Nanodiamonds: Synthesis and Application in Sensing, Catalysis, and the Possible Connection with Some Processes Occurring in Space

Exploring nanodiamonds: leveraging their dual capacities for anticancer photothermal therapy and temperature sensing

Cancer has become a primary global health concern, which has prompted increased attention towards targeted therapeutic approaches like photothermal therapy (PTT). The unique optical and magnetic properties of nanodiamonds (NDs) have made them versatile nanomaterials with promising applications in biomedicine. This comprehensive review focuses on the potential of NDs as a multifaceted platform for anticancer therapy, mainly focusing on their dual functionality in PTT and temperature sensing. The review highlighted NDs' ability to enhance PTT through hybridization or modification, underscoring their adaptability in delivering small molecule reagents effectively. Furthermore, NDs, particularly fluorescent nanodiamonds (FNDs) with negatively charged nitrogen-vacancy centers, enable precise temperature monitoring, enhancing PTT efficacy in anticancer treatment. Integrating FNDs into PTT holds promise for advancing therapeutic efficacy by providing valuable insights into localized temperature variations and cell death mechanisms. This review highlights new insights into cancer treatment strategies, showcasing the potential of NDs to revolutionize targeted therapeutics and improve patient outcomes.

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

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

Nanodiamonds: A Cutting-Edge Approach to Enhancing Biomedical Therapies and Diagnostics in Biosensing

Nanodiamonds (NDs) have garnered attention in the field of nanomedicine due to their unique properties. This review offers a comprehensive overview of NDs synthesis methods, properties, and their uses in biomedical applications. Various synthesis techniques, such as detonation, high-pressure, high-temperature, and chemical vapor deposition, offer distinct advantages in tailoring NDs' size, shape, and surface properties. Surface modification methods further enhance NDs' biocompatibility and enable the attachment of bioactive molecules, expanding their applicability in biological systems. NDs serve as promising nanocarriers for drug delivery, showcasing biocompatibility and the ability to encapsulate therapeutic agents for targeted delivery. Additionally, NDs demonstrate potential in cancer treatment through hyperthermic therapy and vaccine enhancement for improved immune responses. Functionalization of NDs facilitates their utilization in biosensors for sensitive biomolecule detection, aiding in precise diagnostics and rapid detection of infectious diseases. This review underscores the multifaceted role of NDs in advancing biomedical applications. By synthesizing NDs through various methods and modifying their surfaces, researchers can tailor their properties for specific biomedical needs. The ability of NDs to serve as efficient drug delivery vehicles holds promise for targeted therapy, while their applications in hyperthermic therapy and vaccine enhancement offer innovative approaches to cancer treatment and immunization. Furthermore, the integration of NDs into biosensors enhances diagnostic capabilities, enabling rapid and sensitive detection of biomolecules and infectious diseases. Overall, the diverse functionalities of NDs underscore their potential as valuable tools in nanomedicine, paving the way for advancements in healthcare and biotechnology.

Carbon-Based Nanostructures as Emerging Materials for Gene Delivery Applications

Gene therapeutics are promising for treating diseases at the genetic level, with some already validated for clinical use. Recently, nanostructures have emerged for the targeted delivery of genetic material. Nanomaterials, exhibiting advantageous properties such as a high surface-to-volume ratio, biocompatibility, facile functionalization, substantial loading capacity, and tunable physicochemical characteristics, are recognized as non-viral vectors in gene therapy applications. Despite progress, current non-viral vectors exhibit notably low gene delivery efficiency. Progress in nanotechnology is essential to overcome extracellular and intracellular barriers in gene delivery. Specific nanostructures such as carbon nanotubes (CNTs), carbon quantum dots (CQDs), nanodiamonds (NDs), and similar carbon-based structures can accommodate diverse genetic materials such as plasmid DNA (pDNA), messenger RNA (mRNA), small interference RNA (siRNA), micro RNA (miRNA), and antisense oligonucleotides (AONs). To address challenges such as high toxicity and low transfection efficiency, advancements in the features of carbon-based nanostructures (CBNs) are imperative. This overview delves into three types of CBNs employed as vectors in drug/gene delivery systems, encompassing their synthesis methods, properties, and biomedical applications. Ultimately, we present insights into the opportunities and challenges within the captivating realm of gene delivery using CBNs.

