In vivo tumor accumulation of nanoparticles formed by ionic interaction of glycol chitosan and fatty acid ethyl ester

In this study, novel fatty acid ethyl ester (FAEE)-based glycol chitosan (GC) nanoparticles were prepared through an electrostatic interaction. Additionally, the tumor accumulation of the FAEE-GC nanoparticles was evaluated in order to determine the enhanced permeability and retention (EPR) effect in a breast tumor model. FAEE, including eicosapentaenoic acid ethyl ester (EPAEE) and docosahexanoic acid ethyl ester (DHAEE), successfully formed ionic complexes with GC. The FAEE-GC complexes were self-aggregated with a spherical shape and a mean diameter of 110-333 nm in aqueous media. Cy7 was labeled to the FAEE-GC complexes for the in vivo optical imaging. A tumor animal model was developed by inoculating MDA-MB231 breast tumor cells into the right flanks of mice. The Cy7-labeled FAEE-GC nanoparticles were injected into the tail vein of the tumor-bearing mice. Fluorescence signals were strongly observed in the tumor because of the EPR effect. In the ex vivo imaging of the mice, the highest fluorescence intensity, except for the kidney, was observed in the tumor. Therefore, the FAEE-GC nanoparticles could be a useful vehicle for FAEE formulation as well as an in vivo tumor-selective drug delivery carrier.     

Systematic Surface Engineering of Magnetic Nanoworms for In vivo Tumor Targeting

In the design of nanoparticles that can target disease tissue in vivo, parameters such as targeting ligand density, type of target receptor, and nanoparticle shape can play an important role in determining the extent of accumulation. Herein, a systematic study of these parameters for the targeting of mouse xenograft tumors is performed using superparamagnetic iron oxide as a model nanoparticle system. The type of targeting peptide (recognizing cell surface versus extracellular matrix), the surface coverage of the peptide, its attachment chemistry, and the shape of the nanomaterial [elongated (nanoworm, NW) versus spherical (nanosphere, NS)] are varied. Nanoparticle circulation times and in vivo tumor‐targeting efficiencies are quantified in two xenograft models of human tumors (MDA‐MB‐435 human carcinoma and HT1080 human fibrosarcoma). It is found that the in vivo tumor‐targeting ability of the NW is superior to that of the NS, that the smaller, neutral CREKA targeting group is more effective than the larger, positively charged F3 molecule, that a maximum in tumor‐targeting efficiency and blood half‐life is observed with ≈60 CREKA peptides per NW for either the HT1080 or the MDA‐MB‐435 tumor types, and that incorporation of a 5‐kDa polyethylene glycol linker improves targeting to both tumor types relative to a short linker. It is concluded that the blood half‐life of a targeting molecule–nanomaterial ensemble is a key consideration when selecting the appropriate ligand and nanoparticle chemistry for tumor targeting.     

Graphene Nanomesh Promises Extremely Efficient In Vivo Photothermal Therapy

Reduced graphene oxide nanomesh (rGONM), as one of the recent structures of graphene with a surprisingly strong near‐infrared (NIR) absorption, is used for achieving ultraefficient photothermal therapy. First, by using TiO₂ nanoparticles, graphene oxide nanoplatelets (GONPs) are transformed into GONMs through photocatalytic degradation. Then rGONMs functionalized by polyethylene glycol (PEG), arginine–glycine–aspartic acid (RGD)‐based peptide, and cyanine 7 (Cy7) are utilized for in vivo tumor targeting and fluorescence imaging of human glioblastoma U87MG tumors having α_νβ₃ integrin receptors, in mouse models. The rGONM‐PEG suspension (1 μg mL^?1) exhibits about 4.2‐ and 22.4‐fold higher NIR absorption at 808 nm than rGONP‐PEG and graphene oxide (GO) with lateral dimensions of ≈60 nm and ≈2 μm. In vivo fluorescence imaging demonstrates high selective tumor uptake of rGONM‐PEG‐Cy7‐RGD in mice bearing U87MG cells. The excellent NIR absorbance and tumor targeting of rGONM‐PEG‐Cy7‐RGD results in an ultraefficient photothermal therapy (100% tumor elimination 48 h after intravenous injection of an ultralow concentration (10 μg mL^?1) of rGONM‐PEG‐Cy7‐RGD followed by irradiation with an ultralow laser power (0.1 W cm^?2) for 7 min), whereas the corresponding rGO‐ and rGONP‐based composites do not present remarkable treatments under the same conditions. All the mice treated by rGONM‐PEG‐Cy7‐RGD survived over 100 days, whereas the mice treated by other usual rGO‐based composites were dead before 38 days. The results introduce rGONM as one of the most promising nanomaterials in developing highly desired ultraefficient photothermal therapy.     

