molecular docking procedures. The docking studies were performed between ligand molecules and αvβ6 integrin protein. Fluorescent carbon nanoparticles (CNPs, 3) were conjugated with 1,2,4-triazole derivatives (2a-c) and l-carnosine (LC) dipeptide to get their corresponding conjugates (4a-c). The title double conjugates were characterized by spectroscopic (UV/vis spectroscopy, fluorescence spectroscopy, and FTIR spectroscopy) and microscopic (scanning electron microscopy, transmission electron microscopy, and atomic force microscopy) techniques. In vitro efficacy of fluorescent 1,2,4-triazole-peptide conjugates was investigated against two pediatric brain tumor cell lines (CHLA-200 & SJGBM2) and human embryonic kidney cell line (HEK293 as a control) by employing cell proliferation assay/MTS assay and fluorescence microscopy. 1,2,4-Triazole derivatives and their conjugates showed potent and selective anticancer activity against CHLA-200 and SJGBM2 cell lines. Cell proliferation assay and fluorescence microscopy results revealed that conjugates were more highly selective and cytotoxic than control drug temozolomide (TM) against both cell lines. CNPs are highly biocompatible and the quantum-sized conjugates were nontoxic for normal embryonic kidney cell line (HEK 293). The experimental results of MTS bioactivity assay and fluorescence microscopy were in close agreement with the theoretical results of molecular docking studies.

pH-responsive chimeric liposomes: From nanotechnology to biological assessment

The utilization of liposomes in biomedical applications has greatly benefited the diagnosis and treatment of various diseases. These biomimetic nano-entities have been very useful in the clinical practice as drug delivery systems in their conventional form, comprising lipids as structural components. However, the scientific efforts have recently shifted towards the development of more sophisticated nanotechnological platforms, which apply functional biomaterials, such as stimuli-responsive polymers, in order to aid the drug molecule targeting concept. These nanosystems are defined as chimeric/mixed, because they combine more than one different in nature biomaterials and their development requires intensive study through biophysical and thermodynamic approaches before they may reach in vivo application. Herein, we designed and developed chimeric liposomes, composed of a phospholipid and pH-responsive amphiphilic diblock copolymers and studied their morphology and behavior based on crucial formulation parameters, including biomaterial concentration, dispersion medium pH and polymer composition. Additionally, their interactions with biological components, pH-responsiveness and membrane thermodynamics were assessed. Finally, preliminary in vivo toxicity experiments of the developed nanosystems were carried out, in order to establish a future protocol for full in vivo evaluation. The results have been correlated with the properties of the chimeric nanosystems and highlight the importance of such approaches for designing and developing effective nanocarriers for biomedical applications.

"Two in one": Simultaneous functionalization and DOX loading for fabrication of nanodiamond-based pH responsive drug delivery system

Nanodiamond (ND) has been widely studied as a new type of carbon nanomaterials that is expected to be used as a promising candidate in various fields especially in the field of biomedicine. However, its poor water dispersibility and insufficient controlled release limit its practical applications. In this paper, ND-based composites with pH-responsive hydrazone bonds were successfully prepared by a simple chemical reaction between ester groups and hydrazine hydrate, in which ester groups were conjugated on the surface of ND via thiol-ene click reaction. On the other hand, CHO-PEG and doxorubicin hydrochloride (DOX) were linked on the carriers through formation of hydrazone bonds, resulting in improving water dispersibility and high drug loading capacity. The structure, thermal stability, surface morphology and particle size of ND carriers were characterized by different equipment. Results demonstrated that we have successfully prepared these functionalized ND. The release rate of DOX in acidic environment was significantly greater than that in normal physiological environment. More importantly, cell viability and optical imaging results showed that ND-based composites possess good biocompatibility, therapeutic effect, and could successfully transport DOX to HepG2 cells. Considering the above results, we believe that our new ND carriers will become promising candidates for intracellular controlled drug delivery and cancer treatment.

High photoluminescent nitrogen and zinc doped carbon dots for sensing Fe3+ ions and temperature

High photoluminescent quantum yield carbon nanomaterials doped with heteroatoms are of profound attention in various fields like bio-imaging, chemical sensors and electronics. Among all heteroatoms, zinc is one of the low toxic significant elements and also involves in various electron-transfer processes. These properties are added advantages to utilize zinc as a dopant in CDs synthesis. In this investigation, our group reports a one-step microwave digestion method to synthesize nitrogen and Zinc doped carbon dots (N, Zn-CDs). The optical properties of N, Zn-CDs were investigated using UV-Vis and fluorescence spectrophotometry and also the N, Zn-CDs structural features were studied with other characterization tools like XPS, TEM, EDX, FTIR and XRD. N, Zn-CDs inherent the appreciable photoluminescent quantum yields about 63.28%. And the synthesized N, Zn-CDs utilized for detection of Fe³⁺ and temperature. The observed results are promising and exhibited the detection limit of 0.027 μM. Also, the proposed sensing system was successfully adopted for the detection of Fe³⁺ in the river and circulating water samples for the practical applications and satisfactory results are observed. The current synthesis methodology and sensing potential might open up a new prospect to develop potential applications in environmental monitoring.

