Two birds with one stone: A highly sensitive near-infrared BODIPY-based fluorescent probe for the simultaneous detection of Fe2+ and H+ in vivo

Near-Infrared Fluorescent Probe for Simultaneously Imaging Ferrous Ions and Viscosity in a Mouse Model of Hepatocellular Carcinoma

Abnormal ferrous ion (Fe2+) levels lead to an increase in reactive oxygen species (ROS) in cells, disrupting intracellular viscosity and the occurrence of hepatocellular carcinoma (HCC). Simultaneously visualizing Fe2+ and intracellular viscosity is essential for understanding the detailed pathophysiological processes of HCC. Herein, we report the first dual-responsive probe, QM-FV, capable of simultaneously monitoring Fe2+ and viscosity. QM-FV shows highly selective turn-on near-infrared fluorescence (∼30-fold enhancement at 740 nm) for Fe2+ with high sensitivity (LOD = 25 nM) and a significant Stokes shift (290 nm). Moreover, QM-FV shows a distinct orange-red fluorescence enhancement at 587 nm as the viscosity increases. Due to its lower cytotoxicity and high sensitivity, QM-FV can distinguish cancer cells from normal cells by detecting Fe2+ and viscosity in dual channels. More importantly, using QM-FV, we found that the levels of Fe2+ and viscosity elevated in the precancerous stage of HCC and gradually increased as the disease progressed. Overall, this work provides a new potential tool for investigating viscosity and Fe2+-related pathological processes underlying HCC.

Synthesis, Crystal Structure and Fluorimetric Study of 2-phenylphthalazin-1(2H)-one: a Highly Selective Florescent Chemosensor for Detection of Fe3+ and Fe2+ Metal Ions

A ligand, 2-phenylphthalazin-1(2H)-one (K), was synthesized by refluxing 2-formylbenzoic acid with phenyl hydrazine in presence of ethanol. FTIR, elemental analysis and single crystal XRD techniques were used to elucidate the structure. Fluorimetric turn-off response was recorded when solution of ligand (K) in DMF was treated with aqueous solution of Fe3+ and Fe2+ metal ions. No specific changes were observed on addition of other metal ions (Pb2+, Cd2+, Mn2+, Zn2+, Ba2+, Ni2+, Al3+, Ag1+, Co2+, Ca2+, Cu2+, Mg2+, Cr3+). Limit of Detection (LOD) was calculated for Fe2 and Fe3+as 2.4 µM and 2.5µM respectively, which is quite below to the recommended value 5.4 µM of the Environment Protection Agency of USA. Association constants for Fe3+ and Fe2+ metal ions were determined as 6 × 10-4 M-1 and 3.6 × 10-4 M-1 respectively. Benesi-Hildebrand plot confirmed 1:1 binding ratio between metal ions and ligand.

Fluorescent N-oxides: applications in bioimaging and sensing

N-Oxides, due to their zwitterionic nature and ability to form hydrogen bonds through the oxide ion, are highly water-soluble and widely used in biological and pharmacological studies. The N-oxide structural scaffold is introduced into molecules, enabling "turn-on" fluorescence via an intramolecular charge transfer (ICT) process. This process occurs when the N-O bond is cleaved, either through an enzymatic reaction under hypoxic conditions or by using Fe(II), which allows rapid and selective detection of Fe(II) at nanomolar concentrations both in vitro and in vivo. This review focuses on the literature published between 2010 and 2024, particularly emphasising N-oxide fluorophores and their applications in hypoxic cell lines, Fe(II) detection, and bioimaging.

A Near-Infrared Colorimetric Fluorescent Probe for Ferrous Ion Detection and Imaging

Based on the N-redox mechanism, a turn-on near-infrared fluorescence probe (SWJT-15) with cyano isophorone as skeleton was designed and synthesized for the detection of ferrous ions (Fe2+). The probe has a lower detection limit (83 nM) and fast response (200 s) to Fe2+ ions. And the probe has unique selectivity and good anti-interference performance against Fe2+ ions compared to other metal ions. Moreover, the probe has been successfully applied to imaging Fe2+ ions in HeLa cells.

