Biocompatible Graphene Quantum Dots Research Articles

Multiplex Bioimaging with Near-Infrared Fluorescent Graphene Quantum Dots

Due to high tissue penetration depth and low autofluorescence backgrounds, near-infrared (NIR) fluorescence imaging has recently become an advantageous diagnostic technique used in a variety of fields. However, most of the NIR fluorophores do not have therapeutic delivery capabilities, exhibit low photostabilities, and raise toxicity concerns. To address these issues, we developed and tested five types of biocompatible graphene quantum dots (GQDs) exhibiting spectrally separated fluorescence in the NIR range of 928 – 1053 nm with NIR excitation. Their optical properties in the NIR are attributed to either rare-earth metal dopants (Ho-NGQDs, Yb-NGQDs, Nd-NGQDs) or defect-states (NGQDs, RGQDs) as verified by Hartree-Fock calculations. Moderate up to 1.34 % quantum yields of these GQDs are well-compensated by their remarkable >4-hour photostability. At the biocompatible concentrations of up to 0.5 – 2 mg/mL GQDs successfully internalize into HEK-293 cells and enable in vitro imaging in the visible and NIR. Tested all together in HEK-293 cells five GQD types enable simultaneous multiplex imaging in the NIR-I and NIR-II shown for the first time in this work for GQD platforms. Substantial photostability, spectrally-separated NIR emission, and high biocompatibility of five GQD types developed here suggest their promising potential in multianalyte testing and multiwavelength bioimaging of combination therapies.

Ultra-low level detection of biomarker bilirubin by graphene quantum dots and bovine serum albumin enabled turn-on sensing

It is known that concentration of unbound (free) bilirubin (BR) instead of the total bilirubin is the critical determinant of cellular uptake and toxicity of bilirubin. Thus, developing fast, effective and sensitive technique for detecting BR, a unique and important biomarker of liver dysfunction, has a long-standing demand. In this study, attempts were made to explore if biocompatible graphene quantum dots (GQDs) could be employed to probe BR at an ultra-low level in aqueous environment through optical techniques. Thus, understanding the possible interactions involved between GQDs and BR is important and necessary to develop protocol for probing BR. The detailed spectral analysis shows that BR molecule quenches the fluorescence of GQDs which may be attributed to a possible fluorescence resonance energy transfer (FRET) involved between the excited state of GQDs and BR. The micro-calorimetric and circular dichroic (CD) measurements have provided binding and structural information in the process of interactions. It is established that with the help of synthesized GQDs, BR can be detected as low as 0.15 nM selectively and this appears to be the most sensitive amongst other available methods. Interestingly, it is observed that the addition of bovine serum albumin (BSA) facilitates the recovery of the BR-induced loss in fluorescence intensity of GQDs. The adopted strategy demonstrates that GQD may act as a sensitive fluorescent “turn off–on” probe for detection of BR. The proposed optical method based protocol validated with serum samples isolated from blood for rapid detection of BR at ultra-low level may help in developing a suitable sensing device in future.

Graphene quantum dots enhance the biological nitrogen fixation by up-regulation of cellular metabolism and electron transport

Graphene quantum dots (GQDs) are useful nanomaterials of excellent water solubility, biocompatibility and optical stability for various applications. In this study, we achieved the nitrogen fixation activity enhancement of autogenous azotobacters (Azotobacter vinelandii) by GQDs and revealed its mechanism. GQDs (1–10 mg/L) accelerated the logarithmic growth phase of A. vinelandii, making bacteria enter the plateau earlier. Biocompatible GQDs did not cause cell death and oxidative damage of A. vinelandii. The expression levels of metabolism and nitrogen fixation related genes were significantly up-regulated by GQDs, thereby enhancing the activity of nitrogenase. The nitrogen fixation activity of A. vinelandii reached 471.7 % of the control upon the exposure to GQDs. The intracellular polyhydroxyalkanoate vesicles were consumed to provide energy for nitrogen fixation, which involved with a chain reaction of carbohydrate metabolism, lipid metabolism, and energy metabolism pathways accompanied by significant increases in electron transfer rate. The synergistic effect of GQDs on A. vinelandii further facilitated the augmentation of soil nitrogen content in Qinghai-Tibet Plateau. Our results provided an effective approach to enhance the biological nitrogen fixation by GQDs.

