Carbon dot-assisted luminescence of singlet oxygen: the generation dynamics but not the cumulative amount of singlet oxygen is responsible for the photodynamic therapy efficacy

A graphitic C3N4 nanocomposite-based fluorescence platform for label-free analysis of trace mercury ions

In this study, a nanocomposite consisting of graphitic carbon nitride nanosheets loaded with graphitic carbon nitride quantum dots (CNQDs/CNNNs) was synthesized via a one-step pyrolysis method. This nanocomposite exhibited excellent thermal stability, photobleaching and salt resistance. Then a new fluorescence sensing platform based on CNQDs/CNNNs was constructed, which showed high sensitivity and selectivity towards trace mercury ions (Hg2+). By using X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectra and density functional theory, the fluorescence response mechanism was elucidated where Hg2+ could interact with CNQDs/CNNNs, causing a structural change in the nanocomposite, further affecting its bandgap structure, and finally leading to fluorescence quenching. The linear range for detecting Hg2+ was found to be 0.025-4.0 μmol L-1, with a detection limit of 7.82 nmol L-1. This strategy provided the advantages of a rapid response and a broad detection range, making it suitable for quantitative detection of Hg2+ in environmental water.

Highly efficient electrochemical detection of H2O2 utilizing an innovative copper porphyrinic nanosheet decorated bismuth metal-organic framework modified electrode

The ability to detect hydrogen peroxide is important due to the presence in biological systems. Researchers are highly interested in developing efficient electrochemical hydrogen peroxide sensors. Metal-organic frameworks (MOFs) with their composites, an emerging class of porous materials, are ideal candidates for heterogeneous catalysts because of their versatile functionalities. Using a facile solvothermal reaction, we fabricated a 2D Cu-TCPP nanosheet uniformly grown on a 3D Bi-MOF. The process takes advantage of the large surface area and pore volume of the Bi-MOF while maintaining the crystallinity of Bi-BTC when Cu-TCPP is added to the surface. The sensor was fabricated by depositing the Bi-BTC-Cu-TCPP nanocomposites on a glassy carbon electrode to conduct electrochemical measurements such as cyclic voltammetry and electrochemical impedance spectroscopy. Finally, differential pulse voltammetry was utilized to investigate the effect of hydrogen peroxide on the electrochemical activity of Bi-BTC-Cu-TCPP deposited on a glassy carbon electrode. This electrode showed high electrochemical performance activity for the reduction of hydrogen peroxide. The sensor showed a linear response to H2O2 in the 10-120 μM concentration range, with a detection limit of 0.20 μM. The sensor was also stable and selective for H2O2 in the presence of other interfering species. This work demonstrates the potential of nanocomposite-based electrochemical sensors for sensitive and selective detection of H2O2. Besides, the modified electrode has many advantages, including remarkable catalytic activity, long-term stability, good reproducibility, and a good signal response during H2O2 reduction.

Europium-Functionalized Graphitic Carbon Nitride for Efficient Chemiluminescence Detection of Singlet Oxygen

Enhancing the sensitivity and selectivity of chemiluminescence (CL) sensors for detecting chemical species in complex samples poses a significant challenge in nanoparticle surface engineering. Graphitic carbon nitride (CN) shows promise but suffers from weak CL intensity and unknown luminescence mechanisms. In this study, we propose a nitrogen defect strategy to enhance the CL efficiency of europium-functionalized graphitic carbon nitride (Eu-CNNPs). By controlling the dosage of the europium modification, we can adjust the nitrogen defect content to reduce the energy gap and improve the CL performance. Remarkably, Eu-CNNPs with rich nitrogen defects exhibit strong chemiluminescence emission specifically for singlet oxygen (1O2) without responding to other reactive oxygen species (ROS). Building upon this finding, we developed a direct, selective, and sensitive CL sensing platform for 1O2 in PM2.5 and monitored 1O2 production in photosensitizers without interference from metal ions. Through extensive experiments, we attribute the 1O2-driven CL response to the presence of abundant nitrogen defects in the CN material, accelerating electron transfer and yielding a high generation of 1O2. Furthermore, chemiluminescence resonance energy transfer (CRET) between (1O2)2* (1O2 dimeric aggregate) and Eu-CNNPs contributes to strong CL emission. This work provides insights into enhancing the CL performance of CN and offers new possibilities for advancing the practical analysis of nanomaterials using the intriguing mechanism of nitrogen defects.