Detecting labile heme and ferroptosis through 'turn-on' fluorescence and lipid droplet localization post Fe2+ sensing

Iron, a crucial biologically active ion essential for metabolic processes in living organisms, plays a vital role in biological functions, and imbalances in iron levels can lead to various diseases. In this study, we have developed two simple "turn-on" fluorescent probes, NOPy and NOCN, for the quick and selective detection of Fe2+ at nanomolar levels (LOD of 35 nM), accompanied by significant absorption and emission shifts, along with colorimetric demarcation. Both fluorophores exhibit an excellent "turn-on" emission response upon encountering Fe2+ in the cells. Flow cytometry and confocal fluorescence imaging studies demonstrate enhanced fluorescence signals in response to labile iron, efficiently detecting heme during erastin-induced ferroptosis. Interestingly, we also observed that the product formed after Fe2+ sensing localizes within the lipid droplets. These water-soluble and highly sensitive reactive probes, NOPy and NOCN, enable investigations of iron-dependent physiological and pathological conditions. The development of these probes represents an advancement in the field, offering a rapid and selective means for detecting Fe2+ with minimal cytotoxicity.

Fluorescence-Recovered Wearable Hydrogel Patch for In Vitro Detection of Glucose Based on Rare-Earth Nanoparticles

The physiological state of the human body can be indicated by analyzing the composition of sweat. In this research, a fluorescence-recovered wearable hydrogel patch has been designed and realized which can noninvasively monitor the glucose concentration in human sweat. Rare-earth nanoparticles (RENPs) of NaGdF4 doped with different elements (Yb, Er, and Ce) are synthesized and optimized for better luminescence in the near-infrared second (NIR-II) and visible region. In addition, RENPs are coated with CoOOH of which the absorbance has an extensive peak in the visible and NIR regions. The concentration of H2O2 in the environment can be detected by the fluorescence recovery degree of CoOOH-modified RENPs based on the fluorescence resonance energy transfer effect. For in vivo detection, the physiological state of oxidative stress at tumor sites can be visualized through its fluorescence in NIR-II with low background noise and high penetration depth. For the in vitro detection, CoOOH-modified RENP and glucose oxidase (GOx) were doped into a polyacrylamide hydrogel, and a patch that can emit green upconversion fluorescence under a 980 nm laser was prepared. Compared with the conventional electrochemical detection method, the fluorescence we presented has higher sensitivity and linear detection region to detect the glucose. This improved anti-interference sweat patch that can work in the dark environment was obtained, and the physiological state of the human body is conveniently monitored, which provides a new facile and convenient method to monitor the sweat status.

Functional Materials for Subcellular Targeting Strategies in Cancer Therapy: Progress and Prospects

Neoadjuvant and adjuvant therapies have made significant progress in cancer treatment. However, tumor adjuvant therapy still faces challenges due to the intrinsic heterogeneity of cancer, genomic instability, and the formation of an immunosuppressive tumor microenvironment. Functional materials possess unique biological properties such as long circulation times, tumor-specific targeting, and immunomodulation. The combination of functional materials with natural substances and nanotechnology has led to the development of smart biomaterials with multiple functions, high biocompatibilities, and negligible immunogenicities, which can be used for precise cancer treatment. Recently, subcellular structure-targeting functional materials have received particular attention in various biomedical applications including the diagnosis, sensing, and imaging of tumors and drug delivery. Subcellular organelle-targeting materials can precisely accumulate therapeutic agents in organelles, considerably reduce the threshold dosages of therapeutic agents, and minimize drug-related side effects. This review provides a systematic and comprehensive overview of the research progress in subcellular organelle-targeted cancer therapy based on functional nanomaterials. Moreover, it explains the challenges and prospects of subcellular organelle-targeting functional materials in precision oncology. The review will serve as an excellent cutting-edge guide for researchers in the field of subcellular organelle-targeted cancer therapy.

Non-Solvatochromic Cell Membrane-Targeted NIR Fluorescent Probe for Visualization of Polarity Abnormality in Drug-Induced Liver Injury Mice

Noninvasive visualization of liver polarity by using fluorescence imaging technology is helpful to better understand drug-induced liver injury (DILI). However, cell membrane-targeted polarity-sensitive near-infrared (NIR) fluorescent probes are still scarce. Herein, we report a non-solvatochromic cell membrane-targeted NIR small molecular probe (N-BPM-C10) for monitoring the polarity changes on cell membranes in living cells and in vivo. N-BPM-C10 exhibits polarity-dependent fluorescence around 655 nm without an obvious solvatochromic effect, which endows it with good capability for the in vivo imaging study. Moreover, it can rapidly and selectively light up the cell membranes as well as distinguish tumor cells from normal cells due to its excellent polarity-sensitive ability. More importantly, N-BPM-C10 has been successfully applied to visualize liver polarity changes in vivo, revealing the reduction of liver polarity in DILI mice. We believe that N-BPM-C10 provides a new way for the diagnosis of DILI.

