Multiphoton luminescent graphene quantum dots for in vivo tracking of human adipose-derived stem cells

Precision Nanomedicine with Bio-Inspired Nanosystems: Recent Trends and Challenges in Mesenchymal Stem Cells Membrane-Coated Bioengineered Nanocarriers in Targeted Nanotherapeutics

In the recent past, the formulation and development of nanocarriers has been elaborated into the broader fields and opened various avenues in their preclinical and clinical applications. In particular, the cellular membrane-based nanoformulations have been formulated to surpass and surmount the limitations and restrictions associated with naïve or free forms of therapeutic compounds and circumvent various physicochemical and immunological barriers including but not limited to systemic barriers, microenvironmental roadblocks, and other cellular or subcellular hinderances-which are quite heterogeneous throughout the diseases and patient cohorts. These limitations in drug delivery have been overcome through mesenchymal cells membrane-based precision therapeutics, where these interventions have led to the significant enhancements in therapeutic efficacies. However, the formulation and development of nanocarriers still focuses on optimization of drug delivery paradigms with a one-size-fits-all resolutions. As mesenchymal stem cell membrane-based nanocarriers have been engineered in highly diversified fashions, these are being optimized for delivering the drug payloads in more and better personalized modes, entering the arena of precision as well as personalized nanomedicine. In this Review, we have included some of the advanced nanocarriers which have been designed and been utilized in both the non-personalized as well as precision applicability which can be employed for the improvements in precision nanotherapeutics. In the present report, authors have focused on various other aspects of the advancements in stem cells membrane-based nanoparticle conceptions which can surmount several roadblocks and barriers in drug delivery and nanomedicine. It has been suggested that well-informed designing of these nanocarriers will lead to appreciable improvements in the therapeutic efficacy in therapeutic payload delivery applications. These approaches will also enable the tailored and customized designs of MSC-based nanocarriers for personalized therapeutic applications, and finally amending the patient outcomes.

Role of graphene quantum dots with discrete band gaps on SnO2 nanodomes for NO2 gas sensors with an ultralow detection limit

NO₂ is a major air pollutant that should be monitored due to its harmful effects on the environment and human health. Semiconducting metal oxide-based gas sensors have been widely explored owing to their superior sensitivity towards NO₂, but their high operating temperature (>200 °C) and low selectivity still limit their practical use in sensor devices. In this study, we decorated graphene quantum dots (GQDs) with discrete band gaps onto tin oxide nanodomes (GQD@SnO₂ nanodomes), enabling room temperature (RT) sensing towards 5 ppm NO₂ gas with a noticeable response ((R_a/R_g) - 1 = 4.8), which cannot be matched using pristine SnO₂ nanodomes. In addition, the GQD@SnO₂ nanodome based gas sensor shows an extremely low detection limit of 1.1 ppb and high selectivity compared to other pollutant gases (H₂S, CO, C₇H₈, NH₃, and CH₃COCH₃). The oxygen functional groups in GQDs specifically enhance NO₂ accessibility by increasing the adsorption energy. Strong electron transfer from SnO₂ to GQDs widens the electron depletion layer at SnO₂, thereby improving the gas response over a broad temperature range (RT-150 °C). This result provides a basic perspective for utilizing zero-dimensional GQDs in high-performance gas sensors operating over a wide range of temperatures.

Aggregation-induced emission of matrix-free graphene quantum dots via selective edge functionalization of rotor molecules

Graphene quantum dots (GQDs) are nanosized graphene derivatives with unique photoluminescence (PL) properties that have advantages in optoelectronic applications due to their stable blue light emission. However, aggregation-caused quenching (ACQ) of GQDs limits the practical applications on light-emitting diodes. Here, we suppress the ACQ phenomena of GQDs by reducing the size and converting GQDs into aggregation-induced emission (AIE)-active materials. As the size of GQDs is reduced from 5 to 1 nm, their solid-state PL quantum yields (PLQYs) are improved from 0.5 to 2.5%, preventing ACQ. Two different rotor molecules, benzylamine (BA) and 4,4'-(1,2-diphenylethene-1,2-diyl)diphenol (TPE-DOH), are selectively functionalized by substituting carboxylic acid and carbonyl functional groups. All functionalized GQDs show AIE behaviors with significantly enhanced solid-state PLQYs, up to 16.8%. Afterglow measurements and theoretical calculations reveal that selective functionalization hinders inter- and intramolecular charge transfer, which enhances the fluorescence rate of GQDs and corresponding PLQY.

Is Graphene Shortening the Path toward Spinal Cord Regeneration?

