Imaging Probes Research Articles

Water-Soluble Bimodal Magnetic-Fluorescent Radical Dendrimers as Potential MRI-FI Imaging Probes.

Dual or multimodal imaging probes have become potent tools for enhancing detection sensitivity and accuracy in disease diagnosis. In this context, we present a bimodal imaging dendrimer-based structure that integrates magnetic and fluorescent imaging probes for potential applications in magnetic resonance imaging and fluorescence imaging. It stands out as one of the rare examples where bimodal imaging probes use organic radicals as the magnetic source, despite their tendency to entirely quench fluorophore fluorescence. Opting for organic radicals over metal-based contrast agents like gadolinium (Gd3+)-chelates is crucial to mitigate associated toxicity concerns. We utilized an amino-terminated polyamide dendrimer containing a 1,8-naphthalimide (Naft) fluorescent group, amino acid derivatives as linkers to enhance water solubility, and TEMPO organic radicals as terminal groups. The same dendrimer structure, featuring an equivalent number of branches but lacking the fluorophore group, was also functionalized with amino acid and terminal radicals to serve as a reference. Remarkably, we achieved a fully water-soluble dendrimer-based structure exhibiting both magnetic and fluorescent properties simultaneously. The fluorescence of the Naft group in the final structure is somewhat quenched by the organic radicals, likely due to photoinduced electron transfer with the nitroxyl radical acting as an electron acceptor, which has been supported by density functional theory calculations. Molecular dynamics simulations are employed to investigate how the dendrimers' structure influences the electron paramagnetic resonance characteristics, relaxivity, and fluorescence. In summary, despite the influence of the radicals-fluorophore interactions on fluorescence, this bimodal dendrimer demonstrates significant fluorescent properties and effective r1 relaxivity of 1.3 mM-1 s-1. These properties have proven effective in staining the live mesenchymal stem cells without affecting the cell nucleus.

A Near-Infrared Fluorescent Probe for Live-Cell Imaging of RNA in the Cancer Cells.

Ribonucleic acid (RNA), a biomolecular compound polymerized by many riboside monomers, is one of the most essential substances in life. Monitoring RNA changes within organisms will play an important role in the diagnosis and treatment of major genetically related diseases. Herein, we synthesized a novel compound QOT-NA as near-infrared probe for imaging RNA in cancer cells. The synthesis method and photophysical properties of the probe were presented. The titration and selectivity experiments demonstrated that the probe detected RNA in vitro. Moreover, the RNA imaging experiments indicated that the near-infrared RNA probe QOT-NA can locate RNA within cancer cells.

A biocompatible fluorescent probe for endogenous hydrogen sulfide detection and imaging.

Hydrogen sulfide (H2S) acts as a messenger molecule and can mediate a variety of physiological functions. Conventional methods are seldom used to detect endogenous H2S and present some difficulties in selective and accurate detection. Reaction-based recognition of endogenous H2S by organic small molecule probes with good specificity and biocompatibility. To address this challenge, we developed a novel H2S fluorescent probe 4-(2-(6-hydroxy-2-naphthyl) ethyl)-1-methylpyridinium (DSNP) that triggers a thiolysis reaction through a strong electron withdrawing group, releasing a fluorescent molecule. The simple probe DSNP not only have good selectivity, large Stokes shifts and biocompatibility, but also demonstrated a detection limit as low as 28.4 nM and reaction times as quick as 30 minutes. Moreover, it has been successfully applied to imaging intracellular H2S in myeloma cells and zebrafish. This study opens new insights to help push this probe forward for its applicability for detailed H2S localization studies in osteosarcoma.

In vivo evaluation of complex polyps with endoscopic optical coherence tomography and deep learning during routine colonoscopy: a feasibility study.

