Fluorescent TPA@GQDs Probe for Sensitive Assay and Quantitative Imaging of Hydroxyl Radicals in Living Cells

A responsive nanoprobe for ratiometric florescence detection of hydroxyl radicals in macrophage polarization

Quantification of hydroxyl radicals (˙OH), one form of reactive oxygen species (ROS), plays critical roles in early diagnosis and treatment monitoring of various diseases. In this work, we report the development of a responsive nanoprobe for ratiometric fluorescence detection and imaging of ˙OH in macrophage polarization. The nanoprobe, BSA-CCA@LDH-SRB, was designed and prepared using coumarin 3-carboxylic acid (CCA) as the sensing unit for ˙OH, and sulforhodamine B (SRB) loaded on layered double hydroxide (LDH) served as the fluorescent reference component. The coupling of CCA to bovine serum albumin (BSA) and the loading of BSA-CCA on the surface of LDH enabled the nanoprobe for fluorescence detection of ˙OH with high sensitivity and minimal interference from other biomolecules, ions, and ROS. The emission of the prepared BSA-CCA@LDH-SRB at 444 nm emerged and the intensity was increased according to the concentration of ˙OH, while the emission at 580 nm was maintained, allowing the nanoprobe for ratiometric fluorescence (F444/580) detection of ˙OH. Loading of the BSA protein on the LDH surface and the biocompatibility and colloidal stability of the LDH-based fluorescent nanoprobe were further improved, facilitating the detection of ˙OH generation in macrophage polarization stimulated by both biomolecules and physical ultrasound irradiation. This study thus offers a new nanoprobe as the tool for investigating ˙OH evolutions, advancing the biomedical investigations of macrophage polarization associated inflammation.

Ultrathin Ba0.75Sr0.25TiO3 nanosheets with highly exposed {001} polar facets for high-performance piezocatalytic application

The development of piezoelectrics with high catalytic activity to address environmental pollution and energy shortage has long been pursued. In this work, for the first time, a "three-birds-with-one-stone" strategy is proposed to design high-activity piezocatalysts. Interestingly, we achieved ultrathin, highly exposed polar facets and ferroelectric-paraelectric phase transitions in Ba1-xSrxTiO3 nanosheets simultaneously. As expected, Ba0.75Sr0.25TiO3 shows superior piezocatalytic performance for organic pollutant degradation due to its excellent flexibility, highly exposed polar area, and short carrier migration distance. Then, the piezoelectric potential distribution and electron transport ability on the interface of Ba0.75Sr0.25TiO3 were investigated through finite element method (FEM) simulation and density-functional theory (DFT) calculations, which provided a deep insight into the enhanced mechanism. This work thus presents a novel strategy for designing high-performance piezocatalysts and provides new insights for the optimization of the piezocatalytic activity by combining multiple advantages.

Recent Advances in Detection of Hydroxyl Radical by Responsive Fluorescence Nanoprobes

Hydroxyl radical (•OH), a highly reactive oxygen species (ROS), is assumed as one of the most aggressive free radicals. This radical has a detrimental impact on cells as it can react with different biological substrates leading to pathophysiological disorders, including inflammation, mitochondrion dysfunction, and cancer. Quantification of this free radical in-situ plays critical roles in early diagnosis and treatment monitoring of various disorders, like macrophage polarization and tumor cell development. Luminescence analysis using responsive probes has been an emerging and reliable technique for in-situ detection of various cellular ROS, and some recently developed •OH responsive nanoprobes have confirmed the association with cancer development. This paper aims to summarize the recent advances in the characterization of •OH in living organisms using responsive nanoprobes, covering the production, the sources of •OH, and biological function, especially in the development of related diseases followed by the discussion of luminescence nanoprobes for •OH detection.

Piezoelectric catalytic driven advanced oxidation process using two-dimensional metal dichalcogenides for wastewater pollutants remediation

The public and society have increasingly recognized numerous grave environmental issues, including water pollution, attributed to the rapid expansion of industrialization and agriculture. Renewable energy-driven catalytic advanced oxidation processes (AOPs) represent a green, sustainable, and environmentally friendly approach to meet the demands of environmental remediation. In this context, 2D transition metal dichalcogenides (TMDCs) piezoelectric materials, with their non-centrosymmetric crystal structure, exhibit unique features. They create dipole polarization, inducing a built-in electric field that generates polarized holes and electrons and triggers redox reactions, thereby facilitating the generation of reactive oxygen species for wastewater pollutant remediation. A broad spectrum of 2D TMDCs piezoelectric materials have been explored in self-integrated Fenton-like processes and persulfate activation processes. These materials offer a more simplistic and practical method than traditional approaches. Consequently, this review highlights recent advancements in 2D TMDCs piezoelectric catalysts and their roles in wastewater pollutant remediation through piezocatalytic-driven AOPs, such as Fenton-like processes and sulfate radicals-based oxidation processes.

Enhanced oxidation of organic pollutants by regulating the interior reaction region of reactive electrochemical membranes

Reactive electrochemical membrane (REM) emerges as an attractive strategy for the elimination of refractory organic pollutants that exist in wastewater. However, the limited reaction sites in traditional REMs greatly hinder its practical application. Herein, a feed-through coating methodology was developed to realize the uniform loading of SnO2-Sb catalysts on the interior surface of a REM. The uniformly coated REM (Unif-REM) exhibited 2.4 times higher reaction kinetics (0.29 min-1) than that of surface coated REM (Surf-REM) for the degradation of 2 mM 4-chlorophenol (4-CP), rendering an energy consumption as low as 0.016 kWh gTOC-1. The fast degradation of various emerging contaminants, e.g., sulfamethoxazole (SMX), ofloxacin (OFLX), and tetracycline (TC), also confirms its superior oxidation capability. Besides, the Unif-REM exhibited good performance in generating hydroxyl radicals (•OH) and a relatively long service lifetime. The simulation of spatial current distribution demonstrates that the interior reaction region in the Unif-REM channels can be drastically extended, thereby maximizing the surface coupling of mass diffusion and electron transfer. This study offers an in-depth look at the spatially confined reactions in REM and provides a reference for the design of electrochemical systems with economically efficient water purification.

