A Photoacoustic Probe with Blood-Brain Barrier Crossing Ability for Imaging Oxidative Stress Dynamics in the Mouse Brain

Mercury(II)-Triggered Targeted and NIR-II Fluorescence/Photoacoustic Imaging Probe for High-Sensitivity Early Diagnosis and Evaluating Drug against Acute Liver and Kidney Injury

Mercury ions (Hg2+) have been found to disrupt the body's antioxidant defense mechanisms, leading to oxidative stress and physiological dysfunction. Early diagnosis and real-time monitoring of Hg2+ fluctuations in organ damage are crucial but limited due to the lack of noninvasive and deep tissue imaging probes. Herein, a Hg2+-triggered targeted and NIR-II fluorescence/photoacoustic (PA) dual-mode molecular probe (NHG-2) was developed for real-time monitoring Hg2+ fluctuations in Hg2+-induced acute liver and kidney injury mice. NHG-2 was designed through rational adjustment of the conjugated ring structure and further screening processes, enabling it to sensitively recognize Hg2+ and subsequently open mitochondrial targeting, producing NIR-II fluorescence/PA signals. This probe allowed for noninvasive NIR-II fluorescence/PA imaging for real-time monitoring of Hg2+-induced acute liver and kidney injury, demonstrating excellent detection sensitivity. Furthermore, NHG-2 can be utilized to evaluate the efficacy of N-acetylcysteine (NAC) in Hg2+-induced liver and kidney injury through dual signal indication. Mechanism studies suggested that NAC activated the antioxidant Akt/Nrf2 signaling pathway, reversed the changes of related biomarkers, and restored mitochondrial membrane potential. Thus, this study not only presents the first specific NIR-II fluorescence/PA dual-mode probe for Hg2+ but also provides a potential tool for early diagnosis and treatment evaluation and potential pathogenesis study.

Current trends in blood biomarkers detection and neuroimaging for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by both motor and cognitive impairments. A significant challenge in managing PD is the variability of symptoms and disease progression rates. This variability is primarily attributed to unclear biomarkers associated with the disease and the lack of early diagnostic technologies and effective imaging methods. PD-specific biomarkers are essential for developing practical tools that facilitate accurate diagnosis, patient stratification, and monitoring of disease progression. Hence, creating valuable tools for detecting and diagnosing PD based on specific biomarkers is imperative. Blood testing, less invasive than obtaining cerebrospinal fluid through a lumbar puncture, is an ideal source for these biomarkers. Although such biomarkers were previously lacking, recent advancements in various detection techniques related to PD biomarkers and new imaging methods have emerged. However, basic research requires more detailed guidelines on effectively implementing these biomarkers in diagnostic procedures to enhance the diagnostic accuracy of PD blood testing in clinical practice. This review discusses the developmental trends of PD-related blood biomarker detection technologies, including optical analysis platforms. Despite the progress in developing various biomarkers for PD, their specificity and sensitivity remain suboptimal. Therefore, the integration of multimodal biomarkers along with optical and imaging technologies is likely to significantly improve diagnostic accuracy and facilitate the implementation of personalized medicine. This review forms valid research hypotheses for PD research and guides future empirical studies.

Lycium ruthenicum Murray anthocyanin-driven neuroprotection modulates the gut microbiome and metabolome of MPTP-treated mice

Emerging evidence suggests that Parkinson's disease (PD) is strongly associated with altered gut microbiota. The present study investigated the prophylactic effects of anthocyanins (ACNs) from Lycium ruthenicum Murray on Parkinson's disease based on microbiomics and metabolomics. In this study, sixty-six adult male C57BL/6J mice were randomized into the control group, model group, positive drug (Madopar) group, and low-, medium- and high-dose ACN groups. Behavioral experiments were conducted and pathological indicators were determined. Fresh feces were collected for microbiomic analysis using 16S rRNA sequencing. Urine and serum were analyzed by the UPLC-MS method for untargeted metabolomics. The results demonstrated that ACNs ameliorated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced motor deficits, dopamine neuron death, and glial cell activation, while 100 mg kg-1 and 200 mg kg-1 ACNs were more neuroprotective than 50 mg kg-1. Mice with PD-like phenotypes have an altered gut microbiota composition, and ACNs may regulate this disorder by causing an increase in Firmicutes/Bacteroidota ratio and abundance of norank_f__Eubacterium_coprostanoligenes_group and a decrease in the abundance of norank_f__Muribaculaceae, Coriobacteriaceae_UCG-002 and Parvibacter. Furthermore, ACNs increased 14 urinary key metabolites such as DIMBOA-Glc and tauroursodeoxycholic acid, decreased N,N-dimethyllysine, and increased 12 serum key metabolites such as 1-methylguanine and 1-nitro-5-glutathionyl-6-hydroxy-5,6-dihydronaphthalene, and decreased lamivudine-monophosphate and 5-butyl-2- methylpyridine. The present study reveals that ACNs are protective against MPTP-induced PD in mice by modulating anti-inflammatory flora in the gut and endogenous metabolites in serum/urine, and the key mechanisms may be related to Coriobacteriaceae_UCG-002 and glycerophospholipid metabolic pathways. Our findings provide new insights into the pathogenesis and potential treatment of Parkinson's disease.