Standard-of-care (SoC) imaging for assessing colorectal polyps during colonoscopy, based on white-light colonoscopy (WLC) and narrow-band imaging (NBI), does not have sufficient accuracy to assess the invasion depth of complex polyps non-invasively during colonoscopy. We aimed to evaluate the feasibility of a custom endoscopic optical coherence tomography (OCT) probe for assessing colorectal polyps during routine colonoscopy. Patients referred for endoscopic treatment of large colorectal polyps were enrolled in this pilot clinical study, which used a side-viewing OCT catheter developed for use with an adult colonoscope. OCT images of polyps were captured during colonoscopy immediately before SoC treatment. A deep learning model was trained to differentiate benign from deeply invasive lesions for real-time diagnosis. 35 polyps from 32 patients were included. OCT imaging added on average 3:40min (range 1:54-8:20) to the total procedure time. No complications due to OCT were observed. OCT revealed distinct subsurface tissue structures that correlated with histological findings, including tubular adenoma (n = 20), tubulovillous adenoma (n = 10), sessile serrated polyps (n = 3), and invasive cancer (n = 2). The deep learning model achieved an area under the receiver operating characteristic curve (AUROC) of 0.984 (95%CI 0.972-0.996) and Cohen's kappa of 0.845 (95%CI 0.774-0.915) when compared to gold standard histopathology. OCT is feasible and safe for polyp assessment during routine colonoscopy. When combined with deep learning, OCT offers clinicians increase confidence in identifying deeply invasive cancers, potentially improving clinical decision-making. Compared to previous studies, ours offers a nuanced comparison between not just benign and malignant lesions, but across multiple histological subtypes of polyps.

Statistical-based modeling strategy for entrance skin dose estimation in patient undergoing body interventional radiology.

Interventional radiology (IR) provides significant advancements in diagnostic and therapeutic procedures, yet concerns persist regarding radiological risks such as erythema, burns, and epilation. Direct dose measurements observed difficulties regarding the perturbation of the detector probe in X-ray images during fluoroscopy-guided procedures, high-cost expenses, and non-compliant patients. This study aims to develop a statistical-based model for estimating entrance skin dose (ESD) in body IR procedures using patient radiation-dose recording data. Models are categorized into vascular and non-vascular procedures. This study demonstrates that the simplified models are sufficient in estimating patient ESDs for both IR groups, with a 95% confidence interval. This user-friendly method enables radiologists to calculate doses without complex parameters such as the backscatter factor and mass-energy absorption coefficient, as required in conventional calculation methods. It not only does this support to radiologists in effectively refining treatment protocols, but also enables patients to monitor their received doses immediately after treatment ends.

Spontaneously Blinkogenic Probe for Wash-Free Single-Molecule Localization-Based Super-Resolution Imaging in Living Cells.

Single-molecule localization super-resolution fluorescence imaging relies on the fluorescence ON/OFF switching of fluorescent probes to break the diffraction limit. However, the unreacted or nonspecifically bound probes cause non-targeted ON/OFF switching, resulting in substantial fluorescence background that significantly reduces localization precision and accuracy. Here, we report a blinkogenic probe HM-DS655-Halo that remains blinking OFF until it binds to HaloTag, thereby triggering its self-blinking activity and enabling its application in direct SMLM imaging in living cells without wash-out steps. We employed the ratio of the duty cycle before and after self-blinking activation, termed as the parameter "RDC" to characterize blinkogenicity. The covalent binding to HaloTag induces HM-DS655-Halo to transition from a fluorescent OFF state to a fluorescence blinking state. This transition also leads to a change in the RDC value, which is calculated to be 12, ensuring superblinkogenicity to effectively suppress background signals in living cells. HM-DS655-Halo was successfully applied in dynamic SMLM imaging of diverse intracellular sub-structures with minimal background noise, including mitochondrial fission and contact, cell migration, and pseudopod growth.

Thymidine Phosphorylase Imaging Probe for Differential Diagnosis of Metabolic dysfunction-associated Steatohepatitis.