Double‐Targeting Explosible Nanofirework for Tumor Ignition to Guide Tumor‐Depth Photothermal Therapy

This study reports a double‐targeting “nanofirework” for tumor‐ignited imaging to guide effective tumor‐depth photothermal therapy (PTT). Typically, ≈30 nm upconversion nanoparticles (UCNP) are enveloped with a hybrid corona composed of ≈4 nm CuS tethered hyaluronic acid (CuS‐HA). The HA corona provides active tumor‐targeted functionality together with excellent stability and improved biocompatibility. The dimension of UCNP@CuS‐HA is specifically set within the optimal size window for passive tumor‐targeting effect, demonstrating significant contributions to both the in vivo prolonged circulation duration and the enhanced size‐dependent tumor accumulation compared with ultrasmall CuS nanoparticles. The tumors featuring hyaluronidase (HAase) overexpression could induce the escape of CuS away from UCNP@CuS‐HA due to HAase‐catalyzed HA degradation, in turn activating the recovery of initially CuS‐quenched luminescence of UCNP and also driving the tumor‐depth infiltration of ultrasmall CuS for effective PTT. This in vivo transition has proven to be highly dependent on tumor occurrence like a tumor‐ignited explosible firework. Together with the double‐targeting functionality, the pathology‐selective tumor ignition permits precise tumor detection and imaging‐guided spatiotemporal control over PTT operation, leading to complete tumor ablation under near infrared (NIR) irradiation. This study offers a new paradigm of utilizing pathological characteristics to design nanotheranostics for precise detection and personalized therapy of tumors.     

Ultrasmall Near‐Infrared Non‐cadmium Quantum Dots for in vivo Tumor Imaging

The high tumor uptake of ultrasmall near‐infrared quantum dots (QDs) attributed to the enhanced permeability and retention effect is reported. InAs/InP/ZnSe QDs coated by mercaptopropionic acid (MPA) exhibit an emission wavelength of about 800 nm (QD800‐MPA) with very small hydrodynamic diameter (<10 nm). Using 22B and LS174T tumor xenograft models, in vivo and ex vivo imaging studies show that QD800‐MPA is highly accumulated in the tumor area, which is very promising for tumor detection in living mice. The ex vivo elemental analysis (Indium) using inductively coupled plasma (ICP) spectrometry confirm the tumor uptake of QDs. The ICP data are consistent with the in vivo and ex vivo fluorescence imaging. Human serum albumin (HSA)‐coated QD800‐MPA nanoparticles (QD800‐MPA‐HSA) show reduced localization in mononuclear phagocytic system‐related organs over QD800‐MPA plausibly due to the low uptake of QD800‐MPA‐HSA in macrophage cells. QD800‐MPA‐HSA may have great potential for in vivo fluorescence imaging.     