A novel NIR fluorescent probe for copper(ii) imaging in Parkinson's disease mouse brain

Abnormal copper ion (Cu2+) levels are considered to be one of the pathological factors of Parkinson's disease (PD), but the internal relationship between Cu2+ and PD progression remains elusive. Visualizing Cu2+ in the brain will be pivotal for comprehending the underlying pathophysiological processes of PD. In this work, a near-infrared (NIR) fluorescent probe, DDAO-Cu, capable of detecting Cu2+ with exceptional sensitivity (about 1.8 nM of detection limit) and selectivity, rapid response (<3 min), and deep tissue penetration, was designed for quantification and visualization of the Cu2+ level. It could detect not only Cu2+ in cells but also the changes in the Cu2+ level in the rotenone-induced cell and zebrafish PD models. Moreover, DDAO-Cu can cross the blood-brain barrier to image Cu2+ in the brain of PD model mice. The imaging result showed a significant increase in Cu2+ levels in brain regions of PD model mice, including the cerebral cortex, hippocampus, and striatum. Meanwhile, Cu2+ levels in the substantia nigra region were significantly reduced in PD model mice. It revealed the nuanced relationship of Cu2+ levels in different brain regions in the disease and indicated the pathological complexity of PD. Overall, DDAO-Cu represents a novel and practical tool for investigating Cu2+-related physiological and pathological processes underlying Parkinson's disease.

Molecular Engineering of a Doubly Quenched Fluorescent Probe Enables Ultrasensitive Detection of Biothiols in Highly Diluted Plasma and High-Fidelity Imaging of Dihydroartemisinin-Induced Ferroptosis

The occurrence and development of diseases are accompanied by abnormal activity or concentration of biomarkers in cells, tissues, and blood. However, the insufficient sensitivity and accuracy of the available fluorescence probes hinder the precise monitoring of associated indexes in biological systems, which is generally due to the high probe intrinsic fluorescence and false-negative signal caused by the reactive oxygen species (ROS)-induced probe decomposition. To resolve these problems, we have engineered a ROS-stable, meso-carboxylate boron dipyrromethene (BODIPY)-based fluorescent probe, which displays quite a low background fluorescence due to the doubly quenched intrinsic fluorescence by a combined strategy of the photoinduced electron transfer (PET) effect and "ester-to-carboxylate" conversion. The probe achieved a high S/N ratio with ultrasensitivity and good selectivity toward biothiols, endowing its fast detection capability toward the biothiol level in 200×-diluted plasma samples. Using this probe, we achieved remarkable distinguishing of liver injury plasma from normal plasma even at 80× dilution. Moreover, owing to its good stability toward ROS, the probe was successfully employed for high-fidelity imaging of the negative fluctuation of the biothiol level in nonsmall-cell lung cancer (NSCLC) during dihydroartemisinin-induced ferroptosis. This delicate design of suppressing intrinsic fluorescence reveals insights into enhancing the sensitivity and accuracy of fluorescent probes toward the detection and imaging of biomarkers in the occurrence and development of diseases.

