Functionalized carbon quantum dots as fluorescent nanoprobe for determination of tetracyclines and cell imaging

Inhibitory effects of Curcumae Radix carbonisata-based carbon dots against liver fibrosis induced by carbon tetrachloride in mice

As a processed product of traditional Chinese medicine Curcumae Radix, Curcumae Radix Carbonisata (CRC) has been widely used in the treatment of liver diseases in ancient medical books. In this study, novel carbon dots (CDs) extending from 1.0 to 4.5 nm were separated from fluid extricates of CRC. Meanwhile, a liver fibrosis model induced by carbon tetrachloride (CCl4) was utilized to determine the inhibitory effects of CRC-CDs against liver fibrosis. The results exhibited the CRC-CDs with a quantum yield of 1.34% have a significant inhibitory effect on CCl4-induced liver fibrosis, as demonstrated by improving hepatocyte degeneration and necrosis, inflammatory cell infiltration and fibrotic tissue hyperplasia, downregulating the levels of alanine transaminase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL), direct bilirubin (DBIL), total bile acid (TBA), triglyceride (TG), tumour necrosis factor-α (TNF-α), interleukin (IL)-6 and IL-1β in the serum, upregulating the contents of superoxide dismutase (SOD), reduced glutathione (GSH), and downregulating the concentration of malondialdehyde (MDA), which lays an important foundation for the development of CRC-CDs as a novel drug for the treatment of liver fibrosis, and provide a certain experimental basis for the clinical application of CRC-CDs in the future.

Sustainable synthesis of fluorescent polymer carbon dots@PVA for sensitive chlortetracycline detection

Antibiotic residues persist in the environment and represent serious health hazards; thus, it is important to develop sensitive and effective detection techniques. This paper presents a bio-inspired way to make water-soluble fluorescent polymer carbon dots (PCDs@PVA) by heating biomass precursors and polyvinyl alcohol (PVA) together. For example, the synthesized PCDs@PVA are very stable with enhanced emission intensity. This property was observed in a wide range of environmental conditions, including those with changing temperatures, pH levels, UV light, and ionic strength. PCDs@PVA detected the antibiotic chlortetracycline (CTCs) with great selectivity against structurally related compounds and a low detection limit of 20 nM, demonstrating outstanding sensitivity and specificity. We confirmed the sensor's practical application through real sample analysis, yielding recovery rates of 98%-99% in samples of milk, honey, and river water. The synthesized PCDs@PVA fluorescence sensor was successfully used for CTCs detection in real samples.

Sensitive and rapid determination of tetracycline antibiotic by carrot juice-derived carbon dots as a fluorescent probe

The antibiotic tetracycline can be efficiently used as medicine for the deterrence of bacterial infections in humans, animals, and plants. However, the unprecedented use of tetracycline is of great concern owing to its low biodegradability, extensive usage, and adverse impacts on the environment and water quality. In this study, a sensitive spectrofluorometric method was proposed for the direct determination of tetracycline, based on biocompatible fluorescent carbon dots (CDs). The synthesis of CDs was performed by adopting a green hydrothermal procedure from carrot juice without requiring surface passivation or outflowing any environmentally hazardous waste. X-ray diffraction analysis and transmission electron microscopy revealed amorphous spherical-shaped CDs that exhibited blue emission under blue illumination. The fabricated fluorescent probe directly detected tetracycline in the concentration range of 4.00 × 10-6 to 1.55 × 10-5 mol L-1 with an LOD of 1.33 × 10-6 mol L-1. The performance of the probe was assessed in a tap water sample, with recovery values between 80.70 and 103.60%. The method's greenness was evaluated using the Analytical Green metric approach (AGREE) and confirmed to be within the green range. The developed method is facile, rapid, cost-effective, and offers a wide linear range and satisfactory selectivity, making it potentially suitable for determining tetracycline in water applications.

