Vision for Ratiometric Nanoprobes: In Vivo Noninvasive Visualization and Readout of Physiological Hallmarks

Magnetic-susceptibility-dependent ratiometric probes for enhancing quantitative MRI

In magnetic resonance imaging (MRI), quantitative measurements of analytes are hindered by difficulties in distinguishing the MRI signals of activation of the probe by the analyte from those of the accumulation of the intact probe. Here we show that imaging sensitivity and quantitation can be enhanced by ratiometric MRI probes with a high relaxivity-ratio change (more than 2.5-fold at 7 T) via magnetic-susceptibility-dependent magnetic resonance tuning. Specifically, polymeric probes that incorporate paramagnetic Mn-porphyrin and superparamagnetic iron oxide nanoparticles inducing opposite changes in the longitudinal and transverse magnetic relaxivities responded to analyte concentration independently of probe concentration. In mice, the probes allowed for quantitative real-time dynamic imaging of H2O2, H2S or pH in subcutaneous tumours, in livers with drug-induced injury and in orthotropic gliomas. The ratiometric MRI probes may be advantageously used to obtain molecular insight into pathological processes and to circumvent interference from dynamic changes in probe concentration within the body while providing anatomical information.

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.

CRISPR/Cas12a-derived ratiometric fluorescence sensor for high-sensitive Pb2+ detection based on CDs@ZIF-8 and DNAzyme

Benefiting from specific target recognition and trans-cleavage capabilities, the CRISPR/Cas12a system has great application prospects in the design of highly sensitive and rapid fluorescence biosensors. The CRISPR/Cas12a-based fluorophore-quencher molecular beacons exhibit single-color emission and are easily exposed to interference from environmental factors. Herein, we design a CRISPR/Cas12a-derived ratiometric fluorescence sensor for Pb2+ detection based on embedded carbon dots@zeolitic imidazolate framework-8 (CDs@ZIF-8) composites and DNAzyme. The functions of ZIF-8 about encapsulating red emissive CDs in the inner cavity and adsorbing DNA on the outer surface are integrated to establish dual fluorescence signals, thereby reducing the possibility of interference and improving sensing accuracy. The presence of Pb2+ is converted into the change of activator by the GR5 DNAzyme to activate the CRISPR/Cas12a system, which provides signal amplification through multiple turnovers of side branch cutting, achieving highly sensitive detection of Pb2+ with a low detection limit of 18 pM. This method has the advantages of simplicity, universality, and excellent quantitative ability, and has broad prospects in sensing applications.

Rational Design of NIR-II Ratiometric Fluorescence Probes for Accurate Bioimaging and Biosensing In Vivo

Intravital fluorescence imaging in the second near-infrared window (NIR-II, 900-1700 nm) has emerged as a promising method for non-invasive diagnostics in complex biological systems due to its advantages of less background interference, high tissue penetration depth, high imaging contrast, and sensitivity. However, traditional NIR-II fluorescence imaging, which is characterized by the "always on" or "turn on" mode, lacks the ability of quantitative detection, leading to low reproducibility and reliability during bio-detection. In contrast, NIR-II ratiometric fluorescence imaging can realize quantitative and reliable analysis and detection in vivo by providing reference signals for fluorescence correction, generating new opportunities and prospects during in vivo bioimaging and biosensing. In this review, the current design strategies and sensing mechanisms of NIR-II ratiometric fluorescence probes for bioimaging and biosensing applications are systematically summarized. Further, current challenges, future perspectives and opportunities for designing NIR-II ratiometric fluorescence probes are also discussed. It is hoped that this review can provide effective guidance for the design of NIR-II ratiometric fluorescence probes and promote its adoption in reliable biological imaging and sensing in vivo.

Activatable Probes for Ratiometric Imaging of Endogenous Biomarkers In Vivo

Dynamic variations in the concentration and abnormal distribution of endogenous biomarkers are strongly associated with multiple physiological and pathological states. Therefore, it is crucial to design imaging systems capable of real-time detection of dynamic changes in biomarkers for the accurate diagnosis and effective treatment of diseases. Recently, ratiometric imaging has emerged as a widely used technique for sensing and imaging of biomarkers due to its advantage of circumventing the limitations inherent to conventional intensity-dependent signal readout methods while also providing built-in self-calibration for signal correction. Here, the recent progress of ratiometric probes and their applications in sensing and imaging of biomarkers are outlined. Ratiometric probes are classified according to their imaging mechanisms, and ratiometric photoacoustic imaging, ratiometric optical imaging including photoluminescence imaging and self-luminescence imaging, ratiometric magnetic resonance imaging, and dual-modal ratiometric imaging are discussed. The applications of ratiometric probes in the sensing and imaging of biomarkers such as pH, reactive oxygen species (ROS), reactive nitrogen species (RNS), glutathione (GSH), gas molecules, enzymes, metal ions, and hypoxia are discussed in detail. Additionally, this Review presents an overview of challenges faced in this field along with future research directions.