Metabolic dysfunction-associated steatotic liver disease (MASLD) comprises simple steatosis (SS), which has a low risk of mortality, and metabolic dysfunction-associated steatohepatitis (MASH), which can progress to liver cirrhosis and hepatocellular carcinoma. Because differentiation between MASH and SS is the most important issue in the diagnosis of MASLD, the establishment of noninvasive diagnostic methods is urgently needed. In this study, we evaluated the potential of [123I]IIMU, a thymidine phosphorylase (TYMP) targeted SPECT imaging probe, for differential diagnosis of MASLD in a preclinical animal model. SS and MASH mice were prepared by feeding db/db mice with a standard diet and a methionine/choline-deficient diet, respectively. Control mice were prepared by feeding m/m mice with a standard diet. TYMP expression in the liver was evaluated by RT-PCR, western blotting, and immunohistochemistry. The biodistribution of [125I]IIMU in the three model mice was evaluated at 30min post-injection. SPECT/CT imaging studies of the three model mice were performed 30min after injection of [123I]IIMU. Hepatic TYMP expression level was the highest in the SS mice and the lowest in the MASH mice at both mRNA and protein levels. The immunohistochemistry experiment showed a patchy distribution of TYMP only in the liver of MASH mice. In the biodistribution study, the hepatic accumulation of [125I]IIMU was the highest in the SS mice and the lowest in the MASH mice. The SPECT/CT imaging study showed similar results to the biodistribution experiment. Hepatic TYMP expression level may serve as a promising imaging biomarker for differential diagnosis of SS and MASH. SPECT imaging using [123I]IIMU potentially provides a novel noninvasive diagnostic method to differentiate MASH and SS.

Atomically Precise Fluorescent Gold Nanocluster as a Barrier-Permeable and Brain-Specific Imaging Probe.

Photonic nanomaterials play a crucial role in facilitating the necessary signal for optical brain imaging, presenting a promising avenue for early diagnosis of brain-related disorders. However, the blood-brain barrier (BBB) presents a significant challenge, blocking the entry of most molecules or materials from the bloodstream into the brain. To overcome this, photonic nanocrystals in the form of gold clusters (LAuC) with size less than 3 nm, have been developed, with Levodopa conjugated to LAuC (Dop@LAuC) for targeted brain imaging. Dop@LAuC crosses the BBB and emits in the near-infrared (NIR) wavelength, enabling real-time optical brain imaging. An in vitro BBB model using brain endothelial cells showed that 50 % of Dop@LAuC crossed the barrier within 3 hours, compared to only 10 % of LAuC, highlighting the enhanced ability of L-dopa-conjugated gold clusters to penetrate the BBB. In vivo optical imaging in healthy mice further confirmed the material's efficacy to cross BBB without compromising the barrier integrity.

Enhanced Molecular Imaging through a Versatile Peptide Nanofiber for Self-assembly and Precise Recognition.

Designing molecules for multivalent targeting of specific disease markers can enhance binding stability which is critical in molecular imaging and targeted therapy. Through rational molecular design, the nanostructures formed by self-assembly of targeting peptides are expected to achieve multivalent targeting by increasing the density of recognition ligands. However, the balance between targeting peptide self-assembly and molecular recognition remains elusive. In this study, we designed a targeting-peptide-based imaging probe system TAP which consist of the signal unit, the recognition motif, the assembly motif and a Pro-leverage. It is verified that TAP could specifically binds to PD-L1-positive tumor cells in a multivalent manner to produce biological effects, and could also be combined with imaging probes through unique self-assembly strategies. By the balance between the peptide self-assembly and targeting recognition, the specificity and stability can be improved while the accumulation capacity of the probes at the tumor site can be greatly enhanced compared with the conventional strategy, thus reducing side effects, providing an effective tool for diagnostic and therapeutic integration of tumors.

Biomass-Derived Organonanomaterials as Contrast Agents for Efficient Magnetic Resonance Imaging.

