Early diagnosis of diseases is of great importance because it increases the chance of a cure and significantly reduces treatment costs Thus, development of rapid, sensitive, and reliable biosensing techniques is essential for the benefits of human life and health As such, various nanomaterials have been explored to improve performance of biosensors, among which, carbon dots (CDs) have received enormous attention due to their excellent performance In this Review, the recent advancements of CD-based biosensors have been carefully summarized First, biosensors are classified according to their sensing strategies, and the role of CDs in these sensors is elaborated in detail Next, several typical CD-based biosensors (including CD-only, enzymatic, antigen-antibody, and nucleic acid biosensors) and their applications are fully discussed Last, advantages, challenges, and perspectives on the future trends of CD-based biosensors are highlighted

Recent Developments of Carbon Dots in Biosensing: A Review.

Nitrogen-doped fluorescence carbon dots as multi-mechanism detection for iodide and curcumin in biological and food samples.

Multicolor bandgap fluorescent carbon quantum dots (MCBF-CQDs) from blue to red with quantum yield up to 75% are synthesized using a solvothermal method. For the first time, monochrome electroluminescent light-emitting diodes (LEDs) with MCBF-CQDs directly as an active emission layer are fabricated. The maximum luminance of blue LEDs reaches 136 cd m-2 , which is the best performance for CQD-based monochrome electroluminescent LEDs.

Bright Multicolor Bandgap Fluorescent Carbon Quantum Dots for Electroluminescent Light-Emitting Diodes

Nonconventional luminophores devoid of remarkable conjugates have attracted considerable attention due to their unique luminescence behaviors, updated luminescence mechanism of organics and promising applications in optoelectronic, biological and medical fields. Unlike classic luminogens consisting of molecular segments with greatly extended electron delocalization, these unorthodox luminophores generally possess nonconjugated structures based on subgroups such as ether (–O–), hydroxyl (–OH), halogens, carbonyl (CO), carboxyl (–COOH), cyano (CN), thioether (–S–), sulfoxide (SO), sulfone (OSO), phosphate, and aliphatic amine, as well as their grouped functionalities like amide, imide, anhydride and ureido. They can exhibit intriguing intrinsic luminescence, generally featuring concentration-enhanced emission, aggregation-induced emission, excitation-dependent luminescence and prevailing phosphorescence. Herein, we review the recent progress in exploring these nonconventional luminophores and discuss the current challenges and future perspectives. Notably, different mechanisms are reviewed and the clustering-triggered emission (CTE) mechanism is highlighted, which emphasizes the clustering of the above mentioned electron rich moieties and consequent electron delocalization along with conformation rigidification. The CTE mechanism seems widely applicable for diversified natural, synthetic and supramolecular systems.

Nonconventional luminophores: characteristics, advancements and perspectives.

The fluorescent carbon dot is a novel type of carbon nanomaterial. In comparison with semiconductor quantum dots and fluorescence organic agents, it possesses significant advantages such as excellent photostability and biocompatibility, low cytotoxicity and easy surface functionalization, which endow it a wide application prospect in fields of bioimaging, chemical sensing, environmental monitoring, disease diagnosis and photocatalysis as well. Biomass waste is a good choice for the production of carbon dots owing to its abundance, wide availability, eco-friendly nature and a source of low cost renewable raw materials such as cellulose, hemicellulose, lignin, carbohydrates and proteins, etc. This paper reviews the main sources of biomass waste, the feasibility and superiority of adopting biomass waste as a carbon source for the synthesis of carbon dots, the synthetic approaches of carbon dots from biomass waste and their applications. The advantages and deficiencies of carbon dots from biomass waste and the major influencing factors on their photoluminescence characteristics are summarized and discussed. The challenges and perspectives in the synthesis of carbon dots from biomass wastes are also briefly outlined.

https://www.mdpi.com/2079-4991/10/11/2316/pdf

A Review of Carbon Dots Produced from Biomass Wastes.

