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Spermine assumes a pivotal role in assessing food safety due to its potential to induce a spectrum of diseases upon excessive consumption. However, contemporary spermine detection methodologies, exemplified by high-performance liquid chromatography (HPLC), demand costly instrumentation and the expertise of skilled technicians. To address this challenge, the study introduces a portable fluorescence sensing platform. Ratiometric fluorescent probes were realized through the utilization of CdS quantum dots deeply doped with Ag+ (CdS:Ag QDs) and nitrogen-doped carbon quantum dots (N-CQDs). Hydrogen bonds formed between CdS:Ag QDs and spermine result in the formation of the assembly and the decreasing of the fluorescence intensity. In an effort to broaden the applicative scope and streamline deployment processes, fluorescent sensing hydrogels were meticulously engineered, capitalizing on the swelling properties inherent in polyvinyl alcohol (PVA) hydrogels. The systematic delineation of the correlation between 1 − R/B and spermine concentration facilitates the quantitative determination of spermine concentration. The incorporation of this composite construct serves to alleviate environmental influences on the probes, thereby augmenting their precision. The portable fluorescent sensing platform proves pivotal in expeditiously measuring spermine concentration within the fluorescent sensing hydrogel, enabling a quantitative assessment of pork freshness. The utilization of this platform for food freshness evaluation imparts the benefits of convenience, cost-effectiveness, and intuitive operation. [ABSTRACT FROM AUTHOR]

In the realm of food safety, the accumulation and potential health risks posed by persistent residues of broad-spectrum antimicrobials, which degrade slowly in the environment, have prompted the urgent development of efficient and sensitive detection methods. Addressing this challenge, nitrogen-doped carbon quantum dots (N-CQDs) were synthesized through a high-temperature hydrothermal method using citric acid and urea as sources. Utilizing these N-CQDs, a sensor incorporating molecularly imprinted polymers was developed through a sol–gel process with sulfadiazine (SDZ) as the template molecule. This involved using 3-aminopropyltriethoxysilane and tetraethyl orthosilicate as the monomer and cross-linker, respectively. The resulting sensor exhibited a linear detection range of 0 to 30 µmol/L and a notably low detection limit of 0.04 µmol/L. Further testing on actual pork samples revealed recovery rates between 95.10 and 108.30% and a relative standard deviation below 2.0%, emphasizing its high sensitivity and selectivity. This advancement not only enhances SDZ detection capabilities, but also paves the way for broader applications in food safety monitoring, setting a solid foundation for future developments in sensor technology. [ABSTRACT FROM AUTHOR]

Herein, nitrogen is doped into carbon quantum dots (N‐CQDs) using a hydrothermal method for the rapid detection of metolachlor in grain. The morphological features, elemental compositions, and optical properties of the N‐CQDs are then analyzed and investigated using transmission electron microscopy, X‐ray photoelectron spectroscopy, and fluorescence spectroscopy, respectively. Based on the principle of intramolecular charge transfer, a fluorescent probe is constructed for the rapid detection of metolachlor. Under optimal experimental conditions, the fluorescence intensity change values of the N‐CQDs and metolachlor concentration have a good linear relationship when the concentration of metolachlor is in the range of 0.0125−2.5 μg mL−1. An evaluation of the method shows that the method has good selectivity, reproducibility, and stability, with a limit of detection of 1.63 μg kg−1 and a limit of quantification of 3.92 μg kg−1. The spiked recoveries of six real samples are tested using a spiked recovery assay that yielded spiked recoveries in the range of 105.05−87.13%, and their relative standard deviations (n = 3) ranged from 4.62% to 0.61%, indicating that the method can be used for detection in actual samples with good precision and stability. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon quantum dots (N-CQDs) incorporated into highly conductive transition metal nitrides offer enhanced electrochemical performance, delivering a high energy density and outstanding electrochemical stability. The present study reports a high-performance supercapacitor electrode consisting of electrophoretic anchored zero-dimensional N-CQDs with reactively cosputtered titanium chromium nitride nanopyramid (Ti–Cr–N) thin films on flexible stainless-steel mesh (SSM) substrates. The nanopyramids of N-CQDs/Ti–Cr–N offer remarkable electrochemical performance through Li+ storage, ascribed to the abundant electroactive sites and enhanced synergism between the high specific surface area of N-CQDs and higher conductivity of Ti–Cr–N. Subsequently, the N-CQDs/Ti–Cr–N/SSM electrode in a 1 M Li2SO4 aqueous electrolyte exhibits an excellent gravimetric capacitance of 393.8 F·g–1 at a specific current density of 0.32 A·g–1. Further, the N-CQDs/Ti–Cr–N/SSM heterostructure outperforms other multicationic-based supercapacitors with a maximum energy density of 41.41 Wh·kg–1 and a superior power density of 7.0 kW·kg–1. Impressive electrochemical stability of ∼88.6% is retained by the heterostructure even after 5000 continuous charge–discharge cycles. Insights into charge storage mechanisms highlight the dominance of surface-limited capacitive and pseudocapacitive kinetics, with fewer contributions from diffusion-controlled faradaic processes. Furthermore, an exemplary mechanical stability of ∼99.98% over 1200 bending cycles demonstrates the N-CQDs/Ti–Cr–N/SSM heterojunction's excellent resilient structural strength, validating the present electrode potential for high-performance flexible supercapacitor application. [ABSTRACT FROM AUTHOR]

Carbon quantum dots (CQDs) with outstanding fluorescence properties have shown enormous applications in bioimaging due to their biocompatibility and nano size attribute. However, the toxicity of QDs may hinder their implementation in biomedical use. Here, nitrogen-doped carbon quantum dots (N-CQDs) were produced by employing a microwave-assisted approach and then their in vivo and in vitro toxicity has been investigated. An in vitro toxicity study was conducted against human breast adenocarcinoma cell lines (MDA-MB-361) by considering the concentration of 0–600μg mL−1 of the N-CQDs and the in vivo toxicity examination was done in Swiss albino mice for 30 days by considering two concentrations of N-CQDs, i.e., 10mg/kg BW (body weight) and 20mg/kg BW. Several parameters have been inspected by these studies like cell viability, antioxidant enzymes studies, and hematological and histopathological studies, and concluded that the synthesized NCQDs are non-toxic and can be used safely for bioimaging. Furthermore, the luminescence properties of N-CQDs were inquired by labeling them on a variety of fungal and bacterial cells. When the N-CQD-labeled cells were excited at two wavelengths, it leads to the emission of green and red fluorescence enabling them ideal for bioimaging. Briefly, there is a production of inexpensive and biocompatible N-CQDs of an average particle size of ~3.16 nm that can serve as universal fluorescent agents for the detection of diverse groups of pathogenic microorganisms. [ABSTRACT FROM AUTHOR]

