Fluorescent polymer nanoparticle for selective sensing of intracellular hydrogen peroxide

Macromolecule-Nanoparticle-Based Hybrid Materials for Biosensor Applications

Biosensors function as sophisticated devices, converting biochemical reactions into electrical signals. Contemporary emphasis on developing biosensor devices with refined sensitivity and selectivity is critical due to their extensive functional capabilities. However, a significant challenge lies in the binding affinity of biosensors to biomolecules, requiring adept conversion and amplification of interactions into various signal modalities like electrical, optical, gravimetric, and electrochemical outputs. Overcoming challenges associated with sensitivity, detection limits, response time, reproducibility, and stability is essential for efficient biosensor creation. The central aspect of the fabrication of any biosensor is focused towards forming an effective interface between the analyte electrode which significantly influences the overall biosensor quality. Polymers and macromolecular systems are favored for their distinct properties and versatile applications. Enhancing the properties and conductivity of these systems can be achieved through incorporating nanoparticles or carbonaceous moieties. Hybrid composite materials, possessing a unique combination of attributes like advanced sensitivity, selectivity, thermal stability, mechanical flexibility, biocompatibility, and tunable electrical properties, emerge as promising candidates for biosensor applications. In addition, this approach enhances the electrochemical response, signal amplification, and stability of fabricated biosensors, contributing to their effectiveness. This review predominantly explores recent advancements in utilizing macrocyclic and macromolecular conjugated systems, such as phthalocyanines, porphyrins, polymers, etc. and their hybrids, with a specific focus on signal amplification in biosensors. It comprehensively covers synthetic strategies, properties, working mechanisms, and the potential of these systems for detecting biomolecules like glucose, hydrogen peroxide, uric acid, ascorbic acid, dopamine, cholesterol, amino acids, and cancer cells. Furthermore, this review delves into the progress made, elucidating the mechanisms responsible for signal amplification. The Conclusion addresses the challenges and future directions of macromolecule-based hybrids in biosensor applications, providing a concise overview of this evolving field. The narrative emphasizes the importance of biosensor technology advancement, illustrating the role of smart design and material enhancement in improving performance across various domains.

Surface Bio-engineered Polymeric Nanoparticles

Surface bio-engineering of polymeric nanoparticles (PNPs) has emerged as a cornerstone in contemporary biomedical research, presenting a transformative avenue that can revolutionize diagnostics, therapies, and drug delivery systems. The approach involves integrating bioactive elements on the surfaces of PNPs, aiming to provide them with functionalities to enable precise, targeted, and favorable interactions with biological components within cellular environments. However, the full potential of surface bio-engineered PNPs in biomedicine is hampered by obstacles, including precise control over surface modifications, stability in biological environments, and lasting targeted interactions with cells or tissues. Concerns like scalability, reproducibility, and long-term safety also impede translation to clinical practice. In this review, these challenges in the context of recent breakthroughs in developing surface-biofunctionalized PNPs for various applications, from biosensing and bioimaging to targeted delivery of therapeutics are discussed. Particular attention is given to bonding mechanisms that underlie the attachment of bioactive moieties to PNP surfaces. The stability and efficacy of surface-bioengineered PNPs are critically reviewed in disease detection, diagnostics, and treatment, both in vitro and in vivo settings. Insights into existing challenges and limitations impeding progress are provided, and a forward-looking discussion on the field's future is presented. The paper concludes with recommendations to accelerate the clinical translation of surface bio-engineered PNPs.

Low Platinum-Content Electrocatalysts for Highly Sensitive Detection of Endogenously Released H2O2

The commercial viability of electrochemical sensors requires high catalytic efficiency electrode materials. A sluggish reaction of the sensor’s primary target species will require a high overpotential and, consequently, an excessive load of catalyst material to be used. Therefore, it is essential to understand nanocatalysts’ fundamental structures and typical catalytic properties to choose the most efficient material according to the biosensor target species. Catalytic activities of Pt-based catalysts have been significantly improved over the decades. Thus, electrodes using platinum nanocatalysts have demonstrated high power densities, with Pt loading considerably reduced on the electrodes. The high surface-to-volume ratio, higher electron transfer rate, and the simple functionalisation process are the main reasons that transition metal NPs have gained much attention in constructing high-sensitivity sensors. This study has designed to describe and highlight the performances of the different Pt-based bimetallic nanoparticles and alloys as an enzyme-free catalytic material for the sensitive electrochemical detection of H₂O₂. The current analysis may provide a promising platform for the prospective construction of Pt-based electrodes and their affinity matrix.

