π-π conjugated PDI supramolecular regulating the photoluminescence of imine-COFs for sensitive smartphone visual detection of levofloxacin

As the contamination and enrichment in food chain of levofloxacin (LV) antibiotics have caused a significant threat to life safety, the instant detection of LV has become an urgent need. Here, a PDI-functionalized imine-based covalent organic framework (PDI-COF300) was prepared by the electrostatic self-assembly method as fluorescent probe for smartphone visual detection of LV, which exhibited excellent fluorescence quantum yield (82.68%), greater stability, high sensitivity with detection limit of 0.303 μM. Based on the results of molecular docking and Stern-Volmer equation, the LV detection by PDI-COF300 was mainly a static quenching process through π-π stacked hydrophobic interactions and fluorescence resonance energy transfer. Besides, PDI-COF300 was applied to LV detection in environmental medium and milk samples with recoveries from 85.56% to 108.34% and relative standard deviations <2.70%. This work also provided a new general strategy for using PDI-COF in smartphone devices and fluorescent papers for LV fluorescence detection and microanalysis.

Lead Monoxide Nanostructures for Nanophotonics: A Review

Black-phosphorus-analog lead monoxide (PbO), as a new emerging 2D material, has rapidly gained popularity in recent years due to its unique optical and electronic properties. Recently, both theoretical prediction and experimental confirmation have revealed that PbO exhibits excellent semiconductor properties, including a tunable bandgap, high carrier mobility, and excellent photoresponse performance, which is undoubtedly of great interest to explore its practical application in a variety of fields, especially in nanophotonics. In this minireview, we firstly summarize the synthesis of PbO nanostructures with different dimensionalities, then highlight the recent progress in the optoelectronics/photonics applications based on PbO nanostructures, and present some personal insights on the current challenges and future opportunities in this research area. It is anticipated that this minireview can pave the way to fundamental research on functional black-phosphorus-analog PbO-nanostructure-based devices to meet the growing demands for next-generation systems.

Lights and Dots toward Therapy-Carbon-Based Quantum Dots as New Agents for Photodynamic Therapy

The large number of deaths induced by carcinoma and infections indicates that the need for new, better, targeted therapy is higher than ever. Apart from classical treatments and medication, photodynamic therapy (PDT) is one of the possible approaches to cure these clinical conditions. This strategy offers several advantages, such as lower toxicity, selective treatment, faster recovery time, avoidance of systemic toxic effects, and others. Unfortunately, there is a small number of agents that are approved for usage in clinical PDT. Novel, efficient, biocompatible PDT agents are, thus, highly desired. One of the most promising candidates is represented by the broad family of carbon-based quantum dots, such as graphene quantum dots (GQDs), carbon quantum dots (CQDs), carbon nanodots (CNDs), and carbonized polymer dots (CPDs). In this review paper, these new smart nanomaterials are discussed as potential PDT agents, detailing their toxicity in the dark, and when they are exposed to light, as well as their effects on carcinoma and bacterial cells. The photoinduced effects of carbon-based quantum dots on bacteria and viruses are particularly interesting, since dots usually generate several highly toxic reactive oxygen species under blue light. These species are acting as bombs on pathogen cells, causing various devastating and toxic effects on those targets.

The Role of N and S Doping on Photoluminescent Characteristics of Carbon Dots from Palm Bunches for Fluorimetric Sensing of Fe3+ Ion

This work aims to enhance the value of palm empty fruit bunches (EFBs), an abundant residue from the palm oil industry, as a precursor for the synthesis of luminescent carbon dots (CDs). The mechanism of fIuorimetric sensing using carbon dots for either enhancing or quenching photoluminescence properties when binding with analytes is useful for the detection of ultra-low amounts of analytes. This study revealed that EFB-derived CDs via hydrothermal synthesis exceptionally exhibited luminescence properties. In addition, surface modification for specific binding to a target molecule substantially augmented their PL characteristics. Among the different nitrogen and sulfur (N and S) doping agents used, including urea (U), sulfate (S), p-phenylenediamine (P), and sodium thiosulfate (TS), the results showed that PTS-CDs from the co-doping of p-phenylenediamine and sodium thiosulfate exhibited the highest PL properties. From this study on the fluorimetric sensing of several metal ions, PTS-CDs could effectively detect Fe3+ with the highest selectivity by fluorescence quenching to 79.1% at a limit of detection (LOD) of 0.1 µmol L−1. The PL quenching of PTS-CDs was linearly correlated with the wide range of Fe3+ concentration, ranging from 5 to 400 µmol L−1 (R2 = 0.9933).