Along with the development of the next generation of biomedical platforms, the inclusion of graphene-based materials (GBMs) into therapeutics for spinal cord injury (SCI) has potential to nourish topmost neuroprotective and neuroregenerative strategies for enhancing neural structural and physiological recovery. In the context of SCI, contemplated as one of the most convoluted challenges of modern medicine, this review first provides an overview of its characteristics and pathophysiological features. Then, the most relevant ongoing clinical trials targeting SCI, including pharmaceutical, robotics/neuromodulation, and scaffolding approaches, are introduced and discussed in sequence with the most important insights brought by GBMs into each particular topic. The current role of these nanomaterials on restoring the spinal cord microenvironment after injury is critically contextualized, while proposing future concepts and desirable outputs for graphene-based technologies aiming to reach clinical significance for SCI.

Recent Advances in Monitoring Stem Cell Status and Differentiation Using Nano-Biosensing Technologies

In regenerative medicine, cell therapies using various stem cells have received attention as an alternative to overcome the limitations of existing therapeutic methods. Clinical applications of stem cells require the identification of characteristics at the single-cell level and continuous monitoring during expansion and differentiation. In this review, we recapitulate the application of various stem cells used in regenerative medicine and the latest technological advances in monitoring the differentiation process of stem cells. Single-cell RNA sequencing capable of profiling the expression of many genes at the single-cell level provides a new opportunity to analyze stem cell heterogeneity and to specify molecular markers related to the branching of differentiation lineages. However, this method is destructive and distorted. In addition, the differentiation process of a particular cell cannot be continuously tracked. Therefore, several spectroscopic methods have been developed to overcome these limitations. In particular, the application of Raman spectroscopy to measure the intrinsic vibration spectrum of molecules has been proposed as a powerful method that enables continuous monitoring of biochemical changes in the process of the differentiation of stem cells. This review provides a comprehensive overview of current analytical methods employed for stem cell engineering and future perspectives of nano-biosensing technologies as a platform for the in situ monitoring of stem cell status and differentiation.

Graphene Quantum Dots and Their Applications in Bioimaging, Biosensing, and Therapy

Graphene quantum dots (GQDs) are carbon-based, nanoscale particles that exhibit excellent chemical, physical, and biological properties that allow them to excel in a wide range of applications in nanomedicine. The unique electronic structure of GQDs confers functional attributes onto these nanomaterials such as strong and tunable photoluminescence for use in fluorescence bioimaging and biosensing, a high loading capacity of aromatic compounds for small-molecule drug delivery, and the ability to absorb incident radiation for use in the cancer-killing techniques of photothermal and photodynamic therapy. Recent advances in the development of GQDs as novel, multifunctional biomaterials are presented with a focus on their physicochemical, electronic, magnetic, and biological properties, along with a discussion of technical progress in the synthesis of GQDs. Progress toward the application of GQDs in bioimaging, biosensing, and therapy is reviewed, along with a discussion of the current limitations and future directions of this exciting material.

Biological Potential of Polyethylene Glycol (PEG)-Functionalized Graphene Quantum Dots in In Vitro Neural Stem/Progenitor Cells

Stem cell therapy is one of the novel and prospective fields. The ability of stem cells to differentiate into different lineages makes them attractive candidates for several therapies. It is essential to understand the cell fate, distribution, and function of transplanted cells in the local microenvironment before their applications. Therefore, it is necessary to develop an accurate and reliable labeling method of stem cells for imaging techniques to track their translocation after transplantation. The graphitic quantum dots (GQDs) are selected among various stem cell labeling and tracking strategies which have high photoluminescence ability, photostability, relatively low cytotoxicity, tunable surface functional groups, and delivering capacity. Since GQDs interact easily with the cell and interfere with cell behavior through surface functional groups, an appropriate surface modification needs to be considered to get close to the ideal labeling nanoprobes. In this study, polyethylene glycol (PEG) is used to improve biocompatibility while simultaneously maintaining the photoluminescent potentials of GQDs. The biochemically inert PEG successfully covered the surface of GQDs. The PEG-GQDs composites show adequate bioimaging capabilities when internalized into neural stem/progenitor cells (NSPCs). Furthermore, the bio-inertness of the PEG-GQDs is confirmed. Herein, we introduce the PEG-GQDs as a valuable tool for stem cell labeling and tracking for biomedical therapies in the field of neural regeneration.