In vivo assembly enhanced binding effect augments tumor specific ferroptosis therapy

Emerging evidence indicates that the activation of ferroptosis by glutathione peroxidase 4 (GPX4) inhibitors may be a prominent therapeutic strategy for tumor suppression. However, the wide application of GPX4 inhibitors in tumor therapy is hampered due to poor tumor delivery efficacy and the nonspecific activation of ferroptosis. Taking advantage of in vivo self-assembly, we develop a peptide-ferriporphyrin conjugate with tumor microenvironment specific activation to improve tumor penetration, endocytosis and GPX4 inhibition, ultimately enhancing its anticancer activity via ferroptosis. Briefly, a GPX4 inhibitory peptide is conjugated with an assembled peptide linker decorated with a pH-sensitive moiety and ferriporphyrin to produce the peptide-ferriporphyrin conjugate (Gi-F-CAA). Under the acidic microenvironment of the tumor, the Gi-F-CAA self-assembles into large nanoparticles (Gi-F) due to enhanced hydrophobic interaction after hydrolysis of CAA, improving tumor endocytosis efficiency. Importantly, Gi-F exhibits substantial inhibition of GPX4 activity by assembly enhanced binding (AEB) effect, augmenting the oxidative stress of ferriporphyrin-based Fenton reaction, ultimately enabling antitumor properties in multiple tumor models. Our findings suggest that this peptide-ferriporphyrin conjugate design with AEB effect can improve the therapeutic effect via induction of ferroptosis, providing an alternative strategy for overcoming chemoresistance.

Optimization of the tandem enzyme activity of V-MOF and its derivatives for highly sensitive nonenzymatic detection of cholesterol in living cells

It remains a great challenge to properly design and synthesize single-component artificial tandem enzymes for specific substrates with high selectivity. Herein, V-MOF is synthesized by solvothermal method and its derivatives are constructed via pyrolyzing V-MOF in nitrogen atmosphere at different temperatures, which are denoted as V-MOF-y (y = 300, 400, 500, 700 and 800). V-MOF and V-MOF-y possess tandem enzyme-like activity, i.e. cholesterol oxidase-like and peroxidase-like activity. Among them, V-MOF-700 shows the strongest tandem enzyme activity for V-N bonds. Based on the cascade enzyme activity of V-MOF-700, the nonenzymatic detection platform for cholesterol by fluorescent assay can be established in the presence of o-phenylenediamine (OPD) for the first time. The detection mechanism is that V-MOF-700 catalyzes cholesterol to generate hydrogen peroxide and further form hydroxyl radical (•OH), which can oxidize OPD to obtain oxidized OPD (oxOPD) with yellow fluorescence. The linear detection of cholesterol ranges of 2-70 μM and 70-160 μM with a lower detection limit of 0.38 μM (S/N = 3) are obtained. This method is used to detect cholesterol in human serum successfully. Especially, it can be applied to the rough quantification of membrane cholesterol in living tumor cells, indicating that it has the potential for clinical application.

Reactive oxygen species in biological media are they friend or foe? Major In vivo and In vitro sensing challenges

The role of Reactive Oxygen Species (ROS) on biological media has been shifting over the years, as the knowledge on the complex mechanism that lies in underneath their production and overall results has been growing. It has been known for some time that these species are associated with a number of health conditions. However, they also participate in the immunoactivation cascade process, and can have an active role in theranostics. Macrophages, for example, react to the presence of pathogens through ROS production, potentially allowing the development of new therapeutic strategies. However, their short lifetime and limited spatial distribution of ROS have been limiting factors to the development and understanding of this phenomenon. Even though, ROS have shown successful theranostic applications, e.g., photodynamic therapy, their wide applicability has been hampered by the lack of effective tools for monitoring these processes in real time. Thus the development of innovative sensing strategies for in vivo monitoring of the balance between ROS concentration and the resultant immune response is of the utmost relevance. Such knowledge could lead to major breakthroughs towards the development of more effective treatments for neurodegenerative diseases. Within this review we will present the current understanding on the interaction mechanisms of ROS with biological systems and their overall effect. Additionally, the most promising sensing tools developed so far, for both in vivo and in vitro tracking will be presented along with their main limitations and advantages. This review focuses on the four main ROS that have been studied these are: singlet oxygen species, hydrogen peroxide, hydroxyl radical and superoxide anion.

Flammulina velutipes-derived carbon dots for fluorescence detection and imaging of hydroxyl radical

Monitoring hydroxyl radical (•OH) fluctuation is of great importance to study some relative pathological processes and to predict early diagnosis of diseases. Efficient •OH-responsive fluorescent sensors based on carbon dots (CDs) have been reported, but most researches have focused on the new strategies for the synthesis and doping of the CDs. Herein, a kind of biomass CDs (F-CDs) with Flammulina velutipes (F. velutipes) as the carbon source was prepared by a one-step hydrothermal method without any additional modification. The prepared F-CDs have remarkable sensitivity and selectivity and there is a good linear relationship from 0 to 12 μM with a low detection limit of 95 nM for quantitative •OH assay. With excitation-independent emission, favourable biocompatibility and low toxicity, the F-CDs can penetrate cell membranes as •OH-responsive fluorescent sensors to detect intracellular •OH in A549 cells stimulated by phorbol 12-myristate 13-acetate (PMA) and successfully monitor the •OH concentration levels by the corresponding fluorescence change. Given the combined benefits of the green and eco-friendly approach, the F-CDs show promise as novel theranostics tools for early detection and treatment of related diseases.

