Optical molecular imaging for tumor detection and image-guided surgery

Magnetic Particle Imaging: From Tracer Design to Biomedical Applications in Vasculature Abnormality

Magnetic particle imaging (MPI) is an emerging non-invasive tomographic technique based on the response of magnetic nanoparticles (MNPs) to oscillating drive fields at the center of a static magnetic gradient. In contrast to magnetic resonance imaging (MRI), which is driven by uniform magnetic fields and projects the anatomic information of the subjects, MPI directly tracks and quantifies MNPs in vivo without background signals. Moreover, it does not require radioactive tracers and has no limitations on imaging depth. This article first introduces the basic principles of MPI and important features of MNPs for imaging sensitivity, spatial resolution, and targeted biodistribution. The latest research aiming to optimize the performance of MPI tracers is reviewed based on their material composition, physical properties, and surface modifications. While the unique advantages of MPI have led to a series of promising biomedical applications, recent development of MPI in investigating vascular abnormalities in cardiovascular and cerebrovascular systems, and cancer are also discussed. Finally, recent progress and challenges in the clinical translation of MPI are discussed to provide possible directions for future research and development.

Integration of O2-economised tumour-targeted photosensitive magnetic nanomaterials in the diagnosis and therapy of gastric cancer

Hypoxia in the tumour microenvironment is a major limiting factor in photodynamic therapy. The present study employed a novel O2-economised photosensitizer, ACSN, to effectively curtail oxygen consumption by impeding the aerobic respiration of tumour cells, thereby increasing the reactive oxygen species (ROS) production in photodynamic therapy. To enhance the efficacy of photodynamic therapy, the active targeting peptide iRGD was employed to facilitate drug accumulation in the tumour tissue. Therefore, we constructed a targeted drug platform, ACSN/Fe3O4@MSNs-iRGD, that integrates diagnosis and treatment. The drug exhibited excellent active targeting ability towards gastric cancer MGC-803 cells and can efficiently penetrate the mitochondria upon cellular internalisation. The photosensitizer ACSN, released from the drug, effectively suppressed mitochondrial aerobic respiration to conserve oxygen and exhibited robust ROS production upon laser excitation. The core-shell structure comprises Fe3O4, which offers excellent T2 dark contrast for real-time tumour monitoring through MRI imaging. By incorporating excellent photodynamic therapy and MRI imaging capabilities, this drug can serve as an effective platform for the integration of tumour diagnosis and treatment, thus addressing the limitations associated with conventional tumour therapies. It is anticipated that this approach will soon be clinically translated.

Theranostic Fluorescent Probes

The ability to gain spatiotemporal information, and in some cases achieve spatiotemporal control, in the context of drug delivery makes theranostic fluorescent probes an attractive and intensely investigated research topic. This interest is reflected in the steep rise in publications on the topic that have appeared over the past decade. Theranostic fluorescent probes, in their various incarnations, generally comprise a fluorophore linked to a masked drug, in which the drug is released as the result of certain stimuli, with both intrinsic and extrinsic stimuli being reported. This release is then signaled by the emergence of a fluorescent signal. Importantly, the use of appropriate fluorophores has enabled not only this emerging fluorescence as a spatiotemporal marker for drug delivery but also has provided modalities useful in photodynamic, photothermal, and sonodynamic therapeutic applications. In this review we highlight recent work on theranostic fluorescent probes with a particular focus on probes that are activated in tumor microenvironments. We also summarize efforts to develop probes for other applications, such as neurodegenerative diseases and antibacterials. This review celebrates the diversity of designs reported to date, from discrete small-molecule systems to nanomaterials. Our aim is to provide insights into the potential clinical impact of this still-emerging research direction.

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.

Protein-guided biomimetic nanomaterials: a versatile theranostic nanoplatform for biomedical applications

Over the years, bioinspired mineralization-based approaches have been applied to synthesize multifunctional organic-inorganic nanocomposites. These nanocomposites can address the growing demands of modern biomedical applications. Proteins, serving as vital biological templates, play a pivotal role in the nucleation and growth processes of various organic-inorganic nanocomposites. Protein-mineralized nanomaterials (PMNMs) have attracted significant interest from researchers due to their facile and convenient preparation, strong physiological activity, stability, impressive biocompatibility, and biodegradability. Nevertheless, few comprehensive reviews have expounded on the progress of these nanomaterials in biomedicine. This article systematically reviews the principles and strategies for constructing nanomaterials using protein-directed biomineralization and biomimetic mineralization techniques. Subsequently, we focus on their recent applications in the biomedical field, encompassing areas such as bioimaging, as well as anti-tumor, anti-bacterial, and anti-inflammatory therapies. Furthermore, we discuss the challenges encountered in practical applications of these materials and explore their potential in future applications. This review aspired to catalyze the continued development of these bioinspired nanomaterials in drug development and clinical diagnosis, ultimately contributing to the fields of precision medicine and translational medicine.

The LMIT: Light-mediated minimally-invasive theranostics in oncology

Minimally-invasive diagnosis and therapy have gradually become the trend and research hotspot of current medical applications. The integration of intraoperative diagnosis and treatment is a development important direction for real-time detection, minimally-invasive diagnosis and therapy to reduce mortality and improve the quality of life of patients, so called minimally-invasive theranostics (MIT). Light is an important theranostic tool for the treatment of cancerous tissues. Light-mediated minimally-invasive theranostics (LMIT) is a novel evolutionary technology that integrates diagnosis and therapeutics for the less invasive treatment of diseased tissues. Intelligent theranostics would promote precision surgery based on the optical characterization of cancerous tissues. Furthermore, MIT also requires the assistance of smart medical devices or robots. And, optical multimodality lay a solid foundation for intelligent MIT. In this review, we summarize the important state-of-the-arts of optical MIT or LMIT in oncology. Multimodal optical image-guided intelligent treatment is another focus. Intraoperative imaging and real-time analysis-guided optical treatment are also systemically discussed. Finally, the potential challenges and future perspectives of intelligent optical MIT are discussed.

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.

Activatable probes with potential for intraoperative tumor-specific fluorescence-imaging guided surgery

Owing to societal development and aging population, the impact of cancer on human health and quality of life has increased. Early detection and surgical treatment are the most effective approaches for most cancer patients. As the scope of conventional tumor resection is determined by auxiliary examination and surgeon experience, there is often insufficient recognition of tiny tumors. The ability to detect such tumors can be improved by using fluorescent tumor-specific probes for surgical navigation. This review mainly describes the design principles and mechanisms of activatable probes for the fluorescence imaging of tumors. This type of probe is nonfluorescent in normal tissue but exhibits obvious fluorescence emission upon encountering tumor-specific substrates, such as enzymes or bioactive molecules, or changes in the microenvironment, such as a low pH. In some cases, a single-factor response does not guarantee the effective fluorescence labeling of tumors. Therefore, two-factor-activatable fluorescence imaging probes that react with two specific factors in tumor cells have also been developed. Compared with single biomarker testing, the simultaneous monitoring of multiple biomarkers may provide additional insight into the role of these substances in cancer development and aid in improving the accuracy of early cancer diagnosis. Research and progress in this field can provide new methods for precision medicine and targeted therapy. The development of new approaches for early diagnosis and treatment can effectively improve the prognosis of cancer patients and help enhance their quality of life.

