Synthesis of modified carbon dots with performance of ultraviolet absorption used in sunscreen

Graphene quantum dot doped viscoelastic lyotropic liquid crystal nanocolloids for antibacterial applications

Graphene quantum dots (GQDs) are prepared and characterized via X-ray diffraction (XRD), UV-Visible spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM) and photoluminescence (PL). GQDs are doped (5 mg and 10 mg) in the lyotropic liquid crystalline (LLC) lamellar and hexagonal phases to prepare GQD/LLC nanocolloids. Polarizing optical microscopy and X-ray diffraction measurement reveals that GQDs do not affect the lamellar and hexagonal LLC structures and may organize on their interface. Pure LLC phases and nanocolloids are studied for steady and dynamic rheological behavior. LLC phases and GQD/LLC nanocolloids possess shear thinning and frequency dependent liquid viscoelastic behavior. A complex moduli study of LLCs and GQD/LLC nanocolloids is carried out which indicates the gel to viscous transition in LLCs and GQD/LLC nanocolloids as a function of frequency. LLC phases and GQD/LLC nanocolloids are tested for antibacterial activity against Listeria ivanovii. The effect of surfactant concentration, LLC phase geometry and GQD concentration has been studied and discussed. A probable mechanism for the strong antimicrobial activity of LLCs and GQD/LLC nanocolloids is presented considering intermolecular interactions. The viscoelastic behavior and strong antibacterial activity (inhibition zone 49.2 mm) of LLCs and GQD/LLC nanocolloids make them valuable candidates for lubrication, cleaning, cosmetics and pharmaceutical applications.

Fluorescence origin and chirality mechanism of graphene quantum Dots: Twist or Non-Twist?

In this paper, we theoretically investigate the fluorescence origin and chirality mechanism of graphene quantum dots with non-twist and twist geometries, respectively. It is revealed that twist is not necessary for fluorescence; but twist is must for the chirality, which can significantly enhance the intensity of chirality, demonstrated by ECD spectra. Our results provide deeper understanding on the physical mechanism of fluorescence and chirality of graphene quantum dot influenced by geometric twist.

Withania somnifera-derived carbon dots protect human epidermal cells against UVB-induced cell death and support growth factor-mediated wound healing

Solar radiation comprising UVA and UVB regions is considered a skin-damaging factor inducing inflammation, oxidative stress, hyperpigmentation, and photo-aging. Photoluminescent carbon dots (CDs) were synthesized from the root extract of a Withania somnifera (L.) Dunal plant and urea, using a one-step microwave method. These Withania somnifera CDs (wsCDs) were 14.4 ± 0.18 d nm in diameter and presented photoluminescence. UV absorbance showed the presence of π-π* (C[double bond, length as m-dash]C) and n-π* (C[double bond, length as m-dash]O) transition regions in wsCDs. FTIR analysis indicated the presence of nitrogen and carboxylic functional groups on the surface of wsCDs. HPLC analysis of wsCDs showed the presence of withanoside IV, withanoside V, and withanolide A. The wsCDs were found to be biocompatible in human skin epidermal (A431) cells and hindered UVB irradiation-induced loss of metabolic activity and oxidative stress. The wsCDs supported rapid dermal wound healing through augmented TGF-β1 and EGF gene expression levels in A431 cells. Finally, wsCDs were found to be biodegradable through a myeloperoxidase-catalyzed peroxidation reaction. The study concluded that under in vitro conditions, Withania somnifera root extract-derived biocompatible carbon dots provided photo-protection against UVB-stimulated epidermal cell damage and supported rapid wound healing.