Magnetic resonance imaging (MRI) is a popular imaging tool that is valuable for the early detection and monitoring of malignancies because it does not involve radiation and is noninvasive. Metal-based contrast agents (CAs) are commonly used in clinical settings despite concerns about the toxicity of free metals. Therefore, finding alternative nontoxic imaging probes is vital. In this work, we have synthesized and effectively utilized sustainable biomass lignin-based all-organic nanoconjugates linked with nitroxide radicals as MRI CAs. Lignin grafted with poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) (LPGT) exhibits a longitudinal relaxivity of 0.54 mM-1 s-1. LPGT shows exceptional characteristics, including resistance to reduction and nontoxicity toward living organisms. LPGT displays enhanced MRI contrast in the BALB/c mouse model for a duration exceeding 4.35 h. Our primary goal is to design MRI agents that are exceptionally effective sustainable biomass-derived materials and do not require the use of metals. Nicely, LPGT offers adequate contrast enhancement at 5-fold lower (0.020 mmol/kg) than the standard dose (0.1 mmol/kg), easing worries about toxic metal buildup. Consequently, LPGT shows promise as a feasible CA for metal-free MRI.

Utility of Esophageal Physiologic Tests in Eosinophilic Esophagitis

Background: In patients with eosinophilic esophagitis (EoE), the correlation between symptoms of esophageal dysfunction and endoscopic and histologic disease activity is generally poor and probably related to multiple causes such as esophageal remodeling processes that might go undetected using endoscopy and histology as well as esophageal hypervigilance and symptom-specific anxiety. Hence, there is a need for a holistic management of patients that goes beyond the control of eosinophilia and symptoms. Summary & Key messages: Physiological esophageal testing using high-resolution manometry, functional lumen imaging probe, pH-impedance, wireless pH monitoring and mucosal impedance may unveil the effects of chronic transmural fibro-inflammatory changes of the esophageal wall as well as esophageal hypervigilance, thereby assisting to phenotype patients, predict therapeutic response to therapy and identify motility disorders that may need a specific targeted therapy to ameliorate patients’ outcomes. This article discusses the role of functional esophageal examinations in the diagnosis and management of EoE.

Estimation of Scattering Properties Modifications Caused by InVivo Human Skin Optical Clearing Using Line-Field Confocal Optical Coherence Tomography.

The image contrast and probing depth of optical methods applied to invivo skin could be improved by reducing skin scattering using the optical clearing method. The aim of this study was to quantify, from line-field confocal optical coherence tomography (LC-OCT) 3D images, the modifications of skin scattering properties invivo during optical clearing. Nine mixtures of optical clearing agents were used in combination with physical and chemical permeation enhancers on the human skin of three healthy volunteers. Scattering coefficient and anisotropy factor of the epidermis and the upper dermis were estimated from the 3D LC-OCT images of skin using an exponential decay model of the in-depth intensity profile. We were able to demonstrate a decrease in epidermal scattering (down to 33%) related to optical clearing, with the best results obtained by a mixture of polyethylene glycol, oleic acid, and propylene glycol.

Fe(III) Complexes as the Optical Imaging Probe for l-Arginine via the Redox Mechanism

Fe(III) Complexes as the Optical Imaging Probe for <scp>l</scp>-Arginine via the Redox Mechanism

Investigation of magnetic resonance contrast properties of PEG-coated gadolinium oxide nanoparticles in various biological environments

Abstract Magnetic nanoparticles (MNPs) are promising tools for biomedical applications, particularly in molecular imaging using magnetic resonance imaging (MRI). The unique magnetic properties of MNPs, combined with their similarity in size to biological objects, make them ideal candidates for in situ imaging probes. The present study explores the use of magnetic nanoparticles (MNPs) as contrast agents in magnetic resonance imaging (MRI) for improved diagnostic accuracy. Specifically, the study investigates the MR contrast properties of polyethylene glycol-coated gadolinium oxide nanoparticles (PEG@GONPs) in five different biological fluids. The nanoparticles were synthesized using the polyol route and their size, shape, and morphology were characterized using TEM, SEM, and FT-IR spectroscopy. The magnetic resonance (MR) relaxivity of PEG@GONPs was studied in different biologically relevant media, and results revealed highest relaxivity in plasma as compared to other media. In addition, comparative analysis of proton relaxivity of the synthesized nanoparticles was carried out with a well-known gadolinium-based contrast agent, Omniscan, in various medium. The present findings revealed that PEG@GONPs can serve as an effective contrast agent for MRI imaging in biological fluids such as plasma, which is crucial for preclinical diagnosis of specific diseases and lesions. The high relaxivity observed in plasma could be attributed to the interaction of the nanoparticles with plasma proteins, amplifying their magnetic properties which further improve their ability to produce contrast in MR images.

