Blue-emitting Carbon Dots Research Articles

The synthesis of carbon dots by folic acid and utilized as sustainable probe and paper sensor for Hg2+ sensing and cellular imaging

In this work, the blue emission carbon dots (FA-CDs) are synthesized by one-pot solvothermal method by using folic acid as precursor. The FA-CDs emitted bright emission at 445 nm when excited at 360 nm with the QY of 31.2 %. The FA-CDs exhibit sensitive quenching response to Hg2+ with variable concentrations systematically, which determined FA-CDs can be employed as fluorescent probe, with a reliable linear relationship between fluorescence intensity and Hg2+ concentration, and a limit of detection (LOD) of 1.29 nM. Notably, the quenched FA-CDs can be recovered by using EDTA saturated solution with the emission comparable to initial in succession. The FA-CDs based paper sensor can be explored with similar detection performance, and it can also be restored by EDTA saturated solution. Both the restored CDs and paper sensor can be reused in the next turn for detecting Hg2+, which allowed the FA-CDs and their paper sensor can be serviced as sustainable probe for Hg2+ detection. The visual LOD of paper sensor can be determined at 0.1 μM, notably, the paper sensor can be reused at least 3 times with good performance, which is beneficial to environmental protection and saving resources. Possess excellent water solubility and non-toxic properties, the cellular imaging of FA-CDs was evaluated with excellent quality fluorescent image results. The FA-CDs provide a promising convenient fluorescent probe for multi-application in detection and imaging.

Toward visual chiral recognition of amino acids using a wide-range color tonality ratiometric nanoprobe

Chiral recognition has long been a challenging issue to deal with in biological systems, drug design and food authentication. Implementing nanoparticle-based probes with intrinsic or induced chirality in this field has addressed several issues concerning sensitivity, reliability, rapidness and the cost of chiral sensing platforms. Yet, research into chiral nanoprobes that can be used for visual monitoring of chiral substances is still in its infancy. As part of this study, a visual chiral recognition platform has been developed in which a combination of blue-emitting carbon dots (BCDs) and mercaptopropionic acid-capped CdTe quantum dots (MPA-QDs) with inherent chiroptical activity were employed for enantiomeric detection. The ratiometric probe displayed unique fluorescence response patterns in the presence of arginine (Arg) and histidine (His) enantiomers. Upon addition of l-amino acids, successive enhancement and quenching of emission intensity as well as a red-shift in emission wavelength of MPA-QDs were observed. The emission color of the nanoprobe changed from green to pink-red and green to brick-red red by increasing the concentration of L-Arg and L-His, respectively.In contrast, their d-amino acid equivalents have a negligible influence on the emission color and fluorescence signal of the developed nanoprobe. Due to the enantioselective vibrant color changes of the nanoprobe, RGB analysis was applied for the determination of enantiomeric excess (ee) in racemic mixture with satisfactory results, allowing smartphone-based onsite visual evaluation of ee (%). Circular dichroism, lifetime, size distribution and ζ-potential measurements were employed to study the chiroselective responses. First-principle calculations were also carried out with density functional theory (DFT) to confirm the experimental observation. Furthermore, chiroselective response patterns of the ratiometric nanoprobe were manipulated to construct a logic gate system mimicking AND, OR, and INHIBIT functions. The capability of the proposed chiral platform in visual monitoring of the fraction of enantiomers in racemic mixtures has a great potential for rapid and onsite visual discrimination of chiral compounds in the field of clinical diagnostics and drug analysis.

Bright white light emission from blue emitting carbon dot-coated Dy3+-doped luminescent glasses