Cu-Enhanced Efficient Förster Resonance Energy Transfer in PBSA Sunscreen-Associated Ternary Cu x Cd1-x S Quantum Dots

Quantum dots (QDs) are semiconducting nanocrystals that exhibit size- and composition-dependent optical and electronic properties. Recently, Cu-based II-VI ternary Cu _x Cd_1-x S (CCS) QDs have emerged as a promising class of QDs as compared to their binary counterparts (CuS and CdS). Herein, a series of ternary CCS QDs are synthesized by changing the molar concentration of Cu²⁺ ions only keeping the 1:1 ratio of the stoichiometric mixture of Cd²⁺ and S^2-. These CCS QDs are attached to 2-phenylbenzimidazole-5-sulfonic acid (PBSA), an eminent UV-B filter widely used in many commercial sunscreen products to avoid skin erythema and DNA mutagenic photolesions. The photoinduced Förster resonance energy transfer (FRET) is investigated from PBSA to CCS QDs as a function of Cu concentration in CCS QDs using the steady-state photoluminescence and time-resolved photoluminescence measurements. A 2-fold increase in the magnitude of non-radiative energy transfer rate (K _T(r)) is observed as the molar concentration of Cu in CCS QDs increases from 2 to 10 mM. Our findings suggest that in PBSA-CCS QD dyads, the FRET occurrence from PBSA to QDs is dictated by the dynamic mode of photoluminescence (PL) quenching. The bimolecular PL quenching rate constants (k _q) estimated by Stern-Volmer's plots for PBSA-CCS QD dyads are of the order of 10¹⁰ M^-1 s^-1, which signifies that in the PBSA-CCS QD dyad FRET system, the process of PL quenching is entirely diffusion-controlled.

A Review on Carbon Dots: Synthesis, Characterization and Its Application in Optical Sensor for Environmental Monitoring

The development of carbon dots (CDs), either using green or chemical precursors, has inevitably led to their wide range application, from bioimaging to optoelectronic devices. The reported precursors and properties of these CDs have opened new opportunities for the future development of high-quality CDs and applications. Green precursors were classified into fruits, vegetables, flowers, leaves, seeds, stem, crop residues, fungi/bacteria species, and waste products, while the chemical precursors were classified into acid reagents and non-acid reagents. This paper quickly reviews ten years of the synthesis of CDs using green and chemical precursors. The application of CDs as sensing materials in optical sensor techniques for environmental monitoring, including the detection of heavy metal ions, phenol, pesticides, and nitroaromatic explosives, was also discussed in this review. This profound review will offer knowledge for the upcoming community of researchers interested in synthesizing high-quality CDs for various applications.

Carbon Dots: Synthesis, Properties and Applications

Carbon dots (CDs) are known as the rising star of carbon-based nanomaterials and, by virtue of their unique structure and fascinating properties, they have attracted considerable interest in different fields such as biological sensing, drug delivery, photodynamic therapy, photocatalysis, and solar cells in recent years. Particularly, the outstanding electronic and optical properties of the CDs have attracted increasing attention in biomedical and photocatalytic applications owing to their low toxicity, biocompatibility, excellent photostability, tunable fluorescence, outstanding efficient up-converted photoluminescence behavior, and photo-induced electron transfer ability. This article reviews recent progress on the synthesis routes and optical properties of CDs as well as biomedical and photocatalytic applications. Furthermore, we discuss an outlook on future and potential development of the CDs based biosensor, biological dye, biological vehicle, and photocatalysts in this booming research field.

Carbon dots synthesized from microorganisms and food by-products: active and smart food packaging applications

Nanotechnology is rapidly becoming a commercial reality for application in food packaging. In particular, the incorporation of nanoparticles into packaging materials is being used to increase the shelf life and safety of foods. Carbon dots (C-dots) have a diverse range of potential applications in food packaging. They can be synthesized from environmentally friendly sources such as microorganisms, food by-products, and waste streams, or they may be generated in foods during normal processing operations, such as cooking. These processes often produce nitrogen- and sulfur-rich heteroatom-doped C-dots, which are beneficial for certain applications. The incorporation of C-dots into food packaging materials can improve their mechanical, barrier, and preservative properties. Indeed, C-dots have been used as antioxidant, antimicrobial, photoluminescent, and UV-light blocker additives in food packaging materials to reduce the chemical deterioration and inhibit the growth of pathogenic and spoilage microorganisms in foods. This article reviews recent progress on the synthesis of C-dots from microorganisms and food by-products of animal origin. It then highlights their potential application for the development of active and intelligent food packaging materials. Finally, a discussion of current challenges and future trends is given.