Far-Red to Near-Infrared Carbon Dots: Preparation and Applications in Biotechnology

As novel fluorescent nanomaterials, carbon dots (CDs) exhibit excellent photostability, good biocompatibility, and high quantum yield (QY). Their superior properties make them promising candidates for biomedical assays and therapy. Among them, the red-emission (>600 nm) CDs have attracted increasing attention in the past years due to their little damage to the biological matrix, deep tissue penetration, and minimum autofluorescence background of biosamples. This Review, summarizes the recent progress of far-red to near-infrared (NIR) CDs from the preparation and their biological applications. The challenges in designing far-red and NIR CDs and their further applications in biomedical fields are also discussed.

A Perspective on Fluorescent Nanodiamond Bioimaging

The field of fluorescent nanodiamonds (FNDs) has advanced greatly over the past few years. Though historically limited primarily to red fluorescence, the wavelengths available for nanodiamonds have increased due to continuous technical advancement. This Review summarizes the strides made in the synthesis, functionalization, and application of FNDs to bioimaging. Highlights range from super-resolution microscopy, through cellular and whole animal imaging, up to constantly emerging fields including sensing and hyperpolarized magnetic resonance imaging.

Effect of sulfur doping on fluorescence and quantum yield of graphene quantum dots: an experimental and theoretical investigation

Graphene quantum dots (GQDs) are one of the most promising luminescent carbon derived nanomaterials decorated with multiple useful functional groups and remarkable optoelectronic properties. Heteroatom doping of hexagonal carbon sheet of GQDs is an effective strategy to tailor their properties to meet desired application. In this work, sulfur doped GQDs (S-GQDs) were synthesized by simply pyrolyzing citric acid (CA) as a source of carbon and 3-Mercaptopropionic acid as a source of sulfur dopant. The optimal reaction conditions (ratio of the carbon to dopant source, temperature and time of reaction) were obtained while investigating their effect on the quantum yield and fluorescence properties of GQDs and, are hereby, reported for the first time. The as-synthesized S-GQDs were extensively characterized by different analytical techniques such as transmission electron microscopy (TEM), UV-vis Spectroscopy (UV), Fourier transform infrared spectroscopy, photoluminescence (PL) and x-ray Photoelectron Spectroscopy. S-GQDs were found uniform in size (∼4 nm) and spherical in shape with strong blue fluorescence. Further, for in-depth analysis of experimental results and underlying phenomena, theoretical studies based on density functional theory were performed for chemical structure optimization, possible sites of doping and density of states calculation. The synthesized S-GQDs exhibited excellent solubility in water, a stronger fluorescence and desirably higher quantum yield (57.44%) as compared to that of previously reported undoped GQDs. These successfully demonstrated unique and improved properties of S-GQDs present them as a potential candidate for biomedical, optical, electrical and chemical applications.

Water-Soluble Nanoconjugate for Enhanced Cellular Delivery of Receptor-Targeted Magnetic Resonance Contrast Agents

ProGlo is an efficient steroid receptor-targeted magnetic resonance (MR) imaging contrast agent (CA). It has been shown to bind to the progesterone receptor (PR) and produce enhanced image contrast in PR-positive cells and tissues in vitro and in vivo. However, the hydrophobicity of the steroid targeting domain of ProGlo (logP = 1.4) limits its formulation and delivery at clinically relevant doses. In this work, a hydrophobic moiety was utilized to drive efficient adsorption onto nanodiamond (ND) clusters to form a water-soluble nanoconstruct (logP = -2.4) with 80% release in 8 h under biological conditions. In cell culture, the ND-ProGlo construct delivered increased concentrations of ProGlo to target cells compared to ProGlo alone. Importantly, these results were accomplished without the use of solvents such as DMSO, providing a significant advance toward formulating ProGlo for translational applications. Biodistribution studies confirm the delivery of ProGlo to PR(+) tissues with enhanced efficacy over untargeted controls. These results demonstrate the potential for a noncovalent ND-CA construct as a general strategy for solubilizing and delivering hydrophobic targeted MR CAs.