Advances in Stabilization and Enrichment of Shallow Nitrogen-Vacancy Centers in Diamond for Biosensing and Spin-Polarization Transfer

Negatively charged nitrogen-vacancy (NV^-) centers in diamond have unique magneto-optical properties, such as high fluorescence, single-photon generation, millisecond-long coherence times, and the ability to initialize and read the spin state using purely optical means. This makes NV^- centers a powerful sensing tool for a range of applications, including magnetometry, electrometry, and thermometry. Biocompatible NV-rich nanodiamonds find application in cellular microscopy, nanoscopy, and in vivo imaging. NV^- centers can also detect electron spins, paramagnetic agents, and nuclear spins. Techniques have been developed to hyperpolarize ¹⁴N, ¹⁵N, and ¹³C nuclear spins, which could open up new perspectives in NMR and MRI. However, defects on the diamond surface, such as hydrogen, vacancies, and trapping states, can reduce the stability of NV^- in favor of the neutral form (NV⁰), which lacks the same properties. Laser irradiation can also lead to charge-state switching and a reduction in the number of NV^- centers. Efforts have been made to improve stability through diamond substrate doping, proper annealing and surface termination, laser irradiation, and electric or electrochemical tuning of the surface potential. This article discusses advances in the stabilization and enrichment of shallow NV^- ensembles, describing strategies for improving the quality of diamond devices for sensing and spin-polarization transfer applications. Selected applications in the field of biosensing are discussed in more depth.

Nanodiamond surface as a photoluminescent pH sensor

A systematic spectroscopic characterization of highly homogeneous water suspensions of 'buckydiamonds' comprising sp³cubic nanodiamond (ND) core covered with disordered sp²shell densely decorated with oxygen-containing groups demonstrates the excitation-wavelength-dependent photoluminescence (PL) given by at least four types of specific structures on the ND surface (hydroxyl, C=O containing ketones, carboxylic anhydrides, and carboxyl groups). PL properties of NDs suspensions possess concentration-dependent behavior revealing tendency of NDs to agglomerate. PL of NDs has been found to be strongly sensitive to pH of the environment in wide range of pH values, i.e. 2-11. We disclosed the mechanisms of pH sensitivity of the 'buckydiamond' and proved that it can serve as all-optical sensor of tiny pH variations suitable for further exploitation for pH sensing locally in the area where NDs have been delivered for any purpose, e.g. bioimaging or therapeutic needs.

Continuous Glucose Monitoring Enabled by Fluorescent Nanodiamond Boronic Hydrogel

Continuous monitoring of glucose allows diabetic patients to better maintain blood glucose level by altering insulin dosage or diet according to prevailing glucose values and thus to prevent potential hyperglycemia and hypoglycemia. However, current continuous glucose monitoring (CGM) relies mostly on enzyme electrodes or micro-dialysis probes, which suffer from insufficient stability, susceptibility to corrosion of electrodes, weak or inconsistent correlation, and inevitable interference. A fluorescence-based glucose sensor in the skin will likely be more stable, have improved sensitivity, and can resolve the issues of electrochemical interference from the tissue. This study develops a fluorescent nanodiamond boronic hydrogel system in porous microneedles for CGM. Fluorescent nanodiamond is one of the most photostable fluorophores with superior biocompatibility. When surface functionalized, the fluorescent nanodiamond can integrate with boronic polymer and form a hydrogel, which can produce fluorescent signals in response to environmental glucose concentration. In this proof-of-concept study, the strategy for building a miniatured device with fluorescent nanodiamond hydrogel is developed. The device demonstrates remarkable long-term photo and signal stability in vivo with both small and large animal models. This study presents a new strategy of fluorescence based CGM toward treatment and control of diabetes.

