Recent Advances in Graphene Quantum Dots as Bioimaging Probes

Microwave synthesis of boron- and nitrogen-codoped graphene quantum dots and their detection to pesticides and metal ions

Through developing a highly efficient solid-phase microwave-assisted (SPMA) synthesis technique, we were able to synthesize graphene quantum dots (GQDs) that were doped with nitrogen and boron atoms. The as-synthesized GQDs were employed as sensing probes for detecting pesticides and iron ions within aqueous solutions. The SPMA approach is very versatile for in-situ doping of multiple atoms within the graphitic structure of GQDs. The maximal B/C and N/C atomic ratios within the GQD structures were reached as high as 28.6 and 86.4 at.%, respectively. For the B-/N-codoped GQDs, the N dopants comprises of pyrrolic/pyridinic N and graphitic N, whereas the B doping mainly involves two bonding types (i.e., B₄C and BCO₂) inserted into or decorated on the GQD skeleton structure. Based on the analysis of the Stern-Volmer plots, the B-/N-codoped GQDs can be employed as probing nanomaterials toward Fe²⁺ and paraquat detection thanks to their incredible sensitivity throughout the photoluminescent quenching. The PL quenching mechanism of GQDs is usually governed by the GQD‒(paraquat)_x intermediates formation and the resulting π-π stacking that can easily quench and aggregate. The findings of this work pave the pathway to engineering the chemical compositions as well as the crystalline structures of GQDs, used for energy and other sensing devices.

The restructure of Au@Ag nanorods for cell imaging with dark-field microscope

The facile and noninjurious image of cells with high resolution and low toxicity is essential since imaging can offer rich and direct information and insights into metabolic activities, clinical diagnosis, drug delivery and cancer therapy. In this contribution, a smart imaging probe was employed as a contrast agent for dark-field cell imaging. Au core/Ag shell nanorods (Au@Ag NRs) that characterized by X-ray diffraction and X-ray photoelectron spectroscopy, formed Au@Ag@AgI NRs when exposed to iodine, which greatly enhanced the light scattering of nanorods. Herein, the silver shell acted as the response element for iodine as well as the protective agent for Au core. When conjugated with folate, the nanorods can be used to image human cervical cancer cells (HeLa cells) under a dark-field microscope. Nanorods were demonstrated with excellent tumor cellular uptake ability without obvious cytotoxicity, making them ideal candidates in biosensing and bioimaging applications.

Ultrasensitive, high-throughput and multiple cancer biomarkers simultaneous detection in serum based on graphene oxide quantum dots integrated microfluidic biosensing platform

Biomarkers play an important role in disease diagnosis and prognosis, which demand reliable, sensitive, rapid, and economic detection platform to conduct simultaneous multiple-biomarkers analysis in serum or body liquid. Here, we developed a universal biosensing platform through integrating the advantages of unique nanostructure and biochemistry properties of graphene oxide quantum dots and high throughput and low cost of microfluidic chip for reliable and simultaneous detection of multiple cancer antigen and antibody biomarkers. The performance of the proposed biosensing platform is validated through the representative cancer biomarkers including carcino-embryonic antigen (CEA), carbohydrate antigen 125 (CA125), α-fetoprotein (AFP), carbohydrate antigen 199 (CA199) and carbohydrate antigen 153 (CA153). It has a large linear quantification detection regime of 5-6 orders of magnitude and an ultralow detection limit of 1 pg/mL or 0.01 U/mL. Moreover, the proposed biosensing chip is capable of conducting 5-20 kinds of biomarkers from at least 60 persons simultaneously in 40 min with only 2 μL serum of each patient, which essentially reduces the detection cost and time to at least 1/60 of current popular methods. Clinical breast cancer and healthy samples detection results indicated its promising perspective in practical applications including cancer early diagnosis, prognosis, and disease pathogenesis study.

