Luminescent Carbon Quantum Dots Research Articles

Development of a highly sensitive fluorescent probe using Delonix regia (Gulmohar) tree pod shell for precise sarcosine detection in human urine samples: advancing prostate cancer diagnosis

We designed a highly sensitive fluorescent sensor for the early detection of sarcosine, a potential biomarker for prostate cancer. This sensor was based on surface-cobalt-doped fluorescent carbon quantum dots (Co-CD) using a FRET-based photoluminescent sensing platform. Blue luminescent carbon quantum dots (CQD) were synthesised through a hydrothermal approach, utilizing Delonix regia tree pod shells. Cobalt was employed to functionalize the CQD, enhancing the quantum-entrapped effects and minimizing surface flaws. To optimize Co-CD preparation, we employed a Box-Behnken design (BBD), and response surface methodology (RSM) based on single-factor experiments. The Co-CD was then used as a fluorescent probe for selective Cu2+ detection, with Cu2+ quenching Co-CD fluorescence through an energy transfer process, referred to as ‘turn-off’. When sarcosine was introduced, the fluorescence intensity of Co-CD was restored, creating a ‘turn-on’ response. The sensor exhibited a Cu2+ detection limit (LOD) of 2.4 µM with a linear range of 0 μM to 10 µM. The sarcosine detection in phosphate buffer saline (PBS, pH 7.4) resulted in an LOD of 1.54 μM and a linear range of 0 to 10 µM. Importantly, the sensor demonstrated its suitability for clinical analysis by detecting sarcosine in human urine. In summary, our rapid and highly sensitive sensor offers a novel approach for the detection of sarcosine in real samples, facilitating early prostate cancer diagnosis. Communicated by Ramaswamy H. Sarma

Luminescent carbon dots versus quantum dots and gold nanoclusters as sensors.

Ultra-small nanoparticles, including quantum dots, gold nanoclusters (AuNCs) and carbon dots (CDs), have emerged as a promising class of fluorescent material because of their molecular-like properties and widespread applications in sensing and imaging. However, the fluorescence properties of ultra-small gold nanoparticles (i.e., AuNCs) and CDs are more complicated and well distinguished from conventional quantum dots or organic dye molecules. At this frontier, we highlight recent developments in the fundamental understanding of the fluorescence emission mechanism of these ultra-small nanoparticles. Moreover, this review carefully analyses the underlying principles of ultra-small nanoparticle sensors. We expect that this information on ultra-small nanoparticles will fuel research aimed at achieving precise control over their fluorescence properties and the broadening of their applications.

Luminescent carbon quantum dots derived from syzygium cumini seeds with endogenous anti-oxidant and cytotoxic potency including in vitro photoluminescence and live cell imaging

This study focuses on the use of carbon quantum dots (CQDs) from Syzygium cumini seeds prepared through hydrothermal synthesis for anti-oxidant, bioimaging, and anti-neoplastic activities.

Enabling white color tunability in complex 3D-printed composites by using lead-free self-trapped exciton 2D perovskite/carbon quantum dot inks.

The generation of stable white light emission using lead-free perovskites remains a huge challenge in the development of future display and lighting technologies, due to fast material deterioration and the decrease of the color quality. In this work, we report a combination of diverse types of 2D A2SnX4 (A = bulky cation, X = Br, I) perovskites exhibiting self-trapped exciton (STE) emission and blue luminescent carbon quantum dots (CQDs), with the purpose of generating A2SnX4/CQD inks with a broadband emission in the visible region and a tunable white light color. By varying the concentration of the 2D perovskite, the white emission of the mixtures is modulated to cool, neutral, and warm tonalities, with a PL quantum yield up to 45%. From the combinations, the PEA2SnI4/CQD-based ink shows the longest stability, due to suitable surface ligand passivation provided by the capping ligands covering the CQDs, compensating the defect sites in the perovskite. Then, by incorporating the PEA2SnI4/CQDs inks into an acrylate polymer matrix, the quenching of the PL component from the perovskite was restrained, being stable for >400 h under ambient conditions and at a relative humidity of ∼50%, and allowing the preparation of complex 3D-printed composites with stable white emission tonalities. This contribution offers an application of STE-based Sn-perovskites to facilitate the future fabrication of lead-free white-light optoelectronic devices.