Development of a Golgi-targeted fluorescent chemosensor for detecting ferrous ions overload under Golgi stress

Ferrous ion (Fe²⁺) is a crucial metal ion in the body and participates in the diseases related to oxidation and reduction. Golgi apparatus is the main subcellular organelle of Fe²⁺ transport in cells, and the stability of its structure is related to the Fe²⁺ at an appropriate concentration. In this work, a turn-on type Golgi-targeting fluorescent chemosensor Gol-Cou-Fe²⁺ was rationally designed for sensitive and selective detection of Fe²⁺. Gol-Cou-Fe²⁺ showed excellent capacity of detecting exogenous and endogenous Fe²⁺ in HUVEC and HepG2 cells. It was used to capture the up-regulated Fe²⁺ level during the hypoxia. Moreover, the fluorescence of sensor was enhanced over time under Golgi stress combining with the reduce of Golgi matrix protein GM130. However, elimination of Fe²⁺ or addition of nitric oxide (NO) would restore the fluorescence intensity of Gol-Cou-Fe²⁺ and the expression of GM130 in HUVEC. Thus, development of chemosensor Gol-Cou-Fe²⁺ provides a new window for tracking Golgi Fe²⁺ and elucidating Golgi stress-related diseases.

Recent progress of TP/NIR fluorescent probes for metal ions

Metal ions are of significance in various pathological and physiological processes. As such, it is crucial to monitor their levels in organisms. Two-photon (TP) and near-infrared (NIR) fluorescence imaging has been utilized to monitor metal ions because of minimal background interference, deeper tissue depth penetration, lower tissue self-absorption, and reduced photodamage. In this review, we briefly summarize recent progress from 2020 to 2022 of TP/NIR organic fluorescent probes and inorganic sensors in the detection of metal ions. Additionally, we present an outlook for the development of TP/NIR probes for bio-imaging, diagnosis of diseases, imaging-guided therapy, and activatable phototherapy.

H2O2-Activated NIR-II Fluorescent Probe with a Large Stokes Shift for High-Contrast Imaging in Drug-Induced Liver Injury Mice

Drug-induced liver injury (DILI) is the most common clinical adverse drug reaction, which is closely associated with the oxidative stress caused by overproduced reactive oxygen species. Hepatic H₂O₂, as an important biomarker of DILI, plays a crucial role in the progression of DILI. However, there remains a challenge to develop H₂O₂-activatable second near-infrared (NIR-II, 1000-1700 nm) small molecular probes with both a large Stokes shift and a long emission wavelength beyond 950 nm. Herein, we developed an activatable NIR-II fluorescent probe (IR-990) with an acceptor-π-acceptor (A-π-A) skeleton for real-time detection of H₂O₂ in vivo. In the presence of H₂O₂, nonfluorescent probe IR-990 was successfully unlocked by generating a donor-π-acceptor (D-π-A) structure and switched on intense NIR-II fluorescence, exhibiting a peak emission wavelength at 990 nm and a large Stokes shift of 200 nm. Moreover, it was able to detect H₂O₂ with high sensitivity and selectivity in vitro (LOD = 0.59 μM) and monitor the behavior of endogenous H₂O₂ in the HepG2 cell model of DILI for the first time. Notably, probe IR-990 was successfully applied in real-time imaging of endogenous H₂O₂ generation in the DILI mouse model, showing a high signal-to-background ratio of 11.3/1. We envision that IR-990 holds great potential as a powerful diagnosis tool for real-time visualization of H₂O₂ in vivo and revealing the mechanism of DILI in the future.

Aggregation-induced emission (AIE) from poly(1,4-dihydropyridine)s synthesized by Hantzsch polymerization and their specific detection of Fe2+ ions

As an important metal element widely existing in nature and the human body, the simple and specific detection of Fe2+ ions has always been of interest.