Graphene quantum dots: synthesis, properties, and applications to the development of optical and electrochemical sensors for chemical sensing

Box-Behnken design optimization of a green fluorescence sensor based on S,N-Doped graphene quantum dots for glimepiride determination in pharmaceuticals and biological samples

In this study, a fluorescent sensor based on sulfur and nitrogen co-doped graphene quantum dots (S,N-GQDs) was developed for the determination of glimepiride in pharmaceutical formulations and spiked human plasma. The spectral characteristics of the sensor were investigated revealing a blue fluorescence emission at 431 nm upon excitation at 362 nm. Stern-Volmer analysis indicated that the quenching of the sensor's fluorescence by glimepiride followed a static quenching mechanism, which was supported by thermodynamic studies. A Box-Behnken experimental design was employed to optimize the factors affecting the quenching process, including pH, buffer volume, S,N-GQDs concentration and incubation time. A quadratic model was obtained, and the optimum conditions were determined. The sensor exhibited a linear response to glimepiride in the range of 0.5-4.0 μg/mL with a limit of detection (LOD) of 0.078 μg/mL. The developed method was validated according to ICH guidelines and successfully applied for the determination of glimepiride in pharmaceutical formulations and spiked human plasma samples. Additionally, the greenness and blueness of the method was evaluated using the AGREE and BAGI metrics revealing a high level of environmental friendliness and analytical practicability posing the developed sensor as a sustainable analytical tool.

Recent Progress of Fluorescent Carbon Dots and Graphene Quantum Dots for Biosensors: Synthesis of Solution Methods and their Medical Applications

In the fields of health and biology, fluorescent nanomaterials have emerged as highly potential and very useful candidates for use in biosensor applications. These typical highly powerful nanomaterials are carbon dots (CDs) and graphene quantum dots (GQDs) among many other metallic nanomaterials. In the context of medical biosensors, this review article investigates the techniques of synthesis, and many uses of these nanomaterials, the obstacles that they face, and the potential for their future. We cover the significance of fluorescent nanomaterials, their use in the medical field, as well as the several techniques of synthesis for CDs and GQDs, including ultrasonication, hydrothermal, electrochemical method, surface modification, and solvothermal. In addition, we also discuss their biomedical applications, which include biomolecule detection, disease diagnosis and examine the obstacles and prospective possibilities for development of ultra-bright, ultra-sensitive, and selective biosensors for use in in-vivo research.Fluorescent carbon dots and graphene quantum dots is synthesized by using several types of raw material and methods. These Carbon dots and graphene quantum dots are used in the medical field includes detection of biomaterials, detection of cancer, virus and mutation in DNA.

Quantum dot-based non-volatile memory: a comprehensive outlook

With the rise of digital technology, the use of memory devices is swiftly expanding, and this trend is expected to continue in the forthcoming years. Accordingly, researchers are exploring materials that surpass the performance of those used in traditional memory devices, and notably, there is a considerable interest in quantum dots (QDs). This is primarily due to the fact that quantum dots possess exceptional optical and electric properties. As a result, they have become appealing materials to enhance the performance of non-volatile memory devices. In this review, we outlined the various approaches employed for the synthesis of quantum dots as well as different types of quantum dots used for prototyping different non-volatile memory technologies and their current perspective. Additionally, we compared various key parameters, such as the ON/OFF ratio, retention time, memory window, charge trapping capacity, and multiple voltage levels, of these QD-based memories together with future outlook.

Graphene and its modifications for enhanced adhesion in dental restoratives: a molecular docking and dynamics study

