Turn-on fluorescent glutathione detection based on lucigenin and MnO2 nanosheets

Transition Metal (Molybdenum)-Doped Drug-like Conformational Nanoarchitectonics with Altered Valence States (Mn2+/Mn4+ and Mo5+/Mo6+) for Augmented Cancer Theranostics

Despite the advancements in cancer therapy, delivering active pharmaceutical ingredients (APIs) using nanoparticles remains challenging due to the failed conveyance of the required drug payload, poor targeting ability, and poor biodistribution, hampering their clinical translation. Recently, the appropriate design of materials with intrinsic therapeutic functionalities has garnered enormous interest in the development of various intelligent therapeutic nanoplatforms. In this study, we demonstrate the fabrication of transition metal (molybdenum, Mo)-doped manganese dioxide (MnO2) nanoarchitectures, exhibiting diagnostic (magnetic resonance imaging, MRI) and therapeutic (chemodynamic therapy, CDT) functionalities. The facile hydrothermal approach-assisted Mo-doped MnO2 flower-like nanostructures offered tailorable morphologies in altered dimensions, precise therapeutic effects, exceptional biocompatibility, and biodegradability in the tumor microenvironment. The resultant defects due to doped Mo species exhibited peroxidase and oxidase activities, improving glutathione (GSH) oxidation. The two sets of variable valence metal ion pairs (Mn2+/Mn4+ and Mo5+/Mo6+) and their interplay could substantially improve the Fenton-like reaction and generate toxic hydroxyl radicals (•OH), thus achieving CDT-assisted antitumor effects. As inherent T1-MRI agents, these MnO2 nanoparticles displayed excellent MRI efficacy in vitro. Together, we believe that these conformational Mo-doped MnO2 nanoarchitectures with two pairs of variable valence states could potentiate drugless therapy in pharmaceutics.

Multifunctional nitrogen-sulfur codoped carbon quantum dots: Determining reduced glutathione, broad-spectrum antibacterial activity, and cell imaging

In this study, nitrogen-sulfur codoped carbon quantum dots (N-S/CQDs) with various functions and properties were synthesized through a one-step method utilizing citric acid and cysteine as reaction substrates. The fluorescence of N-S/CQDs can be specifically quenched by permanganate ion (MnO4 -), and the quenched fluorescence can be recovered by the presence of reduced glutathione (GSH). A fluorescence sensing system based on N-S/CQDs@MnO4 - was developed and successfully applied for the determination of GSH in pharmaceutical preparations. Additionally, N-S/CQDs demonstrated broad-spectrum antibacterial activity, with minimum inhibitory concentrations of 32 μg/ml against Staphylococcus aureus (gram-positive bacterium) and 64 μg/ml against Escherichia coli (gram-negative bacterium). N-S/CQDs also proved effective for cell imaging, exhibiting excellent biocompatibility. These findings underscore the multifunctional characteristics and promising application potential of N-S/CQDs. Furthermore, this study provides a solid foundation for the development of multifunctional carbon quantum dots and the expansion of their applications in various fields.

An off-on fluorescence method for acid phosphatase assay based on the inner filter effect of MnO2 nanosheets on vitamin B2

Fluorescence analysis has attracted much attention due to its rapidity and sensitivity. The present work describes a novel fluorescence detection method for acid phosphatase (ACP) on the basis of inner-filter effect (IFE), where MnO2 nanosheets (MnO2 NSs) and vitamin B2 (VB2) are served as absorbers and fluorophores, respectively. In the absence of ACP, the absorption band of MnO2 NSs overlaps well with the excitation band of VB2, resulting in effective IFE and inhibition of VB2 fluorescence. In the presence of ACP, 2-phospho-L-ascorbic acid trisodium salt (AAP) is hydrolyzed to generate ascorbic acid (AA), which efficiently trigger the reduction of MnO2 NSs into Mn2+ ions, causing the weakening of the MnO2 NSs absorption band and the recovery of VB2 fluorescence. Further investigation indicates that the fluorescence recovery degree of VB2 increases with the increase of ACP concentration. Under selected experimental conditions, the proposed method can achieve sensitive detection of ACP in the ranges of 0.5-4.0 mU/mL and 4.0-15 mU/mL along with a limit of detection (LOD) as low as 0.14 mU/mL. Finally, this method was successfully applied for the detection of ACP in human serum samples with satisfactory recoveries in the range of 95.0 %-108 %.