Isomer engineering for deep understanding of aggregation-induced photothermal enhancement in conjugated systems

Organic photothermal materials based on conjugated structures have significant potential applications in areas such as biomedical diagnosis, therapy, and energy conversion. Improving their photothermal conversion efficiency through molecular design is critical to promote their practical applications. Especially in similar structures, understanding how the position of heteroatoms affects the conversion efficiency is highly desirable. Herein, we prepared two isomeric small D-A molecules with different sulfur atom positions (TBP-MPA and i-TBP-MPA), which display strong and broad absorption in the UV-visible region due to their strong intramolecular charge transfer characteristics. Compared to i-TBP-MPA, TBP-MPA demonstrates aggregation-induced photothermal enhancement (AIPE). Under simulated sunlight (1 kW m-2) irradiation, the stable temperature of TBP-MPA powder reached 60 °C, significantly higher than the 50 °C achieved by i-TBP-MPA. Experimental and theoretical results indicate that the S⋯N non-covalent interactions in TBP-MPA impart a more rigid conjugated framework to the molecule, inducing ordered molecular stacking during aggregation. This ordered stacking provides additional non-radiative transition channels between TBP-MPA molecules, enhancing their photothermal performance in the aggregated state. Under 1 sun irradiation, TBP-MPA achieved a water evaporation rate of 1.0 kg m-2 h-1, surpassing i-TBP-MPA's rate of 0.92 kg m-2 h-1.

Luminescence Probes in Bio-Applications: From Principle to Practice

Bioanalysis based on optical imaging has gained significant progress in the last few decades. Luminescence probes are capable of detecting, monitoring, and tracing particular biomolecules in complex biological systems to figure out the roles of these molecules in organisms. Considering the rapid development of luminescence probes for bio-applications and their promising future, we have attempted to explore the working principles and recent advances in bio-applications of luminescence probes, in the hope of helping readers gain a detailed understanding of luminescence probes developed in recent years. In this review, we first focus on the current widely used luminescence probes, including fluorescence probes, bioluminescence probes, chemiluminescence probes, afterglow probes, photoacoustic probes, and Cerenkov luminescence probes. The working principles for each type of luminescence probe are concisely described and the bio-application of the luminescence probes is summarized by category, including metal ions detection, secretion detection, imaging, and therapy.

Xanthene-Based Dyes for Photoacoustic Imaging and their Use as Analyte-Responsive Probes

Developing imaging tools that can report on the presence of disease-relevant analytes in multicellular organisms can provide insight into fundamental disease mechanisms as well as provide diagnostic tools for the clinic. Photoacoustic imaging (PAI) is a light-in, sound-out imaging technique that allows for high resolution, deep-tissue imaging with applications in pre-clinical and point-of-care settings. The continued development of near-infrared (NIR) absorbing small-molecule dyes promises to improve the capabilities of this emerging imaging modality. For example, new dye scaffolds bearing chemoselective functionalities are enabling the detection and quantification of disease-relevant analytes through activity-based sensing (ABS) approaches. Recently described strategies to engineer NIR absorbing xanthenes have enabled development of analyte-responsive PAI probes using this classic dye scaffold. Herein, we present current strategies for red-shifting the spectral properties of xanthenes via bridging heteroatom or auxochrome modifications. Additionally, we explore how these strategies, coupled with chemoselective spiroring-opening approaches, have been employed to create ABS probes for in vivo detection of hypochlorous acid, nitric oxide, copper (II), human NAD(P)H: quinone oxidoreductase isozyme 1, and carbon monoxide. Given the versatility of the xanthene scaffold, we anticipate continued growth and development of analyte-responsive PAI imaging probes based on this dye class.

A Practical and Modular Method for Direct C-H Functionalization of the BODIPY Core via Thianthrenium Salts

Direct structural modification of small-molecule fluorophores represents a straightforward and appealing strategy for accessing new fluorescent dyes with desired functionalities. We report herein a general and efficient visible-light-mediated method for the direct C-H functionalization of BODIPY, an important fluorescent chromophore, using readily accessible and bench-stable aryl and alkenylthianthrenium salts. This practical approach operates at room temperature with extraordinary site-selectivity, providing a step-economical means to construct various valuable aryl- and alkenyl-substituted BODIPY dyes. Remarkably, this protocol encompasses a broad substrate scope and excellent functional-group tolerance, and allows for the modular synthesis of sophisticated symmetrical and asymmetrical disubstituted BODIPYs by simply employing different combinations of thianthrenium salts. Moreover, the late-stage BODIPY modification of complex drug molecules further highlights the potential of this novel methodology in the synthesis of fluorophore-drug conjugates.

