A two-photon fluorescent probe for lysosomal zinc ions

Advances in Organic Fluorescent Probes for Intracellular Zn2+ Detection and Bioimaging

Zinc ions (Zn2+) play a key role in maintaining and regulating protein structures and functions. To better understand the intracellular Zn2+ homeostasis and signaling role, various fluorescent sensors have been developed that allow the monitoring of Zn2+ concentrations and bioimaging in live cells in real time. This review highlights the recent development of organic fluorescent probes for the detection and imaging of intracellular Zn2+, including the design and construction of the probes, fluorescent response mechanisms, and their applications to intracellular Zn2+ detection and imaging on-site. Finally, the current challenges and prospects are discussed.

A novel diarylethene-based fluorescence sensor for Zn2+ detection and its application

A series of fluorometric sensors of Zn2+ have been synthesized due to the significant function of Zn2+ in the human body and environment. However, most of probes reported for detecting Zn2+ have high detection limit or low sensitivity. In this paper, an original Zn2+ sensor, namely 1o, was synthesized by diarylethene and 2-aminobenzamide. When Zn2+ was added, the fluorescence intensity of 1o increased by 11 times within 10 s, along with a fluorescence color change from dark to bright blue, and the detection limit (LOD) was calculated to be 0.329 μM. According to Job's plot curves, the binding mode of 1o and Zn2+ was measured as 1:1, which was further proved by 1H NMR spectra, HRMS and FT-IR spectra. The logic circuit was designed to take advantage of the fact that the fluorescence intensity of 1o can be controlled by Zn2+, EDTA, UV and Vis. In addition, Zn2+ in actual water samples were tested, in which the recovery rate of Zn2+ was between 96.5 % and 109 %. Furthermore, 1o was successfully made into a fluorescent test strip, which could be used to detect Zn2+ in the environment economically and conveniently.

Fluorescent Probes Design Strategies for Imaging Mitochondria and Lysosomes

Modern cellular biology faces several major obstacles, such as the determination of the concentration of active sites corresponding to chemical substances. In recent years, the popular small-molecule fluorescent probes have completely changed the understanding of cellular biology through their high sensitivity toward specific substances in various organisms. Mitochondria and lysosomes are significant organelles in various organisms, and their interaction is closely related to the development of various diseases. The investigation of their structure and function has gathered tremendous attention from biologists. The advanced nanoscopic technologies have replaced the diffraction-limited conventional imaging techniques and have been developed to explore the unknown aspects of mitochondria and lysosomes with a sub-diffraction resolution. Recent progress in this field has yielded several excellent mitochondria- and lysosome-targeted fluorescent probes, some of which have demonstrated significant biological applications. Herein, we review studies that have been carried out to date and suggest future research directions that will harness the considerable potential of mitochondria- and lysosome-targeted fluorescent probes.

A fluorescent pH probe for evaluating the freshness of chicken breast meat

A fluorescent probe, Nap-MOR, based on the naphthalimide fluorophore, was designed and developed for pH measurement in aqueous solutions. Nap-MOR had a close linear relationship between fluorescence intensity and pH, in the range 4.5-8, which covers the full range of pH found in normal fresh, defective and spoiled meat. pH measurement with Nap-MOR was free from interference by a wide range of ions and biochemicals found in meat and the results were not significantly different in comparison with a pH meter. Therefore, Nap-MOR is a robust and convenient way to evaluate the freshness of chicken breast meat by measuring its pH.

A red-emissive two-photon fluorescent probe for mitochondrial sodium ions in live tissue

A cyclocyanine (CC)-based organic small molecule two-photon (TP) fluorescent probe (CCNa1) was developed for mitochondrial sodium ion sensing. CCNa1 exhibits a low solvatochromic shift and strong TP fluorescence enhancement at 575 nm upon binding to Na⁺ and is insensitive to other metal ions and to pH. CCNa1 demonstrated fast cell loading ability, biocompatibility, and sensitive response to mitochondrial Na⁺ influx in live cells and mouse brain tissue.