The facile synthesis of nitrogen and sulfur co-doped carbon dots for developing a powerful "on-off-on" fluorescence probe to detect glutathione in vegetables

To determine the glutathione (GSH) content in vegetables, an "on-off-on" fluorescence probe was developed by a synthesis of nitrogen and sulfur co-doped carbon dots (N,S-CDs) using the microwave pyrolysis considering citric acid and L-cysteine as precursors. The fluorescence of N,S-CDs was quenched by adding Cu²⁺ at a concentration of 20-200 μmol/L due to the inner filter effect. The quenched fluorescence of N,S-CDs@Cu²⁺ system was recovered by adding the GSH at a concentration of 10-150 μmol/L due to the sulfhydryl-metal compound mechanism. By observing the GSH concentrations measured by our N,S-CDs@Cu²⁺ system vs. a traditional fluorescent chelating method, the two measurements provided the GSH data with a good consistence by showing the RSD range of 1.86%-2.27%. This indicates the validation and novelty of our N,S-CDs@Cu²⁺ system as being a powerful fluorescent probe for effectively and efficiently determining the GSH in vegetables.

Transforming waste into value: pomelo-peel-based nitrogen-doped carbon dots for the highly selective detection of tetracycline

Tetracycline (TC) is widely used as a veterinary drug, and its residue in livestock products could enter the human body and cause damage. In this study, we developed an eco-friendly approach that utilized pomelo peel as a carbon source to synthesize new water-soluble N-doped carbon dots (P-NCDs) with blue fluorescence, obtaining a high quantum yield of up to 76.47% and achieving the goal of turning waste into value. Our prepared P-NCDs can selectively recognized TC, and their fluorescence was quenched based on the IFE. P-NCDs could measure the TC concentration in the linear range of 0-100 μmol L-1 with a detection limit (LOD, S/N = 3) as low as 0.045 μmol L-1. Furthermore, we have successfully applied our P-NCDs to the detection of TC in milk samples with convincing results within 90 s. Overall, our newly synthesized fluorescent sensor, P-NCDs, demonstrated huge potential to become an alternative way to detect TC in a simple, efficient, sensitive way without using any special instruments.

Application of carbon dots in food preservation: a critical review for packaging enhancers and food preservatives

Carbon dots (CDs) have two unique advantages: one is ease of synthesis at low price, the other is desirable physical and chemical properties, such as ultra-small size, abundant surface functional groups, nontoxic/low-toxicity, good biocompatibility, excellent antibacterial and antioxidant activities etc. These advantages provide opportunities for the development of new food packaging enhancers and food preservatives. This paper systematically reviews the studies of CDs used to strengthen the physical properties of food packaging, including strengthen mechanical strength, ultraviolet (UV) barrier properties and water barrier properties. It also reviews the researches of CDs used to fabricate active packaging with antioxidant and/or antibacterial properties and intelligent packaging with the capacity of sensing the freshness of food. In addition, it analyzes the antioxidant and antibacterial properties of CDs as preservatives, and discusses the effect of CDs applied as coating agents and nano-level food additives for extension the shelf life of food samples. It also provides a brief review on the security and the release behavior of CDs.