Boron-enriched rice-like homologous carbon nanoclusters with a 51.5% photoluminescent quantum yield for highly sensitive determination of endogenous hydroxyl radicals in living cells

Exploring the ultrahigh quantum efficiency of a carbon-based probe via a green and simple technique, and utilisation of its sensing ability for highly bioactive molecule detection is still highly challenging. Herein, we prepared a novel boron-enriched rice-like homologous carbon nanoclusters (BRCNs) with an ultrahigh quantum efficiency of ∼51.5% by introduction of a conjugated structure attached to the CN bond and an electron-withdrawing boron active centre. Unexpectedly, the BRCNs obtained showed a stable dispersion of rice-like carbon nanograins, composed of small carbon dot assembled nanoclusters with an average diameter size of ∼30 nm, and containing boron units of ∼24.68 at%. What's exciting is that the BRCNs obtained exhibited an "on-off-on" three-state emission with the addition of an hydroxyl radical (OH˙) and its antioxidants. Thus, two distinctive fluorescent responses for OH˙ and antioxidants based on the BRCN probe had been developed, and the mechanism has been determined using TEM, XPS, FT-IR, FL, UV-vis spectrophotometry, UPS and fluorescent lifetimes. The OH˙, generated from the Fenton's reagent, preferentially attack the electron-deficient vacancy p orbit of the boron atom in the surface of the BRCNs, which results in the boron atom being easily substituted/attacked by OH˙, and leading to spontaneous aggregation induced quenching (AIQ) due to the existence of a strong intermolecular hydrogen bond between denatured BRCNs. Furthermore, the proposed method was also successfully applied to monitor endogenous OH˙ generation in HeLa cells by confocal imaging, which could be used for elucidating OH˙-induced oxidative damage to biological tissues and proteins.

Enhanced Piezocatalytic Reactive Oxygen Species Production Activity and Recyclability of the Dual Piezoelectric Cu3B2O6/PVDF Composite Membrane

Piezocatalysts have attracted considerable attention due to their ability to convert natural mechanical energy into chemical energy. However, the inefficient chemical reactions of the free charges and the poor mechanical endurance of the powder piezoelectric materials have largely restricted their wide application. Here, by combining piezocatalyst Cu₃B₂O₆ (CBO) and polyvinylidene fluoride (PVDF), a composite membrane CBO/PVDF with superior stability and excellent piezo-performance is prepared for the first time. This composite membrane shows a high efficiency for the degradation of antibiotics and organic dyes under ultrasonication; particularly, the removal efficiency is 33.9 times higher than that of a pure PVDF membrane for amoxicillin degradation, and it maintains a high efficiency after 16 cycling tests. The polarization electric field in the dual piezoelectric composite membrane significantly enhances the redox reaction of the intrinsic free carrier with dissolved oxygen and water molecules to generate reactive oxygen species. The results provide a strategy for combining the borate with the polymer membrane to lead piezocatalysis to real future applications.

Cerium-terephthalic acid metal-organic frameworks for ratiometric fluorescence detecting and scavenging·OH from fuel combustion gas

Hydroxyl radical (•OH) in fuel combustion gas seriously damages human health. The techniques for simultaneously detecting and scavenging •OH in these gases are limited by poor thermal resistance. To meet this challenge, herein, metal organic frameworks (MOFs) with high thermal stability (80-400 °C) and dual function (•OH detection and elimination) are developed by coordinating Ce ions with terephthalic acid (TA) (Ce-BDC). Due to the reversible conversion between Ce³⁺ and Ce⁴⁺, and the high concentration of Ce³⁺ on the surface of Ce-BDC MOFs (89.6%), an •OH scavenging efficiency over 90% is realized. Ratiometric fluorescence (I_440 nm/I_355 nm) detection of •OH with a low detection limit of ∼4 μM is established by adopting Ce ions as an internal standard and TA as an •OH-responsive fluorophore. For real applications, the Ce-BDC MOFs demonstrate excellent •OH detection sensitivity and high •OH scavenging efficiency in gas produced from cigarettes, wood fiber and machine oil. Mouse model results show that the damage caused by •OH in cigarette smoke can be greatly reduced by Ce-BDC MOFs. This work provides a promising strategy for sensitively detecting and efficiently eliminating •OH in fuel combustion gas.

Integrated p-n/Schottky junctions for efficient photocatalytic hydrogen evolution upon Cu@TiO2-Cu2O ternary hybrids with steering charge transfer

Solar-driven photocatalytic H₂ evolution could tackle the issue of fossil fuels-triggered greenhouse gas emission with sustainable clean energy. However, splitting water into hydrogen with high performance by a single semiconductor is challenging because of the poor charge separation efficiency. Herein, a novel ternary Cu@TiO₂-Cu₂O hybrid photocatalyst with multiple charge transfer channels has been designed for efficient solar-to-hydrogen evolution. Indeed, the ternary Cu@TiO₂-Cu₂O hybrid by coupling Cu@TiO₂ with Cu₂O nanoparticles shows highly-efficient photocatalytic hydrogen generation with rate of 12000.6 μmol·g^-1·h^-1, which is 4.4, 2.1, and 1.9 times higher than the pure TiO₂ (2728.8 μmol·g^-1·h^-1), binary Cu@TiO₂ (5595.5 μmol·g^-1·h^-1), and TiO₂-Cu₂O (6076.8 μmol·g^-1·h^-1) composite, respectively. In such a Cu@TiO₂-Cu₂O hybrid, the formed internal electric field in the TiO₂-Cu₂O p-n junction allows the electrons in Cu₂O to migrate to TiO₂, while the electrons in the CB of TiO₂ could flow into Cu via the Schottky junction at the Cu@TiO₂ interface. In this regard, a multiple charge transfer is achieved between the Cu@TiO₂ and Cu₂O, which facilitates promoted charge separation and results in the construction of electron-accumulated center (Cu) and hole-enriched surface (Cu₂O). This p-n/Schottky junctions with steered charge transfer assists the hydrogen production upon the Cu@TiO₂-Cu₂O ternary photocatalyst.