Fabrication of Nitrogen-Doped Reduced Graphene Oxide Modified Screen Printed Carbon Electrode (N-rGO/SPCE) as Hydrogen Peroxide Sensor

In recent years, the electrochemical sensing approach has attracted electrochemists because of its excellent detection process, simplicity, high sensitivity, cost-effectiveness, and high selectivity. In this study, we prepared nitrogen doped reduced graphene oxide (N-rGO) and characterized it using various advanced techniques such as XRD, SEM, EDX, Raman, and XPS. Furthermore, we modified the active surface of a screen printed carbon electrode (SPCE) via the drop-casting of N-rGO. This modified electrode (N-rGO/SPCE) exhibited an excellent detection limit (LOD) of 0.83 µM with a decent sensitivity of 4.34 µAµM-1cm-2 for the detection of hydrogen peroxide (H2O2). In addition, N-rGO/SPCE also showed excellent selectivity, repeatability, and stability for the sensing of H2O2. Real sample investigations were also carried out that showed decent recovery.

Cellular lensing and near infrared fluorescent nanosensor arrays to enable chemical efflux cytometry

Nanosensors have proven to be powerful tools to monitor single cells, achieving spatiotemporal precision even at molecular level. However, there has not been way of extending this approach to statistically relevant numbers of living cells. Herein, we design and fabricate nanosensor array in microfluidics that addresses this limitation, creating a Nanosensor Chemical Cytometry (NCC). nIR fluorescent carbon nanotube array is integrated along microfluidic channel through which flowing cells is guided. We can utilize the flowing cell itself as highly informative Gaussian lenses projecting nIR profiles and extract rich information. This unique biophotonic waveguide allows for quantified cross-correlation of biomolecular information with various physical properties and creates label-free chemical cytometer for cellular heterogeneity measurement. As an example, the NCC can profile the immune heterogeneities of human monocyte populations at attomolar sensitivity in completely non-destructive and real-time manner with rate of ~600 cells/hr, highest range demonstrated to date for state-of-the-art chemical cytometry.

Generation of hydroxyl radicals during photodegradation of chloroacetic acids by 254 nm ultraviolet: A special degradation process revealed by a holistic radical determination methodology

Upon ultraviolet (UV) irradiation, aqueous contaminants may undergo direct and/or indirect photolysis. Direct photolysis refers to transformation of contaminants by UV photon, and indirect photolysis refers to degradation of contaminants by UV-induced reactive species in the presence of photosensitizers. Because hydroxyl radical (•OH) was unexpectedly observed during chloroacetic acids photolysis without using photosensitizer, a question arises regarding whether direct photolysis-induced indirect photolysis (DPIP) was present and how it originated and evolved along the process. To answer these questions, this study employed multiple different yet complementary •OH detection approaches (i.e., probe, scavenger, electron paramagnetic resonance, and hydroxylation products) to prove the presence and role of •OH. Given that hydrogen peroxide (H₂O₂) was produced only in oxygenated water but not in deoxygenated water, we revealed that •OH was mainly generated by reduced oxygen. Meanwhile, several photolysis products like formate, glycolic acid, and glyoxylic acid were able to yield H₂O₂ too, suggesting that they can all trigger formation of •OH under 254 nm UV. In addition to evidences of DPIP phenomenon, this study is also novel in demonstrating a holistic methodology to prove and identify the presence and sources of radicals, which might help enhance understandings of UV processes.

Nanostructured materials as a host matrix to develop robust peroxidases-based nanobiocatalytic systems

Nanostructured materials constitute an interesting and novel class of support matrices for the immobilization of peroxidase enzymes. Owing to the high surface area, robust mechanical stability, outstanding optical, thermal, and electrical properties, nanomaterials have been rightly perceived as immobilization matrices for enzyme immobilization with applications in diverse areas such as nano-biocatalysis, biosensing, drug delivery, antimicrobial activities, solar cells, and environmental protection. Many nano-scale materials have been employed as support matrices for the immobilization of different classes of enzymes. Nanobiocatalysts, enzymes immobilized on nano-size materials, are more stable, catalytically robust, and could be reused and recycled in multiple reaction cycles. In this review, we illustrate the unique structural/functional features and potentialities of nanomaterials-immobilized peroxidase enzymes in different biotechnological applications. After a comprehensive introduction to the immobilized enzymes and nanocarriers, the first section reviewed carbonaceous nanomaterials (carbon nanotube, graphene, and its derivatives) as a host matrix to constitute robust peroxidases-based nanobiocatalytic systems. The second half covers metallic nanomaterials (metals, and metal oxides) and some other novel materials as host carriers for peroxidases immobilization. The next section vetted the potential biotechnological applications of the resulted nanomaterials-immobilized robust peroxidases-based nanobiocatalytic systems. Concluding remarks, trends, and future recommendations for nanomaterial immobilized enzymes are also given.

