Mitochondria-Targetable Near-Infrared Fluorescent Probe for Visualization of Hydrogen Peroxide in Lung Injury, Liver Injury, and Tumor Models.

Hydrogen peroxide (H2O2) overexpressed in mitochondria has been regarded as a key biomarker in the pathological processes of various diseases. However, there is currently a lack of suitable mitochondria-targetable near-infrared (NIR) probes for the visualization of H2O2 in multiple diseases, such as PM2.5 exposure-induced lung injury, hepatic ischemia-reperfusion injury (HIRI), nonalcoholic fatty liver (NAFL), hepatic fibrosis (HF), and malignant tumor tissues containing clinical cancer patient samples. Herein, we conceived a novel NIR fluorescent probe (HCy-H2O2) by introducing pentafluorobenzenesulfonyl as a H2O2 sensing unit into the NIR hemicyanine platform. HCy-H2O2 exhibits good sensitivity and selectivity toward H2O2, accompanied by a remarkable "turn-on" fluorescence signal at 720 nm. Meanwhile, HCy-H2O2 has stable mitochondria-targetable ability and permits monitoring of the up-generated H2O2 level during mitophagy. Furthermore, using HCy-H2O2, we have successfully observed an overproduced mitochondrial H2O2 in ambient PM2.5 exposure-induced lung injury, HIRI, NAFL, and HF models through NIR fluorescence imaging. Significantly, the visualization of H2O2 has been achieved in both tumor-bear mice as well as surgical specimens of cancer patients, making HCy-H2O2 a promising tool for cancer diagnosis and imaging-guided surgery.

Bovine Serum Albumin Template-Mediated Fabrication of Ruthenium Dioxide/Multiwalled Carbon Nanotubes: High-Performance Electrochemical Dopamine Biosensing in Human Serum.

The presence of abnormal dopamine (DA) levels may cause serious neurological disorders, therefore, the quantitative analysis of DA and its related research are of great significance for ensuring health. Herein, the bovine serum albumin (BSA) template method has been proposed for the preparation of catalytically high-performance ruthenium dioxide/multiwalled carbon nanotube (RuO2/MWCNT) nanocomposites. The incorporation of MWCNTs has improved the active surface area and conductivity while effectively preventing the aggregation of RuO2 nanoparticles. The outstanding electrocatalytic performance of RuO2/MWCNTs has promoted the electro-oxidation of DA at neutral pH. The electrochemical sensing platform based on RuO2/MWCNTs has demonstrated a wide linear range (0.5 to 111.1 µM), low detection limit (0.167 µM), excellent selectivity, long-term stability, and good reproducibility for DA detection. The satisfactory recovery range of 94.7% to 103% exhibited by the proposed sensing podium in serum samples signifies its potential for analytical applications. The aforementioned results reveal that RuO2/MWCNT nanostructures hold promising aptitude in the electrochemical sensor to detect DA in real samples, further offering broad prospects in clinical and medical diagnosis.

Simple strategy for dual-responsive ratio electrochemical-colorimetric detection of nitrite in food and environment.

A dual-responsive ratio electrochemical-colorimetric method for nitrite (NO2-) is established based on the combination of nanoenzyme (Mn3O4) catalysis with diazotization reactions. The Mn3O4 can oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue TMBox. The NO2- induces the diazotization reaction of TMBox, leading to a decrease of  the signal at 652 nm and the generation of a new signal from diazotized TMBox at 445 nm. Furthermore, the presence of NO2- reduces the electrochemical oxidation signal of TMB and simultaneously provides its electrochemical signal. Compared with traditional single-mode detection, dual-mode detection offers higher sensitivity, lower detection limits, and better interference resistance. The inherent advantages of this method make it feasible to detect NO2- in real samples, offering broad prospects for applications in food safety and environmental monitoring.

Mitochondria-Targeting Multifunctional Fluorescent Probe toward Polarity, Viscosity, and ONOO- and Cell Imaging.