Real-time detection and imaging of exogenous and endogenous Zn2+ in the PC12 cell model of depression with a NIR fluorescent probe

Depression is closely related to overactivation of N-methyl-d-aspartic acid (NMDA) receptors, and Zn2+ is a vital NMDA receptor modulator involved in the pathophysiological and physiological processes of depression. Therefore, quantitative and real-time detection of Zn2+ is very important for understanding the pathogenesis of depression. In this work, a near-infrared (NIR) fluorescent probe ISO-DPA was designed and synthesized for Zn2+ detection with a large Stokes shift (185 nm), high quantum yield (up to 44%), high sensitivity (LOD = 0.106 μM) and good pH stability. The probe showed rapid response within 10 s, accompanied by a distinct fluorescence change from faint to bright pink with the fluorescence intensity increasing 4.5-fold. Moreover, the sensing mechanism of ISO-DPA towards Zn2+ was supported by MALDI-TOF-MS and Job's plot. The probe ISO-DPA could detect instantaneous variation of exogenous and endogenous Zn2+ in PC12 cells. The bioimaging results reveal the increase of the endogenous Zn2+ concentration in PC12 cells under the oxidative stress induced by glutamate and confirm that overactivation of NMDA receptors results in an increase of the Zn2+ level. All the results proved that ISO-DPA is an excellent probe for detecting Zn2+ in solution and living cells and could help us better understand Zn2+ associated pathogenesis of depression.

Optically superior fluorescent probes for selective imaging of cells, tumors, and reactive chemical species

Fluorescent chemical probes have become powerful tools to study biological events in living cells. They provide a great opportunity to quantitatively and qualitatively analyze the physiological and biochemical properties of living cells in real time. The ability of researchers to manipulate these probes for a desired specific purpose has turned many heads in the scientific community. Despite a slow start, fluorescent probe research has seen exponential growth over the last decade in the world. This change required some adventurous and creative scientists from different fields-like biology, medicine, and chemistry-to come together to facilitate the constant expansion of this field. This review article introduces some fundamental concepts related to fluorescent probe designing and development. It also summarizes various fluorescent probes with superior optical properties used in fields like cell biology, cellular imaging, medical research, and cancer diagnosis. It is hoped that this article will encourage more young and creative scientists to contribute their talents to this field.

Functionalized mesoporous silica as a fluorescence sensor for selective detection of Hg2+ in aqueous medium

We combined the virtues of mesoporous silica and organic functional groups to develop a hybrid fluorescent sensor, PyU-SBA-15, with excellent ability to detect Hg²⁺ in aqueous medium with high selectivity. In this sensor, the pyrene fluorophore acts as the reporter and the urea unit acts as the receptor during Hg²⁺ determination. The control material, PyH-SBA-15, which lacks a carbonyl group in the receptor portion, did not display metal-ion selectivity, thereby demonstrating that introducing an additional metal-chelating unit is necessary to improve the metal-ion selectivity of the hybrid sensor. When the concentration of Hg²⁺ was increased, the fluorescence emission intensities of PyU-SBA-15 at 379, 398, and 476 nm gradually decreased. The emission intensity at 379 nm was linearly proportional to Hg²⁺ concentrations in the range of 0-1.0 × 10^-4 M, and the sensor was determined to have a detection limit of 9.92 × 10^-8 M. This work provides an effective strategy for improving or modulating the metal-ion selectivity of fluorescent sensors based on organic-inorganic hybrid mesoporous silica systems.

Two-photon small-molecule fluorescence-based agents for sensing, imaging, and therapy within biological systems

In this tutorial review, we will explore recent advances for the design, construction and application of two-photon excited fluorescence (TPEF)-based small-molecule probes.

Lysosome-targeting pH indicator based on peri-fused naphthalene monoimide with superior stability for long term live cell imaging

Lysosomal pH is altered in many pathophysiological conditions. We describe synthesis and spectral properties of a new lysosomal fluorescent marker dye suitable for microscopic evaluation of lysosomal distribution and pH changes.

Subcellular localised small molecule fluorescent probes to image mobile Zn2

Zn2+, as the second most abundant d-block metal in the human body, plays an important role in a wide range of biological processes, and the dysfunction of its homeostasis is related to many diseases, including Type 2 diabetes, Alzheimer's disease and prostate and breast cancers. Small molecule fluorescent probes, as effective tools for real-time imaging, have been widely used to study Zn2+ related processes. However, the failure to control their localisation in cells has limited their utility somewhat, as they are generally incapable of studying individual processes in a specific cellular location. This perspective presents an overview of the recent developments in specific organelle localised small molecule fluorescent Zn2+ probes and their application in biological milieu, which could help to extend our understanding of the mechanisms that cells use to respond to dysfunction of zinc homeostasis and its roles in disease initiation and development.