Dy3+-doped luminescent glasses have received great attention due to their ability to emit white light at a suitable yellow-to-blue intensity ratio. However, achieving bright white light using single Dy3+-doped glasses remains a challenge due to the hypersensitivity of the emission band at 575 nm — usually resulting in intense yellow emission. In this work, we present a novel approach for compensating for the blue emission deficiency of Dy3+ to produce resin-free white light-emitting diodes (WLEDs) by synthesizing two series of Dy3+-doped glasses from tellurite and silicate systems on which blue-emitting carbon dots (BCDs) are spin-coated. The structural, chemical, optical, and luminescence properties of tellurite and silicate glasses are compared and discussed in detail. White light emissions are obtained upon 365-nm excitation for BCD-coated Dy3+-doped tellurite and silicate glasses with color coordinates of (x = 0.31, y = 0.33) and (x = 0.31, y = 0.34) and correlated color temperatures (CCT) of 5518 K and 5316 K, respectively. BCDs coating increases photoluminescence quantum yield (PLQY) values from 3.10 % to 5.62 % and from 20.81 % to 31.49 % for tellurite and silicate glasses, respectively. Ultimately, the findings in this work show the potential of BCD-coated luminescent glasses with excellent luminescent properties to be considered in solid-state lighting applications.

Surface amino group modulation of carbon dots with blue, green and red emission as Cu2+ ion reversible detector

The surface functional groups of carbon dots (CDs) play a significant role in the luminescence performances, but it is still unclear about the effects of special groups on the luminescence mechanism since there are different groups on the surface of prepared CDs. Here, electrochemical method was adopted to synthesize initial CDs and graphite rods served as raw materials, and initial CDs were only modified with amino groups to regulate their surface states, which lead to the blue, green and red luminescence for the modified CDs. The amino groups with different contents are only introduced on the surface of CDs without affecting carbon core. With the increased contents of amino groups, the luminescence spectra of CDs can be successfully modulated from blue to red emission. In addition, the blue emitting carbon dots (B-CDs) have a specific response to Cu2+ ions and can be applied as a fluorescent probe to detect Cu2+ ions in the solution. Moreover, the addition of DL-serine can restore the blue emission of B-CDs quenched by Cu2+ ions. Therefore, the B-CDs have great potential application as a fluorescent reversible ion detector.

Point-of-need quantitation of 2,4-dichlorophenoxyacetic acid using a ratiometric fluorescent nanoprobe and a smartphone-based sensing system

This study reports a new ratiometric fluorescence probe (referred to as rQD@PS@bCDs) and a smartphone-based sensing system for on-site quantitation of Fe3+, ascorbic acid (AA), alkaline phosphatase (ALP) and 2,4-dichlorophenoxyacetic acid (2,4-D). rQD@PS@bCDs with well-resolved dual emissions is facilely synthesized by covalent conjugation of red-emissive quantum dots (rQDs), the internal standard, with blue-emissive carbon dots (bCDs), the Fe3+-specific fluorescent indicator. 2,4-D can specifically inhibit the enzymatic activity of ALP, leading to suppress the production of AA which can reduce Fe3+ to Fe2+ and thereafter trigger the fluorescence response of rQD@PS@bCDs. Taking advantages of these highly specific cascade catalytic reactions, ratiometric fluorescence schemes are established for sensing Fe3+, AA, ALP and 2,4-D both in aqueous solution and on paper-based microarray. The smartphone-based fluorescence detector integrated with the rQD@PS@bCDs-based microarray demonstrated good sensing performance with a wide linear range and low detection limit, and is successfully applied to quantitate 2,4-D in cabbage and tap water samples. The reported method which enables point-of-need quantitation in a sample-in-result-out manner and highlights its features of cost-effectiveness and ease-of-use, is ideally for food safety inspection, environment surveillance, health monitoring at point-of-need, especially in low resource settings.

Selectivity Enhancement for Uric Acid Detection via In Situ Preparation of Blue Emissive Carbon Dots Entrapped in Chromium Metal-Organic Frameworks.