Novel Poly(Methyl Methacrylate) Containing Nanodiamond to Improve the Mechanical Properties and Fungal Resistance

Herein we evaluate the effect of nanodiamond (ND) incorporation on the mechanical properties of poly(methyl methacrylate) (PMMA) nanocomposite. Three quantities of ND (0.1, 0.3, and 0.5 wt.%) were tested against the control and zirconium oxide nanoparticles (ZrO). Flexural strength and elastic modulus were measured using a three-point bending test, surface hardness was evaluated using the Vickers hardness test, and surface roughness was evaluated using atomic force microscopy (AFM), while fungal adhesion and viability were studied using Candida albicans. Samples were also analyzed for biofilm thickness and biomass in a saliva-derived biofilm model. All groups of ND-PMMA nanocomposites had significantly greater mean flexural strengths and statistically improved elastic modulus, compared to the control and ZrO groups (P < 0.001). The Vickers hardness values significantly increased compared to the control group (P < 0.001) with 0.3% and 0.5% ND. ND addition also gave significant reduction in fungal adhesion and viability (P < 0.001) compared to the control group. Finally, salivary biofilm formation was markedly reduced compared to the ZrO group. Hence, the incorporation of 0.1–0.5 wt.% ND with auto- polymerized PMMA resin significantly improved the flexural strength, elastic modulus, and surface hardness, and provided considerable fungal resistance.

Nanodiamond uptake in colon cancer cells: the influence of direction and trypsin-EDTA treatment

Nanoparticles are routinely used in cell biology. They deliver drugs or function as labels or sensors. For many of these applications it is essential that the nanoparticles enter the cells. While some cell types readily ingest all kinds of particles, others just don't. We report that uptake can be enhanced for some cells if the particles are administered from the basolateral side of the cells (in this case from below). Compared to apical uptake (from above), we report an 8-fold increase in the number of fluorescent nanodiamonds internalized by the colon cancer cell line HT29. Up to 96% of the cells treated by a modified protocol contain at least one nanodiamond, whereas in the control group we could observe nanodiamonds in less than half of the cells. We were also able to show that simple treatment of cell clusters with trypsin-EDTA leads to the same enhancement of the nanodiamond uptake as seeding the cells on top of the nanoparticles. Although our study is focused on nanodiamonds in HT29 cells, we believe that this method could also be applicable for other nanoparticles and cells with a specific directionality.

Improvement of the anti-proliferative activity of the peptide ERα17p in MCF-7 breast cancer cells using nanodiamonds

Nanodiamonds (NDs) are emerging delivery systems with biomedical applications and interesting perspectives in oncology. Their use has been proposed to assist the internalization of anticancer drugs and to decrease administered drug doses. The pro-apoptotic peptide ERα17p, which is issued from the hinge/N-terminus parts of the AF2 region of the human estrogen receptor α (ERα), is active at a concentration of 10μM on breast cancer cells and particularly on those cancer cells that are ERα-positive. We have synthesized ND@ERα17p conjugates by physisorption of the cationic peptide ERα17p on the surface of anionic NDs. Resulting ND@ERα17p suspensions were characterized by far-UV electronic circular dichroism (ECD), dynamic light scattering (DLS) and zetametry. We then tested the anti-proliferative action of ND@ERα17p on ERα-positive MCF-7 breast carcinoma cells. ND@ERα17p allowed a decrease of the active concentration to 0.1nM (ND@ERα17p), revealing unambiguously that NDs could be used to improve the anti-proliferative action of this peptide. This preliminary study proposes a novel approach for enhancing the apoptotic action displayed by ERα17p, in the context of breast cancer.

Biological impact of nanodiamond particles - label free, high-resolution methods for nanotoxicity assessment

Current methods for the assessment of nanoparticle safety that are based on 2D cell culture models and fluorescence-based assays show limited sensitivity and they lack biomimicry. Consequently, the health risks associated with the use of many nanoparticles have not yet been established. There is a need to develop in vitro models that mimic physiology more accurately and enable high throughput assessment. There is also a need to set up new assays that offer high sensitivity and are label-free. Here we developed 'mini-liver' models using scaffold-free bioprinting and used these models together with label-free nanoscale techniques for the assessment of toxicity of nanodiamond produced by laser-assisted technology. Results showed that NDs induced cytotoxicity in a concentration and exposure-time dependent manner. The loss of cell function was confirmed by increased cell stiffness, decreased cell membrane barrier integrity and reduced cells mobility. We further showed that NDs elevated the production of reactive oxygen species and reduced cell viability. Our approach that combined mini-liver models with label-free high-resolution techniques showed improved sensitivity in toxicity assessment. Notably, this approach allowed for label-free semi-high throughput measurements of nanoparticle-cell interactions, thus could be considered as a complementary approach to currently used methods.

