Enhancing the magnetic relaxivity of MRI contrast agents via the localized superacid microenvironment of graphene quantum dots

Graphene-Oxide Peptide-Containing Materials for Biomedical Applications

This review explores the application of graphene-based materials (GBMs) in biomedicine, focusing on graphene oxide (GO) and its interactions with peptides and proteins. GO, a versatile nanomaterial with oxygen-containing functional groups, holds significant potential for biomedical applications but faces challenges related to toxicity and environmental impact. Peptides and proteins can be functionalized on GO surfaces through various methods, including non-covalent interactions such as π-π stacking, electrostatic forces, hydrophobic interactions, hydrogen bonding, and van der Waals forces, as well as covalent bonding through reactions involving amide bond formation, esterification, thiol chemistry, and click chemistry. These approaches enhance GO's functionality in several key areas: biosensing for sensitive biomarker detection, theranostic imaging that integrates diagnostics and therapy for real-time treatment monitoring, and targeted cancer therapy where GO can deliver drugs directly to tumor sites while being tracked by imaging techniques like MRI and photoacoustic imaging. Additionally, GO-based scaffolds are advancing tissue engineering and aiding tissues' bone, muscle, and nerve tissue regeneration, while their antimicrobial properties are improving infection-resistant medical devices. Despite its potential, addressing challenges related to stability and scalability is essential to fully harness the benefits of GBMs in healthcare.

Carbon dots-based dual-mode sensor for highly selective detection of nitrite in food substrates through diazo coupling reaction

As an antioxidant and preservative agent, nitrite (NO2-) plays an essential role in the food industry to maintain freshness or inhibit microbial growth. However, excessive addition of NO2- is detrimental to health, so accurate and portable detection of NO2- is critical for food quality control. Notably, the selectivity of most carbon dots (CDs)-based fluorescence sensors was not enough due to the nonspecific interaction mechanism of hydrogen bond, electrostatic interaction and inner filter effect etc. Herein, a novel fluorescence/UV-vis absorption (FL/UV-vis) dual-mode sensor was developed on basis of mC-CDs, which were prepared by simple solvothermal treatment of m-Phenylenediamine (m-PDA) and cyanidin cation (CC). The fluorescence of these mC-CDs could be selectively responded by NO2- through the specific diazo coupling reaction between NO2- and amino groups on the surface of mC-CDs, thus effectively improving the selectivity of NO2- detection. The CDs-based fluorescence sensor possessed a low detection limit of 0.091 μM and 0.143 μM for FL and UV-vis methods and the excellent linear range of 0.0-60.0 μM. Furthermore, the mC-CDs sensor was employed to detect NO2- in real samples with a recovery rate of 97.11 %-104.15 % for quantitative addition. Moreover, the smartphone-assisted fluorescence sensing platform developed could identify the subtle color changes that could not be distinguished by the naked eye, and had the advantages of fast detection speed and intelligence. More importantly, the portable solid phase sensor based on mC-CDs had been successfully applied to the specific fluorescence identification and concentration monitoring of NO2-. Accordingly, the designed sensor provided a new strategy for the highly selective and convenient sensing of NO2- in food substrates, and paved the way for the wide application of CDs-based nanomaterials in the detection of food safety.

Accelerated proton dissociation in an excited state induces superacidic microenvironments around graphene quantum dots

Investigating proton transport at the interface in an excited state facilitates the mechanistic investigation and utilization of nanomaterials. However, there is a lack of suitable tools for in-situ and interfacial analysis. Here we addresses this gap by in-situ observing the proton transport of graphene quantum dots (GQDs) in an excited state through reduction of magnetic resonance relaxation time. Experimental results, utilizing 0.1 mT ultra-low-field nuclear magnetic resonance relaxometry compatible with a light source, reveal the light-induced proton dissociation and acidity of GQDs' microenvironment in the excited state (Hammett acidity function: -13.40). Theoretical calculations demonstrate significant acidity enhancement in -OH functionalized GQDs with light induction ( p K a *  = -4.62, stronger than that of H2SO4). Simulations highlight the contributions of edge and phenolic -OH groups to proton dissociation. The light-induced superacidic microenvironment of GQDs benefits functionalization and improves the catalytic performances of GQDs. Importantly, this work advances the understanding of interfacial properties of light-induced sp2-sp3 carbon nanostructure and provides a valuable tool for exploring catalyst interfaces in photocatalysis.

