Fabrication of a Reusable Carbon Dot/Gold Nanoparticle/Metal-Organic Framework Film for Fluorescence Detection of Lead Ions in Water

Advancements in the synthesis of carbon dots and their application in biomedicine

As a sort of fluorescent carbon nanomaterial with a particle size of less than 10 nm, carbon dots (CDs) have their own merits of good dispersibility in water, stable optical properties, strong chemical inertness, stable optical properties, and good biosecurity. These excellent peculiarities facilitated them like sensing, imaging, medicine, catalysis, and optoelectronics, making them a new star in the field of nanotechnology. In particular, the development of CDs in the fields of chemical probes, imaging, cancer therapy, antibacterial and drug delivery has become a hot topic in current research. Although the biomedical applications in CDs have been demonstrated in many research articles, a systematic summary of their role in biomedical applications is scarce. In this review, we introduced the basic information of CDs in detail, including synthesis approaches of CDs as well as their favorable properties including photoluminescence and low cytotoxicity. Subsequently, the application of CDs in the field of biomedicine was emphasized. Finally, the main challenges and research prospects of CDs in this field were proposed, which might provide some detailed information in designing new CDs in this promising biomedical field.

Metal-organic framework (MOF)/C-dots and covalent organic framework (COF)/C-dots hybrid nanocomposites: Fabrications and applications in sensing, medical, environmental, and energy sectors

Developing new hybrid materials is critical for addressing the current needs of the world in various fields, such as energy, sensing, health, hygiene, and others. C-dots are a member of the carbon nanomaterial family with numerous applications. Aggregation is one of the barriers to the performance of C-dots, which causes luminescence quenching, surface area decreases, etc. To improve the performance of C-dots, numerous matrices including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and polymers have been composited with C-dots. The porous crystalline structures, which are constituents of metal nodes and organic linkers (MOFs) or covalently attached organic units (COFs) provide privileged features such as high specific surface area, tunable structures, and pore diameters, modifiable surface, high thermal, mechanical, and chemical stabilities. Also, the MOFs and COFs protect the C-dots from the environment. Therefore, MOF/C-dots and COF/C-dots composites combine their features while retaining topological properties and improving performances. In this review, we first compare MOFs with COFs as matrices for C-dots. Then, the recent progress in developing hybrid MOFs/C-dots and COFs/C-dots composites has been discussed and their applications in various fields have been explained briefly.

One-step solvent thermal synthesis of 3D networked MOF composites for preparation of an ultrasensitive chemosensor for hydroquinone and catechol

Pharmaceuticals and personal care products (PPCPs) have a significant impact on the environment and human health, due to their sometimes toxic and carcinogenic characteristics. Therefore, an innovative chemosensor was constructed for ultrasensitive determination of two typical PCCPs (hydroquinone (HQ) and catechol (CC)) in several minutes. The homemade chemosensor (UiO-67@GO/MWCNTs) consisted of MOF(UiO-67), graphene oxide (GO), and multi-walled carbon nanotubes (MWCNTs) composites; it was a networked, structurally sparse, porosity-rich, homogeneous octahedral composite, and had ultra-high electrical conductivity, which provided lots of active adsorption sites, promote charge transfer, and enrich lots of molecules to be measured in a few minutes. The prepared electrochemical sensor showed good long-term stability, applicability, reproducibility, and immunity to interference for the determination of HQ and CC, with a wide linear range of response of 5.0 ~ 940 µM for both HQ and CC, and a low limit of detection with satisfactory recoveries. In addition, a new strategy of using MOF composites as the basis for electrochemical determination of organic small molecules was established, and a new platform was constructed for the quantitative determination of organic small molecules in various environmental samples.

Luminescent lanthanide complexes based on 4,5-di(3,5-dicarboxylphenoxy)phthalic acid as enhanced fluorescence probes for highly selective detection of lead(II) ions in water