Assessing the range of enzymatic and oxidative tunability for biosensor design

Development of multi-functional materials and biosensors that can achieve an in situ response designed by the user is a current need in the biomaterials field, especially in complex biological environments, such as inflammation, where multiple enzymatic and oxidative signals are present. In the past decade, there has been extensive research and development of materials chemistries for detecting and monitoring enzymatic activity, as well as for releasing therapeutic and diagnostic agents in regions undergoing oxidative stress. However, there has been limited development of materials in the context of enzymatic and oxidative triggers together, despite their closely tied and overlapping mechanisms. With research focusing on enzymatically and oxidatively triggered materials separately, these systems may be inadequate in monitoring the complexity of inflammatory environments, thus limiting in vivo translatability and diagnostic accuracy. The intention of this review is to highlight a variety of enzymatically and oxidatively triggered materials chemistries to draw attention to the range of synthetic tunability available for the construction of novel biosensors with a spectrum of programmed responses. We focus our discussion on several types of macromolecular sensors, generally classified by the causative material response driving ultimate signal detection. This includes sensing based on degradative processes, conformational changes, supramolecular assembly/disassembly, and nanomaterial interactions, among others. We see each of these classes providing valuable tools toward coalescing current gaps in the biosensing field regarding specificity, selectivity, sensitivity, and flexibility in application. Additionally, by considering the materials chemistry of enzymatically and oxidatively triggered biomaterials in tandem, we hope to encourage synthesis of new biosensors that capitalize on their synergistic roles and overlapping mechanisms in inflammatory environments for applications in disease diagnosis and monitoring.

Polyvalent Nanoobjects for Precision Diagnostics

As our ability to synthesize and modify nanoobjects has improved, efforts to explore nanotechnology for diagnostic purposes have gained momentum. The variety of nanoobjects, especially those with polyvalent properties, displays a wide range of practical and unique properties well suited for applications in various diagnostics. This review briefly covers the broad scope of multivalent nanoobjects and their use in diagnostics, ranging from ex vivo assays and biosensors to in vivo imaging. The nanoobjects discussed here include silica nanoparticles, gold nanoparticles, quantum dots, carbon dots, fullerenes, polymers, dendrimers, liposomes, nanowires, and nanotubes. In this review, we describe recent reports of novel applications of these various nanoobjects, particularly as polyvalent entities designed for diagnostics.

Fluorescent protein nanoparticles: Synthesis and recognition of cellular oxidation damage

Intracellular reactive oxygen species (ROS) generation are associated with many diseases. Lots of studies focus on the detection of intracellular ROS by small fluorescent molecules. However, ROS recognized by biocompatible nanoparticles are relatively less reported. It is widely known that albumin-based nanomaterials possess unique advantages in biomedical applications because they are biodegradable and biocompatible. Herein, fluorescent protein nanoparticles (PNPs) were prepared using BSA as a starting material without introducing extra fluorescent molecules. The blue fluorescent PNPs were well characterized by FL, FTIR, CD, TEM, DLS, etc. It was revealed that the PNPs exhibited two types of emissive centers through FL spectra and the fluorescence lifetimes. Further mechanism study indicated that the fluorescence of the PNPs was mainly derived from three kinds of aromatic amino acids, namely tryptophan, tyrosine and phenylalanine. Moreover, the fluorescence properties of the PNPs were tightly related to pH. The PNPs displayed excellent stabilities under harsh conditions as well as physiological conditions. In addition, the PNPs (200 μg/mL) were nontoxic to HeLa and GES-1 cell lines, showing good biocompatibility. The cellular uptake of PNPs was occurred only when the cells were stressed with glucose oxidase or H₂O₂, thereafter the bright blue fluorescence was observed, indicating that it could be utilized for the recognition of cellular oxidation damage. These findings will offer novel clues for the future synthesis of even brighter protein nanoparticles and their biomedical applications.

