Fabrication of highly fluorescent graphene quantum dots using l-glutamic acid for in vitro/in vivo imaging and sensing

Abstract

A facile bottom-up method for the synthesis of highly fluorescent graphene quantum dots (GQDs) has been developed using a one-step pyrolysis of a natural amino acid, L-glutamic acid, with the assistance of a simple heating mantle device. The developed GQDs showed strong blue, green and red luminescence under the irradiation of ultra-violet, blue and green light, respectively. Moreover, the GQDs emitted near-infrared (NIR) fluorescence in the range of 800–850 nm with the excitation-dependent manner. This NIR fluorescence has a large Stokes shift of 455 nm, providing significant advantage for sensitive determination and imaging of biological targets. The fluorescence properties of the GQDs, such as quantum yields, fluorescence life time, and photostability, were measured and the fluorescence quantum yield was as high as 54.5 %. The morphology and composites of the GQDs were characterized using TEM, SEM, EDS, and FT-IR. The feasibility of using the GQDs as a fluorescent biomarker was investigated through in vitro and in vivo fluorescence imaging. The results showed that the GQDs could be a promising candidate for bioimaging. Most importantly, compared to the traditional quantum dots (QDs), the GQDs is chemically inert. Thus, the potential toxicity of the intrinsic heavy metal in the traditional QDs would not be a concern for GQDs. In addition, the GQDs possessed an intrinsic peroxidase-like catalytic activity that was similar to the graphene sheets and carbon nanotubes. Coupled with 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), the GQDs can be used for the sensitive detection of hydrogen peroxide with a limit of detection of 20 μM.

New Nanomaterials and Luminescent Optical Sensors for Detection of Hydrogen Peroxide

“…Upon comparing the C-dot-based detection of H2O2 (and glucose) with other methods using metallic clusters and/or QDs as probes, the proposed method seems to be more ecofriendly, has a large (0.025-50 μM) dynamic range and works at a low pH of 3. The facile one-step pyrolysis of L-glutamic acid can yield nitrogen-doped graphene quantum dots (GQDs) that are highly fluorescent and have an intrinsic peroxidase-like catalytic activity [24]. The GQDs display various fluorescence peaks the main one being at 440 nm (λexc = 360 nm) and a near-infrared fluorescence (NIR) at >800 nm depending on the excitation wavelength ( Figure 7).…”

“…However, the incubation time for the analytical reaction to proceed would need to become much shorter. The graphene QDs (GQDs) presented in [24] would also require a simultaneous supply of H2O2 and ABTS to the QDs immobilized in a sensor foil to then work as a nice continuous sensor both with photometric and luminescence detection.…”

“…After a further mixing loop, the resulting product stream would be measured via fluorescence spectroscopy. FIA-sensors could also be designed for the nanomaterials presented in [12,14,15,[20][21][22]24] if their synthesis can be easily performed and is not too expensive. The continuous feeding of the nanomaterial as required by a FIA instrument would rise the costs for continuous operation, otherwise.…”

Diethyldithiocarbamate Doped Graphene Quantum Dots Based Metal Complex Nanoparticles by Resonance Light Scattering for Green Detection of Lead (II) – A Review

“…The GQDs show a strong and excitation-independent photoluminescent activity. Xu et al, 83 reported a facile bottom-up method for the synthesis of highly fluorescent GQDs by a one-step pyrolysis of a natural amino acid, L-glutamic acid. The results showed that GQDs showed strong blue, green and red luminescence under irradiation with ultra-violet, blue and green light, respectively.…”

Recent Advances in Graphene Quantum Dots as Bioimaging Probes

“…Because of their low cost and easy availability, natural resources such as coffee grounds [100], cow milk [101,102] and neem leaf extract [103] are used to fabricate fluorescent GQDs by hydrothermal or microwave irradiation strategies. Low-cost organic compounds, such as citric acid [104][105][106][107][108][109][110][111][112], acetylacetone [113], glucose [114][115][116][117], fructose [118], ethylene diamine tetraacetic acid (EDTA) [119], adenosine 5′-triphosphate disodium salt (ATP) [119,120], glutamic acid [121] and humic acid [122], are also the most commonly used starting materials for the synthesis of GQDs either via pyrolysis or microwave irradiation or hydrothermal/solvothermal treatment. Moreover, due to their similarity in structure, polycyclic aromatic hydrocarbons are generally regarded as nanoscaled fragments of graphene, which gives them great promise for preparing monodispersed GQDs with precisely tailored structure, morphology and size.…”