A novel naphthofluorescein-based probe for ultrasensitive point-of-care testing of zinc(II) ions and its bioimaging in living cells and zebrafishes

The combination of fluorescence method with paper-based diagnostic device is quite suitable in point-of-care testing (POCT). Herein, we designed a novel hybrid fluorescein-based probe ZN-2 and investigated its fluorescent properties thoroughly in the detection of Zn²⁺. In comparison with the fluorescein-based probe ZN-1, ZN-2 displayed better sensitivity, long-wavelength and faster response to Zn²⁺ within 20 min. Interestingly, we could achieve ultrasensitive, high-throughput and visual detection in the POCT analysis of Zn²⁺ by anchoring this probe ZN-2 on the paper-based device. This device with satisfied performance for Zn²⁺ detection was achieved in real samples including cytochylema, serum and lake water. Finally, the probe ZN-2 was further applied to visualize and monitor the level changes of Zn²⁺ in the living cells and zebrafishes.

pH- and acoustic-responsive platforms based on perfluoropentane-loaded protein nanoparticles for ovarian tumor-targeted ultrasound imaging and therapy

In this study, we developed a multifunctional ultrasound (US) therapeutic agent that encapsulates perfluoropentane (PFP) into ferritin (FRT) and conjugates the tumor-targeting molecule folic acid (FA) (FA-FRT-PFP). The prepared FA-FRT-PFP had an average particle diameter of 42.8 ± 2.5 nm, a zeta potential of - 41.1 ± 1.7 mV and shows good stability in physiological solution and temperatures. FRT is a pH-sensitive cage protein that, at pH 5.0, disassembles to form pores that can load PFP. The adjustment to neutral pH closes the pores and encapsulates the PFP inside the FRT to form nanoparticles. At pH 5.0, 3 min of low-intensity focused ultrasound (LIFU, 2 W/cm2) significantly enhanced the US signal of FA-FRT-PFP through the acoustic droplet vaporization (ADV) effect. Under identical conditions, 4 min of LIFU irradiation caused the bubbles generated by FA-FRT-PFP to break. FA-FRT-PFP could be efficiently targeted into ovarian cancer cells and significantly enhanced the US contrast of FA-FRT-PFP after 3 min of LIFU irradiation. After 4 min of LIFU irradiation, cell viability significantly decreased due to necrosis, likely due to the FA-FRT-PFP mediated release of PFP in the acidic environment of lysosomes after entering the tumor cells. PFP is then transformed into bubbles that burst under LIFU irradiation, forming physical shock waves that lead to the destruction of the cell structure and necrosis, achieving tumor treatment. Taken together, this demonstrates that FA-FRT-PFP is both a novel and promising US theranostics agent for future clinic application.

Endoplasmic reticulum targeting fluorescent probes to image mobile Zn2

Zn2+ plays an important role in the normal function of the endoplasmic reticulum (ER) and its deficiency can cause ER stress, which is related to a wide range of diseases. In order to provide tools to better understand the role of mobile Zn2+ in ER processes, the first custom designed ER-localised fluorescent Zn2+ probes have been developed through the introduction of a cyclohexyl sulfonylurea as an ER-targeting unit with different Zn2+ receptors. Experiments in vitro and in cellulo show that both probes have a good fluorescence switch on response to Zn2+, high selectivity over other cations, low toxicity, ER-specific targeting ability and are efficacious imaging agents for mobile Zn2+ in four different cell lines. Probe 9 has been used to detect mobile Zn2+ changes under ER stress induced by both tunicamycin or thapsigargin, which indicates that the new probes should allow a better understanding of the mechanisms cells use to respond to dysfunction of zinc homeostasis in the ER and its role in the initiation and progression of diseases to be developed.

An alternative modular 'click-SNAr-click' approach to develop subcellular localised fluorescent probes to image mobile Zn2+

Zn2+ is involved in a number of biological processes and its wide-ranging roles at the subcellular level, especially in specific organelles, have not yet been fully established due to a lack of tools to image it effectively. We report a new and efficient modular double 'click' approach towards a range of sub-cellular localised probes for mobile zinc. Through this methodology, endoplasmic reticulum, mitochondria and lysosome localised probes were successfully prepared which show good fluorescence responses to mobile Zn2+in vitro and in cellulo whilst a non-targeting probe was synthesized as a control. The methodology appears to have wide-utility for the generation of sub-cellular localised probes by incorporating specific organelle targeting vectors for mobile Zn2+ imaging.