Advancements in Intraoperative Near-Infrared Fluorescence Imaging for Accurate Tumor Resection: A Promising Technique for Improved Surgical Outcomes and Patient Survival

Clear surgical margins for solid tumor resection are essential for preventing cancer recurrence and improving overall patient survival. Complete resection of tumors is often limited by a surgeon's ability to accurately locate malignant tissues and differentiate them from healthy tissue. Therefore, techniques or imaging modalities are required that would ease the identification and resection of tumors by real-time intraoperative visualization of tumors. Although conventional imaging techniques such as positron emission tomography (PET), computed tomography (CT), magnetic resonance imaging (MRI), or radiography play an essential role in preoperative diagnostics, these cannot be utilized in intraoperative tumor detection due to their large size, high cost, long imaging time, and lack of cancer specificity. The inception of several imaging techniques has paved the way to intraoperative tumor margin detection with a high degree of sensitivity and specificity. Particularly, molecular imaging using near-infrared fluorescence (NIRF) based nanoprobes provides superior imaging quality due to high signal-to-noise ratio, deep penetration to tissues, and low autofluorescence, enabling accurate tumor resection and improved survival rates. In this review, we discuss the recent developments in imaging technologies, specifically focusing on NIRF nanoprobes that aid in highly specific intraoperative surgeries with real-time recognition of tumor margins.

Intra-Operative Definition of Glioma Infiltrative Margins by Visualizing Immunosuppressive Tumor-Associated Macrophages

Accurate delineation of glioma infiltrative margins remains a challenge due to the low density of cancer cells in these regions. Here, a hierarchical imaging strategy to define glioma margins by locating the immunosuppressive tumor-associated macrophages (TAMs) is proposed. A pH ratiometric fluorescent probe CP2-M that targets immunosuppressive TAMs by binding to mannose receptor (CD206) is developed, and it subsequently senses the acidic phagosomal lumen, resulting in a remarkable fluorescence enhancement. With assistance of CP2-M, glioma xenografts in mouse models with a tumor-to-background ratio exceeding 3.0 for up to 6 h are successfully visualized. Furthermore, by intra-operatively mapping the pH distribution of exposed tissue after craniotomy, the glioma allograft in rat models is precisely excised. The overall survival of rat models significantly surpasses that achieved using clinically employed fluorescent probes. This work presents a novel strategy for locating glioma margins, thereby improving surgical outcomes for tumors with infiltrative characteristics.

The role of clinical imaging in oncology drug development: progress and new challenges

In 2008, the role of clinical imaging in oncology drug development was reviewed. The review outlined where imaging was being applied and considered the diverse demands across the phases of drug development. A limited set of imaging techniques was being used, largely based on structural measures of disease evaluated using established response criteria such as response evaluation criteria in solid tumours. Beyond structure, functional tissue imaging such as dynamic contrast-enhanced MRI and metabolic measures using [18F]flourodeoxyglucose positron emission tomography were being increasingly incorporated. Specific challenges related to the implementation of imaging were outlined including standardisation of scanning across study centres and consistency of analysis and reporting. More than a decade on the needs of modern drug development are reviewed, how imaging has evolved to support new drug development demands, the potential to translate state-of-the-art methods into routine tools and what is needed to enable the effective use of this broadening clinical trial toolset. In this review, we challenge the clinical and scientific imaging community to help refine existing clinical trial methods and innovate to deliver the next generation of techniques. Strong industry-academic partnerships and pre-competitive opportunities to co-ordinate efforts will ensure imaging technologies maintain a crucial role delivering innovative medicines to treat cancer.

Recent progress of self-immobilizing and self-precipitating molecular fluorescent probes for higher-spatial-resolution imaging

Flourished in the past two decades, fluorescent probe technology provides researchers with accurate and efficient tools for in situ imaging of biomarkers in living cells and tissues and may play a significant role in clinical diagnosis and treatment such as biomarker detection, fluorescence imaging-guided surgery, and photothermal/photodynamic therapy. In situ imaging of biomarkers depends on the spatial resolution of molecular probes. Nevertheless, the majority of currently available molecular fluorescent probes suffer from the drawback of diffusing from the target region. This leads to a rapid attenuation of the fluorescent signal over time and a reduction in spatial resolution. Consequently, the diffused fluorescent signal cannot accurately reflect the in situ information of the target. Self-immobilizing and self-precipitating molecular fluorescent probes can be used to overcome this problem. These probes ensure that the fluorescent signal remains at the location where the signal is generated for a long time. In this review, we introduce the development history of the two types of probes and classify them in detail according to different design strategies. In addition, we compare their advantages and disadvantages, summarize some representative studies conducted in recent years, and propose prospects for this field.

Fluorescence colposcope with TMTP1-PEG4-ICG is comparable to the conventional colposcope in identifying cervical precancerous lesions: A randomized controlled trial

OBJECTIVE

To compare the diagnostic efficiency of a fluorescence colposcope with TMTP1-PEG4-ICG dye versus a conventional colposcope with acetic acid and Lugol's iodine in identifying cervical precancerous lesions.

METHODS

In all, 218 women with abnormal cervical cancer screening results including cytology and/or human papillomavirus (HPV) test were involved in the randomized controlled trial. Patients in the fluorescence colposcope group had TMTP1-PEG4-ICG dye applied to the cervix uteri before colposcopy. Patients in the conventional colposcope group were routinely administered acetic acid and Lugol's iodine to stain the cervix uteri. Two to four cervical sites per patient were taken out for biopsy. The diagnostic efficiency of fluorescence colposcopy and conventional colposcopy was calculated on a per-patient and per-site basis. χ2 test or Fisher exact test was used.

RESULTS

A total of 194 patients and the corresponding 662 cervical sites were included in the final analysis. There was no statistically significant difference in the diagnostic efficiency between the two groups both on a per-patient and a per-site basis, including accuracy, sensitivity, specificity, positive predictive value, and negative predictive value.

CONCLUSIONS

The fluorescence colposcope with TMTP1-PEG4-ICG dye was comparable to the conventional colposcope in identifying cervical precancerous lesions.

Acid and Hypoxia Tandem-Activatable Deep Near-Infrared Nanoprobe for Two-Step Signal Amplification and Early Detection of Cancer

The early detection of cancers can significantly change outcomes even with existing treatments. However, ~50% of cancers still cannot be detected until they reach an advanced stage, highlighting the great challenges in the early detection. Here, an ultrasensitive deep near-infrared (dNIR) nanoprobe that is successively responsive to tumor acidity and hypoxia is reported. It is demonstrated that the new nanoprobe specifically detects tumor hypoxia microenvironment based on deep NIR imaging in ten different types of tumor models using cancer cell lines and patient-tissue derived xenograft tumors. By combining the acidity and hypoxia specific two-step signal amplification with a deep NIR detection, the reported nanoprobe enables the ultrasensitive visualization of hundreds of tumor cells or small tumors with a size of 260 µm in whole-body imaging or 115 µm metastatic lesions in lung imaging. As a result, it reveals that tumor hypoxia can occur as early as the lesions contain only several hundred cancer cells.

Advances in optical molecular imaging for neural visualization

Iatrogenic nerve injury is a significant complication in surgery, which can negatively impact patients' quality of life. Currently, the main clinical neuroimaging methods, such as computed tomography, magnetic resonance imaging, and high-resolution ultrasonography, do not offer precise real-time positioning images for doctors during surgery. The clinical application of optical molecular imaging technology has led to the emergence of new concepts such as optical molecular imaging surgery, targeted surgery, and molecular-guided surgery. These advancements have made it possible to directly visualize surgical target areas, thereby providing a novel method for real-time identification of nerves during surgery planning. Unlike traditional white light imaging, optical molecular imaging technology enables precise positioning and identifies the cation of intraoperative nerves through the presentation of color images. Although a large number of experiments and data support its development, there are few reports on its actual clinical application. This paper summarizes the research results of optical molecular imaging technology and its ability to realize neural visualization. Additionally, it discusses the challenges neural visualization recognition faces and future development opportunities.