Surface functionalisation of polymers

Many applications of polymers require the functionalisation of their surface for use in sensors, composite materials, membranes, microfluidic and biomedical devices and many others. Such surface modifications endow the surface with new properties independent of those of the bulk polymer. This tutorial review describes the different methods, based on very diverse principles, that are available to perform this surface functionalisation, including plasma and UV irradiation, atomic layer deposition, electrochemistry, oxidation, reduction, hydrolysis, the use of radicals and grafting "on" or "from" polymers. The principles of the different methods are briefly described and many examples are given to highlight the possibilities of the methods and the possible applications. A section is devoted to the surface modification of polymeric nanoparticles.

Investigation of the intracellular oxidative stress amplification, safety and anti-tumor effect of a kind of novel redox-responsive micelle

Redox-responsive FSST micelles with good biocompatibility can increase ROS levels in tumor cells and amplify oxidative stress, ultimately inducing apoptosis.

Distinct ON/OFF fluorescence signals from dual-responsive activatable nanoprobes allows detection of inflammation with improved contrast

Visualization of biochemical changes associated with disease is of great clinical significance, as it should allow earlier, more accurate diagnosis than structural imaging, facilitating timely clinical intervention. Herein, we report combining stimuli-responsive polymers and near-infrared fluorescent dyes (emission max: 790 nm) to create robust activatable fluorescent nanoprobes capable of simultaneously detecting acidosis and oxidative stress associated with inflammatory microenvironments. The spectrally-resolved mechanism of fluorescence activation allows removal of unwanted background signal (up to 20-fold reduction) and isolation of a pure activated signal, which enables sensitive and unambiguous localization of inflamed areas; target-to-background ratios reach 22 as early as 3 h post-injection. This new detection platform could have significant clinical impact in early detection of pathologies, individual tailoring of drug therapy, and image-guided tumor resection.

A Novel Sensitive Luminescence Probe Microspheres for Rapid and Efficient Detection of τ-Fluvalinate in Taihu Lake

Fluorescent molecularly imprinted polymers have shown great promise in biological or chemical separations and detection, due to their high stability, selectivity and sensitivity. In this work, fluorescent molecularly imprinted microsphere was synthesized via precipitation polymerization, which could separate efficiently and rapidly detect τ-fluvalinate (a toxic insecticide) in water samples, was reported. The fluorescent imprinted sensor showed excellent stability, outstanding selectivity and the limit of detection low to 12.14 nM, good regeneration ability which still kept good sensitivity after 8 cycling experiments and fluorescence quenching mechanism was illustrated in details. In addition, the fluorescent sensor was further used to detect τ-fluvalinate in real samples from Taihu Lake. Despite the relatively complex components of the environment water, the fluorescent imprinted microspheres sitll showed good recovery, clearly demonstrating the potental value of this smart sensor nanomaterial in environment monitoring.

Diverse Applications of Nanomedicine

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic.

Improved performance of Schiff based ionophore modified with MWCNT for Fe(ii) sensing by potentiometry and voltammetry supported with DFT studies

A novel potentiometric and voltammetric sensor for creating a cationic response for Fe(ii) is introduced.

Ratiometric Sensing of Hydrogen Peroxide Utilizing Conformational Change in Fluorescent Boronic Acid Polymers

We demonstrate that the copolymers containing boronic acid and pyrene units can be utilized for the fluorometric sensing of hydrogen peroxide (H₂O₂) in aqueous solutions. The copolymer exists in a relatively extended conformation in the absence of H₂O₂, whereas the polymer chain is contracted by the reaction of boronic acid moieties with H₂O₂ to form phenol groups. This conformational change induces aggregation of the originally isolated pyrene groups. As a result, relative intensity of excimer emission with respect to monomer emission increases with H₂O₂ concentration. Accordingly, the present methodology enables us to measure H₂O₂ by means of ratiometric fluorescence change in the range of 0-30 μM.

Cobalt phosphide nanowires: an efficient electrocatalyst for enzymeless hydrogen peroxide detection

In this letter, we demonstrate for the first time that cobalt phosphide nanowires (CoP NWs) exhibit remarkable catalytic activity toward electrochemical detection of hydrogen peroxide (H2O2). As an enzymeless H2O2 sensor, such CoP NWs show a fast amperometric response within 5 s and a low detection limit of 0.48 μM. In addition, this nonenzymatic sensor displays good selectivity, long-term stability and excellent reproducibility.