A ginsenoside G-Rg3 PEGylated long-circulating liposome for hyperglycemia and insulin resistance therapy in streptozotocin-induced type 2 diabetes mice

Ginsenoside (GS), one of the main active components in ginseng, can enhance insulin sensitivity, improve the function of islet β cells, and reduce cell apoptosis in the treatment of diabetes. However, the drawbacks of high lipid solubility, poor water solubility, and low oral availability in Ginsenoside Rg3 (G-Rg3) seriously limit further application of GS. In this work, a G-Rg3 PEGylated long-circulating liposome (PEG-L-Rg3) is designed and developed to improve symptoms in type 2 diabetic mice. The as-prepared PEG-L-Rg3 with a spherical structure shows a particle size of ∼ 140.5 ± 1.4 nm, the zeta potential of -0.10 ± 0.05 mV, and a high encapsulation rate of 99.8 %. Notably, in vivo experimental results demonstrate that PEG-L-Rg3 exhibits efficient ability to improve body weight and food intake in streptozotocin-induced type 2 diabetic mice. Moreover, PEG-L-Rg3 also enhances fasting insulin (FINS) and insulin sensitivity index (ISI). In addition, the glucose tolerance of mice is significantly improved after the treatment of PEG-L-Rg3, indicating that PEG-L-Rg3 can be a potential drug for the treatment of type 2 diabetes, which provides a new way for the treatment of type 2 diabetes using ginsenosides.

Impurities in Polymer-Lined Autoclaves Affect Zeolite Synthesis and Si Incorporation Behavior

Polymer-lined autoclaves are commonly believed to be highly durable and inert in hydrothermal reactions. Herein, we use the hydrothermal synthesis of AlPO-18 zeolite as a case study to demonstrate that the choice of autoclave materials (polytetrafluoroethylene or para-polyphenylene) does significantly affect the product of zeolite synthesis. A small amount of glass fiber in the PPL-lined autoclave unexpectedly functions as a source of silicon and yields SAPO-34 instead of AlPO-18 as the product. The outcomes of 19 successive experiments conducted with a single PPL-lined autoclave exhibit significant variations, further highlighting that the impurities arising from the autoclaves should be considered during the hydrothermal synthesis procedure. In contrast to SAPO-34 synthesized by the conventional method, which displays only Si(4Al) at a low Si/Al ratio, SAPO-34 synthesized in the PPL-lined autoclave exhibits multiple silicon coordination environments. This outcome provides new physical insights into the silicon incorporation mechanism and proposes a viable strategy for regulating the silicon coordination environment at low Si/Al ratios.

Tumor diagnosis using carbon-based quantum dots: Detection based on the hallmarks of cancer

Carbon-based quantum dots (CQDs) have been shown to have promising application value in tumor diagnosis. Their use, however, is severely hindered by the complicated nature of the nanostructures in the CQDs. Furthermore, it seems impossible to formulate the mechanisms involved using the inadequate theoretical frameworks that are currently available for CQDs. In this review, we re-consider the structure-property relationships of CQDs and summarize the current state of development of CQDs-based tumor diagnosis based on biological theories that are fully developed. The advantages and deficiencies of recent research on CQDs-based tumor diagnosis are thus explained in terms of the manifestation of nine essential changes in cell physiology. This review makes significant progress in addressing related problems encountered with other nanomaterials.

Fast proton transport enables the magnetic relaxation response of graphene quantum dots for monitoring the oxidative environment in vivo

A magnetic relaxation switch (MRS) that targets small molecules such as H2O2 is difficult to realize because of the small size of the targets, which cannot gather enough MRS probes to form aggregates and generate a difference in magnetic relaxation times. Therefore, the development of small molecule-targeted MRS is strongly dependent on changes in the interfacial structure of the probe, which modulates the proton transport behavior near the probe. Herein, functionalized graphene quantum dots (GQDs) consisting of GQDs with disulfide bonds, polyethylene glycol (PEG), and paramagnetic Gd3+ were used as the MRS probe to sense H2O2. The structure of GQDs changed after reacting with H2O2. The PEG assembled a tube for transmitting changes in GQDs via proton transport and thus enabled the magnetic relaxation response of the probe towards H2O2. Pentaethylene glycol was experimentally and theoretically proven to have the strongest ability to transport protons. Such a probe can be applied in the differentiation of healthy and senescent cells/tissues using in vitro fluorescent imaging and in vivo magnetic resonance imaging. This work provides a reliable solution for building a proton transport route, which not only enables the response of the MRS probe towards the targets but also demonstrates the design of carbon nanostructures with proton transport behaviors.