Understanding Antibiotic Detection with Fluorescence Quantum Dots: A Review

The utilization of fluorescent quantum dots (FL QDs) has gained significant traction in the realm of antibiotic detection, owing to their exceptional FL properties and versatility. Various types of QDs have been tailored to exhibit superior FL characteristics, employing diverse capping agents such as metals, surfactants, polymers, and biomass to protect and stabilize their surfaces. In their evolution, FL QDs have demonstrated both "turn-off" and "turn-on" mechanisms in response to the presence of analytes, offering promising avenues for biosensing applications. This review article provides a comprehensive overview of the recent advancements in antibiotic detection utilizing FL QDs as biosensors. It encompasses an extensive examination of different types of FL QDs, including carbon, metal, and core-shell QDs, deployed for the detection of antibiotics. Furthermore, the synthesis methods employed for the fabrication of various FL QDs are elucidated, shedding light on the diverse approaches adopted in their preparation. Moreover, this review delves into the intricate sensing mechanisms underlying FL QDs-based antibiotic detection. Various mechanisms, such as photoinduced electron transfer, electron transfer, charge transfer, Forster resonance energy transfer, static quenching, dynamic quenching, inner filter effect, hydrogen bonding, and aggregation-induced emission, are discussed in detail. These mechanisms provide a robust scientific rationale for the detection of antibiotics using FL QDs, showcasing their potential for sensitive and selective sensing applications. Finally, the review addresses current challenges and offers perspectives on the future improvement of FL QDs in sensing applications. Insights into overcoming existing limitations and harnessing emerging technologies are provided, charting a course for the continued advancement of FL QDs-based biosensing platforms in the field of antibiotic detection.

Nitrogen and Chlorine Co-doped Carbon Dots as a Highly Selective and Sensitive Fluorescent Probe for Sensing of PH, Tetracycline Detection and Cell Imaging

Carbon dots have been widely focused on the field of sensing and detection due to their excellent optical property. Herein, novel orange fluorescent nitrogen and chlorine co-doped carbon dots (N,Cl-CDs) are obtained by one-pot hydrothermal method using o-phenylenediamine and neutral red. Based on the inner filter effect, the prepared N,Cl-CDs can be innovatively developed as an effective "signal-off" multifunctional sensing platform for sensitive determination of tetracycline. The proposed sensor was utilized to realize the determination of tetracycline in Rirver water samples/milk samples (λex = 390 nm, λem = 606 nm) with satisfactory recoveries and relative standard deviations. The linear range of are 0.05 to 45 μM and 45 to135 μM, and detection limit is 3.9 nM (3σ/m). Meanwhile, the luminescent intensity of N,Cl-CDs was reduced gradually when pH changed continuously from 12 to 2, showing a pH-responsive fluorescence property with two linear ranges of pH 3-7 and pH 7-10. In addition, due to the characteristics of low toxicity and excellent biocompatibility, the N, Cl-CDs were also used in the imaging of oocystis cells, which is hopeful to realize the detection of tetracycline in living cells.

Construction of a stable fluorescent sensor based on CsPbBr3/CdS core/shell quantum dots for selective and sensitive detection of tetracycline in ethanol

The weakly bound organic ligand shells around perovskite quantum dots (QDs) are easily decomposed and cannot provide sufficient stability in polar solvents, which greatly obstructs their applications in sensing. Herein, a fluorescent sensor based on CsPbBr3/CdS core/shell QDs was developed for the detection of tetracycline (TC) in the polar solvent-ethanol. Pristine CsPbBr3 QDs were treated with cadmium diethyldithiocarbamate (Cd(DDTC)2) to form a shell on the surface at 110 °C, while extra oleylammonium bromide (OAmBr) was added to inhibit the phase transformation of CsPbBr3 into a Cs4PbBr6 impurity phase during high-temperature processing. And finally CsPbBr3/CdS core/shell QDs were successfully synthesized. The capping with the CdS inorganic shell remediated surface defects and improved the stability in ethanol without affecting the emission properties of the parent CsPbBr3 QDs. The results showed that the fluorescent sensor detected TC in the range of 0.05-25 μM with a low detection limit of 22.6 nM, whereas it had high selectivity and anti-interference ability for TC. And the fluorescence quenching mechanism of the sensor was mainly photoinduced electron transfer between TC and CsPbBr3/CdS QDs. Our research provides a unique way to improve the stability of perovskite QDs in polar solvents and applications in fluorescence detection.

Recent Advances in NIR or X-ray Excited Persistent Luminescent Materials for Deep Bioimaging

Due to their persistent luminescence, persistent luminescent (PersL) materials have attracted great interest. In the biomedical field, the use of persistent luminescent nanoparticles (PLNPs) eliminates the need for continuous in situ excitation, thereby avoiding interference from tissue autofluorescence and significantly improving the signal-to-noise ratio (SNR). Although persistent luminescence materials can emit light continuously, the luminescence intensity of small-sized nanoparticles in vivo decays quickly. Early persistent luminescent nanoparticles were mostly excited by ultraviolet (UV) or visible light and were administered for imaging purposes through ex vivo charging followed by injection into the body. Limited by the low in vivo penetration depth, UV light cannot secondary charge PLNPs that have decayed in vivo, and visible light does not penetrate deep enough to reach deep tissues, which greatly limits the imaging time of persistent luminescent materials. In order to address this issue, the development of PLNPs that can be activated by light sources with superior tissue penetration capabilities is essential. Near-infrared (NIR) light and X-rays are widely recognized as ideal excitation sources, making persistent luminescent materials stimulated by these two sources a prominent area of research in recent years. This review describes NIR and X-ray excitable persistent luminescence materials and their recent advances in bioimaging.

