Small ultra-red fluorescent protein nanoparticles as exogenous probes for noninvasive tumor imaging in vivo

True cancer stem cells exhibit relative degrees of dormancy and genomic stability

BACKGROUND

Cancer stem cells in human tumors have been defined by stem cell markers, embryonal signaling pathways and characteristic biology, ie., namely the ability to repopulate the proliferating population. However, even if these properties can be demonstrated within a tumor cell subpopulation, it does not mean that they are truly hierarchical stem cells because they could have been derived from the proliferating population in a reversible manner.

METHODS

Using a human PDX, Mary-X, that overall expressed a strong cancer stem cell phenotype, the study conducted both GPP-labelled retroviral transfection and fluorescent microsphere uptake studies to distinguish proliferating from dormant cells and array CGH to identify regions of amplifications (gains) and deletions (losses) on the overall Mary-X population and then applied derived probes by FISH on individual cells to identify a genomically stable subpopulation.

RESULTS

Whereas 97-99 % of the cells expressed retroviral GFP and not fluorescent particles and showed numerous gene amplifications and deletions, approximately 1-3 % of the cells showed the opposite. The subpopulation with the retained fluorescent microspheres and exhibiting genomic stability was significantly smaller in size than their GFP-expressing and genomically unstable counterparts. Sorting Mary-X spheroids on the basis of either CD133 or ALDH positivity further enriched for this subpopulation.

CONCLUSIONS

These studies indicate that a truly biological cancer stem cell subpopulation exists that exhibits both dormancy and genomic stability. This subpopulation could not have been derived from the proliferating and resulting genomically unstable population and therefore represents a truly hierarchical stem cell subpopulation capable of only unidirectional differentiation.

Protein nanoparticles as drug delivery systems for cancer theranostics

Protein-based nanoparticles have garnered significant attention in theranostic applications due to their superior biocompatibility, exceptional biodegradability and ease of functionality. Compared to other nanocarriers, protein-based nanoparticles offer additional advantages, including biofunctionality and precise molecular recognition abilities, which make them highly effective in navigating complex biological environments. Moreover, proteins can serve as powerful tools with self-assembling structures and reagents that enhance cell penetration. And their derivation from abundant renewable sources and ability to degrade into harmless amino acids further enhance their suitability for biomedical applications. However, protein-based nanoparticles have so far not realized their full potential. In this review, we summarize recent advances in the use of protein nanoparticles in tumor diagnosis and treatment and outline typical methods for preparing protein nanoparticles. The review of protein nanoparticles may provide useful new insights into the development of biomaterial fabrication.

Structural and photophysical characterization of the small ultra-red fluorescent protein

The small Ultra-Red Fluorescent Protein (smURFP) represents a new class of fluorescent protein with exceptional photostability and brightness derived from allophycocyanin in a previous directed evolution. Here, we report the smURFP crystal structure to better understand properties and enable further engineering of improved variants. We compare this structure to the structures of allophycocyanin and smURFP mutants to identify the structural origins of the molecular brightness. We then use a structure-guided approach to develop monomeric smURFP variants that fluoresce with phycocyanobilin but not biliverdin. Furthermore, we measure smURFP photophysical properties necessary for advanced imaging modalities, such as those relevant for two-photon, fluorescence lifetime, and single-molecule imaging. We observe that smURFP has the largest two-photon cross-section measured for a fluorescent protein, and that it produces more photons than organic dyes. Altogether, this study expands our understanding of the smURFP, which will inform future engineering toward optimal FPs compatible with whole organism studies.