Enzyme-responsive macrocyclic metal complexes for biomedical imaging

Metal chelator-based contrast agents are used as tumor navigators for cancer diagnosis. Although approved metal chelators show excellent contrast performance in magnetic resonance imaging (MRI), large doses are required for cancer diagnoses due to rapid clearance and nonspecific accumulation throughout the body, which can compromise safety. The present study describes an enzyme-responsive metal delivery system, in which enzyme overexpressed in the tumor microenvironment selectively activates the tumor uptake of gadolinium (Gd). Gd was loaded into enzyme-responsive macrocyclam (ErMC) modified with a PEGylated enzyme-cleavable peptide resulting in Gd@ErMC. The PEGylated shell layer protected Gd@ErMC from nonspecific binding in the blood, increasing the half-life of the contrast agent. Specific cleavage of the PEGylated shell layer by the enzyme selectively liberated Gd from Gd@ErMC at the tumor site. Evaluation of the in vivo distribution of Gd@ErMC in tumor-bearing mice by MRI and positron emission tomography (PET) showed that Gd@ErMC had an extended half-life and was highly specific. Histological and serological analysis of Gd@ErMC-treated mice showed that this agent was safe. This novel enzyme-responsive contrast agent delivery system shows promise as specific theranostic agent for MR-guided radiotherapy.

A comparative multi-level toxicity assessment of carbon-based Gd-free dots and Gd-doped nanohybrids from coffee waste: hematology, biochemistry, histopathology and neurobiology study

Here, a comparative toxicity assessment of precursor carbon dots from coffee waste (cofCDs) obtained using green chemistry principles and Gd-doped nanohybrids (cofNHs) was performed using hematological, biochemical, histopathological assays in vivo (CD1 mice, intraperitoneal administration, 14 days), and neurochemical approach in vitro (rat cortex nerve terminals, synaptosomes). Serum biochemistry data revealed similar changes in cofCDs and cofNHs-treated groups, i.e. no changes in liver enzymes' activities and creatinine, but decreased urea and total protein values. Hematology data demonstrated increased lymphocytes and concomitantly decreased granulocytes in both groups, which could evidence inflammatory processes in the organism and was confirmed by liver histopathology; decreased red blood cell-associated parameters and platelet count, and increased mean platelet volume, which might indicate concerns with platelet maturation and was confirmed by spleen histopathology. So, relative safety of both cofCDs and cofNHs for kidney, liver and spleen was shown, whereas there were concerns about platelet maturation and erythropoiesis. In acute neurotoxicity study, cofCDs and cofNHs (0.01 mg/ml) did not affect the extracellular level of L-[14C]glutamate and [3H]GABA in nerve terminal preparations. Therefore, cofNHs demonstrated minimal changes in serum biochemistry and hematology assays, had no acute neurotoxicity signs, and can be considered as perspective biocompatible non-toxic theragnostic agent.

Exploring the multifunctional roles of quantum dots for unlocking the future of biology and medicine

With recent advancements in nanomedicines and their associated research with biological fields, their translation into clinically-applicable products is still below promises. Quantum dots (QDs) have received immense research attention and investment in the four decades since their discovery. We explored the extensive biomedical applications of QDs, viz. Bio-imaging, drug research, drug delivery, immune assays, biosensors, gene therapy, diagnostics, their toxic effects, and bio-compatibility. We unravelled the possibility of using emerging data-driven methodologies (bigdata, artificial intelligence, machine learning, high-throughput experimentation, computational automation) as excellent sources for time, space, and complexity optimization. We also discussed ongoing clinical trials, related challenges, and the technical aspects that should be considered to improve the clinical fate of QDs and promising future research directions.

Contrast Enhancement in MRI Using Combined Double Action Contrast Agents and Image Post-Processing in the Breast Cancer Model

Gd- and Fe-based contrast agents reduce T₁ and T₂ relaxation times, respectively, are frequently used in MRI, providing improved cancer detection. Recently, contrast agents changing both T₁/T₂ times, based on core/shell nanoparticles, have been introduced. Although advantages of the T₁/T₂ agents were shown, MR image contrast of cancerous versus normal adjacent tissue induced by these agents has not yet been analyzed in detail as authors considered changes in cancer MR signal or signal-to-noise ratio after contrast injection rather than changes in signal differences between cancer and normal adjacent tissue. Furthermore, the potential advantages of T₁/T₂ contrast agents using image manipulation such as subtraction or addition have not been yet discussed in detail. Therefore, we performed theoretical calculations of MR signal in a tumor model using T₁-weighted, T₂-weighted, and combined images for T₁-, T₂-, and T₁/T₂-targeted contrast agents. The results from the tumor model are followed by in vivo experiments using core/shell NaDyF₄/NaGdF₄ nanoparticles as T₁/T₂ non-targeted contrast agent in the animal model of triple negative breast cancer. The results show that subtraction of T₂-weighted from T₁-weighted MR images provides additional increase in the tumor contrast: over two-fold in the tumor model and 12% in the in vivo experiment.