Structure-property investigations in urea tethered iodinated triphenylamines

Herein, we report structural, computational, and conductivity studies on urea-directed self-assembled iodinated triphenylamine (TPA) derivatives. Despite numerous reports of conductive TPAs, the challenges of correlating their solid-state assembly with charge transport properties hinder the efficient design of new materials. In this work, we compare the assembled structures of a methylene urea bridged dimer of di-iodo TPA (1) and the corresponding methylene urea di-iodo TPA monomer (2) with a di-iodo mono aldehyde (3) control. These modifications lead to needle shaped crystals for 1 and 2 that are organized by urea hydrogen bonding, π⋯π stacking, I⋯I, and I⋯π interactions as determined by SC-XRD, Hirshfeld surface analysis, and X-ray photoelectron spectroscopy (XPS). The long needle shaped crystals were robust enough to measure the conductivity by two contact probe methods with 2 exhibiting higher conductivity values (∼6 × 10^-7 S cm^-1) compared to 1 (1.6 × 10^-8 S cm^-1). Upon UV-irradiation, 1 formed low quantities of persistent radicals with the simple methylurea 2 displaying less radical formation. The electronic properties of 1 were further investigated using valence band XPS, which revealed a significant shift in the valence band upon UV irradiation (0.5-1.9 eV), indicating the potential of these materials as dopant free p-type hole transporters. The electronic structure calculations suggest that the close packing of TPA promotes their electronic coupling and allows effective charge carrier transport. Our results show that ionic additives significantly improve the conductivity up to ∼2.0 × 10^-6 S cm^-1 in thin films, enabling their implementation in functional devices such as perovskite or solid-state dye sensitized solar cells.

Ratiometric fluorescence nanoprobe based on carbon dots and terephthalic acid for determining Fe2+ in environmental samples

A ratiometric fluorescent nanoprobe using carbon dots (CDs) and involving oxidation of terephthalic acid (TPA) induced by hydroxyl radicals (·OH) was developed for sensitively and selectively determining Fe²⁺ ions. When Fe²⁺ ions are added to the TPA@CDs/H₂O₂ system, ·OH produced through the Fenton reaction oxidizes the non-fluorescent TPA to give 2-hydroxyl terephthalic acid, which fluoresces at 423 nm when excited at 286 nm. The ·OH and Fe³⁺ produced quench CD fluorescence at 326 nm. The 2-hydroxyl terephthalic acid to CD fluorescence intensity ratio linearly increased as the Fe²⁺ concentration increased in the range 0.5-50 μM, and the detection limit was 0.25 μM. The new assay is very selective because it involves dual-emission reverse change ratio fluorescence sensing, which can exclude matrix effects. The new nanoprobe was used to determine Fe²⁺ concentrations in real water samples, and the recoveries were found to be acceptable. Schematic of the ratiometric fluorometric method for determining Fe²⁺ based on CDs and TPA.

A nanozyme-based colorimetric sensor array as electronic tongue for thiols discrimination and disease identification

Thiol analysis is of vital significance due to the essential roles in disease diagnosis, while the highly similar structures of thiols are a major challenge in practical determination. Herein, a nanozyme-based colorimetric sensor array has been proposed as electronic tongue for excellent discrimination and sensitive quantitation of thiols. The sensing units are fabricated by integrating the terephthalic acid modified graphene quantum dots (TPA@GQDs) with three transition metal ions (Fe²⁺, Cu²⁺ and Zn²⁺) via coordination, respectively, which not only provide sufficient substrate binding sites but also form the metal ion-regulated catalytic active centers. In this way, disparate promotion degrees on the peroxidase-like catalytic activity have been achieved in different metal ion-TPA@GQD ensembles. Based on the strong binding affinity between metal ions and thiols, the catalytic active centers are removed from TPA@GQDs, which inhibits the catalytic activity of sensing unit to diverse degrees. Accordingly, using 3, 3', 5, 5'-tetramethylbenzidine (TMB) as chromogenic substrate in the presence of hydrogen peroxide (H₂O₂), each sensing unit can generate differential colorimetric signals (fingerprints) for six thiol analytes, which can be accurately discriminated through linear discriminant analysis (LDA) with a detection limit of 50 nM. In addition, the discrimination of the same thiol with different concentrations and thiol mixtures have also been achieved. Furthermore, inspired by the distinct levels of thiols in practical samples, the proposed sensor array enables the identification of thiol-associated diseases by means of machine learning algorithm, which makes a positive contribution to medical diagnosis.

Synergistic Enhancement of Piezocatalytic Activity of BaTiO3 Convex Polyhedrons Nanocomposited with Ag NPs/Co3O4 QDs Cocatalysts

Piezocatalysis is one of the green and promising catalytic technologies for the degradation of organic pollutants. Surface modifications such as exposed facet engineering and surface decoration of nanoparticles (NPs) are simple but useful enhancement strategies for a catalytic system. However, the synergistic effect and mechanism of facet engineering and dual-cocatalyst decoration on piezocatalytic activity are still ambiguous and more investigations are expected. Herein, the piezocatalytic activities of BaTiO₃ (BTO) polyhedrons with anisotropic {001} and {110} facets and BTO cubes with isotropic {001} facets were compared. Furthermore, BaTiO₃ (BTO) convex polyhedrons with selectively deposited Ag NPs and uniformly loaded Co₃O₄ quantum dots (QDs) are rationally synthesized through photochemical deposition. The individual and synergistic effects of Ag NPs and Co₃O₄ QDs on the piezocatalytic activities are systematically studied. It was found that dual-cocatalyst-modified BTO possesses the highest piezocatalytic activity in methyl orange degradation, with a reaction constant k of 0.0539 min^-1, around 5, 2.2, and 1.3 times higher than that of nonmodified and Ag NP- and Co₃O₄ QD-modified BTO, respectively. Moreover, dual-cocatalyst-decorated BTO also exhibits excellent piezocatalytic performance in nondye pollutant degradation, with ∼100% tetracycline hydrochloride decomposed in 60 min. By analyzing the contribution, quantifying the amount of different free radicals, and comparing the chemical states of surface elements before and after piezocatalytic measurements, it was inferred that facet-dependent Ag NPs acted as efficient electron-transport sites, while uniformly loaded Co₃O₄ QDs served as hole-transfer sites to fully facilitate the migration of electrons and holes in a piezocatalytic reaction. This research presents a rational and effectual modification strategy to enhance the piezocatalytic activity of piezocatalysts and gives a thorough discussion of the enhanced mechanism.