Nanometer-precision non-local deformation reconstruction using nanodiamond sensing

Spatially resolved information about material deformation upon loading is critical to evaluating mechanical properties of materials, and to understanding mechano-response of live systems. Existing techniques may access local properties of materials at nanoscale, but not at locations away from the force-loading positions. Moreover, interpretation of the local measurement relies on correct modeling, the validation of which is not straightforward. Here we demonstrate an approach to evaluating non-local material deformation based on the integration of nanodiamond orientation sensing and atomic force microscopy nanoindentation. This approach features a 5 nm precision in the loading direction and a sub-hundred nanometer lateral resolution, high enough to disclose the surface/interface effects in the material deformation. The non-local deformation profile can validate the models needed for mechanical property determination. The non-local nanometer-precision sensing of deformation facilitates studying mechanical response of complex material systems ranging from impact transfer in nanocomposites to mechano-response of live systems.

Polymer/nanodiamond composites - a comprehensive review from synthesis and fabrication to properties and applications

Nanodiamond (ND) is an allotrope of carbon nanomaterials which exhibits many outstanding physical, mechanical, thermal, optical and biocompatibility characteristics. Meanwhile, ND particles possess unique spherical shape containing diamond-like structure at the core with graphitic carbon outer shell which intuitively contains many oxygen-containing functional groups at the outer surface. Such superior properties and unique structural morphology of NDs are essentially attractive to develop polymer composites with multifunctional properties. However, despite a long history from the discovery of NDs, which is dated back to the1960s, this nanoparticle has been less explored in the field of polymer (nano)composites compared with other carbon nanomaterials, e.g. carbon nanotube (CNT) and graphene. However, open literature indicates that research works in the field of polymer/ND (PND) composites have gained great momentum in the past half a decade. The present article provides a comprehensive review on recent achievements in ND based polymer composites. This review covers a very broad aspect from the synthesis, purification and functionalization of NDs to dispersion, preparation and fabrication of polymer/ND (PND) composites with a look in their recent applications for both structural and functional basis. Therefore, the review would be useful to pave the way for researchers to take some advancing steps in this respect.

Molecularly Imprinted Polyacrylamide with Fluorescent Nanodiamond for Creatinine Detection

Creatinine measurement in blood and urine is an important diagnostic test for assessing kidney health. In this study, a molecularly imprinted polymer was obtained by incorporating fluorescent nanodiamond into a creatinine-imprinted polyacrylamide hydrogel. The quenching of peak nanodiamond fluorescence was significantly higher in the creatinine-imprinted polymer compared to the non-imprinted polymer, indicative of higher creatinine affinity in the imprinted polymer. Fourier transform infrared spectroscopy and microscopic imaging was used to investigate the nature of chemical bonding and distribution of nanodiamonds inside the hydrogel network. Nanodiamonds bind strongly to the hydrogel network, but as aggregates with average particle diameter of 3.4 ± 1.8 µm and 3.1 ± 1.9 µm for the non-imprinted and molecularly imprinted polymer, respectively. Nanodiamond fluorescence from nitrogen-vacancy color centers (NV^- and NV⁰) was also used to detect creatinine based on nanodiamond-creatinine surface charge interaction. Results show a 15% decrease of NV^-/NV⁰ emission ratio for the creatinine-imprinted polymer compared to the non-imprinted polymer, and are explained in terms of changes in the near-surface band structure of diamond with addition of creatinine. With further improvement of sensor design to better disperse nanodiamond within the hydrogel, fluorescent sensing from nitrogen-vacancy centers is expected to yield higher sensitivity with a longer range (Coulombic) interaction to imprinted sites than that for a sensor based on acceptor/donor resonance energy transfer.

Monodisperse Five-Nanometer-Sized Detonation Nanodiamonds Enriched in Nitrogen-Vacancy Centers

Nanodiamonds containing negatively charged nitrogen-vacancy (NV^-) centers are versatile nanosensors thanks to their optical and spin properties. While currently most fluorescent nanodiamonds in use have at least a size of a few tens of nanometers, the challenge lies in engineering the smallest nanodiamonds containing a single NV^- defect. Such a tiny nanocrystal with a single NV^- center is an "optical spin label" for biomolecules, which can be detected in a fluorescence microscope. In this paper, we address two key issues toward this goal using detonation nanodiamonds (DNDs) of 4-5 nm in size. The DND samples are treated first with electron irradiation to create more vacancies. With the aid of electron paramagnetic resonance (EPR) spectroscopy, we confirm a steady increase of negatively charged NV^- centers with higher fluence. This leads to a 4 times higher concentration in NV^- defects after irradiation with 2 MeV electrons at a fluence of 5 × 10¹⁸ e^-/cm². Interestingly, we observe that the annealing of DND does not increase the number of NV^- centers, which is in contrast to bulk diamond and larger nanodiamonds. Since DNDs are strongly aggregated after the irradiation process, we apply a boiling acid treatment as a second step to fabricate monodisperse DNDs enriched in NV^- centers. These are two important steps toward "optical spin labels" having a single-digit nanometer range size that could be used for bioimaging and nanosensing.