Recent progress of emitting long-wavelength carbon dots and their merits for visualization tracking, target delivery and theranostics

As a novel strategy for in vivo visualization tracking and monitoring, carbon dots (CDs) emitting long wavelengths (LW, 600-950 nm) have received tremendous attention due to their deep tissue penetration, low photon scattering, satisfactory contrast resolution and high signal-to-background ratios. Although, the mechanism of CDs emitting LW remains controversial and what properties are best for in vivo visualization have not been specifically elucidated, it is more conducive to the in vivo application of LW-CDs through rational design and ingenious synthesis based on the appreciation of the luminescence mechanism. Therefore, this review analyzes the current tracer technologies applied in vivo and their advantages and disadvantages, with emphasis on the physical mechanism of emitting LW fluorescence for in vivo imaging. Subsequently, the general properties and merits of LW-CDs for tracking and imaging are summarized. More importantly, the factors affecting the synthesis of LW-CDs and its luminescence mechanism are highlighted. Simultaneously, the application of LW-CDs for disease diagnosis, integration of diagnosis and therapy are summarized. Finally, the bottlenecks and possible future directions of LW-CDs in visualization tracking and imaging in vivo are detailly discussed.

Protein-Caged Nanoparticles: A Promising Nanomedicine Against Cancer

Cancer is a severe threat to human wellness. A broad range of nanoparticles (NPs) have been developed to treat cancer. Given their safety profile, natural biomolecules such as protein-based NPs (PNPs) are promising substitutes for synthetic NPs that are currently used in drug delivery systems. In particular, PNPs have diverse characteristics and are monodisperse, chemically and genetically changeable, biodegradable, and biocompatible. To promote their application in clinical settings, PNPs must be precisely fabricated to fully exploit their advantages. This review highlights the different types of proteins that can be used to produce PNPs. Additionally, the recent applications of these nanomedicines and their therapeutic benefits against cancer are explored. Several future research directions that can facilitate the clinical application of PNPs are suggested.

Directed Evolution of Fluorescent Proteins in Bacteria

Directed evolution has revolutionized the way scientists create new biomolecules not found in nature. Error-prone polymerase chain reaction (PCR) introduces random mutations and was used to evolve jellyfish and coral fluorescent proteins in bacteria. We describe a novel method for the directed evolution of a far-red fluorescent protein in E. coli. The new method used genes to produce fluorophores inside E. coli and allowed changing the native fluorophore, phycocyanobilin, for a second small-molecule fluorophore, biliverdin. The directed evolution blueshifted the fluorescence, which enhanced the quantum yield to produce a brighter fluorescent protein. Finally, the evolution selected fluorescent proteins that expressed in large quantities in E. coli. The evolved fluorescent protein was named the small ultra-red fluorescent protein (smURFP) and was biophysically as bright as the enhanced green fluorescent protein (EGFP). This chapter describes the materials and methods used to evolve a far-red fluorescent protein in bacteria. While the focus is a fluorescent protein, the protocol is adaptable for the evolution of other biomolecules in bacteria when using a proper selection strategy.

Therapeutic Ultrasound for Topical Corneal Delivery of Macromolecules

Purpose

The objective of this study was to utilize therapeutic ultrasound in enhancing delivery of topical macromolecules into the cornea.

Methods

Rabbit corneas were dissected and placed in a diffusion cell with a small ultra-red fluorescent protein (smURFP; molecular weight of 32,000 Da) as a macromolecule solution. The corneas were treated with continuous ultrasound application at frequencies of 400 or 600 kHz and intensities of 0.8 to 1.0 W/cm2 for 5 minutes, or sham-treated. Fluorescence imaging of the cornea sections was used to observe the delivery of macromolecules into individual epithelial cells. Spectrophotometric analysis at smURFP maximal absorbance of 640 nm was done to determine the presence of macromolecules in the receiver compartment. Safety of ultrasound application was studied through histology analysis.

Results

Ultrasound-treated corneas showed smURFP delivery into epithelial cells by fluorescence in the cytoplasm, whereas sham-treated corneas lacked any appreciable fluorescence in the individual cells. The sham group showed 0% of subcellular penetration, whereas the 400 kHz ultrasound-treated group and 600 kHz ultrasound-treated group showed 31% and 57% of subcellular penetration, respectively. Spectrophotometry measurements indicated negligible presence of smURFP macromolecules in the receiver compartment solution in both the sham and ultrasound treatment groups, and these macromolecules did not cross the entire depth of the cornea. Histological studies showed no significant corneal damage due to ultrasound application.