Efficient FMT reconstruction based on L1-αL2 regularization via half-quadratic splitting and a two-probe separation light source strategy

Fluorescence molecular tomography (FMT) can achieve noninvasive, high-contrast, high-sensitivity three-dimensional imaging in vivo by relying on a variety of fluorescent molecular probes, and has excellent clinical transformation prospects in the detection of tumors in vivo. However, the limited surface fluorescence makes the FMT reconstruction have some ill-posedness, and it is difficult to obtain the ideal reconstruction effect. In this paper, two different emission fluorescent probes and L 1-L 2 regularization are combined to improve the temporal and spatial resolution of FMT visual reconstruction by introducing the weighting factor α and a half-quadratic splitting alternating optimization (HQSAO) iterative algorithm. By introducing an auxiliary variable, the HQSAO method breaks the sparse FMT reconstruction task into two subproblems that can be solved in turn: simple reconstruction and image denoising. The weight factor α (α>1) can increase the weight of nonconvex terms to further promote the sparsity of the algorithm. Importantly, this paper combines two different dominant fluorescent probes to achieve high-quality reconstruction of dual light sources. The performance of the proposed reconstruction strategy was evaluated by digital mouse and nude mouse single/dual light source models. The simulation results show that the HQSAO iterative algorithm can achieve more excellent positioning accuracy and morphology distribution in a shorter time. In vivo experiments also further prove that the HQSAO algorithm has advantages in light source information preservation and artifact suppression. In particular, the introduction of two main emission fluorescent probes makes it easy to separate and reconstruct the dual light sources. When it comes to localization and three-dimensional morphology, the results of the reconstruction are much better than those using a fluorescent probe, which further facilitates the clinical transformation of FMT.

An activatable nanoprobe based on nanocomposites of visible-light-excitable europium(III) complex-anchored MnO2 nanosheets for bimodal time-gated luminescence and magnetic resonance imaging of tumor cells

Bimodal imaging probes that combine magnetic resonance imaging (MRI) and photoluminescence imaging are quite appealing since they can supply both anatomical and molecular information to effectively ameliorate the accuracy of detection. In this study, an activatable nanoprobe, [Eu(BTD)₃(DPBT)]@MnO₂, for bimodal time-gated luminescence imaging (TGLI) and MRI has been constructed by anchoring visible-light-excitable Eu³⁺ complexes on lamellar MnO₂ nanosheets. Due to the luminescence quenching effect and non-magnetic resonance (MR) activity of MnO₂ nanosheets, the developed nanoprobe presents quite weak TGL and MR signals. After exposure to H₂O₂ or GSH, accompanied by the transformation from MnO₂ to Mn²⁺, the nanoprobe exhibits rapid, sensitive, and selective "turn-on" responses towards GSH and H₂O₂ in TGL and MR detection modes. Furthermore, the nanoprobe displays high stability, low cytotoxicity, good biocompatibility and water dispersion. Given the high contents of GSH and H₂O₂ in cancer cells, the nanoprobe was used for the identification of cancer cells by TGLI of intracellular GSH and H₂O₂, as well as for the tracing of tumor cells in tumor-bearing mice by tumor-targeting in vivo MRI and TGLI of tumor tissues. The research outcomes proved the potential of [Eu(BTD)₃(DPBT)]@MnO₂ as a useful nanoprobe for the tracing and accurate detection of cancer cells in vitro and in vivo via bimodal TGLI and MRI.

Noninvasive Strategies for the Treatment of Tiny Liver Cancer: Integrating Photothermal Therapy and Multimodality Imaging EpCAM-Guided Nanoparticles

Surgical resection and ablation therapy have been shown to achieve the purpose of a radical cure for liver cancer with a size of less than 3 cm; however, tiny liver cancer lesions of diameters smaller than 2 cm remain challenging to diagnose and cure due to the failure of the generation of new blood vessels within tumors. Emerging evidence has revealed that optical molecular imaging combined with nanoprobes can detect tiny cancer from the perspective of molecular and cellular levels and kill cancer cells by the photothermal effect of nanoparticles in real time, thereby achieving radical goals. In the present study, we designed and synthesized multicomponent and multifunctional ICG-CuS-Gd@BSA-EpCAM nanoparticles (NPs) with a potent antineoplastic effect on tiny liver cancer. Using subcutaneous and orthotopic liver cancer xenograft mouse models, we found that the components of the NPs, including ICG and CuS-Gd@BSA, showed synergistic photothermal effects on the eradication of tiny liver cancer. We also found that the ICG-CuS-Gd@BSA-EpCAM NPs exhibited triple-modal functions of fluorescence imaging, magnetic resonance imaging, and photoacoustic imaging, with targeted detection and photothermal treatment of tiny liver cancer under near-infrared light irradiation. Together, our study demonstrates that the ICG-CuS-Gd@BSA-EpCAM NPs in combination with optical imaging technique might be a potential approach for detecting and noninvasively and radically curing tiny liver cancer by the photothermal effect.

GAP-43 targeted indocyanine green-loaded near-infrared fluorescent probe for real-time mapping of perineural invasion lesions in pancreatic cancer in vivo

OBJECTIVE

Perineural invasion (PNI) is associated with local recurrence, distant metastasis, and a poor prognosis in pancreatic cancer. However, rare attempt was made to identified the PNI intraoperative. To facilitate precise R0 excision of the tumor, we planned to develop a fluorescent probe for intraoperative imaging of the PNI using GAP-43 as the target and indocyanine green (ICG) as the carrier.

METHODS

The probe was created by binding peptide antibody and ICG. Its targeting was tested in vitro and in vivo using a co-culture model of PC12 and tumor cells to create an in vitro neural invasion model and a mouse sciatic nerve invasion model. The small animal imaging system and surgical navigation system confirmed the probe's potential clinical applicability. The sciatic nerve damage model was created to confirm the probe's targeting.

RESULTS

We used the pancreatic cancer samples and the public database to confirm that GAP-43 was preferentially overexpressed in pancreatic cancer, particularly in PNI. PC12 cells showed high GAP-43RA-PEG-ICG probe-specific absorption after being co-cultured with tumor cells in vitro. In the sciatic nerve invasion experiment, animals in probe group displayed a significantly stronger fluorescence signal at the PNI compared to ICG-NP and the contralateral normal nerves groups. Although only 60 % of mice appeared to have R0 resections by the naked eye, small animal imaging systems and surgical fluorescence navigation systems could remove the tumor with R0 precision. The injury model used in the probe imaging experimental trials demonstrated that the probe was specifically targeted to the injured nerve, regardless of whether the injury was infiltrated by a tumor or physical.

CONCLUSION

We developed the GAP-43Ra-ICG-PEG, an active-targeting near-infrared fluorescent (NIF) probe, that specifically binds to GAP-43-positive neural cells in an in vitro model of PNI. The probe efficiently visualized PNI lesions in pancreatic cancer in preclinical models, opening up new possibilities for NIRF-guided pancreatic surgery, particularly for PNI patients.