Hierarchical Tumor Microenvironment‐Responsive Nanomedicine for Programmed Delivery of Chemotherapeutics

Nanomedicines have been demonstrated to have passive or active tumor targeting behaviors, which are promising for cancer chemotherapy. However, most nanomedicines still suffer from a suboptimal targeting effect and drug leakage, resulting in unsatisfactory treatment outcome. Herein, a hierarchical responsive nanomedicine (HRNM) is developed for programmed delivery of chemotherapeutics. The HRNMs are prepared via the self‐assembly of cyclic Arg‐Gly‐Asp (RGD) peptide conjugated triblock copolymer, poly(2‐(hexamethyleneimino)ethyl methacrylate)‐poly(oligo‐(ethylene glycol) monomethyl ether methacrylate)‐poly[reduction‐responsive camptothecin] (PC7A‐POEG‐PssCPT). In blood circulation, the RGD peptides are shielded by the POEG coating; therefore, the nanosized HRNMs can achieve effective tumor accumulation through passive targeting. Once the HRNMs reach a tumor site, due to the hydrophobic‐to‐hydrophilic conversion of PC7A chains induced by the acidic tumor microenvironment, the RGD peptides will be exposed for enhanced tumor retention and cellular internalization. Moreover, in response to the glutathione inside cells, active CPT drugs will be released rapidly for chemotherapy. The in vitro and in vivo results confirm effective tumor targeting, potent antitumor effect, and reduced systemic toxicity of the HRNMs. This HRNM is promising for enhanced chemotherapeutic delivery.     

Enhanced In Vivo Tumor Detection by Active Tumor Cell Targeting Using Multiple Tumor Receptor‐Binding Peptides Presented on Genetically Engineered Human Ferritin Nanoparticles

Human ferritin heavy‐chain nanoparticle (hFTH) is genetically engineered to present tumor receptor‐binding peptides (affibody and/or RGD‐derived cyclic peptides, named 4CRGD here) on its surface. The affibody and 4CRGD specifically and strongly binds to human epidermal growth factor receptor I (EGFR) and human integrin αvβ3, respectively, which are overexpressed on various tumor cells. Through in vitro culture of EGFR‐overexpressing adenocarcinoma (MDA‐MB‐468) and integrin‐overexpressing glioblastoma cells (U87MG), it is clarified that specific interactions between receptors on tumor cells and receptor‐binding peptides on engineered hFTH is critical in active tumor cell targeting. After labeling with the near‐infrared fluorescence dye (Cy5.5) and intravenouse injection into MDA‐MB‐468 or U87MG tumor‐bearing mice, the recombinant hFTHs presenting either peptide or both of affibody and 4CRGD are successfully delivered to and retained in the tumor for a prolonged period of time. In particular, the recombinant hFTH presenting both affibody and 4CRGD notably enhances in vivo detection of U87MG tumors that express heterogeneous receptors, integrin and EGFR, compared to the other recombinant hFTHs presenting either affibody or 4CRGD only. Like affibody and 4CRGD used in this study, other multiple tumor receptor‐binding peptides can be also genetically introduced to the hFTH surface for actively targeting of in vivo tumors with heterogenous receptors.     

HDL‐Mimicking Peptide–Lipid Nanoparticles with Improved Tumor Targeting

Targeted delivery of intracellularly active diagnostics and therapeutics in vivo is a major challenge in cancer nanomedicine. A nanocarrier should possess long circulation time yet be small and stable enough to freely navigate through interstitial space to deliver its cargo to targeted cells. Herein, it is shown that by adding targeting ligands to nanoparticles that mimic high‐density lipoprotein (HDL), tumor‐targeted sub‐30‐nm peptide–lipid nanocarriers are created with controllable size, cargo loading, and shielding properties. The size of the nanocarrier is tunable between 10 and 30 nm, which correlates with a payload of 15–100 molecules of fluorescent dye. Ligand‐directed nanocarriers targeting epidermal growth factor receptor (EGFR) are confirmed both in vitro and in vivo. The nanocarriers show favorable circulation time, tumor accumulation, and biodistribution with or without the targeting ligand. The EGFR targeting ligand is proved to be essential for the EGFR‐mediated tumor cell uptake of the nanocarriers, a prerequisite of intracellular delivery. The results demonstrate that targeted HDL‐mimetic nanocarriers are useful delivery vehicles that could open new avenues for the development of clinically viable targeted nanomedicine.     