Conclusions

Therapeutic ultrasound application was shown to increase the delivery of smURFP macromolecules into the cornea.

Translational Relevance

Our study offers a clinical potential for a minimally invasive macromolecular treatment of corneal diseases.

Multifunctional photodynamic/photothermal nano-agents for the treatment of oral leukoplakia

Oral leukoplakia (OLK) has gained extensive attention because of the potential risk for malignant transformation. Photosensitizers (PSs) played an indispensable role in the photodynamic therapy (PDT) of OLK, but the poor light sensitivity greatly hampered its clinical application. Herein, a novel organic photosensitive ITIC-Th nanoparticles (ITIC-Th NPs) were developed for OLK photodynamic/photothermal therapy (PTT). ITIC-Th NPs present both high photothermal conversion efficiency (~ 38%) and suitable reactive oxygen species (ROS) generation ability under 660 nm laser irradiation, making them possess excellent PDT and PTT capability. In 4-nitroquinoline 1-oxide (4NQO)-induced oral precancerous animal models, ITIC-Th NPs effectively suppress the OLK's cancerization without apparent topical or systemic toxicity in vivo. This study offers a promising therapeutic strategy for PDT and PTT in OLK treatment, and this study is the first interdisciplinary research in the field of multimodal therapy for OLK.

Protein nanoparticles directed cancer imaging and therapy

Cancer has been a serious threat to human health. Among drug delivery carriers, protein nanoparticles are unique because of their mild and environmentally friendly preparation methods. They also inherit desired characteristics from natural proteins, such as biocompatibility and biodegradability. Therefore, they have solved some problems inherent to inorganic nanocarriers such as poor biocompatibility. Also, the surface groups and cavity of protein nanoparticles allow for easy surface modification and drug loading. Besides, protein nanoparticles can be combined with inorganic nanoparticles or contrast agents to form multifunctional theranostic platforms. This review introduces representative protein nanoparticles applicable in cancer theranostics, including virus-like particles, albumin nanoparticles, silk protein nanoparticles, and ferritin nanoparticles. It also describes the common methods for preparing them. It then critically analyzes the use of a variety of protein nanoparticles in improved cancer imaging and therapy.

Protein Based Biomaterials for Therapeutic and Diagnostic Applications

Proteins are some of the most versatile and studied macromolecules with extensive biomedical applications. The natural and biological origin of proteins offer such materials several advantages over their synthetic counterparts, such as innate bioactivity, recognition by cells and reduced immunogenic potential. Furthermore, proteins can be easily functionalized by altering their primary amino acid sequence and can often be further self-assembled into higher order structures either spontaneously or under specific environmental conditions. This review will feature the recent advances in protein-based biomaterials in the delivery of therapeutic cargo such as small molecules, genetic material, proteins, and cells. First, we will discuss the ways in which secondary structural motifs, the building blocks of more complex proteins, have unique properties that enable them to be useful for therapeutic delivery. Next, supramolecular assemblies, such as fibers, nanoparticles, and hydrogels, made from these building blocks that are engineered to behave in a cohesive manner, are discussed. Finally, we will cover additional modifications to protein materials that impart environmental responsiveness to materials. This includes the emerging field of protein molecular robots, and relatedly, protein-based theranostic materials that combine therapeutic potential with modern imaging modalities, including near-infrared fluorescence spectroscopy (NIRF), single-photo emission computed tomography/computed tomography (SPECT/CT), positron emission tomography (PET), magnetic resonance imaging (MRI), and ultrasound/photoacoustic imaging (US/PAI).