Nitrogen and sulfur co-doped carbon quantum dots as "on-off-on" fluorescence probes to detect Hg2+ and MnO4- and improving the photostability of Rhodamine B

BACKGROUND

Carbon quantum dot (CQDs) are zero-dimensional carbon nanomaterials with a size of less than 10 nm CQDs are widely used in the field of ion detection by virtue of their fluorescence characteristics such as strong fluorescence intensity, good optical stability and tunable emission wavelength. Although the traditional atomic absorption method, electrochemical method and other metal ion detection methods are highly sensitive, the operation is complex, expensive and limited by the site. Therefore, we prepared the N, S-CQDs capable of detecting Hg2+ and MnO4- in water with the advantages of simple operation, low cost, and direct visual signal.

RESULTS

N, S-CQDs with high-quantum yield (77.68%), uniform particle size (0.4 nm-2.6 nm) and green fluorescence were created utilizing a one-pot hydrothermal process with the precursors ASDA-Na4 and m-phenylenediamine. N, S-CQDs has good optical properties such as high fluorescence intensity, wavelength independence, up-conversion luminescence and fluorescence stability. We examined 27 common ions in water and found that the fluorescence of N, S-CQDs could be selectively quenched by Hg2+ and MnO4-, and the detection limits are 0.41 μM and 1.2 μM, respectively. The mechanism of quenching is further investigated. The fluorescence of N, S-CQDs-Hg2+ system can be restored by halogen ions (Cl-, Br-, I-), while the fluorescence of N, S-CQDs-MnO4- system can be partially restored by Fe2+. This forms an "on-off-on" mode of fluorescent probes. In addition, we also studied that trace amounts of N, S-CQDs can improve the photostability of RhB.

SIGNIFICANCE

The N, S-CQDs are fluorescent probes in an "on-off-on" mode. N, S-CQDs with green fluorescence (on) can be quenched by Hg2+ and MnO4- (off). The fluorescence quenched by Hg2+ can be restored by halogen ions again, while the fluorescence quenched by MnO4- can partially be restored (on). This ion detection method can be used to visually detect the two ions in the field, with the advantages of low cost, simple operation and visual intuition.

Recent advances in luminescence and aptamer sensors based analytical determination, adsorptive removal, degradation of the tetracycline antibiotics, an overview and outlook

Tetracycline antibiotics (TCs), one of the important antibiotic groups, have been widely used in human and veterinary medicines. Their residues in foodstuff, soil and sewage have caused serious threats to food safety, ecological environment and human health. Here, we reviewed the potential harms of TCs residues to foodstuff, environment and human beings, discussed the luminescence and aptamer sensors based analytical determination, adsorptive removal, and degradation strategies of TCs residues from a recent 5-year period. The advantages and intrinsic limitations of these strategies have been compared and discussed, the potential challenges and opportunities in TCs residues degradation have also been deliberated and explored.

Exploring the multifunctional roles of quantum dots for unlocking the future of biology and medicine

With recent advancements in nanomedicines and their associated research with biological fields, their translation into clinically-applicable products is still below promises. Quantum dots (QDs) have received immense research attention and investment in the four decades since their discovery. We explored the extensive biomedical applications of QDs, viz. Bio-imaging, drug research, drug delivery, immune assays, biosensors, gene therapy, diagnostics, their toxic effects, and bio-compatibility. We unravelled the possibility of using emerging data-driven methodologies (bigdata, artificial intelligence, machine learning, high-throughput experimentation, computational automation) as excellent sources for time, space, and complexity optimization. We also discussed ongoing clinical trials, related challenges, and the technical aspects that should be considered to improve the clinical fate of QDs and promising future research directions.