Fipronil, as an excellent insecticide, is widely used around the world, but its residues in agricultural products and the environment cause a series of health and ecological risks. In this study, a novel aptamer sensor for the sensitive, selective, and quantitative detection of fipronil in eggs was prepared using nitrogen-doped carbon quantum dots (NCQDs) modified by fipronil aptamer. It is based on the adsorption of apt-NCQDs on the surface of graphene oxide (GO) through π-stacking and hydrophobic interactions, and quenching the fluorescence of apt-NCQDs through the fluorescence resonance energy transfer between NCQDs and GO. In the presence of fipronil, apt-NCQDs were desorbed from GO and the fluorescence resonance energy transfer (FRET) process was inhibited to recover the fluorescence. Under the optimized conditions, the linear range of fipronil was 10–60 nM, R2 = 0.9907, and the LOD was 3.58 nM, which showed good selectivity and sensitivity to fipronil. In addition, the recovery of this method for detection in egg samples ranged 89–104% with an RSD < 8%, which indicates that this method has good prospects for practical application. [ABSTRACT FROM AUTHOR]

A simple, effective, and highly sensitive analytical approach was created and applied in this study for the accurate measurement of three β2-agonist residues (clenbuterol, salbutamol, and ractopamine) in meat samples. In the course of the experiment, new adsorbent molecular sieves (ZMS)@nitrogen-doped carbon quantum dots (N-CQDs) composite materials were synthesized with the aid of hydrothermal synthesis. The composite adsorbent materials were prepared and characterized through scanning electron microscopy, transmission electron microscope, X-ray photoelectron spectroscopy, fluorescence, and zeta potential. Four determinants affecting the extraction and elution's efficiency, such as the amount of adsorbent, the extraction time, desorption time, and the amount of extraction salt, were substantially optimized. The analytes were quantified by gas chromatography–mass spectrometry. Final results of the methodological validation reflected that the ZMS@N-CQDs composite materials were able to adsorb three β2-agonist residues well and had good reproducibility. In the meantime, all analytes indicated good linearity with coefficient of determination R2 ≥ 0.9908. The limit of detection was 0.7–2.0 ng·g−1, the limit of quantification varied from 2.4 to 5.0 ng·g−1, the precision was lower than 11.9%, and the spiked recoveries were in the range of 79.5–97.8%. To sum up, the proposed approach was quite effective, reliable, and convenient for the simultaneous analysis of multiple β2-agonist residues. Consequently, this kind of approach was successfully applied for the analysis of such compounds in meat samples. [ABSTRACT FROM AUTHOR]

Using 2,3-diaminopyridine and citric acid as precursors, blue fluorescent nitrogen-doped carbon quantum dots (NCQDs) with a narrow size distribution (∼7.2 nm) were prepared and applied in the following assay for mercury ion detection at a weight ratio of 2,3-diaminopyridine:citric acid = 1:1 (0.2 g: 0.2 g, 20 mL for H 2 O), 220 °C, and 10 h. NCQDs was characterized by TEM, FT-IR, XPS, UV–Vis and EDS, and the prepared NCQDs display excitation-independent behavior due to less surface defects and uniform size. The optimal excitation and emission wavelengths of the NCQDs were 380 nm and 430 nm, respectively. Interestingly, the fluorescence of the NCQDs could be rapidly and selectively quenched by Hg2+ within 9 min at room temperature without further modification. Under optimal conditions, the limit of detection (LOD) was measured to be at the nanomolar level (42.4 nmol/L) with a linear range of 0–5.0 μmol/L, and fluorescence analysis of NCQDs was successfully used for the qualitative and quantitative analysis of mercury ions in food samples. Furthermore, our results revealed that fluorescence quenching occurred under the common fluences of the inner filter effect, and the static quenching effect was authenticated in the process in which Hg2+ coordinates with the NCQDs to form nonfluorescent complexes. • The NCQDs was applied to the detection of mercury ions. • The NCQDs was characterized by TEM, FT-IR, XPS, UV–Vis and PL. • The detection limit is ∼42.4 nmol/L. • The NCQDs was successfully detected to Hg2+ in food samples. [ABSTRACT FROM AUTHOR]

One of the most promising drugs recently approved for the treatment of various types of cancer is dacomitinib, which belongs to the tyrosine kinase inhibitor class. The US Food and Drugs Administration (FDA) has recently approved dacomitinib as a first-line treatment for patients suffering from non-small cell lung cancer (NSCLC) with epidermal growth factor receptor (EGFR) mutations. The current study proposes the design of a novel spectrofluorimetric method for determining dacomitinib based on newly synthesized nitrogen-doped carbon quantum dots (N-CQDs) as fluorescent probes. The proposed method is simple and does not require pretreatment or preliminary procedures. Since the studied drug does not have any fluorescent properties, the importance of the current study is magnified. When excited at 325   nm , N-CQDs exhibited native fluorescence at 417   nm , which was quantitatively and selectively quenched by the increasing concentrations of dacomitinib. The developed method involved the simple and green microwave-assisted synthesis of N-CQDs, using orange juice as a carbon source and urea as a nitrogen source. The characterization of the prepared quantum dots was performed using different spectroscopic and microscopic techniques. The synthesized dots had consistently spherical shapes and a narrow size distribution and demonstrated optimal characteristics, including a high stability and a high fluorescence quantum yield ( 25.3 % ). When assessing the effectiveness of the proposed method, several optimization factors were considered. The experiments demonstrated highly linear quenching behavior across the concentration range of 1.0 − 20.0   μ g / mL with a correlation coefficient (r) of 0.999. The recovery percentages were found to be in the range of 98.50–100.83% and the corresponding relative standard deviation (%RSD) was 0.984. The proposed method was shown to be highly sensitive with a limit of detection (LOD) as low as 0.11   μ g / mL . The type of mechanism by which quenching took place was also investigated by different means and was found to be static with a complementary inner filter effect. For quality purposes, the assessment of the validation criteria adhered to the ICHQ2(R1) recommendations. Finally, the proposed method was applied to a pharmaceutical dosage form of the drug (Vizimpro® Tablets) and the obtained results were satisfactory. Considering the eco-friendly aspect of the suggested methodology, using natural materials to synthesize N-CQDs and water as a diluting solvent added to its greenness profile. [ABSTRACT FROM AUTHOR]

Current developments in the emerging field of nanotechnology enables researchers to synthesize different types of quantum dots for biomedical applications. Carbon quantum dots (CQDs) has gained special attention due to their unique physicochemical properties, like high quantum yield and electron density. Doping of CQDs with nitrogen is a way forward to enhance their properties, which can be achieved by various approaches using wide range of nitrogen sources. The surface state of CQDs can be passivated by the nitrogen doping, which changes their energy gap width and electron density that aids in modulating their quantum yield to the higher level than without doping. The nitrogen-doped CQDs (N-CQDs) exhibit a broad range of properties, such as fluorescence, high quantum yield, easily accessibility and low cytotoxicity etc., that make them a suitable agent for variety of applications in the field of medical sciences. Due to these outstanding features of N-CQDs, it can be used for various purposes such as imaging, sensing, photocatalysis, solar cells, etc. In this review, a comprehensive synthesis methodology of N-CQDs is provided, along with its in-vitro and in-vivo bioimaging applications. This review will help in analysis of contemporary advances in the development of N-CQDs as unique and versatile nanomaterial so as to derive fruitful result for further improvement of the properties of N-CQDs for futuristic exploration in nanoscience. In this review, the recent progress in N-CQDs-based bioimaging has been summarized during the last 5 years. [ABSTRACT FROM AUTHOR]

