Fluorescent Quantum Dots Research Articles

Enhancing capacitance performance of functional group assisted carbon quantum dots derived from turmeric plant waste

Supercapacitors have attracted significant attention in modern devices as a promising solution for electrical energy storage due to their remarkable capability to undergo rapid charge and discharge cycles. While various materials are employed in the construction of supercapacitors, carbon-based materials emerge as a predominant choice within the commercial realm. In present report, our intention is to develop an effective supercapacitor device derived from natural biomass. Therefore, we have synthesized water soluble, monodisperse and fluorescent carbon quantum dots (CQDs) from turmeric leaves (Curcuma caesia) via a single step hydrothermal carbonization. Further, the doctor blade technique was employed to coat a layer of CQDs on stainless steel substrate using PVA as a binder. We observed the functional groups associated with QDs triggers the fast diffusion of ions and transmission of electrons with conducting substrate and electrolyte and thereby effectively charge and discharge mechanism. The supercapacitor based on carbon quantum dots (CQDs) based electrode exhibits exceptional performance characteristics with a remarkable specific capacitance of 468 F/g and highest energy density of 78.6 Wh/kg, superior to the values reported for most carbon-based supercapacitors. Further, we demonstrated the light dependent capacitive enhancement by depositing a thin P3HT layer over CQDs. Moreover, CQDs-based supercapacitor achieves a maximum power density of 733.2 W/kg when operated in a 1 M KOH electrolyte solution and an excellent capacitive retention of about 80 % even after 5000 cycles.

Unlocking precision: Advancing rapid field molecular identification of Tuta absoluta across its life cycle using locked nucleic acid strategies

Rapid and accurate insect identification is crucial for effective plant quarantine procedures. This study introduced a reverse transcription recombinase-assisted amplification-lateral flow strip (RT RAA-LFS), specifically designed for on-site detection of the globally quarantined pest, Tuta absoluta, within a 25-minute timeframe. A pivotal strategy involved integrating three locked nucleic acid (LNA) modifications into a species-specific probe, enabling RT RAA to selectively and efficiently amplify the unique haplotype of T. absoluta's mitochondrial cytochrome c oxidase subunit I (COI) gene. After determining the amplification product dilution factor and the volumes of primers, magnesium acetate, and nucleic acid lysate in the amplification system, the finalized RT RAA-LFS system is capable of direct visual detection, complemented by handheld fluorescence detection for quantum dots (QDs) fluorescence on the lateral flow strip. This technique successfully identifies various developmental stages of T. absoluta in crude nucleic acid lysates without the need for genomic DNA extraction. Moreover, it detected the target gene in the genomic solution, reaching concentrations as low as 1.6 pg or 51 copies per 50-µL reaction system, aligning with qPCR results. Field validation with 50 insect samples supports the correlation between RT RAA-LFS quantum dots' fluorescence intensity and LFS color intensity, affirming the system's reliability in estimating the target gene copy number (R=0.584, p < 0.01). This validation emphasizes the practical efficacy of the RT RAA-LFS system for T. absoluta detection, highlighting its potential as a rapid on-site tool in agricultural pest management.

Manganese-Doped Carbon Quantum Dots (CQDs) Prepared from Bovine Bone Powder and Their Application for the Fluorescent Determination of Chlorpyrifos

Employing a one-step hydrothermal method with bovine bone powder as the carbon source, Mn-doped fluorescent carbon quantum dots were synthesized. Experimental investigations were conducted on their morphology, structure, composition, and optical properties. The experiments were carried out at 280 °C, pH 7.0, and a reaction period of 12 h. A rapid residual method for organophosphorus pesticides (OPs) was developed based on the fluorescence quenching of quantum dots. A linear correlation between fluorescence quenching and OP concentration was established. Chlorpyrifos was chosen as the analyte for method evaluation. The findings showed that the fluorescence intensity of the Mn-BQDs decreased with the copper ion concentration. Furthermore, the influence of copper ions on the fluorescence quenching of carbon quantum dots varied with pH. At pH 7, copper ions exhibited optimal quenching with a detection limit of 5.8 × 10−4 mg/L. This method offers simplicity in operation and environmental friendliness, rendering it well-suited for the swift on-site screening of OPs.