Planted Graphene Quantum Dots for Targeted, Enhanced Tumor Imaging and Long-Term Visualization of Local Pharmacokinetics

While photoluminescent graphene quantum dots (GQDs) have long been considered very suitable for bioimaging owing to their protein-like size, superhigh photostability and in vivo long-term biosafety, their unique and crucial bioimaging applications in vivo remain unreachable. Herein, planted GQDs are presented as an excellent tool for in vivo fluorescent, sustainable and multimodality tumor bioimaging in various scenarios. The GQDs are in situ planted in the poly(ethylene glycol) (PEG) layer of PEGylated nanoparticles via a bottom-up molecular approach to obtain the NPs-GQDs-PEG nanocomposite. The planted GQDs show more than four times prolonged blood circulation and 7-8 times increased tumor accumulation than typical GQDs in vivo. After accessible specificity modification, the multifunctional NPs-GQDs-PEG provides targeted, multimodal molecular imaging for various tumor models in vitro or in vivo. Moreover, the highly photostable GQDs enable long-term, real-time visualization of the local pharmacokinetics of NPs in vivo. Planting GQDs in PEGylated nanomedicine offers a new strategy for broad in vivo biomedical applications of GQDs.

Smart Biomimetic Nanozymes for Precise Molecular Imaging: Application and Challenges

New nanotechnologies for imaging molecules are widely being applied to visualize the expression of specific molecules (e.g., ions, biomarkers) for disease diagnosis. Among various nanoplatforms, nanozymes, which exhibit enzyme-like catalytic activities in vivo, have gained tremendously increasing attention in molecular imaging due to their unique properties such as diverse enzyme-mimicking activities, excellent biocompatibility, ease of surface tenability, and low cost. In addition, by integrating different nanoparticles with superparamagnetic, photoacoustic, fluorescence, and photothermal properties, the nanoenzymes are able to increase the imaging sensitivity and accuracy for better understanding the complexity and the biological process of disease. Moreover, these functions encourage the utilization of nanozymes as therapeutic agents to assist in treatment. In this review, we focus on the applications of nanozymes in molecular imaging and discuss the use of peroxidase (POD), oxidase (OXD), catalase (CAT), and superoxide dismutase (SOD) with different imaging modalities. Further, the applications of nanozymes for cancer treatment, bacterial infection, and inflammation image-guided therapy are discussed. Overall, this review aims to provide a complete reference for research in the interdisciplinary fields of nanotechnology and molecular imaging to promote the advancement and clinical translation of novel biomimetic nanozymes.

Computational Biomaterials: Computational Simulations for Biomedicine

With the flourishing development of material simulation methods (quantum chemistry methods, molecular dynamics, Monte Carlo, phase field, etc.), extensive adoption of computing technologies (high-throughput, artificial intelligence, machine learning, etc.), and the invention of high-performance computing equipment, computational simulation tools have sparked the fundamental mechanism-level explorations to predict the diverse physicochemical properties and biological effects of biomaterials and investigate their enormous application potential for disease prevention, diagnostics, and therapeutics. Herein, the term "computational biomaterials" is proposed and the computational methods currently used to explore the inherent properties of biomaterials, such as optical, magnetic, electronic, and acoustic properties, and the elucidation of corresponding biological behaviors/effects in the biomedical field are summarized/discussed. The theoretical calculation of the physiochemical properties/biological performance of biomaterials applied in disease diagnosis, drug delivery, disease therapeutics, and specific paradigms such as biomimetic biomaterials is discussed. Additionally, the biosafety evaluation applications of theoretical simulations of biomaterials are presented. Finally, the challenges and future prospects of such computational simulations for biomaterials development are clarified. It is anticipated that these simulations would offer various methodologies for facilitating the development and future clinical translations/utilization of versatile biomaterials.

Progress and challenges of graphene and its congeners for biomedical applications

Nanomaterials by virtue of their small size and enhanced surface area, present unique physicochemical properties that enjoy widespread applications in bioengineering, biomedicine, biotechnology, disease diagnosis, and therapy. In recent years, graphene and its derivatives have attracted a great deal of attention in various applications, including photovoltaics, electronics, energy storage, catalysis, sensing, and biotechnology owing to their exceptional structural, optical, thermal, mechanical, and electrical. Graphene is a two-dimensional sheet of sp2 hybridized carbon atoms of atomic thickness, which are arranged in a honeycomb crystal lattice structure. Graphene derivatives are graphene oxide (GO) and reduced graphene oxide (rGO), which are highly oxidized and less oxidized forms of graphene, respectively. Another form of graphene is graphene quantum dots (GQDs), having a size of less than 20 nm. Contemporary graphene research focuses on using graphene nanomaterials for biomedical purposes as they have a large surface area for loading biomolecules and medicine and offer the potential for the conjugation of fluorescent dyes or quantum dots for bioimaging. The present review begins with the synthesis, purification, structure, and properties of graphene nanomaterials. Then, we focussed on the biomedical application of graphene nanomaterials with special emphasis on drug delivery, bioimaging, biosensing, tissue engineering, gene delivery, and chemotherapy. The implications of graphene nanomaterials on human health and the environment have also been summarized due to their exposure to their biomedical applications. This review is anticipated to offer useful existing understanding and inspire new concepts to advance secure and effective graphene nanomaterials-based biomedical devices.

