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Graphene quantum dots (GQDs) are graphene nanoparticles with a size less than 100 nm. Due to their exceptional properties such as low toxicity, stable photoluminescence, chemical stability and pronounced quantum confinement effect, GQDs are considered as a novel material for biological, opto-electronics, energy and environmental applications.
Graphene quantum dots (GQDs) consist of one or a few layers of graphene and are smaller than 100 nm in size. [1] They are chemically and physically stable, have a large surface to mass ratio and can be dispersed in water easily due to functional groups at the edges. [2] [3] The fluorescence emission of GQDs can extend across a broad spectral range, including the UV, visible, and IR. The origin of GQD fluorescence emission is a subject of debate, as it has been related to quantum confinement effects, defect states and functional groups [4] [5] that might depend on the pH, when GQDs are dispersed in water. [6] Their electronic structure depends sensitively on the crystallographic orientation of their edges, for example zigzag-edge GQDs with 7-8 nm diameter show a metallic behavior. [7] In general, their energy gap decreases, when the number of graphene layers or the number of carbon atoms per graphene layer is increased. [8]
The toxicity of graphene-family nanoparticles is a matter of ongoing research. [9] The toxicity (both in vivo and cytotoxicity) of GQDs are related to a variety of factors including particle size, methods of synthesis, chemical doping and so on. [10] Many authors claim, that GQDs are biocompatible and cause only low toxicity [2] [11] as they are just composed of organic materials, which should lead to an advantage over semiconductor quantum dots. [3] Several in vitro studies, based on cell cultures, show only marginal effects of GQDs on the viability of human cells. [12] [13] [14] An in-depth look at the gene expression changes caused by GQDs with a size of 3 nm revealed that only one, namely the selenoprotein W, 1 out of 20 800 gene expressions was affected significantly in primary human hematopoietic stem cells. [15] On the contrary, other in vitro studies observe a distinct decrease of cell viability and the induction of autophagy after exposure of the cells to GQDs [16] and one in vivo study in zebrafish larvae observed the alteration of 2116 gene expressions. [17] These inconsistent findings may be attributed to the diversity of the used GQDs, as the related toxicity is dependent on particle size, surface functional groups, oxygen content, surface charges and impurities. [18] Currently, the literature is insufficient to draw conclusions about the potential hazards of GQDs. [9]
Presently, a range of techniques have been developed to prepare GQDs. These methods are normally classified into two groups top down and bottom up. Top down approaches applied different techniques to cut bulk graphitic materials into GQDs including graphite, graphene, carbon nanotubes, coal, carbon black and carbon fibres. These techniques mainly include electron beam lithography, chemical synthesis, electrochemical preparation, graphene oxide (GO) reduction, C60 catalytic transformation, the microwave assisted hydrothermal method (MAH), [19] [20] the Soft-Template method, [21] the hydrothermal method, [22] [23] [24] and the ultrasonic exfoliation method. [25] Top down methods usually need intense purification as strong mixed acids are used in these methods. On the other hand, bottom up methods assemble GQDs from small organic molecules such as citric acid [26] and glucose. These GQDs have better biocompatibility. [10]
Graphene quantum dots are studied as an advanced multifunctional material due to their unique optical, electronic, [7] spin, [27] and photoelectric properties induced by the quantum confinement effect and edge effect. They have possible applications in treatment of Alzheimer's disease, bioimaging, [28] photothermal therapy, [1] [29] temperature sensing, [30] drug delivery, [31] [32] LEDs lighter converters, photodetectors, OPV solar cells, and photoluminescent material, biosensors fabrication. [33]
Quantum dots (QDs) or semiconductor nanocrystals are semiconductor particles a few nanometres in size with optical and electronic properties that differ from those of larger particles via quantum mechanical effects. They are a central topic in nanotechnology and materials science. When a quantum dot is illuminated by UV light, an electron in the quantum dot can be excited to a state of higher energy. In the case of a semiconducting quantum dot, this process corresponds to the transition of an electron from the valence band to the conduction band. The excited electron can drop back into the valence band releasing its energy as light. This light emission (photoluminescence) is illustrated in the figure on the right. The color of that light depends on the energy difference between the discrete energy levels of the quantum dot in the conduction band and the valence band.
Nanomaterials describe, in principle, chemical substances or materials of which a single unit is sized between 1 and 100 nm.
Graphene is a carbon allotrope consisting of a single layer of atoms arranged in a honeycomb planar nanostructure. The name "graphene" is derived from "graphite" and the suffix -ene, indicating the presence of double bonds within the carbon structure.
A nanoparticle or ultrafine particle is a particle of matter 1 to 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. At the lowest range, metal particles smaller than 1 nm are usually called atom clusters instead.
Erbium(III) oxide is the inorganic compound with the formula Er2O3. It is a pink paramagnetic solid. It finds uses in various optical materials.
Harry Albert Atwater, Jr. is an American physicist and materials scientist and is the Otis Booth Leadership Chair of the division of engineering and applied science at the California Institute of Technology. Currently he is the Howard Hughes Professor of Applied Physics and Materials Science and the director for the Liquid Sunlight Alliance (LiSA), a Department of Energy Hub program for solar fuels. Atwater's scientific effort focuses on nanophotonic light-matter interactions and solar energy conversion. His current research in energy centers on high efficiency photovoltaics, carbon capture and removal, and photoelectrochemical processes for generation of solar fuels. His research has resulted in world records for solar photovoltaic conversion and photoelectrochemical water splitting. His work also spans fundamental nanophotonic phenomena, in plasmonics and 2D materials, and also applications including active metasurfaces and optical propulsion.