Sustainable fabrication of fluorescent carbon quantum dots as an optical amplifier in modern agriculture, anti-counterfeiting, food packing and intelligent pH detection

Carbon quantum dots (CQDs) have received a great deal of attention due to their distinctive luminescent features and exciting potential applications in the fields of agronomy, enhanced anti-counterfeiting, drug tracking and intelligent sensing and detection. The focus of the current effort is on easily transforming toxic, non-biodegradable waste expanded polystyrene foam (WEPS) into extremely luminescent CQDs and investigating their various applications. As a nano-priming agent for Cajanus cajan (L.), the green pigeon pea (GPP), WEPS derived CQDs are used. The outcomes showed that seed priming had beneficial effects at all CQDs concentrations (100–900 mg/L), including accelerated seed germination rate, increased shoot and root length, augmented root vigour, higher chlorophyll content and biomass accumulation in comparison to the control groups. The most crucial data coding can be protected under 365 nm UV light using the optimized CQDs concentration (700 mg/L) blue fluorescent ink. In addition, a straightforward sensing platform with high sensitivity and selectivity is needed for the detection of dual metal ions, as well as one with a "turn-on and turn-off" fluorescence (FL) response. Additionally, a composite film containing well-dispersed CQDs (700 mg/L) in polyvinyl alcohol and strong hydrogen-bond interaction is successfully developed to alleviate the FL quenching caused by CQD aggregation. The resulting film had extraordinary FL performance, good mechanical flexibility and high transparency (transmittance of 90 %). Even more remarkably, this luminescent film showed sensitive pH responsiveness, signifying that when pH is stimulated, the FL intensity changed. A smart pH-detector based on this luminescent film is logically created as a proof-of-concept for real-time sensing and detection of pH changes in human sweat. These results show that WEPS derived CQDs have enormous potential as nano-priming agents for seed germination, seedling development, anti-counterfeiting ink, food packaging and intelligent pH-detector in wearable, real-time health monitoring.

Improving Three-Photon Fluorescence of Near-Infrared Quantum Dots for Deep Brain Imaging by Suppressing Biexciton Decay.

Three-photon fluorescence microscopy (3PFM) is a promising brain research tool with submicrometer spatial resolution and high imaging depth. However, only limited materials have been developed for 3PFM owing to the rigorous requirement of the three-photon fluorescence (3PF) process. Herein, under the guidance of a band gap engineering strategy, CdTe/CdSe/ZnS quantum dots (QDs) emitting in the near-infrared window are designed for constructing 3PF probes. The formation of type II structure significantly increased the three-photon absorption cross section of QDs and caused the delocalization of electron-hole wave functions. The time-resolved transient absorption spectroscopy confirmed that the decay of biexcitons was significantly suppressed due to the appropriate band gap alignment, which further enhanced the 3PF efficiency of QDs. By utilizing QD-based 3PF probes, high-resolution 3PFM imaging of cerebral vasculature was realized excited by a 1600 nm femtosecond laser, indicating the possibility of deep brain imaging with these 3PF probes.

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.

Fluorescence Enhancement of CdS:Ag Quantum Dots Co-Assembled with Au Nanoparticles in a Hollow Nanosphere Form.

Colloidal quantum dots (QDs) have exceptional fluorescence properties. Overcoming aggregation-induced quenching and enhancing the fluorescence of colloidal QDs have remained a challenging issue in this field. In this study, composite hollow nanospheres composed of Au nanoparticles (NPs) and CdS:Ag-doped QDs were successfully constructed through controlled microemulsion-based cooperative assembly. This method harnessed the localized surface plasmon resonance (LSPR) effect of Au NPs nearby doped QDs, resulting in enhanced doped QD fluorescence and the observation of the Purcell effect. The composite hollow nanospheres show a fluorescence enhancement compared to that of the pure CdS:Ag QDs. The enhanced fluorescence was demonstrated to come from the synergetic enhancement of the absorption and emission transition of the doped QDs. This approach provides a feasible technological pathway to address the challenge of improving the fluorescence performance of the doped QDs.