Abnormal changes occurring in the mitochondrial microenvironment are important markers indicating mitochondrial and cell dysfunction. Herein, we designed and synthesized a multifunctional fluorescent probe DPB that responds to polarity, viscosity, and peroxynitrite (ONOO-). DPB is composed of an electron donor (diethylamine group) and electron acceptor (coumarin, pyridine cations, and phenylboronic acid esters), in which the pyridine group with a positive charge is responsible for targeting to mitochondria. D-π-A structure with strong intramolecular charge transfer (ICT) and twisted intramolecular charge transfer (TICT) properties give rise to respond to polarity and viscosity. The introduction of cyanogroup and phenylboronic acid esters increases the electrophilicity of the probe, which is prone to oxidation triggered by ONOO-. The integrated architecture satisfies the multiple response requirements. As the polarity increases, the fluorescence intensity of probe DPB at 470 nm is quenched by 97%. At 658 nm, the fluorescence intensity of DPB increases with viscosity and decreases with the concentration of ONOO-. Furthermore, the probe is not only successfully used to monitor mitochondrial polarity, viscosity, and endogenous/exogenous ONOO- level fluctuations but also to distinguish cancer cells from normal cells by multiple parameters. Therefore, as-prepared probe provides a reliable tool for better understanding of the mitochondrial microenvironment and also a potential approach for the diagnosis of disease.

Multifunctional Fluorescent Probe for Simultaneous Detection of ONOO-, Viscosity, and Polarity and Its Application in Ferroptosis and Cancer Models.

Intracellular peroxynitrite anions (ONOO-) and microenvironments (such as viscosity and polarity) play an important role in maintaining redox homeostasis, regulating diffusion, transportation, and signal transduction in living cells. The abnormality of these factors is often closely related to various physiological/pathological processes. However, owing to the lack of suitable probes, the simultaneous visualization of ONOO-, viscosity, and polarity in ferroptosis and cancer models has not been achieved. To meet urgent needs, we presented a multifunctional near-infrared (NIR) fluorescent probe, named MQA-P, for simultaneously detecting ONOO-, viscosity, and polarity within mitochondria. The probe exhibited a remarkable turn-on response to ONOO- with the far-red emission of about 645 nm and was highly sensitive to viscosity/polarity in the NIR channel with λem > 704 nm. Facilitated by MQA-P, for the first time, we revealed that erastin-induced ferroptosis was accompanied by a significant upregulation of ONOO- and an increase of viscosity (or decrease of polarity) at the same time. Moreover, the concurrent use of ONOO-, viscosity, and polarity for the diagnosis of cancer has been successfully achieved not only at cell/tissue levels but also in tumor mice models. Compared with detecting only one factor, this simultaneous detection of multimarkers provides a more sensitive and reliable method/tool for tracking ferroptosis-related pathological processes and cancer diagnosis, holding great potential in preclinical research, medical diagnosis, and imaging-guided surgery.

Rational Design of Orange-Red Emissive Carbon Dots for Tracing Lysosomal Viscosity Dynamics in Living Cells and Zebrafish.

Lysosomal viscosity is an essential microenvironment parameter in lysosomes, which is closely associated to the occurrence and development of various diseases, including cancer. Thus, accurately quantifying lysosomal viscosity changes is highly desirable for a better understanding of the dynamics and biological functions of lysosomes. In this study, lysosome self-targetable orange-red emissive carbon dots (OR-CDs) were rationally designed and developed for monitoring lysosomal viscosity fluctuations. The enhanced fluorescence of OR-CDs could be obviously observed as the viscosity increased from 1.07 to 950 cP. Moreover, the as-prepared OR-CDs could quickly enter cells for lysosome-targeting imaging and visualize viscosity variations in living cells and zebrafish. More importantly, by utilizing OR-CDs, we successfully achieved tracing the variations in lysosomal viscosity during the autophagy process. Additionally, as cancer cells possess high viscosity than normal cells, the OR-CDs have been effectively utilized for cancer imaging from cell, tissue, and organ to in vivo levels. It is expected that the developed OR-CDs not only provide a meaningful tool for visualizing investigations of lysosome viscosity-related diseases but also shed light on the development based on the nanomaterial for the clinical diagnosis of cancer.

Engineering a gold nanoparticles-carbon dots nanocomposite with pH-flexibility for monitoring hydrogen peroxide released from living cells.