In vivo near-infrared fluorescence imaging of gastric cancer in an MKN-45 gastric cancer xenograft mouse model using intraoperative ureteral identification agent ASP5354

Accurate intraoperative identification of gastric cancer lesions and determination of the extent of resection are important for curability and function preservation. This study aimed to investigate the potential of the near-infrared fluorescence (NIRF) imaging agent ASP5354 for in vivo fluorescence imaging of gastric cancer. The capability of ASP5354 was evaluated using an MKN-45 human gastric cancer xenograft mouse model. A single dose of ASP5354 was intravenously administered to the mice at a concentration of 120 nmol (0.37 mg)/kg body weight. In vivo NIRF images of the mouse backs were obtained using an NIRF camera system. Moreover, the cancer tissues were dissected, and the NIRF intensity in the tissue sections was measured using the NIRF camera system. ASP5354 uptake in MKN-45 cells was assessed in vitro using the NIRF microscope. The NIRF signal of ASP5354 was selectively detected in gastric cancer tissues immediately after the intravenous administration of ASP5354. The cancer tissues emitted stronger NIRF signals than adjacent normal tissues. The difference in the NIRF intensity between the normal and cancer tissues was clearly observed at the boundary between them in the macrolevel NIRF images. Cancer tissues can be distinguished from normal tissues based on the measurement of the NIRF of ASP5354, using an NIRF camera system. ASP5354 is a promising agent for NIRF imaging of gastric cancer tissues.

An "AND" Molecular Logic Gate as a Super-Enhancers for De Novo Designing Activatable Probe and Its Application in Atherosclerosis Imaging

Developing activatable fluorescent probes with superlative fluorescence enhancement factor (F/F0 ) to improve the signal-to-noise (S/N) ratio is still an urgent issue. "AND" molecular logic gates are emerging as a useful tool for enhanced probes selectivity and accuracy. Here, an "AND" logic gate is developed as super-enhancers for designing activatable probes with huge F/F0 and S/N ratio. It utilizes lipid-droplets (LDs) as controllable background input and sets the target analyte as variable input. The fluorescence is tremendously quenching due to double locking, thus an extreme F/F0 ratio of target analyte is obtained. Importantly, this probe can transfer to LDs after a response occurs. The target analyte can be directly visualized through the spatial location without a control group. Accordingly, a peroxynitrite (ONOO- ) activatable probe (CNP2-B) is de novo designed. The F/F0 of CNP2-B achieves 2600 after reacting with ONOO- . Furthermore, CNP2-B can transfer from mitochondria to lipid droplets after being activated. The higher selectivity and S/N ratio of CNP2-B are obtained than commercial probe 3'-(p-hydroxyphenyl) fluorescein (HPFin vitro and in vivo. Therefore, the atherosclerotic plaques at mouse models are delineated clearly after administration with in situ CNP2-B probe gel. Such input controllable "AND" logic gate is envisioned to execute more imaging tasks.

Activatable fluorescent probes for real-time imaging-guided tumor therapy

Surgery and drug therapy are the two principal options for cancer treatment. However, their clinical benefits are hindered by the difficulty of accurate location of the tumors and timely monitoring of the treatment efficacy of drugs, respectively. Rapid development of imaging techniques provides promising tools to address these challenges. Compared with conventional imaging techniques such as magnetic resonance imaging and computed tomography etc., fluorescence imaging exhibits high spatial resolution, real-time imaging capability, and relatively low costs devices. The advancements in fluorescent probes further accelerate the implementation of fluorescence imaging in tumor diagnosis and treatment monitoring. In particular, the emergence of site-specifically activatable fluorescent probes fits the demands of tumor delineation and real-time feedback of the treatment efficacy. A variety of small molecule probes or nanoparticle-based probes have been developed and explored for the above-mentioned applications. This review will discuss recent advances in fluorescent probes with a special focus on activatable nanoprobes and highlight the potential implementation of activatable nanoprobes in fluorescence imaging-guided surgery as well as imaging-guided drug therapy.

In Vivo Evaluation of a Gallium-68-Labeled Tumor-Tracking Cyanine Dye for Positron Emission Tomography/Near-Infrared Fluorescence Carcinoma Imaging, Image-Guided Surgery, and Photothermal Therapy

Positron emission tomography (PET)/near-infrared fluorescence (NIRF) dual-modal imaging presents an enticing prospect for tumor diagnosis and surgical navigation. In this study, we developed a novel probe IR808-DOTA for tumor-targeted PET/NIRF imaging, image-guided surgery, and photothermal therapy. This construct had better water solubility and pharmacokinetics than IR808 and had similar photophysical properties, tumor targeting ability, and photothermal anticancer effect to IR808. By a simple labeling process, IR808-DOTA was labeled with gallium-68 and applied as a PET probe for tumor imaging in MCF-7 tumor xenografted mice. IR808-DOTA itself acted as an NIRF imaging agent in the following surgery for intraoperative navigation to aid surgeons in the delineation of tumor margins and visualizing sentinel lymph nodes to facilitate a more thorough tumor resection. Irradiation by laser, IR808-DOTA could prominently inhibit tumor growth in MCF-7 subcutaneous tumor model mice by directly ablating tumor cells, inhibiting tumor proliferation, and promoting tumor cell apoptosis. In summary, ⁶⁸Ga-DOTA-IR808 could enable a convenient and user-friendly workflow for tumor imaging and guided surgery, and therefore, it may have great prospects for clinical translation as a PET/NIRF dual-modal probe.

Ultrasound molecular imaging of p32 protein translocation for evaluation of tumor metastasis

Protein translocation is an essential process for living cells to respond to different physiological, pathological or environmental stimuli. However, its abnormal occurrence usually results in undesirable outcomes such as tumors. To date, there is still a lack of appropriate methods to detect this event in live animals in a real-time manner. Here, we identified the gradually increased cell-surface translocation of p32 protein from mitochondria during tumor progression. LyP-1-modified gas vesicles (LyP-1-GVs) were developed through conjugating LyP-1 (p32-targeting peptide) to the biosynthetic GVs to monitor the cell-surface level of p32 translocation. The resulting LyP-1-GVs have about 200 nm particle size and good tumor cell targeting performance. Upon systemic administration, LyP-1-GVs can traverse through blood vessels and bind to the tumor cells, producing strong contrast imaging signals in comparison with the non-targeted GVs. The contrast imaging signals correlate well with the cell-surface translocation level of p32 protein and tumor metastatic ability. To our knowledge, this is the first report about the in vivo detection of protein translocation to cell membrane from mitochondria by ultrasound molecular imaging. Our study provides a new strategy to explore the molecular events of protein membrane translocations for evaluation of tumor metastasis at the live animal level.

Early detection of gastric cancer via high-resolution terahertz imaging system

Terahertz (THz) wave has demonstrated a good prospect in recent years, but the resolution is still one of the problems that restrict the application of THz technology in medical imaging. Paraffin-embedded samples are mostly used in THz medical imaging studies, which are thicker and significantly different from the current gold standard slice pathological examination in sample preparation. In addition, THz absorption in different layers of normal and cancerous tissues also remains to be further explored. In this study, we constructed a high-resolution THz imaging system to scan non-tumorous adjacent tissue slices and gastric cancer (GC) tissue slices. In this system, a THz quantum cascade laser emitted a pulsed 3 THz signal and the transmitted THz wave was received by a THz detector implemented in a 65 nm CMOS process. The slice thickness was only 20 μm, which was close to that of the medical pathology examination. We successfully found THz transmittance differences between different layers of normal gastric tissues based on THz images, and the resolution could reach 60 μm for the first time. The results indicated that submucosa had a lower THz transmittance than that of mucosa and muscular layer in non-tumorous adjacent tissue. However, in GC tissue, THz transmittance of mucosa and submucosa was similar, caused by the decreased transmittance of mucosa, where the cancer occurs. Therefore, we suppose that the similar terahertz transmittance between gastric mucosa and submucosa may indicate the appearance of cancerization. The images obtained from our THz imaging system were clearer than those observed with naked eyes, and can be directly compared with microscopic images. This is the first application of THz imaging technology to identify non-tumorous adjacent tissue and GC tissue based on the difference in THz wave absorption between different layers in the tissue. Our present work not only demonstrated the potential of THz imaging to promote early diagnosis of GC, but also suggested a new direction for the identification of normal and cancerous tissues by analyzing differences in THz transmittance between different layers of tissue.