A smartphone-based fluorescent biosensor with metal-organic framework biocomposites and cotton swabs for the rapid determination of tetrodotoxin in seafood

BackgroundTetrodotoxin (TTX) is a potent neurovirulent marine biotoxin that is present in puffer fish and certain marine animals. It is capable of causing severe neurotoxic symptoms and even death when consumed through contaminated seafood. Due to its high toxicity, developing an effective assay for TTX determination in seafood has significant benefits for food safety and human health. Currently, it remains challenging to achieve on-site determination of TTX in seafood. To facilitate mass on-site assays, more affordable technologies utilizing accessible equipment that require no skilled personnel are needed. ResultsA smartphone-based portable fluorescent biosensor is proposed for TTX determination by using metal-organic framework (MOF) biocomposites and cotton swabs. Oriented antibody (Ab)-decorated and fluorescent quantum dot (QD)-loaded MOF biocomposites (QD@MOF*Ab) are rapidly synthesized for binding targets and fluorescent responses by utilizing the tunability of zinc-based MOF. Moreover, facile Ab-immobilized household cotton swabs are utilized as TTX capture tools. TTX forms sandwich immune complexes with QD@MOF*Ab probes, achieving signal amplification. These probes are excited by a portable device to generate bright fluorescent signals, which can be detected by the naked eye, and TTX quantitative results are obtained using a smartphone. When observed with the naked eye, the limit of detection (LOD) is 0.4 ng/mL, while intelligent quantitation presents an LOD of 0.13 ng/mL at logarithmic concentrations of 0.2–400 ng/mL. SignificanceThis biosensor is convenient to use, and an easy-to-operate analysis is completed within 15 min, thus demonstrating excellent performance in terms of detection speed and portability. Furthermore, it successfully determines TTX contents in puffer fish and clam samples, demonstrating its potential for monitoring seafood. Herein, this work provides a favorable rapid sensing platform that is easily portable.

SPECTRAL PROPERTIES OF CHLOROPHYLLS IN EDIBLE PLANTS INTENDED FOR DIAGNOSTICS

Abstract. This study examined the absorption and fluorescence spectra of chlorophylls and other pigments extracted in ethanol solutions from common edible plant species. Chlorophyll-a was the dominant fluorescent chromophore in all plant varieties. The fluorescence curves for all extracted solutions exhibit after optimizing by concentration dilution an increase in the fluorescence with a typical prominent leading Gaussian peak at a wavelength of 674 nm. This peak is followed by a decreasing shoulder extending into the near-infrared range beyond 724 nm. The dilution of the solutions with ethanol reduces the optical absorption from the other pigments and shows simultaneously an improved resolution of the chlorophyll-a spectral absorption peaks. This investigation provides new insights into the optical absorbance and other photo-excited processes that impact the fluorescence of chlorophylls, such as agglomeration, photobleaching and photo-aggregation. The findings may be used for biodiagnostics, fluorescent quantum dots and bio-sensors.

Fluorescent carbon quantum dots synthesized from coconut shell for the detection of Fe3+ ion

Fluorescent carbon quantum dots synthesized from coconut shell for the detection of Fe3+ ion

Polyaspartic acid modified by fluorescent carbon quantum dots as an environmentally friendly scale inhibitor for calcium sulphate