Chromium (VI) detection by microbial carbon dots: Microwave synthesis and mechanistic study

Functionalized carbon dots (CDs) derived from Citrobacter freundii bacterial cells were used for selective detection of Cr(VI). A microwave-heating-based green synthesis approach is adopted to produce functionalized CDs from C. freundii bacterial cells (CF-CDs). The reaction was carried out in a 500 W microwave digester at 200°C for 20 min. The supernatant was filtered with a 0.2 µm filter and highly monodisperse CDs were obtained. Inherent functionalization of CF-CDs with nitrogen and oxygen-containing functional groups made them extremely selective toward Cr(VI) with a lower limit of detection of ~1.7 ppm. More importantly, CF-CDs could distinguish between Cr(VI) and Cr(III), which is highly desirable for practical applications. The fabricated sensor had a dual linear response range between 0 and 50 µM and 50-250 µM. The synthesized CDs were inherently functionalized which made them highly selective for Cr(VI) detection. CF-CDs also possess high stability over long storage period. This study reports the facile synthesis and characterization of a highly selective sensor for Cr(VI). As opposed to similar CDs sensors reported for Cr(VI), based on inner-filter effect, CF-CDs exhibit a strong, specific interaction toward Cr(VI), indicated by the large binding constant.

Bioinspired Camellia japonica carbon dots with high near-infrared absorbance for efficient photothermal cancer therapy

Since carbon dots (CDs) exhibit excellent biocompatibility, low cytotoxicity, near-infrared (NIR) absorbance, and superior photostability, many types of CDs are considered as powerful candidates for photothermal therapy (PTT) applications. However, the development of a desirable CD is still difficult due to insufficient photothermal conversion, thus resulting in the use of high laser power densities at a high dose of CDs for the PTT effect. Herein, bioinspired sulfur-doped CDs (S-CDs) with strong NIR absorbance were prepared from Camellia japonica flowers via a facile hydrothermal method for enhancing the photothermal conversion efficiency. The as-prepared S-CDs exhibited various advantages including cost-effective preparation, good water-solubility, high biocompatibility, intense NIR absorption, and excellent photothermal effect with robust photostability. Most importantly, the optimal low dose of S-CDs (45 μg mL^-1) successfully led to efficient PTT performance with a high photothermal conversion efficiency (55.4%) under moderate laser power (808 nm, 1.1 W cm^-2) for safe and effective cancer therapy.

Facile Synthesis of Water-soluble Carbon Spheres for the Sensitive and Selective Determination of Fe3+, Cr3+, and Hg2+ Ions

Water-soluble carbon spheres (CS) were prepared by a facile one-step hydrothermal synthetic method using glucose as a carbon source and sodium hydroxide as additives. The morphology and the chemical structure were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS). In addition, the ultraviolet-visible (UV-vis) absorption spectrum and the fluorescence spectrum of the prepared CS were also investigated. The emission spectrum of the obtained CS depends on the excitation wavelength, which is similar to that of most carbon quantum dots. The fluorescence of the CS is quenched in the presence of Cr³⁺, Fe³⁺ and Hg²⁺. Based on this feature, the selective and sensitive detections of Cr³⁺, Fe³⁺ and Hg²⁺ were performed, and the detection limits were 6.72, 7.26, and 9.51 μM, respectively.

Green Preparation of Fluorescent Nitrogen-Doped Carbon Quantum Dots for Sensitive Detection of Oxytetracycline in Environmental Samples

Nitrogen-doped carbon quantum dots (N-CQDs) with strong fluorescence were prepared by a one-step hydrothermal method using natural biomass waste. Two efficient fluorescent probes were constructed for selective and sensitive detection of oxytetracycline (OTC). The synthesized N-CQDs were characterized by UV-visible absorption spectra, fluorescence spectra, Fourier transform infrared spectroscopy (FT-IR), X-ray photon spectroscopy (XPS), atomic force microscopy (AFM), and high-resolution transmission electron microscopy (HRTEM), which proved that the synthesized N-CQDs surface were functionalized and had stable fluorescence performance. The basis of N-CQDs detection of OTC was discussed, and various reaction conditions were studied. Under optimized conditions, orange peel carbon quantum dots (ON-CQDs) and watermelon peel carbon quantum dots (WN-CQDs) have a good linear relationship with OTC concentrations in the range of 2-100 µmol L^-1 and 0.25-100 µmol L^-1, respectively. ON-CQDs and WN-CQDs were both successfully applied in detecting the OTC in pretreated tap water, lake water, and soil, with the recovery rate at 91.724-103.206%, and the relative standard deviation was less than 5.35%. The results showed that the proposed N-CQDs proved to be green and simple, greatly reducing the detection time for OTC in the determination environment.