Balancing Brightness and Photobasicity: Modulating Excited-State Proton Transfer Pathways in Push-Pull Fluorophores for Biological Two-Photon Imaging.

Push-pull fluorophores with donor-π-acceptor architectures are attractive scaffolds for the design of probes and labels for two-photon microscopy. Such fluorophores undergo a significant charge-delocalization in the excited state, which is essential for achieving a large two-photon absorption cross-section and brightness. The polarized excited state may, however, also facilitate excited-state proton transfer (ESPT) pathways that can interfere with the probe response. Herein, we employed steady-state and time-resolved spectroscopic studies to elucidate whether ESPT is responsible for the pH-dependent emission response of the Zn(II)-selective fluorescent probe chromis-1. Composed of a push-pull architecture with a pyridine ring as the acceptor, the chromis-1 fluorophore core acts as a photobase that promotes ESPT upon acidification. Although the pKa of the pyridine acceptor increases more than six orders of magnitude upon excitation, the photobasicity is not sufficient to deprotonate solvent water molecules under neutral conditions. Rather, the pH-dependent emission response is caused by the pendant bis-isonicotinic acid chelating group which upon protonation facilitates an excited-state intramolecular proton transfer to the pyridine acceptor. A simple permutation of the core pyridine nitrogen from the para- to the ortho-position relative to the thiazole substituent was sufficient to reduce the excited-state basicity by two orders of magnitude without compromising the two-photon excited brightness. These results highlight the importance of choosing the appropriate fluorophore core and chelating moiety for minimizing pH-dependent responses in the design of fluorescent probes for biological imaging.

Axl and EGFR Dual-Specific Binding Affibody for Targeted Therapy in Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma (NPC) is a tumor of the head and neck, with a higher incidence in southern China and Southeast Asia. Radiotherapy and chemotherapy are the main treatments; however, metastasis and recurrence remain the main causes of treatment failure. Further, the majority of patients are diagnosed in the late stage due to lack of tumor-specific biomarker for early diagnosis. Therefore, an effective treatment and early detection can improve the outcome of patient with NPC. Axl and EGFR are co-expressed in NPC tissues and play key roles in tumor proliferation, migration, and invasion, which are often correlated with poor prognosis and therapy resistance. In this study, we generated a novel bispecific affibody (Z239-1907) for the dual targeting and inhibition of Axl and EGFR expression in NPC-positive cells both in vitro and in vivo. The in vitro experiments demonstrated that Z239-1907 had more pronounced antitumor effects than either modality alone (ZAXL239 or ZEGFR1907) in NPC-positive cells. Further, mice bearing NPC-positive tumors showed significant inhibition in tumor growth after treatment with Z239-1907 compared to ZAXL239 and ZEGFR1907. The in vivo tumor targeting ability and imaging also showed that Z239-1907 specifically and selectively targeted NPC xenograft mice models and accumulate at tumor site as early as 30 min and disappeared within 24 h post-injection. Collectively, these results suggest that Z239-1907 dual-target affibody is a promising therapeutic agent and a molecular imaging probe for early diagnosis in NPC.

Evaluation of a novel forward-looking optical coherence tomography probe for endoscopic applications: an ex vivo feasibility study.