Polysuccinimide (PSI), as the precursor of polyaspartic acid (PASP), can easily react with amino (NH2) groups under mild conditions. A novel scale inhibitor, designed as PASP/N-CDs, is synthesised through the ring-opening reaction of PSI with nitrogen-doped carbon quantum dots (N-CDs). XPS, TEM, FT-IR and Raman spectroscopy are used to analyse the micro structure and spectral characteristics of synthesised inhibitors. The efficiency of PASP/N-CDs in inhibiting calcium sulphate (CaSO4) scale is tested through static scale inhibition experiments. The comparative analysis reveals a significant enhancement in the scaling resistance of PASP/N-CDs over PASP, particularly noticeable at reduced concentrations. The scale inhibition efficiency of PASP/N-CDs reaches nearly 100 % at 5 mg/L. The underlying mechanism of scale inhibition in PASP/N-CDs is investigated using SEM and XRD. It indicates that the PASP/N-CDs inhibits the formation of CaSO4 scale via a combination of chelation, adsorption, and lattice distortion.

Photoinduced Dehalogenation‐Based Direct In Situ Photolithography of CsPbBr3 Quantum Dots Micropatterns for Encryption and Anti‐Counterfeiting with High Capacity

Fluorescent lead halide perovskite quantum dots (LH PQDs) micropatterns hold great potential for photonic applications. However, current photolithography for LH PQDs micropatterning is hindered by their incompatibility with traditional photolithography methods, which involve development processes using numerous solvents and exhibit poor stability due to the ionic characteristics of LH PQDs. Herein, a direct in situ photolithography to fabricate CsPbBr3 PQDs micropatterns based on ultraviolet‐C light‐driven debromination is developed. Using this approach, fluorescent CsPbBr3 PQDs micropatterns with high theoretical information storage capacity (up to 10750205) can be achieved in a single step, without the need for tedious development processes. Furthermore, the fabricated CsPbBr3 PQDs micropatterns show high stability, remaining undamaged even after immersion in water for 6 months. The combination of excellent optical properties, development‐free process, high stability, and low cost makes the in situ photolithography strategy very promising for patterning LH PQDs toward photonic integrations.

Fluorescent Quantum Dots Based Lateral Flow Assay for Rapid Quantitative Detection of Ciliary Neurotrophic Factor in Glaucoma

AbstractEarly and accurate diagnosis of glaucoma is crucial to prevent the progressive deterioration that leads to irreversible vision loss. It is imperative to develop an effective screening tool for glaucoma. Ciliary neurotrophic factor (CNTF) is a tear biomarker implicated in glaucoma pathogenesis. Lateral flow assay (LFA) provides an ideal platform for detection of glaucoma in tear fluid. A quantum dot‐based fluorescence LFA, integrated with a 3D printed readout box, is developed for fast (30 min), sensitive, and quantitative CNTF detection in tears. A standard curve is firstly generated for the quantitative detection of CNTF. The limit of detection (LOD) of the obtained LFA strip at 6.45 pg·mL−1 is comparable to that of the enzyme‐linked immunosorbent assay (ELISA) at 6.42 pg·mL−1. This enables the identification of low CNTF levels (25.7 ± 14.9 pg·mL−1) reported in tear fluid from glaucoma patients. This LFA is found to be highly selective for CNTF and maintained consistent results in different pH condition. The strip remaines stablewhen stored in the darkat room temperature. A smartphone app is developed to simplify analysis and enable prompt and easily obtainable results. This method shows great potential to be a powerful tool for point‐of‐care glaucoma screening.

Fabrication of methylated carbon quantum dot-based fluorescent films for highly sensitive and stable temperature probes