Nitrogen-doped carbon quantum dots-decorated 2D graphitic carbon nitride as a promising photocatalyst for environmental remediation: A study on the importance of hybridization approach

Growing concerns of water pollution by dye pollutants from the textile industry has led to vast research interest to find green solutions to address this issue. In recent years, heterogeneous photocatalysis has harvested tremendous attention from researchers due to its powerful potential applications in tackling many important energy and environmental challenges at a global level. To fully utilise the broad spectrum of solar energy has been a common aim in the photocatalyst industry. This study focuses on the development of an efficient, highly thermal and chemical stable, environmentally friendly and metal-free graphitic carbon nitride (g-C₃N₄) to overcome the problem of fast charge recombination which hinders photocatalytic performances. Nitrogen-doped carbon quantum dots (NCQDs) known for its high electronic and optical functionality properties is believed to achieve photocatalytic enhancement by efficient charge separation through forming heterogeneous interfaces. Hence, the current work focuses on the hybridisation of NCQDs and g-C₃N₄ to produce a composite photocatalyst for methylene blue (MB) degradation under LED light irradiation. The optimal hybridisation method and the mass loading required for maximum attainable MB degradation were systematically investigated. The optimum photocatalyst, 1 wt% NCQD/g-C₃N₄ composite was shown to exhibit a 2.6-fold increase in photocatalytic activity over bare g-C₃N₄. Moreover, the optimum sample displayed excellent stability and durability after three consecutive degradation cycles, retaining 91.2% of its original efficiency. Scavenging tests were also performed where reactive species, photon-hole (h⁺) was identified as the primary active species initiating the pollutant degradation mechanism. The findings of this study successfully shed light on the hybridisation methods of NCQDs which improve existing g-C₃N₄ photocatalyst systems for environmental remediation by utilising solar energy.

Nitrogen, phosphorus and sulfur tri-doped carbon dots are specific and sensitive fluorescent probes for determination of chromium(VI) in water samples and in living cells

A rapid, sensitive, and selective fluorometric assay is described for the determination of chromium(VI) in real waters and living cells. The method is making use of nitrogen, phosphorus, and sulfur tri-doped carbon dots (NPS-CDs) which have absorption/emission maxima at 360/505 nm/nm. Cr(VI) has an absorption maximum at 350 nm and causes an inner filter effect (IFE) on the blue fluorescence of the NPS-CDs. The NPS-CDs were hydrothermally synthesized using p-aminobenzenesulfonic acid and tetrakis(hydroxymethyl)phosphonium chloride as precursors. The NPS-CDs were characterized by transmission electron microscopy, X-ray diffraction, and several spectroscopic methods. They are biocompatible and negligibly cytotoxic when tested with HeLa cells and MCF-7 cells even after 48 h of incubation. The NPS-CDs were used as fluorescent probes for Cr(VI). The detection limit is 0.23 μM (three times standard deviation versus slope), and the linear response covers the 1 to 500 μM chromate concentration range. The NPS-CDs were applied to the determination of Cr(VI) in real waters and living cells (HeLa and MCF-7) and gave satisfying results. Graphical abstractSchematic representation of hydrothermal synthesis of nitrogen, phosphorus, and sulfur tri-doped carbon dots (NPS-CDs) for Cr(VI) detection via inner filter effect (IFE). NPS-CDs were applied to the determination of Cr(VI) in living cells (HeLa and MCF-7) with satisfying results.

One-step synthesis of S,B co-doped carbon dots and their application for selective and sensitive fluorescence detection of diethylstilbestrol

S,B co-doped carbon dots were synthesized, and their application in the detection of diethylstilbestrol.