Label-free bioassay with graphene oxide-based fluorescent aptasensors: A review

Bioassays using a fluorophore and DNA aptamer have been extensively developed due to the ultrasensitivity of fluorophores and recognition ability of DNA aptamers. Conventional fluorescent aptamer-based sensors (aptasensors) require chemical labeling between the fluorophore and aptamer and is technologically impracical for various sensing and assay applications. A simple "mix and go" strategy has been introduced that uses label-free technology as a platform for sensor development. The biosensors comprise a fluorophore, a ssDNA aptamer, and eco-friendly graphene oxide (GO). In the absence of the sensor target, GO quenches the fluorescence of the fluorophore and single-strand DNA aptamer complex. When the target is added, the DNA aptamer conformationally turns into a duplex, G-quadruplexe, or other secondary structure. This structure change leads to release of GO by the fluorophore-aptamer-target complex, generating dramatic fluorescence recovery and amplification. With this sensing method, the DNA aptamer does not need to be chemically labeled. Therefore, flexible fluorophore indicators and ssDNA aptamers can be used in this label-free aptasensing strategy. In this review, we discuss various unlabeled fluorophores, including synthetic small molecular fluorophores and genetically encoded fluorescent proteins, as indicators for generating GO-based fluorescent DNA aptasensors for label-free bioassay.

An atherosclerotic plaque-targeted single-chain antibody for MR/NIR-II imaging of atherosclerosis and anti-atherosclerosis therapy

Background

Oxidation-specific epitopes (OSEs) are rich in atherosclerotic plaques. Innate and adaptive immune responses to OSEs play an important role in atherosclerosis. The purpose of this study was to develop novel human single-chain variable fragment (scFv) antibody specific to OSEs to image and inhibit atherosclerosis.

Results

Here, we screened a novel scFv antibody, named as ASA6, from phage-displayed human scFv library. ASA6 can bind to oxidized LDL (Ox-LDL) and atherosclerotic plaques. Meanwhile, ASA6 can also inhibit the uptake of Ox-LDL into macrophage to reduce macrophage apoptosis. The atherosclerotic lesion area of ApoE^−/− mice administrated with ASA6 antibody was significantly reduced. Transcriptome analysis reveals the anti-atherosclerosis effect of ASA6 is related to the regulation of fatty acid metabolism and inhibition of M1 macrophage polarization. Moreover, we conjugated ASA6 antibody to NaNdF₄@NaGdF₄ nanoparticles for noninvasive imaging of atherosclerotic plaques by magnetic resonance (MR) and near-infrared window II (NIR-II) imaging.

Conclusions

Together, these data demonstrate the potential of ASA6 antibody in targeted therapy and noninvasive imaging for atherosclerosis.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01047-4.

A self-labeling protein based on the small ultra-red fluorescent protein, smURFP

Self-labeling proteins have revolutionized super-resolution and sensor imaging. Tags recognize a bioorthogonal substrate for covalent attachment. We show the small Ultra-Red Fluorescent Protein (smURFP) is a self-labeling protein. The substrate is fluorogenic, fluoresces when attached, and quenches fluorescent cargo. The smURFP-tag has novel properties for tool development.

Protease-triggered bioresponsive drug delivery for the targeted theranostics of malignancy

Proteases have a fundamental role in maintaining physiological homeostasis, but their dysregulation results in severe activity imbalance and pathological conditions, including cancer onset, progression, invasion, and metastasis. This striking importance plus superior biological recognition and catalytic performance of proteases, combining with the excellent physicochemical characteristics of nanomaterials, results in enzyme-activated nano-drug delivery systems (nanoDDS) that perform theranostic functions in highly specific response to the tumor phenotype stimulus. In the tutorial review, the key advances of protease-responsive nanoDDS in the specific diagnosis and targeted treatment for malignancies are emphatically classified according to the effector biomolecule types, on the premise of summarizing the structure and function of each protease. Subsequently, the incomplete matching and recognition between enzyme and substrate, structural design complexity, volume production, and toxicological issues related to the nanocomposites are highlighted to clarify the direction of efforts in nanotheranostics. This will facilitate the promotion of nanotechnology in the management of malignant tumors.