Multifunctional nanotheranostics for near infrared optical imaging-guided treatment of brain tumors

Malignant brain tumors, a heterogeneous group of primary and metastatic neoplasms in the central nervous system (CNS), are notorious for their highly invasive and devastating characteristics, dismal prognosis and low survival rate. Recently, near-infrared (NIR) optical imaging modalities including fluorescence imaging (FLI) and photoacoustic imaging (PAI) have displayed bright prospect in innovation of brain tumor diagnoses, due to their merits, like noninvasiveness, high spatiotemporal resolution, good sensitivity and large penetration depth. Importantly, these imaging techniques have been widely used to vividly guide diverse brain tumor therapies in a real-time manner with high accuracy and efficiency. Herein, we provide a systematic summary of the state-of-the-art NIR contrast agents (CAs) for brain tumors single-modal imaging (e.g., FLI and PAI), dual-modal imaging (e.g., FLI/PAI, FLI/magnetic resonance imaging (MRI) and PAI/MRI) and triple-modal imaging (e.g., MRI/FLI/PAI and MRI/PAI/computed tomography (CT) imaging). In addition, we update the most recent progress on the NIR optical imaging-guided therapies, like single-modal (e.g., photothermal therapy (PTT), chemotherapy, surgery, photodynamic therapy (PDT), gene therapy and gas therapy), dual-modal (e.g., PTT/chemotherapy, PTT/surgery, PTT/PDT, PDT/chemotherapy, PTT/chemodynamic therapy (CDT) and PTT/gene therapy) and triple-modal (e.g., PTT/PDT/chemotherapy, PTT/PDT/surgery, PTT/PDT/gene therapy and PTT/gene/chemotherapy). Finally, we discuss the opportunities and challenges of the CAs and nanotheranostics for future clinic translation.

Dextran Fluorescent Probes Containing Sulfadiazine and Rhodamine B Groups

Fluorescent imaging has been expanded, as a non-invasive diagnostic modality for cancers, in recent years. Fluorescent probes in the near-infrared window can provide high sensitivity, resolution, and signal-to-noise ratio, without the use of ionizing radiation. Some fluorescent compounds with low molecular weight, such as rhodamine B (RhB) and indocyanine green (ICG), have been used in fluorescent imaging to improve imaging contrast and sensitivity; however, since these probes are excreted from the body quickly, they possess significant restrictions for imaging. To find a potential solution to this, this work investigated the synthesis and properties of novel macromolecular fluorescent compounds. Herein, water-soluble dextran fluorescent compounds (SD-Dextran-RhB) were prepared by the attachment of RhB and sulfadiazine (SD) derivatives to dextran carrier. These fluorescent compounds were then characterized through IR, ¹H NMR, ¹³C NMR, UV, GPC, and other methods. Assays of their cellular uptake and cell cytotoxicity and fluorescent imaging were also performed. Through this study, it was found that SD-Dextran-RhB is sensitive to acidic conditions and possesses low cell cytotoxicities compared to normal 293 cells and HepG2 and HeLa tumor cells. Moreover, SD-Dextran-RhB demonstrated good fluorescent imaging in HepG2 and HeLa cells. Therefore, SD-Dextran-RhB is suitable to be potentially applied as a probe in the fluorescent imaging of tumors.

Dual-modal polypeptide-containing contrast agents for magnetic resonance/fluorescence imaging

Dual-modal magnetic resonance/fluorescent imaging (MRI/FI) attracts moreandmoreattentions in diagnosis of tumors. A corresponding dual-modal imaging agent with sufficient tumor sensitivity and specificity should be matched to improve imaging quality. Tripeptide (RGD) and pentapeptide (YIGSR) were selected as the tumor-targeting groups and attached to gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) and rhodamine B (RhB), and then make two novel polypeptide-based derivatives (RGD-Gd-DTPA-RhB and YIGSR-Gd-DTPA-RhB), respectively. These derivatives were further characterized and their properties, such as cell uptake, cell cytotoxicity, MRI and FI assay, were measured. YIGSR-Gd-DTPA-RhB and RGD-Gd-DTPA-RhB had high relaxivity, good tumor-targeting property, low cell cytotoxicity and good red FI in B16F10 melanoma cells. Moreover, YIGSR-Gd-DTPA-RhB and RGD-Gd-DTPA-RhB possessed high uptake to B16F10 melanoma, and then achieve highly enhanced FI and MRI of tumors in mice for a prolonged time. Therefore, YIGSR-Gd-DTPA-RhB and RGD-Gd-DTPA-RhB can be applied as the potential agents for tumor targeted MRI/FI in vivo.

Optical diagnostic imaging and therapy for thyroid cancer

Thyroid cancer, as one of the most common endocrine cancers, has seen a surge in incidence in recent years. This is most likely due to the lack of specificity and accuracy of its traditional diagnostic modalities, leading to the overdiagnosis of thyroid nodules. Although there are several treatment options available, they are limited to surgery and ¹³¹I radiation therapy that come with significant side effects and hence cannot meet the treatment needs of anaplastic thyroid carcinoma with very high malignancy. Optical imaging that utilizes optical absorption, refraction and scattering properties, not only observes the structure and function of cells, tissues, organs, or even the whole organism to assist in diagnosis, but can also be used to perform optical therapy to achieve targeted non-invasive and precise treatment of thyroid cancer. These applications of screening, diagnosis, and treatment, lend to optical imaging's promising potential within the realm of thyroid cancer surgical navigation. Over the past decade, research on optical imaging in the diagnosis and treatment of thyroid cancer has been growing year by year, but no comprehensive review on this topic has been published. Here, we review key advances in the application of optical imaging in the diagnosis and treatment of thyroid cancer and discuss the challenges and potential for clinical translation of this technology.

Bimodal Imaging of Tumors via Genetically Engineered Escherichia coli

Although there are emerging innovations of molecular imaging probes to detect and image tumors, most of these molecular dyes and nanoparticles have limitations of low targetability in tumors and fast clearance when administered systemically. In contrast, some bacteria, such as Escherichia coli MG1655, can selectively proliferate in a hypoxic environment inside of a tumor for several days, which highlights the potential for the development of a genetically encoded multimodal imaging probe to monitor the progress of the tumor. Here, we developed bimodal imaging tumor-homing bacteria (GVs-miRFP680 MG1655) that allow both optical and acoustic imaging in tumor-bearing mice. An in vivo optical image system and a Vevo 2100 imaging system were applied to detect different imaging properties of the engineered bacteria in vivo. Our results show that the GVs-miRFP680 MG1655 bacteria can effectively integrate the advantages of low tissue absorbance from near-infrared fluorescent proteins and non-invasiveness from gas vesicles. We successfully developed GVs-miRFP680 MG1655 bacteria, which have both acoustic and optical imaging abilities in vitro and in vivo. The acoustic signal can last for up to 25 min, while the near-infrared fluorescence signal can last for up to 96 h. The combination of different imaging modalities in the tumor-homing bacteria may contribute to the non-invasive monitoring of the therapeutic effect of bacterial therapy in the future.

