Rheology of a carbon dot gel

Carbon Nanotubes, Graphene, and Carbon Dots as Electrochemical Biosensing Composites

Carbon nanomaterials (CNMs) have been extensively used as electrochemical sensing composites due to their interesting chemical, electronic, and mechanical properties giving rise to increased performance. Due to these materials' unknown long-term ecological fate, care must be given to make their use tractable. In this review, the design and use of carbon nanotubes (CNTs), graphene, and carbon dots (CDs) as electrochemical sensing electrocatalysts applied to the working electrode surface are surveyed for various biosensing applications. Graphene and CDs are readily biodegradable as compared to CNTs. Design elements for CNTs that carry over to graphene and CDs include Coulombic attraction of components and using O or N atoms that serve as tethering points for attaching electrocatalytically active nanoparticles (NPs) and/or other additives.

Metformin derived carbon dots: Highly biocompatible fluorescent nanomaterials as mitochondrial targeting and blood-brain barrier penetrating biomarkers

Carbon dots (CDs) have been intensively studied since their discovery in 2004 because of their unique properties such as low toxicity, excellent biocompatibility, high photoluminescence (PL) and good water dispersibility. In this study metformin derived carbon dots (Met-CDs) were synthesized using a microwave assisted method. Met-CDs were meticulously characterized using ultra-violet spectroscopy (UV-vis), photoluminescence (PL), Fourier Transform Infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force (AFM) and transmission electron (TEM) microscopies. According to results of cytotoxicity studies, Met-CDs possess low-toxicity and excellent biocompatibility towards both non-tumor and tumor cell lines indicating that Met-CDs are outstanding candidates for living cell bioimaging studies. Furthermore, bioimaging studies have displayed that Met-CDs can penetrate the cell membrane and disperse throughout the cell structure including the nucleus and mitochondria. More specifically, Met-CDs tend to start localizing selectively inside the mitochondria of cancer cells, but not of non-tumor cells after 1 h of incubation. Finally, a zebrafish study confirmed that Met-CDs cross the blood-brain barrier (BBB) without the need of any other ligands. In summary, this study presents synthesis of Met-CDs which feature abilities such as mitochondrial and nucleus localizations along with BBB penetration.

Direct conjugation of distinct carbon dots as Lego-like building blocks for the assembly of versatile drug nanocarriers

As a promising drug nanocarrier, carbon dots (CDs) have exhibited many excellent properties. However, some properties such as bone targeting and crossing the blood-brain barrier (BBB) only apply to a certain CD preparation with limited drug loading capacity. Therefore, it is significant to conjugate distinct CDs to centralize many unique properties on the novel drug nanocarrier. Considering that CDs have abundant and tunable surface functionalities, in this study, a direct conjugation was initiated between two distinct CD models, black CDs (B-CDs) and gel-like CDs (G-CDs) via an amidation reaction. As a result of conjugation at a mass ratio of 5:3 (B-CDs to G-CDs) and a two-step purification process, the conjugate, black-gel CDs (B-G CDs) (5:3) inherited functionalities from both CDs and obtained an enhanced thermostability, aqueous stability, red-shifted photoluminescence (PL) emission, and a figure-eight shape with a width and length of 3 and 6 nm, respectively. In addition, the necessity of high surface primary amine (NH₂) content in the CD conjugation was highlighted by replacing G-CDs with other CDs with lower surface NH₂ content. Meanwhile, the carboxyl groups (COOH) on G-CDs were not enough to trigger self-conjugation between G-CDs. Moreover, the drug loading capacity was enhanced by 54.5% from B-CDs to B-G CDs (5:3). Furthermore, when the mass ratio of B-CDs to G-CDs was decreased from 5:30, 5:100 to 5:300, the obtained nanostructures revealed a great potential of CDs as Lego-like building blocks. Also, bioimaging of zebrafish demonstrated that various B-G CDs exhibited properties of both bone targeting and crossing the BBB, which are specific properties of B-CDs and G-CDs, respectively.

Recent development of carbon quantum dots regarding their optical properties, photoluminescence mechanism, and core structure

Carbon quantum dots (CDs) are a relatively new class of carbon nanomaterials which have been studied very much in the last fifteen years to improve their already favorable properties. The optical properties of CDs have drawn particular interest as they display the unusual trait of excitation-dependent emission, as well as high fluorescence quantum yields (QY), long photoluminescence (PL) decay lifetimes, and photostability. These qualities naturally lead researchers to apply CDs in the field of imaging (particularly bio-imaging) and sensing. Since the amount of publications regarding CDs has been growing nearly exponentially in the last ten years, many improvements have been made in the optical properties of CDs such as QY and PL lifetime. However, a great deal of confusion remains regarding the PL mechanism of CDs as well as their structural properties. Therefore, presented in this review is a summary and discussion of the QYs and PL lifetimes reported in recent years. The effect of method as well as precursor has been evaluated and discussed appropriately. The current theories regarding the PL mechanism of CDs are discussed, with special attention to the concept of surface state-controlled PL. With this knowledge, the improvement of preparation and applications of CDs related to their optical properties will be easily accomplished. Further improvements can be made to CDs through the understanding of their structural and optical properties.