Nanodiamond as a vector for siRNA delivery to Ewing sarcoma cells

Breaking barriers: Innovative approaches for skin delivery of RNA therapeutics

RNA therapeutics represent a rapidly expanding platform with game-changing prospects in personalized medicine. The disruptive potential of this technology will overhaul the standard of care with reference to both primary and specialty care. To date, RNA therapeutics have mostly been delivered parenterally via injection, but topical administration followed by intradermal or transdermal delivery represents an attractive method that is convenient to patients and minimally invasive. The skin barrier, particularly the lipid-rich stratum corneum, presents a significant hurdle to the uptake of large, charged oligonucleotide drugs. Therapeutic oligonucleotides need to be engineered for stability and specificity and formulated with state-of-the-art delivery strategies for efficient uptake. This review will cover various passive and active strategies deployed to enhance permeation through the stratum corneum and achieve effective delivery of RNA therapeutics to treat both local skin disorders and systemic diseases. Some strategies to achieve selectivity between local and systemic administration will also be discussed.

Ground and excited state charge transfer at aqueous nanodiamonds

Nanodiamonds (NDs) are unique carbonaceous materials with exceptionally high stability, hardness, and notable electronic properties. Their applications in photocatalysis, biomedicine, and energy materials are usually carried out in aqueous environments, where they interact with aqueous adsorbates. Especially, electron density may rearrange from the diamond material toward oxidative adsorbates such as oxygen, which is known as charge transfer doping. In this article, we quantify the charge transfer doping for NDs with inhomogeneous surface coverings (hydroxyl, fluorine, and amorphous carbon), as well as NDs doped with heteroatoms (B, Si, N) using hybrid density functional theory (DFT) calculations. The transfer doping magnitude is largely determined by the NDs' highest occupied molecular orbital energies, which can in turn be modified by the surface covering and doping. However, local modifications of the ND structures do not have any local effects on the magnitude of the charge transfer. We furthermore analyze the impact of aqueous adsorbates on the excited states of an aqueous ND in the context of photocatalysis via time-dependent DFT. Here, we find that the excited electrons are biased to move in the direction of the respective oxidative adsorbate. Surprisingly, we find that also unreactive species such as nitrous oxide may attract the excited electrons, which is probably due to the positive partial charge that is induced by the local N2 O solvation geometry.

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.

Cellular uptake and fate of cationic polymer-coated nanodiamonds delivering siRNA: a mechanistic study

Gene silencing using small interfering RNAs (siRNAs) is a selective and promising approach for treatment of numerous diseases. However, broad applications of siRNAs are compromised by their low stability in a biological environment and limited ability to penetrate cells. Nanodiamonds (NDs) coated with cationic polymers can enable cellular delivery of siRNAs. Recently, we developed a new type of ND coating based on a random copolymer consisting of (2-dimethylaminoethyl) methacrylate (DMAEMA) and N-(2-hydroxypropyl) methacrylamide (HPMA) monomers. These hybrid ND-polymer particles (Cop+-FND) provide near-infrared fluorescence, form stable complexes with siRNA in serum, show low toxicity, and effectively deliver siRNA into cells in vitro and in vivo. Here, we present data on the mechanism of cellular uptake and cell trafficking of Cop+-FND : siRNA complexes and their ability to selectively suppress mRNA levels, as well as their cytotoxicity, viability and colloidal stability. We identified clathrin-mediated endocytosis as the predominant entry mechanism for Cop+-FND : siRNA into U-2 OS human bone osteosarcoma cells, with a substantial fraction of Cop+-FND : siRNA following the lysosome pathway. Cop+-FND : siRNA potently inhibited the target GAPDH gene with negligible toxicity and sufficient colloidal stability. Based on our results, we suggest that Cop+-FND : siRNA can serve as a suitable in vivo delivery system for siRNA.

The emerging potential of siRNA nanotherapeutics in treatment of arthritis

RNA interference (RNAi) using small interfering RNA (siRNA) has shown potential as a therapeutic option for the treatment of arthritis by silencing specific genes. However, siRNA delivery faces several challenges, including stability, targeting, off-target effects, endosomal escape, immune response activation, intravascular degradation, and renal clearance. A variety of nanotherapeutics like lipidic nanoparticles, liposomes, polymeric nanoparticles, and solid lipid nanoparticles have been developed to improve siRNA cellular uptake, protect it from degradation, and enhance its therapeutic efficacy. Researchers are also investigating chemical modifications and bioconjugation to reduce its immunogenicity. This review discusses the potential of siRNA nanotherapeutics as a therapeutic option for various immune-mediated diseases, including rheumatoid arthritis, osteoarthritis, etc. siRNA nanotherapeutics have shown an upsurge of interest and the future looks promising for such interdisciplinary approach-based modalities that combine the principles of molecular biology, nanotechnology, and formulation sciences.

Biomedical applications of nanodiamonds: From drug-delivery to diagnostics

Advances in nanotechnology have great potential to address many unmet clinical and biomedical needs. Nanodiamonds, as a class of carbon nanoparticles with unique properties, may be useful towards a versatile range of biomedical applications from drug delivery to diagnostics. This review describes how these properties of nanodiamonds facilitate their application in different fields of biomedicine, including delivery of chemotherapy drugs, peptides, proteins, nucleic acids and biosensors. Additionally, clinical potential of nanodiamonds, with studies in both preclinical and clinical stages, is also reviewed here, highlighting the translational potential of nanodiamonds in biomedical research.