Structural and Optical Properties of Graphene Quantum Dots-Polyvinyl Alcohol Composite Thin Film and Its Potential in Plasmonic Sensing of Carbaryl

In this study, graphene quantum dots (GQDs) and polyvinyl alcohol (PVA) composite was prepared and then coated on the surface of gold thin film via the spin coating technique. Subsequently, Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), and ultraviolet-visible spectroscopy (UV-Vis) were adopted to understand the structure, surface morphology, and optical properties of the prepared samples. The FT-IR spectral analysis revealed important bands, such as O-H stretching, C=O stretching, C-H stretching, and O=C=O stretching vibrations. The surface roughness of the GQDs-PVA composite thin film was found to be increased after exposure to carbaryl. On the other hand, the optical absorbance of the GQDs-PVA thin film was obtained and further analysis was conducted, revealing a band gap E_g value of 4.090 eV. The sensing potential of the thin film was analyzed using surface plasmon resonance (SPR) spectroscopy. The findings demonstrated that the developed sensor's lowest detection limit for carbaryl was 0.001 ppb, which was lower than that previously reported, i.e., 0.007 ppb. Moreover, other sensing performance parameters, such as full width at half maximum, detection accuracy, and signal-to-noise ratio, were also investigated to evaluate the sensor's efficiency.

Synergistic Effect of Oxygen- and Nitrogen-Containing Groups in Graphene Quantum Dots: Red Emitted Dual-Mode Magnetic Resonance Imaging Contrast Agents with High Relaxivity

Contrast agents (CAs) in magnetic resonance imaging generally involve the dissociative Gd³⁺. Because of the limited ligancy of Gd³⁺, the balance between Gd³⁺ coordination stability (reducing the concentration of dissociative Gd³⁺) and increases in the number of coordination water molecules (enhancing the relaxivity) becomes crucial. Herein, the key factor of the synergistic effect between the O- and N-containing groups of graphene quantum dots for the structural design of CAs with both high relaxivity and low toxicity was obtained. The nitrogen-doped graphene quantum dots (NGQDs) with an O/N ratio of 0.4 were selected to construct high-relaxivity magnetic resonance imaging (MRI)-fluorescence dual-mode CAs. The coordination stability of Gd³⁺ can be increased through the synergetic coordination of O- and N-containing groups. The synergetic coordination of O- and N-containing groups can result in the short residency time of the water ligand and achieve high relaxivity. The resulting CAs (called NGQDs-Gd) exhibit a high relaxivity of 32.04 mM^-1 s^-1 at 114 μT. Meanwhile, the NGQDs-Gd also emit red fluorescence (614 nm), which can enable the MRI-fluorescence dual-mode imaging as the CAs. Moreover, the bio-toxicity and tumor-targeting behavior of NGQDs-Gd were also evaluated, and NGQDs-Gd show potential in MRI-fluorescence imaging in vivo.

Emerging nanobiotechnology-encoded relaxation tuning establishes new MRI modes to localize, monitor and predict diseases

Magnetic resonance imaging (MRI) is one of the most important techniques in the diagnosis of many diseases including cancers, where contrast agents (CAs) are usually necessary to improve its precision and sensitivity. Previous MRI CAs are confined to the signal-to-noise ratio (SNR) elevation of lesions for precisely localizing lesions. As nanobiotechnology advances, some new MRI CAs or nanobiotechnology-enabled MRI modes have been established to vary the longitudinal or transverse relaxation of CAs, which are harnessed to detect lesion targets, monitor disease evolution, predict or evaluate curative effect, etc. These distinct cases provide unexpected insights into the correlation of the design principles of these nanobiotechnologies and corresponding MRI CAs with their potential applications. In this review, first, we briefly present the principles, classifications and applications of conventional MRI CAs, and then elucidate the recent advances in relaxation tuning via the development of various nanobiotechnologies with emphasis on the design strategies of nanobiotechnology and the corresponding MRI CAs to target the tumor microenvironment (TME) and biological targets or activities in tumors or other diseases. In addition, we exemplified the advantages of these strategies in disease theranostics and explored their potential application fields. Finally, we analyzed the present limitations, potential solutions and future development direction of MRI after its combination with nanobiotechnology.