As a result of recent advances in the development of small microelectromechanical system mirrors, a novel forward-looking optical coherence tomography (OCT) probe with a uniquely large field of view is being commercially developed. The aim of this study is to prospectively assess the feasibility of this advanced OCT probe in interpreting ex vivo images of colorectal polyp tissue and to identify necessary steps for further development. A total of 13 colorectal lesions from 9 patients, removed during endoscopic resection, were imaged ex vivo with the OCT device and compared with histopathological images that served as the gold standard for diagnostics. Normal tissue from one patient, removed during the endoscopic procedure, was imaged as a negative control. We assessed the presence of features indicative for polyp type and degree of dysplasia, by comparing OCT images to histopathological images and by evaluating the presence of OCT-specific features identified by previous studies, such as effacement (loss of layered tissue structure), a hyperreflective epithelial layer, and irregularity of the surface. As verified by corresponding histological images, tissue structures such as blood vessels and tissue layers could be distinguished in OCT images of the normal tissue sample. Detailed structures on histological images such as crypts and cell nuclei could not be identified in the OCT images. However, we did identify OCT features specific for colorectal lesions, such as effacement and a hyperreflective epithelial layer. In general, the imaging depth was about 1mm. Some relevant tissue structures could be observed in OCT images of the novel device. However, some adaptations, such as increasing imaging depth using a laser with a longer central wavelength, are required to improve its clinical value for the imaging of colorectal lesions.

Trimethyl Lock Based Tools for Drug Delivery and Cell Imaging - Synthesis and Properties.

Trimethyl lock (TML) systems have become increasingly important in medicinal and bioorganic chemistry, particularly for their roles in the targeted delivery of therapeutic agents and as integral components in fluorogenic probes for cellular imaging. The simplicity and efficiency of their synthesis have established TML systems as versatile platforms for the controlled release of active molecules under particular physiological conditions. This review consolidates recent advancements in the application of TML systems, with a focus on their use in drug delivery, cellular imaging, and other areas where precise molecular release is crucial. Additionally, we discuss the synthetic strategies employed to construct TML-based conjugates, underscoring their potential to enhance the specificity and efficacy of bioactive compounds in various biomedical applications.

Sustained Regeneration of Hydrogen Peroxide at the Water-Gas Interface of Electrogenerated Microbubbles on an Electrode Surface.

Microbubbles, inside-out microdroplets, act as extraordinary microreactors to facilitate thermodynamically unfavorable reactions in bulk solutions of water. We explored the formation of hydrogen peroxide (H2O2) and its sustained regeneration at the interface of water-gas microbubbles. For this purpose, the chemiluminescence of luminol was recorded by a digital camera to map the intensity of blue light emission over the time of about 20 min. The formation and regeneration of hydrogen peroxide were also monitored by fluorescence microscopic imaging of a hydrogen peroxide probe. The microscopic images consistently show a stable glow around the microbubbles over time during which the formed hydrogen peroxide diffuses into the bulk solution. This observation confirms that the concentration of H2O2 at the interface is 30 times higher than that in the water solution bulk after several minutes, which can be attributed to its regeneration at the water-gas interface. These findings increase our understanding of why the chemistries of gas microbubbles in water and water microdroplets surrounded by gas are so distinct from those of bulk-phase water.

Unlocking Single-Particle Multiparametric Sensing: Decoupling Temperature and Viscosity Readouts through Upconverting Polarized Spectroscopy.

Upconverting particles (UCPs), renowned for their capability to convert infrared to visible light, serve as invaluable imaging probes. Furthermore, their responsiveness to diverse external stimuli holds promise for leveraging UCPs as remote multiparametric sensors, capable of characterizing medium properties in a single assessment. However, the utility of UCPs in multiparametric sensing is impeded by crosstalk, wherein distinct external stimuli induce identical alterations in UCP luminescence, hindering accurate interpretation, and yielding erroneous outputs. Overcoming crosstalk requires alternative strategies in upconverting luminescence analysis. In this study, it is shown how a single spinning NaYF4:Er3+, Yb3+ upconverting particle enables simultaneous and independent readings of temperature and viscosity. This is achieved by decoupling thermal and rehological measurements-employing the luminescence of thermally-coupled energy levels of Er3+ ions for thermal sensing, while leveraging the polarization of luminescence from non-thermally coupled levels of Er3+ ions to determine viscosity. Through simple proof-of-concept experiments, the study validates the capability of a single spinning UCP to perform unbiased, simultaneous temperature, and viscosity sensing, thereby opening new avenues for advanced sensing in microenvironments.