Recent advances of aggregation-induced emission materials for fluorescence image-guided surgery

Real-time intraoperative guidance is essential during various surgical treatment of many diseases. Aggregation-induced emission (AIE) materials have shown great potential for guiding surgeons during complex interventions, with the merits of deep tissue penetration, high quantum yield, high molar absorptivity, low background, good targeting ability and excellent photostability. Herein, we provided insights to design efficient AIE materials regarding three key parameters, i.e., deep-tissue penetration ability, high brightness of AIE luminogens (AIEgens), and precise tumor/other pathology nidus targeting strategies, for realizing better application of fluorescence image-guided surgery. Representative interdisciplinary achievements were outlined for the demonstration of this emerging field. Challenges and future opportunities of AIE materials were briefly discussed. The aim of this review is to provide a comprehensive view of AIE materials for intraoperative guidance for researchers and surgeons, and to inspire more further correlational studies in the new frontiers of image-guided surgery.

Synthesis and preclinical application of a Prussian blue-based dual fluorescent and magnetic contrast agent (CA)

The aim of this study was to develop and characterize a Prussian Blue based biocompatible and chemically stable T1 magnetic resonance imaging (MRI) contrast agent with near infrared (NIR) optical contrast for preclinical application. The physical properties of the Prussian blue nanoparticles (PBNPs) (iron (II); iron (III);octadecacyanide) were characterized with dynamic light scattering (DLS), zeta potential measurement, atomic force microscopy (AFM), and transmission electron microscopy (TEM). In vitro contrast enhancement properties of PBNPs were determined by MRI. In vivo T1-weighted contrast of the prepared PBNPs was investigated by MRI and optical imaging modality after intravenous administration into NMRI-Foxn1 nu/nu mice. The biodistribution studies showed the presence of PBNPs predominantly in the cardiovascular system. Briefly, in this paper we show a novel approach for the synthesis of PBNPs with enhanced iron content for T1 MRI contrast. This newly synthetized PBNP platform could lead to a new diagnostic agent, replacing the currently used Gadolinium based substances.

Optical molecular imaging and theranostics in neurological diseases based on aggregation-induced emission luminogens

Optical molecular imaging and image-guided theranostics benefit from special and specific imaging agents, for which aggregation-induced emission luminogens (AIEgens) have been regarded as good candidates in many biomedical applications. They display a large Stokes shift, high quantum yield, good biocompatibility, and resistance to photobleaching. Neurological diseases are becoming a substantial burden on individuals and society that affect over 50 million people worldwide. It is urgently needed to explore in more detail the brain structure and function, learn more about pathological processes of neurological diseases, and develop more efficient approaches for theranostics. Many AIEgens have been successfully designed, synthesized, and further applied for molecular imaging and image-guided theranostics in neurological diseases such as cerebrovascular disease, neurodegenerative disease, and brain tumor, which help us understand more about the pathophysiological state of brain through noninvasive optical imaging approaches. Herein, we focus on representative AIEgens investigated on brain vasculature imaging and theranostics in neurological diseases including cerebrovascular disease, neurodegenerative disease, and brain tumor. Considering different imaging modalities and various therapeutic functions, AIEgens have great potential to broaden neurological research and meet urgent needs in clinical practice. It will be inspiring to develop more practical and versatile AIEgens as molecular imaging agents for preclinical and clinical use on neurological diseases.

Fabrication of tumor targeting rare-earth nanocrystals for real-time NIR-IIb fluorescence imaging-guided breast cancer precise surgery

The near-infrared fluorescence imaging has been integrated into the operating room to guide tumor resection, potentially reducing the positive margin rates in breast-conserving surgery (BCS). Relative to the widely used first near-infrared fluorescence imaging, imaging in the second near-infrared (NIR-II) region possesses higher contrast and deeper tissue penetration, particularly in the NIR-IIb window, offering many new opportunities for imaging-guided BCS. Here, we fabricated the c(RGDfC) functionalized erbium-based rare-earth nanoparticles (ErNPs@cRGD) with superior optical property in NIR-IIb region. Owing to deeper tissue penetration and efficient tumor targeting, ErNPs@cRGD-based NIR-IIb fluorescence imaging achieved enhanced signal-to-background ratios in tumor visualization, which was able to guide more complete tumor resection, identify multiple microtumors and distinguish malignant lesions from normal tissues in various mice models. Based on these, this NIR-IIb imaging strategy for surgical navigation can significantly reduce positive margin rates and improve prognosis, laying a foundation for the clinical resection of breast cancer.

Topical pH Sensing NIR Fluorophores for Intraoperative Imaging and Surgery of Disseminated Ovarian Cancer

Fluorescence-guided surgery (FGS) aids surgeons with real-time visualization of small cancer foci and borders, which improves surgical and prognostic efficacy of cancer. Despite the steady advances in imaging devices, there is a scarcity of fluorophores available to achieve optimal FGS. Here, 1) a pH-sensitive near-infrared fluorophore that exhibits rapid signal changes in acidic tumor microenvironments (TME) caused by the attenuation of intramolecular quenching, 2) the inherent targeting for cancer based on chemical structure (structure inherent targeting, SIT), and 3) mitochondrial and lysosomal retention are reported. After topical application of PH08 on peritoneal tumor regions in ovarian cancer-bearing mice, a rapid fluorescence increase (< 10 min), and extended preservation of signals (> 4 h post-topical application) are observed, which together allow for the visualization of submillimeter tumors with a high tumor-to-background ratio (TBR > 5.0). In addition, PH08 is preferentially transported to cancer cells via organic anion transporter peptides (OATPs) and colocalizes in the mitochondria and lysosomes due to the positive charges, enabling a long retention time during FGS. PH08 not only has a significant impact on surgical and diagnostic applications but also provides an effective and scalable strategy to design therapeutic agents for a wide array of cancers.

Biodegradable iron oxide nanoparticles for intraoperative parathyroid gland imaging in thyroidectomy

Parathyroid gland (PG) injury is the most common complication of thyroidectomy owing to the lack of approaches for surgeons to effectively distinguish PGs from surrounding thyroid glands (TGs) in the operation room. Herein, we report the development of biodegradable iron oxide nanoparticles (IONPs) as a promising contrast agent candidate for intraoperative PG visualization. We elucidated that locally administrated dark-colored IONPs readily diffuse in TGs but cannot infiltrate tissue-dense PGs, yielding a distinguishable contrast enhancement between PGs and TGs by naked eye observation. We performed unbiased and quantitative in vivo screenings to optimize particle size and concentration of IONPs for PG/TG contrast enhancement. Moreover, in vivo applications of IONPs via the local administration route demonstrate no adverse toxicities and can be biodegraded in the thyroid microenvironment within 3 months. To our knowledge, these promising findings provide the first in vivo evidence that IONPs can serve as a safe, biodegradable, and effective contrast agent candidate for improving PG visualization in thyroidectomy.