Ixora coccinea flower-derived green luminescent carbon quantum dots for Fe3+ recognition and preparation of Pd nanoparticles for the Suzuki–Miyaura coupling and cyanation process

Solvothermal method of producing fluorescent tiny (∼3 nm) nitrogen-doped carbon quantum dots from Ixora coccinea flowers and o-phenylenediamine has been explained. These quantum dots are used for sensing Fe3+ and for producing Pd nanoparticles.

Luminescent carbon quantum dots: synthesis and optical applications

In the current study, carbon nanoparticles i.e., carbon quantum dots have been prepared via the hydrothermal method using Citrus limon juice as a precursor. The method used is low-cost and environmentally friendly, besides the precursor is easily available and non-toxic. Various studies were performed on the synthesized CQDs to gain insight into the functional groups present on their surface, excitation and emission spectra, and their photostability. The obtained results showed that CQDs show various functional groups on their surface, emission and excitation bands are broad rather than characteristic peaks, the emission is excitation dependent, Temperature-dependency of photoluminescence, and good photostability in large salt concentrations, with UV-irradiation and storage time of CQDs. These characteristics suggest that the synthesized CQDs can find applications in metal ion detection, cell imaging, drug delivery, and many optoelectronic devices.

Preparation of Highly Luminescent Carbon Quantum Dots and Study of Bioimaging

Using ammonium citrate as the carbon source and urea, ammonia and ethylenediamine as the nitrogen sources, CQDs with different nitrogen sources were prepared by hydrothermal method, and the preparation conditions were optimized to obtain CQDs with the best fluorescence performance for three different nitrogen sources.The fluorescence colors of the three CQDs were not significantly different, all of them were blue, indicating that different nitrogen sources did not have significant differences on the fluorescence color, but had some effects on the fluorescence intensity, and the yields of 1-CQDs, 2-CQDs and 3-CQDs were 0.22, 0.29 and 0.529, respectively.The UV, natural light, pH and ionic stability of CQDs with different nitrogen sources were investigated, and the results showed that 3-CQDs have UV, natural light and ionic stability, and all three CQDs have pH instability.The MTT method shows that 3-CQDs have lower cytotoxicity than the other two CQDs, and the bioimaging experiments show that 3-CQDs bind to yeast in greater numbers and have stronger fluorescence intensity, which proves that they are more suitable for bioimaging, laying a theoretical foundation for the bioimaging of CQDs at a later stage.

All-in-One Photoactivated Inhibition of Butyrylcholinesterase Combined with Luminescence as an Activation and Localization Indicator: Carbon Quantum Dots@Phosphonate Hybrids.

Photopharmacology is a booming research area requiring a new generation of agents possessing simultaneous functions of photoswitching and pharmacophore. It is important that any practical implementation of photopharmacology ideally requires spatial control of the medicinal treatment zone. Thus, advances in the study of substances meeting all the listed requirements will lead to breakthrough research in the coming years. In this study, CQDs@phosphonate nanohybrids are presented for the first time and combine biocompatible and nontoxic luminescent carbon quantum dots (CQDs) with photoactive phosphonate enabling inhibition of butyrylcholinesterase (BChE), which is a prognostic marker of numerous diseases. The conjunction of these components in hybrids maintains photoswitching and provides enhancement of BChE inhibition. After laser irradiation with a wavelength of 266 nm, CQDs@phosphonate hybrids demonstrate a drastic increase of butyrylcholinesterase inhibition from 38% up to almost 100% and a simultaneous luminescence decrease. All the listed hybrid properties are demonstrated not only for in vitro experiments but also for complex biological samples, i.e., chicken breast. Thus, the most important achievement is the demonstration of hybrids characterized by a remarkable combination of all-in-one properties important for photopharmacology: (i) bioactivity toward butyrylcholinesterase inhibition, (ii) strong change of inhibition degree as a result of laser irradiation, luminescence as an indicator of (iii) bioactivity state, and of (iv) spatial localization on the surface of a sample.