Determination of Acetylcholinesterase Activity Based on Ratiometric Fluorescence Signal Sensing

Acetylcholinesterase (AChE) plays an important role in the treatment of human diseases, environmental security and global food supply. In this study, the simple fluorescent indicators and MnO2 nanosheets were developed and integrated to establish a ratiometric fluorescence sensing system for the detection of AChE activity. Two fluorescence signals could be recorded independently at the same excitation wavelength, which extended the detection range and enhanced the visibility of results. Fluorescence of F-PDA was quenched by MnO2 nanosheets on account of inner filtering effect. Meanwhile, the nonfluorescent OPD was catalytically oxidized to 2,3-diaminophenazine by MnO2 nanosheets. The acetylcholine (ATCh) was catalytically hydrolyzed by AChE to enzymatic thiocholine, which decomposed MnO2 to Mn2+, recovered the fluorescence of F-PDA and reduced the emission of ox-OPD. Utilizing the fluorescence intensity ratio F468/F558 as the signal readout, the ratiometric fluorescence method was established to detect AChE activity. Under the excitation wavelength of 410 nm, the ratio F460/F558 against the AChE concentration demonstrated two linear relationships in the range 0.05 -1.0 and 1.0-50 U·L- 1 with a limit of detection (LOD) of 0.073 U·L- 1. The method was applied to the detection of AChE activity and the analysis of the inhibitor Huperzine-A. Due to the advantages of high sensitivity and favorable selectivity, the method possesses an application prospect in the activity deteceion of AChE and the screening of inhibitors.

Construction of a Functional Nucleic Acid-Based Artificial Vesicle-Encapsulated Composite Nanoparticle and Its Application in Retinoblastoma-Targeted Theranostics

Retinoblastoma (RB) is an aggressive tumor of the infant retina. However, the ineffective targeting of its theranostic agents results in poor imaging and therapeutic efficacy, which makes it difficult to identify and treat RB at an early stage. In order to improve the imaging and therapeutic efficacy, we constructed an RB-targeted artificial vesicle composite nanoparticle. In this study, the MnO2 nanosponge (hMNs) was used as the core to absorb two fluorophore-modified DNAzymes to form the Dual/hMNs nanoparticle; after loaded with the artificial vesicle derived from human red blood cells, the RB-targeted DNA aptamers were modified on the surface, thus forming the Apt-EG@Dual/hMNs complex nanoparticle. The DNA aptamer endows this nanoparticle to target the nucleolin-overexpressed RB cell membrane specifically and enters cells via endocytosis. The nanoparticle could release fluorophore-modified DNAzymes and supplies Mn2+ as a DNAzyme cofactor and a magnetic resonance imaging (MRI) agent. Subsequently, the DNAzymes can target two different mRNAs, thereby realizing fluorescence/MR bimodal imaging and dual-gene therapy. This study is expected to provide a reliable and valuable basis for ocular tumor theranostics.

Dual-mode fluorescence and colorimetric sensing of sulfide anion in natural water based on near-infrared Ag2S quantum dots and MnO2 nanosheets complex

Near infrared (NIR) emission Ag2S quantum dots (QDs) are of great value for biochemical sensing with strong anti-interference and low toxicity. Herein, NIR fluorescence Ag2S QDs were synthesized successfully. Combined with the excellent oxidase-like characteristics of manganese dioxide (MnO2) nanosheets, a fluorescence and colorimetric dual-mode sensor for sulfide anion was developed. MnO2 nanosheets could effectively catalyze the oxidation of TMB to produce blue TMB oxide (ox TMB), at the same time, the fluorescence of Ag2S QDs could be effectively quenched by fluorescence internal filtration effect (IFE) and dynamic quenching effect. The enzyme-like activity was weakened and the NIR fluorescence of Ag2S QDs was restored when sulfide anion (S2-) was added, due to the reduction of MnO2 to Mn2+.The linear ranges for fluorescence and colorimetric analysis of S2- were 2-250 μM and 0.3-50 μM, with detection limits of 0.6 and 0.215 μM, correspondingly. The dual-mode sensor had a wider detection range, higher sensitivity and shorter reaction time, which could be used for highly selective detection of S2- in different concentration ranges. In addition, it had been successfully applied to the determination of sulfide in water samples with satisfactory accuracy and sensitivity.