Six novel lanthanide complexes ([Nd2(L)(H2O)6]n·4.58n(H2O) (1), [Ln(H3L)(H2O)]n·0.5n(H2O), Ln = Sm (2), Eu (3), Gd (4), Tb (5), Eu0.18Gd0.62Tb0.20 (6)) have been hydrothermally synthesized based on the ligand 4,5-di(3,5-dicarboxylphenoxy)phthalic acid (H6L). Single crystal X-ray diffraction reveals that complexes 1-6 are 2D structures, where 2-6 are isomorphic. Complexes 3 and 5 exhibit the characteristic fluorescence of Eu(III) and Tb(III) ions respectively, while complex 4 shows blue-green light emission based on the ligand. In particular, the ternary Eu/Gd/Tb complex 6 shows white light emission with a CIE (Commission International del'Eclairage) chromaticity coordinate of (0.330, 0.339) and hence close to pure white light emission. Moreover, complexes 3 and 5 display specific fluorescence-enhanced detection performance for Pb2+ ions: The interaction between Pb2+ ions and the ligand enhances the charge transfer efficiency between the ligand and the Eu(III) and Tb(III) ions and thus leads to fluorescence enhancement of complexes 3 and 5. More importantly, complex 3 exhibits the lowest detection limit of 4.72 nM for Pb2+ ions among the existing complex fluorescent probes. In addition, both complexes 3 and 5 show good performance for recycling and for the detection of Pb2+ in real water samples.

A Novel Ion Species- and Ion Concentration-Dependent Anti-Counterfeiting Based on Ratiometric Fluorescence Sensing of CDs@MOF-Nanofibrous Films

Traditional fluorescent anti-counterfeiting labels based on "on-off" fluorescence can be easily cloned. It is important to explore advanced anti-counterfeiting fluorescent labels with high-level security. Here, a pioneering ion species- and ion concentration-dependent anti-counterfeiting technique is developed. By successive loading Cu2+ -sensitive yellow emitted carbon dots (Y-CDs) and Cu2+ non-sensitive blue emitted carbon dots (B-CDs) into metal-organic frameworks (MOFs) and followed by electrospinning, the B&Y-CDs@MOF-nanofibrous films are prepared. The results show that the use of MOF not only avoids the fluorescence quenching of CDs but also improves the fluorescence stability. The fluorescence Cu2+ -sensitivity of the CDs@MOF-nanofibrous films can be regulated by polymer coating or lamination. The fluorescent label consisting of different Cu2+ -sensitivity films will show Cu2+ concentration-dependent decryption information. Only at a specific ion species and concentration (Cu2+ solution of 40-90 µm), the true information can be read out. Less or more concentration (<40 or >90 µm) will lead to false information. The identification of the real information depends on both the species and the concentration. After Cu2+ treatment, the fluorescence of the label can be recovered by ethylenediaminetetraacetic acid disodium (EDTA-2Na) for further recycling. This work will open up a new door for designing high-level fluorescent anti-counterfeiting labels.

Localized electron-accepted yellow-emission carbon dots encapsulated in UiO-66 for efficient visible-light driven photocatalytic activity

Metal organic frameworks (MOFs) possess a large surface area, inherent porosity and high crystallinity. Nevertheless, they lack electron acceptors, which limit the exploitation of their photocatalytic properties. Carbon dots (CDs) known for excellent optical properties can serve as localized electron acceptors. As a novel hybrid nanomaterial, the structure of CDs@MOFs effectively facilitates charge separation and carrier transfer, bring about a marked improvement of photocatalytic activity. In this study, yellow-emission carbon dots (YCDs) were encapsulated within zirconium-based metal organic framework (UiO-66) via a dynamic adsorption method. Compared with blue carbon dots (BCDs), the YCDs@UiO-66 exhibited superior degradation performance. It demonstrates that incorporation of YCDs broadens the UV absorption range of UiO-66, thereby enhancing light utilization. The degradation efficiency of YCDs@UiO-66 was 92.6%, whereas UiO-66 alone achieved only 63.1%. Notably, the results of the radical quenching experiment and electron paramagnetic resonance (EPR) revealed that h+ and •O2- played a prominent role in the photodegradation of tetracycline hydrochloride (TCH). This study highlights that the introducing YCDs in MOFs-mediated photocatalytic reactions is a viable strategy to improve catalytic efficiency.

Two Stable Bifunctional Zinc Metal-Organic Frameworks with Luminescence Detection of Antibiotics and Proton Conduction