Five near-infrared-emissive graphene quantum dots for multiplex bioimaging

Due to high tissue penetration depth and low autofluorescence backgrounds, near-infrared (NIR) fluorescence imaging has recently become an advantageous diagnostic technique used in a variety of fields. However, most of the NIR fluorophores do not have therapeutic delivery capabilities, exhibit low photostabilities, and raise toxicity concerns. To address these issues, we developed and tested five types of biocompatible graphene quantum dots (GQDs) exhibiting spectrally-separated fluorescence in the NIR range of 928–1053 nm with NIR excitation. Their optical properties in the NIR are attributed to either rare-earth metal dopants (Ho-NGQDs, Yb-NGQDs, Nd-NGQDs) or defect-states (nitrogen doped GQDS (NGQDs), reduced graphene oxides) as verified by Hartree-Fock calculations. Moderate up to 1.34% quantum yields of these GQDs are well-compensated by their remarkable >4 h photostability. At the biocompatible concentrations of up to 0.5–2 mg ml−1 GQDs successfully internalize into HEK-293 cells and enable in vitro imaging in the visible and NIR. Tested all together in HEK-293 cells five GQD types enable simultaneous multiplex imaging in the NIR-I and NIR-II shown for the first time in this work for GQD platforms. Substantial photostability, spectrally-separated NIR emission, and high biocompatibility of five GQD types developed here suggest their promising potential in multianalyte testing and multiwavelength bioimaging of combination therapies.

Enhanced in vivo antiviral activity against pseudorabies virus through transforming gallic acid into graphene quantum dots with stimulation of interferon-related immune responses.

With the urgent need for antiviral agents, antiviral materials with high biocompatibility and antiviral effects have attracted a lot of attention. In this study, gallic acid, a natural polyphenolic compound, was transformed into biocompatible graphene quantum dots (GAGQDs) which exhibit enhanced antiviral activity against pseudorabies virus (PRV). The as-prepared GAGQDs inhibit PRV proliferation with a 104-fold reduction in viral titers. Investigation of the antiviral mechanism revealed that GAGQDs inhibit the adsorption, invasion and replication of PRV infection. Treatment with GAGQDs regulates the expression levels of interferon-related antiviral proteins, including mitochondrial antiviral-signaling protein (MAVS), signal transducer and activator of transcription 1 (STAT1) and 2',5'-oligoadenylate synthetase 1 (OAS1), suggesting that GAGQDs can stimulate innate antiviral immune responses, resulting in enhanced antiviral effects. More importantly, GAGQD treatments alleviate clinical symptoms and reduce mortality in PRV-infected mice. Our results reveal the enhanced therapeutic effects of GAGQDs against PRV infection in vitro and in vivo, suggesting the potential of GAGQDs as a promising novel antiviral agent.

Doped Graphene Quantum Dots as Biocompatible Radical Scavenging Agents.

Oxidative stress is proven to be a leading factor in a multitude of adverse conditions, from Alzheimer's disease to cancer. Thus, developing effective radical scavenging agents to eliminate reactive oxygen species (ROS) driving many oxidative processes has become critical. In addition to conventional antioxidants, nanoscale structures and metal-organic complexes have recently shown promising potential for radical scavenging. To design an optimal nanoscale ROS scavenging agent, we have synthesized ten types of biocompatible graphene quantum dots (GQDs) augmented with various metal dopants. The radical scavenging abilities of these novel metal-doped GQD structures were, for the first time, assessed via the DPPH, KMnO4, and RHB (Rhodamine B protectant) assays. While all metal-doped GQDs consistently demonstrate antioxidant properties higher than the undoped cores, aluminum-doped GQDs exhibit 60-95% radical scavenging ability of ascorbic acid positive control. Tm-doped GQDs match the radical scavenging properties of ascorbic acid in the KMnO4 assay. All doped GQD structures possess fluorescence imaging capabilities that enable their tracking in vitro, ensuring their successful cellular internalization. Given such multifunctionality, biocompatible doped GQD antioxidants can become prospective candidates for multimodal therapeutics, including the reduction of ROS with concomitant imaging and therapeutic delivery to cancer tumors.