Novel preparation of red fluorescent carbon dots for tetracycline sensing and its application in trace determination

The controllable design of red-emitting carbon dots and further exploration of their application in the trace determination of environmental pollutants remains a tremendous challenge. Herein, the novel strategy for red fluorescent carbon dots (R-CDs) with a higher quantum yield of 58.9% was proposed by doping small-molecule urea into the bio-dye of resazurin for the first time, which can retain the luminophore of precursors and exhibit exceptional optical, advantageous reversibility and outstanding photostability. Importantly, the R-CDs exhibit a remarkable fluorescence reduction towards tetracyclines (TCs) accompanied by a noticeable color change of R-CDs solution from red to yellow, which can realize the trace detection of TCs at strelatively low levels, including tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC). The linear range of TC, CTC, and OTC are 3-40 μM, 4-50 μM, and 2-50 μM, and the corresponding detection limits are 38.5 nM, 64.6 nM, and 45.4 nM, respectively (S/N = 3). Furthermore, the R-CDs demonstrate sensitivity to the physiological pH in the linear range of 4.0-5.0 and 5.0-6.2 with a pKa of 5.61. As a multifunctional fluorescent sensor, R-CDs can provide a new perspective for the preparation of long-wavelength CDs, and further realize the trace determination of environmental pollutants.

Low-cost Posidonia oceanica bio-adsorbent for efficient removal of antibiotic oxytetracycline from water

The presence of antibiotics as micro-contaminants in the water and aqueous environments is a health concern to humans and the ecosystem. Therefore, their elimination by adsorption to available and cheap materials in water treatment plants is a research topic of high relevance. The present paper reports on the adsorption behavior of oxytetracycline on a bio-adsorbent prepared from Posidonia oceanica; an abundant Mediterranean biomass. Characterization of the pretreated Posidonia biomaterial was achieved using several analyses such as Boehm acid-base titration method, pH_PZC determination, and analysis techniques (FTIR, ¹³C CP-MAS NMR, optical microscopy, and TGA). The pH_PZC occurred around pH 2.11. Posidonia biomaterial showed a fast and high uptake rate throughout the adsorption process, which is a definite advantage for analytical applications such as water decontamination. The experimental kinetic data fitted very rightly the pseudo-second-order kinetic model and the equilibrium uptake can adopt the bi-Langmuir isotherm model for all studied pH values which assumes adsorptions at the two localized sites. Maximum adsorption capacities of 11.8 mg∙g^-1 and 4.4 mg∙g^-1 for the two adsorption sites are reached at pH 6. The oxytetracycline adsorption process onto Posidonia bio-adsorbent is spontaneous (Δ_adsG⁰ < 0), exothermic (Δ_adsH⁰ < 0), and entropically favorable (Δ_adsS⁰ > 0). The effect of pH on adsorption behavior and the thermodynamic parameters of adsorption are consistent with a possible origin of adsorption of oxytetracycline by means of hydrogen bonding interactions between surface hydroxyl and phenolic groups of the biomaterial and oxytetracycline. The proposed green and environmentally friendly biomaterial offers potential benefits as a bio-adsorbent in the remediation of aquatic environments contaminated by various organic materials.

Facile Synthesis of N, S-Doped Carbon Quantum Dots from Food Waste as Fluorescent Probe for Sensitive Detection of Thiamphenicol and Its Analogues in Real Food Samples along with an Application in Bioimaging

Herein, N, S co-doped carbon quantum dots (N, S-CDs) with high absolute quantitative yield (Abs-QY) of 50.2% were produced by hydrothermal treatment of food residue crayfish shells. A new detection method of thiamphenicol (TAP) and its analogues was established by discovering the obvious fluorescence response between TAP and N, S-CDs, which achieved a wide linear range of 20–300 μg·L⁻¹ with a detection limit (LOD) of 11.12 μg·L⁻¹. This novel probe exhibited strong sensitivity and shows rapid response in complex food matrices (overall detection time is less than 45 min) mainly induced by static quenching. Spiked food sample recovery ranged from 97.3 to 99.34%. Further, the cell experiments of N, S-CDs were conducted, and the cell viability remained 91.76% under high concentration of N, S-CDs due to the environmentally friendly materials. The low cytotoxicity and good cytocompatibility make these N, S-CDs compatible for cell bioimaging and intracellular detection of TAP.

Protective Effects of Zingiberis Carbonisata-Based Carbon Dots on Diabetic Liver Injury in Mice

To explain the active components of ZRC-CDs from the perspective of nanomaterials and investigate the potential mechanism for the treatment of diabetic liver injury, the structure, electron transfer properties, and elemental composition of ZRC-CDs were characterized. The protective effects of ZRC-CDs on the diabetic liver injury were demonstrated using the Alloxan-induced diabetic model. The ZRC-CDs are spherical, with a diameter ranging from 1.0–4.5 nm and a yield of 0.56%. The results showed that ZRC-CDs decreased the levels of blood glucose in diabetic mice and had a mitigating effect on elevated ALT and AST. More studies found that ZRC-CDs were able to decrease the levels of inflammatory cytokines and suppress the protein expression in related signaling pathways.