Nanoparticle- and Nanoporous-Membrane-Mediated Delivery of Therapeutics

Pharmaceutical particulates and membranes possess promising prospects for delivering drugs and bioactive molecules with the potential to improve drug delivery strategies like sustained and controlled release. For example, inorganic-based nanoparticles such as silica-, titanium-, zirconia-, calcium-, and carbon-based nanomaterials with dimensions smaller than 100 nm have been extensively developed for biomedical applications. Furthermore, inorganic nanoparticles possess magnetic, optical, and electrical properties, which make them suitable for various therapeutic applications including targeting, diagnosis, and drug delivery. Their properties may also be tuned by controlling different parameters, e.g., particle size, shape, surface functionalization, and interactions among them. In a similar fashion, membranes have several functions which are useful in sensing, sorting, imaging, separating, and releasing bioactive or drug molecules. Engineered membranes have been developed for their usage in controlled drug delivery devices. The latest advancement in the technology is therefore made possible to regulate the physico-chemical properties of the membrane pores, which enables the control of drug delivery. The current review aims to highlight the role of both pharmaceutical particulates and membranes over the last fifteen years based on their preparation method, size, shape, surface functionalization, and drug delivery potential.

Synthesis of "Dahlia-Like" Hydrophilic Fluorescent Carbon Nanohorn as a Bio-Imaging PROBE

Carbon nanohorns (CNH) were synthesized by a simple conventional hydrothermal method in this study. The CNHs were prepared by the chemical oxidation from the carbonation of Nafion (catalyst) with heparin (carbon resource). The formation of CNH involved two major steps, as described followed. First, the formation of carbon nanorice (CNR) was achieved by carbonation and self-assembly of heparin inside the Nafion structure. Second, the further oxidation of CNR resulted the heterogeneous and porous micelle domains showed at the outer layer of the CNR particles. These porous domains exhibited hydrophobic carbon and resulted self-assembly of the CNR to form the structure of CNHs. The resulting CNHs aggregated into a “dahlia-like” morphology with fluorescence in a diameter of 50–200 nm. The “dahlia-like” CNH showed better fluorescence (450nm) than CNR particles because of the presence of more structural defect. These findings suggest that the hydrophilic fluorescent carbon nanohorns (HFCNHs) synthesized in this study have the potential to be used for in vitro bio-imaging

Knockdown of microRNA-135b in Mammary Carcinoma by Targeted Nanodiamonds: Potentials and Pitfalls of In Vivo Applications

Nanodiamonds (ND) serve as RNA carriers with potential for in vivo application. ND coatings and their administration strategy significantly change their fate, toxicity, and effectivity within a multicellular system. Our goal was to develop multiple ND coating for effective RNA delivery in vivo. Our final complex (NDA135b) consisted of ND, polymer, antisense RNA, and transferrin. We aimed (i) to assess if a tumor-specific coating promotes NDA135b tumor accumulation and effective inhibition of oncogenic microRNA-135b and (ii) to outline off-targets and immune cell interactions. First, we tested NDA135b toxicity and effectivity in tumorospheres co-cultured with immune cells ex vivo. We found NDA135b to target tumor cells, but it binds also to granulocytes. Then, we followed with NDA135b intravenous and intratumoral applications in tumor-bearing animals in vivo. Application of NDA135b in vivo led to the effective knockdown of microRNA-135b in tumor tissue regardless administration. Only intravenous application resulted in NDA135b circulation in peripheral blood and urine and the decreased granularity of splenocytes. Our data show that localized intratumoral application of NDA135b represents a suitable and safe approach for in vivo application of nanodiamond-based constructs. Systemic intravenous application led to an interaction of NDA135b with bio-interface, and needs further examination regarding its safety.

Bioorthogonal Fluorescent Nanodiamonds for Continuous Long-Term Imaging and Tracking of Membrane Proteins

Real-time tracking of membrane proteins is essential to gain an in-depth understanding of their dynamics on the cell surface. However, conventional fluorescence imaging with molecular probes like organic dyes and fluorescent proteins often suffers from photobleaching of the fluorophores, thus hindering their use for continuous long-term observations. With the availability of fluorescent nanodiamonds (FNDs), which have superb biocompatibility and excellent photostability, it is now possible to conduct the imaging in both short and long terms with high temporal and spatial resolution. To realize the concept, we have developed a facile method (e.g., one-pot preparation) to produce alkyne-functionalized hyperbranched-polyglycerol-coated FNDs for bioorthogonal labeling of azide-modified membrane proteins and azide-modified antibodies of membrane proteins. The high specificity of this labeling method has allowed us to continuously monitor the movements of the proteins of interest (such as integrin α5) on/in living cells over 2 h. The results open a new horizon for live cell imaging with functional nanoparticles and fluorescence microscopy.