Multicolor detection of glutathione by manganese dioxide nanosheets and gold nanotetrapods based on an anti-etching mechanism

Glutathione (GSH) is a crucial non-protein thiol and an indispensable endogenous antioxidant. The aberrant expression of GSH in plasma and cytosol is closely related to numerous diseases, including cancer. Therefore, establishing a sensitive method for analyzing GSH has important application value for biomedical research and clinical medical detection. Herein, A method for the rapid and simple detection of GSH was proposed, which is based on an anti-etching mechanism by utilizing gold nanotetrapods (Au NTPs) and manganese dioxide nanosheets (MnO2 NSs). In the absence of GSH, Au NTPs solution can cause a distinct color change from gray-green to red through the etching effect of MnO2 NSs. However, in the presence of GSH, the redox reaction between GSH and MnO2 NSs inhibits the etching of Au NTPs by MnO2 NSs, and Au NTPs solution maintains persistent gray-green color. The colorimetric probe exhibited excellent selectivity for GSH. The limits of detection for GSH were 43.5 nM (UV-vis spectrum) and 0.25 μM (naked eyes). The sensing technique exhibited excellent linearity between wavelength shift and GSH concentration within the range of 0.25 μM-1.5 μM. The outcomes of GSH detection in actual biological samples demonstrate that this probe has the potential to be applied to GSH detection in intricate biological samples.

Biomedical applications of MnO2 nanomaterials as nanozyme-based theranostics

Manganese dioxide (MnO₂) nanoenzymes/nanozymes (MnO₂-NEs) are 1-100 nm nanomaterials that mimic catalytic, oxidative, peroxidase, and superoxide dismutase activities. The oxidative-like activity of MnO₂-NEs makes them suitable for developing effective and low-cost colorimetric detection assays of biomolecules. Interestingly, MnO₂-NEs also demonstrate scavenging properties against reactive oxygen species (ROS) in various pathological conditions. In addition, due to the decomposition of MnO₂-NEs in the tumor microenvironment (TME) and the production of Mn²⁺, they can act as a contrast agent for improving clinical imaging diagnostics. MnO₂-NEs also can use as an in situ oxygen production system in TME, thereby overcoming hypoxic conditions and their consequences in the progression of cancer. Furthermore, MnO₂-NEs as a shell and coating make the nanosystems smart and, therefore, in combination with other nanomaterials, the MnO₂-NEs can be used as an intelligent nanocarrier for delivering drugs, photosensitizers, and sonosensitizers in vivo. Moreover, these capabilities make MnO₂-NEs a promising candidate for the detection and treatment of different human diseases such as cancer, metabolic, infectious, and inflammatory pathological conditions. MnO₂-NEs also have ROS-scavenging and anti-bacterial properties against Gram-positive and Gram-negative bacterial strains, which make them suitable for wound healing applications. Given the importance of nanomaterials and their potential applications in biomedicine, this review aimed to discuss the biochemical properties and the theranostic roles of MnO₂-NEs and recent advances in their use in colorimetric detection assays of biomolecules, diagnostic imaging, drug delivery, and combinatorial therapy applications. Finally, the challenges of MnO₂-NEs applications in biomedicine will be discussed.