Controllable synthesis of a sponge-like Z-scheme N,S-CQDs/Bi2MoO6@TiO2 film with enhanced photocatalytic and antimicrobial activity under visible/NIR light irradiation

Multifunctional photocatalytic surfaces for pollutant degradation and antimicrobial application are often in high demand, however they confront many challenges in charge transfer and light capture ability. In this work, a sponge-like N,S-CQDs/Bi₂MoO₆@TiO₂ film was constructed via hydrothermal technique aiming to solve above problems. As a result, the ternary film showed enhanced photocatalytic efficiency under visible and near-infrared (NIR) light, in which 85.8% and 44.6% of ciprofloxacin (CIP) were degraded after 240 min irradiation with visible and NIR light, respectively. Moreover, the composite film effectively realized photocatalytic sterilization of gram-positive B. subtilis and gram-negative E. coli under visible light irradiation. The bacterial colony decreased significantly from 7.56-log to 1-log cfu/mL after adding the ternary film within 1.5 h. The enhanced photocatalytic efficiency was closely related to both introduction of surface-functional N,S-CQDs and the construction of N,S-CQDs/Bi₂MoO₆@TiO₂ Z-scheme system, in which the transfer efficiency of photoinduced carriers and the light absorption property were significantly improved. We consider that the N,S-CQDs/Bi₂MoO₆@TiO₂ film is promising for the degradation of refractory pollutants and antimicrobial application under visible/NIR light irradiation. The relatively convenient recycling property and excellent photocatalytic performance of the N,S-CQDs/Bi₂MoO₆@TiO₂ film are beneficial for industrial applications.

A convenient fluorescence sensor of tetracycline based on B, N codoped carbon dots/polymer composite film

A convenient fluorescence sensor of tetracycline (TC) was constructed based on carbon dots (CDs) and polyvinyl alcohol (PVA) hydrogel film. The immobilization of CDs in PVA carrier can stabilize the fluorescence of CDs by inhibiting the fluorescence quench due to the aggregation of CDs with time. CDs were prepared by a hydrothermal method. CDs showed bright blue fluorescence with the quantum yield of 0.35. The fluorescence of CDs was quenched by TC owing to the inner filter effect. The linear range for TC detection was 0-350 µM and the limit of detection was 0.17 µM. To test conveniently, PVA film was employed to upload CDs. Therefore, a novel sensor for TC was constructed in a visual mode. By comparison with the most of previous works, the present method displayed higher sensitivity and better selectivity. The results suggest that the present sensor has potential applications in the real-time detection of TC in food analysis.

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.

Recent progress of carbon dot fluorescent probes for tetracycline detection

We made a detailed discussion about TCs and CDs, including the synthetic methods, doping strategies and promising prospects.

Smartphone-assisted ratiometric fluorescence sensing platform and logical device based on polydopamine nanoparticles and carbonized polymer dots for visual and point-of-care testing of glutathione

As a crucial biothiol, glutathione (GSH) plays a key role in the organisms. Monitoring GSH level is of great significance for disease diagnosis and biomedical research. In this work, polydopamine (PDA) nanoparticles-red fluorescent carbonized polymer dots (r-CPDs) based ratiometric fluorescence sensing platform was constructed and employed for GSH assay. Dopamine (DA) could be oxidized by cobalt oxyhydroxide (CoOOH) nanosheets and further polymerized into PDA nanoparticles with green fluorescence. However, in the presence of GSH, CoOOH nanosheets were reduced and decomposed, which prevented the production of PDA nanoparticles. In the sensing system, green-emitting PDA nanoparticles were employed as a response unit and r-CPDs were used as an internal reference unit. With the addition of GSH, the green fluorescence of PDA nanoparticles decreased as well as the red fluorescence of system remained relatively stable. Importantly, a distinct fluorescence color evolution from green to red was presented with a serious of GSH concentrations. Based on this, a portable smartphone-assisted ratiometric chromaticity analytical method was developed to achieve the on-site visual detection of GSH. Both the established ratiometric fluorescence and ratiometric chromaticity sensing methods for GSH assay have the merits of wide linear range, high sensitivity and excellent accuracy, which are suitable for the determination of GSH in human serum and exhibit great application potential in rapid and accurate monitoring of the GSH levels in clinical. Moreover, an ingenious logical device reflecting GSH levels was designed based on the two different fluorescence signals, which provided a new strategy for the intelligent online detection of GSH in complex biological matrices.