Imaging breast cancer cells and tissues using peptide-labeled fluorescent silica nanoparticles

The imaging of tumor cells and tumor tissue samples is very important for cancer detection and therapy. We have taken advantages of fluorescent silica nanoparticles (FSiNPs) coupled with a molecular recognition element that allows for effective in vitro and ex vivo imaging of tumor cells and tissues. In this study, we report on the targeting and imaging of MDA-MB-231 human breast cancer cells using arginine-glycine-aspartic acid (RGD) peptide-labeled FSiNPs. When linked with RGD peptide using the cyanogen bromide (CNBr) method, the FSiNPs exhibited high target binding to alphavbeta3 integrin receptor (ABIR)-positive MDA-MB-231 breast cancer cells in vitro. Further study regarding the ex vivo imaging of tumor tissue samples was also carried out by intravenously injecting RGD peptide-labeled FSiNPs into athymic nude mice bearing the MDA-MB-231 tumors. Tissue images demonstrated that the high integrin alphavbeta3 expression level of the MDA-MB-231 tumors was clearly visible due to the special targeting effects of the RGD peptide-labeled FSiNPs, and the tumor fluorescence reached maximum intensity at 1 h postinjection. Our results break new ground for using FSiNPs to optically image tumors, and may also broaden the applications of silica nanoparticles in biomedicine.     

Dose‐Dependent Therapeutic Distinction between Active and Passive Targeting Revealed Using Transferrin‐Coated PGMA Nanoparticles

The paradigm of using nanoparticle‐based formulations for drug delivery relies on their enhanced passive accumulation in the tumor interstitium. Nanoparticles with active targeting capabilities attempt to further enhance specific delivery of drugs to the tumors via interaction with overexpressed cellular receptors. Consequently, it is widely accepted that drug delivery using actively targeted nanoparticles maximizes the therapeutic benefit and minimizes the off‐target effects. However, the process of nanoparticle mediated active targeting initially relies on their passive accumulation in tumors. In this article, it is demonstrated that these two tumor‐targeted drug delivery mechanisms are interrelated and dosage dependent. It is reported that at lower doses, actively targeted nanoparticles have distinctly higher efficacy in tumor inhibition than their passively targeted counterparts. However, the enhanced permeability and retention effect of the tumor tissue becomes the dominant factor influencing the efficacy of both passively and actively targeted nanoparticles when they are administered at higher doses. Importantly, it is demonstrated that dosage is a pivotal parameter that needs to be taken into account in the assessment of nanoparticle mediated targeted drug delivery.     

Single Chain Epidermal Growth Factor Receptor Antibody Conjugated Nanoparticles for in vivo Tumor Targeting and Imaging

Epidermal growth factor receptor (EGFR) targeted nanoparticle are developed by conjugating a single‐chain anti‐EGFR antibody (ScFvEGFR) to surface functionalized quantum dots (QDs) or magnetic iron oxide (IO) nanoparticles. The results show that ScFvEGFR can be successfully conjugated to the nanoparticles, resulting in compact ScFvEGFR nanoparticles that specifically bind to and are internalized by EGFR‐expressing cancer cells, thereby producing a fluorescent signal or magnetic resonance imaging (MRI) contrast. In vivo tumor targeting and uptake of the nanoparticles in human cancer cells is demonstrated after systemic delivery of ScFvEGFR‐QDs or ScFvEGFR‐IO nanoparticles into an orthotopic pancreatic cancer model. Therefore, ScFvEGFR nanoparticles have potential to be used as a molecular‐targeted in vivo tumor imaging agent. Efficient internalization of ScFvEGFR nanoparticles into tumor cells after systemic delivery suggests that the EGFR‐targeted nanoparticles can also be used for the targeted delivery of therapeutic agents.     