Construction of a novel nano-enzyme for ultrasensitive glucose detection with surface-enhanced Raman scattering

Fabricating more sensitive, stable and low-cost nanomaterials for the detection of glucose is important for the disease diagnosis and monitoring. Herein, we established a nanocomposite (polypyrrole bridging GO@Au@MnO₂) as a novel surface-enhanced Raman scattering (SERS) nanoprobe for the quantitative detection of glucose in trace serum. Each component in the nanocomposites played an irreplaceable role in SERS detection of glucose. Polypyrrole (PPy) could act as Raman signal and extra SERS signal molecules didn't need to be introduced; Graphene oxide (GO) and gold nanoparticles (Au NPs) could enhance Raman signal of PPy; Au NPs also acted as glucose oxidase, which can oxidize glucose to produce gluconic acid and hydrogen peroxide(H₂O₂); Manganese oxide (MnO₂) further enhanced Raman signal of PPy and responded to hydrogen peroxide, which will induce the decrease of Raman intensity of PPy. Thus, glucose can be quantified according to Raman signal output of PPy, which displayed a liner range from 1 to 10 μM, with detectable limit of 0.114 μM. Because of the merits in sensitivity, convenience and versatility, the novel method shows large potential space for disease-related substance detection in the future.

Glutathione Fluorescence Sensing Based on a Co-Doped Carbon Dot/Manganese Dioxide Nanocoral Composite

Glutathione (GSH) is an antioxidant thiol that has a vital role in the pathogenesis of various human diseases such as cardiovascular disease and cancer. Hence, it is necessary to study effective methods of GSH evaluation. In our work, an effective GSH sensor based on a nitrogen and phosphorus co-doped carbon dot (NPCD)-MnO₂ nanocoral composite was fabricated. In addition to utilizing the strong fluorescence of the NPCDs, we utilized the reductant ability of the NPCDs themselves to form MnO₂ and then the NPCD-MnO₂ nanocoral composite from MnO₄^-. The characteristics of the nanocoral composite were analyzed using various electron microscopy techniques and spectroscopic techniques. The overlap between the absorption spectrum of MnO₂ and the fluorescence emission spectrum of the NPCDs led to effective fluorescence resonance energy transfer (FRET) in the nanocoral composite, causing a decrease in the fluorescent intensity of the NPCDs. A linear recovery of the fluorescent intensity of the NPCDs was observed with the GSH level raising from 20 to 250 µM. Moreover, our GSH sensor showed high specificity and sensing potential in real samples with acceptable results.

Chemiluminescence Detection in the Study of Free-Radical Reactions. Part 2. Luminescent Additives That Increase the Chemiluminescence Quantum Yield

The present review examines the use of chemiluminescence detection to evaluate the course of free radical reactions in biological model systems. The application of the method is analyzed by using luminescent additives that enhance the luminescence thanks to a triplet-singlet transfer of the electron excitation energy from radical reaction products and its emission in the form of light with a high quantum yield; these additives are called chemiluminescence enhancers or activators. Examples of these substances are provided; differences between the so-called chemical and physical enhancers are described; coumarin derivatives, as the most promising chemiluminescence enhancers for studying lipid peroxidation, are considered in detail. The main problems related to the use of coumarin derivatives are defined, and possible ways of solving these problems are presented. Intrinsic chemiluminescence and the mechanism of luminescence accompanying biomolecule peroxidation are discussed in the first part of the review.

In situ synthesis of chiral AuNCs with aggregation-induced emission using glutathione and ceria precursor nanosheets for glutathione biosensing

Au(i)–SG/Ce(CO3)2 NS conjugated nanoprobe was developed for selective GSH detection. The redox reaction between GSH and the NS could release Ce3+ ions to initiate the intense AIE of Au(i)–SG oligomers.

A ratiometric fluorescence platform composed of MnO2 nanosheets and nitrogen, chlorine co-doped carbon dots and its logic gate performance for glutathione determination

Illustration of the principle of a dual-emission ratiometric fluorescence strategy for the selective detection of GSH based on an N, Cl-CD-assisted MnO2 nanosheet–OPD system.