In this work, a novel, sensitive, and rapid electrochemical biosensor was employed to detect lysozyme (Lys) using a double receptor of molecular imprinted polymer (MIP)-aptamer. First, a glassy carbon electrode (GCE) was modified with a nanocomposite consisting of multi-wall carbon nanotubes (MWCNTs), nitrogen-doped carbon quantum dots (N-CQDs), and chitosan. Subsequently, aptamer (Apt)-Lys complex was immobilized on MWCNTs-N-CQDs-chitosan/GCE via binding between carboxyl groups present in the nanocomposite and the terminal amine groups of the aptamer. Following that, methylene blue monomer was electrochemically polymerized around the Apt-Lys complex on the MWCNTs-N-CQDs-chitosan/GCE surface. Finally, after the template removal, the remaining cavities along with the aptamers created a new hybrid receptor of MIP-aptamer. The MWCNTs-N-CQDs-chitosan nanocomposite could provide large amounts of carboxyl groups for binding to amino-functionalized aptamers, considerable electrical conductivity, and a high surface-to-volume ratio. These beneficial features facilitated the Apt-Lys complex immobilization and gave improved electrochemical signal. The obtained MIP-aptamer hybrid receptor allowed lysozyme determination even at concentrations as low as 4.26 fM within the functional range of 1 fM to 100 nM. [ABSTRACT FROM AUTHOR]

The knowledge of the ways in which post-synthesis treatments may influence the properties of carbon quantum dots (CDs) is of paramount importance for their employment in biosensors. It enables the definition of the mechanism of sensing, which is essential for the application of the suited design strategy of the device. In the present work, we studied the ways in which post-synthesis thermal treatments influence the optical and electrochemical properties of Nitrogen-doped CDs (N-CDs). Blue-emitting, N-CDs for application in biosensors were synthesized through the hydrothermal route, starting from citric acid and urea as bio-synthesizable and low-cost precursors. The CDs samples were thermally post-treated and then characterized through a combination of spectroscopic, structural, and electrochemical techniques. We observed that the post-synthesis thermal treatments show an oxidative effect on CDs graphitic N-atoms. They cause their partially oxidation with the formation of mixed valence state systems, [CDs]0+, which could be further oxidized into the graphitic N-oxide forms. We also observed that thermal treatments cause the decomposition of the CDs external ammonium ions into ammonia and protons, which protonate their pyridinic N-atoms. Photoluminescence (PL) emission is quenched. [ABSTRACT FROM AUTHOR]

N-doped carbon quantum dots (N-CDs) with polyaminobenzene hydrazine as precursor were prepared by solvothermal method for the monitoring of pH fluctuation in HeLa cells via fluorescence imaging. The N-CDs show two emission wavelengths at 582 and 640 nm under different pH with two excitation wavelengths. The fluorescence intensity at 640 nm (λex = 520 nm) and the ratio of F582/F640 (λex = 470 nm) linearly increase with pH in the range of 2.4 ~ 3.6 (R2 = 992) and 5.6 ~ 7.6 (R2 = 0.987), respectively. The sensor exhibits high sensitivity and reversibility and anti-interference capability, thus enabling sensing pH change in intracellular environment in real time, as demonstrated by successful monitoring of intracellular pH fluctuation during H2O2 stimulation in HeLa cells. [ABSTRACT FROM AUTHOR]

High sensitivity, low concentration, and excellent selectivity are pronounced primary challenges for semiconductor gas sensors to monitor acetone from exhaled breath. In this study, nitrogen-doped carbon quantum dots (N-CQDs) with high reactivity were used to activate dandelion-like hierarchical tungsten oxide (WO 3 ) microspheres to construct an efficient and stable acetone gas sensor. Benefiting from the synergistic effect of both the abundant active sites provided by the unique dandelion-like hierarchical structure and the high reaction potential generated by the sensitization of the N-CQDs, the resulting 16 wt % N-CQDs/WO 3 sensor shows an ultrahigh response value ( R a / R g = 74@1 ppm acetone), low detection limit (0.05 ppm), outstanding selectivity, and reliable stability to acetone at the optimum working temperature of 210 °C. Noteworthy that the N-CQDs facilitate the carrier migration and intensify the reaction between acetone and WO 3 during the sensing process. Considering the above advantages, N-CQDs as a sensitizer to achieve excellent gas-sensitive properties of WO 3 are a promising new strategy for achieving accurate acetone detection in real time and facilitating the development of portable human-exhaled gas sensors.

The aim of this study was to establish a rapid detection method of rutin in food based on nitrogen-doped carbon quantum dots (N-CDs) as the fluorescent probe. N-CDs were prepared via a single-step hydrothermal process using citric acid as the carbon source and thiourea as the nitrogen source. The optical properties of N-CDs were characterized using an electron transmission microscope, X-ray diffractometer, Fourier-transform infrared spectrometer, and nanoparticle size potential analyzer. The UV/Vis absorption property and fluorescence intensity of N-CDs were also characterized using the respective spectroscopy techniques. On this basis, the optimal conditions for the detection of rutin by N-CDs fluorescent probes were also explored. The synthesized N-CDs were amorphous carbon structures with good water solubility and optical properties, and the quantum yield was 24.1%. In phosphate-buffered solution at pH = 7.0, Rutin had a strong fluorescence-quenching effect on N-CDs, and the method showed good linearity (R2 = 0.9996) when the concentration of Rutin was in the range of 0.1–400 μg/mL, with a detection limit of 0.033 μg/mL. The spiked recoveries in black buckwheat tea and wolfberry were in the range of 93.98–104.92%, the relative standard deviations (RSD) were in the range of 0.35–4.11%. The proposed method is simple, rapid, and sensitive, and it can be used for the rapid determination of rutin in food. [ABSTRACT FROM AUTHOR]