NanoBeacon.AI: AI-Enhanced Nanodiamond Biosensor for Automated Sensitivity Prediction to Oxidative Phosphorylation Inhibitors

Spalt-like transcription factor 4 (SALL4) is an oncofetal protein that has been identified to drive cancer progression in hepatocellular carcinoma (HCC) and hematological malignancies. Furthermore, a high SALL4 expression level is correlated to poor prognosis in these cancers. However, SALL4 lacks well-structured small-molecule binding pockets, making it difficult to design targeted inhibitors. SALL4-induced expression of oxidative phosphorylation (OXPHOS) genes may serve as a therapeutically targetable vulnerability in HCC through OXPHOS inhibition. Because OXPHOS functions through a set of genes with intertumoral heterogeneous expression, identifying therapeutic sensitivity to OXPHOS inhibitors may not rely on a single clear biomarker. Here, we developed a workflow that utilized molecular beacons, nucleic-acid-based, activatable sensors with high specificity to the target mRNA, delivered by nanodiamonds, to establish an artificial intelligence (AI)-assisted platform for rapid evaluation of patient-specific drug sensitivity. Specifically, when the HCC cells were treated with the nanodiamond-medicated OXPHOS biosensor, high sensitivity and specificity of the sensor allowed for improved identification of OXPHOS expression in cells. Assisted by a trained convolutional neural network, drug sensitivity of cells toward an OXPHOS inhibitor, IACS-010759, could be accurately predicted. AI-assisted OXPHOS drug sensitivity assessment could be accomplished within 1 day, enabling rapid and efficient clinical decision support for HCC treatment. The work proposed here serves as a foundation for the patient-based subtype-specific therapeutic research platform and is well suited for precision medicine.

Long-term biophysical stability of nanodiamonds combined with lipid nanocarriers for non-viral gene delivery to the retina

Nanodiamonds were combined with niosome, and resulting formulations were named as nanodiasomes, which were evaluated in terms of physicochemical features, cellular internalization, cell viability and transfection efficiency both in in vitro and in in vivo conditions. Such parameters were analyzed at 4 and 25 ^°C, and at 15 and 30 days after their elaboration. Nanodiasomes showed a particle size of 128 nm that was maintained over time inside the ±10% of deviation, unless after 30 days of storage at 25°C. Something similar occurred with the initial zeta potential value, 35.2 mV, being both formulations more stable at 4°C. The incorporation of nanodiamonds into niosomes resulted in a 4-fold increase of transfection efficiency that was maintained over time at 4 and 25°C. In vivo studies reported high transgene expression of nanodiasomes after subretinal and intravitreal administration in mice, when injected freshly prepared and after 30 days of storage at 4°C.

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.

3D self-assembled nanocarriers for drug delivery

There are many benefits to drug delivery from drug-carrier nanostructure systems. It might be developed to carefully control drug release rates or to deliver a precise amount of a therapeutic substance to particular body areas. Self-assembling is the process by which molecules and nanoparticles spontaneously organize into organized clusters. For instance, proteins and peptides can interact with one another to create highly organized supramolecular structures with various properties, such as helical ribbons and fibrous scaffolds. Another advantage of self-assembly is that it may be effective with a variety of materials, including metals, oxides, inorganic salts, polymers, semiconductors, and even organic semiconductors. Fullerene, graphene, and carbon nanotubes (CNTs), three of the most fundamental classes of three-dimensionally self-assembling nanostructured carbon-based materials, are essential for the development of modern nanotechnologies. Self-assembled nanomaterials are used in a variety of fields, including nanotechnology, imaging, and biosensors. This review study begins with a summary of various major 3D nanomaterials, including graphene oxide, CNTs, and nanodiamond, as well as 3D self-assembled polyfunctionalized nanostructures and adaptable nanocarriers for drug delivery.

Nanodiamonds Doped with Manganese for Applications in Magnetic Resonance Imaging

Nanodiamonds (NDs) are emerging with great potential in biomedical applications like biomarking through fluorescence and magnetic resonance imaging (MRI), targeted drug delivery, and cancer therapy. The magnetic and optical properties of NDs could be tuned by selective doping. Therefore, we report multifunctional manganese-incorporated NDs (Mn-NDs) fabricated by Mn ion implantation. The fluorescent properties of Mn-NDs were tuned by inducing the defects by ion implantation and enhancing the residual nitrogen vacancy density achieved by a two-step annealing process. The cytotoxicity of Mn-NDs was investigated using NCTC clone 929 cells, and the results revealed no cytotoxicity effect. Mn-NDs have demonstrated dual mode contrast enhancement for both T ₁- and T ₂-weighted in vitro MR imaging. Furthermore, Mn-NDs have illustrated a significant increase in longitudinal relaxivity (fivefold) and transversal relaxivity (17-fold) compared to the as-received NDs. Mn-NDs are employed to investigate their ability for in vivo MR imaging by intraperitoneal (ip) injection of Mn-NDs into mice with liver tumors. After 2.5 h of ip injection, the enhancement of contrast in T ₁- and T ₂-weighted images has been observed via the accumulation of Mn-NDs in liver tumors of mice. Therefore, Mn-NDs have great potential for in vivo imaging by MR imaging in cancer therapy.