Graphene has attracted significant attention in dentistry due to its structural and adhesive properties, enhancing the mechanical performance of dental composites. This study investigates the behavior and interaction of monomers and graphene-based adhesives using molecular docking and molecular dynamics (MD) simulations. Binding energies and interactions between monomers and graphene derivatives were assessed using molecular docking, while MD simulations with the Forcite module and COMPASS II force field provided insights into the mechanical properties of the composites. The simulations involved energy minimization, NVT/NPT ensembles, and equilibration for 50 ns. The binding energies of the monomer-graphene complexes ranged from - 16.27 to -18.55 kcal/mol, with the Bis-GMA-Graphene Quantum Dot complex showing the most stable interaction. Mechanical properties such as Young's modulus, shear modulus, and flexural strength were calculated for selected complexes: Bis-GMA-Graphene Quantum Dot (14.74 GPa, 9.32 GPa, 120.51 MPa), EBPADMA-Graphene Quantum Dot (14.28 GPa, 9.13 GPa, 118.22 MPa), HEMA-Nitrogen-doped Graphene (9.85 GPa, 6.86 GPa, 95.7 MPa), TEGDMA-Graphene Oxide (11.96 GPa, 8.12 GPa, 110.23 MPa), and UDMA-CCOOH Functionalized Graphene (13.82 GPa, 8.43 GPa, 115.4 MPa). The Bis-GMA-Graphene Quantum Dot complex showed the highest stability with 20 hydrogen bonds. These results highlight graphene quantum dots and functionalized graphene derivatives as promising candidates for high-performance dental composites, offering strong adhesive properties and improved mechanical strength. Future research may focus on further optimizing these interactions and exploring additional graphene modifications.

Synergistic Interactions of Metals and Quantum Dots: Expanding Frontiers in Fluorescent Sensing

Fluorescent sensing technologies have emerged as powerful tools in analytical science, offering exceptional sensitivity and selectivity for detecting a wide range of analytes. Among the advanced materials driving these technologies, quantum dots (QDs) and metal nanoparticles (MNPs) stand out due to their unique optical and electronic properties. When combined, these materials exhibit synergistic interactions those significantly enhance the fluorescence signals, enable efficient quenching, and offer tunable optical properties. This review explores the various protocols involved in the development, characterization, and performance evaluation of metal-QD composites; typically, metal-enhanced fluorescence (MEF) and Förster resonance energy transfer (FRET). The applications of the materials in the domain of biomedical diagnostics, environmental monitoring, and biosensing have been highlighted. The review also discusses the current challenges and future scope in the field of metal-QD-based fluorescent sensors and their possible transformative impact on next-generation sensing technologies.

An Aptamer Sensor Based on Alendronic Acid-Modified Upconversion Nanoparticles Combined with Magnetic Separation for Rapid and Sensitive Detection of Thiamethoxam

The widespread use of thiamethoxam has led to pesticide residues that have sparked global concerns regarding ecological and human health risks. A pressing requirement exists for a detection method that is both swift and sensitive. Herein, we introduced an innovative fluorescence biosensor constructed from alendronic acid (ADA)-modified upconversion nanoparticles (UCNPs) linked with magnetic nanoparticles (MNPs) via aptamer recognition for the detection of thiamethoxam. Through base pairing, thiamethoxam-specific aptamer-functionalized MNPs (apt-MNPs) were integrated with complementary DNA-functionalized UCNPs (cDNA-UCNPs) to create the MNPs@UCNPs fluorescence biosensor. Thiamethoxam specifically attached to apt-MNPs, leading to their separation from cDNA-UCNPs, which in turn led to a reduction in fluorescence intensity at 544 nm following separation by an external magnetic field. The change in fluorescence intensity (ΔI) was directly correlated with the concentration of thiamethoxam, enabling the quantitative analysis of the pesticide. With optimized detection parameters, the biosensor was capable of quantifying thiamethoxam within a concentration span of 0.4-102.4 ng·mL-1, and it achieved a detection limit as minute as 0.08 ng·mL-1. Moreover, leveraging the swift magnetic concentration properties of MNPs, the assay duration could be abbreviated to 25 min. The research exhibited a swift and precise sensing platform that yielded promising results in samples of cucumber, cabbage, and apple.

Harnessing the Potential of Graphene Quantum Dots for Multifunctional Biomedical Applications

The existing and emerging demand for materials for life and health has contributed to the cultivation and development of respective markets. Nevertheless, the current generation of biomedical materials has yet to fully satisfy the clinical requirements of the market, which is still in its relative infancy. Research and development in this area must be prioritized in light of the pivotal role of new life and health materials in the biological field. Among many life and health materials, GQDs, an emerging nanomaterial, exhibit considerable promise in the biomedical field, primarily due to their exceptional properties. Furthermore, the direct preparation and functionalization of GQDs have facilitated the development of specific functional composites based on GQDs. The biological applications of GQDs are undergoing rapid growth, which makes it necessary to publish a review article presenting the latest advances in this field. This review provides an overview of the significant advances in synthesizing GQDs, the techniques employed for structural characterizations, and the properties that have been elucidated. Furthermore, it presents recent findings on applying GQDs in antimicrobial, anticancer, biosensing, drug delivery, and bioimaging applications. Finally, it explores the potential of GQDs in biomedicine and biotechnology, highlighting the current challenges that remain to be addressed.