A label-free and specific FRET-based interleukin-6 (IL-6) aptasensor was developed using a DNA aptamer modified with nitrogen-doped carbon quantum dots (NCDs) and gold nanoparticles (AuNPs) as a donor-quencher pair. The assayed target was capable of disrupting the donor–acceptor assemblies yielding a concentration-related fluorescence recovery of NCDs (λem = 445 nm and λex = 350 nm). By designing two different probes, the interaction of DNA aptamers with IL-6 protein was studied using FRET efficiency. It appeared that the sensing probes showed slightly different sensing profiles. One of the aptasensors showed a linear response of 1.5–5.9 pg/mL for IL-6 with a coefficient of determination of R2 ≥ 0.99 and the a detection limit of 0.82 pg/mL (at S/N = 3). The experimental results indicated that the biosensor can be applied to determine IL-6 in human serum (with recovery of 95.7–102.9%). Due to the high sensitivity, excellent selectivity, and simplicity of the procedure, this strategy represents a promising alternative for IL-6 sensing in clinical applications. [ABSTRACT FROM AUTHOR]

Direct absorption solar collector (DASC) using nanofluids is an efficient way to utilize solar energy. The heat collection efficiency in DASC is constrained by the stability and optical absorption capacity of nanofluids. Carbon quantum dots (CQDs) nanofluids are used in DASC due to the excellent dispersion stability. However, the optical absorption range of current CQDs is primarily confined to the ultraviolet region, resulting in the visible and near-infrared regions of sunlight being underutilized. To solve this problem, this study synthesized novel N-doped carbon quantum dots (FPNCQDs) using ammonium bifluoride (NH 4 F) and perylene derivatives. The addition of NH 4 F and perylene derivatives during synthesis increased the sp2 conjugated structure and the content of graphite N in FPNCQDs. The doping of N, especially graphite N, significantly reduces the band gap by injecting excess electrons into the unoccupied π∗ orbitals. The temperature of FPNCQDs/EG nanofluids increased from 24 °C to 65.7 °C within 60 min, demonstrating excellent photothermal conversion performance. What's more, the FPNCQDs/EG nanofluids achieved high stability with nearly consistent transmittance over a 14-day storage test. Finally, a theoretical model for the photothermal conversion process of the nanofluids was developed to investigate the effect to carbon quantum dots on the solar collection performance. The simulation results indicated that the FPNCQDs/EG nanofluids at 10 ppm demonstrated the highest solar collection efficiency considering both photothermal conversion and heat loss from the surface. The novel FPNCQDs/EG nanofluid will be a promising photothermal fluids in direct absorption solar collector. • The novel Nitrogen-doped carbon quantum dots (FPNCQDs) were synthesized. • The FPNCQDs demonstrated much superior photothermal conversion ability in all solar spectrum. • The excellent optical property was achieved by expanding the sp2 structural domains in carbon core. • Theoretical simulation identified that nanofluids at 10 ppm achieved the highest solar collection efficiency. [ABSTRACT FROM AUTHOR]

The development of photocatalysts with high charge separation and migration efficiencies for environmental remediation using sunlight had been a research priority. In this study, a ternary composite photocatalyst, P-CN/BC/NCDs, was successfully synthesized by thermal condensation and hydrothermal methods, incorporating graphitic carbon nitride (P-CN), biochar (BC), and nitrogen-doped carbon quantum dots (NCDs). Alizarin red S (ARS) was selected as the model pollutant to evaluate the photocatalytic degradation performance. P-CN/BC/NCDs exhibited enhanced photocatalytic degradation performance under visible light irradiation, with a 4.5-fold improvement compared to P-CN alone. The optimally NCDs-loaded P-CN/BC nanocomposites exhibited high visible light absorption and high specific surface area. The increased photocatalytic activity was further confirmed by the increase in photocurrent intensity and the decrease in fluorescence intensity and resistance. XPS and FT-IR tests showed that NCDs, as co-catalysts of P-CN/BC, effectively promoted charge separation through ether bonds and electrostatic interactions. It was experimentally verified by free radical trapping experiments and EPR tests that •O 2 − was the primary active species in the photocatalytic process, while •OH served as an auxiliary site during the degradation process. Cyclic experiments demonstrated high reusability and excellent stability, with an activity exceeding 93.8 %. Decomposition intermediates and reaction pathways were identified by liquid-quality analysis. Photocatalyst pervasiveness was evaluated by using different pollutants including methyl orange (MO), rhodamine B (Rh B) under similar conditions. This design concept of functional synergistic modification of P-CN materials holds promise for application in various fields. [Display omitted] • The Doping of NCDs improves the charge distribution and provides moreactive sites. • NCDs act as electronic acceptor to guide the flow of photogenerated charge carriers. • ·O 2 − was identified as the main active substance. • Broad applicability (Five pollutants) and strong catalytic activity(14 times of conventional g-C₃N₄). [ABSTRACT FROM AUTHOR]

PPy nanoparticles are widely employed as PTT agents, because of their exceptional near-infrared absorption properties. Nonetheless, the efficacy of PTT with PPy nanoparticles is hindered by a challenge, specifically, a lack of precise targeting. In this study, a PTT imaging agent was developed by combining NCQDs having bright green fluorescent properties with PPy nanoparticles along with the masking of folic acid to overcome the challenge of targeting. The synthesized PPy:NCQDs:FA nanocomposite, characterized by extraordinary photothermal property, was utilized for imaging of folate receptor positive (FA+) MCF-7 cancer cells through the emission of green fluorescence by NCQDs incorporated within the nanocomposite. Additionally, these nanoparticles demonstrated a good level of cell viability, exceeding 82 %, even at a concentration of 600 μg mL−1. Even the in vivo toxicity inspection of the nanocomposite exemplified no observed acute toxicity at experimental dosages of 1 and 3 mg per kg body weight. By subjecting MCF-7 cells, inoculated with 100 μg mL−1 of nanocomposite, to NIR laser irradiation for 5 min, a significant decline in cell viability was witnessed, establishing the photothermal therapeutic potency of the nanocomposite. The death of cancer cells induced by nanocomposite was verified through MTT assay, imaging of cells by NCQDs alone, with nanocomposite, and by live/dead cell Calcein AM/PI staining assay. Quantification of induced apoptosis post-laser treatment is conducted through staining with Annexin V-FITC/PI. These findings establish potential use of PPy:NCQDs:FA nanocomposite as versatile theranostic agents, capable of targeted bioimaging and treatment for cancer cells exhibiting folate receptors. A visual summary representing all aspects of the research conducted. [Display omitted] • Synthesis of theranostic composite comprising PPy, NCQDs and FA as guiding ligand. • Composite enables targeted bioimaging & photothermal killing of cancer cells. • Simultaneous cancer detection & elimination, offering innovative tumor theranostics. • In vivo and in vitro toxicity tests ensure nanocomposite's biocompatibility. [ABSTRACT FROM AUTHOR]