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In this research, a facile, two-step synthesis of Fe₃O₄–L_Cysteine–graphene quantum dots (GQDs) nanocomposite is reported. This synthesis method comprises the preparation of GQDs via hydrothermal route, which should be conjugated to the L_Cysteine functionalized core–shell magnetic structure with the core of about 7.5-nm iron oxide nanoparticle and 3.5-nm L_Cysteine shell. L_Cysteine, as a biocompatible natural amino acid, was used to link magnetite nanoparticles (MNPs) with GQDs. X-ray powder diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray were used to investigate the presence and formation of MNPs, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{L}}_{{{\text{Cysteine}}}}$$\end{document}LCysteine functionalized MNPs, and final hybrid nanostructure. Morphology and size distribution of nanoparticles were demonstrated by scanning electron microscopy and transmission electron microscopy. Finally, the magnetic and optical properties of the prepared nanocomposite were measured by vibrating sample magnetometer, ultraviolet–visible, and photoluminescence spectroscopy. The results show that Fe₃O₄–L_Cysteine–GQDs nanocomposite exhibits a superparamagnetic behavior at room temperature with high saturation magnetization and low magnetic coercivity, which are 28.99 emu/g and 0.09 Oe, respectively. This nanocomposite also shows strong and stable emission at 460 nm and 530 nm when it is excited with the 235 nm wavelength. The magnetic GQDs structure also reveals the absorption wavelength at 270 nm. Therefore, Fe₃O₄–L_Cysteine–GQDs nanocomposite can be considered as a potential multifunctional hybrid structure with magnetic and optical properties simultaneously. This nanocomposite can be used for a wide range of biomedical applications like magnetic resonance imaging (MRI) contrast agents, biosensors, photothermal therapy, and hyperthermia.

Preparation, biodistribution and dosimetry study of Tc-99m labeled N-doped graphene quantum dot nanoparticles as a multimodular radiolabeling agent

Preparation, dosimetry and biodistribution study of ^99mTc-(N-GQDs) as multipurpose nanoparticles.

Orange red-emitting carbon dots for enhanced colorimetric detection of Fe3+

Orange red-emitting CDs were constructed from 2,3-diaminopyridine and successfully used for visual colorimetry and near-infrared cellular imaging.

Carbon-based sustainable nanomaterials for water treatment: State-of-art and future perspectives

The supply of safe drinking and clean water is becoming increasingly challenging proposition throughout the world. The deployment of environmentally sustainable nanomaterials with unique advantages namely high efficiency and selectivity, earth-abundance, recyclability, low-cost of production processes, and stability, has been a priority although several important challenges and constraints still remained unresolved. Carbon nanomaterials namely activated carbon, multi-walled- and single-walled carbon nanotubes, have been developed and applied as adsorbents for wastewater treatment and purification; graphene and graphene oxide-based nanomaterials as well as carbon and graphene quantum dots-derived nanomaterials have shown significant promise for water and wastewater treatment and purification, especially, for industrial- and pharmaceutical-laden wastes. This review encompasses advanced carbonaceous nanomaterials and methodologies that are deployed for the elimination of contaminants and ionic metals in aqueous media, and as novel nanosorbents for wastewater, drinking and ground water treatment. Additionally, recent trends and challenges pertaining to the sustainable carbon and graphene quantum dots-derived nanomaterials and their appliances for treating and purifying wastewater are highlighted.

Exploring the role of triazole functionalized heteroatom co-doped carbon quantum dots against human coronaviruses

Preventing the trajectory of human coronaviruses including the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic could rely on the sprint to design a rational roadmap using breakneck strategies to counter its prime challenges. Recently, carbon quantum dots (CQDs), zero-dimensional (0D) carbon-based nanomaterials, have emerged as a fresh antiviral agent owing to their unique physicochemical properties. Additionally, doping instils beneficial properties in CQDs, augmenting their antiviral potential. The antiviral properties of CQDs can be reinforced by heteroatom doping. Bestowed with multifaceted features, functionalized CQDs can interact with the spike protein of the human coronaviruses and perturb the virus-host cell recognition. Recently, triazole derivatives have been explored as potent inhibitors of human coronaviruses by blocking the viral enzymes such as 3-chymotrypsin-like protease (3CLpro) and helicase, important for viral replication. Moreover, they offer a better aromatic heterocyclic core for therapeutics owing to their higher thermodynamic stability. To curb the current outbreak, triazole functionalized heteroatom co-doped carbon quantum dots (TFH-CQDs) interacting with viral cells spanning the gamut of complexity can be utilized for deciphering the mystery of its inhibitory mechanism against human coronaviruses. In this quest to unlock the potential of antiviral carbon-based nanomaterials, CQDs and triazole conjugated CQDs template comprising a series of bioisosteres, CQDs-1 to CQDs-9, can extend the arsenal of functional antiviral materials at the forefront of the war against human coronaviruses.