Nanomaterial-assisted theranosis of bone diseases

Bone-related diseases refer to a group of skeletal disorders that are characterized by bone and cartilage destruction. Conventional approaches can regulate bone homeostasis to a certain extent. However, these therapies are still associated with some undesirable problems. Fortunately, recent advances in nanomaterials have provided unprecedented opportunities for diagnosis and therapy of bone-related diseases. This review provides a comprehensive and up-to-date overview of current advanced theranostic nanomaterials in bone-related diseases. First, the potential utility of nanomaterials for biological imaging and biomarker detection is illustrated. Second, nanomaterials serve as therapeutic delivery platforms with special functions for bone homeostasis regulation and cellular modulation are highlighted. Finally, perspectives in this field are offered, including current key bottlenecks and future directions, which may be helpful for exploiting nanomaterials with novel properties and unique functions. This review will provide scientific guidance to enhance the development of advanced nanomaterials for the diagnosis and therapy of bone-related diseases.

Nanoparticles in Drug Delivery: From History to Therapeutic Applications

Current research into the role of engineered nanoparticles in drug delivery systems (DDSs) for medical purposes has developed numerous fascinating nanocarriers. This paper reviews the various conventionally used and current used carriage system to deliver drugs. Due to numerous drawbacks of conventional DDSs, nanocarriers have gained immense interest. Nanocarriers like polymeric nanoparticles, mesoporous nanoparticles, nanomaterials, carbon nanotubes, dendrimers, liposomes, metallic nanoparticles, nanomedicine, and engineered nanomaterials are used as carriage systems for targeted delivery at specific sites of affected areas in the body. Nanomedicine has rapidly grown to treat certain diseases like brain cancer, lung cancer, breast cancer, cardiovascular diseases, and many others. These nanomedicines can improve drug bioavailability and drug absorption time, reduce release time, eliminate drug aggregation, and enhance drug solubility in the blood. Nanomedicine has introduced a new era for drug carriage by refining the therapeutic directories of the energetic pharmaceutical elements engineered within nanoparticles. In this context, the vital information on engineered nanoparticles was reviewed and conferred towards the role in drug carriage systems to treat many ailments. All these nanocarriers were tested in vitro and in vivo. In the coming years, nanomedicines can improve human health more effectively by adding more advanced techniques into the drug delivery system.

Ewing Sarcoma Meets Epigenetics, Immunology and Nanomedicine: Moving Forward into Novel Therapeutic Strategies

Simple Summary

Ewing Sarcoma treatment is traditionally based on chemotherapy, surgery, and radiotherapy. Although these standard of care regimens are efficient at early disease stages, many patients fail to respond appropriately, which has prompted the search for more efficacious and specific treatments. A deeper understanding of the basic molecular mechanisms underlying the biology of both tumor cells and the tumor microenvironment, as well as advances in drug delivery, has led to the development of different approaches to improve the treatment in Ewing Sarcoma patients. Thus, epigenetic, and immunotherapy-based drugs, along with nanotechnology delivery strategies, represent novel preclinical and clinical studies in the treatment of Ewing Sarcoma. In this review, we provide a comprehensive overview of these emerging therapeutic strategies and summarize the potential of the latest preclinical and clinical trials in Ewing Sarcoma research. Finally, we underline the value and future directions of these new treatments.

Abstract

Ewing Sarcoma (EWS) is an aggressive bone and soft tissue tumor that mainly affects children, adolescents, and young adults. The standard therapy, including chemotherapy, surgery, and radiotherapy, has substantially improved the survival of EWS patients with localized disease. Unfortunately, this multimodal treatment remains elusive in clinics for those patients with recurrent or metastatic disease who have an unfavorable prognosis. Consistently, there is an urgent need to find new strategies for patients that fail to respond to standard therapies. In this regard, in the last decade, treatments targeting epigenetic dependencies in tumor cells and the immune system have emerged into the clinical scenario. Additionally, recent advances in nanomedicine provide novel delivery drug systems, which may address challenges such as side effects and toxicity. Therefore, therapeutic strategies stemming from epigenetics, immunology, and nanomedicine yield promising alternatives for treating these patients. In this review, we highlight the most relevant EWS preclinical and clinical studies in epigenetics, immunotherapy, and nanotherapy conducted in the last five years.

Functionalized Fluorescent Nanodiamonds for Simultaneous Drug Delivery and Quantum Sensing in HeLa Cells

Here, we present multifunctional fluorescent nanodiamonds (FNDs) for simultaneous drug delivery and free radical detection. For this purpose, we modified FNDs containing nitrogen vacancy (NV) centers with a diazoxide derivative. We found that our particles enter cells more easily and are able to deliver this cancer drug into HeLa cells. The particles were characterized by infrared spectroscopy, dynamic light scattering, and secondary electron microscopy. Compared to the free drug, we observe a sustained release over 72 h rather than 12 h for the free drug. Apart from releasing the drug, with these particles, we can measure the drug's effect on free radical generation directly. This has the advantage that the response is measured locally, where the drug is released. These FNDs change their optical properties based on their magnetic surrounding. More specifically, we make use of a technique called relaxometry to detect spin noise from the free radical at the nanoscale with subcellular resolution. We further compared the results from our new technique with a conventional fluorescence assay for the detection of reactive oxygen species. This provides a new method to investigate the relationship between drug release and the response by the cell via radical formation or inhibition.

