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

BODIPY-based small molecular probes for fluorescence and photoacoustic dual-modality imaging of superoxide anion in vivo

Superoxide anion contributes significantly in the pathological process of acute liver injury. Therefore, real-time in vivo imaging of superoxide anion is of great significance for understanding the pathogenesis. Nevertheless, developing superoxide anion probes that possess high sensitivity and resolution continues to be a challenge. Herein, we report the design of BODIPY-based molecule probes (BDPOS1-2) for fluorescence and photoacoustic dual-modality imaging of superoxide anion. The probes exhibited exceptional selectivity and specificity towards superoxide anion, with a "turn-on" photoacoustic and "turn-off" fluorescence response. They maintained good stability and demonstrated the response behavior to superoxide anion within the pH range of 5-10. BDPOS1-2 can be used for fluorescence imaging endogenous and exogenous superoxide anion in HepG2 cells with detection in the 670-750 nm channel. Notably, galactose-modified BDPOS2 demonstrated selective hepatocyte-targeting capability and achieved dual-modality imaging of superoxide anions during acute liver injury in live mice via capturing photoacoustic signals at 715 nm and fluorescence signals in the 650-690 nm channel. Our findings offer a powerful approach for high-sensitivity and high-resolution in vivo imaging, with considerable potential for early and precise diagnosis of liver injury.

A Self-Immobilizing Photoacoustic Probe for Ratiometric In Vivo Imaging of Cu(II) in Tumors

Cu(II) ions play a critical role in tumor growth and metastasis, making in vivo high-resolution imaging of Cu(II) crucial for understanding its role in tumor pathophysiology. However, designing suitable molecular probes for this purpose remains challenging. Herein, we report the development of a photoacoustic probe for specific in vivo imaging of Cu(II) in tumors. This probe utilizes β-galactoside as a targeting group and incorporates a unique self-immobilization strategy. Upon β-galactosidase-mediated cleavage, the probe generates a reactive quinone methide intermediate that covalently binds to intracellular proteins, enabling selective tumor accumulation. The probe exhibits a ratiometric photoacoustic response to Cu(II) with high selectivity over that of other biological species. In vitro and in vivo studies demonstrated the efficacy of the probe for Cu(II) imaging in tumors. This research provides valuable insights into the role of Cu(II) in tumorigenesis and may facilitate the development of diagnostic and therapeutic approaches for cancer.

Enzyme-free amplification-enhanced ratiometric fluorescence method for highly sensitive detection of acute myocardial infarction biomarkers

A wide range of proteins, including enzymes, hormones, immune factors and regulatory proteins, are essential for a variety of physiological processes. Dysregulation of the levels of specific proteins in organisms is known to adversely affects the human body. Given the pathophysiological significance of cardiac troponin I (cTnI), simple methods for detecting the sensitivity and selectivity of cTnI in biological systems are in high demand and have therefore been extensively explored. Nonetheless, the early detection of low concentrations of cTnI in the human body continues to be a focal point and area of interest in bioassays, due to the low levels and intricate composition of biomarkers in bodily fluids (e.g., blood, sweat, urine, and saliva), which impose rigorous demands on the sensitivity and stability of detection methods. The assay platform is isothermal, homogeneous and has simple experimental conditions without proteases. Using ratiometric fluorescence with built-in self-correction, we achieved low background values and improved the accuracy of the assay results. Our method enhances detection sensitivity by utilizing the cycling of probe X during strand replacement. Triple sensitization was achieved by combining ratiometric fluorescence on the basis of normal strand displacement reaction. In the experiment, the dual sensitization was reflected by the high sensitivity (0.001 ng/mL) and wide linear detection range (0.001 ng/mL∼1000 ng/mL) of cTnI in real serum samples. In particular, the snapshots of the simulation process were recorded through accurate simulation calculations and multidimensional characterization analysis, which revealed the changes in the system energy during the simulation process. The sensing platform combines multiple technological advantages, and we are optimistic that the versatility of this research has great potential for application in the fields of early screening and diagnosis and military medical applications.

Ratiometric Photoacoustic Imaging Probe for Self-Predicting Nanozyme Therapeutic Effects

Nanozymes with intrinsic enzyme-like properties have garnered significant attention in cancer treatment. However, effective methods to evaluate in situ the catalytic activity of nanozymes in living systems remain lacking. Herein, we pioneeringly present a novel probe (1-FCuSA) for self-reporting nanozyme catalytic activity, which integrates a diene electrochromic material (EM 1) and a copper single-atom nanozyme (FCuSA) with peroxidase (POD)-like activity. This system is designed to self-predict its catalytic activity through a ratiometric photoacoustic (PA) imaging signal. Initially, 1-FCuSA exhibits a low PA ratio (PA808/PA1064) between 808 and 1064 nm. Upon reaction with hydroxyl radicals (•OH) generated by the POD-like activity of FCuSA, the PA signal at 808 nm significantly increases, while the signal at 1064 nm remains stable. This results in an obvious increase in PA808/PA1064, enabling accurate monitoring of •OH production during nanozyme-catalyzed therapy. Thus, 1-FCuSA not only induces specific POD-like activity for in vivo tumor treatment but also provides real-time monitoring of catalytic efficiency through ratiometric PA imaging. This innovative approach may offer new insights into the early prediction of anticancer efficacy and guide the application of nanozymes in living systems.

Designing small-molecule and macromolecule sensors for imaging redox-active transition metal signaling

Transition metals play essential roles in biology, where these nutrients regulate protein activity as active site cofactors or via metalloallostery. In contrast, dysregulation of transition metal homeostasis can lead to unique metal-dependent signaling pathways connected to aging and disease, such as cuproptosis and ferroptosis for copper- and iron-dependent cell death or cuproplasia and ferroplasia for copper- and iron-dependent cell growth and proliferation, respectively. New methods that enable detection of bioavailable transition metal pools with both metal and oxidation state specificity can help decipher their contributions to health and disease. Here we summarize recent advances in designing sensors for imaging transition metals and their applications to uncover new metal biology.

Visualization of drug release in a chemo-immunotherapy nanoplatform via ratiometric 19F magnetic resonance imaging

Visualization of drug release in vivo is crucial for improving therapeutic efficacy and preventing inappropriate medication dosing, yet, challenging. Herein, we report a pH-activated chemo-immunotherapy nanoplatform with visualization of drug release in vivo by ratiometric 19F magnetic resonance imaging (19F MRI). This nanoplatform consists of ultra-small histamine-modified perfluoro-15-crown-5-ether (PFCE) nanodroplets loaded with doxorubicin (Dox), which are packaged in trifluoromethyl-containing metal-organic assemblies via coordination-driven self-assembly. The chemical shifts of two types of 19F atoms in the nanoplatform are significantly different in 19F nuclear magnetic resonance (NMR) spectra, which facilitates the implementation of ratiometric 19F MRI without any signal crosstalk. In an acidic tumor microenvironment, this nanoplatform gradually degrades, which results in a sustained drug release with a real-time change in the ratiometric 19F MRI signal. Therefore, a linear correlation between the Dox release profile and ratiometric 19F MRI signal is established to visualize Dox release. Moreover, the pH-triggered disassembly of the nanoplatform leads to cell pyroptosis, which evokes immunogenic cell death (ICD), resulting in the regression of the primary tumor and inhibition of distal tumor growth. This study provides the proof-of-concept application of ratiometric 19F MRI to visualize drug release in vivo.

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.