Tumor-Selective Biodegradation-Regulated Photothermal H2 S Donor for Redox Dyshomeostasis- and Glycolysis Disorder-Enhanced Theranostics

H₂ S-mediated tumor therapy has received great attention due to its unique physiological activity and synergistical enhancement, but suffers from limited H₂ S donors with promised biosafety to regulate the H₂ S delivery and subsequently the elusive pathway to augment the combined therapy. Herein, a PEGylated porous molybdenum disulfide nanoflower (MSP) with abundant defects is facilely synthesized for tumor-targeted theranostics. MSP possesses good water-dispersity and high photothermal ability, which is used for photoacoustic imaging and photothermal therapy. Interestingly, MSP is selectively degraded upon exposure to superfluous glutathione (GSH) within tumor cells, the mechanism of which is investigated, as a reduction-coordination reaction. This special degradation induces redox dyshomeostasis via GSH depletion for reactive oxygen species-accumulated chemodynamic therapy. Meanwhile, the selective biodegradation of MSP regulates a sustained H₂ S release within tumor and achieves a targeted H₂ S gas therapy via enhancing the glycolysis to acidify the tumor cells (glycolysis disorder). Synergistically, these performances are further enhanced via near-infrared photothermal heating, where excellent therapeutic outcomes with good biosafety are accomplished in vitro and in vivo. These characteristics, together with the unique biodegradation and no obvious side-effects of the nanoparticles, suggest a potential therapeutic strategy for precise tumor treatments.

Promising Graphene-Based Nanomaterials and Their Biomedical Applications and Potential Risks: A Comprehensive Review

Graphene-based nanomaterials (GBNs) have been the subject of research focus in the scientific community because of their excellent physical, chemical, electrical, mechanical, thermal, and optical properties. Several studies have been conducted on GBNs, and they have provided a detailed review and summary of various applications. However, comprehensive comments on biomedical applications and potential risks and strategies to reduce toxicity are limited. In this review, we systematically summarized the following aspects of GBNs in order to fill the gaps: (1) the history, synthesis methods, structural characteristics, and surface modification; (2) the latest advances in biomedical applications (including drug/gene delivery, biosensors, bioimaging, tissue engineering, phototherapy, and antibacterial activity); and (3) biocompatibility, potential risks (toxicity in vivo/vitro and effects on human health and the environment), and strategies to reduce toxicity. Moreover, we have analyzed the challenges to be overcome in order to enhance application of GBNs in the biomedical field.

Ten Years of Knowledge of Nano-Carrier Based Drug Delivery Systems in Ophthalmology: Current Evidence, Challenges, and Future Prospective

The complex drug delivery barrier in the eye reduces the bioavailability of many drugs, resulting in poor therapeutic effects. It is necessary to investigate new drugs through appropriate delivery routes and vehicles. Nanotechnology has utilized various nano-carriers to develop potential ocular drug delivery techniques that interact with the ocular mucosa, prolong the retention time of drugs in the eye, and increase permeability. Additionally, nano-carriers such as liposomes, nanoparticles, nano-suspensions, nano-micelles, and nano-emulsions have grown in popularity as an effective theranostic application to combat different microbial superbugs. In this review, we summarize the nano-carrier based drug delivery system developments over the last decade, particularly review the biology, methodology, approaches, and clinical applications of nano-carrier based drug delivery system in the field of ocular therapeutics. Furthermore, this review addresses upcoming challenges, and provides an outlook on potential future trends of nano-carrier-based drug delivery approaches in ophthalmology, and hopes to eventually provide successful applications for treating ocular diseases.

Structural features regulated photoluminescence intensity and cell internalization of carbon and graphene quantum dots for bioimaging

Carbon-based nanostructures with nanometer dimensions have been identified as potential photoluminescence probes for bioimaging due to their biocompatibility, tunable bandgap, and resistance to photobleaching. However, the influence of structural features of carbon quantum dots (CQDs) and graphene quantum dots (GQDs) in bioimaging has not been explored previously. In the present investigation, we elucidated the mechanism of higher PL in GQDs as compared to CQDs as a function of their structural features. TEM and AFM studies revealed that CQDs were spherical (size ~5 nm), while GQDs showed zigzag edges (size ~3 nm). Further, XRD and NMR studies confirmed that CQDs and GQDs show amorphous and crystalline structures with greater sp² clusters, respectively. While both the QDs demonstrated multicolor fluorescence against variable excitations with similar lifetime, GQDs showed 7-fold higher QY than CQDs. Bioimaging studies in 2D cell culture, 3D tumoroids, and in vivo suggested a greater intensity of fluorescence in GQDs than CQDs. Additionally, rapid cell internalization was observed in GQDs owing to their positive surface potential by heterogeneous atomic (N and S) doping. Moreover, both CQDs and GQDs have demonstrated better time dependent stability for fluorescence properties. Taken together, the proposed mechanism elucidates the greater PL intensity in GQDs due to quantum confinement effect, crystallinity, and surface edge effects and is a better candidate for bioimaging amongst the carbon family.