Constructing nanozymes with satisfactory catalytic efficiency under physiological conditions is still in great demand for facilitating the advancement of biocatalysts. We herein present a gold nanoparticles-carbon dots nanocomposite (Au-CDs) as an efficient photo-activated nanozyme for monitoring H2O2 released from living cells. The integration of CDs with AuNPs remarkably accelerates the catalytic activity at neutral pH via engaging Mn3+ ions as the mediators. Meanwhile, the reserved cyclodextrin cavities also enhance the adsorption capacity towards chromogenic substrates through host-guest interactions. Moreover, taking advantage of the inhibitory effect of H2O2 on the photo-oxidation ability of the Au-CDs nanocomposite, the Au-CDs based colorimetric method was able to realize in situ assessment of the hydrogen peroxide (H2O2) released from living cells. This method paves a new way to establish a promising biosensing platform for unraveling biological events.

A novel electrochemical sensor based on AuPd/UiO-66-NH2/GN composites for sensitive dopamine detection.

Metal-organic frameworks (MOFs) have emerged as interesting nanomaterials owing to their large surface area, high porosity, tunable pore architecture and easy functionalization. However, an inferior electrical conductivity hinders their application in electrochemical sensing. In this paper, gold-palladium alloy/UiO-66-NH2/graphene (AuPd/UiO-66-NH2/GN) composites were synthesized by loading alloys on the surfaces of MOFs and then attaching them to the graphene surface. The addition of metal nanoparticles and graphene enhanced the electron transfer ability of MOFs. Then, composites were used to modify a glassy carbon electrode (GCE) to construct a sensitive dopamine (DA) electrochemical sensor. The developed sensor manifested two linear relationships in lower concentration ranges and in higher concentration ranges with a 0.21 × 10-6 mol L-1 low detection limit (3σ/k) under optimal conditions. The results certified that the constructed sensor had high selectivity, excellent reproducibility and good stability, and had been used successfully for DA detection in actual human serum samples.

The highly sensitive "turn-on" detection of morin using fluorescent nitrogen-doped carbon dots.

Herein, a novel "turn-on" fluorescent sensor was designed based on nitrogen-doped carbon dots (N-CDs) for the highly sensitive determination of morin. The N-CDs with orange fluorescent emission were prepared using neutral red and poly(ethyleneimine) as main sources via a hydrothermal approach. Interestingly, an enhanced fluorescence of N-CDs could be observed with the introduction of morin, which was attributed to the aggregation-induced emission-enhancement (AIEE) mechanism. The N-CDs presented a high sensitivity of fluorescence response to morin in the concentration range of 0.033-12.83 µM with a satisfactory detection limit of 29 nM. This method was also utilized for the quantitative determination of morin in human urine and serum samples with recoveries of 97.60%-103.90%. Moreover, the fluorescent hydrogel was further prepared by incorporating N-CDs into agarose and integrated with a smartphone-assisted platform, enabling semi-quantitative visual morin detection. Notably, this fluorescent sensor could also be applied for intracellular morin imaging due to its excellent hypotoxicity and biocompatibility, demonstrating that the proposed methodology holds great promise for biosensing applications.

A selective electrochemical chiral interface based on a carboxymethyl-ß-cyclodextrin/Pd@Au nanoparticles/3D reduced graphene oxide nanocomposite for tyrosine enantiomer recognition.

Palladium@gold nanoparticle modified three-dimensional-reduced graphene oxide (3D-rGO/Pd@Au) was coupled with carboxymethyl-ß-cyclodextrin to form a novel nanocomposite (3D-rGO/Pd@Au/CM-ß-CD). The 3D-rGO/Pd@Au/CM-ß-CD served as a chiral sensing interface for the electrochemical enantiorecognition of tyrosine (Tyr) via a differential pulse voltammetry (DPV) approach. The 3D-rGO/Pd@Au demonstrates good electrical conductivity and efficient catalytic activity as an electrochemical indicator. Simultaneously, the CM-ß-CD displays a supramolecular chiral selectivity to reveal a higher binding affinity to the target L-tyrosine (L-Tyr) than to D-tyrosine (D-Tyr). Under the optimized determining conditions, the oxidation peak current ratio of L-Tyr to D-Tyr (IL/ID) was 2.12, meanwhile, the peak currents of the two isomers were linearly proportional to the concentration over the range of 0.8-130 µM with LODs of 52 nM and 96 nM for L- and D-Tyr (S/N = 3), respectively. This approach exhibits distinguished sensitivity, excellent selectivity and good reproducibility, as well as great stability, which can accurately determine the relative content of L- or D-Tyr enantiomers in a racemic solution.