Abstract This research explores into the eco-friendly synthesis of nitrogen-doped carbon quantum dots (NCQDs) utilizing discarded banana peel waste as a sustainable carbon source and ethylenediamine as a nitrogen dopant. The study aims on the critical gap in environmentally sustainable ion detection system by optimizing the fluorescent properties of CQDs for Fe2+ detection applications through nitrogen doping at an optimum ratio. Herein, we reported a facile one-step hydrothermal method to synthesize NCQDs with varying nitrogen dopant concentrations. The precursor material was characterized by thermal gravimetric analysis and Raman spectroscopy which exhibited a more amorphous carbon structure. Fourier-transform infrared spectroscopy and Proton nuclear magnetic resonance spectroscopy proves the successful bonding of nitrogen functional group to pristine CQDs. The obtained nitrogen-doped CQDs (NCQDs) exhibited precise size control, with an average size of 5.05 nm. Optical analysis showed that NCQDs with a nitrogen doping level of 1.25 % had the best photostability, brightness, and fluorescence stability. These NCQDs demonstrated high selectivity in detecting Fe2+ through a fluorescent quenching mechanism. These findings suggested that obtained NCQDs has potential as environmentally friendly fluorescence probes in the application water filtration systems and medical diagnostics, particularly in Fe2+ detection and sensing due to their high selectivity and efficient fluorescent properties. [Display omitted] • Nitrogen-doped CQDs (NCQDs) was obtained via green synthesis methodology. • NCQDs with nitrogen doping level of 1.25 % showcased the best optical properties. • Fluorescence of NCQD can be effectively quenched by Fe2+ ions. • The NCQDs has potential in the application of Fe2+ sensor probe. [ABSTRACT FROM AUTHOR]

The challenges of secondary pollution and limited stability of metallic catalysts/quantum dots that are used for water treatment must be resolved in the emerging ecofriendly environmental systems. Conversely, carbon materials, specifically, conventional carbon quantum dots (C-CQDs) have emerged as an abundant, stable, and biocompatible alternative for visible-light-driven photocatalysts, that are used for water treatment. Despite these advantages, the fast charge recombination in quantum-confined systems, complex purification, and limited optoelectronic performance are bottlenecks in the practical application of C-CQDs. To address these issues, we proposed a scalable structural design of C-CQDs with enhanced photocatalytic properties. The synthesis process of CQDs was modified to yield a highly amorphous core carbon quantum dots (AC-CQDs), which was controlled by varying the synthesis temperature. The low initial temperature during the synthesis of the AC-CQDs yields an amorphous core, which provides a high electrical resistance; hence, the indirect recombination occurring through core conductivity is significantly suppressed. To ensure scalable synthesis and stability, AC-CQDs were directly grown on reduced graphene oxide, which was coated on a carbon fabric to fabricate a textile-structured electrode. Efficient charge separation in the proposed catalyst electrode structure offers significantly improved photoelectrocatalytic activity, i.e., 100% effluent dye degradation in 25 min. [Display omitted] • Scalable structural design of CQDs with enhanced photocatalytic and diverse optical properties is proposed. • Bi-phase (amorphous and crystalline domains) were formed by incorporating gradient heating in the synthesis process. • Achieved heterogeneous growth of CQDs through a one-step process, which provides a strong interface between CQDs and rGO. • AD@rGO electrode achieved 100% photoelectrocatalytic effluent dye degradation in 25 min. [ABSTRACT FROM AUTHOR]

A new fluorescence method was established for sensitive detection of β-galactosidase (β-gal) activity in spiked human serum and screening of inhibitor. Nitrogen-doped carbon quantum dots (N-CQDs) were prepared by solvothermal polymerization of N-methyl-2-pyrrolidinone in an alkaline condition. The colloidal N-CQDs exhibit good water solubility, stability, and emit bright green fluorescence with a maximum emission peak at 528 nm upon excitation at 420 nm. β-gal specifically catalyzes the decomposition of its substrate P-nitrophenyl-β-D-galactopyranoside into 4-nitrophenol, whose absorption spectrum overlaps well with the excitation spectrum of the N-CQDs. As a result, the fluorescence of the N-CQDs is remarkably quenched by 4-nitrophenol via an inner filter effect. The sensing platform presents a linear response range for β-gal activity from 0.05 to 3.0 U·L−1 with a low limit of detection of 0.023 U·L−1. An acceptable precision is obtained with a relative standard deviation (RSD) of 3.1% for 1.0 U·L−1 β-gal (n = 11). The method was applied to determine β-gal in spiked human serums with recoveries in the range 96.3–104.7%. The method was employed to evaluate inhibitor screening with D-galactal and chloroquine diphosphate as models. [ABSTRACT FROM AUTHOR]

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A novel solid-state electrochemiluminescence (ECL) sensor for 17β-estradiol detection based on an intermolecular hydrogen bonds-induced self-enhanced ECL composite (Ru(dcbpy) 3 2+-NCQDs) was constructed for the first time. • A hydrogen-bonds induced self-enhanced ECL composite was generated on GCE surface. • Superior ECL properties of Ru(dcbpy) 3 2+-NCQDs composite was obtained without signal amplifier. • Excellent analytical performances were acquired using 17β-estradiol as a target. Herein, an induced self-enhanced electrochemiluminescence (ECL) sensor with superior ECL performances was simply fabricated by just dropping the ECL reagent (tris(4,4′-dicarboxylicacid-2,2′-bipyridyl) ruthenium (II) dichloride, Ru(dcbpy) 3 Cl 2) and coreactant (nitrogen-doped carbon quantum dots, NCQDs) pair onto the surface of glassy carbon electrode. In this strategy, based on the carboxyl (–COOH) groups in Ru(dcbpy) 3 2+ and oxygen, nitrogen-containing groups on NCQDs surface, an intermolecular hydrogen bonds-induced self-enhanced ECL composite was generated in the solid contact layer for the first time. Since Ru(dcbpy) 3 2+ and NCQDs were co-existing in the same composite, the electron-transfer distance between them was shortened and the energy loss was decreased, thereby higher ECL efficiency was acquired. This working process greatly avoided the introduction of signal amplifier and simplified the experimental operation. On this basis, 17β-estradiol (E2) was selected as a target model to fabricate a self-enhanced ECL aptamer sensor for the investigation of its analytical performances. Resultantly, excellent detection properties of E2, including wider linear range of 1.0 × 10-14 − 1.0 × 10-6 mol L-1 and lower detection limit of 1.0 × 10-15 mol L-1 with superior selectivity, were successfully achieved. Finally, E2 spiked into milk powder was quantified to assess the practicability of this sensor. Prospectively, this strategy could be extensively applied for other analytes determination by adjusting the corresponding target aptamers. [ABSTRACT FROM AUTHOR]

As a new type of fluorescent carbon nanomaterials, carbon quantum dots have been widely concerned in recent years because of their good biocompatibility, low cytotoxicity and easy surface functionalization. In this paper, nitrogen-doped carbon quantum dots (N-CQDs) were prepared by one-step hydrothermal method with citric acid as the carbon source and urea as a nitrogen source. The fluorescence spectrophotometer, Fourier infrared spectrometer, X-ray diffractometer, and transmission electron microscope were utilized to discover the luminescence properties, structural characteristics, morphology and size of the synthesized N-CQDs. The results showed that the best reaction conditions for preparing N-CQDs were as follows: the hydrothermal process parameters were 240 °C for 10 h, and the concentration of nitrogen doping was 0.6 wt%. Under these conditions, the prepared N-CQDs with bright blue fluorescence solution was uniform and stable. And the results showed the structural characteristics were weak crystalline graphite carbon, and the shape characteristics were nearly spherical quantum dot with about 5-10nm diameters. [ABSTRACT FROM AUTHOR]

