Anchored Proteinase-Targetable Optomagnetic Nanoprobes for Molecular Imaging of Invasive Cancer Cells

Intracellular lipophilic network transformation induced by protease-specific endocytosis of fluorescent Au nanoclusters

The understanding of the endocytosis process of internalized nanomedicines through membrane biomarker is essential for the development of molecular-specific nanomedicines. In various recent reports, the metalloproteases have been identified as important markers during the metastasis of cancer cells. In particular, MT1-MMP has provoked concern due to its protease activity in the degradation of the extracellular matrix adjacent to tumors. Thus, in the current work, we have applied fluorescent Au nanoclusters which present strong resistance to chemical quenching to the investigation of MT1-MMP-mediated endocytosis. We synthesized protein-based Au nanocluster (PAuNC) and MT1-MMP-specific peptide was conjugated with PAuNC (pPAuNC) for monitoring protease-mediated endocytosis. The fluorescence capacity of pPAuNC was investigated and MT1-MMP-mediated intracellular uptake of pPAuNC was subsequently confirmed by a co-localization analysis using confocal microscopy and molecular competition test. Furthermore, we confirmed a change in the intracellular lipophilic network after an endocytosis event of pPAuNC. The identical lipophilic network change did not occur with the endocytosis of bare PAuNC. By classification of the branched network between the lipophilic organelles at the nanoscale, the image-based analysis of cell organelle networking allowed the evaluation of nanoparticle internalization and impaired cellular components after intracellular accumulation at a single-cell level. Our analyses suggest a methodology to achieve a better understanding of the mechanism by which nanoparticles enter cells.

Biosensors and bioassays for determination of matrix metalloproteinases: state of the art and recent advances

Matrix metalloproteinases (MMPs) are closely associated with various physiological and pathological processes, and have been regarded as potential biomarkers for severe diseases including cancer. Accurate determination of MMPs would advance our understanding of their roles in disease progression, and is of great significance for disease diagnosis, treatment and prognosis. In this review, we present a comprehensive overview of the developed bioassays/biosensors for detection of MMPs, and highlight the recent advancement in nanomaterial-based immunoassays for MMP abundance measurements and nanomaterial-based biosensors for MMP activity determination. Enzyme-linked immunosorbent assay (ELISA)-based immunoassays provide information about total levels of MMPs with high specificity and sensitivity, while target-based biosensors measure the amounts of active MMPs, and allow imaging of MMP activities in vivo. For multiplex and high-throughput analysis of MMPs, microfluidics and microarray-based assays are described. Additionally, we put forward the existing challenges and future prospects from our perspective.

MT1-MMP activatable fluorogenic probes with enhanced specificity via high-affinity peptide conjugation for tumor imaging

Overlapping substrate specificities within the family of matrix metalloproteinases (MMPs), usually caused by their highly conserved structural topology, increase the potential for a substrate to be cleaved by multiple enzymes within this family, which leads to the decrease in the selectivity of MMP substrate-based probes. To resolve this issue, MT1-MMP activatable fluorogenic probes for tumor detection with enhanced specificity were developed by combining a fluorescence resonance energy transfer (FRET) peptide substrate and its specific binding peptide with different lengths of linkers. The specificity of the probes increased profiting from the high affinity of the MT1-MMP specific binding peptide while keeping the ability to amplify the output imaging signals in response to MMP activity with the FRET substrate. Enzyme kinetics analysis clearly demonstrated that the conjugation of P-1 and MT1-AF7p enhanced both the specificity and selectivity of the fluorogenic probes for MT1-MMP, and introducing a linker composed of 12 PEG subunits into these two fragments led to optimized specificity and selectivity of the fluorogenic probe for MT1-MMP. Both in vitro and in vivo results revealed that the imaging probe with the linker composed of 12 PEG subunits based on our designed strategy could be effectively applied for MT1-MMP positive tumor imaging. Since this strategy for enhancing the specificity of protease sensing probes can be applied to other proteases and is not just limited to MT1-MMP, it is an appealing platform to achieve selective tumor imaging.