Ratiometric fluorescence probe of Cu2+ and biothiols by using carbon dots and copper nanoclusters

A novel dual-emission ratiometric fluorescent probe based on N-doped yellow fluorescent carbon dots (y-CDs) and blue fluorescent copper nanoclusters (CuNCs) was established for quantitative determination of Cu2+ and biothiols. In this work, the Cu2+-(y-CDs) complexes formed by the chelation of y-CDs with Cu2+, showed an absorption peak at 430 nm that not only enhanced the fluorescence of y-CDs through inhibiting photoinduced electron transfer (PET) but also effectively quenched the fluorescence of CuNCs due to Förster resonance energy transfer (FRET). In addition, the chelation of y-CDs with Cu2+ could be inhibited by biothiols that prevented the fluorescence of y-CDs from being enhanced and the fluorescence of CuNCs from being quenched. On account of the changes of ratiometric signal, a dual-emission fluorescence probe for Cu2+ and biothiols determination was achieved. The proposed method exhibited high sensitivity for Cu2+ and biothiols in the ranges of 0.5-100 μM and 0.8-50 μM and the limits of detection (LODs) of Cu2+, glutathione (GSH), cysteine (Cys) and homocysteine (Hcy) were 0.21 μM, 0.33 μM, 0.39 μM and 0.46 μM, respectively. Subsequently, the established strategy presented an application prospect for the detection of Cu2+ and biothiols in real samples.

One-step synthesis of N, S-doped carbon dots with orange emission and their application in tetracycline antibiotics, quercetin sensing, and cell imaging

Water soluble N, S-doped carbon dots (N, S-CDs) with orange emission were synthesized from basic fuchsin and sulfosalicylic acid by the typical hydrothermal route. Based on the inner filter effect (IFE), the prepared N, S-CDs can be innovatively developed as an effective "signal-off" multifunctional sensing platform for sensitive determination of tetracycline antibiotics (for example, chlortetracycline (CTC)) and quercetin. The proposed sensor was utilized to realize the determination of CTC in water and milk samples and quercetin in beer sample (λex = 375 nm, λem = 605 nm) with satisfactory recoveries and relative standard deviations (RSD). The linear range and detection limit (LOD) of CTC is 1.24-165 μM and 32.36 nM, respectively. For quercetin, the linear ranges are 0.98-34 μM and 34-165 μΜ, and the LOD is 6.87 nM (3σ/m). By virtue of the good biocompatibility and long-wavelength emission, N, S-CDs were also used in the imaging of oocystis cells and yeast cells, which demonstrated promising applicability for bio-imaging and sensing. In this paper, N, S-doped carbon dots (N, S-CDs) with orange emission (λem = 605 nm) were synthesized from basic fuchsin and sulfosalicylic acid. Based on the inner filter effect (IFE), the prepared N, S-CDs can be innovatively developed as an effective "signal-off" multifunctional sensing platform for the sensing of tetracycline antibiotics (for example: chlortetracycline (CTC)) and quercetin. The sensor has been successfully applied to the determination of CTC in water and milk samples and quercetin in beer sample (λex = 375 nm, λem = 605 nm). The linear range and detection limit (LOD) of CTC is 1.24-165 μM and 32.36 nM respectively. For quercetin, the linear ranges are 0.98-34 μM and 34-165 μΜ, and the LOD is 6.87 nM (3σ/m). In addition, due to the characteristics of good biocompatibility and long-wavelength emission, the N, S-CDs were also used in the imaging of oocystis cells and yeast cells, which demonstrated promising applicability for bioimaging and sensing.

Facile synthesis of carbon nitride quantum dots as a highly selective and sensitive fluorescent sensor for the tetracycline detection

Enhanced blue fluorescent carbon nitride quantum dots (g-C₃N₄QDs) were synthesized by a simple solvothermal “tailoring” process from bulk g-C₃N₄ and analyzed by various characterization methods. The as-obtained g-C₃N₄QDs were successfully applied in the determination of tetracycline (TC) with a good linear relationship in the range of 0.23–202.70 μM. The proposed fluorescent sensor shows excellent stability, good repeatability, high selectivity and outstanding sensitivity to TC with a low detection limit of 0.19 μM. The fluorescence quenching mechanism of g-C₃N₄QDs with TC was mainly governed by static quenching and the inner filter effect. The method was successfully applied to monitor TC in tap water and milk powder samples.