Small-molecule fluorescent probes for specific detection and imaging of chemical species inside lysosomes

In the past few years, the preparation of novel small-molecule fluorescent probes for specific detection and imaging of chemical species inside lysosomes has attracted considerable attention because of their wide applications in chemistry, biology, and medical science. This feature article summarizes the recent advances in the design and preparation of small-molecule fluorescent probes for specific detection of chemical species inside lysosomes. In addition, their properties and applications for the detection and imaging of pH, H2O2, HOCl, O2˙-, lipid peroxidation, H2S, HSO3-, thiols, NO, ONOO-, HNO, Zn2+, Cu2+, enzymes, etc. in lysosomes are discussed as well.

Diketopyrrolopyrrole-based fluorescence probes for the imaging of lysosomal Zn2+ and identification of prostate cancer in human tissue

A series of diketopyrrolopyrrole-based fluorescent probes (DPP-C2, LysoDPP-C2, LysoDPP-C3, and LysoDPP-C4) have been developed for the detection of low pH and Zn2+ in an AND logic fashion. The chelation of Zn2+ or the protonation of a morpholine moiety within these probes results in a partial increase in the fluorescence intensity, an effect ascribed to suppression of one possible photo-induced electron transfer (PET) pathway. In contrast, a large increase in the observed fluorescence intensity is observed at low pH and in the presence of Zn2+; this is rationalized in terms of both possible PET pathways within the probes being blocked. Job plots, fluorescence titration curves, and isothermal titration calorimetry proved consistent with a 1 : 1 Zn2+ complexation stoichiometry. Each probe demonstrated an excellent selectivity towards Zn2+ and the resulting Zn2+ complexes demonstrated pH sensitivity over the 3.5-9 pH range. Fluorescence imaging experiments confirmed that LysoDPP-C4 was capable of imaging lysosomal Zn2+ in live cells. Little evidence of cytotoxicity was seen. LysoDPP-C4 was successfully applied to the bioimaging of nude mice, wherein it was shown capable of imaging the prostate. Histological studies using a human sample revealed that LysoDPP-C4 can discriminate cancerous prostate tissue from healthy prostate tissue.

Tuning the π-bridge of quadrupolar triarylborane chromophores for one- and two-photon excited fluorescence imaging of lysosomes in live cells

A series of tetracationic quadrupolar chromophores containing three-coordinate boron π-acceptors linked by different π-bridges, namely 4,4'-biphenyl, 2,7-pyrene, 2,7-fluorene, 3,6-carbazole and 5,5'-di(thien-2-yl)-3,6-diketopyrrolopyrrole, were synthesized. While their neutral precursors 1-5 displayed highly solvatochromic fluorescence, the water-soluble tetracationic target molecules 1M-5M, did not, but their emission colour could be tuned from blue to pink by changing the π-bridge. Compound 5M, containing the diketopyrrolopyrrole bridge, exhibits the most red-shifted absorption and emission maxima and the largest two-photon absorption cross-section (4560 GM at 740 nm in MeCN). Confocal laser scanning fluorescence microscopy studies in live cells confirm localization of the dye at the lysosome. Moreover, the low cytotoxicity, and high photostability of 5M combined with two-photon excited fluorescence imaging studies demonstrate its excellent potential for lysosomal imaging in live cells.

Mixed organic ligand-based colorimetric and ratiometric chemosensors for Co2+: structure-activity relationships

In this work, chemosensors based on mixed ligands were proposed for the cooperative detection of Co²⁺. The relationship between the specifically selected mixed organic ligands and the detection activities is discussed. Diverse responses to metal ions can be tuned by controlling the structural features of organic ligands, such as different sizes, geometries, substituents, and connectivity. Among the nine investigated systems, DHAB-Tpy, DHAB-Phen, and DHAB-Dpa displayed high selectivity and sensitivity for Co²⁺, with detection limits of 4.5 × 10^-7 M, 1.1 × 10^-7 M, and 8.0 × 10^-8 M, respectively. The detection of Co²⁺ was not affected by other metal ions, anions, amino acids, proteins, nucleic acids, lipids and pH conditions. Furthermore, the proposed method was validated in the analysis of Co²⁺ in real water samples with satisfactory recovery and relative standard deviation values. TAC-Phen and TAC-Dpa could recognize Co²⁺ qualitatively, but could not detect Co²⁺ quantitatively. While TAC-Tpy, PAN-Tpy, PAN-Phen, and PAN-Dpa showed no metal ion selectivity. The experimental results were also rationalized by theoretical studies. A mixed ligand system can be used to produce a ratiometric absorption signal to avoid most ambiguities, such as the chemosensor environment and concentration, via self-calibration of two absorption bands. Structural insights derived from detection activities can provide valuable information for the design of new metal ion chemosensors by varying the type of organic ligands. Graphical abstracts The work represents a simple strategy for obtaining synthesis-free, inexpensive, and sensitivity-tunable chemosensors through mixing organic ligands of different sizes, substitutions, geometries, and connectivity to modulate the sensing behaviors.