Locating the Site of Neuropathic Pain In Vivo Using MMP-12-Targeted Magnetic Nanoparticles

Neuropathic pain remains underrecognised and ineffectively treated in chronic pain sufferers. Consequently, their quality of life is considerably reduced, and substantial healthcare costs are incurred. The anatomical location of pain must be identified for definitive diagnosis, but current neuropsychological tools cannot do so. Matrix metalloproteinases (MMP) are thought to maintain peripheral neuroinflammation, and MMP-12 is elevated particularly in such pathological conditions. Magnetic resonance imaging (MRI) of the peripheral nervous system has made headway, owing to its high-contrast resolution and multiplanar features. We sought to improve MRI specificity of neural lesions, by constructing an MMP-12-targeted magnetic iron oxide nanoparticle (IONP). Its in vivo efficiency was evaluated in a rodent model of neuropathic pain, where the left lumbar 5 (L5) spinal nerve was tightly ligated. Spinal nerve ligation (SNL) successfully induced mechanical allodynia, and thermal hyperalgesia, in the left hind paw throughout the study duration. These neuropathy characteristics were absent in animals that underwent sham surgery. MMP-12 upregulation with concomitant macrophage infiltration, demyelination, and elastin fibre loss was observed at the site of ligation. This was not observed in spinal nerves contralateral and ipsilateral to the ligated spinal nerve or uninjured left L5 spinal nerves. The synthesised MMP-12-targeted magnetic IONP was stable and nontoxic in vitro. It was administered onto the left L5 spinal nerve by intrathecal injection, and decreased magnetic resonance (MR) signal was observed at the site of ligation. Histology analysis confirmed the presence of iron in ligated spinal nerves, whereas iron was not detected in uninjured left L5 spinal nerves. Therefore, MMP-12 is a potential biomarker of neuropathic pain. Its detection in vivo, using IONP-enhanced MRI, may be further developed as a tool for neuropathic pain diagnosis and management.

MMP-2-responsive fluorescent nanoprobes for enhanced selectivity of tumor cell uptake and imaging

It is difficult to develop highly selective substrate-based fluorescent nanoprobes for specific matrix metalloproteinases (MMPs) due to overlapping substrate specificities among the family of MMP enzymes. To resolve this issue, we have developed novel fluorescent nanoprobes that are highly selective for soluble MMP-2. Herein, MMP-2-responsive nanoprobes were prepared by immobilizing fluorescent fusion proteins on nickel ferrite nanoparticles via the His-tag nickel chelation mechanism. The fusion protein consisted of a fluorescent mCherry protein with a cell penetrating peptide (CPP) moiety. An MMP-2 cleavage site was also introduced within the fusion protein, which was directly linked to the nickel ferrite nanoparticles. The selectivity of nanoprobes was modulated by hiding the cleavage site of MMP-2 substrates deeply inside the system, which could result in strong steric hindrance between the nanoprobes and MMPs, especially for membrane-tethered MMPs such as MMP-14. A cell-based assay demonstrated that the nanoprobes could only be activated by tumor cells secreting soluble MMP-2, but not membrane-tethered MMP-14. To further evaluate the contribution of the steric hindrance effect on the nanoprobes, a truncated recombinant MMP-14 was employed to confer their cleavage activity as compared to native membrane-tethered MMP-14. Furthermore, a designed probe with a diminished steric hindrance effect was proved to be activated by membrane-tethered type MMP-14. The results indicated that the design of fluorescent nanoprobes employing the steric hindrance effect can greatly enhance the selectivity of MMP-responsive nanoprobes realizing the specific detection of soluble MMP-2 in a tumor microenvironment. We believe that highly selective MMP-2-responsive fluorescent nanoprobes have broad impacts on biomedical applications including molecular imaging and labeling for tumor detection.