As a new type of fluorescent carbon nanomaterials, carbon quantum dots have been widely concerned in recent years because of their good biocompatibility, low cytotoxicity and easy surface functionalization. In this paper, nitrogen-doped carbon quantum dots (N-CQDs) were prepared by one-step hydrothermal method with citric acid as the carbon source and urea as a nitrogen source. The fluorescence spectrophotometer, Fourier infrared spectrometer, X-ray diffractometer, and transmission electron microscope were utilized to discover the luminescence properties, structural characteristics, morphology and size of the synthesized N-CQDs. The results showed that the best reaction conditions for preparing N-CQDs were as follows: the hydrothermal process parameters were 240 °C for 10 h, and the concentration of nitrogen doping was 0.6 wt%. Under these conditions, the prepared N-CQDs with bright blue fluorescence solution was uniform and stable. And the results showed the structural characteristics were weak crystalline graphite carbon, and the shape characteristics were nearly spherical quantum dot with about 5–10 nm diameters. [ABSTRACT FROM AUTHOR]

A novel photoelectrochemical (PEC) immunosensor for the determination of cardiac troponin I (cTnI) was constructed. The flower-like stannic oxide (SnO2) with large specific surface area was prepared by hydrothermal synthesis. Nitrogen-doped carbon quantum dots (NCQDs) with excellent surface property were used as a sensitizer for SnO2. Bismuth oxyiodide (BiOI) is a narrow band gap (1.83 eV) nanomaterial, which was firstly modified on NCQDs-sensitized SnO2 through in situ growth method. After NCQDs with small size and BiOI nanoparticles are successively combined with SnO2, the SnO2/NCQDs/BiOI microflower was obtained, which possessed good photochemical properties. Using visible light as excitation source and ascorbic acid (AA) as electron donor, the ultrasensitive and quantitative determination of cTnI was realized by detecting the changes of photocurrent under different concentrations of cTnI. The PEC immunosensor showed a large-scaled response (0.001–100 ng mL−1) and a low detection limit (0.3 pg mL−1) under optimised experimental conditions. The sensor has potential clinical value in the prediction and diagnosis of cardiovascular diseases in elderly patients with diabetes. [ABSTRACT FROM AUTHOR]

Green emissive, nitrogen-doped carbon quantum dots prepared from Morinda coreia fruits used as fluorescent sensor for the detection of ferric ions from water. [Display omitted] • Synthesis of nitrogen-doped carbon quantum dots from Morinda coreia fruits. • Sensitive fluorescent detection of Fe3+ ions from ideal and real waters. • Spherical carbon dots of very small size (1.99 nm) with a quantum yield of 17.1 %. • A low detection limit of 1.32 μM towards Fe3+. Carbon quantum dot containing nitrogen has been prepared by utilizing a green biomass resource, Morinda coreia fruits, by a single step hydrothermal procedure. The spherical carbon dots are analysed by HR-TEM, XPS, FT-IR, UV–visible and photoluminescence studies. With a mean diameter of 1.99 nm, they possessed functional groups like carboxyl and amide on their surface and emit light of wavelength of 490 nm under 390 nm excitation. The fluorescent Morinda coreia carbon dots (MCCDs), whose quantum yield is found to be 17.1 %, are very sensitive to the presence of iron (III) ions with a low detection limit of 1.32 μM. Successful fluorometric determination of Fe3+ ions from tap water and borewell water were also achieved with good recovery rates. Interactions between surface groups on MCCDs and Fe3+ ions lead to the formation of a non-fluorescent complex, and a static quenching mechanism is proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Citric acid and arginine are used to synthesize N-CDs. • PL of the N-CDs avoids the autofluorescence of CF. • The N-CDs are used to detect the concentration of Fe3+ in CF. • The detection range of Fe3+ is 2 to 80 μM, and the detection limit is 1.2 μM. • The N-CDs can be used for life cycle assessment of CF. Cutting fluid (CF) ensures machining accuracy and improves tool life in machining, which is of great significance for its impurity content detection and life cycle evaluation. In this paper, citric acid and arginine were used as carbon and nitrogen sources, photoluminescent (PL) nitrogen-doped carbon quantum dots (N-CDs) with a particle size ranging from 8 to 14 nm and well dispersion in water-based CF were synthesized by a one-pot hydrothermal reaction method. The N-CDs have the best signal under 360 nm ultraviolet light excitation, which well avoids the autofluorescence of the CF. The N-CDs dispersion have good selectivity and linearity in the Fe3+ concentration range of 2 to 80 μM, and the detection limit is 1.2 μM. The N-CDs were used to detect the concentration of Fe3+ in CF with different working hours, and the results were consistent with the results of coupled plasma emission spectroscopy. This study provides an intelligent sensing platform for the highly sensitive and selective detection of Fe3+ in the CF environment, and provides a promising strategy for the evaluation of the CF lifetime. [ABSTRACT FROM AUTHOR]

• A ternary heterostructure BiVO 4 /CNQDs/NCDs photocatalyst was firstly fabricated. • The BiVO 4 /CNQDs/NCDs exhibited enhanced activity for RhB and TC degradation. • The BiVO 4 /CNQDs/NCDs can use as a promising candidate for water purification. In this study, a ternary heterostructure photocatalyst was synthesized by co-anchoring the graphitic carbon nitride quantum dots (CNQDs) and nitrogen-doped carbon quantum dots (NCDs) on the surface of BiVO 4 microspheres. The as-synthesized BiVO 4 /CNQDs/NCDs ternary heterostructure exhibits the excellent photocatalytic activity for degradation of rhodamine B (RhB, dye) and tetracycline (TC, antibiotic) under visible-light illumination. Eventually, it is found that the BiVO 4 /CNQDs/NCDs shows the much better photoreactivity both for RhB and TC degradation in comparison with that of pure BiVO 4 , BiVO 4 /CNQDs, and BiVO 4 /NCDs samples, respectively. The improvement of photocatalytic performance is due to the efficient separation and transport of photogenerated charge carriers, resulting in formation of a ternary heterostructure system. This work will be useful for the construction of other ternary heterostructure photocatalysts application in waste water purification. [ABSTRACT FROM AUTHOR]