Functionalized crystalline solids based on metal-organic frameworks (MOFs) enable efficient luminescence detection and high proton conductivity, making them crucial in the realms of environmental monitoring and clean energy. Here, two structurally and functionally distinct zinc-based MOFs, [Zn(TTDPa)(bodca)]·H2O (1) and [Zn(TTDPb)(bodca)]·H2O (2), were successfully designed and synthesized using 3,6-di(pyridin-4-yl)thieno[3,2-b]thiophene (TTDPa) and 2,5-di(pyridin-4-yl)thieno[3,2-b]thiophene (TTDPb) as ligands, in the presence of bicyclo[2.2.2]octane-1,4-dicarboxylic acid (H2bodca). Both 1 and 2 display a three-dimensional (3D) structure with 5-fold interpenetration, and notably, 2 forms a larger one-dimensional pore measuring 17.16 × 10.81 Å2 in size. Fluorescence experiments demonstrate that 1 and 2 can function as luminescent sensors for nitrofurantoin (NFT) and nitrofurazone (NFZ) with low detection limits, remarkable selectivity, and good recyclability. A comprehensive analysis was conducted to investigate the differing sensing effects of compounds 1 and 2 and to explore potential sensing mechanisms. Additionally, at 328 K and 98% relative humidity, 1 and 2 exhibit proton conductivity values of 2.13 × 10-3 and 4.91 × 10-3 S cm-1, respectively, making them suitable proton-conducting materials. Hence, the integration of luminescent sensing and proton conductivity in monophasic 3D Zn-MOFs holds significant potential for application in intelligent multitasking devices.

Luminescence of carbon quantum dots and their application in biochemistry

Similar to fullerenes, carbon nanotubes and graphene, carbon dots (CDs) are causing a lot of research work in their own right. CDs are a type of surface-passivated quantum dot that contain carbon atoms. Their distinctive characteristics, such as luminescent emission that varies with size and wavelength, resistance to photobleaching, easy biological binding, lack of toxicity, and economical production without the need for intricate synthetic processes, have led to a noteworthy surge in attention within the research community. Different techniques can be utilized to create these CDs, spanning from basic candle burning to laser ablation. This review article delves into the principles of fluorescence technology, providing insights into how different synthesis methods of quantum dots impact their luminescent properties. Additionally, it highlights the latest applications of quantum dots in catalysis and biomedical fields, with special emphasis on the current status of luminescent properties in biology and chemistry. Towards the end, the article discusses the limitations of quantum dots in current practical applications, pointing out that CDs hold promising potential for future applications.

Ratiometric Fluorescent Detection of Ultrasound-Regulated ATP Release: An Ultrasound-Resistant Cu,N-Doped Carbon Nanosphere

Focused ultrasound, as a protocol of cancer therapy, might induce extracellular adenosine triphosphate (ATP) release, which could enhance cancer immunotherapy and be monitored as a therapeutic marker. To achieve an ATP-detecting probe resistant to ultrasound irradiation, we constructed a Cu/N-doped carbon nanosphere (CNS), which has two fluorescence (FL) emissions at 438 and 578 nm to detect ultrasound-regulated ATP release. The addition of ATP to Cu/N-doped CNS was conducted to recover the FL intensity at 438 nm, where ATP enhanced the FL intensity probably via intramolecular charge transfer (ICT) primarily and hydrogen-bond-induced emission (HBIE) secondarily. The ratiometric probe was sensitive to detect micro ATP (0.2-0.6 μM) with the limit of detection (LOD) of 0.068 μM. The detection of ultrasound-regulated ATP release by Cu,N-CNS/RhB showed that ATP release was enhanced by the long-pulsed ultrasound irradiation at 1.1 MHz (+37%, p < 0.01) and reduced by the short-pulsed ultrasound irradiation at 5 MHz (-78%, p < 0.001). Moreover, no significant difference in ATP release was detected between the control group and the dual-frequency ultrasound irradiation group (+4%). It is consistent with the results of ATP detection by the ATP-kit. Besides, all-ATP detection was developed to prove that the CNS had ultrasound-resistant properties, which means it could bear the irradiation of focused ultrasound in different patterns and detect all-ATP in real time. In the study, the ultrasound-resistant probe has the advantages of simple preparation, high specificity, low limit of detection, good biocompatibility, and cell imaging ability. It has great potential to act as a multifunctional ultrasound theranostic agent for simultaneous ultrasound therapy, ATP detection, and monitoring.

Red-emissive carbon nanostructure-anchored molecularly imprinted Er-BTC MOF: a biosensor for visual anthrax monitoring

Investigating effective fluorescence strategies for real-time monitoring of dipicolinic acid (DPA) is of paramount importance in safeguarding human health. Herein, we present the design of a desirable red-emissive carbon nanostructure anchoring a molecularly imprinted Er-BTC MOF as a fluorescence biosensor for the visual determination of DPA. DPA is a biomarker of Bacillus anthracis, a subcategory of serious infectious diseases and bioweapons. We introduce a paper test strip sensitized with the aforementioned nanostructure, which is integrated with online UV excitation and smartphone digital imaging, resulting in a DPA signal-off sensing platform. The proposed fluorometric visual paper-based biosensor demonstrates wide linear ranges for DPA (10-125 μM) with a LOQ and LOD of 4.32 and 1.28 μM, respectively. The designed platform exhibits impressive emission properties and adaptable surface functional groups, which confirm its desirable selective sensing capabilities against other biological molecules and DPA isomers. As a proof of concept, DPA monitoring is successfully applied to real samples of tap water and urine. This integrated selective paper-based nano-biosensor, coupled with smartphone signal recording, holds great promise for state-of-the-art practical applications including fluorometric/colorimetric detection in healthcare and environmental monitoring, food safety analysis, and point-of-care testing.