Synthesis of metal ion-tolerant Mn-doped fluorescence silicon quantum dots with green emission and its application for selective imaging of ·OH in living cells

Monitoring hydroxyl radical (·OH) in living cells remains a big challenge on account of its high reactivity and short half-life. In this work, we designed a fluorescent probe based on manganese-doped silicon quantum dots (Mn-SiQDs) for detecting and imaging of ·OH with good water solubility. The manganese was doped in its ethylene diamine tetra-acetic acid (EDTA) complex form and effectively improved the metal ion tolerance of fluorescence of SiQDs. And m-dihydroxybenzene was used as the reductant to extend the emission of SiQDs to the green region at 515 nm when the excitation wavelength was 424 nm. Basing on the fluorescence quenching of Mn-SiQDs, a linear response of ·OH was observed in the range 0.8-50 μM with a limit of detection (LOD) of 88.4 nM, which is lower than those reported with SiQDs. The interference from other ROS or RNS has been assessed and no impact was found. In fully aqueous systems, the Mn-SiQDs have been applied to monitor and image the endogenous ·OH in HeLa cells. Our work provided a new strategy for designing SiQDs with good biocompatibility, high selectivity and long monitoring wavelength. Synthesis of green-emitting silicon quantum dots with N-[3 -(trimethoxysilyl) propyl] ethylenediamine (DAMO), Ethylenediamine tetraacetic acid disodium salt dehydrate (EDTA-2Na·2H₂O), manganese acetate tetrahydrate (Mn(CH₃COO)₂·4H₂0) and m-dihydroxybenzene. The green fluorescence of the silicon quantum dots can be selectively quenched by hydroxyl radicals.

Green synthetic nitrogen-doped graphene quantum dot fluorescent probe for the highly sensitive and selective detection of tetracycline in food samples

Tetracycline (TC) is a broad-spectrum antibiotic. When humans consume too much food containing tetracycline residues, it can be a serious health hazard. Therefore, it is essential to develop a strategy to detect TC. In this study, we prepared light blue-green luminescent nitrogen-doped graphene quantum dots (N-GQDs) by a hydrothermal method using the natural products potato straight-chain starch and urea as precursors; the fluorescence quantum yield of the prepared N-GQDs was 5.2%. We investigated the detection of tetracycline (TC) by this N-GQD fluorescent sensor based on the internal filtration effect (IFE) of TC on N-GQDs. The reaction is green, simple and no other contaminating products are present. A good linear relationship was established between the relative fluorescence intensity ratio of the system and the logarithm of the TC concentration of 2.5 × 10⁻¹⁰ to 5 × 10⁻⁶ M (R² = 0.9930), with a detection limit of 9.735 × 10⁻¹³ M. The method has been used to analyze TC in three real food samples (whole milk, skim milk, honey) with low detection limits (3.750 × 10⁻¹¹ to 2.075 × 10⁻⁹ M), wide linear range, and satisfactory recoveries of 93.80–109.20% were obtained. In conclusion, the proposed method is a green, rapid, highly sensitive and selective method for the detection of tetracycline in real food samples, demonstrating the potential application of N-GQDs in food detection.

Tetracycline (TC) is a broad-spectrum antibiotic.

One-pot alkali cutting-assisted synthesis of fluorescence tunable amino-functionalized graphene quantum dots as a multifunctional nanosensor for sensing of pH and tannic acid

Herein, a one-pot alkali cutting-assisted synthesis approach has been developed to gain fluorescence (FL) tunable amino functionalized GQDs (NH₂-GQDs), which exhibit concentration- and excitation-dependent FL behaviors, due to the self-assembled J-type aggregation effect and different electronic transitions governed by graphene basal plane and functional groups. While NH₂-GQDs possess brighter FL emission than pristine GQDs, owning to the functionalization of amino groups with strong electron withdrawing ability. Particularly, the pH-dependent FL behavior of NH₂-GQDs further reflects the FL emission mechanism originated from the intrinsic zigzag sites and introduced amino and carboxylic groups, which is available for pH sensing. Moreover, the NH₂-GQDs also show a FL quenching upon reaction with tannic acid (TA), resulting in the construction of a FL turn-off TA sensing platform. A good linear relationship is obtained between logarithm of FL intensity (log F) and TA concentration in a linear dynamic range of 1-40 μM and a limit of detection of 43.3 nM (3σ/s, n = 9) is achieved, with a precision of 0.08% RSD at a concentration level of 5 μM (n = 9). This work features a simple and direct approach to acquire multifunctional nanosensor, providing great potential for further applications in chem/biosensing.

A Water-Dispersible Carboxylated Carbon Nitride Nanoparticles-Based Electrochemical Platform for Direct Reporting of Hydroxyl Radical in Meat

In this paper, carboxylated carbon nitride nanoparticles (carboxylated-g-C₃N₄ NPs) were prepared through a one-step molten salts method. The synthesized material was characterized by transmission electron microscope (TEM), Fourier transform-infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS), etc. An electrochemical sensor based on single-stranded oligonucleotide/carboxylated-g-C₃N₄/chitosan/glassy carbon electrode (ssDNA/carboxylated-g-C₃N₄/chitosan/GCE) was constructed for determination of the hydroxyl radical (^•OH), and methylene blue (MB) was used as a signal molecule. The sensor showed a suitable electrochemical response toward ^•OH from 4.06 to 122.79 fM with a detection limit of 1.35 fM. The selectivity, reproducibility, and stability were also presented. Application of the sensor to real meat samples (i.e., pork, chicken, shrimp, and sausage) was performed, and the results indicated the proposed method could be used to detect ^•OH in practical samples. The proposed sensor holds a great promise to be applied in the fields of food safety.

A colorimetric and fluorescent dual-readout probe based on red emission carbon dots for nitrite detection in meat products

Nitrite (NO₂^-) is widely present in the human environment and accurate, sensitive and selective detecting of nitrite is of vital significance for food safety and water quality. Herein, a novel red emission carbon dots (r-CDs) fluorescent probe was fabricated for dual-mode detection of nitrite, which was capable of both convenient colorimetric analysis and accurate fluorometric detection. When NO₂^- is added to the rose-red r-CDs solution, NO₂^- interacts with the amino groups which on the surface of r-CDs to form diazotized substance, resulting in that the colorimetric color of r-CDs solution realizes the transition from rose red to light purple, and the red fluorescence is gradually quenched. The detection limits of colorimetric and fluorescence for NO₂^- were 0.193 μM and 0.149 μM, respectively. Furthermore, the dual-readout probe revealed satisfactory recovery and reliability when analyzing the concentration of NO₂^- in ham and bacon samples..