A bifunctional fluorescence probe for dual-channel detecting of mitochondrial viscosity and endogenous/exogenous peroxynitrite.

The irregular viscosity in the mitochondrial can induce mitochondrial dysfunction. The content of peroxynitrite (ONOO-) is related to various physiological and pathological processes. However, many mitochondrial probes only realized the detection of viscosity or ONOO- in single channel, thus it is necessary to explore single fluorescence probe for dual-detecting mitochondrial viscosity and ONOO-. In this work, we designed and synthesized a novel fluorescence probe (PV) for dual-detecting viscosity and ONOO-, which was composed by intergrating a ONOO-- responsive arlyboronate with a twisting intramolecular charge transfer (TICT) mechanism and possessed the mitochondria-targeting ability due to its pyridinium cation. PV exhibited a significant increase in viscosity with red emission at 582 nm and high sensitivity to ONOO- levels with yellow emission at 507 nm. PV was also applied to living systems (including living cells and zebrafish) for viscosity and ONOO- detection using two different channels. Moreover, the ability of PV to track mitophagy may make ONOO- a powerful tool for its role in mitophagy.

Lipid Droplet-Specific Fluorescent Probe for In Vivo Visualization of Polarity in Fatty Liver, Inflammation, and Cancer Models.

Elucidating the intrinsic relationship between diseases and lipid droplet (LD) polarity remains a great challenge owing to the lack of the research on multiple disease models. Until now, the visualization of abnormal LD polarity in models of inflammation and clinical cancer patient samples has not been achieved. To meet the urgent challenge, we facilely synthesized a robust LD-specific and polarity-sensitive fluorescent probe (LD-TTP), which consists of a triphenylamine segment as an electron-donor group (D) and a pyridinium as an electron-acceptor moiety (A), forming a typical D-π-A molecular configuration. Owing to the unique intramolecular charge transfer effect, LD-TTP exhibits high sensitivity to polarity change in the linear range from Δf = 0.258 to 0.312, with over 278-fold fluorescence enhancement. Moreover, we revealed that LD-TTP possessed satisfactory ability for sensitively monitoring LD-polarity changes in living cells. Using LD-TTP, we first demonstrated the detection of LD-polarity changes in fatty liver tissues and inflammatory living mice via confocal laser scanning fluorescence imaging. Surprisingly, the visualization of LD polarity has been achieved not only at the cellular levels and living organs but also in surgical specimens from cancer patients, thus holding great potential in the clinical diagnosis of human cancer. All these features render LD-TTP an effective tool for medical diagnosis of LD polarity-related diseases.

Real-Time Monitoring Mitochondrial Viscosity during Mitophagy Using a Mitochondria-Immobilized Near-Infrared Aggregation-Induced Emission Probe.

Mitophagy plays a crucial role in maintaining intracellular homeostasis through the removal of dysfunctional mitochondria and recycling their constituents in a lysosome-degradative pathway, which leads to microenvironmental changes within mitochondria, such as the pH, viscosity, and polarity. However, most of the mitochondrial fluorescence viscosity probes only rely on electrostatic attraction and readily leak out from the mitochondria during mitophagy with a decreased membrane potential, thus easily leading to an inaccurate detection of viscosity changes. In this work, we report a mitochondria-immobilized NIR-emissive aggregation-induced emission (AIE) probe CS-Py-BC, which allows for an off-on fluorescence response to viscosity, thus enabling the real-time monitoring viscosity variation during mitophagy. This system consists of a cyanostilbene skeleton as the AIE active core and viscosity-sensitive unit, a pyridinium cation for the mitochondria-targeting group, and a benzyl chloride subunit that induces mitochondrial immobilization. As the viscosity increased from 0.903 cP (0% glycerol) to 965 cP (99% glycerol), CS-Py-BC exhibited an about 92-fold increase in fluorescence intensity at 650 nm, which might be attributed to the restriction of rotation and inhibition of twisted intramolecular charge transfer in a high viscosity system. We also revealed that CS-Py-BC could be well immobilized onto mitochondria, regardless of the mitochondrial membrane potential fluctuation. Most importantly, using CS-Py-BC, we have successfully visualized the increased mitochondrial viscosity during starvation or rapamycin-induced mitophagy in real time. All these features render CS-Py-BC a promising candidate to investigate mitophagy-associated dynamic physiological and pathological processes.