Dynamically PEGylated and Borate‐Coordination‐Polymer‐Coated Polydopamine Nanoparticles for Synergetic Tumor‐Targeted,Chemo‐Photothermal Combination Therapy

Multifunctional nanomaterials with efficient tumor‐targeting and high antitumor activity are highly anticipated in the field of cancer therapy. In this work, a synergetic tumor‐targeted, chemo‐photothermal combined therapeutic nanoplatform based on a dynamically PEGylated, borate‐coordination‐polymer‐coated polydopamine nanoparticle (PDA@CP‐PEG) is developed. PEGylation on the multifunctional nanoparticles is dynamically achieved via the reversible covalent interaction between the surface phenylboronic acid (PBA) group and a catechol‐containing poly(ethylene glycol) (PEG) molecule. Due to the acid‐labile PBA/catechol complex and the weak‐acid‐stable PBA/sialic acid (SA) complex, the nanoparticles can exhibit a synergetic targeting property for the SA‐overexpressed tumor cells, i.e., the PEG‐caused “passive targeting” and PBA‐triggered “active targeting” under the weakly acidic tumor microenvironment. In addition, the photothermal effect of the polydopamine core and the doxorubicin‐loading capacity of the porous coordination polymer layer endow the nanoparticles with the potential for chemo‐photothermal combination therapy. As expected, the in vitro and in vivo studies both verify that the multifunctional nanoparticles possess relatively lower systematic toxicity, efficient tumor targeting ability, and excellent chemo‐photothermal activity for tumor inhibition. It is believed that these multifunctional nanoparticles with synergetic tumor targeting property and combined therapeutic strategies would provide an insight into the design of a high‐efficiency antitumor nanoplatform for potential clinical applications.     

Hierarchical Targeting Strategy for Enhanced Tumor Tissue Accumulation/Retention and Cellular Internalization

Targeted delivery of therapeutic agents is an important way to improve the therapeutic index and reduce side effects. To design nanoparticles for targeted delivery, both enhanced tumor tissue accumulation/retention and enhanced cellular internalization should be considered simultaneously. So far, there have been very few nanoparticles with immutable structures that can achieve this goal efficiently. Hierarchical targeting, a novel targeting strategy based on stimuli responsiveness, shows good potential to enhance both tumor tissue accumulation/retention and cellular internalization. Here, the recent design and development of hierarchical targeting nanoplatforms, based on changeable particle sizes, switchable surface charges and activatable surface ligands, will be introduced. In general, the targeting moieties in these nanoplatforms are not activated during blood circulation for efficient tumor tissue accumulation, but re‐activated by certain internal or external stimuli in the tumor microenvironment for enhanced cellular internalization.     

Multimodal Precision Imaging of Pulmonary Nanoparticle Delivery in Mice: Dynamics of Application,Spatial Distribution,and Dosimetry

Targeted delivery of nanomedicine/nanoparticles (NM/NPs) to the site of disease (e.g., the tumor or lung injury) is of vital importance for improved therapeutic efficacy. Multimodal imaging platforms provide powerful tools for monitoring delivery and tissue distribution of drugs and NM/NPs. This study introduces a preclinical imaging platform combining X‐ray (two modes) and fluorescence imaging (three modes) techniques for time‐resolved in vivo and spatially resolved ex vivo visualization of mouse lungs during pulmonary NP delivery. Liquid mixtures of iodine (contrast agent for X‐ray) and/or (nano)particles (X‐ray absorbing and/or fluorescent) are delivered to different regions of the lung via intratracheal instillation, nasal aspiration, and ventilator‐assisted aerosol inhalation. It is demonstrated that in vivo propagation‐based phase‐contrast X‐ray imaging elucidates the dynamic process of pulmonary NP delivery, while ex vivo fluorescence imaging (e.g., tissue‐cleared light sheet fluorescence microscopy) reveals the quantitative 3D drug/particle distribution throughout the entire lung with cellular resolution. The novel and complementary information from this imaging platform unveils the dynamics and mechanisms of pulmonary NM/NP delivery and deposition for each of the delivery routes, which provides guidance on optimizing pulmonary delivery techniques and novel‐designed NM for targeting and efficacy.     

