Multifunctional N-doped graphene quantum dots towards tetracycline detection, temperature sensing and high-performance WLEDs

Recent progress in lanthanide-based fluorescent nanomaterials for tetracycline detection and removal

Tetracycline (TC) has been widely used in clinical medicine and animal growth promotion due to its broad-spectrum antibacterial properties and affordable prices. Unfortunately, the high toxicity and difficult degradation rate of TC molecules make them easy to accumulate in the environment, which breaks the ecological balance and seriously threatens human health. Rapid and accurate detection of TC residue levels is important for ensuring water quality and food safety. Recently, fluorescence detection technology of TC residues has developed rapidly. Lanthanide nanomaterials, based on the high luminescence properties of lanthanide ions and the high matching with TC energy levels, are favored in the real-time trace detection of TC due to their advantages of high sensitivity, rapidity, and high selectivity. Therefore, they are considered potential substitutes for traditional detection methods. This review summarizes the synthesis strategy, TC response mechanism, removal mechanism, and applications in intelligent sensing. Finally, the development of lanthanide nanomaterials for TC fluorescence detection and removal is reasonably summarized and prospected. This review provides a reference for the establishment of a method for the accurate determination of TC content in complex food matrices.

Room temperature, ultrafast and one-step synthesis of highly fluorescent sulfur quantum dots probe and their logic gate operation

The direct and rapid conversion of abundant and cheap elemental sulfur into fluorescent sulfur quantum dots (SQDs) at room temperature is a critical and urgent challenge. Conventional synthesis methods require high temperatures, high pressures, or specific atmospheric conditions, making them complex and impractical for real applications. Herein, we propose a simple method for synthesizing SQDs simply by adding H2O2 to an elemental sulfur-ethylenediamine (S-EDA) solution at room temperature. Remarkably, within a mere 10 min, SQDs with a photoluminescence quantum yield of 23.6 % can be obtained without the need for additional steps. A comprehensive analysis of the mechanism has demonstrated that H2O2 is capable of converting Sx2- ions generated in the S-EDA solution into zero-valent sulfur atoms through oxidation. The obtained SQDs can be utilized as a fluorescent probe for detection of tetracycline (TC) and Ca2+ ions with the limit of detection (LOD) of 0.137 μM and 0.386 μM respectively. Moreover, we have developed a sensitive logic gate sensor based on SQDs, harnessing the activated cascade effect to create an intelligent probe for monitoring trace levels of TC and Ca2+ ions. This paper not only presents a viable approach for ultrafast and scalable synthesis of SQDs at room temperature, but also contributes to the efficient utilization of elemental sulfur resources.

Multi-color polymer carbon dots synthesized from waste polyolefins through phenylenediamine-assisted hydrothermal processing

The large accumulation and low recycling rates of polyolefin waste have posed a threat to the environment and human health. The shortage of chemical recycling methods for polyolefins strongly demands the development of new and sustainable treatment technologies for hydrocarbon plastics to improve their waste management. In this study, polyethylene (PE) and polypropylene (PP) were utilized for the preparation of multi-color polymer carbon dots (PCDs) via a two-step hydrothermal (HT) synthesis involving (i) thermo-oxidative degradation of polyolefins to precursors containing plentiful oxygen-based functional groups, and (ii) modification with phenylenediamine (PDA). The fluorescence of PCDs depends on the structure of isomeric PDA and PCDs modified by ortho-, meta-, and para-PDA emit blue, green, and yellow color fluorescence, respectively. The formation mechanism of PCDs, involving dehydrative condensation and amination of PE or PP-derived precursors by PDA, was proposed. The obtained PCDs were utilized for the detection and quantification of Fe3+ ions at ppm concentrations. The proposed strategy here aims to broaden the scope of the chemical recycling methods for polyolefin plastic waste as well as to develop a conversion route of polyolefin to value-added materials.