Peroxidase-mimicking evodiamine/indocyanine green nanoliposomes for multimodal imaging-guided theranostics for oral squamous cell carcinoma

Here, evodiamine (EVO) and the photosensitizer indocyanine green (ICG) were integrated into a liposomal nanoplatform for noninvasive diagnostic imaging and combinatorial therapy against oral squamous cell carcinoma (OSCC). EVO, as an active component extracted from traditional Chinese medicine, not only functioned as an antitumor chemotherapeutic agent but was also capable of 68Ga-chelation, thus working as a contrast agent for positron emission tomography/computed tomography (PET/CT) imaging. Moreover, EVO could exhibit peroxidase-like catalytic activity, converting endogenous tumor H2O2 into cytotoxic reactive oxygen species (ROS), enabling Chemo catalytic therapy beyond the well-known chemotherapy effect of EVO. As proven by in vitro and in vivo experiments, guided by optical imaging and PET/CT imaging, we show that the theragnostic liposomes have a significant inhibiting effect on in situ tongue tumor through photodynamic therapy combined with chemodynamic chemotherapy.

Ultrasound lighting up AIEgens for potential surgical navigation

Multifunctional contrast-enhanced agents suitable for application in surgical navigation by taking advantage of the merits of their diverse imaging modalities at different surgical stages are highly sought-after. Herein, an amphipathic polymer composed of aggregation-induced emission fluorogens (AIEgens) and Gd³⁺ chelates was successfully synthesized and assembled into ultrasound responsive microbubbles (AIE-Gd MBs) to realize potential tri-modal contrast-enhanced ultrasound (US) imaging, magnetic resonance imaging (MRI), and AIEgen-based fluorescence imaging (FI) during the perioperative period. Through ultrasound targeted microbubble destruction (UTMD) and cavitation effect, the as-prepared AIE-Gd MBs went through a MBs-to-nanoparticles (NPs) conversion, which not only resulted in targeted accumulation in tumor tissues but also led to stronger fluorescence being exhibited due to the more aggregated AIE-Gd molecules in the NPs. As a proof-of-concept, our work proposes a strategy of US-lit-up AIEgens in tumors which could offer a simple and powerful tool for surgical navigation in the future.

Plasmid DNA-Based Bioluminescence-Activated System for Photodynamic Therapy in Cancer Treatment

The low depth of tissue penetration by therapeutic light sources severely restricts photodynamic therapy (PDT) in treating deep-seated tumors. Using a luciferase/d-luciferin bioluminescence system to artificially create internal light sources in cells instead of external light sources is an effective means of solving the above problems. However, high-efficiency bioluminescence requires a higher concentration of luciferase in the cell, which poses a considerable challenge to the existing system of enzyme loading, delivery, activity and retention of drugs, and dramatically increases the cost of treatment. We loaded the substrate D-luciferin, and the photosensitizer hypericin into a polyethyleneimine (PEI)-modified nano-calcium phosphate (CaP) to solve this problem. Subsequently, the plasmid DNA containing the luciferase gene was loaded onto it using the high-density positive charge characteristic of PEI from the nanodrug (denoted DHDC). After the DHDC enters the tumor cell, it collapses and releases the plasmid DNA, which uses the intracellular protein synthesis system to continuously and massively express luciferase. Using endogenous ATP, Mg²⁺ , and O₂ in cells, luciferase oxidizes d-luciferin and produces luminescence. The luminescence triggers hypericin excitation to generate ROS and kill cancer cells. This study provides a new strategy for the application of bioluminescence in PDT treatment.

A review on recent advances in amino acid and peptide-based fluorescence and its potential applications

Fluorescence is widely used to detect functional groups and ions, and peptides are used in various fields due to their excellent biological activity.