Holo‐Lactoferrin Modified Liposome for Relieving Tumor Hypoxia and Enhancing Radiochemotherapy of Cancer

Hypoxic microenvironments in the solid tumor play a negative role in radiotherapy. Holo‐lactoferrin (holo‐Lf) is a natural protein, which acts as a potential ligand of transferrin receptor (TfR). In this work, an anticancer drug, doxorubicin (Dox)‐loaded liposome‐holo‐Lf nanocomposites, is developed for tumor targeting and imaging guided combined radiochemotherapy. Dox‐loaded liposome‐holo‐Lf (Lf‐Liposome‐Dox) nanocomposites exhibit significant cellular uptake likely owing to the TfR receptor‐mediated targeting accumulation of Lf‐Liposome‐Dox nanocomposites. Additionally, the nanocomposites exhibit high accumulation in the tumor site after intravenous injection as evidenced from in vivo fluorescence imaging. More importantly, it is found that the holo‐Lf has the ability to catalyze the conversion of hydrogen peroxide (H₂O₂) to oxygen for relieving the tumor hypoxic microenvironment. Photoacoustic imaging further confirms the abundant generation of oxygen in the presence of Lf‐Liposome‐Dox nanocomposites. Based on these findings, in vivo combined radiochemotherapy is performed using Lf‐Liposome‐Dox as therapeutic agent, achieving excellent cancer treatment effect. The study further promotes the potential biomedical application of holo‐Lf in cancer treatment.     

Tumor‐Targeting Multifunctional Rattle‐Type Theranostic Nanoparticles for MRI/NIRF Bimodal Imaging and Delivery of Hydrophobic Drugs

The development of theranostic systems capable of diagnosis, therapy, and target specificity is considerably significant for accomplishing personalized medicine. Here, a multifunctional rattle‐type nanoparticle (MRTN) as an effective biological bimodal imaging and tumor‐targeting delivery system is fabricated, and an enhanced loading ability of hydrophobic anticancer drug (paclitaxel) is also realized. The rattle structure with hydrophobic Fe₃O₄ as the inner core and mesoporous silica as the shell is obtained by one‐step templates removal process, and the size of interstitial hollow space can be easily adjusted. The Fe₃O₄ core with hydrophobic poly(tert‐butyl acrylate) (PTBA) chains on the surface is not only used as a magnetic resonance imaging (MRI) agent, but contributes to improving hydrophobic drug loading amount. Transferrin (Tf) and a near‐infrared fluorescent dye (Cy 7) are successfully modified on the surface of the nanorattle to increase the ability of near‐infrared fluorescence (NIRF) imaging and tumor‐targeting specificity. In vivo studies show the selective accumulation of MRTN in tumor tissues by Tf‐receptor‐mediated endocytosis. More importantly, paclitaxel‐loaded MRTN shows sustained release character and higher cytotoxicity than the free paclitaxel. This theranostic nanoparticle as an effective MRI/NIRF bimodal imaging probe and drug delivery system shows great potential in cancer diagnosis and therapy.     

Direct Solvent‐Derived Polymer‐Coated Nitrogen‐Doped Carbon Nanodots with High Water Solubility for Targeted Fluorescence Imaging of Glioma

Cancer imaging requires biocompatible and bright contrast‐agents with selective and high accumulation in the tumor region but low uptake in normal tissues. Herein, 1‐methyl‐2‐pyrrolidinone (NMP)‐derived polymer‐coated nitrogen‐doped carbon nanodots (pN‐CNDs) with a particle size in the range of 5–15 nm are prepared by a facile direct solvothermal reaction. The as‐prepared pN‐CNDs exhibit stable and adjustable fluorescence and excellent water solubility. Results of a cell viability test (CCK‐8) and histology analysis both demonstrate that the pN‐CNDs have no obvious cytotoxicity. Most importantly, the pN‐CNDs can expediently enter glioma cells in vitro and also mediate glioma fluorescence imaging in vivo with good contrast via elevated passive targeting.     