Recent Advances in Gadolinium Based Contrast Agents for Bioimaging Applications

Gadolinium (Gd) based contrast agents (CAs) (Gd-CAs) represent one of the most advanced developments in the application of Gd for magnetic resonance imaging (MRI). Current challenges with existing CAs generated an urgent requirement to develop multimodal CAs with good biocompatibility, low toxicity, and prolonged circulation time. This review discussed the Gd-CAs used in bioimaging applications, addressing their advantages and limitations. Future research is required to establish the safety, efficacy and theragnostic capabilities of Gd-CAs. Nevertheless, these Gd-CAs offer extraordinary potential as imaging CAs and promise to benefit bioimaging applications significantly.

Functionalized Graphene Platforms for Anticancer Drug Delivery

Two-dimensional nanomaterials are emerging as promising candidates for a wide range of biomedical applications including tissue engineering, biosensing, pathogen incapacitation, wound healing, and gene and drug delivery. Graphene, due to its high surface area, photothermal property, high loading capacity, and efficient cellular uptake, is at the forefront of these materials and plays a key role in this multidisciplinary research field. Poor water dispersibility and low functionality of graphene, however, hamper its hybridization into new nanostructures for future nanomedicine. Functionalization of graphene, either by covalent or non-covalent methods, is the most useful strategy to improve its dispersion in water and functionality as well as processability into new materials and devices. In this review, recent advances in functionalization of graphene derivatives by different (macro)molecules for future biomedical applications are reported and explained. In particular, hydrophilic functionalization of graphene and graphene oxide (GO) to improve their water dispersibility and physicochemical properties is discussed. We have focused on the anticancer drug delivery of polyfunctional graphene sheets.

Magnetic graphene quantum dots facilitate closed-tube one-step detection of SARS-CoV-2 with ultra-low field NMR relaxometry

The rapid and sensitive diagnosis of the highly contagious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is one of the crucial issues at the outbreak of the ongoing global pandemic that has no valid cure. Here, we propose a SARS-CoV-2 antibody conjugated magnetic graphene quantum dots (GQDs)-based magnetic relaxation switch (MRSw) that specifically recognizes the SARS-CoV-2. The probe of MRSw can be directly mixed with the test sample in a fully sealed vial without sample pretreatment, which largely reduces the testers' risk of infection during the operation. The closed-tube one-step strategy to detect SARS-CoV-2 is developed with home-made ultra-low field nuclear magnetic resonance (ULF NMR) relaxometry working at 118 μT. The magnetic GQDs-based probe shows ultra-high sensitivity in the detection of SARS-CoV-2 due to its high magnetic relaxivity, and the limit of detection is optimized to 248 Particles mL^‒1. Meanwhile, the detection time in ULF NMR system is only 2 min, which can significantly improve the efficiency of detection. In short, the magnetic GQDs-based MRSw coupled with ULF NMR can realize a rapid, safe, and sensitive detection of SARS-CoV-2.

Amphiphilic Au Nanoclusters Modulated by Magnetic Gemini Surfactants as a Cysteine Chemosensor and an MRI Contrast Agent

Cationic magnetic Gemini surfactants (mag-G-surfs), [C₁₄H₂₉(CH₃)₂N(CH₂)₂N(CH₃)₂C₁₄H₂₉]²⁺·2[XCl₃Br]^- (14-2-14·2X, X = Ce, Gd, or Ho), efficiently induce the aggregation of glutathione-protected Au nanoclusters (NCs) (GSH-Au NCs). These magnetic luminescent aggregates not only possess aggregation-induced emission (AIE) behavior but also display aggregation-induced magnetic enhancement. In particular, 14-2-14·2Ce and 14-2-14·2Gd have a better effect on boosting the luminescence intensity, quantum yield (QY), and luminescence lifetime (τ). The luminescent aggregates of GSH-Au NCs triggered by 14-2-14·2Gd or 14-2-14·2Ho exhibit more favorable paramagnetic behavior. Other Au NCs containing a Au(I)-thiolate complex shell also exhibit the obvious AIE phenomenon after introducing 14-2-14·2Gd, demonstrating the luminescence enhancement effect of mag-G-surfs. The luminescent aggregate 14-2-14·2Ce@GSH-Au NCs can serve as a "light up" fluorometric probe to detect cysteine selectively with the detection limit (DL) of 36 μM, and the magnetic luminescent aggregate 14-2-14·2Gd@GSH-Au NCs has the potential to be a novel contrast agent in T₁-weighted magnetic resonance (MR) imaging due to its satisfactory contrasting ability.