Antioxidative and Photo-Induced Effects of Different Types of N-Doped Graphene Quantum Dots.

Due to the increasing number of bacterial infections and the development of resistivity toward antibiotics, new materials and approaches for treatments must be urgently developed. The production of new materials should be ecologically friendly considering overall pollution with chemicals and economically acceptable and accessible to the wide population. Thus, the possibility of using biocompatible graphene quantum dots (GQDs) as an agent in photodynamic therapy was studied. First, dots were obtained using electrochemical cutting of graphite. In only one synthetic step using gamma irradiation, GQDs were doped with N atoms without any reagent. Obtained dots showed blue photoluminescence, with a diameter of 19–89 nm and optical band gap of 3.23–4.73 eV, featuring oxygen-containing, amino, and amide functional groups. Dots showed antioxidative activity; they quenched •OH at a concentration of 10 μg·mL−1, scavenged DPPH• radicals even at 5 μg·mL−1, and caused discoloration of KMnO4 at 30 μg·mL−1. Under light irradiation, dots were able to produce singlet oxygen, which remained stable for 10 min. Photoinduced effects by GQDs were studied on several bacterial strains (Listeria monocytogenes, Bacillus cereus, clinical strains of Streptococcus mutans, S. pyogenes, and S. sangunis, Pseudomonas aeruginosa, and one yeast strain Candida albicans) but antibacterial effects were not noticed.

Photoluminescence Brightening of Single-Walled Carbon Nanotubes Using Graphene Quantum Dots

Single-walled carbon nanotubes (SWCNTs) emit near-infrared (NIR) photoluminescence (PL) that spans the tissue transparency window, allowing them to optically penetrate biological tissue for deep-tissue optical sensing. Such optical SWCNT sensors are often functionalized with single stranded DNA (ssDNA) to promote biocompatibility, responsivity, and selectivity. However, the low brightness of these ssDNA-wrapped sensors restricts the depth at which such sensors can be implanted in biological tissue. In this work, we overcome this limitation by demonstrating the PL enhancement of ssDNA-wrapped SWCNTs through the incorporation of biocompatible graphene quantum dots (GQDs). We compare the enhancement effects of two preparations of GQDs, pristine (PGQDs) and nitrogen-doped (NGQDs) graphene quantum dots. Both preparations of GQDs were shown to significantly increase the fluorescence emissions of ssDNA-SWCNTs to a comparable extent after 3 h of incubation. We further observed a diameter dependence of this enhancement, with the larger (8,6) SWCNT chirality demonstrating a 30-fold enhancement as compared to the 2-fold enhancement observed for the (6,5) SWCNT chirality. This PL enhancement was shown to vary with the exposed surface area of the SWCNTs, whereby SWCNT chiralities with wrappings that yield larger exposed SWCNT surfaces resulted in increased PL enhancement on conjugation with the GQDs.Despite the similarities in the final fluorescence enhancements, the NGQDs and PGQDs showed kinetic differences in their brightening effects. The NGQDs were able to achieve stabilized SWCNT fluorescence brightening 2 min after their addition, whereas the SWCNTs showed continued PL increases even 1 h after the addition of the PGQDs. Electrochemical analysis of the NGQDs confirms their behavior as reducing agents, which have been previously shown to enhance the rate of SWCNT brightening through the passivation of oxygen defect sites. The brightening effects of the NGQDs were further demonstrated in confocal single-molecule measurements, where we observed a 3-fold increase in the detection of individual SWCNTs on conjugation to the NGQDs compared to the unconjugated ssDNA-SWCNTs. The photoluminescence enhancements enabled by the GQDs thus provides a promising tool for engineering the brightness of NIR sensors for biomedical applications and enabling improved detection in deep-tissue sensing and imaging applications.