In the present work, for the first time, the in situ formation of blue emissive carbon dots (bCDs) and encapsulation into the pores of chromium-based metal–organic frameworks (Cr-MOFs) are described. The luminescent bCDs via in situ process are formed and entrapped inside the pores of Cr-MOFs to form a nanocomposite of bCDs@Cr-MOFs. The bCDs@Cr-MOFs showed a strong broad blue emission at 420 nm (excited at 310 nm), which corresponds to both, the ligand (2-aminoterephthalic acid) in the Cr-MOF and the entrapped bCDs. This is assigned for the entrapping of bCDs in the pores of the MOFs. Additionally, transmission electron microscopy (TEM) images showed two types of particles, 150 rod-like shapes for Cr-MOF and 5–10 nm spherical shapes assigned for the presence of bCDs. The bCDs alone (without Cr-MOF) showed no selectivity, and their emission was quenched by different biomolecules and ions, such as ascorbic acid, uric acid, Fe3+, Cu2+, and Hg2+. The selectivity of bCDs toward uric acid was increased dramatically when they were encapsulated in the Cr-MOF. The linear range for uric acid was 20–50 μM, and the LOD was measured as 1.3 μM. Spike recoveries for the detection of uric acid in serum samples were between 94 and 108%. The relative standard deviation (RSD, n = 3) at each concentration value was less than 2%. The results showed high ruggedness and robustness of the assay due to its high shelf-life stability of probe (four weeks), water stability, and long working pH range. Validation experiments showed that the established MOF-based sensing system is appropriate for uric acid detection in real samples.

Carbon dots embedded in lead-free luminescent metal halide crystals toward single-component white emitters

The development of single-component white emitters for white light-emitting diodes (WLEDs) remains challenging. Herein, a rare earth-free white light-emitting composite is developed by assembling blue-emitting carbon dots (CDs) and yellow-emitting Cs2InCl5·H2O:Sb3+ metal halide crystals via a facile liquid-liquid diffusion-assisted crystallization approach. The encapsulation mechanism is then analyzed. Depending on the ratios of blue/yellow emitters, these luminescent composites exhibit white light emission with tunable cold and warm hues. The composites also possess prominent ultraviolet resistance, thermal tolerance, and good stability at about 200°C. By employing such “CDs in metal halide” composites as a converter, a WLED is successfully fabricated with a high color rendering index of 93.6, benefiting from the assembled blue and yellow broadband emission. With this strategy, the developed composites show great promise in next-generation WLED lighting.

Dual-reverse-signal ratiometric fluorescence method for malachite green detection based on multi-mechanism synergistic effect

The proposition of ratiometric detection mode has demonstrated great superiority in improving analysis accuracy by forming self-calibration. Herein, the novel dual-reverse-signal ratiometric fluorescence detection for malachite green (MG) was first achieved based on synergistic effect of fluorescence resonance energy transfer (FRET) and inner filter effect (IFE). The ratiometric fluorescence probe (B-RCDs) was self-assembled via electrostatic attraction between blue-emission carbon dots (BCDs) and red-emission carbon dots (RCDs), followed with FRET effect from BCDs to RCDs and exhibited dual-emission at 450 nm and 627 nm. In the presence of MG, the IFE effect between MG and RCDs quenched the fluorescence at 627 nm and restored the fluorescence at 450 nm, sending out two reverse signals along with an obvious color change from pink to purple (302 nm UV lamp). This ratiometric method not only simplified the preparation process, but also improved the detection sensitivity, showing a low limit of detection (LOD) of 41.8 nM, which exhibited superiority than that of single-signal RCDs (157.3 nM). This method held a rapid response of 10 min and represented satisfactory recoveries (99.14%−109.08%) in real water samples, revealing it was a promising candidate in the fast, sensitive and practical detection of MG. Moreover, the design of synergistic effect supplied a new perspective for the development of ratiometric sensing in the future.

Determination of spermine and spermidine in meat with a ratiometric fluorescence nanoprobe and a combinational logic gate

A ratiometric fluorescent nanoprobe is developed with a wide color variation for visual determination of spermine (SP) and spermidine (SD) in meat samples. The green emission provided from the combination of yellow emissive quantum dots and blue emissive carbon dots turns into pink when SP or SD are present. The results show that the developed sensor has good linearity in the range of 0.5–10 and 0.5–80 µM for SP and SD and suitable detection limits were achieved including 0.2 and 2.1 µM for SP and SD. The probe was highly selective in the presence of amino acids and other biogenic amines. RGB indices were extracted to build a combinational logic gate for visual and simultaneous detection of SP and SD. The dual functional logic gate was easy to design and convenient to operate. Finally, a portable sensor was fabricated for visual, rapid and on-site assessment of meat freshness.

Dual Fluorescence in Glutathione-Derived Carbon Dots Revisited.