Novel activated NIR-II fluorescence/Ratio photoacoustic probe for dual-modality accurate imaging of palladium ions overload in mouse liver

Palladium contaminants can pose risks to human health and the natural environment. Once Pd2+ enters the body, it can bind with DNA, proteins, and other macromolecules, disrupting cellular processes and causing serious harm to health. Therefore, it becomes critical to develop simple, highly selective and precise methods for detecting Pd2+in vivo. Here, we have successfully developed the first activated second near-infrared region fluorescence (NIR-II FL) and ratio photoacoustic (PA) probe NYR-1 for dual-modal accurate detection of Pd2+ levels. NYR-1 is capable of rapidly (< 60 s) and sensitively detection of Pd2+ in solution, providing switched on NIR-II FL920 and ratio PA808/PA720 dual-mode signal change. More notably, the probe NYR-1 was successfully used for non-invasive imaging of Pd2+ overload in mouse liver by NIR-II FL/Ratio PA dual-modality imaging technology for the first time. Thus, this work opens up a promising dual-modal detection method for the precise detection of Pd2+ in organisms and in the environment.

Near-Infrared Absorbing BODIPY-Xanthene Hybrids for Multiplexed Photoacoustic Imaging

We report a series of ethenylene-bridged D-π-A BODIPY-xanthene hybrid dyes with precisely regulated absorption bands ranging from the far-red to the near-infrared region (NIR, 700-1000 nm) through rational molecular design. These dyes have excellent photoacoustic properties, and their biocompatibility can be significantly improved by facilely introducing water-soluble groups. In vivo two-channel multiplexed photoacoustic imaging demonstrated their high-resolution imaging capabilities, making them promising candidates for future NIR bioimaging applications.

A Small-Molecule Ratiometric Photoacoustic Probe for the High-Spatiotemporal-Resolution Imaging of Copper(II) Dynamics in the Mouse Brain

Copper dysmetabolism is associated with various neurodegenerative disorders, making high-spatiotemporal-resolution imaging of Cu2+ in the brain essential for understanding the underlying pathophysiological processes. Nevertheless, the current probes encounter obstacles in crossing the blood-brain barrier (BBB) and providing high-spatial-resolution in deep tissues. Herein, we present a photoacoustic probe capable of imaging Cu2+ dynamics in the mouse brain with high-spatiotemporal-resolution. The probe demonstrates selective ratiometric and reversible responses to Cu2+ , while also efficiently crossing the BBB. Using the probe as the imaging agent, we successfully visualized Cu2+ in the brain of Parkinson's disease (PD) model mouse with a remarkable micron-level resolution. The imaging results revealed a significant increase in Cu2+ levels in the cerebral cortex as PD progresses, highlighting the close association between Cu2+ alternations in the region and the disease. We also demonstrated that the probe can be used to monitor changes in Cu2+ distribution in the PD model mouse brain during L-dopa intervention. Mechanism studies suggest that the copper dyshomeostasis in the PD mouse brain was dominated by the expression levels of divalent metal transporter 1. The application of our probe in imaging Cu2+ dynamics in the mouse brain offers valuable insights into the copper-related molecular mechanisms underlying neurodegenerative diseases.

Reversible Dual Fluorescence-Lifetime Imaging of Mitochondrial GSH and Microviscosity: Real-Time Evaluation of Ferroptosis Status

Ferroptosis, as a new form of regulated cell death, is implicated in various physiological and pathological processes. Developing a single probe for an independent analysis of multiple analytes related to ferroptosis can provide more accurate information and simplify the detection procedures, but it faces great challenges. In this work, we develop a fluorescent probe for the simultaneous detection of GSH through ratiometric fluorescence response and microviscosity via a fluorescence lifetime model. Based on the reversible Michael addition reaction between GSH and unsaturated C═C bond, the probe responds reversibly to GSH with a ratiometric fluorescence variation and a fast response time (t1/2 = 4.7 s). At the same time, the probe is sensitive to environmental viscosity by changing its fluorescence lifetimes. The probe was applied to monitor the drug-induced ferroptosis process through both the classical Xc-/GSH/GPX4- and DHODH-mediated defense mechanisms. We hope that the probe will provide a useful molecular tool for the real-time live-cell imaging of GSH dynamics, which is benefit to unveiling related physiological and pathological processes.