Dual-mode glucose nanosensor as an activatable theranostic platform for cancer cell recognition and cascades-enhanced synergetic therapy

Integration of disease diagnosis and therapy is crucial in precise medicine, while the "always on" mode often hinders its clinical applications. Herein, inspired by cascaded catalysis, an integrated dual-mode glucose nanosensor as an activable theranostic platform is developed, which is further exploited for cancer cell recognition and enhanced synergistic therapy of lymph cancer. This nanosensor is prepared through the in-situ growth of silver nanoparticles (AgNPs) with the synergetic reduction of tannic acid (TA) and graphene quantum dots (GQDs), which are further decorated with glucose oxidase (GOx). A cascaded catalytic reaction is triggered by glucose, in which GOx catalyzes the oxidation of glucose into gluconic acid and hydrogen peroxide (H₂O₂), and hydroxyl radical (•OH) is further produced with the catalysis of GQDs nanozyme with peroxidase-like activity, resulting in the degradation of AgNPs@GQDs-GOx with the release of Ag⁺. Accordingly, a "turn-off" colorimetric and "turn-on" fluorescence dual-mode glucose nanosensor is fabricated, which is readily applied for cancer cell recognition via fluorescence imaging based on the high glucose level in tumor microenvironment. Moreover, the degradation of AgNPs@GQDs-GOx in response to glucose facilitates the cascades-enhanced synergistic therapy of lymph cancer with the combination of starving-like therapy, metal ion therapy and TA-induce apoptosis. This study highlights a glucose-activated theranostic nanoplatform, which provides a great opportunity for cancer-related biosensing, bioimaging and biomedical applications.

Exfoliation of 2D materials by saponin in water: Aerogel adsorption / photodegradation organic dye

The biggest challenge for the paint industry is to clean the contaminated waste dye solution before it released into the water or to reuse it to create new paint and to protect the water from environmental pollution. Here in this work, exfoliating layered transition metal dichalcogenide materials prepare to the exfoliated 2D materials thin sheets in water with the assistance of natural saponin. Then, the three-dimensional (3D) MoS₂-aerogel composite was synthesized by using greenway exfoliated two-dimensional (2D) MoS₂ thin sheets to form MoS₂-aerogel composite. The prepared 3D MoS₂-aerogel composite demonstrates excellent 94% methylene blue (MB) dye adsorption ability over 5 min. Moreover, the adsorbed MB of the MoS₂-aerogel shows ∼80% dye degradation activity in the presence of visible light. Therefore, these synthesized 3D MoS₂-aerogel composite could be an excellent candidate for photocatalytic applications in the future.

Dual-emission copper nanoclusters-based ratiometric fluorescent probe for intracellular detection of hydroxyl and superoxide anion species

A fluorescent nanoprobe based on copper nanoclusters (CuNCs) has been developed for ratiometric detection of hydroxyl radicals (^•OH) and superoxide anion radicals (O₂^•-). Two differently luminescent CuNCs, namely cyan-emissive poly(methacrylic acid)-protected copper nanoclusters (PCuNCs) and orange-emissive bovine serum albumin-protected CuNCs (BCuNCs), were conjugated to obtain a hybrid, dual-emission nanoprobe (PCuNCs-BCuNCs) with the corresponding peaks at 445 nm and 652 nm at an excitation wavelength of 360 nm. In particular, the fluorescence peak at 445 nm gradually enhanced with the incremental addition of ^•OH and O₂^•-. However, the fluorescence emission at 652 nm was greatly quenched in the presence of ^•OH, while in case of O₂^•-, the fluorescence intensity remained constant. The differential response of the PCuNCs-BCuNCs towards ^•OH and O₂^•- formed the basis of ratiometric detection. Under optimal conditions, the PCuNCs-BCuNCs exhibited good sensitivity and linearity towards ^•OH and O₂^•- with limits of detection of 0.15 μM and 1.8 μM, respectively. Moreover, the nanoprobe exhibited high selectivity for ^•OH and O₂^•- over other potential ROS interferences. Besides, PCuNCs-BCuNCs were eventually applied for qualitative and quantitative ratiometric assessment of intracellular ^•OH and O₂^•- in L-132 cells. Therefore, this strategy unveils a new potential for copper nanocluster-based sensing of ROS.

Ultra-low background signaling cascade amplifiers for in vivo fluorescence imaging of hydroxyl radical production induced by testosterone

A novel ultra-low background signal cascade amplifier was developed to understand the production mechanism of ˙OH pools in situ stimulated by testosterone.

Copper-coordination induced fabrication of stimuli-responsive polymersomes from amphiphilic block copolymer containing pendant thioethers

Cu²⁺-Containing hybrid polymersomes were fabricated via a co-assembly approach. The polymersomes exhibited stimuli-responsiveness to the competitive ligand and H₂O₂/GSH and mediated a Fenton-like reaction to produce ˙OH.

Ratiometric Fluorescent Probe Based on Diazotization-Coupling Reaction for Determination of Clenbuterol

In view of the potential harm caused by illegal feeding of clenbuterol (CLB) in the livestock industry, herein, a novel ratiometric fluorescent probe based on graphene quantum dots (GQDs)@[Ru(bpy)₃]²⁺ was elaborately constructed for CLB detection. In this probe, GQDs acted as response signals, and their fluorescence was remarkably quenched by CLB through the diazotization-coupling reaction. As for [Ru(bpy)₃]²⁺ as a reference signal, its fluorescence was hardly affected. The intensity ratio of two fluorophores showed good linearity with CLB concentration in the range of 0.05-40 μM, accompanied by visualization of fluorescence variation from yellow to red. The detection limit was as low as 0.029 μM. Particularly, the probe was successfully used to detect CLB in pork and beef samples with satisfactory recoveries. To our knowledge, this is the first report on a ratiometric fluorescent probe for the detection of CLB, which possesses broad application prospects in food safety risk monitoring.