Molecular Surface Functionalization of Carbon Materials via Radical-Induced Grafting of Terminal Alkenes

Formation of functional monolayers on surfaces of carbon materials is inherently difficult because of the high bond strength of carbon and because common pathways such as SN2 mechanisms cannot take place at surfaces of solid materials. Here, we show that the radical initiators can selectively abstract H atoms from H-terminated carbon surfaces, initiating regioselective grafting of terminal alkenes to surfaces of diamond, glassy carbon, and polymeric carbon dots. Nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) demonstrate formation of self-terminating organic monolayers linked via the terminal C atom of 1-alkenes. Density functional theory (DFT) calculations suggest that this selectivity is at least partially thermodynamic in origin, as significantly less energy is needed to abstract H atoms from carbon surfaces as compared to typical aliphatic compounds. The regioselectivity favoring binding to the terminal C atom of the reactant alkenes arises from steric hindrance encountered in bond formation at the adjacent carbon atom. Our results demonstrate that carbon surface radical chemistry yields a versatile, selective, and scalable approach to monolayer formation on H-terminated carbon surfaces and provide mechanistic insights into the surface selectivity and regioselectivity of molecular grafting.

Fluorescence microscopy for visualizing single-molecule protein dynamics

BACKGROUND

Single-molecule fluorescence imaging (smFI) has evolved into a valuable method used in biophysical and biochemical studies as it can observe the real-time behavior of individual protein molecules, enabling understanding of their detailed dynamic features. smFI is also closely related to other state-of-the-art microscopic methods, optics, and nanomaterials in that smFI and these technologies have developed synergistically.

SCOPE OF REVIEW

This paper provides an overview of the recently developed single-molecule fluorescence microscopy methods, focusing on critical techniques employed in higher-precision measurements in vitro and fluorescent nanodiamond, an emerging promising fluorophore that will improve single-molecule fluorescence microscopy.

MAJOR CONCLUSIONS

smFI will continue to improve regarding the photostability of fluorophores and will develop via combination with other techniques based on nanofabrication, single-molecule manipulation, and so on.

GENERAL SIGNIFICANCE

Quantitative, high-resolution single-molecule studies will help establish an understanding of protein dynamics and complex biomolecular systems.

Quantification and Imaging of Antigens on Cell Surface with Lipid-Encapsulated Fluorescent Nanodiamonds

Quantifying the density and locating the position of antigens on cell surface has been a challenge in molecular biology research. The challenge lies in the need for a chemically and photophysically stable fluorophore to achieve the required sensitivity and accuracy. Here, we present a method suitable for the purpose by using lipid-encapsulated fluorescent nanodiamonds (FNDs) of 35 nm in diameter as biolabels. The encapsulation of FNDs in biotinylated phospholipids not only facilitates good dispersion of the particles in biological buffers, but also endows them with high specific targeting ability. We demonstrated a viable application of the technique for biotin-mediated immunostaining of antigens on fixed human cells, identifying their positions by two-color confocal fluorescence imaging, and determining their densities by magnetically modulated fluorescence detection. A binding capacity of 6 ± 1 × 10⁴ antigens/cell was measured specifically for CD44 on HeLa cell surface. The result agreed well with the assay of R-phycoerythrin-conjugated antibodies by flow cytometry, supporting the reliability of this new nanoparticle-based method.

Review Article: Synthesis, properties, and applications of fluorescent diamond particles

Diamond particles containing color centers-fluorescent crystallographic defects embedded within the diamond lattice-outperform other classes of fluorophores by providing a combination of unmatched photostability, intriguing coupled magneto-optical properties, intrinsic biocompatibility, and outstanding mechanical and chemical robustness. This exceptional combination of properties positions fluorescent diamond particles as unique fluorophores with emerging applications in a variety of fields, including bioimaging, ultrasensitive metrology at the nanoscale, fluorescent tags in industrial applications, and even potentially as magnetic resonance imaging contrast agents. However, production of fluorescent nanodiamond (FND) is nontrivial, since it requires irradiation with high-energy particles to displace carbon atoms and create vacancies-a primary constituent in the majority color centers. In this review, centrally focused on material developments, major steps of FND production are discussed with emphasis on current challenges in the field and possible solutions. The authors demonstrate how the combination of fluorescent spectroscopy and electron paramagnetic resonance provides valuable insight into the types of radiation-induced defects formed and their evolution upon thermal annealing, thereby guiding FND performance optimization. A recent breakthrough process allowing for production of fluorescent diamond particles with vibrant blue, green, and red fluorescence is also discussed. Finally, the authors conclude with demonstrations of a few FND applications in the life science arena and in industry.