Dye-functionalized metal-organic frameworks with the uniform dispersion of MnO2 nanosheets for visualized fluorescence detection of alanine aminotransferase

The wide applications of metal-organic framework (MOF) luminescent materials in the field of optics have attracted the general attention of researchers. Therefore, the development of simple and multifunctional MOF light-emitting platforms have become a research hotspot. The composites (MnO2@ZIF-8-luminol) were prepared by an in situ synthesis method and room-temperature covalent reaction. The composites and o-phenylenediamine (OPD) constitute a dual emission sensor for detecting alanine aminotransferase (ALT). OPD can be oxidized by MnO₂ to 2,3-diaminophenazine (DAP) with yellow fluorescence emission, which inhibits the blue emission of luminol through fluorescence resonance energy transfer (FRET). The presence of tiopronin (TP) will destroy the FRET process, extinguishing the yellow fluorescence emission and restoring the blue fluorescence emission. The special effect between ALT and TP will further reverse the changes in the two fluorescent signals. Moreover, in the detection process, when the blue and yellow fluorescence energies in the system are within a certain range, a new white light emission will be generated, which causes the sensing of ALT to present ternary visualization. In addition, a high-security anti-counterfeiting platform is constructed by using the prepared materials and agarose hydrogels. The anti-counterfeiting platform can encrypt information on demand according to the luminous characteristics of different materials. This study not only provides a typical case of ternary visualization sensing by MOF-based materials but also develops a possible method for the construction of a MOF-based hydrogel anti-counterfeiting platform.

An ultrasensitive chemiluminescent biosensor for tracing glutathione in human serum using BSA@AuNCs as a peroxidase-mimetic nanozyme on a luminol/artesunate system

In this work, a nanosensor chemiluminescent (CL) probe for sensing glutathione (GSH) was developed, for the first time, based on its inhibition of the intrinsic peroxidase-mimetic effect of BSA@AuNCs. The endoperoxide linkage of artesunate could be hydrolyzed by BSA@AuNCs resulting in the release of reactive oxygen species (ROS), and the consequent generation of strong CL emission. By virtue of the strong covalent interactions of -S⋯Au-, GSH could greatly suppress the peroxidase-mimetic effect of BSA@AuNCs, leading to a drastic CL quenching. The CL quenching efficiency increased proportionally to the logarithm of GSH concentration through the linearity range of 50.0-5000.0 nM with a limit of detection of 5.2 nM. This CL-based strategy for GSH tracing demonstrated the advantages of ultrasensitivity, high selectivity and simplicity. This strategy was successfully utilized to measure GSH levels in human serum with reasonable recovery results of 98.71%, 103.18%, and 101.68%, suggesting that this turn-off CL sensor is a promising candidate for GSH in biological and clinical samples.

Ratiometric fluorescence and smartphone dual-mode detection of glutathione using carbon dots coupled with Ag+-triggered oxidation of o-phenylenediamine

Developing ratiometric fluorescence and smartphone dual-mode bioanalysis methods is important but challenging. A ratiometric fluorescence method for determining glutathione (GSH) using carbon dots (CDs) and Ag⁺-triggered o-phenylenediamine (OPD) oxidation is described here. Ag⁺oxidizes OPD to give 2,3-diaminophenazine (oxOPD), which effectively quenches CD fluorescence at 436 nm through the inner filter effect and causes a new emission peak at 561 nm. GSH chelates with Ag⁺and prevents the Ag⁺oxidizing OPD and therefore effectively preserves CD emission at 436 nm (blue) and allows only weak oxOPD fluorescence at 561 nm (orange) to occur. The oxOPD to CD fluorescence intensity ratio decreased linearly as the GSH concentration increased in the range 0-150 nM, and the detection limit was 15 nM. The ratiometric fluorescence probe lit with an ultraviolet lamp clearly changed color from orange to blue as the GSH concentration increased. An image was acquired using a smartphone camera and converted into digital values. The blue and red channel ratio was calculated and used to quantify GSH. The method therefore allows dual-mode detection of GSH.

Crossing the blood-brain barrier with carbon dots: uptake mechanism and in vivo cargo delivery