Mitochondria‐Targeting Magnetic Composite Nanoparticles for Enhanced Phototherapy of Cancer

Photothermal therapy (PTT) and photodynamic therapy (PDT) are promising cancer treatment modalities in current days while the high laser power density demand and low tumor accumulation are key obstacles that have greatly restricted their development. Here, magnetic composite nanoparticles for dual‐modal PTT and PDT which have realized enhanced cancer therapeutic effect by mitochondria‐targeting are reported. Integrating PTT agent and photosensitizer together, the composite nanoparticles are able to generate heat and reactive oxygen species (ROS) simultaneously upon near infrared (NIR) laser irradiation. After surface modification of targeting ligands, the composite nanoparticles can be selectively delivered to the mitochondria, which amplify the cancer cell apoptosis induced by hyperthermia and the cytotoxic ROS. In this way, better photo therapeutic effects and much higher cytotoxicity are achieved by utilizing the composite nanoparticles than that treated with the same nanoparticles missing mitochondrial targeting unit at a low laser power density. Guided by NIR fluorescence imaging and magnetic resonance imaging, then these results are confirmed in a humanized orthotropic lung cancer model. The composite nanoparticles demonstrate high tumor accumulation and excellent tumor regression with minimal side effect upon NIR laser exposure. Therefore, the mitochondria‐targeting composite nanoparticles are expected to be an effective phototherapeutic platform in oncotherapy.     

Water‐Dispersible,pH‐Stable and Highly‐Luminescent Organic Dye Nanoparticles with Amplified Emissions for In Vitro and In Vivo Bioimaging

A new strategy is presented for using doped small‐molecule organic nanoparticles (NPs) to achieve high‐performance fluorescent probes with strong brightness, large Stokes shifts and tunable emissions for in vitro and in vivo imaging. The host organic NPs are used not only as carriers to encapsulate different doped dyes, but also as fluorescence resonance energy transfer donors to couple with the doped dyes (as acceptors) to achieve multicolor luminescence with amplified emissions (AE). The resulting optimum green emitting NPs show high brightness with quantum yield (QY) of up to 45% and AE of 12 times; and the red emitting NPs show QY of 14% and AE of 10 times. These highly‐luminescent doped NPs can be further surface modified with poly(maleic anhydride‐alt‐1‐octadecene)‐polyethylene glycol (C18PMH‐PEG), endowing them with excellent water dispersibility and robust stability in various bio‐environments covering wide pH values from 2 to 10. In this study, cytotoxicity studies and folic acid targeted cellular imaging of these multicolor probes are carried out to demonstrate their potential for in vitro imaging. On this basis, applications of the NP probes in in vivo and ex vivo imaging are also investigated. Intense fluorescent signals of the doped NPs are distinctly, selectively and spatially resolved in tumor sites with high sensitivity, due to the preferential accumulation of the NPs in tumor sites through the passive enhanced permeability and retention effect. The results clearly indicate that these doped NPs are promising fluorescent probes for biomedical applications.     

Tumor Microenvironment‐Triggered Aggregation of Antiphagocytosis 99mTc‐Labeled Fe3O4 Nanoprobes for Enhanced Tumor Imaging In Vivo

A tumor microenvironment responsive nanoprobe is developed for enhanced tumor imaging through in situ crosslinking of the Fe₃O₄ nanoparticles modified with a responsive peptide sequence in which a tumor‐specific Arg‐Gly‐Asp peptide for tumor targeting and a self‐peptide as a “mark of self” are linked through a disulfide bond. Positioning the self‐peptide at the outmost layer is aimed at delaying the clearance of the nanoparticles from the bloodstream. After the self‐peptide is cleaved by glutathione within tumor microenvironment, the exposed thiol groups react with the remaining maleimide moieties from adjacent particles to crosslink the particles in situ. Both in vitro and in vivo experiments demonstrate that the aggregation substantially improves the magnetic resonance imaging (MRI) contrast enhancement performance of Fe₃O₄ particles. By labeling the responsive particle probe with ^99mTc, single‐photon emission computed tomography is enabled not only for verifying the enhanced imaging capacity of the crosslinked Fe₃O₄ particles, but also for achieving sensitive dual modality imaging of tumors in vivo. The novelty of the current probe lies in the combination of tumor microenvironment‐triggered aggregation of Fe₃O₄ nanoparticles for boosting the T₂ MRI effect, with antiphagocytosis surface coating, active targeting, and dual‐modality imaging, which is never reported before.