Synthesis of N-Doped Micropore Carbon Quantum Dots with High Quantum Yield and Dual-Wavelength Photoluminescence Emission from Biomass for Cellular Imaging

Pursuit of a simple, fast, and cost-effective method to prepare highly and dual-wavelength fluorescent carbon quantum dots (CQDs) is a persistent objective in recent years. Here, we fabricated N-doped micropore carbon quantum dots (NM-CQDs) with a high quantum yield and dual-wavelength photoluminescence (PL) emission from sustainable biomass using a pulsed laser ablation method. Interestingly, two coexisting indigo⁻blue photoluminescence (PL) emissions were clearly observed, elucidating that the excited electrons transited from the intrinsic π* orbital to the surface state (SS) formed from the saturation passivation. The quantum yield (QY) and fluorescence lifetime (FL) of the obtained NM-CQDs were as high as 32.4% and 6.56 ns. Further investigations indicated that the emission behaviors of NM-CQDs were still stable and independent in various conditions such as various excitation wavelengths, salt ionic concentrations, pH values, irradiation times, and temperatures. The obtained NM-CQDs are very suitable for cellular staining images due to strong and stable PL emission and show good internalization in different cells. Therefore, we propose a new and cost-effective preparation strategy for highly fluorescent NM-CQDs with great potential in biomedical imaging and engineering.

Targeting EGFR of triple-negative breast cancer enhances the therapeutic efficacy of paclitaxel- and cetuximab-conjugated nanodiamond nanocomposite

Breast cancer is the most common malignancy and a leading cause of cancer-related mortality among women worldwide. Triple-negative breast cancer (TNBC) is characterized by the lack of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor-2 (HER2). However, epidermal growth factor receptor (EGFR) is highly expressed in most of the TNBCs, which may provide a potential target for EGFR targeting therapy. Nanodiamond (ND) is a carbon-based nanomaterial with several advantages, including fluorescence emission, biocompatibility, and drug delivery applications. In this study, we designed a nanocomposite by using ND conjugated with paclitaxel (PTX) and cetuximab (Cet) for targeting therapy on the EGFR-positive TNBC cells. ND-PTX inhibited cell viability and induced mitotic catastrophe in various human breast cancer cell lines (MDA-MB-231, MCF-7, and BT474); in contrast, ND alone did not induce cell death. ND-PTX inhibited the xenografted human breast tumors in nude mice. We further investigated ND-PTX-Cet drug efficacy on the TNBC of MDA-MB-231 breast cancer cells. ND-PTX-Cet could specifically bind to EGFR and enhanced the anticancer effects including drug uptake levels, mitotic catastrophe, and apoptosis in the EGFR-expressed MDA-MB-231 cells but not in the EGFR-negative MCF-7 cells. In addition, ND-PTX-Cet increased the protein levels of active caspase-3 and phospho-histone H3 (Ser10). Furthermore, ND-PTX-Cet showed more effective on the reduction of TNBC tumor volume by comparison with ND-PTX. Taken together, these results demonstrated that ND-PTX-Cet nanocomposite enhanced mitotic catastrophe and apoptosis by targeting EGFR of TNBC cells, which can provide a feasible strategy for TNBC therapy. STATEMENT OF SIGNIFICANCE: Current TNBC treatment is ineffective against the survival rate of TNBC patients. Therefore, the development of new treatment strategies for TNBC patients is urgently needed. Here, we have designed a nanocomposite by targeting on the EGFR of TNBC to enhance therapeutic efficacy by ND-conjugated PTX and Cet (ND-PTX-Cet). Interestingly, we found that the co-delivery of Cet and PTX by ND enhanced the apoptosis, mitotic catastrophe and tumor inhibition in the EGFR-expressed TNBC in vitro and in vivo. Consequently, this nanocomposite ND-PTX-Cet can be applied for targeting EGFR of human TNBC therapy.

Carbon quantum dots and their biomedical and therapeutic applications: a review

In recent years, nano carbon quantum dots (CQDs) have received increasing attention due to their properties such as small size, fluorescence emission, chemical stability, water solubility, easy synthesis, and the possibility of functionalization. CQDs are fluorescent 0D carbon nanostructures with sizes below 10 nm. The fluorescence in CQDs originates from two sources, the fluorescence emission from bandgap transitions of conjugated π-domains and fluorescence from surface defects. The CQDs can emit fluorescence in the near-infrared (NIR) spectral region which makes them appropriate for biomedical applications. The fluorescence in these structures can be tuned with respect to the excitation wavelength. The CQDs have found applications in different areas such as biomedicine, photocatalysis, photosensors, solar energy conversion, light emitting diodes (LEDs), etc. The biomedical applications of CQDs include bioimaging, drug delivery, gene delivery, and cancer therapy. The fluorescent CQDs have low toxicity and other exceptional physicochemical properties in comparison to heavy metals semiconductor quantum dots (QDs) which make them superior candidates for biomedical applications. In this review, the synthesis routes and optical properties of the CQDs are clarified and recent advances in CQDs biomedical applications in bioimaging (in vivo and in vitro), drug delivery, cancer therapy, their potential to pass blood-brain barrier (BBB), and gene delivery are discussed.