The blood-brain barrier (BBB) is a major obstacle for drug delivery to the central nervous system (CNS) such that most therapeutics lack efficacy against brain tumors or neurological disorders due to their inability to cross the BBB. Therefore, developing new drug delivery platforms to facilitate drug transport to the CNS and understanding their mechanism of transport are crucial for the efficacy of therapeutics. Here, we report (i) carbon dots prepared from glucose and conjugated to fluorescein (GluCD-F) cross the BBB in zebrafish and rats without the need of an additional targeting ligand and (ii) uptake mechanism of GluCDs is glucose transporter-dependent in budding yeast. Glucose transporter-negative strain of yeast showed undetectable GluCD accumulation unlike the glucose transporter-positive yeast, suggesting glucose-transporter-dependent GluCD uptake. We tested GluCDs' ability to cross the BBB using both zebrafish and rat models. Following the injection to the heart, wild-type zebrafish showed GluCD-F accumulation in the central canal consistent with the transport of GluCD-F across the BBB. In rats, following intravenous administration, GluCD-F was observed in the CNS. GluCD-F was localized in the gray matter (e.g. ventral horn, dorsal horn, and middle grey) of the cervical spinal cord consistent with neuronal accumulation. Therefore, neuron targeting GluCDs hold tremendous potential as a drug delivery platform in neurodegenerative disease, traumatic injury, and malignancies of the CNS.

Two-photon fluorescence and MR bio-imaging of endogenous H2O2 in the tumor microenvironment using a dual-mode nanoprobe

The dual-mode bio-imaging nanoprobe TP-CQDs@MnO2, based on two-photon carbon quantum dots and MnO2, has been developed for the two-photon fluorescence and MR imaging of endogenous H2O2 in the tumor microenvironment, and it achieved high selectivity, a great signal-to-noise ratio, a limit of detection (LOD) of 1.425 pM for H2O2, and a two-photon tissue penetration depth of 280 μm.

Elucidating Gold-MnO2 Core-Shell Nanoenvelope for Real Time SERS-Guided Photothermal Therapy on Pancreatic Cancer Cells

Pancreatic cancer represents one of the most aggressive in nature with a miserable prognosis that warrants efficient diagnostic and therapeutic interventions. Herein, a MnO₂ overlaid gold nanoparticle (AuNPs) based photothermal theranostic nanoenvelope (PTTNe:MnO₂@AuNPs) was fabricated to substantiate surface-enhanced Raman spectroscopy (SERS) guided real-time monitoring of photothermal therapy (PTT) in pancreatic cancer cells. A sharp enhancement of the fingerprint Raman signature of MnO₂ at 569 cm^-1 exhibited as a marker peak for the first time to elucidate the intracellular PTT event. In this strategic design, the leftover bare AuNPs after the degradation of the MnO₂ layer from the nanoenvelope in the presence of intracellular H₂O₂ enabled real-time tracking of biomolecular changes of Raman spectral variations during PTT. Moreover, the surface of the as-synthesized nanoenvelope was functionalized with a pancreatic cancer cell targeting peptide sequence for cholecystokinin fashioned the PTTNe with admirable stability and biocompatibility. Finally, the precise cell death mechanism was explicitly assessed by SERS spectral analysis as a complementary technique. This targeted phototheranostic approach demonstrated in pancreatic cancer cells presented a therapeutically viable prototype for futuristic personalized cancer nanomedicine.

Engineered two-dimensional nanomaterials: an emerging paradigm for water purification and monitoring

Water scarcity has become an increasingly complex challenge with the growth of the global population, economic expansion, and climate change, highlighting the demand for advanced water treatment technologies that can provide clean water in a scalable, reliable, affordable, and sustainable manner. Recent advancements on 2D nanomaterials (2DM) open a new pathway for addressing the grand challenge of water treatment owing to their unique structures and superior properties. Emerging 2D nanostructures such as graphene, MoS₂, MXene, h-BN, g-C₃N₄, and black phosphorus have demonstrated an unprecedented surface-to-volume ratio, which promises ultralow material use, ultrafast processing time, and ultrahigh treatment efficiency for water cleaning/monitoring. In this review, we provide a state-of-the-art account on engineered 2D nanomaterials and their applications in emerging water technologies, involving separation, adsorption, photocatalysis, and pollutant detection. The fundamental design strategies of 2DM are discussed with emphasis on their physicochemical properties, underlying mechanism and targeted applications in different scenarios. This review concludes with a perspective on the pressing challenges and emerging opportunities in 2DM-enabled wastewater treatment and water-quality monitoring. This review can help to elaborate the structure-processing-property relationship of 2DM, and aims to guide the design of next-generation 2DM systems for the development of selective, multifunctional, programmable, and even intelligent water technologies. The global significance of clean water for future generations sheds new light and much inspiration in this rising field to enhance the efficiency and affordability of water treatment and secure a global water supply in a growing portion of the world.