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.

Nanomaterials in Bone Regeneration

Nanomaterials are promising in the development of innovative therapeutic options that include tissue and organ replacement, as well as bone repair and regeneration. The expansion of new nanoscaled biomaterials is based on progress in the field of nanotechnologies, material sciences, and biomedicine. In recent decades, nanomaterial systems have bridged the line between the synthetic and natural worlds, leading to the emergence of a new science called nanomaterial design for biological applications. Nanomaterials replicating bone properties and providing unique functions help in bone tissue engineering. This review article is focused on nanomaterials utilized in or being explored for the purpose of bone repair and regeneration. After a brief overview of bone biology, including a description of bone cells, matrix, and development, nanostructured materials and different types of nanoparticles are discussed in detail.

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.

Carbon-based Nanomaterials for delivery of small RNA molecules: a focus on potential cancer treatment applications

BACKGROUND

Nucleic acid-mediated therapy holds immense potential in the treatment of recalcitrant human diseases such as cancer. This is underscored by advances in understanding the mechanisms of gene regulation. In particular, the endogenous protective mechanism of gene silencing known as RNA interference (RNAi) has been extensively exploited.

METHODS

We review here the developments from 2011 to 2021, in the use of nanographene oxide, carbon nanotubes, fullerenes, carbon nanohorns, carbon nanodots and nanodiamonds for the delivery of therapeutic small RNA molecules.

RESULTS

Appropriately designed effector molecules such as small interfering RNA (siRNA), can, in theory, silence the expression of any disease-causing gene. Alternatively, siRNA can be generated in vivo through the introduction of plasmid-based short hairpin RNA (shRNA) expression vectors. Other small RNAs such as micro RNA (miRNA) also function in post-transcriptional gene regulation and are aberrantly expressed under disease conditions. The miRNA-based therapy involves either restoration of miRNA function through the introduction of miRNA mimics; or the inhibition of miRNA function by delivering anti-miRNA oligomers. However, the large size, hydrophilicity, negative charge and nuclease-sensitivity of nucleic acids necessitate an appropriate carrier for their introduction as medicine into cells.

CONCLUSION

While numerous organic and inorganic materials have been investigated for this purpose, the perfect carrier agent remains elusive. In recent years, carbon-based nanomaterials have received widespread attention in biotechnology due to their tunable surface characteristics, mechanical, electrical, optical and chemical properties.

Effects of oxidative adsorbates and cluster formation on the electronic structure of nanodiamonds

Nanodiamonds (NDs) are modern high-potential materials relevant for applications in biomedicine, photocatalysis, and various other fields. Their electronic surface properties, especially in the liquid phase, are key to their function in the applications, but we show that they are sensitively modified by their interactions with the environment. Two important interaction modes are those with oxidative aqueous adsorbates as well as ND self-aggregation towards the formation of ND clusters. For planar diamond surfaces it is known that the electron density migrates from the diamond towards oxidative adsorbates, which is known as transfer doping. Here, we quantify this effect for highly curved NDs of varying sizes (35-147 C atoms) and surface terminations (H, OH, F), focusing on their interactions with the most abundant aqueous oxidative adsorbates (H₃ O⁺ , O₂ , O₃ ). We prove that the concept of transfer doping stays valid for the case of the high-curvature NDs and can be tuned via the ND's specific properties. Secondly, we investigate the electronic structures of clusters of NDs which are known to form in particular in aqueous dispersions. Upon cluster formation, we find that the optical gaps of the structures are significantly reduced, which explains why different experimental values were obtained for the optical gap of the same structures, and the cluster's LUMO shapes resemble atom-type orbitals, as in the case of isolated spherical NDs. Our findings have implications for ND applications as photocatalysts or electronic devices, where the specific electronic properties are key to the functionality of the ND material.

Nanodiamond Integration into Niosomes as an Emerging and Efficient Gene Therapy Nanoplatform for Central Nervous System Diseases

Nanodiamonds (NDs) are promising materials for gene delivery because of their unique physicochemical and biological features, along with their possibility of combination with other nonviral systems. Our aim was to evaluate the biophysical performance of NDs as helper components of niosomes, named nanodiasomes, to address a potential nonviral gene delivery nanoplatform for therapeutic applications in central nervous system (CNS) diseases. Nanodiasomes, niosomes, and their corresponding complexes, obtained after genetic material addition at different ratios (w/w), were evaluated in terms of physicochemical properties, cellular uptake, intracellular disposition, biocompatibility, and transfection efficiency in HEK-293 cells. Nanodiasomes, niosomes, and complexes fulfilled the physicochemical features for gene therapy applications. Biologically, the incorporation of NDs into niosomes enhanced 75% transfection efficiency (p < 0.001) and biocompatibility (p < 0.05) to values over 90%, accompanied by a higher cellular uptake (p < 0.05). Intracellular trafficking analysis showed higher endocytosis via clathrins (p < 0.05) in nanodiaplexes compared with nioplexes, followed by higher lysosomal colocalization (p < 0.05), that coexisted with endosomal escape properties, whereas endocytosis mediated by caveolae was the most efficient pathway in the case of nanodiaplexes. Moreover, studies in CNS primary cells revealed that nanodiaplexes successfully transfected neuronal and retinal cells. This proof-of-concept study points out that ND integration into niosomes represents an encouraging nonviral nanoplatform strategy for the treatment of CNS diseases by gene therapy.