Sensitive electrochemical detection of methimazole based on a unique copper and exfoliated graphene oxide nanocomposite

Herein, we report the creation of a novel sensitive electrochemical sensing platform based on a copper and exfoliated graphene oxide (Cu-eGO) nanocomposite using a facile synthesis technique, which simultaneously removes the sodium ions that result from the exfoliation process to generate eGO from graphite. This novel Cu-eGO nanocomposite was characterized via SEM, EDX, Raman and XPS. The Cu-eGO/GCE exhibited much greater activity for the electrochemical oxidation of methimazole than the eGO/GCE or bare GCE. The electrochemical properties and kinetics involved in the oxidation of methimazole at the Cu-eGO were examined using voltammetry and electrochemical impedance spectroscopy (EIS). This Cu-eGO based sensing platform demonstrated high sensitivity at 1.32 μAμM-1cm-2, a low limit of detection at 0.06 μM, robust stability, and strong anti-interference against potential interferents that may exist in biological systems for the detection of methimazole. The developed electrochemical sensor was successfully employed in blood serum samples that mimicked real biological environments, showing its high applicability.

Uricase biofunctionalized plasmonic sensor for uric acid detection with APTES-modified gold nanotopping

Current uric acid detection methodologies lack the requisite sensitivity and selectivity for point-of-care applications. Plasmonic sensors, while promising, demand refinement for improved performance. This work introduces a biofunctionalized sensor predicated on surface plasmon resonance to quantify uric acid within physiologically relevant concentration ranges. The sensor employs the covalent immobilization of uricase enzyme using 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-Hydroxysuccinimide (NHS) crosslinking agents, ensuring the durable adherence of the enzyme onto the sensor probe. Characterization through atomic force microscopy and Fourier transform infrared spectroscopy validate surface alterations. The Langmuir adsorption isotherm model elucidates binding kinetics, revealing a sensor binding affinity of 298.83 (mg/dL)-1, and a maximum adsorption capacity of approximately 1.0751°. The biofunctionalized sensor exhibits a sensitivity of 0.0755°/(mg/dL), a linear correlation coefficient of 0.8313, and a limit of detection of 0.095 mg/dL. Selectivity tests against potentially competing interferents like glucose, ascorbic acid, urea, D-cystine, and creatinine showcase a significant resonance angle shift of 1.1135° for uric acid compared to 0.1853° for interferents at the same concentration. Significantly, at a low uric acid concentration of 0.5 mg/dL, a distinct shift of 0.3706° was observed, setting it apart from the lower values noticed at higher concentrations for all typical interferent samples. The uricase enzyme significantly enhances plasmonic sensors for uric acid detection, showcasing a seamless integration of optical principles and biological recognition elements. These sensors hold promise as vital tools in clinical and point-of-care settings, offering transformative potential in biosensing technologies and the potential to revolutionize healthcare outcomes in biomedicine.

A minireview on the utilization of petroleum coke as a precursor for carbon-based nanomaterials (CNMs): perspectives and potential applications

The remarkable properties of carbon-based nanomaterials (CNMs) have stimulated a significant increase in studies on different 0D, 1D and 2D nanostructures, which have promising applications in various fields of science and technology. However, the use of graphite as a raw material, which is essential for their production, limits the scalability of these nanostructures. In this context, petroleum coke (PC), a by-product of the coking process in petrochemical industry with a high carbon content (>80 wt%), is emerging as an attractive and low-cost option for the synthesis of carbonaceous nanostructures. This brief review presents recent research related to the use of PC as a precursor for CNMs, such as graphene and its oxidized (GO) and reduced (RGO) variants, among other carbon-based nanostructures. The work highlights the performance of these materials in specific areas of application. In addition, this review describes and analyzes strategies for transforming low-cost, environmentally friendly waste into advanced technological innovations with greater added value, in line with the UN's 2030 Agenda.