Comparative Evaluation of Bioefficiency and Photocatalytic Activity of Green Synthesized Bismuth Oxide Nanoparticles Using Three Different Leaf Extracts

Nanotechnology has emerged as a promising method for wastewater recycling. In this line, the current study emphasizes the leaf-extract-mediated biosynthesis of bismuth oxide nanostructures (BiONPs) using three different plants, namely Coldenia procumbens Linn (Creeping Coldenia), Citrus limon (Lemon), and Murraya koenigii (Curry) through a greener approach and evaluates their biological properties as well as photocatalytic performance for the first time. As-synthesized BiONPs were physiochemically characterized using UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) with energy dispersive X-ray analysis (EDAX). Using the well diffusion method, research on the antibacterial efficiency of BiONPs against human pathogenic Gram-positive bacteria, such as Staphylococcus aureus and Enterococcus faecalis, and Gram-negative bacteria, including Escherichia coli and Klebsiella pneumonia, revealed that Gram-negative bacteria exhibited relatively strong activity. The larvicidal activity assessed against Aedes aegypti and Aedes albopictus mosquito larvae reveals promising larvicidal activity with a minimal dosage of BiONPs with LC₅₀ values of 5.53 and 19.24 ppm, respectively, after 24 h of exposure. The excellent photocatalytic activity of as-synthesized BiONPs was demonstrated through the photodegradation of malachite green (MG) and methylene blue (MB) dyes with respective degradation performance parameters of 70 and 90%. The biogenic synthetic approach reported here enables the scalable commercial synthesis of bismuth nanostructures for their widespread use in catalysis for wastewater treatment and environmental cleanup.

Adsorption properties of metal functionalized fullerene (C59Au, C59Hf, C59Ag, and C59Ir) nanoclusters for application as a biosensor for hydroxyurea (HXU): insight from theoretical computation

This theoretical study was conducted to evaluate the efficiency of fullerene C60 and its metal functionalized nano clusters (C59Au, C59Hf, C59Ag and C59Ir) as a sensor for hydroxyurea (HXU). The various conclusions concerning the adsorption and sensing properties of the studied nano surfaces were achieved using density functional theory (DFT) at the M062X-D3/gen/LanL2DZ/def2svp level of theory. Among the nano clusters studied for this interaction, analysis of the HOMO–LUMO energy differences (E g) showed that HXU@C59Hg (H2) reflects the least energy gap of 3.042 eV, indicating its greater reactivity, sensitivity and conductivity. Also, the adsorption phenomenon in this current study is best described as chemisorptions owing to the negative adsorption enthalpies observed. Thus, the adsorption energy (E Ad) follows an increasing pattern of: HXU@C60 (C1) (−0.218 eV) < HXU@C59Ir (I1) (−1.361 eV) < HXU@C59Au (A1) (−1.986 eV) < HXU@C59Hf (H1) (−2.640 eV) < HXU@C59Hg (H2) (−3.347 eV). Least E g, highest E Ad and non-covalent nature of interaction attributed to C59Hg surface are sufficient to show that, among all studied surfaces, C59Hg surface emerged as the most suitable adsorbent for the adsorption of HXU. Hence, it can be used in modeling future adsorbent material for hydroxyurea.

Sensitive, Selective and Reliable Detection of Fe3+ in Lake Water via Carbon Dots-Based Fluorescence Assay

In this study, C-dots were facilely synthesized via microwave irradiation using citric acid and ethylenediamine as carbon precursors. The fluorescence emissions of the C-dots could be selectively quenched by Fe³⁺, and the degree of quenching was linearly related to the concentrations of Fe³⁺ presented. This phenomenon was utilized to develop a sensitive fluorescence assay for Fe³⁺ detection with broad linear range (0–250, 250–1200 μmol/L) and low detection limit (1.68 μmol/L). Most importantly, the assay demonstrated high reliability towards samples in deionized water, tap water and lake water, which should find potential applications for Fe³⁺ monitoring in complicated environments.