Facile Synthesis of Oxidized Boron Nanosheets for Chemo- and Biosensing

As recently emerging nanomaterials, boron nanosheets (BNSs) have attracted more and more attention in various fields such as supercapacitors, photodetectors, bioimaging, and electrocatalysis due to their advantages of good biological compatibility, environmental friendliness, and good electro-optical properties. However, the study and application of BNSs in chemical and biological sensing are still in the infant stage, mainly due to the requirement of complicated, high-cost, and time-consuming preparation strategies. In this work, a new class of BNSs, namely oxidized-BNSs (i.e., ox-BNSs), were easily and rapidly synthesized by chemically treating boron powder with diluted HNO₃ in a very short time (less than 15 min). The composition, morphology, optical property, and peroxidase mimetic activity of obtained ox-BNSs were investigated in detail. The prepared ox-BNSs were several-layered nanosheets with abundant oxygen-containing groups, emitted blue fluorescence, and possessed good intrinsic peroxidase mimetic activity, based on which a sensitive and selective colorimetric sensor was developed for detection of H₂O₂ and glucose. The new easy preparation strategy and good sensing performances of the prepared ox-BNSs would greatly stimulate the study and application of BNSs in chemo- and biosensing.

An enhanced chemiluminescence hybrids of luminol by sulfonated polyaniline decorated copper-based metal organic frame composite applicable to the measurement of hydrogen peroxide in a wide pH range

Here, sulfonated polyaniline (SPAN) was decorated on the surface of copper-based metal organic frame (HKUST-1) and the composite was functionalized by luminol to construct a chemiluminescence (CL) hybrids (SPAN/HKUST-1@Luminol). The as-prepared SPAN/HKUST-1@Luminol demonstrated a great dispersion and stability performance in aqueous solution. Moreover, the resultant SPAN/HKUST-1@Luminol hybrids exhibited extremely strong CL properties, and the CL quantum yield was 136 times higher than that of luminol. In particular, it exhibited outstanding CL activity not only under alkaline conditions, but also under neutral conditions. The sensitive response of the hybrid to hydrogen peroxide was used to construct CL methods for the detection of hydrogen peroxide at a wide range of pH, with the detection limit of 60 nM at a neutral condition and 25 pM at alkaline condition. Due to strong and stable signal of the SPAN/HKUST-1@Luminol, the CL method provides a viable tool for determination of H₂O₂ in biological systems and enabled the monitoring of stimulated production of H₂O₂ released by living cells.

Preparation of Functional Nanoparticles-Loaded Magnetic Carbon Nanohorn Nanocomposites towards Composite Treatment

Combination therapy for cancer is expected for the synergetic effect of different treatments, and the development of promising carrier materials is demanded for new therapeutics. In this study, nanocomposites including functional nanoparticles (NPs) such as samarium oxide NP for radiotherapy and gadolinium oxide NP as a magnetic resonance imaging agent were synthesized and chemically combined with iron oxide NP-embedded or carbon dot-coating iron oxide NP-embedded carbon nanohorn carriers, where iron oxide NP is a hyperthermia reagent and carbon dot exerts effects on photodynamic/photothermal treatments. These nanocomposites exerted potential for delivery of anticancer drugs (doxorubicin, gemcitabine, and camptothecin) even after being coated with poly(ethylene glycol). The co-delivery of these anticancer drugs played better drug-release efficacy than the independent drug delivery, and the thermal and photothermal procedures enlarged the drug release. Thus, the prepared nanocomposites can be expected as materials to develop advanced medication for combination treatment.

Dithiothreitol-Lucigenin Chemiluminescent System for Ultrasensitive Dithiothreitol and Superoxide Dismutase Detection

1,4-Dithiothreitol (DTT), a highly water-soluble and well-known reducing agent for preservation and regeneration of sulfhydryl groups in biomedical applications, has been developed as an efficient and stable coreactant of lucigenin for the first time. DTT efficiently reacts with lucigenin to generate intense chemiluminescence (CL), eliminating the need for external catalysts to facilitate the lucigenin CL. The DTT-lucigenin CL is approximately 15-fold more intense when compared with the lucigenin-H₂O₂ classical system. Superoxide dismutase (SOD) remarkably quenches the DTT-lucigenin CL. Based on this phenomenon, a newly developed CL approach for the determination of SOD was proposed with a linear range of 0.01-1.5 μg/mL and a limit of detection of 2.2 ng/mL. Various factors affecting the CL emission of the DTT-lucigenin probe were studied and optimized. Plausible mechanistic pathways for the CL coreaction of lucigenin with DTT were proposed and fully discussed. Our proposed method not only has the merit of being selective toward the target analytes but also eliminates the need for the complex synthesis of luminescent probes and facilitates the sensitive detection of SOD in human serum and cosmetics SOD raw material with satisfactory recoveries.