Graphene Oxide Quantum Dots Promote Osteogenic Differentiation of Stem Cells from Human Exfoliated Deciduous Teeth via the Wnt/β-Catenin Signaling Pathway

Graphene oxide quantum dots (GOQDs) are a carbon nanomaterial with broad potential for application in the field of nanomaterial biomedicine. Stem cells from human exfoliated deciduous teeth (SHEDs) play an important role in tissue engineering and regenerative medicine. This study investigated the effects of GOQDs on SHED osteogenic differentiation. GOQDs were synthesized; then, the proliferation of SHEDs incubated in GOQDs at different concentrations was evaluated; and the live cells were observed. We observed that live SHEDs incubated in GOQDs emitted green fluorescence in the absence of chemical dyes, and 1, 10, and 50 μg/mL GOQDs significantly promoted SHED proliferation. Culture with the osteogenic induction medium containing 10 μg/mL GOQDs induced calcium nodule formation, increased alkaline phosphatase (ALP) activity, and upregulated SHED mRNA and protein levels of OCN, RUNX2, COL I, and β-catenin. With the addition of Dickkopf 1 (DKK-1) or β-catenin knockdown, expression levels of the above mRNAs and proteins were decreased in GOQD-treated SHEDs. In summary, at a concentration of 10 μg/mL, GOQDs promote SHED proliferation and osteogenic differentiation via the Wnt/β-catenin signaling pathway. This work provides new ideas and fundamental information on interactions between GOQDs and SHEDs that are relevant for the biomedical engineering field.

Silicon Nanofluidic Membrane for Electrostatic Control of Drugs and Analytes Elution

Individualized long-term management of chronic pathologies remains an elusive goal despite recent progress in drug formulation and implantable devices. The lack of advanced systems for therapeutic administration that can be controlled and tailored based on patient needs precludes optimal management of pathologies, such as diabetes, hypertension, rheumatoid arthritis. Several triggered systems for drug delivery have been demonstrated. However, they mostly rely on continuous external stimuli, which hinder their application for long-term treatments. In this work, we investigated a silicon nanofluidic technology that incorporates a gate electrode and examined its ability to achieve reproducible control of drug release. Silicon carbide (SiC) was used to coat the membrane surface, including nanochannels, ensuring biocompatibility and chemical inertness for long-term stability for in vivo deployment. With the application of a small voltage (≤ 3 V DC) to the buried polysilicon electrode, we showed in vitro repeatable modulation of membrane permeability of two model analytes-methotrexate and quantum dots. Methotrexate is a first-line therapeutic approach for rheumatoid arthritis; quantum dots represent multi-functional nanoparticles with broad applicability from bio-labeling to targeted drug delivery. Importantly, SiC coating demonstrated optimal properties as a gate dielectric, which rendered our membrane relevant for multiple applications beyond drug delivery, such as lab on a chip and micro total analysis systems (µTAS).

Properties of differentiated SH-SY5Y grown on carbon-based materials

Neural cell differentiation has been extensively studied in two-dimensional (2D) cell culture plates. However, the cellular microenvironment and extracellular matrix (ECM) are much more complex and flat 2D surfaces are hard to mimic in ECM. Carbon nanotubes (CNTs) and graphenes are multidimensional carbon-based nanomaterials and may be able to provide extra dimensions on cell growth and differentiation. To determine the effect of CNTs and graphene surfaces on the growth, gene expression, differentiation and functionality of neuroblastoma to a neural cell, SH-SY5Y cells were grown on a 2D (control) surface, a CNT network and a graphene film. The data suggest that SH-SY5Y cells grown on CNT surfaces show an average 20.2% increase in cell viability; 5.7% decrease in the ratio of cells undergoing apoptosis; 78.3, 43.4 and 38.1% increases in SOX2, GFAP and NeuN expression, respectively; and a 29.7% increase in mean firing rate on a multi-electrode array. SH-SY5Y cells grown on graphene film show little or no changes in cell properties compared to cells grown in 2D. The data indicate that the three-dimensional (3D) surface of CNTs provides a favorable environment for SH-SY5Y cells to proliferate and differentiate to neurons.

Near-infrared-persistent luminescence/bioluminescence imaging tracking of transplanted mesenchymal stem cells in pulmonary fibrosis

A dual-labeling strategy integrating near-infrared-persistent luminescence and RfLuc-based bioluminescence imaging techniques has been developed to track the transplanted stem cells, deepening the understanding of the role played by stem cells in PF treatment.

Graphene Quantum Dots for Optical Bioimaging

Graphene quantum dots (GQDs) have shown great potential in bioimaging applications due to their excellent biocompatibility, low cytotoxicity, feasibility for surface functionalization, physiological stability, and tunable fluorescence properties. This Review first introduces the intriguing optical properties of GQDs that are suitable for biological imaging, and is followed by the GQDs' synthetic strategies. The emergent and latest development methods for tuning GQDs' optical properties are further described in detail. The recent advanced applications of GQDs in vitro, particularly in cell imaging, targeted imaging, and theranostic nanoplatform fabrication, are included. The applications of GQDs for in vivo bioimaging are also covered. Finally, the Review is concluded with the challenges and prospectives that face this nascent yet exciting field.