Nanotechnology-Enhanced No-Wash Biosensors for in Vitro Diagnostics of Cancer

In vitro biosensors have been an integral component for early diagnosis of cancer in the clinic. Among them, no-wash biosensors, which only depend on the simple mixing of the signal generating probes and the sample solution without additional washing and separation steps, have been found to be particularly attractive. The outstanding advantages of facile, convenient, and rapid response of no-wash biosensors are especially suitable for point-of-care testing (POCT). One fast-growing field of no-wash biosensor design involves the usage of nanomaterials as signal amplification carriers or direct signal generating elements. The analytical capacity of no-wash biosensors with respect to sensitivity or limit of detection, specificity, stability, and multiplexing detection capacity is largely improved because of their large surface area, excellent optical, electrical, catalytic, and magnetic properties. This review provides a comprehensive overview of various nanomaterial-enhanced no-wash biosensing technologies and focuses on the analysis of the underlying mechanism of these technologies applied for the early detection of cancer biomarkers ranging from small molecules to proteins, and even whole cancerous cells. Representative examples are selected to demonstrate the proof-of-concept with promising applications for in vitro diagnostics of cancer. Finally, a brief discussion of common unresolved issues and a perspective outlook on the field are provided.

Instantaneous pH-Boosted Functionalization of Stellate Gold Nanoparticles for Intracellular Imaging of miRNA

Various types of nanoprobes have recently been utilized to monitor living organisms by detecting and imaging intracellular biomarkers, such as microRNAs (miRs). We here present a simple one-pot method to prepare stellate gold nanoparticles functionalized with miR-detecting molecular beacons (SGNP-MBs); low pH conditions permitted the rapid-high loading of MBs on the surface of SGNPs. Compared to the conventional gold nanoparticle-based MBs, SGNPs carried a 4.5-fold higher load of MBs and exhibited a 6.4-fold higher cellular uptake. We demonstrated that SGNP-MBs were successfully internalized in human gastric cancer cell lines and could be used to accurately detect and image intracellular miRs in an miR-specific manner. Furthermore, the relative levels of intracellular miRs in three different cell lines expressing miR-10b (high, moderate, and low levels) could be monitored using SGNP-MBs. Consequently, these results indicated that SGNP-MBs could have applications as highly potent, efficient nanoprobes to assess intracellular miR levels in living cells.

Strategies for using nanoprobes to perceive and treat cancer activity: a review

Nanomedicine has seen a significant increase in research on stimuli-responsive activatable nanoprobes for tumor-specific delivery and diagnosis. The tumor microenvironment has particular characteristics that can be exploited to implement therapeutic strategies based on disparities between normal tissues and tumor tissues, including differences in pH, oxygenation, enzymatic expression, gene activation/inactivation, and vasculature. The nanocarriers of activatable nanoparticles maintain their structure while circulating in the body and, upon reaching the tumor site, are altered by unique tumoral stimuli, leading to the release of a drug or other agent. This review demonstrates the latest achievements in the use of internal stimuli-responsive, activatable nanoparticles with respect to unique design strategies and applications.

MT1-MMP Responsive Doxorubicin Conjugated Poly(lactic-co-glycolic Acid)/Poly(styrene-alt-maleic Anhydride) Core/Shell Microparticles for Intrahepatic Arterial Chemotherapy of Hepatic Cancer

In this study, we demonstrated that the MT1-MMP-responsive peptide (sequence: GPLPLRSWGLK) and doxorubicin-conjugated poly(lactic-co-glycolic acid/poly(styrene-alt-maleic anhydride) core/shell microparticles (PLGA/pSMA MPs) can be applied for intrahepatic arterial injection for hepatocellular carcinoma (HCC). PLGA/pSMA MPs were prepared with a capillary-focused microfluidic device. The particle size, observed by scanning electron microscopy (SEM), was around 22 ± 3 μm. MT1-MMP-responsive peptide and doxorubicin (DOX) were chemically conjugated with pSMA segments on the shell of MPs to form a PLGA/pSMA-peptide-DOX complex, resulting in high encapsulation efficiency (91.1%) and loading content (2.9%). DOX was released from PLGA/pSMA-peptide-DOX MPs in a pH-dependent manner (∼25% at pH 5.4 and ∼8% at pH 7.4) and accumulated significantly in an MT1-MMP-overexpressing Hep3B cell line. An in vivo intrahepatic injection study showed localization of MPs on the hepatic vessels and hepatic lobes up to 24 h after the injection without any shunting to the lung. Moreover, MPs efficiently inhibited tumor growth of Hep3B hepatic tumor xenografted mouse models. We expect that PLGA/pSMA-peptide-DOX MPs can be utilized as an effective intrahepatic drug delivery system for the treatment of HCC.