Carbon dot based nucleus targeted fluorescence imaging and detection of nuclear hydrogen peroxide in living cells

Investigation of the intracellular generation of H₂O₂, one of the most important reactive oxygen species (ROS), is crucial for preventing various diseases since it is closely linked with different physiological and complex cell signaling pathways. Despite the development of various fluorescent probes, the majority of the fluorescent probes cannot move across the nuclear membrane. However, detection of the nuclear level of H₂O₂ is very important since it can directly cause oxidative DNA damage which ultimately leads to various diseases. Therefore, in this study, p-phenylenediamine based carbon quantum dots (B-PPD CDs) have been synthesized and integrated with 4-formylbenzeneboronic acid as a doping agent for the detection of H₂O₂. The detection mechanism showed that, upon exposure to H₂O₂, the fluorescence of the B-PPD CDs was immediately quenched. Further investigation has been done in the in vitro RAW 264.7 cell line by both exogenous and endogenous exposure of H₂O₂ to demonstrate the feasibility of the method. It is shown successfully that the exogenous presence and endogenous generation of H₂O₂ in RAW 264.7 cells can be detected using B-PPD CDs. The limit of detection (LOD) was determined to be 0.242 μM. The development of such imaging probes using carbon quantum dots will lead to live-cell imaging as well as ROS detection.

Film Nanoarchitectonics of Pillar[5]arene for High-Performance Fluorescent Sensing: a Proof-of-Concept Study

Substrates play crucial roles for the sensing performances of fluorescent films owing to their effect on the formation of a fluorescent adlayer. However, no such film has been developed through synthesizing a substrate with a defined structure. We herein report a kind of self-standing, uniform, and thickness tunable pillar[5]arene-based nanofilms to serve as substrates for fabricating fluorescent sensing films. In comparison with a glass plate, the pillar[5]arene-based nanofilms can ensure spatial and electronic isolation of immobilized fluorophores and circumvent aggregation-caused quenching in a film state. For conceptual proof, a formic acid fluorescent sensing film was developed through simple loading of a fluorophore, a 4-azetidine-1,8-naphthalimide derivative of cholesterol (NA-Ch), onto the prepared nanofilm. Sensing performance studies demonstrated that the fluorescent film showed a sensitive, fast, and highly selective response to formic acid in air with a detection limit of lower than 2.8 mg m^-3 and a response time of less than 3 s. Moreover, the sensing is fully reversible and highly repeatable. Further studies showed that the film sensor can be used for fast determination of methanol acidity via vapor sampling. Clearly, innovation of substrates with defined structures can be taken as an effective and efficient way to develop new sensing films via combination with known fluorophores.

Nano-photosensitizers for enhanced photodynamic therapy

Photodynamic therapy (PDT) utilizes photosensitizers (PSs) together with irradiation light of specific wavelength interacting with oxygen to generate cytotoxic reactive oxygen species (ROS), which could trigger apoptosis and/or necrosis-induced cell death in target tissues. During the past two decades, multifunctional nano-PSs employing nanotechnology and nanomedicine developed, which present not only photosensitizing properties but additionally accurate drug release abilities, efficient response to optical stimuli and hypoxia resistance. Further, nano-PSs have been developed to enhance PDT efficacy by improving the ROS yield. In addition, nano-PSs with additive or synergistic therapies are significant for both currently preclinical study and future clinical practice, given their capability of considerable higher therapeutic efficacy under safer systemic drug dosage. In this review, nano-PSs that allow precise drug delivery for efficient absorption by target cells are introduced. Nano-PSs boosting sensitivity and conversion efficiency to PDT-activating stimuli are highlighted. Nano-PSs developed to address the challenging hypoxia conditions during PDT of deep-sited tumors are summarized. Specifically, PSs capable of synergistic therapy and the emerging novel types with higher ROS yield that further enhance PDT efficacy are presented. Finally, future demands for ideal nano-PSs, emphasizing clinical translation and application are discussed.

Photomodulating Carbon Dots for Spatiotemporal Suppression of Alzheimer's β-Amyloid Aggregation

Extracellular deposition of β-amyloid (Aβ) peptide aggregates is a major characteristic of Alzheimer's disease (AD) brain. Because Aβ peptide aggregates aggravate neuropathy and cognitive impairment for AD patients, numerous efforts have been devoted to suppressing Aβ self-assembly as a prospective AD treatment option. Here, we report Aβ-targeting, red-light-responsive carbon dots (CDs), and their therapeutic functions as a light-powered nanomodulator to spatiotemporally suppress toxic Aβ aggregation both in vitro and in vivo. Our aptamer-functionalized carbon dots (Apta@CDs) showed strong targeting ability toward Aβ₄₂ species. Moreover, red LED irradiation induced Apta@CDs to irreversibly denature Aβ peptides, impeding the formation of β-sheet-rich Aβ aggregates and attenuating Aβ-associated cytotoxicity. Consequently, Apta@CDs-mediated photomodualtion modality achieved effective suppression of Aβ aggregation in vivo, which significantly reduced the Aβ burden at the targeted sites in the brain of 5xFAD mice by ∼40% and ∼25% according to imaging and ELISA analyses, respectively. Our work demonstrates the therapeutic potential of photomodulating CDs for light-driven suppression against Aβ self-assembly and related neurotoxicity.