Graphene Quantum Dots with Pyrrole N and Pyridine N: Superior Reactive Oxygen Species Generation Efficiency for Metal-Free Sonodynamic Tumor Therapy

Those responsible for the development of sonosensitizers are faced with a dilemma between high sonosensitization efficacy and good biosecurity that limited the development of sonodynamic therapy (SDT). Herein, inspired by the intriguing therapeutic features of SDT and the potential catalytic activity of graphene quantum dots, the potential of N-doped graphene quantum dots (N-GQDs) to act as a sonosensitizer is demonstrated. The superior sonosensitization effect of N-GQDs is believed to be three to five times higher than that of traditional sonosensitizers (such as porphyrin, porphyrin Mn, porphyrin Zn, TiO₂ , etc.). More importantly, the sonochemical mechanism of N-GQDs is revealed. Pyrrole N and pyridine N are believed to form catalytic centers in sonochemical processing of N-GQDs. This knowledge is important from the perspective of understanding the structure-dependent SDT enhancement of carbon nanostructure. Moreover, N-GQDs modified by folic acid (FA-N-GQDs) show a high marker rate for tumor cells (greater than 96%). Both in vitro and in vivo therapeutic results have exhibited high tumor inhibition efficiency (greater than 90%) of FA-N-GQDs as sonosensitizers while the oxidative stress response of tumor cells is activated through the PEX pathway and induced apoptosis via the p53 pathway.

Microarray analysis of gene expression differences in microglia after exposure to graphene quantum dots

Graphene quantum dots (GQDs) have been broadly applied in biomedicine in recent years. So far, researches have reported that GQDs might contribute to the injury of the central nervous system (CNS), yet the latent toxicological mechanism is not clear. This study aims to investigate the underlying biological mechanism responsible for the neurotoxicity of nitrogen-doped GQDs (N-GQDs) and amino-functionalized GQDs (A-GQDs) by use of genome-wide transcription microarray. The findings showed that 174 and 1341 genes were altered significantly in the BV2 cells treated by 25 μg/mL N-GQDs and 100 μg/mL N-GQDs compared with the control, respectively. As for the BV2 cells exposed to 100 μg/mL A-GQDs, 1396 diversely expressed genes were detected. By comparing the 100 μg/mL N-GQDs exposed group with 100 μg/mL A-GQDs exposed group, the expression of 256 genes was extensively altered, including 58 upregulated genes and 198 downregulated genes. From Gene Ontology (GO) analysis, the altered genes were mainly enriched in functions of ion channel activation and cellular processes. Based on the KEGG pathway and signal-net analysis, the toxicity of GQDs in BV2 cells was closely related to calcium signaling pathway, cell cycle and endocytosis. And the pathways that the shared mRNAs involved all served as the crucial roles in the neurotoxicity of GQDs despite the chemical functionalization (N-GQDs or A-GQDs). In addition, the consequences from qRT-PCR, Western blot, intracellular calcium level measurements and comet assay further confirmed that calcium dyshomeostasis, DNA damage and cell cycle arrest were the key factors responsible for the GQDs-induced neurotoxicity through affecting several classical signaling pathways. In conclusion, our research will supply essential data for further studies on mechanisms of GQDs-induced neurotoxicity by use of genome-wide screening.

Carbon-Based Quantum Dots with Solid-State Photoluminescent: Mechanism, Implementation, and Application

Carbon-based quantum dots (CQDs), including spherical carbon dots and graphene quantum dots, are an emerging class of photoluminescent (PL) materials with unique properties. Great progress has been made in the design and fabrication of high-performance CQDs, however, the challenge of developing solid-state PL CQDs have aroused great interest among researchers. A clear PL mechanism is the basis for the development of high-performance solid-state CQDs for light emission and is also a prerequisite for the realization of multiple practical applications. However, the extremely complex structure of a CQD greatly limits the understanding of the solid-state PL mechanism of CQDs. So far, a variety of models have been proposed to explain the PL of solid-state CQDs, but they have not been unified. This review summarizes the current understanding of the solid-state PL of solid-state CQDs from the perspective of energy band theory and electronic transitions. In addition, the common strategies for realizing solid-state PL in CQDs are also summarized. Furthermore, the applications of CQDs in the fields of light-emitting devices, anti-counterfeiting, fingerprint detection, etc., are proposed. Finally, a brief outlook is given, highlighting current problems, and directions for development of solid-state PL of CQDs.