TRAIL/S-layer/graphene quantum dot nanohybrid enhanced stability and anticancer activity of TRAIL on colon cancer cells

Tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL), known as a cytokine of the TNF superfamily, is considered a promising antitumor agent due to its ability to selectively induce apoptosis in a wide variety of cancer cells. However, failure of its successful translation into clinic has led to development of nano-based platforms aiming to improve TRAIL therapeutic efficacy. In this regard, we fabricated a novel TRAIL-S-layer fusion protein (S-TRAIL) conjugated with graphene quantum dots (GQDs) to benefit both the self-assembly of S-layer proteins, which leads to elevated TRAIL functional stability, and unique optical properties of GQDs. Noncovalent conjugation of biocompatible GQDs and soluble fusion protein was verified via UV–visible and fluorescence spectroscopy, size and ζ-potential measurements and transmission electron microscopy. The potential anticancer efficacy of the nanohybrid system on intrinsically resistant cells to TRAIL (HT-29 human colon carcinoma cells) was investigated by MTT assay and flow cytometry, which indicated about 80% apoptosis in cancer cells. These results highlight the potential of TRAIL as a therapeutic protein that can be extensively improved by taking advantage of nanotechnology and introduce S-TRAIL/GQD complex as a promising nanohybrid system in cancer treatment.

Graphene Quantum Dots for Fluorescent Labeling of Gelatin‐Based Shear‐Thinning Hydrogels

Injectable Biomaterials In article number 2000113, Ali Khademhosseini, Samad Ahadian, and co-workers use biocompatible graphene quantum dots for imaging a physically crosslinked and injectable shear-thinning biomaterial of gelatin hydrogel and silicate nanoplatelets. The biomaterial shows a robust and stable fluorescence signal in vitro and in animal models, suggesting a great potential in long-term tracking and non-invasive monitoring of the biomaterial in therapeutic applications.

Rare‐Earth Metal Ions Doped Graphene Quantum Dots for Near‐IR In Vitro/In Vivo/Ex Vivo Imaging Applications

AbstractNear‐infrared (NIR) emitting biocompatible nanomaterials are desired in biotechnology as higher penetration depth fluorescence imaging probes. In this work, novel NIR‐emissive Nd3+‐doped or Tm3+‐doped biocompatible graphene quantum dots (GQDs) are developed via scalable, single‐step bottom‐up synthesis. Water‐soluble Nd‐GQDs/Tm‐GQDs with average diameters of 5.6–8.2 nm possess crystalline graphene lattice with <1 atomic percent of Nd/Tm and exhibit NIR fluorescence at ≈1060/≈925 nm attributed to the intrinsic transitions of Nd3+/Tm3+. High biocompatibility with >80% cell viability at 1 mg mL−1 for Nd‐GQDs and 0.25 mg mL−1 for Tm‐GQDs makes them well‐suited for bioimaging. In vitro, both GQD types exhibit efficient internalization with their intracellular emission maximized at 6 h. The pH‐dependence of this emission can serve as plethora of diagnostic applications. GQDs enable in vivo NIR imaging in live sedated NCr nude mice with IV administration: their NIR emission maximized at 6 h post‐injection is primarily detected in intestine, kidneys, liver, and spleen, however, diminishing to none at 48 h. Ex vivo organ/slice imaging shows significant Tm‐GQD fluorescence signatures in the aforementioned organs/slices. This capability of NIR fluorescence imaging in cells, tissues, and real‐time detection in live animals makes biocompatible rare‐earth metal‐doped GQDs an attractive new candidate for in vitro/in vivo/ex vivo theranostics.

Highly biocompatible graphene quantum dots: green synthesis, toxicity comparison and fluorescence imaging

Graphene quantum dots (GQDs) have tremendous potential in biological imaging due to their bright visible photoluminescence mission. However, the tedious preparation procedures and potential toxicity of GQDs greatly limit their application in biological field. Here, highly biocompatible GQDs (HGQDs) have been successfully prepared only by glucose in aqueous solution. Compared with GQDs prepared from conventional methods (CGQDs), the cytotoxicity of HGQDs reduced by more than 60%, and the flow cytometric analysis of the normal cells treated with HGQDs showed that the early and late apoptotic rate reduced by more than 72% and 40%, respectively. In vitro fluorescence imaging showed that both cells and bacteria could be imaged by HGQDs, and the morphology of cells and bacteria could be kept to a maximum extent. A long-term in vivo study revealed that no obvious organ (heart, liver, spleen, lung and kidney) damage or lesions were observed, and the blood–brain barrier (BBB) could be overcome, which provides the possibility for treatment and diagnosis of brain-related diseases. With adequate studies of biocompatibility, both in vitro and in vivo, HGQDs may be considered for further biological application.