Carbon dots (CDs) display tunable photoluminescence and excitation-wavelength dependent emission. The color of fluorescence is affected by electronic bandgap transitions of conjugated π-domains, surface defect states, local fluorophores and element doping. In this review (with 145 refs.), the studies performed in the past 5 years on the relationship between the fluorescence mechanism and modes for modulating the emission color of CDs are summarized. The applications of such CDs in sensors and assays are then outlined. A concluding section then gives an outlook and describes current challenges in the design of CDs with different emission colors. Graphical abstract Schematic representation of the relationship between the color-emitting (blue, green, yellow, red and multicolor) modulation of carbon dots and fluorescence mechanism including bandgap transitions of conjugated π-domains and surface defect states.

The fluorescence mechanism of carbon dots, and methods for tuning their emission color: a review

Since carbon dots (CDs) were reported in 2004, they have been widely used in various fields due to their outstanding optical properties. However, most CDs are self-quenched due to the direct π–π in...

Color Emission Carbon Dots with Quench-ResixAstant Solid-State Fluorescence for Light-Emitting Diodes

Carbon dots (CDs), as a new kind of carbon-based luminescent nanomaterials, have drawn widespread attention in the fields of fluorescence sensing, optoelectronic devices, and biological imaging. This work uses citric acid (CA) and Nile Blue A (NBA) as precursors. By simply changing the solvent in the reaction, their bandgaps were systematically controlled, thereby successfully obtaining bright blue, yellow and red fluorescence emission CDs (B-, Y- and RCDs). The higher quantum yield (QY) of B-, Y- and RCDs are 64%, 57% and 51%, respectively. The selected precursors and different solvents are the key to the formation of three emission CDs. Detailed characterization and density functional theory (DFT) calculations further indicate that the difference in emission color of CDs is due to the size of the sp2 conjugate domain. In addition, we used multicolor CDs as fluorescent probes to investigate their performance in detection. Among them, BCDs and YCDs can detect Sudan Red I with high selectivity and sensitivity. In the concentration range of 0 to 80 µM, the detection limits are 56 and 41 nM, respectively. Multicolor emitting phosphors and fluorescent films are also obtained by mixing CDs with other matrices. Using Ultraviolet (UV) chip as the excitation source and combining with multicolor fluorescent film and a certain proportion of B-, Y-, and RCDs/epoxy resin composites, bright monochromatic light-emitting diodes (LEDs) and white LED (WLED) with high color rendering index (CRI) were prepared. The above results indicate that the multicolor CDs prepared by us have great application potential in the fields of food safety control and optical devices.

Solvent-controlled synthesis strategy of multicolor emission carbon dots and its applications in sensing and light-emitting devices

During the heretofore several years, Carbon dots (CDs) have achieved the widely used in fluorescence sensing, optoelectronics and bio imaging owing to their distinctive photoluminescence attribute. Here, CDs with bule to red emission were prepared by solvent heat treatment of phenol-derived with regulation the reaction time in the synthetic system, and their fluorescence spectra ranged from 450 ∼ 650 nm. Characterization through variety of methods and density functional theory calculations clearly demonstrates that the achieve stable long-wavelength emission caused in solvent is mainly due to the increase in conjugate area and oxygen elements of CDs. Importantly, conjugate area and oxidation degree can affect the level of HOMO-LUMO, further changing the band gap leading to fluorescent red-shift. Because of their excellent photoluminescent properties, we examined the performance in detection of non-metal ions by green and yellow-color CDs. The results show that they have high accuracy and rapid reaction to ClO− within the scope of 0 ∼ 50 μM and 4 ∼ 44 μM, with response limits are 31.1 nM and 56.5 nM, respectively. Moreover, we also prepared CDs/PMMA films and CDs/epoxy resin films with highly transparent and stability. Subsequently, the white-light emission diodes (0.32, 0.31; ClE coordinate) was obtained through mixing CDs in a certain proportion. This study provides a novel platform for fluorescence sensing of multi-color emission CDs, and provides strong potential for new optoelectronic equipment.

Hao Zhang

Papers

The fluorescence mechanism of carbon dots, and methods for tuning their emission color: a review

Color Emission Carbon Dots with Quench-ResixAstant Solid-State Fluorescence for Light-Emitting Diodes

Solvent-controlled synthesis strategy of multicolor emission carbon dots and its applications in sensing and light-emitting devices

Conjugate area-controlled synthesis of multiple-color carbon dots and application in sensors and optoelectronic devices

A fluorescein-coumarin based ratiometric fluorescent probe for detecting hydrazine and its real applications in cells imaging.