Umeå University's logo

To develop a safe, efficient, water-soluble, and targeted antibacterial substance for medical applications, we synthesized carbon dots using citric acid and urea as precursors by a solvothermal method. We then coupled the carbon dots and lysozyme by using a simple 1-ethyl-3-(3′-dimethylaminopropyl) carbodiimide-N–hydroxysuccinimide (EDC-NHS) coupling method. After coupling, the carbon dots exhibited improved water dispersibility with particle sizes ranging from 12 to 20 nm. Notably, the highest carbon dot concentration associated with cytotoxicity increased from 2.5 to 5 mg/mL when coupled with lysozyme, implying that coupling could enhance the biocompatibility of carbon nanodots. Furthermore, coupled carbon dots extended the effective inhibition time against Streptococcus mutans from 12 to 36 h, compared to carbon dots alone. The improved biocompatibility and prolonged effective antibacterial duration highlight the potential of lysozyme-coupled carbon dots as a safe, efficient, and water-soluble antibacterial agent for a variety of oral healthcare and medical applications.

The intrinsically disordered periodic architecture inherent in natural biomaterials exhibits significant potential for serving as resonant cavities, enabling the development of eco-friendly, biocompatible, and cost-effective microlaser systems. In this study, we demonstrate a biomaterial-based random laser utilizing birch leaf-derived carbon dots (CDs) as the gain medium. CDs ethanol solution was introduced into the peanut via microinjection, successfully fabricating CDs-doped peanut samples that preserved the fluorescence characteristics of the CDs in solution. Random lasing was observed on multiple surfaces of the CDs-doped peanut under pulsed laser excitation, with varying thresholds across different regions. This demonstrates that the natural disordered microstructure of biological materials can facilitate random lasing. Analysis of surface morphology and scattering patterns indicates that the lasing mechanism arises from multiple light scattering within the disordered structure of the peanut surface, forming coherent feedback loops. Furthermore, the intrinsic biocompatibility of bio-derived CDs effectively addresses the persistent toxicity concerns associated with synthetic laser materials. Such biomaterial-based random lasers could enable eco-friendly and cost-effective photonic applications.

The synthesis of carbon dots (CDs) with tailored properties commonly requires time-consuming trial-and-error experimentation, in part because of a poorly understood and controlled chemical conversion of the precursor material. Here, we first report on the solid-state pyrolysis or solvothermal conversion of an ortho-aminophenol (oAP) precursor, comprising ortho-disposed amino and hydroxyl groups on a benzene ring. We find that both conversion reactions resulted in a two emission-colour product, which could be separated into distinct blue-emitting CDs (bCDs, λpeak = 420 nm) and yellow-emitting CDs (yCDs, λpeak = 565 nm) by repetitive column chromatography. Systematic characterization revealed that both CDs comprise a planar graphene-like interior, but that they are distinguished by that the bCDs comprise an intermixed significant amino-rich fluorophore while the yCDs instead comprise a pyridinic-rich fluorophore. This implies that the bCDs are formed via activation of the amino group of the oAP precursor, whereas the synthesis of the yCDs constituted a simultaneous activation of both the amino and hydroxyl groups. With this knowledge at hand, we managed to direct the chemical conversion of the oAP precursor to yield either solely bCDs or yCDs by adding a catalyst (either the Lewis acid AlCl3·6H2O or the Lewis base NaOH) that selectively and efficiently activated only one of the reaction pathways. This demonstration is important in that it shows that the synthesis of CDs with desired properties can be realized with efficient rational instead of trial-and-error means.