Fluorescent Carbonized Polymer Dots Prepared from Sodium Alginate Based on the CEE Effect

In recent years, as a new type of carbon dots, carbonized polymer dots (CPDs) have attracted more and more attention in many fields. In this experiment, a new kind of CPDs was synthesized by the hydrothermal treatment of the chemically cross-linked sodium alginate (SA) via glutaraldehyde. The fluorescence of CPDs was greatly enhanced because of the cross-linking enhanced emission effect. The formation process of CPDs at different reaction temperatures was explored. In addition, it was found that CPDs have stable fluorescence properties in mild acidic/basic and metal-ion environments. The in vitro toxicity of CPDs was tested, and based on their nontoxic property, SA films with anti-ultraviolet aging properties were prepared by using CPDs as the additive.

Photonic Carbon Dots as an Emerging Nanoagent for Biomedical and Healthcare Applications

As a class of carbon-based nanomaterials, carbon dots (CDs) have attracted enormous attention because of their tunable optical and physicochemical properties, such as absorptivity and photoluminescence from ultraviolet to near-infrared, high photostability, biocompatibility, and aqueous dispersity. These characteristics make CDs a promising alternative photonic nanoagent to conventional fluorophores in disease diagnosis, treatment, and healthcare managements. This review describes the fundamental photophysical properties of CDs and highlights their recent applications to bioimaging, photomedicine (e.g., photodynamic/photothermal therapies), biosensors, and healthcare devices. We discuss current challenges and future prospects of photonic CDs to give an insight into developing vibrant fields of CD-based biomedicine and healthcare.

Self-formed C-dot-based 2D polysiloxane with high photoluminescence quantum yield and stability

C-Dots and composites based on them face the challenges of poor stability, especially under photo-radiation, and low solid-state photoluminescence quantum yields (PLQYs), which hinder their application in optical devices. Herein, a novel 2-dimensional hybrid material of polysiloxane embedded with Si-doped carbon dots (P-E-Si-CDs) was synthesized by a self-assembly approach, and the hybrid composite exhibited broadband blue-green fluorescence emission, outstanding photostability, high thermal stability, and a high PLQY of 82.8%. Moreover, the dual fluorescent emissions were demonstrated the creation of two closed-loop fluorophores. Using the as-prepared hybrid fluorescent material, fabricated light-emitting diodes (LEDs) based on UV and blue-emitting LED chips present safe warm white light emission and adjustable white emission with a high color rendering index of up to 91, respectively. This work provides a novel strategy for the design and realization of Si-CD-based hybrid composites, thus promising their prospective use commercially in LED lighting.

Enhancement of Fluorescence Emission for Tricolor Quantum Dots Assembled in Polysiloxane toward Solar Spectrum-Simulated White Light-Emitting Devices

Commercial white light-emitting diodes (LEDs) have the undesirable characteristics of blue-rich emission and low color rendering index (CRI), while the constituent quantum dots (QDs) suffer from aggregation-induced fluorescence quenching and poor stability. Herein, a strategy is developed to assemble tricolor QDs into a polysiloxane matrix using a polymer-mediated hybrid approach whereby the hybrid composite exhibits a significant enhancement of aggregation-dispersed emission, outstanding photostability, high thermal stability, and outstanding fluorescence recovery. Using the as-prepared hybrid fluorescent materials, the fabricated LEDs exhibit solar spectrum-simulated emission with adjustable Commission Internationale de L'Eclairage coordinates, correlated color temperature, and a recorded CRI of 97. Furthermore, they present no ultraviolet emission and weak blue emission, thus indicating an ideal healthy and high-CRI white LED lighting source.