Fluorescent-based nanosensors for selective detection of a wide range of biological macromolecules: A comprehensive review

Thanks to their unique attributes, such as good sensitivity, selectivity, high surface-to-volume ratio, and versatile optical and electronic properties, fluorescent-based bioprobes have been used to create highly sensitive nanobiosensors to detect various biological and chemical agents. These sensors are superior to other analytical instrumentation techniques like gas chromatography, high-performance liquid chromatography, and capillary electrophoresis for being biodegradable, eco-friendly, and more economical, operational, and cost-effective. Moreover, several reports have also highlighted their application in the early detection of biomarkers associated with drug-induced organ damage such as liver, kidney, or lungs. In the present work, we comprehensively overviewed the electrochemical sensors that employ nanomaterials (nanoparticles/colloids or quantum dots, carbon dots, or nanoscaled metal-organic frameworks, etc.) to detect a variety of biological macromolecules based on fluorescent emission spectra. In addition, the most important mechanisms and methods to sense amino acids, protein, peptides, enzymes, carbohydrates, neurotransmitters, nucleic acids, vitamins, ions, metals, and electrolytes, blood gases, drugs (i.e., anti-inflammatory agents and antibiotics), toxins, alkaloids, antioxidants, cancer biomarkers, urinary metabolites (i.e., urea, uric acid, and creatinine), and pathogenic microorganisms were outlined and compared in terms of their selectivity and sensitivity. Altogether, the small dimensions and capability of these nanosensors for sensitive, label-free, real-time sensing of chemical, biological, and pharmaceutical agents could be used in array-based screening and in-vitro or in-vivo diagnostics. Although fluorescent nanoprobes are widely applied in determining biological macromolecules, unfortunately, they present many challenges and limitations. Efforts must be made to minimize such limitations in utilizing such nanobiosensors with an emphasis on their commercial developments. We believe that the current review can foster the wider incorporation of nanomedicine and will be of particular interest to researchers working on fluorescence technology, material chemistry, coordination polymers, and related research areas.

Superior Fluorescent Nanoemulsion Illuminates Hepatocellular Carcinoma for Surgical Navigation

Hepatocellular carcinoma (HCC), the fifth most common cancer worldwide, poses a severe threat to public health. Intraoperative fluorescence imaging provides a golden opportunity for surgeons to visualize tumor-involved margins, thereby implementing precise HCC resection with minimal damage to normal tissues. Here, a novel-acting contrast agent, which facilely bridges indocyanine green (ICG) and lipiodol using self-emulsifying nanotechnology, was developed for optical surgical navigation. Compared to clinically available ICG probe, our prepared nanoemulsion showed obviously red-shifted optical absorption and enhanced fluorescence intensity. Further benefiting from the shielding effect of lipiodol, the fluorescence stability and anti-photobleaching ability of nanoemulsion were highly improved, indicating a great capacity for long-lasting in vivo intraoperative imaging. Under the fluorescence guidance of nanoemulsion, the tumor tissues were clearly delineated with a signal-to-noise ratio above 5-fold, and then underwent a complete surgical resection from orthotopic HCC-bearing mice. Such superior fluorescence performances, ultrahigh tumor-to-liver contrast, as well as great bio-safety, warrants the great translational potential of nanoemulsion in precise HCC imaging and intraoperative navigation.

Rational synthesis of IR820-albumin complex for NIR-II fluorescence imaging-guided surgical treatment of tumors and gastrointestinal obstruction

IR820, an analog of FDA-approved indocyanine green, is a promising second near-infrared window (NIR-II) fluorescence probe with better NIR-II fluorescence stability and great clinical transformation potential. Moreover, its fluorescence can be further remarkably enhanced by the interaction with albumin. Therefore, it is significant to flexibly design IR820-albumin complex using endogenous or exogenetic albumin to meet the requirements of different biological applications. Herein, we show the rational synthesis of IR820-albumin complex for NIR-II fluorescence imaging-guided surgical treatment of tumors and gastrointestinal obstruction. We compared the NIR-II fluorescence imaging ability of IR820 pre-incubated with albumin or not to visualize tumors and the gastrointestinal tract in vivo and found that the formation of IR820-albumin was essential for the intense NIR-II fluorescence. For imaging-guided tumor treatment, after intravenous injection of free IR820, IR820-albumin complex can be formed in vivo due to the presence of plenty of albumin in the blood. For imaging-guided gastrointestinal obstruction removal, IR820-albumin complex should be synthesized in vitro before oral administration. NIR-II fluorescence imaging-guided surgeries were successfully realized in both tumor resection and gastrointestinal obstruction removal. Besides, toxicity assessments in vitro and in vivo confirmed the good biocompatibility of IR820. Our study provides a flexible paradigm for IR820-based NIR-II fluorescence imaging and surgical navigation towards different diseases.

Recent development of a magneto-optical nanoplatform for multimodality imaging of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer. Given its inconspicuous and atypical early symptoms and hidden location, most patients have already reached the terminal stage before diagnosis. At present, the diagnosis of PDAC mainly depends on serological and imaging examinations. However, serum tests cannot identify specific tumor locations and each imaging technology has its own defects, bringing great challenges to the early diagnosis of PDAC. Therefore, it is of great significance to find new strategies for the early and accurate diagnosis of PDAC. In recent years, a magneto-optical nanoplatform integrating near infrared fluorescence, photoacoustic, magnetic resonance imaging, etc. has attracted widespread attention, giving full play to the complementary advantages of each imaging modality. Herein, we summarize the recent advances of imaging modalities in the diagnosis of pancreatic cancer, and then discuss in detail the construction and modification of magneto or/and optical probes for multimodal imaging, and advances in early diagnosis using the combination of various imaging modalities, which can provide potential tools for the early diagnosis or even intraoperative navigation and post-treatment follow-up of PDAC patients.

A metabolic acidity-activatable calcium phosphate probe with fluorescence signal amplification capabilities for non-invasive imaging of tumor malignancy

Dysregulated energy metabolism has recently been recognized as an emerging hallmark of cancer. Tumor cells, which are characterized by abnormal glycolysis, exhibit a lower extracellular pH (6.5-7.0) than normal tissues (7.2-7.4), providing a promising target for tumor-specific imaging and therapy. However, most pH-sensitive materials are unable to distinguish such a subtle pH difference owing to their wide and continuous pH-responsive range. In this study, we developed an efficient strategy for the fabrication of a tumor metabolic acidity-activatable calcium phosphate (CaP) fluorescent probe (termed MACaP9). Unlike traditional CaP-based biomedical nanomaterials, which only work within more acidic organelles, such as endosomes and lysosomes (pH 4.0-6.0), MACaP9 could not only specifically respond to the tumor extra-cellular pH but also rapidly convert pH variations into a distinct fluorescence signal to visually distinguish tumor from normal tissues. The superior sensitivity and specificity of MACaP9 enabled high-contrast visualization of a broad range of tumors, as well as small tumor lesions.

The Exception that Proves the Rule: How Sodium Chelation Can Alter the Charge-Cell Binding Correlation of Fluorescein-Based Multimodal Imaging Agents

In the present study we describe and explain an aberrant behavior in terms of receptor binding profile of a fluorescein-based multimodal imaging agent for gastrin releasing peptide receptor (GRPR) visualization by elucidating a chelating mechanism on sodium ions of its fluorescent dye moiety. This hypothesis is supported by both biological results and spectroscopic analyses of different fluorescein-carrying conjugates and an equally charged set of analogous tartrazine-based GRPR-binding imaging agents. Fluorescein interacts with sodium which reduces the overall negative charge of the dye molecule by one. This reduction in apparent total net charge explains the exceptional behavior found for the fluorescein-based multimodal bioconjugate in the context of the charge-cell binding correlation hypothesis.