Recent Advances in Paclitaxel-based Self-Delivery Nanomedicine for Cancer Therapy

Paclitaxel (PTX) is the first natural plant-derived chemotherapeutic drug approved by the Food and Drug Administration. However, the clinical applications of PTX are limited by some drawbacks, such as poor water solubility, rapid blood clearance, nonspecific distribution, and adverse side effects. Nanocarriers have made important contributions to drug delivery and cancer therapy in recent years. However, low drug loading capacity, nanocarrier excipients-induced toxicity or immunogenicity, and complicated synthesis technologies pose a challenge for the clinical application of nanocarriers. To address these issues, the self-delivery nanomedicine (SDNs), in which pure drug molecules directly self-assemble into nanomedicine, have been developed for drug delivery and enhancing antitumor efficacy. In this review, we comprehensively summarize the recent advances in PTX-based SDNs for cancer therapy. First, the self-assembly strategies to develop pure PTX nanodrugs are discussed. Then, the emerging strategies of co-assembly PTX and other therapeutic agents for effective combination therapy are presented, composing of combination chemotherapy, chemo-photothermal therapy, chemo-photodynamic therapy, chemo-immunotherapy, and chemo-gene therapy. Finally, the limitations and future outlook of SDNs are discussed. The rational design of these unique nanoplatforms may make a new direction to develop highly efficient drug delivery systems for cancer therapy.

Modeling better in vitro models for the prediction of nanoparticle toxicity: a review

Exposure to nanoparticles (NPs) is plausible in real life due to ambient particulate exposure or development of nanotechnologies, hence the evaluation of NP toxicity as well as mechanism-based studies are necessary. The in vitro models allow rapid testing of NP toxicity, but it is required that the developed in vitro models are reliable to reflect the toxicity of NPs. In this review, we discussed the principles to model better in vitro models to predict the toxicity of NPs based on our own experiences and works of literature. We suggested that in vitro nanotoxicological studies should consider (1) using normal cells because the commonly used cancer cell lines might not reflect the toxicity of NPs to normal tissues; (2) the possible influence of biological molecules to reflect the toxicity of NPs in a biological microenvironment; (3) the influence of pathophysiological conditions to mimic the responses of NPs under different in vivo conditions; and (4) developing advanced tissue-based models to reflect the responses of tissues/organs to NPs. It is our hope that this review may provide useful information for the future design of in vitro nanotoxicological studies.

Fluorescent proteins for in vivo imaging, where's the biliverdin?

Noninvasive fluorescent imaging requires far-red and near-infrared fluorescent proteins for deeper imaging. Near-infrared light penetrates biological tissue with blood vessels due to low absorbance, scattering, and reflection of light and has a greater signal-to-noise due to less autofluorescence. Far-red and near-infrared fluorescent proteins absorb light >600 nm to expand the color palette for imaging multiple biosensors and noninvasive in vivo imaging. The ideal fluorescent proteins are bright, photobleach minimally, express well in the desired cells, do not oligomerize, and generate or incorporate exogenous fluorophores efficiently. Coral-derived red fluorescent proteins require oxygen for fluorophore formation and release two hydrogen peroxide molecules. New fluorescent proteins based on phytochrome and phycobiliproteins use biliverdin IXα as fluorophores, do not require oxygen for maturation to image anaerobic organisms and tumor core, and do not generate hydrogen peroxide. The small Ultra-Red Fluorescent Protein (smURFP) was evolved from a cyanobacterial phycobiliprotein to covalently attach biliverdin as an exogenous fluorophore. The small Ultra-Red Fluorescent Protein is biophysically as bright as the enhanced green fluorescent protein, is exceptionally photostable, used for biosensor development, and visible in living mice. Novel applications of smURFP include in vitro protein diagnostics with attomolar (10-18 M) sensitivity, encapsulation in viral particles, and fluorescent protein nanoparticles. However, the availability of biliverdin limits the fluorescence of biliverdin-attaching fluorescent proteins; hence, extra biliverdin is needed to enhance brightness. New methods for improved biliverdin bioavailability are necessary to develop improved bright far-red and near-infrared fluorescent proteins for noninvasive imaging in vivo.