Advanced metal and carbon nanostructures for medical, drug delivery and bio-imaging applications

Nanoparticles (NPs) offer great promise for biomedical, environmental, and clinical applications due to their several unique properties as compared to their bulk counterparts. In this review article, we overview various types of metal NPs and magnetic nanoparticles (MNPs) in monolithic form as well as embedded into polymer matrices for specific drug delivery and bio-imaging fields. The second part of this review covers important carbon nanostructures that have gained tremendous attention recently in such medical applications due to their ease of fabrication, excellent biocompatibility, and biodegradability at both cellular and molecular levels for phototherapy, radio-therapeutics, gene-delivery, and biotherapeutics. Furthermore, various applications and challenges involved in the use of NPs as biomaterials are also discussed following the future perspectives of the use of NPs in biomedicine. This review aims to contribute to the applications of different NPs in medicine and healthcare that may open up new avenues to encourage wider research opportunities across various disciplines.

siRNA nanohybrid systems: false hope or feasible answer in cancer management

Finding out predisposition and makeup alterations in cancer cells has prompted the exploration of exogenous small interference RNA (siRNA) as a therapeutic agent to deal with cancer. siRNA is subjected to many limitations that hinders its cellular uptake. Various nanocarriers have been loaded with siRNA to improve their cellular transportation and have moved to clinical trials. However, many restrictions as low encapsulation efficiency, nanocarrier cytotoxicity and premature release of siRNA have impeded the single nanocarrier use. The realm of nanohybrid systems has emerged to overcome these limitations and to synergize the criteria of two or more nanocarriers. Different nanohybrid systems that were developed as cellular pathfinders for the exogenous siRNA to target cancer will be illustrated in this review.

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.

Selective cytotoxicity mechanisms and biodistribution of diamond nanoparticles on the skin cancer in C57 mouse

The cytotoxicity of diamond nanoparticles (DNs) to various cell lines has been on focus by numerous scientists. The cellular toxicity system of DNs has not been fully understood or explained in skin cancer, at this point. This research was carried out to discover and reveal the potential impacts of DNs on the secluded brain, heart, liver, kidney, and skin in addition to evaluation of their cytotoxicity mechanism under test conditions. Their biological activities, for example cell viability, the level of reactive oxygen species (ROS), lipid peroxidation, cytochrome c release and Apoptosis/Necrosis were evaluated. Additionally, the bio-distribution of these nanomaterials in tissues was examined in the C57 mouse. Relying on the findings of the investigation, DNs were found to increase the ROS level, Malondialdehyde (MDA) content, release of cytochrome c, and cell death in skin significantly compared to other groups. In the C57 mouse, DNs were observed to have accumulated in skin tissue more intensively than they did in other organs. The present study presents for the proof that DNs can completely induce cell death signaling in skin cancer without bringing about a high cytotoxicity in other tissues. Results suggest that DNs can be valuable in recognition of skin cancer.

Enhanced penetrative siRNA delivery by a nanodiamond drug delivery platform against hepatocellular carcinoma 3D models

Small interfering RNA (siRNA) can cause specific gene silencing and is considered promising for treating a variety of cancers, including hepatocellular carcinoma (HCC). However, siRNA has many undesirable physicochemical properties that limit its application. Additionally, conventional methods for delivering siRNA are limited in their ability to penetrate solid tumors. In this study, nanodiamonds (NDs) were evaluated as a nanoparticle drug delivery platform for improved siRNA delivery into tumor cells. Our results demonstrated that ND-siRNA complexes could effectively be formed through electrostatic interactions. The ND-siRNA complexes allowed for efficient cellular uptake and endosomal escape that protects siRNA from degradation. Moreover, ND delivery of siRNA was more effective at penetrating tumor spheroids compared to liposomal formulations. This enhanced penetration capacity makes NDs ideal vehicles to deliver siRNA against solid tumor masses as efficient gene knockdown and decreased tumor cell proliferation were observed in tumor spheroids. Evaluation of ND-siRNA complexes within the context of a 3D cancer disease model demonstrates the potential of NDs as a promising gene delivery platform against solid tumors, such as HCC.

Harnessing subcellular-resolved organ distribution of cationic copolymer-functionalized fluorescent nanodiamonds for optimal delivery of active siRNA to a xenografted tumor in mice

Diamond nanoparticles (nanodiamonds) can transport active drugs in cultured cells as well as in vivo. However, in the latter case, methods allowing the determination of their bioavailability accurately are still lacking. A nanodiamond can be made fluorescent with a perfectly stable emission and a lifetime ten times longer than that of tissue autofluorescence. Taking advantage of these properties, we present an automated quantification method of fluorescent nanodiamonds (FND) in histological sections of mouse organs and tumors, after systemic injection. We use a home-made time-delayed fluorescence microscope comprising a custom pulsed laser source synchronized on the master clock of a gated intensified array detector. This setup allows ultra-high-resolution images (120 Mpixels in size) of whole mouse organ sections to be obtained, with subcellular resolution and single-particle sensitivity. As a proof-of-principle experiment, we quantified the biodistribution and aggregation state of new cationic FNDs capable of transporting small interfering RNA inhibiting the oncogene responsible for Ewing sarcoma. Image analysis showed a low yield of nanodiamonds in the tumor after intravenous injection. Thus, for the in vivo efficacy assay, we injected the nanomedicine into the tumor. We achieved a 28-fold inhibition of the oncogene. This method can readily be applied to other nanoemitters with ≈100 ns lifetime.