Utilizing ultraviolet light by using Energy Down Shift (EDS) of quantum dots is a recent approach to efficiently utilize a broader spectrum of light, for energy harvesting. Other than higher efficiency, EDS is highly promising for increasing the stability of Dye-Sensitized Solar cells (DSSC); as it decreases the UV degradation of the cell. Previously, heavy metals-based (Cadmium etc) quantum dots are used for the purpose, which are not only toxic but also have less stability and have complicated synthesis methods. To overcome these issues, a thin coating of green emissive Nitrogen-doped Carbon Quantum Dots (N-CQDs) on DSSC, as a stable and efficient EDS layer is proposed here. N-CQDs were synthesized by a scalable, green and facile one-pot hydrothermal pyrolysis of citric acid in presence of nitrogen source, with a production yield of 65%, and quantum yield of 70%. The readily dispersible and highly stable colloid of N-CQDs was coated on the device, and with an optimized thickness, the power conversion efficiency was increased by 10%. This increase was further confirmed by external quantum efficiency (EQE) test, i.e. N-CQDs coated device showed EQE enhancement majorly in the UV spectrum and enhanced stability in UV light was recorded. The transmittance of FTO-glass was increased due to EDS and it also has an antireflection effect, which intern produces a small increase in EQE in the visible spectrum. UV light is converted to green light by quantum dots energy down shift layer, thus enhancing the efficiency and stability of organic dye sensitized solar cell. Unlabelled Image • Green emissive Nitrogen doped Carbon Quantum Dots (N-CQDs) are synthesized with a high quantum yield of 70 %. • Overlayer of N-CQDs efficiently convert UV light to green light, thus enhancing the efficiency (by 10 %) and UV stability. • N-CQDs are scalable, eco-friendly, low-cost and efficient alternative compared to existing energy down shifting layers. [ABSTRACT FROM AUTHOR]

• NCQDs showed specific antibacterial activity against Staphylococcus. • NCQDs killing S. aureus and MRSA caused negligible toxicity to the main rat organs. • NCQDs treating wounds infected with MRSA showed the same effect as vancomycin. • GSH could enhance the antibacterial effect of NCQDs against Staphylococcus. Antimicrobial resistance is becoming more and more serious and has become a potential hazard to human life and health. The fabrication of some new antibacterial substances against resistant bacteria is demanded. With the wide application and research of carbon nanomaterials, nitrogen-doped carbon quantum dots (NCQDs) were synthesized by a one-step chemical route herein. The particle size of NCQDs in the range of 2–5 nm were characterized by transmission electron microscopy (TEM), atomic force microscopy, and dynamic light scattering. The functional groups and optical properties of NCQDs were investigated by UV–vis absorption spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Disk-diffusion tests showed that the NCQDs had specific antibacterial activity against Staphylococcus. TEM showed that the NCQDs could destroy the cell structure of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) but could not combat Escherichia coli. The antibacterial mechanism may be that positively charged NCQDs firstly interacted with the negatively charged bacteria, and then specifically anchored on some specific sites on the surface of Staphylococcus. The NCQDs were applied to treat wounds infected with MRSA and showed the same therapeutic effect as vancomycin. Photomicrographs of hematoxylin-eosin-stained histological sections showed that the NCQDs at concentrations effectively killing S. aureus and MRSA caused negligible toxicity to the main rat organs, including heart, liver, spleen, lung, and kidney. Thus, the NCQDs can be developed as a promising antibacterial agent for Staphylococcus. And the NCQDs are likely to treat local infections caused by Staphylococcus clinically, especially S. aureus and MRSA. [ABSTRACT FROM AUTHOR]

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.

Graphical abstract Highlights • A strongest multiple fluorescent N-CQDs were synthesized from the P. acidus fruits. • Synthesized N-CQDs showed low-toxic and were employed for in vivo live-cell imaging. • The N-CQDs were uniformly stained within the body of the nematodes (C. elegans). • The live-cell imaging result reveals the usage of N-CQDs in drug delivery. Abstract In this work, nitrogen-doped carbon quantum dots (N-CQDs) have been synthesized successfully by a simple hydrothermal method and demonstrated its application for multicolor imaging in Caenorhabditis elegans (C. elegans) as an in vivo model. The synthesized N-CQDs were characterized by various physicochemical techniques such as XRD, Raman spectroscopy, ATR-FTIR spectroscopy, XPS, HRTEM, UV–vis spectroscopy, and fluorescence spectroscopy. The synthesized N-CQDs exhibited a strong fluorescence due to the uniform size distribution with nitrogen-containing and oxygen-containing functional groups onto the surface of N-CQDs which induce the excellent dispersibility in aqueous media. The N-CQDs has an excitation-dependent fluorescence behavior and the strongest fluorescence appeared at 411 nm (emission peak position) under the excitation of 340 nm. Also, the N-CQDs displayed a high quantum yield (QY) of 12.5. The fluorescence behaviour of the aqueous N-CQDs suspension retains for a long time up to 1 year. The prolonging fluorescent N-CQDs was utilized as a staining agent for bioimaging and toxicity of N-CQDs on C. elegans that was conducted by killing assay. In-vivo studies suggested that the N-CQDs displayed excellent biocompatibility and successfully used for high-contrast imaging of N-CQDs in living and dead C. elegans. Based on the strongest fluorescence along with excellent aqueous dispersibility and biocompatibility, the green synthesized N-CQDs would be an ideal candidate for many biological applications. [ABSTRACT FROM AUTHOR]