Microfluidic steam-based synthesis of luminescent carbon quantum dots as sensing probes for nitrite detection

Abstract In this work, an efficient and green approach has been presented to prepare carbon quantum dots (CQDs) from watermelon juice through a microfluidic steam-based method, with a view to enabling continuous production at scale, i.e., to save time, costs, or energy as compared to conventional production using an autoclave. The evolution of the product formation through multifarious intermediates generated in different stages of the reaction process was characterized. Computational fluid dynamics simulations reveal the pressure and velocity profiles in the microchannel to exert process control. These determine the quality of the obtained CQDs by influencing the particle size transformations and manifold chemicals along the microchannel axis. The optimal reaction conditions and reaction mechanism for the synthesis of CQDs were investigated. Additionally, the synthesized CQDs demonstrated good fluorescence properties as well as a specific response to NO 2 − {\text{NO}}_{2}^{-} in both fluorescence and spectrophotometric modes, providing great potential for their application in environmental monitoring.

Selective detection of folate and analogs employing highly luminescent manganese-nitrogen co-doped carbon quantum dots: a fluorimetric turn-off strategy

Selective detection of folate and analogs employing highly luminescent manganese-nitrogen co-doped carbon quantum dots: a fluorimetric turn-off strategy

Green emissive Carbon quantum dots produced from Plantago Psyllium by thermal carbonization as heterogenous catalyst

The water retention and metal ion binding efficiency of Plantago Psyllium hemicellulose has been well explored. But there are no reports available on its conversion to carbon quantum dots (CQDs) for potential applications. This study is focused on the correlation of the microstructural features of CQDs with its catalytic and emission properties. The green synthesis of CQDs was explored using hemicellulose rich Plantago psyllium as precursor by a one-step thermal carbonization approach. The functional groups, microstructure, surface and the morphological analysis of CQDs indicate the formation of zero-dimensional carbon material with predominately sp2 carbon framework with oxygen and nitrogen atoms. The characterization reports of the carbonized psyllium husk showed that the hemicellulose rich biomass was converted into luminescent CQDs. The CQDs exhibited green emission under the UV lamp. The experimental results of the adsorption study indicate that the CQDs derived from hemicellulose can act as good adsorbent for the removal of Xanthene-based dye. The obtained results promise the effective conversion of biomass and potential application of CQDs as adsorption catalyst for the efficient and economic removal of cationic dyes in waste water.

Solubility tuning of alkyl amine functionalized carbon quantum dots for selective detection of nitroexplosive

The major issue of luminescent carbon quantum dots (CQDs) is the solubility in wide range of solvent and disappearance of luminescence behavior in its solid state due to aggregation caused quenching. To resolve this issue, in the present work, we have tuned the solubility of carbon quantum dots in different kinds of solvents through surface functionalization technique. Here, we have synthesized three sets of alkyl amine functionalized carbon quantum dots from citric acid and alkyl amine by solvothermal method. We have observed that the solubility of CQDs increases from aqueous medium to organic medium with increasing length of hydrophobic alkyl chains attached at the surface of CQDs. It is seen that n-butyl amine functionalized CQDs (C4-CQD) are soluble in any type of solvents. Here we have also observed that the C4-CQD shows aggregation induced emission instead of aggregation caused quenching in solid state and shows bright yellow luminescence color upon excitation. Besides this, we also report selective detection of both dinitroaniline (DNA) and dinitrophenol (DNP) using this C4-CQD via fluorescence quenching and colorimetric methods. In organic medium both shows significant quenching with emission peak of carbon quantum dots is red shifted (∼30 nm) in presence of DNP whereas no significant peak shift is observed for DNA. CQDs containing paper strip shows yellow spot in presence of DNP but no such characteristic color is appeared after addition of DNA. Using these two techniques, we have selectively identified both DNA and DNP among other nitro compounds by our as-synthesized carbon dots.

Picomolar Detection of Lead Ions (Pb2+) by Functionally Modified Fluorescent Carbon Quantum Dots from Watermelon Juice and Their Imaging in Cancer Cells.

Water contamination due to the presence of lead is one of the leading causes of environmental and health hazards because of poor soil and groundwater waste management. Herein we report the synthesis of functionally modified luminescent carbon quantum dots (CQDs) obtained from watermelon juice as potential nanomaterials for the detection of toxic Pb2+ ions in polluted water and cancer cells. By introducing surface passivating ligands such as ethanolamine (EA) and ethylenediamine (ED) in watermelon juice, watermelon-ethanolamine (WMEA)-CQDs and watermelon-ethylenediamine (WMED)-CQDs exhibited a remarkable ~10-fold and ~6-fold increase in fluorescence intensity with respect to non-doped WM-CQDs. The relative fluorescence quantum yields of WMEA-CQDs and WMED-CQDs were found to be 8% and 7%, respectively, in an aqueous medium. Among various functionally-modified CQDs, only WMED-CQDs showed high selectivity towards Pb2+ ions with a remarkably good limit of detection (LoD) of 190 pM, which is less than that of the permissible limit (72 nM) in drinking water. The functionally altered WMED-CQDs detected Pb2+ metal ions in polluted water and in a human cervical cancer cell line (HeLa), thus advocating new vistas for eco-friendly nanomaterials for their use as diagnostic tools in the environment and biomedical research areas.