Dual-fluorescence carbon dots have great potential as nanosensors in life and materials sciences. Such carbon dots can be obtained via a solvothermal synthesis route with glutathione and formamide. In this work, we show that the dual-fluorescence emission of the synthesis products does not originate from a single carbon dot emitter, but rather from a mixture of physically separate compounds. We characterized the synthesis products with UV–vis, Raman, infrared, and fluorescence spectroscopy, and identified blue-emissive carbon dots and red-emissive porphyrin. We demonstrate an easy way to separate the two compounds without the need for time-consuming dialysis. Understanding the nature of the system, we can now steer the synthesis toward the desired product, which paves the way for a cheap and environmentally friendly synthesis route toward carbon dots, water-soluble porphyrin, and mixed systems.

Surface state modulation of blue-emitting carbon dots with high quantum yield and high product yield.

In order to explore the surface state modulation mechanism of carbon dots (CDs) with high quantum yield (QY) and high product yield (PY), CDs were synthesized from different carbon sources with different contents of oxygen-containing functional groups and different silane coupling agents with nitrogen-containing functional groups. The highest QY of as-prepared CDs can reach 97.32% and the PY values of CDs are all high ranging from 46.33–58.76%. It is found that the high content of C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O and pyrrolic N on the surface of CDs can endow CDs with high QY. Moreover, the PY of CDs not only depends on whether CDs have the crosslinked structure, but also is closely and positively correlated with pyridinic N. Consequently, our findings suggest that raw materials rich in carboxyl groups and amino groups are beneficial to the synthesis of CDs with high QY, and whether CDs with crosslinked structure and high content of pyridinic N decide the high PY of CDs. This work provides a theoretical guidance for large-scale synthesis of CDs with high QY and high PY.

A cascade-triggered ratiometric fluorescent sensor based on nanocomposite for lactate determination

For this study, a cascade-triggered ratiometric fluorescent sensor based on nanocomposites was designed to detect lactate. This sensor was established by breaking the inner-filter effect (IFE) between blue emission carbon dots (bCDs) and silver nanoparticles (AgNPs) and activating the dynamic quenching process of red emission quantum dots (rQDs) and Ag+. In this sensor (bCDs/AgNPs-rQDs), the fluorescence of bCDs was quenched by the formation of CDs/AgNPs, and recovered by adding lactate. Subsequently, the quenching of rQDs was triggered by Ag+, which originated from the disintegration of AgNPs. This cascade-triggered ratiometric fluorescent sensor for lactate detection was established with the LOD (limit of detection) of 0.12 μM. The developed probe was applied to lactate detection in human serum with satisfactory results, indicating that the probe has enormous potential in clinical practice.

Rapid FRET-based homogeneous immunoassay of procalcitonin using matched carbon dots labels

A novel method for the detection of procalcitonin in a homogeneous system by matched carbon dots (CDs) labeled immunoprobes was proposed based on the principle of FRET and double antibody sandwich method. Blue-emitting carbon dots with a strong fluorescence emission range of 400–550 nm and red-emitting carbon dots with the best excitation range of 410–550 nm were prepared before they reacted with procalcitonin protoclone antibody pairs to form immunoprobes. According to the principles of FRET, blue-emitting carbon dots were selected as the energy donor and red-emitting carbon dots as the energy receptor. The external light source excitation (310 nm) could only cause weak luminescence of CDs. However, once procalcitonin was added, procalcitonin and antibodies would be combined with each other quickly (≤20 min). Here, blue-emitting carbon dots acquired energy could be transferred to red-emitting carbon dots efficiently, causing the emitted fluorescence enhancement of red-emitting carbon dots. The fluorescence detection results in PBS buffer solution and diluted rabbit blood serum showed that the fluorescence intensity variation was linear with the concentration of procalcitonin. There was a good linear relationship between F/F0 and procalcitonin concentrations in PBS buffer solution that ranged from 0 to 100 ng ml−1, and the linear equation was F/F0 = 0.004 * C pct + 0.98359. Detection in the diluted rabbit serum led to the results that were linear in two concentration ranges, including 0–40 ng ml−1 and 40–100 ng ml−1, and the detection limit based on 3σ K−1 was 0.52 ng ml−1. It is likely that this matched CDs labeled immunoprobes system can provide a new mode for rapid homogeneous detection of disease markers.