The g-C₃N₄QDs were synthesized by a simple solvothermal “tailoring” process from bulk g-C₃N₄ which have a “strong quenching” behaviour in the presence of TC. The proposed fluorescent sensor has been successfully applied to detect TC in actual samples.

Green preparation of carbon dots from Momordica charantia L. for rapid and effective sensing of p-aminoazobenzene in environmental samples

p-Aminoazobenzene (pAAB) is a hazardous azo dye that causes considerable harm to human health and the environment. The development of novel and sensitive sensors for the rapid detection of pAAB is in high demand. In this study, a simple fluorescent sensor for pAAB detection is designed based on carbon dots (CDs) which are prepared using green carbon source of Momordica charantia L. via a facile hydrothermal approach. The fluorescence spectra of CDs exhibit considerable overlap with the absorption band of pAAB, and the fluorescence is specifically suppressed in the presence of pAAB ascribed to the inner filter effect. Good and wide linearity is observed in the pAAB concentration range of 0.01-12.5 μg mL^-1 with a lower detection limit of 3.9 ng mL^-1. The established method achieves good results with a rapid analysis of pAAB in different practical water and soil samples. The as-constructed fluorescent sensor provides a simple, rapid, economical and eco-friendly platform and possesses prospective applications for the effective, selective and sensitive detection of pAAB in the environmental field.

Sensitive and selective determination of tetracycline in milk based on sulfur quantum dot probes

A novel fluorescent probe based on sulfur quantum dots (SQDs) was fabricated for sensitive and selective detection of tetracycline (TC) in milk samples. The blue emitting SQDs were synthesized via a top-down method with assistance of H2O2. The synthesized SQDs showed excellent monodispersity, water solubility and fluorescence stability, with a quantum yield (QY) of 6.30%. Furthermore, the blue fluorescence of the obtained SQDs could be effectively quenched in the presence of TC through the static quenching effect (SQE) and inner filter effect (IFE) between TC and SQDs. Under the optimum conditions, a rapid detection of TC could be accomplished within 1 min and a wide linear range could be obtained from 0.1 to 50.0 μM with a limit of detection (LOD) of 28.0 nM at a signal-to-noise ratio of 3. Finally, the SQD-based fluorescent probe was successfully applied for TC determination in milk samples with satisfactory recovery and good relative standard deviation (RSD). These results indicate that the SQD-based fluorescent probe shows great potential in practical analysis of TC in real samples with high rapidity, selectivity, and sensitivity.

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.

Ratiometric fluorescent probe for tetracycline detection based on waste printing paper

Tetracycline (TC) is a broad-spectrum antibiotic used to treat bacterial infections. In this study, a ratiometric fluorescence (FL) probe was developed to detect TC in water samples using waste printing paper extract as a FL indicator. For this ratiometric probe, the emission of printing paper extract at 436 nm gradually decreased and the emission of a mixed solution at 538 nm significantly increased with the sequential addition of TC upon excitation at 390 nm, coupled with a marked FL colour change from bright blue to faint yellow. Therefore, a ratiometric F₅₃₈ /F₄₃₆ FL probe was created for TC detection by simply mixing the printing paper extraction and TC. Under the optimized conditions, a linear range from 1 to 100 μM and a detection limit of 0.48 μM (S/N = 3) for TC were obtained. Importantly, the FL probe can be easily prepared with rapid response, high sensitivity, and good selectivity. The application of waste printing paper extract for detection of TC in environmental water samples was demonstrated.

Protective Effects of Radix Sophorae Flavescentis Carbonisata-Based Carbon Dots Against Ethanol-Induced Acute Gastric Ulcer in Rats: Anti-Inflammatory and Antioxidant Activities

AIM

To explore the effects of Radix Sophorae Flavescentis carbonisata-based carbon dots (RSFC-CDs) on an ethanol-induced acute gastric ulcer rat model.

METHODS

The structure, optical properties, functional groups and elemental composition of RSFC-CDs synthesized by one-step pyrolysis were characterized. The gastric protective effects of RSFC-CDs were evaluated and confirmed by applying a rat model of ethanol-induced acute gastric ulcers. The underlying mechanisms were investigated through the nuclear factor-kappa B (NF-κB) signalling pathway and oxidative stress.