A brief review of cytotoxicity of nanoparticles on mesenchymal stem cells in regenerative medicine

Multipotent mesenchymal stem cells have shown great promise for application in regenerative medicine owing to their particular therapeutic effects, such as significant self-renewability, low immunogenicity, and ability to differentiate into a variety of specialized cells. However, there remain certain complicated and unavoidable problems that limit their further development and application. One of the challenges is to noninvasively monitor the delivery and biodistribution of transplanted stem cells during treatment without relying on behavioral endpoints or tissue histology, and it is important to explore the potential mechanisms to clarify how stem cells work in vivo. To solve these problems, various nanoparticles (NPs) and their corresponding imaging methods have been developed recently and have made great progress. In this review, we mainly discuss NPs used to label stem cells and their toxic effects on the latter, the imaging techniques to detect such NPs, and the current existing challenges in this field.

Strategies to improve the photocatalytic activity of TiO2: 3D nanostructuring and heterostructuring with graphitic carbon nanomaterials

TiO2-based photocatalysis has been considered to be one of the most promising avenues for environmental remediation including water purification. However, several technical issues such as the limited surface area of bulk TiO2, the large band gap of TiO2, and rapid charge recombination still limit the practical application of TiO2 photocatalysts. Therefore, here we focus on two structural design strategies: (i) monolithic three-dimensional (3D) nanostructuring, and (ii) heterostructuring with graphitic carbon nanomaterials. A monolithic 3D nanostructure enables maximal surface area in a given volume and efficient reuse of the photocatalyst without recollection. Heterostructuring with carbon nanomaterials helps achieve maximal utilization of the solar spectrum and charge separation and provides efficient TiO2 photocatalysts. In this review, recent progress on TiO2 photocatalysts toward the abovementioned strategies will be summarized. Further discussion and direction will provide insights into the rational design of highly efficient TiO2 photocatalysts, and help develop advanced photocatalyst models.

In Vivo Imaging Technology of Transplanted Stem Cells Using Quantum Dots for Regenerative Medicine

Quantum dots (QDs) have excellent fluorescence properties in comparison to traditional fluorescence probes. Thus, the optical application of QDs is rapidly expanding to each field of analytical chemistry. In this review paper, we reviewed the application of QDs to regenerative medicine, especially stem cell transplantation therapy. The labeling of stem cells using QDs composed of semiconductor materials in combination with a chemical substance, poly-cationic liposome and cell penetrating peptide is reported. In addition, the influence of QD labeling on the pluripotency of stem cells is also reported. Finally, the in vivo imaging of transplanted stem cells in mice by QDs emitting fluorescence in the near-infrared region, which can be detected by in vivo fluorescence imaging systems such as IVIS and SAI-1000, is described. The future prospects for stem cell imaging technology by QDs are also discussed.

Recent review of the effect of nanomaterials on stem cells

The field of stem-cell-therapy offers considerable promise as a means of delivering new treatments for a wide range of diseases. Recent progress in nanotechnology has stimulated the development of multifunctional nanomaterials (NMs) for stem-cell-therapy. Several clinical trials based on the use of NMs are currently underway for stem-cell-therapy purposes, such as drug/gene delivery and imaging. However, the interactions between NMs and stem cells are far from being completed, and the effects of the NMs on cellular behavior need critical evaluation. In this review, the interactions between several types of mostly used NMs and stem cells, and their associated possible mechanisms are systematically discussed, with specific emphasis on the possible differentiation effects induced by NMs. It is expected that the enhanced understanding of NM-stem cell interactions will facilitate biomaterial design for stem-cell-therapy and regenerative medicine applications.

On-chip analysis of carbon dots effect on yeast replicative lifespan

Carbon dots (CDs) are promising nanomaterials for biosensing, bioimaging, and drug delivery due to their large surface area, excellent optical properties, and thermal and chemical stability. However, biosafety of CDs is still understudied, and there is not a generally accepted standard to evaluate the toxicity of CDs. We present a gradient network generator microfluidic device for dose-dependent testing of toxicity of CDs to a unicellular eukaryotic model organism, yeast Pichia pastoris. We fully characterized the microfluidic model and compare its performance with a conventional method. The gradient generator increased the contact area between the mixing species and enabled a high-throughput testing of CDs in a wide range of concentrations in cell chambers. Real time monitoring of yeast cell proliferation in the presence of CDs showed dose-dependent growth inhibition and various budding cell shape profiles. Comparing the result of microfluidic platform and conventional method revealed statistically significant differences in the proliferation rate of the cells between the two platforms. To understand the toxicity mechanism, we studied binding of CDs to P. pastoris and found increasing interactions of CDs with the cell surface at CDs larger concentrations. This study demonstrated the utility of the gradient generator microfluidic device as a convenient tool for toxicity assessment of nanomaterials at a cellular level.