Photonic control of image-guided ferroptosis cancer nanomedicine

Photonic nanomaterials, characterized by their remarkable photonic tunability, empower a diverse range of applications, including cutting-edge advances in cancer nanomedicine. Recently, ferroptosis has emerged as a promising alternative strategy for effectively killing cancer cells with minimizing therapeutic resistance. Novel design of photonic nanomaterials that can integrate photoresponsive-ferroptosis inducers, -diagnostic imaging, and -synergistic components provide significant benefits to effectively trigger local ferroptosis. This review provides a comprehensive overview of recent advancements in photonic nanomaterials for image-guided ferroptosis cancer nanomedicine, offering insights into their strengths, constraints, and their potential as a future paradigm in cancer treatment.

Single Atom Stabilization of Phosphinate Ester-Containing Rhodamines Yields Cell Permeable Probes for Turn-On Photoacoustic Imaging

Photoacoustic imaging (PAI) is an emerging imaging technique that uses pulsed laser excitation with near-infrared (NIR) light to elicit local temperature increases through non-radiative relaxation events, ultimately leading to the production of ultrasound waves. The classical xanthene dye scaffold has found numerous applications in fluorescence imaging, however, xanthenes are rarely utilized for PAI since they do not typically display NIR absorbance. Herein, we report the ability of Nebraska Red (NR) xanthene dyes to produce photoacoustic (PA) signal and provide a rational design approach to reduce the hydrolysis rate of ester containing dyes, affording cell permeable probes. To demonstrate the utility of this approach, we construct the first cell permeable rhodamine-based, turn-on PAI imaging probe for hypochlorous acid (HOCl) with maximal absorbance within the range of commercial PA instrumentation. This probe, termed SNR700 -HOCl, is capable of detecting exogenous HOCl in mice. This work provides a new set of rhodamine-based PAI agents as well as a rational design approach to stabilize esterified versions of NR dyes with desirable properties for PAI. In the long term, the reagents described herein could be utilized to enable non-invasive imaging of HOCl in disease-relevant model systems.

Reaction-Activated Disassembly of the NIR-II Probe Enables Fast Detection and Ratiometric Photoacoustic Imaging of Glutathione In Vivo

Glutathione (GSH), the most abundant nonprotein biothiol, is a significant endogenous molecule that plays a key role in redox equilibrium in vivo and is regarded as a critical biomarker of cancer. Currently, various fluorescent probes have been designed and synthesized for imaging GSH at the cellular level in the visible range and the first near-infrared window (NIR-I, 750-900 nm). However, the application of these fluorescent probes for bioimaging and biosensing in vivo has been extremely hindered by the high biobackground and low tissue penetration. Herein, based on the self-assembly and disassembly of J-aggregation, we designed and synthesized a GSH-activatable probe MC-PSE for second near-infrared window (NIR-II) fluorescence and ratiometric photoacoustic imaging of GSH in vivo. The anionic cyanine-based MC-PSE tends to form stable J-aggregates in an aqueous solution. Upon the reaction with GSH, the J-aggregates of MC-PSE disassembled, the emission peak intensity of MC-PSE at 940 nm significantly increased by about 20 times, and the PA900/PA980 ratio increased by 4 times within 15 min in vitro. Notably, we used MC-PSE to visualize GSH in tumor-bearing mice and to distinguish normal and tumor areas successfully by virtue of NIR-II FL and PA dual-modal imaging. The design strategy of MC-PSE provides a novel method for ratiometric photoacoustic imaging, and MC-PSE is expected to be a powerful tool for the accurate detection of GSH in cancer diagnosis.

A Reversible Fluorescent Probe for In Situ Monitoring Redox Imbalance during Mitophagy

Mitophagy is the lysosome-dependent degradation of damaged and dysfunctional mitochondria, which is closely associated with H2O2-related redox imbalance and pathological processes. However, development of fast-responding and highly sensitive reversible fluorescent probes for monitoring of mitochondrial H2O2 dynamics is still lacking. Herein, we report a reversible fluorescent probe (M-HP) that enables real-time imaging of H2O2-related redox imbalance. In vitro studies demonstrated that M-HP had a rapid response and high sensitivity to the H2O2/GSH redox cycle, with a detection limit of 17 nM for H2O2. M-HP was applied to imaging of H2O2 fluctuation in living cells with excellent reversibility and mitochondrial targeting. M-HP reveals an increase in mitochondrial H2O2 under lipopolysaccharide stimulation and a decrease in H2O2 following the combined treatment with rapamycin. This suggests that the level of oxidative stress is significantly suppressed after the enhancement of mitophagy. The rationally designed M-HP offers a powerful tool for understanding redox imbalance during mitophagy.