Due to their distinct physicochemical characteristics and outstanding biocompatibility, carbon quantum dots have shown to offer enormous potential in the field of temperature sensing. However, there is still much to learn about the mechanism underlying carbon quantum dots' thermal sensing capabilities, and developing incredibly precise thermometers based on it is still an enormous obstacle. Herein, we successfully fabricated carbon quantum dots with variable luminescence wavelength and temperature-sensitive properties by adjusting the ingredients to modify the composition of functional groups (-NH2, -OH, -COOH and -CH2OH) on the surface of quantum dots in a simple hydrothermal synthesis process, followed by encapsulation with polyvinyl alcohol (PVA). Subsequently, structural/optical characterisation and temperature-dependent studies were utilized for investigations into the quantum dot fluorescence mechanisms as well as the thermal sensing characteristics connected to surface functional groups, respectively. Notably, the designed red-emitting methylenated carbon quantum dot film probe displayed more linear segmented temperature sensing properties (R2>0.99), a wider temperature applicability range (20–160 °C), and high temperature reversibility (20–80 °C, at least 4 cycles). Finally, the mechanism by which functional groups affect the thermal characteristics of carbon quantum dots was addressed, and we hypothesized that intramolecular and intermolecular hydrogen bonding interactions are important factors affecting the thermal properties of carbon dots. This work presents great promise and theoretical guidance for the development of highly reliable carbon quantum dot temperature sensing systems.

Synthesis, Characterization, and Applications of Carbon Dots for Determination of Pharmacological and Biological Samples: A Review.

Carbon dots (CDs) are a novel category of carbon-based nanomaterials characterized by their small size, often less than 10 nm. CDs physical, chemical, and optical properties can be tuned using one-pot assembly. Because of their non-toxicity, biocompatibility, chemical and physical responsiveness, photo- and chemical-bleaching resistance, and low cost, nanoparticles have become incredibly versatile. They find various applications in detecting inorganic substances, bio sensing, visualizing cells, studying biological processes in live cells, and aiding in medication delivery. Additionally, CDs exhibit versatility in electronics and energy storage, making them promising candidates for applications in solar cells, light-emitting diodes, and supercapacitors. CDs are more photo stable for hours than typical fluorescent semiconductor quantum dots. Before applying CDs, they must be characterized. Techniques such as UV-VIS spectroscopy, fluorescence spectrophotometry, FT-IR, TEM, XRD, Raman spectroscopy, and NMR are commonly used to assess their photophysical and structural properties. This article review explores the synthesis, characterization applications of CDs in analytical techniques for the determination of various analytes. The article provides a detailed analysis of the different methodologies used to make nanomaterials and devices for the characterization of CDs. It also discusses the challenges that arise when using CDs in analytical techniques for detecting different analytes. The focus of this review is on accurately determining pharmaceutical and biological samples using CDs as sensing probes.

CdS/ZnS quantum dots based on an amphipathic polymer platform for fluorescent probe of dopamine with high sensitivity and selectivity

Due to the widespread presence of dopamine in living organisms and its physiological and pharmacological effects, developing rapid and sensitive methods for detecting dopamine has been of great significance. Fluorescent probes are a commonly used and highly sensitive detection method. In this work, based on a self-developed amphipathic polymer template, CdS/ZnS fluorescent quantum dots (QDs) with a maximum absorption wavelength of 500–550 nm were synthesized and characterized. They exhibited stable fluorescence in the pH range from weak acid to alkaline, and fluorescence quenching occurred at pH = 4.5. The QDs could be applied as fluorescent probes for detecting dopamine, with a limit of detection 0.027 mM and high selectivity, unaffected by common metal ions, amino acids, glucose, etc. Compared to the high activity of dopamine being oxidized easily, this fluorescent QDs and its template polymer PEI played a stabilizing role during the testing process. Therefore, this work provides a promising dopamine fluorescent probe with application prospects.

Lentils/urea as precursors for profound S and N doping of carbon dots for selective sequential determination of Hg(II) and S(II) in food and environmental samples