High-Energy Excimer Annealing of Nanodiamond Layers

Here, we aimed to achieve exposure of a nanodiamond layer to a high-energy excimer laser. The treatment was realized in high-vacuum conditions. The carbon, in the form of nanodiamonds (NDs), underwent high-temperature changes. The induced changes in carbon form were studied with Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction (XRD) and we searched for the Q-carbon phase in the prepared structure. Surface morphology changes were detected by atomic force microscopy (AFM) and scanning electron microscopy (SEM). NDs were exposed to different laser energy values, from 1600 to 3000 mJ cm-2. Using the AFM and SEM methods, we found that the NDs layer was disrupted with increasing beam energy, to create a fibrous structure resembling Q-carbon fibers. Layered micro-/nano-spheres, representing the role of diamonds, were created at the junction of the fibers. A Q-carbon structure (fibers) consisting of 80% sp3 hybridization was prepared by melting and quenching the nanodiamond film. Higher energy values of the laser beam (2000 and 3000 mJ cm-2), in addition to oxygen bonds, also induced carbide bonds characteristic of Q-carbon. Raman spectroscopy confirmed the presence of a diamond (sp3) phase and a low-intensity graphitic (G) peak occurring in the Q-carbon form samples.

Does age pay off? Effects of three-generational experiments of nanodiamond exposure and withdrawal in wild and longevity-selected model animals

Nanodiamonds (NDs) are considered a material with low toxicity. However, no studies describe the effects of ND withdrawal after multigenerational exposure. The aim was to evaluate ND exposure (in the 1st and 2nd generations) effects at low concentrations (0.2 or 2 mg kg^-1) and withdrawal (in the 3rd generation) in the wild (H) and longevity-selected (D) model insect Acheta domesticus. We measured selected oxidative stress parameters, immunity, types of cell death, and DNA damage. Most of the results obtained in the 1st generation, e.g., catalase (CAT), total antioxidant capacity (TAC), heat shock proteins (HSP70), defensins, or apoptosis level, confirmed no significant toxicity of low doses of NDs. Interestingly, strain-specific differences were observed. D-strain crickets reduced autophagy, the number of ROS+ cells, and DNA damage. The effect can be a symptom of mobilization of the organism and stimulation of physiological defense mechanisms in long-living organisms. The 2nd-generation D-strain insects fed ND-spiked food at higher concentrations manifested a reduction in CAT, TAC, early apoptosis, and DNA damage, together with an increase in HSP70 and defensins. ROS+ cells and cells with reduced membrane potential and autophagy did not differ significantly from the control. H-strain insects revealed a higher number of ROS+ cells and cells with reduced membrane potential, decreased CAT activity, and early apoptosis. Elimination of NDs from the diet in the 3rd generation did not cause full recovery of the measured parameters. We noticed an increase in the concentration of HSP70 and defensins (H-strain) and a decrease in apoptosis (D-strain). However, the most visible increase was a significant increase in DNA damage, especially in H-strain individuals. The results suggest prolonged adverse effects of NDs on cellular functions, reaching beyond "contact time" with these particles. Unintentional and/or uncontrolled ND pollution of the environment poses a new challenge for all organisms inhabiting it, particularly during multigenerational exposure.

Carbon Graphitization: Towards Greener Alternatives to Develop Nanomaterials for Targeted Drug Delivery

Carbon nanomaterials have attracted great interest for their unique physico-chemical properties for various applications, including medicine and, in particular, drug delivery, to solve the most challenging unmet clinical needs. Graphitization is a process that has become very popular for their production or modification. However, traditional conditions are energy-demanding; thus, recent efforts have been devoted to the development of greener routes that require lower temperatures or that use waste or byproducts as a carbon source in order to be more sustainable. In this concise review, we analyze the progress made in the last five years in this area, as well as in their development as drug delivery agents, focusing on active targeting, and conclude with a perspective on the future of the field.