Comparison of cytotoxicity of Ag/ZnO and Ag@ZnO nanocomplexes to human umbilical vein endothelial cells in vitro

Novel metal and metal oxide-based nanocomplexes are being developed due to their superior properties compared with nanoparticles (NPs) based on single composition. In this study, we synthesized Ag-coated ZnO (Ag/ZnO) and Ag-doped ZnO (Ag@ZnO) NPs. The cytotoxicity and mechanisms associated with the synthesized NPs were investigated to understand the influence of Ag positions on biocompatibility of the NPs. After exposure to human umbilical vein endothelial cells (HUVECs), Ag/ZnO, Ag@ZnO, and ZnO NPs all significantly induced cytotoxicity, but the cytotoxic effects of Ag/ZnO and Ag@ZnO NPs were more modest in comparison with ZnO NPs. At cytotoxic concentrations, all NPs significantly induced intracellular Zn ions, which suggested a role of excessive Zn ions on cytotoxicity of NPs. All types of NPs significantly induced the expression of endoplasmic reticulum (ER) stress genes including DNA damage-inducible transcript 3 (DDIT3), X-box binding protein 1 (XBP-1), and ER to nucleus signaling 1 (ERN1), but Ag/ZnO and Ag@ZnO NPs were less effective to induce DDIT3 and XBP-1 expression compared with ZnO NPs. Not surprisingly, only ZnO NPs significantly induced the expression of caspase 3. Combined, the results from this study showed that Ag/ZnO and Ag@ZnO NPs were less cytotoxic and less potent to induce ER stress gene expression compared with ZnO NPs, but there were no significant differences between Ag/ZnO and Ag@ZnO NPs. Our results may provide novel understanding about the biocompatibility of Ag-ZnO nanocomplexes.

Target Area Extraction Algorithm for the In Vivo Fluorescence Imaging of Small Animals

Bio-optical imaging can noninvasively describe specific biochemical reaction events in small animals using endogenous or exogenous imaging reagents to label cells, proteins, or DNA. The fluorescence optical bio-imaging system excites the fluorescent group to a high energy state by excitation light and then generates emission light. However, many substances in the organism will also emit fluorescence after being excited by the excitation light, and the nonspecific fluorescence generated will affect the detection sensitivity. This paper designs and develops a set of high-level biosafety in vivo fluorescence imaging system for small animals suitable for virology research and proposes a target area extraction algorithm for fluorescence images. The fluorescence image target extraction algorithm first maps the nonlinear separation data in the low-dimensional space to the high-dimensional space. Then, based on the analysis of the characteristics of the fluorescent region, a method for discriminating the target fluorescent region based on the two-step entropy function is proposed, and the real target fluorescent region is obtained according to the set connected region. Based on the experiment of collecting and analyzing the in vivo fluorescent images of mice, it is verified that the proposed algorithm can automatically extract the target fluorescent region better than the classical linear model. It shows that the proposed algorithm is less affected by background fluorescence, and the estimated separated spectrum based on this method is closer to the real target spectrum.

Supramolecular Encapsulation of Small-Ultrared Fluorescent Proteins in Virus-Like Nanoparticles for Noninvasive In Vivo Imaging Agents

Icosahedral virus-like particles (VLPs) derived from bacteriophages Qβ and PP7 encapsulating small-ultrared fluorescent protein (smURFP) were produced using a versatile supramolecular capsid disassemble-reassemble approach. The generated fluorescent VLPs display identical structural properties to their nonfluorescent analogs. Encapsulated smURFP shows indistinguishable photochemical properties to its unencapsulated counterpart, exhibits outstanding stability toward pH, and produces bright in vitro images following phagocytosis by macrophages. In vivo imaging allows the biodistribution to be imaged at different time points. Ex vivo imaging of intravenously administered encapsulated smURFP reveals a localization in the liver and kidneys after 2 h blood circulation and substantial elimination after 16 h of imaging, highlighting the potential application of these constructs as noninvasive in vivo imaging agents.

Zirconium doping level modulation combined with chalconylthiourea organic frameworks induced enhancement of luminescence applied to cell imaging

Derivatives of a zirconium metal–organic framework as the center polymer material with a chalconylthiourea polymer (CT) were applied to cell imaging.