A sensitive fluorescent assay for the determination of parathion-methyl using AHNSA probe with MnO2 nanosheets

In this paper, a novel fluorescence assay has been constructed for the determination of parathion-methyl (PM) by using 4-amino-3-hydroxy-1-naphthalenesulfonic acid (AHNSA) as probe. MnO₂ nanosheets (MnO₂ NS) could quench the fluorescence of AHNSA, while Mn²⁺, the reduction product of MnO₂ NS, has no influence on it, resulting in fluorescence recovery. This is because that MnO₂ NS have oxidized characteristic, and they can react with choline (TCh), which is the product of acetylthiocholine (ATCh) catalyzed by acetylcholinesterase (AChE). In the presence of OPs, the activity of AChE was inhibited, accompanied by the restraint of the redox reaction of MnO₂ NS, therefore the fluorescence of AHNSA was quenched. Under the optimized experimental conditions, a linear range of PM was determined to be 0.4-40 ng/mL (R² = 0.997) by the proposed method with the limit of detection for 0.18 ng/mL (S/N = 3). The assay was successfully applied to the determination of PM in lake water, which average recoveries were between 86.5% and 114.4%.

Integrating gold nanoclusters, folic acid and reduced graphene oxide for nanosensing of glutathione based on "turn-off" fluorescence

Glutathione (GSH) is a useful biomarker in the development, diagnosis and treatment of cancer. However, most of the reported GSH biosensors are expensive, time-consuming and often require complex sample treatment, which limit its biological applications. Herein, a nanobiosensor for the detection of GSH using folic acid-functionalized reduced graphene oxide-modified BSA gold nanoclusters (FA-rGO-BSA/AuNCs) based on the fluorescence quenching interactions is presented. Firstly, a facile and optimized protocol for the fabrication of BSA/AuNCs is developed. Functionalization of rGO with folic acid is performed using EDC/NHS cross-linking reagents, and their interaction after loading with BSA/AuNCs is demonstrated. The formation of FA-rGO, BSA/AuNCs and FA-rGO-BSA/AuNCs are confirmed by the state-of-art characterization techniques. Finally, a fluorescence turn-off sensing strategy is developed using the as-synthesized FA-rGO-BSA/AuNCs for the detection of GSH. The nanobiosensor revealed an excellent sensing performance for the detection of GSH with high sensitivity and desirable selectivity over other potential interfering species. The fluorescence quenching is linearly proportional to the concentration of GSH between 0 and 1.75 µM, with a limit of detection of 0.1 µM under the physiological pH conditions (pH 7.4). Such a sensitive nanobiosensor paves the way to fabricate a "turn-on" or "turn-off" fluorescent sensor for important biomarkers in cancer cells, presenting potential nanotheranostic applications in biological detection and clinical diagnosis.

Black titanium dioxide@manganese dioxide for glutathione-responsive MR imaging and enhanced photothermal therapy

Multifunctional nanoprobes with tumor microenvironment response are playing important roles in highly efficient theranostics of cancers. Herein, a kind of theranostic nanoprobe was synthesized by coating manganese dioxide (MnO₂) on the surface of black commercial P25 titanium dioxide (b-P25). The resultant nanoprobe (b-P25@MnO₂) possessed glutathione (GSH)-responsive magnetic resonance (MR) imaging and enhanced photothermal therapy (PTT). In tumor microenvironments, the excessive GSH was consumed by reacting with MnO₂ to generate Mn²⁺ for GSH-responsive MR imaging, in which the longitudinal relaxation rate of b-P25@MnO₂ was up to 30.44 mM^-1 s^-1, showing excellent cellular and intratumoral MR imaging. Moreover, the prepared b-P25@MnO₂ exhibited stable and strong photothermal conversion capability with a high photothermal conversion efficiency of 30.67%, by which the 4T1 tumors disappeared completely, indicating safe and highly efficient PTT performance. The current work developed GSH-responsive b-P25@MnO₂ nanoprobes, demonstrated for MR imaging and enhanced PTT in cancers.