Targeting Fluorescent Nanodiamonds to Vascular Endothelial Growth Factor Receptors in Tumor

The increased expression of vascular endothelial growth factor (VEGF) and its receptors is associated with angiogenesis in a growing tumor, presenting potential targets for tumor-selective imaging by way of targeted tracers. Though fluorescent tracers are used for targeted in vivo imaging, the lack of photostability and biocompatibility of many current fluorophores hinder their use in several applications involving long-term, continuous imaging. To address these problems, fluorescent nanodiamonds (FNDs), which exhibit infinite photostability and excellent biocompatibility, were explored as fluorophores in tracers for targeting VEGF receptors in growing tumors. To explore FND utility for imaging tumor VEGF receptors, we used click-chemistry to conjugate multiple copies of an engineered single-chain version of VEGF site-specifically derivatized with trans-cyclooctene (scVEGF-TCO) to 140 nm FND. The resulting targeting conjugates, FND-scVEGF, were then tested for functional activity of the scVEGF moieties through biochemical and tissue culture experiments and for selective tumor uptake in Balb/c mice with induced 4T1 carcinoma. We found that FND-scVEGF conjugates retain high affinity to VEGF receptors in cell culture experiments and observed preferential accumulation of FND-scVEGF in tumors relative to untargeted FND. Microspectroscopy provided unambiguous determination of FND within tissue by way of the unique spectral shape of nitrogen-vacancy induced fluorescence. These results validate and invite the use of targeted FND for diagnostic imaging and encourage further optimization of FND for fluorescence brightness.

A review on nanostructured carbon quantum dots and their applications in biotechnology, sensors, and chemiluminescence

Carbon quantum dots (CQDs) are a member of carbon nanostructures family which have received increasing attention for their photoluminescence (PL), physical and chemical stability and low toxicity. The classical semiconductor quantum dots (QDs) are semiconductor particles that are able to emit fluorescence by excitation. The CQDs is mainly referred to photoluminescent carbon nanoparticles less than 10 nm, with surface modification or functionalization. Contrary to other carbon nanostructures, CQDs can be synthesized and functionalized fast and easily. The fluorescence origin of the CQDs is a controversial issue which depends on carbon source, experimental conditions, and functional groups. However, PL emissions originated from conjugated π-domains and surface defects have been proposed for the PL emission mechanisms of the CQDs. These nanostructures have been used as nontoxic alternatives to the classical heavy metals containing semiconductor QDs in some applications such as in-vivo and in-vitro bio-imaging, drug delivery, photosensors, chemiluminescence (CL), and etc. This paper will introduce CQDs, their structure, and PL characteristics. Recent advances of the application of CQDs in biotechnology, sensors, and CL is comprehensively discussed.

Molecular imaging with nanoparticles: the dwarf actors revisited 10 years later

We explore present-day trends and challenges in nanomedicine. Creativity in the laboratories continues: the published literature on novel nanoparticles is now vast. Nanoagents are discussed here which are composed entirely of strongly photoluminescent materials, tunable to desired optical properties and of inherently low toxicity. We focus on "quantum nanoparticles" prepared from allotropes of carbon. The principles behind strong, tunable photoluminescence are quantum mechanical: we present them in simple outline. The major industries racing to develop these materials can offer significant technical guidance to nanomedicine, which could help to custom-design strongly signalling nanoagents specifically for stated clinical applications. Since such agents are small, they can be targeted easily, making active targeting possible. We consider it timely now to study the interactions nanoparticles undergo with tissue components in living animals and to learn to understand and overcome the numerous barriers the organism interposes between the blood and targets in or on parenchymal cells. As the near infra-red spectrum opens up, detection of glowing nanoparticles several centimeters deep in a living human subject becomes calculable and we present a simple way to do this. Finally, we discuss the slow-fuse and resource-inefficient entry of nanoparticles into clinical application. A first possible reason is failure to target across the body's barriers, see above. Second, in the sparse translational landscape funding and support gaps yawn widely between academic research and subsequent development. We consider the agendas of the numerous "stakeholders" participating in this sad landscape and point to some faint glimmers of hope for the future.