Nanobatteries are fabricated batteries employing technology at the nanoscale, particles that measure less than 100 nanometers or 10−7 meters. These batteries may be nano in size or may use nanotechnology in a macro scale battery. Nanoscale batteries can be combined to function as a macrobattery such as within a nanopore battery.
As the world's energy demand continues to grow, the development of more efficient and sustainable technologies for generating and storing energy is becoming increasingly important. According to Dr. Wade Adams from Rice University, energy will be the most pressing problem facing humanity in the next 50 years and nanotechnology has potential to solve this issue. Nanotechnology, a relatively new field of science and engineering, has shown promise to have a significant impact on the energy industry. Nanotechnology is defined as any technology that contains particles with one dimension under 100 nanometers in length. For scale, a single virus particle is about 100 nanometers wide.
Photothermal therapy (PTT) refers to efforts to use electromagnetic radiation for the treatment of various medical conditions, including cancer. This neurotherapy is an extension of photodynamic therapy, in which a photosensitizer is excited with specific band light. This activation brings the sensitizer to an excited state where it then releases vibrational energy (heat), which is what kills the targeted cells.
Graphite oxide (GO), formerly called graphitic oxide or graphitic acid, is a compound of carbon, oxygen, and hydrogen in variable ratios, obtained by treating graphite with strong oxidizers and acids for resolving of extra metals. The maximally oxidized bulk product is a yellow solid with C:O ratio between 2.1 and 2.9, that retains the layer structure of graphite but with a much larger and irregular spacing.
Graphyne is an allotrope of carbon. Although it has been studied in theoretical models, it is very difficult to synthesize and only small amounts of uncertain purity have been created. Its structure is one-atom-thick planar sheets of sp and sp2-bonded carbon atoms arranged in crystal lattice. It can be seen as a lattice of benzene rings connected by acetylene bonds. The material is called graphyne-n when benzene rings are connected by n sequential acetylene molecules, and graphdiyne for a particular case of n = 2.
CytoViva, Inc. is a scientific imaging and instrumentation company that develops and markets optical microscopy and hyperspectral imaging technology for nanomaterials, pathogen and general biology applications.
Potential graphene applications include lightweight, thin, and flexible electric/photonics circuits, solar cells, and various medical, chemical and industrial processes enhanced or enabled by the use of new graphene materials, and favoured by massive cost decreases in graphene production.
A two-dimensional semiconductor is a type of natural semiconductor with thicknesses on the atomic scale. Geim and Novoselov et al. initiated the field in 2004 when they reported a new semiconducting material graphene, a flat monolayer of carbon atoms arranged in a 2D honeycomb lattice. A 2D monolayer semiconductor is significant because it exhibits stronger piezoelectric coupling than traditionally employed bulk forms. This coupling could enable applications. One research focus is on designing nanoelectronic components by the use of graphene as electrical conductor, hexagonal boron nitride as electrical insulator, and a transition metal dichalcogenide as semiconductor.
Carbon quantum dots also commonly called carbon nano dots or simply carbon dots are carbon nanoparticles which are less than 10 nm in size and have some form of surface passivation.
Quantum dots (QDs) are semiconductor nanoparticles with a size less than 10 nm. They exhibited size-dependent properties especially in the optical absorption and the photoluminescence (PL). Typically, the fluorescence emission peak of the QDs can be tuned by changing their diameters. So far, QDs were consisted of different group elements such as CdTe, CdSe, CdS in the II-VI category, InP or InAs in the III-V category, CuInS2 or AgInS2 in the I–III–VI2 category, and PbSe/PbS in the IV-VI category. These QDs are promising candidates as fluorescent labels in various biological applications such as bioimaging, biosensing and drug delivery.
Nanoparticle deposition refers to the process of attaching nanoparticles to solid surfaces called substrates to create coatings of nanoparticles. The coatings can have a monolayer or a multilayer and organized or unorganized structure based on the coating method used. Nanoparticles are typically difficult to deposit due to their physical properties.
Graphene is a semimetal whose conduction and valence bands meet at the Dirac points, which are six locations in momentum space, the vertices of its hexagonal Brillouin zone, divided into two non-equivalent sets of three points. The two sets are labeled K and K′. The sets give graphene a valley degeneracy of gv = 2. By contrast, for traditional semiconductors the primary point of interest is generally Γ, where momentum is zero. Four electronic properties separate it from other condensed matter systems.
Ramakrishna Podila is an Indian-born American physicist and nanomaterials researcher. He is currently an associate professor of physics in the Department of Physics and Astronomy at Clemson University and is the director of the Clemson Nano-bio lab. He is known for his interdisciplinary research at the interface of physics, biology, and nanoscience. His lab integrates the principles of condensed matter physics, optical spectroscopy, and physiological chemistry to understand physics at the nanoscale and nano-bio interfaces. He became a fellow of the Royal Society of Chemistry in July 2024.
Silicon quantum dots are metal-free biologically compatible quantum dots with photoluminescence emission maxima that are tunable through the visible to near-infrared spectral regions. These quantum dots have unique properties arising from their indirect band gap, including long-lived luminescent excited-states and large Stokes shifts. A variety of disproportionation, pyrolysis, and solution protocols have been used to prepare silicon quantum dots, however it is important to note that some solution-based protocols for preparing luminescent silicon quantum dots actually yield carbon quantum dots instead of the reported silicon. The unique properties of silicon quantum dots lend themselves to an array of potential applications: biological imaging, luminescent solar concentrators, light emitting diodes, sensors, and lithium-ion battery anodes.