Electrogenerated Chemiluminescence and Electroluminescence of N-Doped Graphene Quantum Dots Fabricated from an Electrochemical Exfoliation Process in Nitrogen-Containing Electrolytes

Artificial lighting sources are one of the most important technological developments for our modern lives; the search for cost-effective and efficient luminophores is therefore crucial to a sustainable future. Graphene quantum dots (GQDs) are carbon-based nanomaterials that exhibit exceptional optical and electronic properties, making them a prime candidate for a luminophore in a light-emitting device. Nitrogen-doped GQDs fabricated from a facile top-down electrochemical exfoliation process with a nitrogen-containing electrolyte in this report showed strong photoluminescent emission at 450 nm, and electrogenerated chemiluminescence at 660 nm in the presence of benzoyl peroxide as a coreactant. When introduced into solid-state light-emitting electrochemical cells, for the first time, the GQDs displayed a broad white emission centered at 610 nm, corresponding to Commision Internationale de l'eclairage (CIE) colour coordinates of (0.38, 0.36).

Recent Advances on Graphene Quantum Dots for Bioimaging Applications

Being a zero-dimensional (0D) nanomaterial of the carbon family, graphene quantum dots (GQDs) showed promising biomedical applications owing to their ultra-small size, non-toxicity, biocompatibility, excellent photo stability, tunable fluorescence, and water solubility, etc., thus capturing a considerable attention in biomedical field. This review summarizes the recent advances made in the research field of GQDs and place special emphasis on their bioimaging applications. We briefly introduce the synthesis strategies of GQDs, including top-down and bottom-up strategies. The bioimaging applications of GQDs are also discussed in detail, including optical [fluorescence (FL)], two-photon FL, magnetic resonance imaging (MRI), and dual-modal imaging. In the end, the challenges and future prospects to advance the clinical bioimaging applications of GQDs have also been addressed.

Graphene and silicene quantum dots for nanomedical diagnostics

In the present work, the prominent effects of edge functionalization, size variation and base material on the structural, electronic and optical properties of diamond shaped graphene and silicene quantum dots are investigated. Three functional groups, namely (–CH₃, –OH and –COOH) are investigated using the first principles calculations based on the density functional, time-dependent density functional and many-body perturbation theories. Both the HOMO–LUMO energy gap, the optical absorption and the photoluminescence are clearly modulated upon functionalization compared to the H-passivated counterparts. Besides the functional group, the geometric distortion induced in some QDs also influences their optical features ranging from near ultra-violet to near infra-red. All these results indicate that edge-functionalizations provide a favorable key factor for adjusting the optoelectronic properties of quantum dots for a wide variety of nanomedical applications, including in vitro and in vivo bioimaging in medical diagnostics and therapy.

In the present work, the prominent effects of edge functionalization, size variation and base material on the structural, electronic and optical properties of diamond shaped graphene and silicene quantum dots are investigated.

Polyfluorene-Based Multicolor Fluorescent Nanoparticles Activated by Temperature for Bioimaging and Drug Delivery

Multifunctional nanoparticles have been attracting growing attention in recent years because of their capability to integrate materials with different features in one entity, which leads them to be considered as the next generation of nanomedicine. In this work, we have taken advantage of the interesting properties of conjugated polyelectrolytes to develop multicolor fluorescent nanoparticles with integrating imaging and therapeutic functionalities. With this end, thermosensitive liposomes were coated with three recently synthesized polyfluorenes: copoly-((9,9-bis(6'-N,N,N-trimethylammonium)hexyl)-2,7-(fluorene)-alt-1,4-(phenylene)) bromide (HTMA-PFP), copoly-((9,9-bis(6'-N,N,N-trimethylammonium)hexyl)-2,7-(fluorene)-alt-4,7-(2- (phenyl)benzo(d) (1,2,3) triazole)) bromide (HTMA-PFBT) and copoly-((9,9-bis(6'-N,N,N- trimethylammonium)hexyl)-2,7-(fluorene)-alt-1,4-(naphtho(2,3c)-1,2,5-thiadiazole)) bromide (HTMA-PFNT), in order to obtain blue, green and red fluorescent drug carriers, respectively. The stability, size and morphology of the nanoparticles, as well as their thermotropic behavior and photophysical properties, have been characterized by Dynamic Light Scattering (DLS), Zeta Potential, transmission electron microscope (TEM) analysis and fluorescence spectroscopy. In addition, the suitability of the nanostructures to carry and release their contents when triggered by hyperthermia has been explored by using carboxyfluorescein as a hydrophilic drug model. Finally, preliminary experiments with mammalian cells demonstrate the capability of the nanoparticles to mark and visualize cells with different colors, evidencing their potential use for imaging and therapeutic applications.