Nanodiamond conjugated SARS-CoV-2 spike protein: electrochemical impedance immunosensing on a gold microelectrode

A promising immunosensing strategy in diagnosing SARS-CoV-2 is proposed using a 10-µm gap-sized gold interdigitated electrode (AuIDE) to target the surface spike protein (SP). The microelectrode surface was modified by (3-glycidyloxypropyl) trimethoxysilane to enforce the epoxy matrix, which facilitates the immobilization of the anti-SP antibody. The immunosensing performance was evaluated by integrating a nanosized (~ 10 nm) diamond-complexed SP as a target. The proposed immunoassay was quantitatively evaluated through electrochemical impedance spectroscopy (EIS) with the swept frequency from 0.1 to 1 MHz using a 100 mV_RMS AC voltage supply. The immunoassay performed without diamond integration showed low sensitivity, with the lowest SP concentration measured at 1 pM at a determination coefficient of R² = 0.9681. In contrast, the nanodiamond-conjugated SP on the immunosensor showed excellent sensitivity with a determination coefficient of R² = 0.986. SP detection with a nanodiamond-conjugated target on AuIDE reached the low limit of detection at 189 fM in a linear detection range from 250 to 8000 fM. The specificity of the developed immunosensor was evaluated by interacting influenza-hemagglutinin and SARS-CoV-2-nucleocapsid protein with anti-SP. In addition, the authentic interaction of SP and anti-SP was validated by enzyme-linked immunosorbent assay.

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

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

Synergies between Hyperpolarized NMR and Microfluidics: A Review

Hyperpolarized nuclear magnetic resonance and lab-on-a-chip microfluidics are two dynamic, but until recently quite distinct, fields of research. Recent developments in both areas increased their synergistic overlap. By microfluidic integration, many complex experimental steps can be brought together onto a single platform. Microfluidic devices are therefore increasingly finding applications in medical diagnostics, forensic analysis, and biomedical research. In particular, they provide novel and powerful ways to culture cells, cell aggregates, and even functional models of entire organs. Nuclear magnetic resonance is a non-invasive, high-resolution spectroscopic technique which allows real-time process monitoring with chemical specificity. It is ideally suited for observing metabolic and other biological and chemical processes in microfluidic systems. However, its intrinsically low sensitivity has limited its application. Recent advances in nuclear hyperpolarization techniques may change this: under special circumstances, it is possible to enhance NMR signals by up to 5 orders of magnitude, which dramatically extends the utility of NMR in the context of microfluidic systems. Hyperpolarization requires complex chemical and/or physical manipulations, which in turn may benefit from microfluidic implementation. In fact, many hyperpolarization methodologies rely on processes that are more efficient at the micro-scale, such as molecular diffusion, penetration of electromagnetic radiation into a sample, or restricted molecular mobility on a surface. In this review we examine the confluence between the fields of hyperpolarization-enhanced NMR and microfluidics, and assess how these areas of research have mutually benefited one another, and will continue to do so.

Carbon Nanomaterials (CNMs) and Enzymes: From Nanozymes to CNM-Enzyme Conjugates and Biodegradation

Carbon nanomaterials (CNMs) and enzymes differ significantly in terms of their physico-chemical properties-their handling and characterization require very different specialized skills. Therefore, their combination is not trivial. Numerous studies exist at the interface between these two components-especially in the area of sensing-but also involving biofuel cells, biocatalysis, and even biomedical applications including innovative therapeutic approaches and theranostics. Finally, enzymes that are capable of biodegrading CNMs have been identified, and they may play an important role in controlling the environmental fate of these structures after their use. CNMs' widespread use has created more and more opportunities for their entry into the environment, and thus it becomes increasingly important to understand how to biodegrade them. In this concise review, we will cover the progress made in the last five years on this exciting topic, focusing on the applications, and concluding with future perspectives on research combining carbon nanomaterials and enzymes.