Study on Structure, Thermal Behavior and Viscoelastic Properties of Nanodiamond-Reinforced Poly (vinyl alcohol) Nanocomposites

In this work, advanced polymer nanocomposites comprising of polyvinyl alcohol (PVA) and nanodiamonds (NDs) were developed using a single-step solution-casting method. The properties of the prepared PVA/NDs nanocomposites were investigated using Raman spectroscopy, small- and wide-angle X-ray scattering (SAXS/WAXS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). It was revealed that the tensile strength improved dramatically with increasing ND content in the PVA matrix, suggesting a strong interaction between the NDs and the PVA. SEM, TEM, and SAXS showed that NDs were present in the form of agglomerates with an average size of ~60 nm with primary particles of diameter ~5 nm. These results showed that NDs could act as a good nanofiller for PVA in terms of improving its stability and mechanical properties.

Recent Developments in Nanomedicine for Pediatric Cancer

Cancer is the second biggest cause of death in children in the US. With the development of chemotherapy, there has been a substantial increase in the overall survival rate in the last 30 years. However, the overall mortality rate in children with cancer remains 25%, and many survivors experience a decline in overall quality of life and long-term adverse effects caused by treatments. Although cancer cells share common characteristics, pediatric cancers are different from adult cancers in their prevalence, mutation load, and drug response. Therefore, there is an urgent unmet need to develop therapeutic approaches specifically designed for children with cancer. Nanotechnology can potentially overcome the deficiencies of conventional methods of administering chemotherapy and ultimately improve clinical outcomes. The nanoparticle-based drug delivery systems can decrease the toxicity of therapy, provide a sustained or controlled drug release, improve the pharmacokinetic properties of loading contents, and achieve a targeted drug delivery with achievable modifications. Furthermore, therapeutic approaches based on combining nanoformulated drugs with novel immunotherapeutic agents are emerging. In this review, we discussed the recently developed nanotechnology-based strategies for treating blood and solid pediatric cancers.

Cell-Penetrating Peptides Delivering siRNAs: An Overview

Cell-Penetrating Peptides (CPP) are valuable tools capable of crossing the plasma membrane to deliver therapeutic cargo inside cells. Small interfering RNAs (siRNA) are double-stranded RNA molecules capable of silencing the expression of a specific protein triggering the RNA interference (RNAi) pathway, but they are unable to cross the plasma membrane and have a short half-life in the bloodstream. In this overview, we assessed the many different approaches used and developed in the last two decades to deliver siRNA through the plasma membrane through different CPPs sorted according to three different loading strategies: covalent conjugation, complex formation, and CPP-decorated (functionalized) nanocomplexes. Each of these strategies has pros and cons, but it appears the latter two are the most commonly reported and emerging as the most promising strategies due to their simplicity of synthesis, use, and versatility. Recent progress with siRNA delivered by CPPs seems to focus on targeted delivery to reduce side effects and amount of drugs used, and it appears to be among the most promising use for CPPs in future clinical applications.

Fluorescent and Electron-Dense Green Color Emitting Nanodiamonds for Single-Cell Correlative Microscopy

Correlative light and electron microscopy (CLEM) is revolutionizing how cell samples are studied. CLEM provides a combination of the molecular and ultrastructural information about a cell. For the execution of CLEM experiments, multimodal fiducial landmarks are applied to precisely overlay light and electron microscopy images. Currently applied fiducials such as quantum dots and organic dye-labeled nanoparticles can be irreversibly quenched by electron beam exposure during electron microscopy. Generally, the sample is therefore investigated with a light microscope first and later with an electron microscope. A versatile fiducial landmark should offer to switch back from electron microscopy to light microscopy while preserving its fluorescent properties. Here, we evaluated green fluorescent and electron dense nanodiamonds for the execution of CLEM experiments and precisely correlated light microscopy and electron microscopy images. We demonstrated that green color emitting fluorescent nanodiamonds withstand electron beam exposure, harsh chemical treatments, heavy metal straining, and, importantly, their fluorescent properties remained intact for light microscopy.

The protein corona determines the cytotoxicity of nanodiamonds: implications of corona formation and its remodelling on nanodiamond applications in biomedical imaging and drug delivery

The use of nanodiamonds for biomedical and consumer applications is growing rapidly. As their use becomes more widespread, so too do concerns around their cytotoxicity. The cytotoxicity of nanodiamonds correlates with their cellular internalisation and circulation time in the body. Both internalisation and circulation time are influenced by the formation of a protein corona on the nanodiamond surface. However, a precise understanding of both how the corona forms and evolves and its influence on cytotoxicity is lacking. Here, we investigated protein corona formation and evolution in response to two classes of nanodiamonds, pristine and aminated, and two types of proteins, bovine serum albumin and fibronectin. Specifically, we found that a corona made of bovine serum albumin (BSA), which represents the most abundant protein in blood plasma, reduced nanodiamond agglomeration. Fibronectin (FN9-10), the second most abundant protein found in the plasma, exhibited a significantly higher nanodiamond binding affinity than BSA, irrespective of the nanodiamond surface charge. Finally, nanodiamonds with a BSA corona displayed less cytotoxicity towards nonphagocytic liver cells. However, regardless of the type of corona (FN9-10 or BSA), both classes of nanodiamonds induced substantial phagocytic cell death. Our results emphasise that a precise understanding of the corona composition is fundamental to determining the fate of nanoparticles in the body.