Acylhydrazone functionalized benzimidazole-based metallogel for the efficient detection and separation of Cr3

Chromium(iii) is a kind of microelement and can be converted to the more toxic chromium(vi), which is a carcinogen, by redox cycling. Thus, the development of novel materials for the detection and removal of Cr³⁺ is a very important issue. A novel metallogel chemosensor (BMG-Fe) based on functionalized benzimidazole (BM) and Fe³⁺ was constructed, which could fluorescently detect and separate Cr³⁺. The detection limit of BMG-Fe for Cr³⁺ is 2.62 × 10^-8 M, and it exhibited high sensitivity and selectivity for Cr³⁺. Meanwhile, the absorbing percentage of BMG-Fe for Cr³⁺ is 96.36%, indicating a high separation rate. Interestingly, the sensitivity and ingestion capacity of BMG-Fe for Cr³⁺ are better than that of the simple organogel (BMG). So, the metallogel BMG-Fe could be utilized for the efficient removal of heavy metal ions from waste water.

Fluorescent Proteins for Investigating Biological Events in Acidic Environments

The interior lumen of acidic organelles (e.g., endosomes, secretory granules, lysosomes and plant vacuoles) is an important platform for modification, transport and degradation of biomolecules as well as signal transduction, which remains challenging to investigate using conventional fluorescent proteins (FPs). Due to the highly acidic luminal environment (pH ~ 4.5⁻6.0), most FPs and related sensors are apt to lose their fluorescence. To address the need to image in acidic environments, several research groups have developed acid-tolerant FPs in a wide color range. Furthermore, the engineering of pH insensitive sensors, and their concomitant use with pH sensitive sensors for the purpose of pH-calibration has enabled characterization of the role of luminal ions. In this short review, we summarize the recent development of acid-tolerant FPs and related functional sensors and discuss the future prospects for this field.

Two-photon imaging of formaldehyde in live cells and animals utilizing a lysosome-targetable and acidic pH-activatable fluorescent probe

Lyso-TPFP presents lysosomal targetability and an acidic pH-activatable response toward formaldehyde. Thus, it exclusively visualizes lysosomal formaldehyde and is immune against it in neutral cytosol and other organelles. In addition, two-photon fluorescence imaging endows Lyso-TPFP with the capability of in situ tracking formaldehyde in live cells and animals.

A highly sensitive fluorescent probe for bioimaging zinc ion in living cells and zebrafish models

A simple OFF–ON fluorescent probe was prepared and successfully applied for bioimaging Zn²⁺ in living systems.

Amino-Si-rhodamines: A new class of two-photon fluorescent dyes with intrinsic targeting ability for lysosomes

Noninvasive and specific visualization of lysosomes by fluorescence technology is critical for studying lysosomal trafficking in health and disease and for evaluating new cancer therapeutics that target tumor cell lysosomes. To date, there are two basic types of lysosomal probes whose lysosomal localization correlates with lysosomal acidity and endocytosis pathway, respectively. However, the former may suffer from pH-sensitive lysosomal localization and alkalization-induced lysosomal enzyme inactivation, and the latter need long incubation time to penetrate cell membrane due to the energy-dependency of endocytosis process. In this work, a new class of two-photon fluorescent dyes, termed amino-Si-rhodamines (ASiRs), were developed, which possess the intrinsic lysosome-targeted ability that is independent of lysosomal acidity and endocytosis pathway. As a result, ASiRs show not only the stable lysosomal localization against lysosomal pH changes and negligible interference to lysosomal function, but also excellent cell-membrane-permeability due to the energy-independent passive diffusion pathway. These merits, coupled with their excellent two-photon photophysical properties, long-term retention ability in lysosomes, and negligible cytotoxicity, make ASiRs very suitable for real-time and long-term tracking of lysosomes in living cells or tissues without interference to normal cellular processes. Moreover, the easy functionalization via amino linker further allows the construction of various fluorescent probes for biological targets of interest based on ASiR skeleton, as indicated by the cancer-targeted fluorescent probe ASiR6 as well as a fluorescent peroxynitrite probe ASiR-P.