Self-Assembling Peptides and Carbon Nanomaterials Join Forces for Innovative Biomedical Applications

Self-assembling peptides and carbon nanomaterials have attracted great interest for their respective potential to bring innovation in the biomedical field. Combination of these two types of building blocks is not trivial in light of their very different physico-chemical properties, yet great progress has been made over the years at the interface between these two research areas. This concise review will analyze the latest developments at the forefront of research that combines self-assembling peptides with carbon nanostructures for biological use. Applications span from tissue regeneration, to biosensing and imaging, and bioelectronics.

Several Aspects of Application of Nanodiamonds as Reinforcements for Metal Matrix Composites

After detonation synthesis, primary nanodiamond particles are around 4–6 nm in size. However, they join into agglomerates with larger parameters and weak bonds between particles. The introduction of agglomerates into a metal matrix can lead to the weakness of composites. This paper demonstrates the possibility of obtaining a non-agglomerated distribution of nanodiamonds inside a metal matrix. The fabrication method was based on mechanical alloying to create additional stresses and deformations by phase transformations during treatment in a planetary mill. According to the findings, the starting temperature of the reaction between the non-agglomerated nanodiamonds and aluminium matrix reduces to 450 °C. Furthermore, the paper shows that existing methods (annealing for the transformation of a diamond structure into graphitic material and cleaning from this graphitic material) cannot reduce the sizes of nanodiamonds in the agglomerated state. Agglomerated nanodiamonds transform into carbon onions (graphitic material) during annealing in a vacuum in the following way: the nanodiamonds located in the surface layers of the agglomerate are the first to undergo the complete transformation followed by the transformation of nanoparticles in its deeper layers. In the intermediate state, the agglomerate has a graphitic surface layer and a core from nanodiamonds: cleaning from graphite cannot reduce nanodiamond particle size.

Smart Hydrogels Meet Carbon Nanomaterials for New Frontiers in Medicine

Carbon nanomaterials include diverse structures and morphologies, such as fullerenes, nano-onions, nanodots, nanodiamonds, nanohorns, nanotubes, and graphene-based materials. They have attracted great interest in medicine for their high innovative potential, owing to their unique electronic and mechanical properties. In this review, we describe the most recent advancements in their inclusion in hydrogels to yield smart systems that can respond to a variety of stimuli. In particular, we focus on graphene and carbon nanotubes, for applications that span from sensing and wearable electronics to drug delivery and tissue engineering.

Green Approaches to Carbon Nanostructure-Based Biomaterials

The family of carbon nanostructures comprises several members, such as fullerenes, nano-onions, nanodots, nanodiamonds, nanohorns, nanotubes, and graphene-based materials. Their unique electronic properties have attracted great interest for their highly innovative potential in nanomedicine. However, their hydrophobic nature often requires organic solvents for their dispersibility and processing. In this review, we describe the green approaches that have been developed to produce and functionalize carbon nanomaterials for biomedical applications, with a special focus on the very latest reports.

Optimization of Wide-Field ODMR Measurements Using Fluorescent Nanodiamonds to Improve Temperature Determination Accuracy

Fluorescent nanodiamonds containing nitrogen-vacancy centers have attracted attention as nanoprobes for temperature measurements in microenvironments, potentially enabling the measurement of intracellular temperature distributions and temporal changes. However, to date, the time resolution and accuracy of the temperature determinations using fluorescent nanodiamonds have been insufficient for wide-field fluorescence imaging. Here, we describe a method for highly accurate wide-field temperature imaging using fluorescent nanodiamonds for optically detected magnetic resonance (ODMR) measurements. We performed a Monte Carlo simulation to determine the optimal frequency sweep range for ODMR temperature determination. We then applied this sweep range to fluorescent nanodiamonds. As a result, the temperature determination accuracies were improved by a factor ~1.5. Our result paves the way for the contribution of quantum sensors to cell biology for understanding, for example, differentiation in multicellular systems.