Ratiometric sensing of Zn2+ with a new benzothiazole-based fluorescent sensor and living cell imaging.

A new fluorescent probe, 3-(benzo[d]thiazol-2-yl)-5-bromosalicylaldehyde-4N-phenyl thiosemicarbazone (BTT), for ratiometric sensing of Zn2+ ions in methanol/HEPES buffer solution (3 : 2, pH = 7.4) is reported in this paper. The presence of Zn2+ ions yields a significant blue shift in the maximum emission of BTT from 570 nm to 488 nm, accompanied by a clear color change from orange to green. This emission change of BTT upon binding to Zn2+ in a 1 : 1 ratio may be due to the block of excited state intramolecular proton transfer (ESIPT) as well as chelation enhanced fluorescence (CHEF) on complex formation. The limit of detection (LOD) determined for Zn2+ quantitation was down to 37.7 nM. In addition, the probe BTT displays the ability to image both exogenous Zn2+ ions loaded into HeLa cells and endogenous Zn2+ distribution in living SH-SY5Y neuroblastoma cells.

Alizarin-based molecular probes for the detection of hydrogen peroxide and peroxynitrite.

Phenol fluorophores are a large family of fluorophores, which have attracted more and more attention in the design of probes. Using the self-assembly of aromatic boronic acid with Alizarin Red S (ARS) and Gallein (GAL), the novel chemosensors ARS-CBA and GAL-CBA were provided for hydrogen peroxide (H2O2), which demonstrated their ability to detect H2O2 with indicator displacement assay (IDA) by colorimetric and electrochemical measurements. After ARS-CBA and GAL-CBA reacted with H2O2, the systems displayed a red-shifted visible color change in aqueous media and off-on electrochemical signals showing generation of phenol. The chemosensor ARS-CBA also had good performance in fluorometric measurements and turn-off fluorescent response indicated removal of aromatic boronic acid. In addition, a designed near-infrared (NIR) dual-modal fluorescent probe alizarin blue S (ABS) was used for peroxynitrite (ONOO-) with a visible colorimetric change in dimethyl sulfoxide (DMSO) and "on-off" fluorescent response indicating the oxidation of hydroxyl. The flexible Phenol fluorophores are allowed to prepare multiple fluorescent probes towards H2O2 or ONOO- for environmental and physiological applications.

N-Doped carbon dots for the fluorescence and colorimetry dual-mode detection of curcumin.

Nitrogen doped carbon dots (N-CDs) were synthesized by a one-step hydrothermal method with dopamine and ethylenediamine. The as-prepared N-CDs were characterized via transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fluorescence spectrophotometer, UV-Vis spectrophotometry and Fourier transform infrared spectroscopy (FTIR). The average particle dimension of the as-prepared N-CDs was 2.68 nm, and the best excitation and emission wavelengths were 405 nm and 535 nm, separately. N-CDs exhibits excellent selectivity and sensitivity to detect the curcumin (Cur), attaining a wider linear range of 97.5 nM-67.9 µM and a limit of detection (LOD) of as low as 94 nM. Interestingly, N-CDs can also give responsive signals of a visible colour change (yellow to red). Moreover, a novel fluorescent/colorimetric dual-mode method has been successfully employed for the determination of Cur in real samples with good recoveries (94%-110%) and precision (RSD = 0.3-2.9%).

Orange emissive carbon nanodots for fluorescent and colorimetric bimodal discrimination of Cu2+ and pH.