Review for chiral-at-metal complexes and metal-organic framework enantiomorphs

This review discusses chiral-at-metal complexes and introduces enantiomorphs from assembly structure. Owing to the diverse coordination number and activity of metal ions as chiral centers, abundant structures for chiral selectivity, catalysis, and polarized light-response are the notable advantages of the chiral-at-metal complexes. The rational design and preparation of linear multi-dentate ligands is a good choice to improve the stability of chiral complexes, such as multi-bonding structure for high stability as a self-limiting system. The bio-significance and potential application of chiral-at-metal complexes are discussed, such as the synergistic effect of catalysis and chiral selectivity of the metal center in enzymes. Enzyme could be remolded to replace the original central metal ions with highly active rare earth or precious metal ions to form artificial metalloenzyme or to remove the "redundant" part around the metal center to improve the accessibility of substrate. The polarized light-response mechanism of chiral opsin is introduced in relation to its role in animal migration. Metal-organic frameworks (MOFs) are crystalline and porous materials built from metal nodes or clusters and organic linkers and provide the possibility to prepare artificial enantiomorphs. The preparations, applications, and characterization methods of MOF enatiomorphs are therefore introduced. We hope this review inspires researchers at all levels of their career to consider the title topic in their own research in terms of its application and potential value.

A two-photon NIR-to-NIR fluorescent probe for imaging hydrogen peroxide in living cells

Hydrogen peroxide (H₂O₂), one of the reactive oxygen species (ROS), plays vital roles in diverse physiological processes. Imbalance of the H₂O₂ is concerned with serious diseases such as cardiovascular disorders, neurodegenerative diseases, Alzheimer's disease and cancer. Therefore, it is critical to develop efficient methods for monitoring H₂O₂ in vivo. In this work, a two-photon excitation (860nm) NIR fluorescent turn-on probe TPNR-H₂O₂ for H₂O₂ based on Dicyanomethylene-4H-pyran fluorophore is reported, which can be used in solution detection with 13.2-fold NIR fluorescence enhancement, fast response (completed within 40min), excellent sensitivity (DL 72.48nM), and lower cellular auto-fluorescence interference. Importantly, the perfect photostability of TPNR-H₂O₂ clearly demonstrated that the probe could be applied to imaging intracellular H₂O₂ for a long time without photobleaching. In addition, through two-photon imaging, this probe was cell permeable and used to monitor the level of endogenous and exogenous H₂O₂ with promising biological application.

Bulky 4,6-disubstituted tetraphenylethene–naphthalimide dyad: synthesis, copolymerization, stimuli-responsive fluorescence and cellular imaging

We report the design and synthesis of a tetraphenylethene substituted with naphthalimide at the 4, 6 positions, named NI-2TPE. NI-2TPE exhibits strong solvent-dependent emission properties with combined ICT and AIE characteristics in THF–H₂O systems. This probe was used directly on test papers to distinguish normal organic solvents using their emission colours under UV light based on its AIE and ICT nature. Thanks to the vinyl group in NI-2TPE, we synthesized a copolymer of NIPAM and NI-2TPE, termed P(NIPAM-co-NI-2TPE). The resulting polymer is highly soluble and fluorescent in water (Φ_F = 15.4%). Due to the well-known thermo-responsive character of NIPAM, P(NIPAM-co-NI-2TPE) exhibits an interesting fluorescence change in response to various temperatures. Due to the thermo-induced shrinking of the PNIPAM chain, the fluorescence intensity gradually increased from 20 to 34 °C. As the temperature further increased from 34 to 90 °C, the fluorescence intensity decreased sharply, which was caused by the well-known thermal effects. Furthermore, we synthesized a P(HEA-co-NI-2TPE–TPP acrylate) copolymer, in which HEA is a hydrophilic unit, TPP is a mitochondria label and NI-2TPE a fluorescent probe. The corresponding polymer probe is highly soluble in water with FLQY = 7% and we have further applied this probe as a mitochondria targeted imaging tracker in HeLa cells successfully.

A lysosome targetable fluorescent probe for endogenous imaging of hydrogen peroxide in living cells

A lysosome targetable naphthalimide based fluorescent probe has been designed and synthesized for selective imaging of H₂O₂ in different cells, tissues and in vivo models.