In Vivo Photoacoustic Imaging of Brain Injury and Rehabilitation by High-Efficient Near-Infrared Dye Labeled Mesenchymal Stem Cells with Enhanced Brain Barrier Permeability

Stem cell migration and interaction with pathology are critical to understand the complexity and status of disease recovery progress. However, the dynamic visualization still remains a great challenge due to imaging technical limitation, cell labeling difficulty, or blood-brain barrier (BBB). Herein, fast photoacoustic tomography (PAT) with optical molecular probes is applied to noninvasively monitor traumatic brain injury (TBI) and its rehabilitation. The vascular distribution and TBI hemorrhage are clearly imaged, longitudinally monitored, and quantified. Bone mesenchymal stem cells (BMSCs) labeled with modified Prussian blue particles (PBPs), excellent near-infrared dyes and photoacoustic contrasts, are intravenously injected to the mice for improved observation and efficient therapy. BMSCs are demonstrated to be capable of overcoming BBB with enhanced delivery of PBPs to the brain parenchyma. Notably, the versatile BMSCs are observed by PAT to home to the damage region and repair the ruptured vasculature. Moreover, the wound treated by BMSCs exhibits much faster recovery speed than that without treatment. These findings can potentially provide a new noninvasive and high-resolution approach to image TBI, monitor recovery process, and especially trace BMSCs. This study will stimulate extensive researches on brain diseases and provide promising strategies of dye labeled BMSCs in regenerative medicine.

Tuning the optical properties of graphene quantum dots for biosensing and bioimaging

This review highlights new insights into the various strategies used to tune the optical features of graphene quantum dots, and their use as attractive and powerful probes for bio-sensing/imaging.

Tracking and protection of transplanted stem cells using a ferrocenecarboxylic acid-conjugated peptide that mimics hTERT

In vivo tracking of transplanted stem cells has been a central aim of stem cell therapy. Although many tracking systems have been introduced, no method has yet been validated for clinical applications. We developed a novel sophisticated peptide (GV1001) that mimics hTERT (human telomerase reverse transcriptase) and analysed its ability to track and protect stem cells after transplantation. Ferrocenecarboxylic acid-conjugated GV1001 (Fe-GV1001) efficiently penetrated stem cells with no adverse effects. Moreover, Fe-GV1001 improved the viability, proliferation, and migration of stem cells under hypoxia. After Fe-GV1001-labelled stem cells were transplanted into the brains of rats after stroke, the labelled cells were easily tracked by MRI. Our findings indicate that Fe-GV1001 can be used for the in vivo tracking of stem cells after transplantation into the brain and can improve the efficacy of stem cell therapy by sustaining and enhancing stem cell characteristics under disease conditions.

Technical synthesis and biomedical applications of graphene quantum dots

Graphene quantum dots (GQDs) have generated enormous excitement because of their superiority in chemical inertness, biocompatibility and low toxicity. Due to quantum confinement and edge effects, GQDs have excellent properties, attracting extensive attention from scientists in the fields of chemistry, physics, materials science, biology, and other interdisciplinary sciences. In this review, we aim to present a comprehensive view on the synthesis of GQDs for biological applications. We highlight potential methods like acid oxidation, hydrothermal and solvothermal reactions, microwave-assisted methods, electrochemical oxidation, as well as pyrolysis and carbonization for the successful preparation of GQDs. Meanwhile, four representative types of biomedical application based on GQDs, bioimaging, biosensing, drug delivery, and antimicrobial materials, are introduced and discussed in detail. This work will be very useful for quickly gaining knowledge and experience for synthesizing various GQDs, and developing advanced strategies for creating novel functional GQD-based nanomaterials for further applications in biomedicine, materials science, analytical science, and optical nanodevices.

Oxygenated graphene quantum dots (GQDs) synthesized using laser ablation for long-term real-time tracking and imaging

Synthesis of graphene quantom dots for single live cell imaging andin vivofluorescence imaging.

The toxicity of graphene quantum dots

This review provides a comprehensive account on the current research status regarding the toxicity of graphene quantum dots (GQDs) – a new nano material with profound potential in various advanced applications.