Graphene quantum dots for biosensing and bioimaging

Graphene Quantum Dots (GQDs) are low dimensional carbon based materials with interesting physical, chemical and biological properties that enable their applications in numerous fields. GQDs possess unique electronic structures that impart special functional attributes such as tunable optical/electrical properties in addition to heteroatom-doping and more importantly a propensity for surface functionalization for applications in biosensing and bioimaging. Herein, we review the recent advancements in the top-down and bottom-up approaches for the synthesis of GQDs. Following this, we present a detailed review of the various surface properties of GQDs and their applications in bioimaging and biosensing. GQDs have been used for fluorescence imaging for visualizing tumours and monitoring the therapeutic responses in addition to magnetic resonance imaging applications. Similarly, the photoluminescence based biosensing applications of GQDs for the detection of hydrogen peroxide, micro RNA, DNA, horse radish peroxidase, heavy metal ions, negatively charged ions, cardiac troponin, etc. are discussed in this review. Finally, we conclude the review with a discussion on future prospects.

Challenges for Field-Effect-Transistor-Based Graphene Biosensors

Owing to its outstanding physical properties, graphene has attracted attention as a promising biosensor material. Field-effect-transistor (FET)-based biosensors are particularly promising because of their high sensitivity that is achieved through the high carrier mobility of graphene. However, graphene-FET biosensors have not yet reached widespread practical applications owing to several problems. In this review, the authors focus on graphene-FET biosensors and discuss their advantages, the challenges to their development, and the solutions to the challenges. The problem of Debye screening, in which the surface charges of the detection target are shielded and undetectable, can be solved by using small-molecule receptors and their deformations and by using enzyme reaction products. To address the complexity of sample components and the detection mechanisms of graphene-FET biosensors, the authors outline measures against nonspecific adsorption and the remaining problems related to the detection mechanism itself. The authors also introduce a solution with which the molecular species that can reach the sensor surfaces are limited. Finally, the authors present multifaceted approaches to the sensor surfaces that provide much information to corroborate the results of electrical measurements. The measures and solutions introduced bring us closer to the practical realization of stable biosensors utilizing the superior characteristics of graphene.

Detection of mcr-1-harbouring Escherichia coli by quantum dot labelling of synthetic small peptides mimicking lipopolysaccharide receptors

Overuse of antibiotics and the emergence of multidrug-resistant bacteria has made colistin the last line of defence against complex infections. In previous studies, MCR-1-mediated colistin resistance was mainly detected through PCR or antimicrobial susceptibility testing. However, intuitive detection methods for phenotype are rarely reported. In this study, two small peptide antibodies were constructed for immunofluorescence detection of mcr-1-harbouring Escherichia coli: one was a small peptide labelled with a quantum dot antibody; and the other was a small peptide labelled with a fluorescein isothiocyanate (FITC) antibody. Whether using FITC or quantum dots, colistin-resistant bacteria in the sample could be qualitatively detected. The assembled antibodies achieved the desired goals in terms of sensitivity, specificity, precision and repeatability. The non-specific problem of sandwich antigen recognition of lipid A binding to small peptides in modified lipopolysaccharide (LPS) was resolved, and this relatively developed immunofluorescence technique standardised the detection process. Together, in addition to PCR, both fluorescent antibodies can be used for immunofluorescent detection of mcr-1-harbouring E. coli.

Sustainable Preparation of Graphene Quantum Dots from Leaves of Date Palm Tree

The date palm (Phoenix dactylifera), a subtropical and tropical tree, included in the family Palmae (Arecaceae) is one of the oldest cultivated plants of mankind. Date palm is a major agricultural product in the semi-arid and arid areas of the world, particularly in Arab countries. These trees generate high quantities of agricultural waste in the form of dry leaves, seeds, etc. In this study, dried date palm leaves were used as green precursors for synthesizing graphene quantum dots (GQDs). This work reported the preparation of GQDs using two different sustainable methods. GQD-1 was developed using a simple, hydrothermal technique at 200 °C for 12 h in water, with no requirement of reducing or passivizing agents or organic solvents. GQD-2 was prepared using a hydrothermal technique at 200 °C for 12 h in water, with the usage of just distilled water and absolute ethanol. The compositional analysis of the leaf extract was performed, along with the morphological, compositional, and optical examination of the sustainably developed GQDs. The characterization results confirmed the successful formation of GQDs, with average sizes ranging from 3.5 to 8 nm. This study helps to obtain GQDs in an economical, eco-friendly, and biocompatible manner and can assist in large-scale production and in recycling date palm tree waste products from Middle East countries into value-added products.