We have facilely synthesized orange emissive carbon nanodots (O-CDs) via a hydrothermal method using citric acid and 5-aminosalicylic acid. The obtained O-CDs show the excellent characteristics of excitation independence, low toxicity, fabulous photostability and superior biocompatibility. Based on these captivating properties, as-prepared O-CDs have been successfully implemented as a multi-functional sensing platform for fluorescent and colorimetric bimodal recognition of Cu2+ and pH. Upon adding Cu2+, the orange fluorescence of the O-CDs is evidently quenched with a linear range of 0 µM-300 µM, and a detection limit of 28 nM. Additionally, as the pH increases from 7.0 to 10.2, the O-CDs manifest an obvious decrease in orange fluorescence, which shows a pKa value of 8.73 and excellent linearity in the pH range of 8.0-9.2. Appealingly, the laser confocal imaging of O-CD-stained cells demonstrates that the fluctuations of Cu2+ and pH can be visualized in living cells.

A label-free fluorescent aptasensor based on HCR and G-quadruplex DNAzymes for the detection of prostate-specific antigen.

Prostate specific antigen (PSA) has been considered as the most potential serological biomarker for the early stage detection of prostate cancer. Here, a label-free fluorescence aptasensing strategy for detecting PSA based on hybridization chain reaction (HCR) and G-quadruplex DNAzymes has been developed. This designed strategy consists of three DNA probes, aptamer probe (AP), hairpin probe 1 (H1) and hairpin probe 2 (H2). In the presence of target PSA, the aptamer sequences in AP specifically recognized PSA to form a PSA-aptamer complex, causing an AP conformation change and thus releasing the initiator, which triggered the chain-like assembly of H1 and H2 that yielded extended nicked double-stranded DNA through HCR. Upon the addition of hemin, the G-rich segments at the end of H1 and H2 self-assembled into the peroxidase-mimicking hemin/G-quadruplex DNAzymes, which catalyzed the hydrogen peroxide-mediated oxidation of thiamine to give a fluorescence signal dependent on the concentration of PSA. Under optimal conditions, a limit of detection of 0.05 nM and a linear range from 0.1 nM to 1 nM (R2 = 0.9942) were achieved by this assay. In addition, other interfering proteins, such as IgG, AFP and CEA, did not produce any significant change in the fluorescence intensity response, indicating good selectivity of this sensor for PSA detection. Finally, this proposed aptasensor was successfully used for diluted serum samples.

Development of a piperazinyl-NBD-based fluorescent probe and its dual-channel detection for hydrogen sulfide.

To selectively detect H2S based on the thiolysis reaction of 7-nitro-1,2,3-benzoxadiazole (NBD), amines attracted increasing attention since NBD amine is regarded as a new H2S reaction site. Herein, a novel fluorescent probe, triphenylamine piperazine NBD (TPA-Pz-NBD), was developed. The results showed that it exhibited high selectivity towards H2S via fluorescence spectroscopy and solution color. Furthermore, TPA-Pz-NBD not only detected H2S by a dual-channel, turn-on fluorescence signal at 500 nm and turn-off fluorescence signal at 545 nm, respectively, but also displayed a wide detection range of 0-125 µM. In addition, living cell imaging results indicated that TPA-Pz-NBD holds potential for the detection of intracellular H2S.

N, Cl-doped carbon dots for fluorescence and colorimetric dual-mode detection of water in tetrahydrofuran and development of a paper-based sensor.

N, Cl-doped carbon dots (N, Cl-CDs) were prepared by hydrothermal method from rhodamine B (RhB) and ethylenediamine (EDA). The resulting N, Cl-CDs exhibited fascinating solvent dependence and strict excitation independence. As the polarity of the solvent increased (from tetrahydrofuran (THF) to water), the emission spectrum of N, Cl-CDs was redshifted and the fluorescence efficiency decreased, which were attributed to hydrogen bond-induced aggregation. Taking advantage of these attributes, the N, Cl-CDs were used as suitable probes for fluorescence and colorimetric dual-mode detection of water in THF. The linear relationship was 0.5-100% water with the detection limit down to 0.093%. Moreover, the sensing platform was converted into a paper-based sensor for handy, real-time, and visible humidity sensing. N, Cl-CDs/PVA films were fabricated and realized continuously tunable solid-state fluorescence, further expanding their practical application.