Fluorescent nanoparticles with ultralow chromophore loading for long-term tumor-targeted imaging

Recently, organic dyes with aggregation-induced emission (AIE) have attracted much attention in bioimaging and diagnostics. Relatively, the application of traditional dyes has diminished because of aggregation-caused quenching (ACQ). In this work, we compare the imaging ability of nanoparticle formulations of these two kinds of dyes. Boron dipyrromethene (BODIPY) was chosen as a representative of the ACQ dyes, and an aggregation-induced emission (AIE) dye BPMT was used for comparison. BODIPY and BPMT were entrapped into PEG_5k-PLA_10k to form BODIPY-loaded NPs (BNPs) and BPMT-loaded NPs (ANPs), respectively. In vivo and ex vivo imaging demonstrated that BNP1 with ultralow BODIPY load (0.07%) can effectively accumulate in tumor tissues and enable long-term noninvasive imaging. In contrast, ANP4 with high BPMT load (1.6%) has poor bioimaging ability. In general, our work has certain reference significance for the application of ACQ dyes and AIEgens in bioimaging, diagnostics, and theranostics. STATEMENT OF SIGNIFICANCE: In this work, Boron dipyrromethene (BODIPY) was chosen as a representative of ACQ dyes. As a control, (Z)-2-(4'-(9H-carbazol-9-yl)-[1,1'-biphenyl]-4-yl)-3-(7-(4-(bis(4methoxyphenyl)amino) phenyl) benzo[c] [1,2,5] thiadiazol-4-yl) acrylonitrile (BPMT) was selected as an aggregation-induced emission (AIE) dye. BODIPY and BPMT was entrapped into PEG5k-PLA10k to form BODIPY-loaded NPs (BNPs) and BPMT-loaded NPs (ANPs), respectively. In vivo and ex vivo imaging demonstrated that BNP1 with ultralow BODIPY load (0.07%) can effectively accumulate in tumor tissues and realize long-term noninvasive imaging. The weaknesses of ACQ effect can be converted into advantages by skillful use of nanotechnology, which can not only save the cost but also realize high efficiency targeted cancer imaging.

Sialic acid–targeted drug delivery and imaging system for pH- and glutathione-triggered multiple anticancer drug release and enhanced oxidative stress

The emergence of multiple drug delivery systems can solve the disadvantages of single-drug therapy, such as high dose and easy generation of drug resistance. Here, we designed a sialic acid–targeted dextran-mercaptopurine prodrug linked by carbonyl vinyl sulfide for coordinate ZnO quantum dots to achieve multiple drug delivery (doxorubicin, 5-fluorouracil, 6-mercaptopurine), which can be released under the trigger of pH and glutathione. To enhance the antitumor effect, we used inorganic photosensitizer CdSe quantum dots to achieve photodynamic therapy, which can produce cytotoxic reactive oxygen species (hydroxyl radicals) under light conditions. Notably, we found that glutathione is consumed by the delivery of 6-mercaptopurine. It is able to efficiently amplify intracellular oxidative stress via increasing •OH generation. After chelating 99mTc4+ radioisotopes by diethylenetriamine pentaacetic acid, the drug delivery system could be tracked under in vivo single-photon emission computed tomography imaging. The results showed that the phenylboronic acid targeting substance can specifically recognize sialic acid, so that the drug system has a good accumulation in the tumor site, which can better increase the therapeutic effect. Compared to free doxorubicin, the drug system can reduce the IC50 value of cells 4.4-fold under light conditions and significantly inhibit tumor growth in vivo. These data indicate that the sialic acid–targeted nanomedicine system has achieved ideal antitumor effects and apparent photodynamic therapy effects and has broad application prospects.

A hollow-structured nanohybrid: Intelligent and visible drug delivery and photothermal therapy for cancer

It is of great valuable in drug delivery to fabricate multifunctional nanovehicle for cancer therapy. Herein, hollow-structured hCu_2-xS@Au nanoshell/satellite composite with doxorubicin-carrying was designed and synthesized for intelligent and visible drug delivery and satisfactory photothermal therapy. By modification of disulfide linkage bridged Au nanoshell and multi-carboxylic graphene quantum dots (MC-GODs) on the surface of hCu_2-xS@Au nanoparticles, both the high concentration of glutathione and low pH in cancer cell/tissue can induce responsive drug release. The satisfactory photothermal conversion efficiency (32%) of hCu_2-xS@Au@MC-GODs under 808 nm near-infrared (NIR) laser irradiation ascribed to the reduced bandgap and more circuit paths for electron transitions for hCuS modified with Au nanoparticles depend on density functional theory, which antitumor therapy efficacy was greatly enhanced by combining chemo- and photothermal therapy. Moreover, the fluorescence of MC-GODs was quenched/"turn off" as linking to the surface of hCu_2-xS@Au, and also restored/"turn on" as the MC-GODs detaching from the surface of hCu_2-xS@Au. The fluorescent switch of MC-GODs can serve as both a controllable drug release "guard" and "eyes" for visualized monitoring. The multi-modality therapy with controllable drug delivery, visual monitoring and high photothermal conversion efficiency may be anticipated by this versatile strategy.

Insight into triphenylamine and coumarin serving as copper (II) sensors with "OFF" strategy and for bio-imaging in living cells

Chemosensing is one of the widest and powerful techniques for response to anions and cations in living systems serving as bio-probes. Meanwhile, copper(II) (Cu(II)) widely exists in the environment and the human body as a common trace element, which plays an necessary role in most physiological processes. Thus, it is extremely urgent to explore means for effective, rapid and convenient detection of Cu(II) in living cells. Herein, we introduce a novel strategy for designing triphenylamine (TS) and coumarin-based (CS) functional sensors for Cu(II) detection with fluorescence "OFF" switching mechanism by blocking intramolecular charge transfer (ICT). Based on this design strategy, we have demonstrated two kinds of fluorophores sensors with aunique new fluorescent dye and excellent photophysical properties, which have shown rapid recognition of Cu(II) via a stoichiometric ratio of 2:1 and the proposed binding mode was confirmed by the single-crystal structure of CS-Cu(II) complex. In addition, we have carried out density functional theory (DFT) calculation with the B3LYP exchange functional employing RB3LYP/6-31G basis sets to get insight into the mechanism of Cu(II)-sensors alongside their optical properties. Furthermore, the sensors were capable of bio-imaging Cu(II) in living cancer cells (HepG2, A549 and Hela) with low cytotoxicity and good biocompatibility shown. Taken together, We expect that this novel strategy would provide new insight into the development of Cu(II) detection techniques and could be used more for biomedical applications.