Insights into engineered graphitic carbon nitride quantum dots for hazardous contaminants degradation in wastewater

Increased environmental pollution is a critical issue that must be addressed. Photocatalytic, adsorption, and membrane filtration methods are suitable in environmental governance because of their high selectivity, low cost, environment-friendly nature, and excellent treatment efficiency. Graphitic carbon nitride (g-C₃N₄) quantum dots (QDs) have been considered as photocatalysts, adsorbents, and membrane materials for wastewater treatments, owing to their stability, adsorption capacity, photochemical properties, and low toxicity and cost. This review summarizes g-C₃N₄ QD synthesis techniques, operating parameters affecting the removal performance in the treatment process, modification effects with other semiconductors, and benefits and drawbacks of g-C₃N₄ QD-based materials. Furthermore, this review discusses the practical applications of g-C₃N₄ QDs as adsorbents, photocatalysts, and membrane materials for organic and inorganic contaminant treatments and their value-added product formation potential. Modified g-C₃N₄ QD-based material adsorbents, photocatalysts, and membranes present potentially applicable effects, such as removal of most waterborne contaminants. Excellent results were obtained for the reduction of methyl orange, bisphenol A, tetracycline, ciprofloxacin, phenol, rhodamine B, E. coli, and Hg. Overall, this paper provides comprehensive background on g-C₃N₄ QD-based materials and their diverse applications in wastewater treatment, and it presents a foundation for the enhancement of similar unique materials in the future.

Facile Synthesis of Aminated Graphene Quantum Dots for Promising and Selective Detection of Cobalt and Copper Ions in Aqueous Media

Due to the rapid development of industrialization, various environmental problems such as water resource pollution are gradually emerging, among which heavy metal pollution is harmful to both human beings and the environment. As a result, there are many metal ion detection methods, among which fluorescence detection stands out because of its rapid, sensitive, low cost and non-toxic characteristics. In recent years, graphene quantum dots have been widely used and studied due to their excellent properties such as high stability, low toxicity and water solubility, and have a broad prospect in the field of metal ion detection. A novel high fluorescence Cu²⁺, Co²⁺ sensing probe produced by graphene quantum hydrothermal treatment is reported. After heat treatment with hydrazine hydrate, the small-molecule precursor nitronaphthalene synthesized by self-nitrification was transformed from blue fluorescent GQDs to green fluorescent amino-functionalized N-GQDs. Compared with other metal ions, N-GQDs are more sensitive to Cu²⁺ and Co²⁺ on the surface, and N-GQDs have much higher selectivity to Cu²⁺ and Co²⁺ than GQDs. The strategy proposed here is simple and economical in design.

A dual-recognition MIP-ECL sensor based on boric acid functional carbon dots for detection of dopamine

We report a molecularly imprinted polymer electrochemiluminescence (MIP-ECL) sensor with dual recognition effects on dopamine (DA). Boric-acid-functionalized carbon dots (B-CDs) with good ECL performance at - 2.0 V (vs. Ag/AgCl) were prepared and immobilized on a glassy carbon electrode (GCE). The MIP was then introduced via electropolymerization using o-phenylenediamine (OPD) as a functional monomer and DA as a template molecule to fabricate the MIP-ECL sensor. The cavities in the MIP after elution were used to capture the target molecular DA. The affinity of boric acid of B-CDs to the cis-diol of DA, as well as the special recognition of MIP, provides dual recognition effects on DA. The selective readsorption of DA onto the sensor leads to the ECL quenching of B-CDs. The quenching effect was used to detect DA from 1.0 × 10^-9 to 1.0 × 10^-5 mol·L^-1 with a detection limit of 2.1 × 10^-10 mol·L^-1. The dual recognition caused the MIP-ECL sensor exhibiting excellent selectivity and sensitivity toward  DA. The sensor was successfully used to determine DA in real samples.