Horseradish peroxidase supported on porous graphene as a novel sensing platform for detection of hydrogen peroxide in living cells sensitively

A viable and simple method for preparing porous graphene network using silver nanoparticles (AgNPs) etching was proposed, and a sensitive biosensor was constructed based on the porous graphene (PGN) and horseradish peroxidase (HRP) to measure the release of H₂O₂ from living cells. Owing to the large surface area and versatile porous structure, the use of nanoporous materials can significantly improve the analysis performance of the biosensor by loading large amounts of enzyme and accelerating diffusion rate. Meanwhile, the constructed electrode exhibited excellent electrochemical performance toward H₂O₂ with a determination limit as low as 0.0267nM and wide linear range of 7 orders of magnitude, which was superior to other H₂O₂ electrochemical sensors. Thus, this novel biosensor can detect the H₂O₂ release from living cells not only under normal physiological conditions (10^-8-10^-7M) but also in emergency state with the increased concentration (~10^-4M). This work provides tremendous potential for real-time tracking of the secretion of H₂O₂ in different types of physiological and pathological investigations.

Physical, Chemical, and Biological Structures based on ROS-Sensitive Moieties that are Able to Respond to Oxidative Microenvironments

Reactive oxygen species (ROS) (H2 O2 , OCl(-) , (•) OH, O2 (-) ) are a family of reactive molecules that are generated intracellularly and are engaged in many biological processes. In physiological concentrations, ROS act as signaling molecules to a number of metabolic pathways; however, in excess they can be harmful to living organisms. Overproduction of ROS has been related to many pathophysiological conditions and a number of studies have been reported in elucidating their mechanism in these conditions. With the aim of harnessing this role, a number of imaging tools and therapeutic compounds have been developed. Here these imaging and therapeutic tools are reviewed and particularly those structures with ROS-sensitivity based on their biomedical applications and their functional groups. There is also a brief discussion about the method of preparation as well as the mechanism of action.

Self-Assembled ROS-Sensitive Polymer-Peptide Therapeutics Incorporating Built-in Reporters for Evaluation of Treatment Efficacy

One of the major challenges in current cancer therapy is to maximize therapeutic effect and evaluate tumor progression under the scheduled treatment protocol. To address these challenges, we synthesized the cytotoxic peptide (KLAKLAK)2 (named KLAK) conjugated amphiphilic poly(β-thioester)s copolymers (H-P-K) composed of reactive oxygen species (ROS) sensitive backbones and hydrophilic polyethylene glycol (PEG) side chains. H-P-K could self-assemble into micelle-like nanoparticles by hydrophobic interaction with copolymer backbones as cores and PEG and KLAK as shells. The assembled polymer-peptide nanoparticles remarkably improved cellular internalization and accumulation of therapeutic KLAK in cells. Compared to free KLAK peptide, the antitumor activity of H-P-K was significantly enhanced up to ∼400 times, suggesting the effectiveness of the nanoscaled polymer-peptide conjugation as biopharmaceuticals. The higher antitumor activity of nanoparticles was attributed to the efficient disruption of mitochondrial membranes and subsequent excessive ROS production in cells. To realize the ROS monitoring and treatment evaluation, we encapsulated squaraine (SQ) dyes as built-in reporters in ROS-sensitive H-P-K micelles. The overgenerated ROS around mitochondria stimulated the swelling of nanoparticles and subsequent release of SQ, which formed H-aggregates and significantly increased the photoacoustic (PA) signal. We believed that this self-assembled polymer-peptide nanotherapeutics incorporating built-in reporters has great potential for high antitumor performance and in situ treatment evaluation.

Multifunctional self-assembled polymeric nanoprobes for FRET-based ratiometric detection of mitochondrial H2O2 in living cells

A ratiometric, multifunctional nanoprobe was prepared consisting of a self-assembled polymeric micelle as the carrier, tetraphenylethene (TPE) as the donor, fluorescent boronate as the H2O2-responsive acceptor, and triphenylphosphonium as a mitochondria-targeted moiety. The assembled nanoparticles could detect both exogenous and endogenous mitochondrial H2O2 changes in living cells.

Mesoporous Pt Nanotubes as a Novel Sensing Platform for Sensitive Detection of Intracellular Hydrogen Peroxide

Controlling the shape, structure, and surface morphology of nanomaterials is of great significance in optimizing sensitivity and catalytic performances in biosensing applications. The main goal of employing Pt-based nanomaterials is to increase their utilization efficiency due to their high cost. Herein, we report the synthesis of mesoporous Pt nanotubes using Pluronic P123 as soft templates and Ag nanowires with 50 nm in diameter as hard templates. The resultant materials with unique structures show high sensitivity and stability toward H2O2 detection with low cellular cytotoxicity. The high sensitivity and catalytic properties are attributed to the mesopores and hollow structures making the inner Pt surfaces accessible to reaction media and enlarging the total surface area and one-dimensional structure facilitating the mass diffusion rate.