Preparation of highly luminescent nitrogen-doped carbon quantum dots and their detection of tetracycline antibiotics

The massive use of tetracyclines poses a risk to human health and their quantitative testing is urgent. This work provides a novel nitrogen-doped carbon quantum dots (N-CQDs) fluorescent probe which was prepared by a facile one-pot hydrothermal method using glucose and ethylenediamine as precursors for the detection of tetracycline antibiotics. The fluorescence intensity of the CQDs was greatly enhanced by the doping of nitrogen. The fabricated N-CQDs exhibited a spherical shape with an average diameter of 2.66 nm. It displayed blue fluorescence, a quantum yield of 10.97 % and an excitation-dependent emission behavior. It also had excellent stability, such as resistance to the effects of varying ionic strength, pH and continuous UV light irradiation. The N-CQDs detect tetracycline antibiotics including tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) based on fluorescence quenching caused by the inner filter effect (IFE) with excellent specificity. The limits of detection (LOD) were 0.344, 0.265, and 0.117 μM, respectively. The proposed method has been successfully applied to the determination of tetracycline antibiotics in rat serum and milk samples with satisfactory recoveries, confirming that the proposed fluorescent probe has practical application prospects.

Nitrogen doped carbon quantum dots (N-CQDs) with high luminescence for sensitive and selective detection of hypochlorite ions by fluorescence quenching

A highly luminescent nitrogen-doped carbon quantum dots (N-CQDs) with a quantum yield of 44% was prepared by a facile hydrothermal synthesis method using citric acid (CA) and ethylenediamine (EDA) with a molar ratio of 1:1 at 200 °C for 5 h. The hypochlorite (ClO−) ions significantly quench the fluorescence of the N-CQDs according to a pseudo-second-order kinetic model. A sensitive and selective quantification method with an excellent linearity in the range of 1.0–10.0 μM was developed to detect ClO− ions based on the fluorescence quenching. The limit of detection (LOD) of 0.43 μM and the limit of quantification (LOQ) of 1.04 μM were achieved, respectively. This approach was successfully applied to detect the residual ClO− ions in local tap water and in swimming pool water. In addition, the developed fluorescence quenching method was also successfully applied in anti-counterfeiting and paper encryption. Both of the applications in real world suggest that the as-prepared N-CQDs is a kind of promising fluorescence probe for rapid detecting ClO− ions in environment fields, and has potential applications in text secrecy fields.

Highly luminescent pH-responsive carbon quantum dots for cell imaging

Carbon quantum dots (CDs) have attracted tremendous interest owing to their idiosyncratic functions and wide-ranging applications. However, it remains a great challenge to empolder an integrated CDs combining high luminescence, biocompatibility and luminescence color tunability for bioimaging via simple approach. In this work, pH-responsive carbon quantum dots (Si-CDs) with high luminescence (quantum yield = 74.8%) were fabricated by one-step hydrothermal method using (3-mercaptopropyl) triethoxysilane (KH-580) as modifier for the first time. The optical properties of the as-prepared Si-CDs can be controlled from obvious green–blue–violet transformation by altering the pH. More importantly, the change is reversible and repeatable. In addition, the Si-CDs have good biocompatibility and chemically inert in vitro cell system simulation. Such non-toxic, environmental friendly, low-cost, inert CDs materials are promising candidates for biomedical and pH-sensitive sensors.

Chemical Fabrication of Efficient Blue‐luminescent Carbon Quantum Dots from Coal Washery Rejects (Waste) for Detection of Hg2+ and Cr6+ Ions in Water

AbstractAn economical facile method was established for the preparation of luminescent carbon quantum dots (CQDs) by utilizing the waste coal washery rejects as precursor materials. The derived CQDs were extensively characterized for their physio‐chemical properties and they (Mcqds and Dcqds) show an efficient maximum quantum yield of 11 % with an average particle size of 2.5‐3.0 nm. The derived CQDs exhibited better physical and chemical properties at maximum excitation and emission wavelengths of 360 nm and 450 nm, respectively, with blue‐light emission. The as‐synthesized CQDs (Mcqds) were applied as a fluorescent sensing probe for sensitive detection of Hg2+ and Cr6+ ions in water samples, showing reasonable limit of detection and quantification with recovery percentage of 96–100 %. The study has shown potential for using such cheap waste‐material derived CQDs as for further development of sensing devices in future.