Emissive carbon dots (CDs) that are synthesized from biomass can be highly sustainable, but the number of reported biomass-derived CDs that emit in the ultraviolet (UV) range is small. Moreover, current commercial UV-emitting materials rely heavily on the use of non-sustainable resources, such as rare metals, heavy metals, and petroleum chemicals. This yields that the development of efficient biomass-derived UV-CDs is desired. Here, we report on the hydrothermal conversion of a common green-tea extract (Polyphenon 60) into UV-CDs, which feature a photoluminescence (PL) peak wavelength of 384 nm, a full width at half maximum of 72 nm, and a photoluminescence quantum yield (PLQY) of 17% in water. By shifting to a lower-polarity solvent of 3-phenoxyanisole, the PLQY is strongly enhanced to 81%, and the PL peak blue-shifts to 370 nm, while the maximum solubility is lowered. These observations support the notion that the UV-CDs feature aggregation-induced emission and that they are endowed with hydrophilic surface groups. Moreover, the findings of excitation-wavelength-independent PL and a nanosecond-level short emission lifetime reveal that it is a single distinct fluorophore that produces the UV emission. We finally report preliminary results that the UV-CDs exhibit potential for inhibiting the proliferation of cancer cells.

Quercetin, a flavonoid known for its antioxidant properties, has recently garnered attention as a potential neuroprotective agent for treatment of the injured nervous system. The repair of peripheral nerve injuries hinges on the proliferation and migration of Schwann cells, which play a crucial role in supporting axonal growth and myelination. In this study we synthesized Quercetin-derived carbon dots (QCDs) and investigated their effects on cultured Schwann cells and the NG108-15 cell line. QCDs was obtained by solvothermal synthesis and characterized via UV–vis absorption spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction analysis. The particles demonstrated significant dose-dependent free radical scavenging activity in DPPH and ABTS radical scavenging assays, supported in vitro proliferation and migration of Schwann cells, expression of neurotrophic and angiogenic growth factors, and stimulated neurite outgrowth from NG108-15 cells. Thus, QCDs could serve as a potential novel treatment strategy to promote regeneration in the injured peripheral nervous system.

Carbon dots (CDs) are an emerging class of nanomaterials with attractive optical properties, which promise to enable a variety of applications. An important and timely question is whether CDs can become a functional and sustainable alternative to incumbent optical nanomaterials, notably inorganic quantum dots. Herein, the current CD literature is comprehensively reviewed as regards to their synthesis and function, with a focus on sustainability aspects. The study quantifies why it is attractive that CDs can be synthesized with biomass as the sole starting material and be free from toxic and precious metals and critical raw materials. It further describes and analyzes employed pretreatment, chemical-conversion, purification, and processing procedures, and highlights current issues with the usage of solvents, the energy and material efficiency, and the safety and waste management. It is specially shown that many reported synthesis and processing methods are concerningly wasteful with the utilization of non-sustainable solvents and energy. It is finally recommended that future studies should explicitly consider and discuss the environmental influence of the selected starting material, solvents, and generated byproducts, and that quantitative information on the required amounts of solvents, consumables, and energy should be provided to enable an evaluation of the presented methods in an upscaled sustainability context.

The shift from depleting petroleum compounds to regenerating biomass as the raw material for organic semiconductors is a prerequisite if organic electronics is to become truly sustainable. Here, we report on a one-pot solvothermal synthesis of a biomass-based carbon dot (bio-CD) fluorescent semiconductor, using birch leaves as the sole raw material. These bio-CDs are highly soluble in ethanol (45 g L^-1), and deliver deep-red and narrowband emission (peak wavelength = 675 nm, full width at half maximum, FWHM = 28 nm) at a high photoluminescence quantum yield of 26% in ethanol solution. Systematic structural characterization shows that molecular pheophytin a is the single fluorophore, and that this fluorophore is localized in the bulk of the bio-CD away from its polar surface. The functionality of the birch-leaf-derived bio-CDs in sustainable organic electronics is demonstrated by its employment as the printable emitter in a light-emitting electrochemical cell, which delivers narrowband deep-red luminance of 110 cd m^-2, with a FWHM of 29 nm, at an external quantum efficiency of 0.29%. This study thus reveals a promising avenue for the functional benign synthesis and the practical solution-based implementation of narrowband bio-CDs in sustainable optoelectronic technologies.