QD-based fluorescent nanosensors: Production methods, optoelectronic properties, and recent food applications

Food quality and safety are crucial public health concerns with global significance. In recent years, a series of fluorescence detection technologies have been widely used in the detection/monitoring of food quality and safety. Due to the advantages of wide detection range, high sensitivity, convenient and fast detection, and strong specificity, quantum dot (QD)-based fluorescent nanosensors have emerged as preferred candidates for food quality and safety analysis. In this comprehensive review, several common types of QD production methods are introduced, including colloidal synthesis, self-assembly, plasma synthesis, viral assembly, electrochemical assembly, and heavy-metal-free synthesis. The optoelectronic properties of QDs are described in detail at the electronic level, and the effect of food matrices on QDs was summarized. Recent advancements in the field of QD-based fluorescent nanosensors for trace level detection and monitoring of volatile components, heavy metal ions, food additives, pesticide residues, veterinary-drug residues, other chemical components, mycotoxins, foodborne pathogens, humidity, and temperature are also thoroughly summarized. Moreover, we discuss the limitations of the QD-based fluorescent nanosensors and present the challenges and future prospects for developing QD-based fluorescent nanosensors. As shown by numerous publications in the field, QD sensors have the advantages of strong anti-interference ability, convenient and quick operation, good linear response, and wide detection range. However, the reported assays are laboratory-focused and have not been industrialized and commercialized. Promising research needs to examine the potential applications of bionanotechnology in QD-based fluorescent nanosensors, and focus on the development of smart packaging films, labeled test strips, and portable kits-based sensors.

The Green Synthesis of Carbon Quantum Dots through One-step Hydrothermal Approach by Orange Juice for Rapid, and Accurate Detection of Dopamine

In the current study, the fluorescent Carbon quantum dots (CDs) were synthesized through one-step hydrothermal approach by orange juice without any additional agents. The as-prepared green-CDs (GCDs) were quasi-spherical shape ranged from 2 to 8 nm with an average diameter of 5 nm, and emitted bright blue fluorescent (FL) under ultraviolet light irradiation (Uv). Different detailed analyses proved that the as-prepared GCDs had good morphologies, various functional groups, high water solubility, great optical features, and excellent stability towards diverse environmental conditions. The results indicated that the as-prepared GCDs can detect different concentrations of dopamine from 1 to 100 µM based on the quenching of their native fluorescent. Furthermore, the good linear relationship was obtained for dopamine in the broad range of concentrations from 1 to 100 µM with the limit of detection (LOD) of 0.81 µM. In addition, the as-prepared GCDs can be applied as a fluorescent probe for detection of dopamine in the different real samples.

Upcycling Waste: Citrus limon Peel-Derived Carbon Quantum Dots for Sensitive Detection of Tetracycline in the Nanomolar Range

In this work, a sustainable method was developed for the production of water-soluble carbon quantum dots employing a green approach. The synthetic protocol was employed using the microwave pyrolysis technique, while lemon peel served as a carbon precursor. Fabrication of highly fluorescent lemon-peel-derived CQDs (LP-CQDs) having inherent nitrogen functionality was validated by X-ray photoelectron spectroscopy, FTIR, X-ray diffraction, Raman spectroscopic analysis, and TEM techniques. The average particle size of fabricated LP-CQDs was 4.46 nm. LP-CQDs yielded a remarkable quantum yield of 49.5%, which displayed excellent salinity, photostability, storage time, conditions, and pH stability. LP-CQDs displayed encouraging results for tetracycline (TC) detection using a PL turn-off approach. The sensitivity of LP-CQDs toward TC was seen in a nanomolar range having a detection limit of 50.4 nM. Method validation was comprehensively studied to ensure the precision of the nanosensor. A complete analysis of different photophysical parameters of LP-CQDs was performed with TC to gain a deeper understanding of the sensing mechanism. Fabricated LP-CQDs showed fluorescence quenching toward TC, elucidated by the inner filter effect (IFE) mechanism. The synthesized nanoprobe demonstrated a lesser detection limit with a broad linear range, enabling facile, cheap, environmentally friendly, and fast detection of TC. Practicality of the detection method was assessed through analysis of real samples, resulting in satisfactory recovery percentage and relative standard deviation with respect to the developed probes. Furthermore, LP-CQDs were used as fluorescent inks and to fabricate paper-based fluorescent strips. This study lays the door for the sensing platform of LP-CQDs toward detection of TC, which may impact the potential role of environmental sustainability.