Fluorescent paper-based analytical devices for ultra-sensitive dual-type RNA detections and accurate gastric cancer screening

Demand on the quick screening of gastric cancer (GC) has significantly stimulated the development of biomarker sensing techniques. Herein, we report the novel fluorescent paper-based analytical devices (PADs) for detections of GC-related microRNA-21 (miRNA-21) and circular RNA from Hippocampus Abundant Transcript 1 gene (circRNA-HIAT1) with prominent reliability and sensitivity. The PADs, constructed by in-situ synthesis of blue-emissive carbon dots (CDs) and conjugations of probe DNAs, exhibit the superior uniformity and stability. In the presence of targets, rolling circle amplifications (RCA) are triggered to generate long DNA strands for the assemblies of green-/red-emissive labels. Consequently, remarkable blue-to-green and blue-to-red emission color transitions of the PADs are achieved, implementing the color-analysis of miRNA-21 and circRNA-HIAT1, respectively. Benefited from the efficient RCA, coupled with the drastic ratiometric fluorescent changes, the limit of detections (LODs) of PADs are found to be several fM with the upper limit of the linear detection range at 1 nM. More importantly, the fluorescent PADs possess excellent specificity, as well as anti-interference capability in biological settings, enabling their applications in accurate GC screening with plasma samples. Overall, the proposed fluorescent PADs are featured with robust sensing platform, facile signal readout, and exceptional dual-type RNA sensing performance, holding high potential in point-of-care testing (POCT).

Ultrasonic-assisted green extraction of peach gum polysaccharide for blue-emitting carbon dots synthesis

Raw peach gum is hard crystalline-like solid with very poor solubility, significantly restricting its application in various fields. This study optimized the parameters for ultrasonic-assisted peach gum polysaccharides (UPGP) extraction. The results showed that the maximum extraction rate was up to 80.1% under the optimized conditions of 5 h extraction time, 90 mL/g water to raw peach gum ratio and 532 W ultrasonic intensity at 95 °C. The acquired UPGP mainly consisted of Ara, Gal and Man with a molecular weight of 8.18×106 g/mol. Moreover, the UPGP has been used as a green precursor for carbon dots (CDs) preparation through a simple one-step hydrothermal reaction. The synthesized CDs had a mean particle diameter of 7.66 nm and showed excellent fluorescence intensity and stability. Thus, this study improved the utilization of raw peach gum and further broadened the UPGP application.

Dual-Mode Fluorescence and Visual Fluorescent Test Paper Detection of Copper Ions and EDTA.

In this study, blue-emission carbon dots were prepared from the legumes of the vegetable Pisum sativum Linn. by one-step carbonization. The fluorescence of a carbon dot (CDs) solution can be quenched by copper ions and recovered by ethylenediaminetetraacetic acid (EDTA). In addition, two kinds of visual fluorescent filter papers were prepared. Finally, a dual-mode fluorescence and visual fluorescent test paper was employed for the detection of copper ions and EDTA. The simple synthesis method and the high safety enable this material to have more application possibilities.

High Quantum Yield Fluorescent Chitosan-Based Carbon Dots for the Turn-On-Off-On Detection of Cr(VI) and H2O2

One-pot hydrothermal carbonization approach was employed to synthesize the blue-emission carbon dots derived from chitosan (Cs) and o-phenylenediamine (OPD). The Cs-based carbon dots (Cs–CDs) possessed a certain high quantum yield of 58% and exhibited excellent solubility, stability and fluorescence response in aqueous solutions. The Cs–CDs were designed as a sensor for Cr(VI) and H2O2 determination. The sensing strategy of Cr(VI) was based on the inner filter effect (IFE) and static quenching effect (SQE), showing a good linear correlation ranging from 1 to 130[Formula: see text][Formula: see text]M with a detection limit (LOD) of 0.91[Formula: see text][Formula: see text]M. In addition, the determination for H2O2 was attributed to the elimination of IFE (EIFE) due to the reduction reaction and the detection for H2O2 was in the linear range from 1.0 to 200.0[Formula: see text][Formula: see text]M with LOD of 0.51[Formula: see text][Formula: see text]M. Finally, the proposed designed sensor could be simply applied for detection of Cr(VI) and H2O2 in real samples.