In vitro characterization of osteoblast cells on polyelectrolyte multilayers containing detonation nanodiamonds

Nanoparticle-enhanced coatings of bone implants are a promising method to facilitate sustainable wound healing, leading to an increase in patient well-being. This article describes the in vitro characterization of osteoblast cells interacting with polyelectrolyte multilayers, which contain detonation nanodiamonds (NDs), as a novel class of carbon-based coating material, which presents a unique combination of photoluminescence and drug-binding properties. The cationic polyelectrolyte, namely polydiallyldimethylammonium chloride (PDDA), has been used to immobilize NDs on silica glass. The height of ND-PDDA multilayers varies from a minimum of 10 nm for one bilayer to a maximum of 90 nm for five bilayers of NDs and PDDA. Human fetal osteoblasts (hFOBs) cultured on ND-PDDA multilayers show a large number of focal adhesions, which were studied via quantitative fluorescence imaging analysis. The influence of the surface roughness on the filopodia formation was assessed via scanning electron microscopy and atomic force microscopy. The nano-rough surface of five bilayers constrained the filopodia formation. The hFOBs grown on NDs tend to show not only a similar cell morphology compared to cells cultured on extracellular matrix protein-coated silica glass substrates, but also increased cell viability by about 40%. The high biocompatibility of the ND-PDDA multilayers, indicated via high cell proliferation and sound cell adhesion, shows their potential for biomedical applications such as drug-eluting coatings and biomaterials in general.

Delivery of siRNA to Ewing Sarcoma Tumor Xenografted on Mice, Using Hydrogenated Detonation Nanodiamonds: Treatment Efficacy and Tissue Distribution

Nanodiamonds of detonation origin are promising delivery agents of anti-cancer therapeutic compounds in a whole organism like mouse, owing to their versatile surface chemistry and ultra-small 5 nm average primary size compatible with natural elimination routes. However, to date, little is known about tissue distribution, elimination pathways and efficacy of nanodiamonds-based therapy in mice. In this report, we studied the capacity of cationic hydrogenated detonation nanodiamonds to carry active small interfering RNA (siRNA) in a mice model of Ewing sarcoma, a bone cancer of young adults due in the vast majority to the EWS-FLI1 junction oncogene. Replacing hydrogen gas by its radioactive analog tritium gas led to the formation of labeled nanodiamonds and allowed us to investigate their distribution throughout mouse organs and their excretion in urine and feces. We also demonstrated that siRNA directed against EWS-FLI1 inhibited this oncogene expression in tumor xenografted on mice. This work is a significant step to establish cationic hydrogenated detonation nanodiamond as an effective agent for in vivo delivery of active siRNA.

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.

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.

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.

NDs@PDA@ICG Conjugates for Photothermal Therapy of Glioblastoma Multiforme

The growing incidence of cancer is a problem for modern medicine, since the therapeutic efficacy of applied modalities is still not satisfactory in terms of patients' survival rates, especially in the case of patients with brain tumors. The destructive influence of chemotherapy and radiotherapy on healthy cells reduces the chances of full recovery. With the development of nanotechnology, new ideas on cancer therapy, including brain tumors, have emerged. Photothermal therapy (PTT) is one of these. It utilizes nanoparticles (NPs) that can convert the light, preferably in the near-infrared (NIR) region, into heat. In this paper, we report the use of nanodiamonds (NDs) conjugated with biomimetic polydopamine (PDA) and indocyanine green (ICG) for glioblastoma cancer PTT therapy. The obtained materials were thoroughly analyzed in terms of their PTT effectiveness, as well as their physicochemical properties. The performed research demonstrated that NDs@PDA@ICG can be successfully applied in the photothermal therapy of glioblastoma for PTT and exhibited high photothermal conversion efficiency η above 40%, which is almost 10 times higher than in case of bare NDs. In regard to our results, our material was found to lead to a better therapeutic outcome and higher eradication of glioblastoma cells, as demonstrated in vitro.

Extremely rapid isotropic irradiation of nanoparticles with ions generated in situ by a nuclear reaction

Energetic ions represent an important tool for the creation of controlled structural defects in solid nanomaterials. However, the current preparative irradiation techniques in accelerators show significant limitations in scaling-up, because only very thin layers of nanoparticles can be efficiently and homogeneously irradiated. Here, we show an easily scalable method for rapid irradiation of nanomaterials by light ions formed homogeneously in situ by a nuclear reaction. The target nanoparticles are embedded in B2O3 and placed in a neutron flux. Neutrons captured by 10B generate an isotropic flux of energetic α particles and 7Li+ ions that uniformly irradiates the surrounding nanoparticles. We produced 70 g of fluorescent nanodiamonds in an approximately 30-minute irradiation session, as well as fluorescent silicon carbide nanoparticles. Our method thus increased current preparative yields by a factor of 102-103. We envision that our technique will increase the production of ion-irradiated nanoparticles, facilitating their use in various applications.