Luminescent properties of carbon quantum dots synthesized by microplasma method

The luminescent carbon quantum dots were synthesized by microplasma treatment of a glucose solution at atmospheric pressure at room temperature. The spectral and kinetic characteristics of synthesized quantum dots were studied by time-resolved confocal scanning luminescent microscopy and time-correlated single photon counting. The emission spectra are wide non-elementary bands. Their maxima were located at 476, 500, 547 and 580 nm at the wavelengths of the exciting radiation of 375, 405, 470 and 532 nm, respectively. Three exponential components with decay time constants of 0.65, 2.2, and 6.2 ns were detected in the luminescence kinetics. The presence of these components is due to the formation of three different types of luminescence centers at quantum dots with different probabilities of quantum transitions. Presumably, it may be related to the activation of quantum dots by various impurities or other defects formed luminescence centers. The concentration of quantum dots was controlled by changing the microplasma processing time of the glucose solution.

Au modified spindle-shaped cerium phosphate as an efficient co-reaction accelerator to amplify electrochemiluminescence signal of carbon quantum dots for ultrasensitive analysis of aflatoxin B1

In various detection methods of aflatoxin B1 (AFB1), false positives and false negatives are common due to the low sensitivity, expensive equipment or improper pretreatment during operation. Here, a sandwich electrochemiluminescence (ECL) immunosensor armed with a synergistic co-reaction acceleration strategy was employed for the ultra-sensitive detection of AFB1. Benefiting from the catalytic properties of Ce3+/Ce4+ redox pairs, cerium phosphate@gold (CePO4@Au), for the first time, was introduced into the immunosensor as a new type of co-reaction accelerator, and it significantly improved the ECL intensity of the nitrogen doped hydrazide conjugated carbon dots (NHCDs)-H2O2 system. CePO4@Au has the ability to promote the decomposition of H2O2 and accelerate the formation of O2•−. The more of O2•− reacts with NHCDs to produce a stronger and more robust ECL signal response. Furthermore, the spindle-shaped sensing interface formed by oxidation cerium and phosphate has a high loading area and good biocompatibility, and the modification of Au nanoparticles further achieves the stable binding of the capture antibody. Striving for further improvement, Ag modifies Barium titanate (BaTiO3), as the signal carrier with amplification ability, loads with a large number of anodic luminescent carbon quantum dots, were adopted as detection markers for the construction of sandwich ECL biosensors. The co-reaction amplification system achieves high precision quantitative detection of AFB1 in the linear range of 0.01 pg/mL–100 ng/mL, and the detection limit is 9.55 fg/mL. In addition, the constructed biosensor also showed good stability, reproducibility and specificity, with a promising application prospect.

Full color fluorescent carbon quantum dots synthesized from triammonium citrate for cell imaging and white LEDs

Multicolor fluorescent carbon quantum dots (CDs) exhibit prospective applications but the intrinsic reaction and luminescence mechanisms of CDs remain unclear. In this work, full color fluorescent CDs were synthesized through a facile solvothermal treatment with triammonium citrate as the carbon source. By adjusting the reaction temperature, the maximum emission wavelength is tuned from 440 nm for blue CDs (B-CDs) to 625 nm for red CDs (R-CDs), covering the whole visible spectrum range. The emission mechanism is proposed as surface-state-controlled, which results from different degrees of graphitization and increasing of functional groups on the surfaces. Three different surface states are derived from the overlap of the absorption and excitation spectra and the mechanism is established by XRD, Raman, XPS and UV–Vis absorption. The full-color luminescent CDs with high light and pH stability as well as good biocompatibility are successfully employed to image HeLa cells. White LED is fabricated by B-, G-, and R-CDs/polymer films with a near ultraviolet (NUV) semiconductor chip. The results of this research demonstrate that the synthesized CDs can be potentially applied in multi-color displays, white LEDs and biological imaging probes.