Hierarchical supramolecules and organization using boronic acid building blocks

Current progress on hierarchical supramolecules using boronic acids has been highlighted in this feature article. The feasibility of the structure-directing ability is fully discussed from the standpoint of the generation of new smart materials.

Development of organically modified silica nanoparticles for monitoring the intracellular level of oxygen using a frequency-domain FLIM platform

The dynamic quenching of luminescence derived from Ru(dpp₃)²⁺-doped ORMOSIL nanoparticles is used for monitoring of the intracellular oxygen concentration.

Highly fluorescent amidine/schiff base dual-modified polyacrylonitrile nanoparticles for selective and sensitive detection of copper ions in living cells

Highly fluorescent surface modified polyacrylonitrile nanoparticles (PAN NPs) of 50 nm diameter were fabricated for selective Cu(2+) sensing. After surface modification, the PAN NPs were converted to amidine/Schiff base dual-modified PAN nanoparticles (tPAN NPs) with a Cu(2+) sensing property and high QY (0.19). The selectivity of tPAN NPs for Cu(2+) is much higher than that of other metal ions due to the fact that amidine group on the surface of tPAN NPs has a higher binding affinity with Cu(2+). The effect of other metal ions on the fluorescence intensity of the tPAN NPs was also studied, and other metal ions showed a low interference response in the detection of Cu(2+). Furthermore, as a metal ion chelator, ethylenediaminetetraacetate can competitively interact with Cu(2+) to recover the quenched fluorescence of tPAN NPs. The tPAN NPs are easily introduced into cells and exhibit low toxicity, enabling their use as a fluorescence sensor for Cu(2+) in living cells. The tPAN NPs provide a new direction for the development of copper ion sensors in living cells.

Synthesis of Copolymers from Phenylboronic Acid-Installed Cyclic Carbonates

Organoboron polymers play important roles in biomedical applications. An ample number of monomers bearing boronic acid derivatives have been synthesized, particularly focusing on controlled free radical polymerization methods. Organoboron polymers synthesized by ring-opening polymerization (ROP) routes are far less explored. We report on the ROP of boronic acid-installed cyclic carbonates, catalyzed by DBU from a poly(ethylene glycol) macroinitiator. Controlled polymerization proceeded to relatively high conversions (∼70%) with low polydispersity. Deprotection of the copolymer to generate the boronic acid pendant group was readily achieved by displacement of the protecting group with free diboronic acid. The resulting amphiphilic copolymers self-assembled in water into spherical nanoparticles or vesicles, depending on hydrophilic/hydrophobic ratio. We envision these functional carbonates finding direct applications for core stabilization of biodegradable amphiphilic assemblies or in drug and protein encapsulation.

A targeted and FRET-based ratiometric fluorescent nanoprobe for imaging mitochondrial hydrogen peroxide in living cells

Hydrogen peroxide (H2 O2 ) is a prominent member of the reactive oxygen species family and plays crucial roles in living organisms, thus detecting H2 O2 and elucidating its biological functions has become an important area of biological and biomedical research. Herein, a multifunctional fluorescent nanoprobe is demonstrated for detecting mitochondrial H2 O2 . The nanoprobe is prepared by covalently linking a mitochondria-targeting ligand (triphenylphosphonium, TPP) and a H2 O2 recognition element (PFl) onto carbon dots (CDs). For this nanoprobe, the CD serves as the carrier and the FRET donor. In the presence of H2 O2 , the PFl moieties on a CD undergo structural and spectral conversion, affording the nanoplatform a FRET-based ratiometric probe for H2 O2 . The nanoprobe displays excellent water dispersibility, high sensitivity and selectivity, satisfactory cell permeability, and very low cytotoxicity. Following the living cell uptake, this nanoprobe can specifically target and stain the mitochondria; and it can detect the exogenous H2 O2 in L929 cells, as well as the endogenously produced mitochondrial H2 O2 in Raw 264.7 cells upon stimulation by PMA. This study shows that CDs can serve as promising nano-carriers for fabricating practical multifunctional fluorescent nanosensors.