RESULTS

RSFC-CDs with a diameter ranging from 2-3 nm mainly showed gastric protective effects by reducing the levels of NF-κB, tumour necrosis factor-α (TNF-α), interleukin (IL)-6, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione (GSH), malondialdehyde (MDA) and inducible nitric oxide synthase (iNOS) to inhibit ethanol-induced inflammation and oxidative stress.

CONCLUSION

RSFC-CDs have anti-inflammatory and anti-oxidative effects, making them promising for application in ethanol-induced gastric injury.

Concentration-dependent photoluminescence carbon dots for visual recognition and detection of three tetracyclines

Concentration-dependent photoluminescence carbon dots (CDs) have been successfully synthesized through the one-step hydrothermal treatment of o-phthalic acid and ethylenediamine. The CDs possessed higher fluorescence quantum yield, up to 39.22%, exhibiting distinguished optical property, water solubility, and stability. The CDs that emit strong blue-green fluorescence can visually identify and determine tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC). TC quenched the fluorescence of CDs at 500 nm owing to the inner filter effect; OTC behaved similarly, but the emission wavelength of CDs was red-shifted to 515 nm. Inversely, once CTC was introduced to CDs solution, the fluorescence increased and the emission peak was blue-shifted to 450 nm. Bandgap transition and electrostatic interaction were proposed to be the mechanisms for the detection of OTC and CTC by CDs. Wide linear relationships were established for TC, OTC, and CTC with the limits of detection to be 50 nM, 36 nM, and 373 nM, respectively. Furthermore, the nanoscale probe constructed by this system has been applied to detect tetracyclines (TCs) in complex samples with satisfying recoveries (93.2-114%) and was designed as a portable test strip sensor for visually on-site TCs of honey sample screening. Accordingly, the preparation process of the nano fluorescent probe is simple and environmentally friendly, and the probe has a specific recognition ability for tetracyclines. The synthesized CDs in this work provide a new orientation for fast, effective, and visual real-time detection of tetracycline in actual samples.

Ratiometric fluorescence determination of alkaline phosphatase activity based on dual emission of bovine serum albumin-stabilized gold nanoclusters and the inner filter effect

A novel and convenient method for the ratiometric fluorescence detection of alkaline phosphatase (ALP) activity was proposed based on dual emission of bovine serum albumin-templated gold nanoclusters (BSA-AuNCs) and the mechanism of the inner filter effect between BSA-AuNCs and p-nitrophenol (PNP). First, ALP catalyzed the hydrolysis of the substrate p-nitrophenyl phosphate (PNPP) to produce PNP. PNP effectively quenched the emission peak of BSA-AuNCs at 410 nm because of the overlap in absorbance feature of PNP and the fluorescence spectrum of BSA-AuNCs, and the peak at 650 nm was almost unaffected. Thus, a sensitive ratiometric method for detection of ALP activity was developed using the fluorescence intensity of BSA-AuNCs at 650 nm as a reference signal. ALP activity versus the ratio of fluorescence intensities at 410 and 650 nm showed good linearity between 0.2 and 5 mU mL^-1 (R² = 0.9931) and high sensitivity with a detection limit of 0.03 mU mL^-1 (S/N = 3). The developed sensing method was successfully applied to investigate ALP inhibitors and detect ALP in serum samples.

Bimodal size distribution immuno-quantum dots for fluorescent western blotting assay with high sensitivity and extended dynamic range

A highly sensitive quantum dot (QD)-based western blot assay with extended dynamic range was developed. Bimodal size distribution QD (BQ) immunoprobes composed of small size single QD (7.3 nm) and big size QD nanobead (QB) (82.9 nm) were employed for fluorescent western blot immunoassay on a membrane. Small size QD immunoprobes contributed to wider dynamic range of assay, while big size QB immunoprobes provided higher detection sensitivity. This BQ-based western blot assay can achieve a wide dynamic range (from 7.8 to 4000 ng IgG) and is nearly as sensitive as commercial available ultrasensitive chemiluminescent methods, just using a simple gel imager with UV light (365 nm) excitation and red light filter (610 nm). The fluorescent signals of BQ western blot were stable for 10 min, while chemiluminescent signals faded after 1 min. Moreover, this BQ immunoprobe was utilized for the detection of housekeeping protein and specific target proteins in complex cell lysate samples. The limit of detection of housekeeping protein is 0.25 μg of cell lysate, and the signal intensities were proportional to loading protein amount in a wide range from 0.61 to 80 μg. We believe that this new strategy of bimodal size distribution nanoparticles can also be expanded for other functional nanoparticle-based biological assays to improve the sensitivity and extend the dynamic range. Graphical abstract.