In this article, we described a new platform for probing toxic pollutants, namely Hg2+ and S2-, in aquatic environment by tracing the “on–off-on” fluorescence signals of quantum dots. To achieve this, red lentils and urea, as natural precursors, were utilized as sources of S and N doping, respectively, to fabricate blue fluorescent carbon quantum dots, namely, lentils/urea quantum dots (LUQDs) with good quantum yield and plentiful S-doping. In the present work, the quality-by-design (QbD) strategy was applied to control and select the optimum conditions for the microwave-aided synthesis of the carbon dots. LUQDs exhibit excitation-dependent emissions, where the maximum fluorescence emission was at 360 nm after excitation at 300 nm. During the detection step, the fluorescence of LUQDs is quenched by the incorporation of Hg2+ over the range of 0.50–70.0 μM. Next, S2- reacts with Hg2+, resulting in turning on the fluorescence emission of LUQDs in the range of 10.0–150.0 µM.The method was applied for the detection of both Hg2+ and S2- in tap, sewage, and river water samples with a recovery rate ranging between 98.96 % and 101.26 %; in addition, Hg2+ was detected in canned Tuna samples with a recovery of 98.70 %. Furthermore, the greenness of the developed method was confirmed through various greenness metrics.

A Portable RGB-Type Quantum Dot-Based Water Sensing Device for Heavy Metal Ion Detection

Using fluorescent quantum dots to detect heavy metal ions in water resources has attracted extensive attention. However, bulky photoluminescence spectrometers are generally required to read the signals, which are not suitable for on-site detection.

A sensitive analytical strategy of oligonucleotide functionalized fluorescent probes for detection of nusinersen sodium in human serum

Spinal muscular atrophy (SMA) is a rare autosomal recessive neuromuscular disease. Nusinersen sodium (NS) is the world's first antisense oligonucleotide (ASO) drug for SMA precise targeted therapy. However, the limited half-life of oligonucleotides and their tendency to accumulate in hepatic and renal tissues presented significant challenges for clinical investigation and therapeutic drug monitoring. In this study, we proposed an analytical strategy based on the specific capture of oligonucleotide functionalized fluorescent probes by single stranded binding proteins (SSB) for ultra-sensitive and high-throughput detection of nusinersen sodium in human serum. The magnetic nanoparticles modified with single-strand binding protein (MNPs-SSB) selectively bonded to the red fluorescent quantum dots functionalized with oligonucleotides (RQDs-ssDNA) that were complementary to nusinersen sodium. Upon interaction with nusinersen sodium, RQDs-ssDNA formed a double-stranded complex (RQDs-ssDNA-NS), resulting in enhanced red fluorescence after magnetic separation as it was no longer captured by MNPs-SSB but remained in the supernatant. A quantitative analysis of nusinersen sodium in biological samples was successfully achieved by establishing a relationship between fluorescence intensity and its concentration. The detection signal F/F0 exhibited a linear correlation (R2 = 0.9871) over a wide range from 0.1 nM to 200 nM, with a limit of detection (LOD) of 0.03 nM, demonstrating the high specificity and rapid analysis time (only 30 min). This method provided a novel approach for sensitive, high-throughput, and specific analysis of nusinersen sodium and similar ASO drugs.

Fluorescent carbon dots for labeling of bacteria: mechanism and prospects-a review.

The search for bacteria-labeling agents that are more efficient and less toxic compared to existing staining dyes is ongoing. Fluorescent quantum dots and carbon dots (CDs) have been extensively researched for various bioimaging applications. Priority is given to CDs due to several advantages, including lower toxicity, versatility in tuning their properties, and better photostability compared to metal-based quantum dots. Although significant progress is still needed to replace existing dyes with CDs for bacteria labeling, they offer promising potential for further improvement in efficiency. Surface charges and functional groups have been reported as decisive factors for bacterial discrimination and live/dead assays; however, a complete guideline for preparing CDs with optimum properties for efficient staining and predicting their labeling performance is lacking. In this review, we discuss the application of fluorescent CDs for bacterial labeling and the underlying mechanisms and principles. We primarily focus on the application and mechanism of CDs for Gram differentiation, live imaging, live/dead bacteria differentiation, bacterial viability testing, biofilm imaging, and the challenges associated with application of CDs. Based on proposed mechanisms of bacterial labeling and ambiguous results reported, we provide our view and guidelines for the researchers in this field to overcome the challenges associated with bacteria labeling using fluorescent CDs.