Cane Molasses Derived N-Doped Graphene Quantum Dots: Dynamic Quenching Synergistically Photoinduced Electron Transfer for the Instant Detection of Nitrofuran Antibiotics

The development of a highly selective, simple, and rapid detection method for nitrofuran antibiotics (NFs) is of great significance for food safety, environmental protection, and human health. To meet these needs, in this work, cyan-color highly fluorescent N-doped graphene quantum dots (N-GQDs) were synthesized using cane molasses as the carbon source and ethylenediamine as the nitrogen source. The synthesized N-GQDs have an average particle size of 6 nm, a high fluorescence intensity with 9 times that of undoped GQDs, and a high quantum yield (24.4%) which is more than 6 times that of GQDs (3.9%). A fluorescence sensor based on N-GQDs for the detection of NFs was established. The sensor shows advantages of fast detection, high selectivity, and sensitivity. The limit of detection for furazolidone (FRZ) was 0.29 μM, the limit of quantification (LOQ) was 0.97 μM, and the detection range was 5-130 μM. The fluorescence quenching mechanism of the sensor was explored by fluorescence spectroscopy, UV-vis absorption spectroscopy, Stern-Volmer quenching constant, Zeta potential, UV-vis diffuse reflectance spectroscopy, and cyclic voltammetry. A fluorescence quenching mechanism of dynamic quenching synergized with photoinduced electron transfer was revealed. The developed sensor was also successfully applied for detecting FRZ in various real samples, and the results were satisfactory.

Facile and scalable synthesis of un-doped, doped and co-doped graphene quantum dots: a comparative study on their impact for environmental applications

In recent years, graphene quantum dots (GQDs) received huge attention due to their unique properties and potential applicability in different area. Here, we report simple and facile method for the synthesis of GQDs and their functionalization by doping and co-doping using different heteroatom under the optimized conditions. The doping and co-doping of GQDs using boron and nitrogen have been confirmed by FTIR and TEM. The UV-visible and fluorescence techniques have been used to study the optical properties and stability of functionalized GQDs. Further, the screening for enhancement of quantum yields of all GQDs were performed with fluorescence and UV-visible spectra under the optimized conditions. The average QY was obtained as 16.0%, 83.6%, 18.2% and 29.6% for GQDs, B-GQDs, N-GQDs and B,N-GQDs, respectively. The sensor was used to determine paraoxon in water samples. The LOD was observed to be 1.0 × 10^-4 M with linearity range of 0.001 to 0.1 M. The RSD was calculated for the developed B,N-GQDs based sensor and observed to be 2.99% with the regression coefficient as 0.997. All the doped, co-doped and un-doped GQDs possess remarkable properties as a fluorescent probe.

Quantum dots based sensitive nanosensors for detection of antibiotics in natural products: A review

Residual antibiotics in food products originated from administration of the antibiotics to animals may be accumulated through food metabolism in the human body and endanger safety and health. Thus, developing a prompt and accurate way for detection of antibiotics is a crucial issue. The zero-dimensional fluorescent probes including metals based, carbon and graphene quantum dots (QDs), are highly sensitive materials to use for the detection of a wide range of antibiotics in natural products. These QDs demonstrate unique optical properties like tunable photoluminescence (PL) and excitation-wavelength dependent emission. This study investigates the trends related to carbon and metal based QDs preparation and modification, and their diverse detection application. We discuss the performance of QDs based sensors application in various detection systems such as photoluminescence, photoelectrochemical, chemiluminescence, electrochemiluminescence, colorimetric, as well as describing their working principles in several samples. The detecting mechanism of a QDs-based sensor is dependent on its properties and specific interactions with particular antibiotics. This review also tries to describe environmental application and future perspective of QDs for antibiotics detection.

Green synthetic nitrogen-doped graphene quantum dot fluorescent probe for the highly sensitive and selective detection of tetracycline in food samples

Tetracycline (TC) is a broad-spectrum antibiotic. When humans consume too much food containing tetracycline residues, it can be a serious health hazard. Therefore, it is essential to develop a strategy to detect TC. In this study, we prepared light blue-green luminescent nitrogen-doped graphene quantum dots (N-GQDs) by a hydrothermal method using the natural products potato straight-chain starch and urea as precursors; the fluorescence quantum yield of the prepared N-GQDs was 5.2%. We investigated the detection of tetracycline (TC) by this N-GQD fluorescent sensor based on the internal filtration effect (IFE) of TC on N-GQDs. The reaction is green, simple and no other contaminating products are present. A good linear relationship was established between the relative fluorescence intensity ratio of the system and the logarithm of the TC concentration of 2.5 × 10⁻¹⁰ to 5 × 10⁻⁶ M (R² = 0.9930), with a detection limit of 9.735 × 10⁻¹³ M. The method has been used to analyze TC in three real food samples (whole milk, skim milk, honey) with low detection limits (3.750 × 10⁻¹¹ to 2.075 × 10⁻⁹ M), wide linear range, and satisfactory recoveries of 93.80–109.20% were obtained. In conclusion, the proposed method is a green, rapid, highly sensitive and selective method for the detection of tetracycline in real food samples, demonstrating the potential application of N-GQDs in food detection.