Nanoparticle-Mediated Combination Therapy: Two-in-One Approach for Cancer

Cancer represents a group of heterogeneous diseases characterized by uncontrolledgrowth and spread of abnormal cells, ultimately leading to death. Nanomedicine plays a significantrole in the development of nanodrugs, nanodevices, drug delivery systems and nanocarriers. Someof the major issues in the treatment of cancer are multidrug resistance (MDR), narrow therapeuticwindow and undesired side effects of available anticancer drugs and the limitations of anticancerdrugs. Several nanosystems being utilized for detection, diagnosis and treatment such as theranosticcarriers, liposomes, carbon nanotubes, quantum dots, polymeric micelles, dendrimers and metallicnanoparticles. However, nonbiodegradable nanoparticles causes high tissue accumulation andleads to toxicity. MDR is considered a major impediment to cancer treatment due to metastatictumors that develop resistance to chemotherapy. MDR contributes to the failure of chemotherapiesin various cancers, including breast, ovarian, lung, gastrointestinal and hematological malignancies.Moreover, the therapeutic efficiency of anticancer drugs or nanoparticles (NPs) used alone is lessthan that of the combination of NPs and anticancer drugs. Combination therapy has long beenadopted as the standard first-line treatment of several malignancies to improve the clinical outcome.Combination therapy with anticancer drugs has been shown to generally induce synergistic drugactions and deter the onset of drug resistance. Therefore, this review is designed to report andanalyze the recent progress made to address combination therapy using NPs and anticancer drugs.We first provide a comprehensive overview of the angiogenesis and of the different types of NPscurrently used in treatments of cancer; those emphasized in this review are liposomes, polymericNPs, polymeric micelles (PMs), dendrimers, carbon NPs, nanodiamond (ND), fullerenes, carbonnanotubes (CNTs), graphene oxide (GO), GO nanocomposites and metallic NPs used forcombination therapy with various anticancer agents. Nanotechnology has provided the convenienttools for combination therapy. However, for clinical translation, we need continued improvementsin the field of nanotechnology.

Multifunctional Carbon-Based Nanomaterials: Applications in Biomolecular Imaging and Therapy

Molecular imaging has been widely used not only as an important detection technology in the field of medical imaging for cancer diagnosis but also as a theranostic approach for cancer in recent years. Multifunctional carbon-based nanomaterials (MCBNs), characterized by unparalleled optical, electronic, and thermal properties, have attracted increasing interest and demonstrably hold the greatest promise in biomolecular imaging and therapy. As such, it should come as no surprise that MCBNs have already revealed a great deal of potential applications in biomedical areas, such as bioimaging, drug delivery, and tumor therapy. Carbon nanomaterials can be categorized as graphene, single-walled carbon nanotubes, mesoporous carbon, nanodiamonds, fullerenes, or carbon dots on the basis of their morphologies. In this article, reports of the use of MCBNs in various chemical conjugation/functionalization strategies, focusing on their applications in cancer molecular imaging and imaging-guided therapy, will be comprehensively summarized. MCBNs show the possibility to serve as optimal candidates for precise cancer biotheranostics.

Nanodiamonds and Their Applications in Cells

Diamonds owe their fame to a unique set of outstanding properties. They combine a high refractive index, hardness, great stability and inertness, and low electrical but high thermal conductivity. Diamond defects have recently attracted a lot of attention. Given this unique list of properties, it is not surprising that diamond nanoparticles are utilized for numerous applications. Due to their hardness, they are routinely used as abrasives. Their small and uniform size qualifies them as attractive carriers for drug delivery. The stable fluorescence of diamond defects allows their use as stable single photon sources or biolabels. The magnetic properties of the defects make them stable spin qubits in quantum information. This property also allows their use as a sensor for temperature, magnetic fields, electric fields, or strain. This Review focuses on applications in cells. Different diamond materials and the special requirements for the respective applications are discussed. Methods to chemically modify the surface of diamonds and the different hurdles one has to overcome when working with cells, such as entering the cells and biocompatibility, are described. Finally, the recent developments and applications in labeling, sensing, drug delivery, theranostics, antibiotics, and tissue engineering are critically discussed.

Fluorescent Nanodiamond Applications for Cellular Process Sensing and Cell Tracking

Diamond nanocrystals smaller than 100 nm (nanodiamonds) are now recognized to be highly biocompatible. They can be made fluorescent with perfect photostability by creating nitrogen-vacancy (NV) color centers in the diamond lattice. The resulting fluorescent nanodiamonds (FND) have been used since the late 2000s as fluorescent probes for short- or long-term analysis. FND can be used both at the subcellular scale and the single cell scale. Their limited sub-diffraction size allows them to track intracellular processes with high spatio-temporal resolution and high contrast from the surrounding environment. FND can also track the fate of therapeutic compounds or whole cells in the organs of an organism. This review presents examples of FND applications (1) for intra and intercellular molecular processes sensing, also introducing the different potential biosensing applications based on the optically detectable electron spin resonance of NV^- centers; and (2) for tracking, firstly, FND themselves to determine their biodistribution, and secondly, using FND as cell tracking probes for diagnosis or follow-up purposes in oncology and regenerative medicine.