Development of novel blue emissive carbon dots for sensitive detection of dual metal ions and their potential applications in bioimaging and chelation therapy

In recent years, there has been an increased interest in the use of fluorescent carbon dots (C-dots) as an alternative to toxic synthetic organic dyes in live cell imaging, medical diagnostics and other diverse biomedical applications. In the present work, highly fluorescent C-dots have been prepared from commercially available peptic digest of animal tissue, without using any additional chemical reagent for surface functionalization. The synthesized C-dots are monodispersed nanomaterials with hydroxyl, carboxyl and amino surface functionalities and remain stable in high ionic strength media and over a wide range of pH. They exhibit a strong blue fluorescence upon excitation at 350 nm with a high quantum yield of 61%. The potential use of these C-dots as fluorescent nanoprobe for specific metal ions (Cu2+ and Hg2+) detection through chelation, radical scavenging and cellular imaging has been investigated. These highly fluorescent labels show rapid cellular internalization without hampering cellular integrity. Cell proliferation assay demonstrates that these C-dots have minimal cell toxicity even at a high concentration of 3 mg/mL. They show significant quenching on incubation with cells pretreated with Cu2+ and Hg2+ ions. They also show rapid exocytosis from cells showcasing their high potential for chelation therapy. Thus, this study offers a scalable synthesis approach for highly fluorescent and bio-compatible C-dots from a cost-effective precursor, which can be used for specific metal ions detection and their removal from cells through chelation via exocytosis. They can also be used as an alternate to synthetic organic dyes for fluorescence-based cell-imaging.

Fluorescent Carbon Dots an Effective Nano-Thermometer in Vitro Applications.

Fluorescent sensing of temperature in nanoscale regions has many advantages and applications in the biological field. Herein, blue emitting carbon dots (CDs) are designed and successfully developed using a one step hydrothermal method. As synthesized CDs exhibit temperature dependent photoluminescent (PL) intensity and PL decay lifetime over the physiological temperature ranging from room temperature (RT) to 70 °C. The PL intensity and PL decay lifetime of the obtained CDs correlate linearly to temperature (RT-70 °C) with correlation coefficient of 0.997 and 0.996, respectively. Additionally, dual mode thermal sensing (PL intensity/lifetime) make these CDs a promising optical nanothermometer over alternative semiconductors quantum dots and CD-based quantum dots. Moreover, the resultant aqueous CDs demonstrate excitation-independent blue emission, and the PL quantum yield (QY) is reached at 44.5%. The obtained CDs illustrate stable performance to high ionic environments and photobleaching even after keeping them for 2 h under continues UV irradiation. Furthermore, blue emitting CDs have low cytotoxicity for T-ca. cells and illuminate deep blue fluorescence under the excitation of 406 nm. As a result, high thermal sensitivity of these fluorescent CDs has potential to detect temperature in living cells in the range of 25-40 °C.

One-step ratiometric fluorescence sensing of ascorbic acid in food samples by carbon dots-referenced lanthanide probe

We report a ratiometric fluorescence sensor formed via the self-assembly of the lanthanide ion Eu3+ and blue-emitting carbon dots (CDs) for the direct detection of ascorbic acid (AA). The obtained sensor exhibited the characteristic emission of 2,6-pyridinedicarboxylic acid (DPA)-sensitized Eu3+ (Eu–DPA) at 615 nm and the weak emission of CDs at 440 nm under excitation at 283 nm. After the addition of AA, the fluorescence emission of Eu–DPA, which served as the AA recognition site, was significantly quenched, whereas the emission of CDs changed slightly, resulting in a ratiometric fluorescent response toward AA. A wide linear range from 0.5 μM to 820 μM was achieved in the detection of AA with an LOD of 60 nM. Moreover, this CDs/Eu–DPA sensor, which displayed excellent sensitivity and selectivity, was successfully applied for the determination of AA in fruits, vegetables and beverage samples, suggesting a great potential for applications in foods.