Tetracycline (TC) is a broad-spectrum antibiotic.

Shedding Light on Graphene Quantum Dots: Key Synthetic Strategies, Characterization Tools, and Cutting-Edge Applications

During the last 20 years, the scientific community has shown growing interest towards carbonaceous nanomaterials due to their appealing mechanical, thermal, and optical features, depending on the specific nanoforms. Among these, graphene quantum dots (GQDs) recently emerged as one of the most promising nanomaterials due to their outstanding electrical properties, chemical stability, and intense and tunable photoluminescence, as it is witnessed by a booming number of reported applications, ranging from the biological field to the photovoltaic market. To date, a plethora of synthetic protocols have been investigated to modulate the portfolio of features that GQDs possess and to facilitate the use of these materials for target applications. Considering the number of publications and the rapid evolution of this flourishing field of research, this review aims at providing a broad overview of the most widely established synthetic protocols and offering a detailed review of some specific applications that are attracting researchers’ interest.

Synthesis of multi-color fluorine and nitrogen co-doped graphene quantum dots for use in tetracycline detection, colorful solid fluorescent ink, and film

Fluorine-doped graphene quantum dots have unique chemical bonds and charge distribution, which can bring unexpected properties compared to other common atom-doped graphene quantum dots. In the present work, fluorine and nitrogen co-doped graphene quantum dots (F, N-GQDs) are synthesized from levofloxacin via a simple hydrothermal method. Systematic studies demonstrate that F, N-GQDs can emit various fluorescence with the wavelength ranging from blue to green by dispersing F, N-GQDs into different solvents. Moreover, multi-color fluorescence is available by simply changing the concentration of F, N-GQDs. In addition to these unique characteristics, F, N-GQDs also exhibit a sensitive fluorescence response to tetracycline with an ultralow detection limit of 77 nM in water. Because of high photostability and high quantum yield, the F, N-GQDs are exploited as a unique invisible ink, which is printable and writable on paper. Meanwhile, based on the solvatochromism of F, N-GQDs, we realized the color adjustable fluorescent ink. Finally, large-area flexible multi-color fluorescent films are realized. Our synthesized F, N-GQDs, with tunable fluorescence in wavelength and intensity, have numerous opportunities for optical molecular sensors, information security, flexible optics, and others.

Fluorescent sensing system based on molecularly imprinted phase-change microcapsules and carbon quantum dots for high-efficient detection of tetracycline

Aiming at enhancing the detection efficiency and identification accuracy of tetracycline under a high-temperature condition, this study focuses on an innovative fluorescent sensing system (MIP@CQD-PCM) based on molecularly imprinted phase-change microcapsules along with the carbon quantum dots (CQDs) embedded in their shell. This system was fabricated by microencapsulating n-eicosane as a phase change material (PCM) core within a CQDs-embedded SiO₂ shell, followed by coating a tetracycline-templated molecularly imprinted polymer (MIP) layer onto the surface of the SiO₂ shell. The specific recognition sites to tetracycline molecules were finally achieved by removal of tetracycline template from the MIP layer. Comprehensive characterizations and investigations on the structure and performance of the fluorescent sensing system were given to confirm its successful fabrication in accordance to our design strategy. The resultant MIP@CQD-PCM exhibits a satisfactory thermal storage capacity and phase-change cycle stability for temperature regulation and thermal management applications under a phase-change enthalpy of over 162 J/g. Most of all, a typical fluorescence-quenching effect was obtained from the combination of the CQDs embedded in the SiO₂ shell and the tetracycline molecules adsorbed in the MIP layer. This makes the MIP@CQD-PCM achieve an enhanced capability for the fluorescence identification of tetracycline in a high-temperature environment through the in situ thermal management of its PCM core. The MIP@CQD-PCM also displays high selectivity and good reusability for tetracycline detection in industrial applications. This work provides a promising strategy for the design and development of fluorescent sensing systems with high recognition efficiency and identification accuracy in the detection of hazardous substances.