Tuning the photophysical properties of lanthanide(iii)/zinc(ii) ‘encapsulated sandwich’ metallacrowns emitting in the near-infrared range

A family of Zn₁₆Ln(HA)₁₆ metallacrowns (MCs; Ln = Yb^III, Er^III, and Nd^III; HA = picoline- (picHA²⁻), pyrazine- (pyzHA²⁻), and quinaldine- (quinHA²⁻) hydroximates) with an ‘encapsulated sandwich’ structure possesses outstanding luminescence properties in the near-infrared (NIR) and suitability for cell imaging. Here, to decipher which parameters affect their functional and photophysical properties and how the nature of the hydroximate ligands can allow their fine tuning, we have completed this Zn₁₆Ln(HA)₁₆ family by synthesizing MCs with two new ligands, naphthyridine- (napHA²⁻) and quinoxaline- (quinoHA²⁻) hydroximates. Zn₁₆Ln(napHA)₁₆ and Zn₁₆Ln(quinoHA)₁₆ exhibit absorption bands extended into the visible range and efficiently sensitize the NIR emissions of Yb^III, Er^III, and Nd^III upon excitation up to 630 nm. The energies of the lowest singlet (S₁), triplet (T₁) and intra-ligand charge transfer (ILCT) states have been determined. Ln^III-centered total (Q^L_Ln) and intrinsic (Q^Ln_Ln) quantum yields, sensitization efficiencies (η_sens), observed (τ_obs) and radiative (τ_rad) luminescence lifetimes have been recorded and analyzed in the solid state and in CH₃OH and CD₃OD solutions for all Zn₁₆Ln(HA)₁₆. We found that, within the Zn₁₆Ln(HA)₁₆ family, τ_rad values are not constant for a particular Ln^III. The close in energy positions of T₁ and ILCT states in Zn₁₆Ln(picHA)₁₆ and Zn₁₆Ln(quinHA)₁₆ are preferred for the sensitization of Ln^III NIR emission and η_sens values reach 100% for Nd^III. Finally, the highest values of Q^L_Ln are observed for Zn₁₆Ln(quinHA)₁₆ in the solid state or in CD₃OD solutions. With these data at hand, we are now capable of creating MCs with desired properties suitable for NIR optical imaging.

We have created a family of ‘encapsulated sandwich’ Zn₁₆Ln(HA)₁₆ metallacrowns and by detailed quantitative analysis demonstrated how the nature of the hydroximate ligand impacts photophysical properties of these complexes.

Molecular-engineered highly photosensitive triarylphosphine oxide compounds for apoptosis imaging and selectively inducing apoptosis of tumor cells by photodynamic therapy

Although photodynamic therapy (PDT) has wide applications, tumor-targeting probes with high photosensitivity or apoptosis-monitoring capability are still scarce, which possess low phototoxicity and can be used for evaluating the therapeutic...

Activatable molecular probes for fluorescence-guided surgery, endoscopy and tissue biopsy

The real-time, dynamic optical visualization of lesions and margins ensures not only complete resection of the malignant tissues but also better preservation of the vital organs/tissues during surgical procedures. Most imaging probes with an "always-on" signal encounter high background noise due to their non-specific accumulation in normal tissues. By contrast, activatable molecular probes only "turn on" their signals upon reaction with the targeted biomolecules that are overexpressed in malignant cells, offering high target-to-background ratios with high specificity and sensitivity. This review summarizes the recent progress of activatable molecular probes in surgical imaging and diagnosis. The design principle and mechanism of activatable molecular probes are discussed, followed by specific emphasis on applications ranging from fluorescence-guided surgery to endoscopy and tissue biopsy. Finally, potential challenges and perspectives in the field of activatable molecular probe-enabled surgical imaging are discussed.

Lipid Droplet-Specific Probe for Rapidly Locating Atherosclerotic Plaques and Intraoperative Imaging via In Situ Spraying

The ability to visualize the full extent of atherosclerotic plaques during surgery has major implications for therapeutic outcomes. Fluorescence imaging is a promising approach for atherosclerotic plaque inspection during surgery. However, a specific strategy for the intraoperative fluorescence imaging of atherosclerosis has not been established. This study presents an in situ spraying aerosol of a lipid droplet-specific probe to rapidly and precisely locate atherosclerotic plaques during surgery. Stable imaging of the plaque was achieved within 5 min by nebulizing the aqueous solution of the lipid droplet-specific probe (CN-PD) into 3 μm droplets and rapidly permeating it in situ. The visible fluorescence bioimaging of CN-PD can accurately delineate the plaque margins and size even with a diameter ≤0.5 mm, which are capable of being swiftly captured during the stable plaque imaging window (>2 h). This strategy combines the consideration of a specific probe design and an efficient in situ delivery, which results in weak interference from the background signals. Therefore, the plaque-to-normal tissue ratio (P/N) is sufficient to facilitate the surgical delineation of carotid atherosclerotic plaques. The originality of the intraoperative fluorescence imaging of the plaques via in situ delivery of the lipid droplet-specific probe holds promise for effective clinical application.

PEG-Polymer Encapsulated Aggregation-Induced Emission Nanoparticles for Tumor Theranostics

In the field of tumor imaging and therapy, the aggregation-caused quenching (ACQ) effect of fluorescent dyes at high concentration is a great challenge. In this regard, the aggregation-induced emission luminogens (AIEgens) show great potential, since AIEgens effectively overcome the ACQ effect and have better fluorescence quantum yield, photobleaching resistance, and photosensitivity. Polyethylene glycol (PEG)-polymer is the most commonly used carrier to prepare nanoparticles (NPs). The advantage of PEGylation is that it can greatly prolong the metabolic half-life and reduce immunogenicity and toxicity. Considering that the hydrophobicity of most AIEgens hinders their application in organisms, the use of PEG-polymer encapsulation is an effective strategy to overcome this obstacle. Importantly, bioactive functional groups can be modified on PEG-polymers to enhance the biological effect of NPs. The combination of powerful AIEgens and PEG-polymers provides a new strategy for tumor imaging and therapy, which is promising for clinical application.

In vivo optical imaging-guided targeted sampling for precise diagnosis and molecular pathology

Conventional tissue sampling can lead to misdiagnoses and repeated biopsies. Additionally, tissue processed for histopathology suffers from poor nucleic acid quality and/or quantity for downstream molecular profiling. Targeted micro-sampling of tissue can ensure accurate diagnosis and molecular profiling in the presence of spatial heterogeneity, especially in tumors, and facilitate acquisition of fresh tissue for molecular analysis. In this study, we explored the feasibility of performing 1–2 mm precision biopsies guided by high-resolution reflectance confocal microscopy (RCM) and optical coherence tomography (OCT), and reflective metallic grids for accurate spatial targeting. Accurate sampling was confirmed with either histopathology or molecular profiling through next generation sequencing (NGS) in 9 skin cancers in 7 patients. Imaging-guided 1–2 mm biopsies enabled spatial targeting for in vivo diagnosis, feature correlation and depth assessment, which were confirmed with histopathology. In vivo 1-mm targeted biopsies achieved adequate quantity and high quality of DNA for next-generation sequencing. Subsequent mutational profiling was confirmed on 1 melanoma in situ and 2 invasive melanomas, using a 505-gene mutational panel called Memorial Sloan Kettering-Integrated mutational profiling of actionable cancer targets (MSK-IMPACT). Differential mutational landscapes, in terms of number and types of mutations, were found between invasive and in situ melanomas in a single patient. Our findings demonstrate feasibility of accurate sampling of regions of interest for downstream histopathological diagnoses and molecular pathology in both in vivo and ex vivo settings with broad diagnostic, therapeutic and research potential in cutaneous diseases accessible by RCM-OCT imaging.