Molecular imaging of tumour-associated pathological biomarkers with smart nanoprobe: From "Seeing" to "Measuring"

Although the extraordinary progress has been made in molecular biology, the prevention of cancer remains arduous. Most solid tumours exhibit both spatial and temporal heterogeneity, which is difficult to be mimicked in vitro. Additionally, the complex biochemical and immune features of tumour microenvironment significantly affect the tumour development. Molecular imaging aims at the exploitation of tumour-associated molecules as specific targets of customized molecular probe, thereby generating image contrast of tumour markers, and offering opportunities to non-invasively evaluate the pathological characteristics of tumours in vivo. Particularly, there are no "standard markers" as control in clinical imaging diagnosis of individuals, so the tumour pathological characteristics-responsive nanoprobe-based quantitative molecular imaging, which is able to visualize and determine the accurate content values of heterogeneous distribution of pathological molecules in solid tumours, can provide criteria for cancer diagnosis. In this context, a variety of "smart" quantitative molecular imaging nanoprobes have been designed, in order to provide feasible approaches to quantitatively visualize the tumour-associated pathological molecules in vivo. This review summarizes the recent achievements in the designs of these nanoprobes, and highlights the state-of-the-art technologies in quantitative imaging of tumour-associated pathological molecules.

Ratiometric Optical and Photoacoustic Imaging In Vivo in the Second Near-Infrared Window

Optical imaging and photoacoustic (PA) imaging have become essential tools to investigate physiological or pathological processes at the molecular level in vivo. The detection of variations at the molecular level in vivo is particularly important owing to the rapid progression of diseases. However, most studies have mainly focused on plain qualitative molecular imaging and detection, which is characterized by the absence of a reference signal in one-channel responsive imaging. To overcome the limitation and quantitatively detect molecules in situ, this Account reviews the recent contributions of our group to the quantitative imaging field in the form of ratiometric optical and PA imaging in vivo in the second near-infrared window (NIR-II, 950-1700 nm).In this Account, we present recent advances that our group has made in ratiometric imaging probe design and biomedical applications by constructing probes based on ratiometric optical imaging and ratiometric PA imaging. First, we highlight the design strategies of ratiometric optical probes that were based on organic ratiometric molecular probes, radio-activated organic ratiometric probes, and hybrid organic-inorganic assembled ratiometric probes. Subsequently, the design strategies of the ratiometric NIR-II optical nanoprobes with activated bioluminescence resonance energy transfer (BRET), Förster resonance energy transfer (FRET), and nonradiative energy transfer (NRET) effects provide a reliable tool to achieve the ratiometric detection of endogenous signaling molecules and thereby apply it to the monitoring and evaluation of the efficacy of photodynamic therapy, radiotherapy, and immunotherapy to guide the treatment process. In addition, we systematically introduce the functional design principles of ratiometric PA imaging probes based on core-shell nanoprobes, core-satellite nanoprobes, and universal hybrid nanoprobes, where we have established that reference signal and sensing signal can be obtained from the random assortment of plasmonic components and organic semiconducting molecules using a phase separation strategy. On these insights, we discuss the rational and detailed biomedical applications of ratiometric PA imaging probes which include accurate quantitative detection of disease-related molecules in inflammation or tumors in real time. In these champion implementations of ratiometric PA imaging probes, different diagnostic modules have been linked through compound modification with activation characteristics (e.g., pH, redox, enzyme, hypoxia). Finally, we present the challenges and perspectives for ratiometric probes based on optical imaging and PA imaging for multitarget design and future clinical translation. We believe that the upcoming generations of ratiometric imaging probes would have promising potential applications in the precise diagnosis of diseases. Finally, this Account may stimulate innovative studies in the design of ratiometric imaging probes and exploration of their clinical applications.

Precise visualization and ROS-dependent photodynamic therapy of colorectal cancer with a novel mitochondrial viscosity photosensitive fluorescent probe

BACKGROUND

Colorectal cancer (CRC) is a prominent global cancer with high mortality rates among human beings. Efficient diagnosis and treatment have always been a challenge for CRC management. Fluorescence guided cancer therapy, which combines diagnosis with therapy into one platform, has brought a new chance for achieving precise cancer theranostics. Among this, photosensitizers, applied in photodynamic therapy (PDT), given the integration of real-time imaging capacity and efficacious treatment feasibility, show great potential to serve as remarkable tools. Although much effort has been put into constructing photosensitizers for locating and destroying CRC cells, it is still in high need to develop novel photosensitizers to attain specific detection and fulfil effective therapy.

METHODS

Probe HTI was rational synthesized for the diagnosis and treatment of CRC. Spectrometric determination was carried out first, followed by the 1O2 generation ability test. Then, HTI was displayed in distinguishing CRC cells from normal cells Further, the PDT effect of the photosensitizer was studied in vitro. Additionally, HTI was used in CRC BALB/c nude mice model to validate its viscosity labelling and tumor suppression characteristics.

RESULTS

We successfully fabricated a mitochondrial targeting probe, HTI, together with remarkable viscosity sensitivity, ultralow background interference, and excellent 1O2 generation capacity. HTI was favorably applied to the viscosity detection, displaying a 11-fold fluorescent intensity enhancement in solvents from 1.57 cp to 2043 cp. Then, it was demonstrated that HTI could distinguish CRC cells from normal cells upon the difference in mitochondrial viscosity. Moreover, HTI was qualified for producing 1O2 with high efficiency in cells, supported by the sparkling signals of DCFH after incubation with HTI under light irradiation. More importantly, the viscosity labelling and tumor suppression performance in CRC CDX model was determined, enriching the multifunctional validation of HTI in vivo.

CONCLUSIONS

In this study, HTI was demonstrated to show a sensitive response to mitochondrial viscosity and possess a high 1O2 generation capacity. Both in vitro cell imaging and in vivo tumor treatment trials proved that HTI was effectively served as a robust scaffold for tumor labeling and CRC cells clearance. This breakthrough discovery held immense potential for advancing the early diagnosis and management of CRC through PDT. By leveraging HTI's properties, medical professionals could benefit from improved diagnostic accuracy and targeted treatment in CRC management, ultimately leading to enhanced patient outcomes.