A new FRET probe for ratiometric fluorescence detecting mitochondria-localized drug activation and imaging endogenous hydroxyl radicals in zebrafish

A new FRET probe has been prepared and successfully used for imaging hydroxyl radicals generated by drug activation and endogenous hydroxyl radicals in zebrafish.

A sensitive BODIPY-based fluorescent probe for detecting endogenous hydroxyl radicals in living cells

A novel “turn-on” NIR fluorescent probe was designed and used for monitoring endogenous hydroxyl radical in living cells, which also showed higher selectivity toward hydroxyl radical over other reactive oxygen/nitrogen species.

Antioxidant Activity of Graphene Quantum Dots Prepared in Different Electrolyte Environments

Antioxidants can reduce or inhibit damage such as oxidative decay caused by elevated levels of free radicals. Therefore, pursuing antioxidants with excellent properties has attracted more and more attention. Graphene quantum dots (GQDs) are considered a promising material because of their good free radical scavenging activity, low toxicity, and excellent water solubility. However, their scavenging efficiency, antioxidant mechanism, and effective control methods need to be improved. Herein, in order to further reveal the antioxidant mechanism of GQDs, the role of electrolytes in improving the antioxidant activity of GQDs is explored. In addition, 1,1-diphenyl-2-picrazine (DPPH∙), hydroxyl (∙OH), and superoxide (∙O₂⁻) free radicals are used to evaluate the antioxidant activity of the as-prepared GQDs. Combined with transmission electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and cyclic volt–ampere characteristic curves, the effects of an electrolytic environment on the surface functional groups, charge transfer capability, and defect states of GQDs are obtained. The antioxidant mechanism of GQDs and how to improve their antioxidant activity are further elucidated.

Dynamic Imaging of Transferrin Receptor Molecules on Single Live Cell with Bridge Gaps-Enhanced Raman Tags

A metal nanoparticles-based surface-enhanced Raman scattering (SERS) technique has been developed for biosensing and bioimaging due to its advantages in ultra-narrow line width for multiplexing, ultra-high sensitivity and excellent photostability. However, the "hotspots" effect between nanoparticles usually leads to unstable and nonuniform Raman enhancement, and this will greatly reduce the quality of SERS imaging. In this study, we employ the bridge gaps-enhanced Raman tags (BGERTs) to perform SERS imaging, in which BGERTs can not only reduce the influence of the "hotspots" effect between nanoparticles on Raman signal intensity but provide a great Raman enhancement when the Gold (Au) shell is thick enough. Based on BGERTs and its conjugation with the thiol-terminated polyethylene glycol (PEG) and transferrin, we construct a targeted Transferrin (TF)-PEG-BGERTs SERS nanoprobe and achieve the dynamic imaging of transferrin receptor (TfR) molecules on a single live cell, in which the role of transferrin-conjugated PEG-BGERT is for targeting TfR molecules located in cellular membrane surface. Importantly, this BGERTs-based SERS imaging could potentially provide a useful tool for studying the precise mechanism during the receptor-mediated nanoparticles endocytosis or cell proliferation, apoptosis, and other complicated molecular events.

Small-Molecule-Based Fluorescent Sensors for Selective Detection of Reactive Oxygen Species in Biological Systems

Reactive oxygen species (ROS) encompass a collection of intricately linked chemical entities characterized by individually distinct physicochemical properties and biological reactivities. Although excessive ROS generation is well known to underpin disease development, it has become increasingly evident that ROS also play central roles in redox regulation and normal physiology. A major challenge in uncovering the relevant biological mechanisms and deconvoluting the apparently paradoxical roles of distinct ROS in human health and disease lies in the selective and sensitive detection of these transient species in the complex biological milieu. Small-molecule-based fluorescent sensors enable molecular imaging of ROS with great spatial and temporal resolution and have thus been appreciated as excellent tools for aiding discoveries in modern redox biology. We review a selection of state-of-the-art sensors with demonstrated utility in biological systems. By providing a systematic overview based on underlying chemical sensing mechanisms, we wish to highlight the strengths and weaknesses in prior sensor works and propose some guiding principles for the development of future probes.

A literature review on multimodality molecular imaging nanoprobes for cancer detection

Molecular imaging techniques using nanoparticles have significant potential to be widely used for the detection of various types of cancers. Nowadays, there has been an increased focus on developing novel nanoprobes as molecular imaging contrast enhancement agents in nanobiomedicine. The purpose of this review article is to summarize the use of a variety of nanoprobes and their current achievements in accurate cancer imaging and effective treatment. Nanoprobes are rapidly becoming potential tools for cancer diagnosis by using novel molecular imaging modalities such as Ultrasound (US) imaging, Computerized Tomography (CT), Single Photon Emission Tomography (SPECT) and Positron Emission Tomography (PET), Magnetic Resonance Imaging (MRI), and Optical Imaging. These imaging modalities may facilitate earlier and more accurate diagnosis and staging the most of cancers.

Medical imaging modalities using nanoprobes for cancer diagnosis: A literature review on recent findings

Medical imaging modalities are used for different types of cancer detection and diagnosis. Recently, there have been a lot of studies on developing novel nanoparticles as new medical imaging contrast agents for the early detection of cancer. The aim of this review article is to categorize the medical imaging modalities accompanying with using nanoparticles to improve potential imaging for cancer detection and hence valuable therapy in the future. Nowadays, nanoparticles are becoming potentially transformative tools for cancer detection for a wide range of imaging modalities, including computed tomography (CT), magnetic resonance imaging, single photon emission CT, positron emission tomography, ultrasound, and optical imaging. The study results seen in the recent literature provided and discussed the diagnostic performance of imaging modalities for cancer detections and their future directions. With knowledge of the correlation between the application of nanoparticles and medical imaging modalities and with the development of targeted contrast agents or nanoprobes, they may provide better cancer diagnosis in the future.