A facile, economical and straightforward hydrothermal strategy was used to prepare highly luminescent nitrogen‐doped carbon quantum dots (N‐CQDs) by using citric acid and urea as the precursors. The as‐prepared N‐CQDs exhibited excellent excitation‐wavelength‐dependent photoluminescence property, high relative fluorescence quantum yield of up to 82.4%, and high selective response to Hg2+ over other examined metal ions in water samples. Under the optimal conditions, the response was linearly proportional to the Hg2+ concentration in the range of 0–250 μM with a detection limit of 1.3 nM. The established N‐CQDs based fluorescent sensor was then successfully applied for label‐free detection of Hg2+ in environmental water samples (tap, lake, and well water). Satisfactory repeatability, reproducibility, recovery results (92.6‐116.8%) are achieved for the determination of Hg2+ in real water samples. Nitrogen‐doped carbon quantum dots (N‐CQDs) was synthesized by using citric acid and urea as the precursors at 220 °C for 6 h. The as‐prepared N‐CQDs exhibited excellent excitation‐wavelength‐dependent photoluminescence property, high relative fluorescence quantum yield of up to 82.4%, highly selective and sensitive response to Hg2+ over other examined metal ions. The developed N‐CQDs sensor was proposed for sensing of Hg2+ Ions in environmental water samples. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • N-CQD/SnO 2 nanocomposite was prepared using sonochemical approach for first time. • N-CQD/SnO 2 nanocomposite modified electrode exhibits sensitive electrochemical reaction towards riboflavin. • Modified electrode shows wide linear range and very low detection limit. Abstract We report a simple preparation of novel nanocomposite for the sensitive determination of riboflavin (RF) in real samples. Nitrogen-doped carbon quantum dots/SnO 2 (N-CQD/SnO 2) nanocomposite was prepared using sonochemical approach and applied as a voltammetric sensor for the sensitive determination of RF for the first time. The crystallographic phase, functional groups, surface analysis, and elemental distribution were examined using XRD, FT-IR, HR-TEM and EDS spectroscopic techniques respectively. This N-CQD/SnO 2 nanocomposite-modified electrode shows a fast and sensitive electrochemical response to RF sensing with a good sensitivity (2.496 μA μM−1 cm-2), wide linear range (0.05–306 μM), low detection limit (8 nM) and excellent anti-interference ability. Furthermore, the developed sensor was investigated in commercial riboflavin tablets and milk powder and obtained results are quite satisfactory. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitrogen-doped carbon quantum dots from banana peel for real-time OTC detection. • Ratiometric fluorescent probe sensors were prepared using N-CQDs with Eu3+ ions. • N-CQDs/Eu3+-based ratiometric sensors detected OTC in pork muscle and swine urine. • Smartphone-assisted N-CQDs/Eu3+-based sensors can be applied in food safety testing. Oxytetracycline (OTC) residues have serious adverse effects on human health. Thus, selective and sensitive field detection methods are needed. Here, we successfully synthesized nitrogen-doped carbon quantum dots (N-CQDs) with good water-solubility, prominent fluorescence (FL), and favorable stability via a one-step hydrothermal method using banana peel as a carbon source and diethylenetriamine as a nitrogen source. We used the N-CQDs to create a ratiometric FL probe by self-assembling them with europium ions (Eu3+), enabling OTC detection. The FL intensity of N-CQDs at 445 nm was quenched due to the inner filter effect, while the FL intensity of Eu3+ at 621 nm markedly increased via the antenna effect upon OTC introduction. The ratiometric FL sensor demonstrated two linear relationships with OTC concentrations, ranging from 0.01 to 5 μg mL−1 and 5 to 25 μg mL−1, with a limit-of-detection of 4.9 ng mL−1 for OTC. Additionally, this platform depicted an apparent color change from blue to purple under a 365 nm ultraviolet–visible lamp, and a visual semi-quantitative analysis of OTC was achieved using a mobile phone application. We successfully implemented this method to detect OTC in pork muscle and swine urine, achieving remarkable recovery results (96.89–103.20%). Therefore, our findings demonstrate the potential of this approach for real-time and semi-quantitative OTC detection. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bovine serum albumin and tertbutyl titanate are used to prepare by one-step method. • The photonic conversion function of N-CQDs reduce band gap widths of TiO 2 to 2.84 eV. • N-CQDs/TiO 2 exhibits complete degradation of Congo red and killing of E. coli. • N-CQDs/TiO 2 can degrade of Cr(VI) and the reaction rate reaches 10.7 times of TiO 2. Hexavalent chromium (Cr (VI)) is a typical heavy metal ion caused numerous wastewater, and the photocatalysis is an attractive advanced treatment process for Cr (VI) removal. Biomass material bovine serum albumin and tetrabutyl titanate were used to prepare nitrogen-doped carbon quantum dots and TiO 2 (N-CQDs/TiO 2) nanoparticles by a facile one-step hydrothermal method. The excellent photonic conversion function of N-CQDs narrowed band gap widths of TiO 2 to 2.84 eV due to the N element and the CQDs introduced to the TiO 2 successfully. When the mass ratio of BSA and TiO 2 was 1 and the hydrothermal reaction time was 48 h, the obtained nanoparticle can rapidly and efficiently degrade of Cr (VI) in 40 min of reaction, and the kinetic reaction rate reached 10.7 times that of pure TiO 2 nanoparticles. And the Cr (VI) was reduced in 10 min by 1 mg/L nanoparticle under the pH of 2 or tartaric acid content of 1 g/L due to the electrons were transferred from N-CQDs to the TiO 2 surface to achieve effective electron/hole separation and reacted with the Cr (VI) to reduce it to Cr (III). The N-CQDs/TiO 2 also exhibited degradation of Congo red completely and killing of E. coli under simulated solar light. [ABSTRACT FROM AUTHOR]

Dye-sensitized solar cells are regarded as promising candidates to resolve the energy and environmental issues in recent years, arising from their solution-processable fabrication technology and high power conversion efficiency. However, there are still several problems regarding how to accelerate the development of this type of photovoltaics, including the limited light-harvesting ability and high-production cost of molecular dye. In the current work, we have systematically studied the role of nitrogen-doped carbon quantum dots (N-CQDs) as co-sensitizers in traditional dye sensitized solar cells. A series of N-CQDs have been prepared by employing chitosan as a precursor via one-pot hydrothermal technology for various times, demonstrating a maximized efficiency as high as 0.089% for an only N-CQDs-based device. Moreover, the co-sensitized solar cell based on N719 dye (C58H86N8O8RuS2) and optimized N-CQDs shows significantly enhanced performance, yielding a solar-to-electric conversion efficiency of up to 9.15% under one standard sun (AM 1.5G) irradiation, which is much higher than the 8.5%-efficiency of the controlled device without N-CQDs. The matched characteristics of energy level, excellent up-convention, and FRET (Förster resonance energy transfer) abilities of N-CQDs are responsible for their improved power conversion efficiency.

Pursuit of low-cost and large-scale method to prepare carbon quantum dots (CQDs) is a persistent objective in recent years. In this work, we have successfully synthesized a series of nitrogen-doped carbon quantum dots (N-CQDs) under different hydrothermal temperature employing Eichhornia crassipes (ECs) as precursors. Considering the pollution ability to water and low-cost, this study may direct the novel path to convert waste material to useful quantum dots. After measurements such as TEM, XRD, Raman, XPS, PL as well as the UV–vis absorbance ability, outstanding optical properties have been discovered. In this fashion, solar cells are tentative to be fabricated, yielding the maximized solar-to-electrical conversion efficiency of 0.17% with a good fill factor of 67%. Meanwhile, the above-mentioned quantum dots also show the up-conversion ability, suggesting the potential application in infrared detection or broadening light-absorbing devices. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon quantum dots (N-CQDs) were synthesized though a facile, economical and straightforward hydrothermal method by using polyacrylamide as both carbon and nitrogen sources. The as-prepared N-CQDs offered high quantum yield of 23.1%, exhibited good water solubility and fluorescence properties. Moreover, the N-CQDs can be used as effective probes for sensitive and selective detection of dopamine. Fluorescence of N-CQDs was effectively quenched after the addition of dopamine owing to dopamine would be transformed into dopamine-quinone under alkaline conditions. A good linear relationship between fluorescence quenching and the concentration of dopamine in the range 0.1–200 μM was obtained with a low detection limit of 0.05 μM. The proposed method showed high selectivity for dopamine in the presence of potential interfering species. Moreover, this method was successfully applied to the determination of DA in urine sample with satisfactory recoveries. [ABSTRACT FROM AUTHOR]