Preparation and investigation of the heat transfer properties of a novel nanofluid based on graphene quantum dots

In the present research, the biocompatible graphene quantum dots were used to prepare heat transfer nanofluids for the first time. Graphene quantum dots are a new generation of carbon nanoparticles capable of being synthesized from biodegradable and non-toxic resources. In this research, graphene quantum dots were produced by hydrothermal method using citric acid and urea as precursor. Nanofluid samples were synthesized based on car radiator coolant and graphene quantum dots at very low concentrations including 100, 200, 500, and 1000ppm. One of the advantages of the graphene quantum dots was their long-term stability within the base fluid without using any chemical surfactants. In order to investigate the nanofluids’ heat transfer properties, thermal conductivity (k) and convection heat transfer (h) coefficients of the samples were measured. The results for 100ppm concentration indicated 5.2% and 17% improvement of k and h, compared to the base fluid, respectively. Further, the results demonstrated that the nanofluids containing graphene quantum dots had better stability and performance at low concentrations. Thus, it can be concluded that heat transfer nanofluids based on graphene quantum dots not only reduce probable environmental risks, but also are economically appropriate options for industrial applications; leading to reducing the energy consumption.

A fluorescent nanosensor based on graphene quantum dots–aptamer probe and graphene oxide platform for detection of lead (II) ion

The sensitive detection of heavy metal ions in the organism and aquatic ecosystem using nanosensors based on environment friendly and biocompatible materials still remains a challenge. A fluorescent turn-on nanosensor for lead (II) detection based on biocompatible graphene quantum dots and graphene oxide by employment of Pb2+-induced G-quadruplex formation was reported. Graphene quantum dots with high quantum yield, good biocompatibility were prepared and served as the fluorophore of Pb2+ probe. Fluorescence turn-off of graphene quantum dots is easily achieved through efficient photoinduced electron transfer between graphene quantum dots and graphene oxide, and subsequent fluorescence turn-on process is due to the formation of G-quadraplex aptamer–Pb2+ complex triggered by the addition of Pb2+. This nanosensor can distinguish Pb2+ ion from other ions with high sensitivity and good reproducibility. The detection method based on this nanosensor possesses a fast response time of one minute, a broad linear span of up to 400.0nM and ultralow detection limit of 0.6nM.

Simultaneous Detection of Multiple DNA Targets by Integrating Dual‐Color Graphene Quantum Dot Nanoprobes and Carbon Nanotubes

Simultaneous detection of multiple DNA targets was achieved based on a biocompatible graphene quantum dots (GQDs) and carbon nanotubes (CNTs) platform through spontaneous assembly between dual-color GQD-based probes and CNTs and subsequently self-recognition between DNA probes and targets.

DNA nanosensor based on biocompatible graphene quantum dots and carbon nanotubes

An ultrasensitive nanosensor based on fluorescence resonance energy transfer (FRET) between biocompatible graphene quantum dots and carbon nanotubes for DNA detection was reported. We take advantage of good biocompatibility and strong fluorescence of graphene quantum dots, base pairing specificity of DNA and unique fluorescence resonance energy transfer between graphene quantum dots and carbon nanotubes to achieve the analysis of low concentrations of DNA. Graphene quantum dots with high quantum yield up to 0.20 were prepared and served as the fluorophore of DNA probe. FRET process between graphene quantum dots-labeled probe and oxidized carbon nanotubes is easily achieved due to their efficient self-assembly through specific π–π interaction. This nanosensor can distinguish complementary and mismatched nucleic acid sequences with high sensitivity and good reproducibility. The detection method based on this nanosensor possesses a broad linear span of up to 133.0nM and ultralow detection limit of 0.4nM. The constructed nanosensor is expected to be highly biocompatible because of all its components with excellent biocompatibility.

A universal fluorescence sensing strategy based on biocompatible graphene quantum dots and graphene oxide for the detection of DNA.

A novel and efficient fluorescence sensing platform based on biocompatible graphene quantum dots and graphene oxide was established. It showed high selectivity and sensitivity for DNA detection.