Luminescent iridium(iii) complexes as COX-2-specific imaging agents in cancer cells

This is the first application of iridium(iii) complexes as imaging agents for COX-2.

Simple, rapid detection of influenza A (H1N1) viruses using a highly sensitive peptide-based molecular beacon

A peptide-based molecular beacon (PEP-MB) was prepared for the simple, rapid, and specific detection of H1N1 viruses using a fluorescence resonance energy transfer (FRET) system. The PEP-MB exhibited minimal fluorescence in its "closed" hairpin structure. However, in the presence of H1N1 viruses, the specific recognition of the hemagglutinin (HA) protein of H1 strains by the PEP-MB causes the beacon to assume an "open" structure that emits strong fluorescence. The PEP-MB could detect H1N1 viruses within 15 min or even 5 min and can exhibit strong fluorescence even at low viral concentrations, with a detection limit of 4 copies.

Biomarker-specific conjugated nanopolyplexes for the active coloring of stem-like cancer cells

Stem-like cancer cells possess intrinsic features and their CD44 regulate redox balance in cancer cells to survive under stress conditions. Thus, we have fabricated biomarker-specific conjugated polyplexes using CD44-targetable hyaluronic acid and redox-sensible polyaniline based on a nanoemulsion method. For the most sensitive recognition of the cellular redox at a single nanoparticle scale, a nano-scattering spectrum imaging analyzer system was introduced. The conjugated polyplexes showed a specific targeting ability toward CD44-expressing cancer cells as well as a dramatic change in its color, which depended on the redox potential in the light-scattered images. Therefore, these polyaniline-based conjugated polyplexes as well as analytical processes that include light-scattering imaging and measurements of scattering spectra, clearly establish a systematic method for the detection and monitoring of cancer microenvironments.

Cancer biomarker detection: recent achievements and challenges

We provide an overview covering the existing challenges and latest developments in achieving high selectivity and sensitivity cancer-biomarker detection.

Micro- and nanotechnologies for intracellular delivery

The majority of drugs and biomolecules need to be delivered into cells to be effective. However, the cell membranes, a biological barrier, strictly resist drugs or biomolecules entering cells, resulting in significantly reduced intracellular delivery efficiency. To overcome this barrier, a variety of intracellular delivery approaches including chemical and physical ways have been developed in recent years. In this review, the focus is on summarizing the nanomaterial routes involved in making use of a collection of receptors for the targeted delivery of drugs and biomolecules and the physical ways of applying micro- and nanotechnologies for high-throughput intracellular delivery.

Amphiphilic star copolymer-based bimodal fluorogenic/magnetic resonance probes for concomitant bacteria detection and inhibition

Four-arm star-shaped copolymers, TPE-star-P(DMA-co-BMA-co-Gd), containing TPE cores with an aggregation-induced emission (AIE) feature, a T 1 -type magnetic resonance (MR) contrast agent, and amphiphilic cationic arms, are synthesized. By taking advantage of non-covalent interactions between star copolymers and bacteria surfaces, bimodal fluorometric/MR detection and concomitant inhibition of both Gram-positive and Gram-negative bacteria strains in aqueous media are explored.

A smart "sense-act-treat" system: combining a ratiometric pH sensor with a near infrared therapeutic gold nanocage

Herein, we design a "sense-act-treat" system via the combination of a ratiometric pH sensor with a therapeutic gold nanocage. Our design could "sense" the tumor through two-state switching of fluorescence and further provide chemotherapy and hyperthermia for "treating" the tumor, showing the potential for future biomedical applications.

Extremely High Two-Photon Absorbing Graphene Oxide for Imaging of Tumor Cells in the Second Biological Window

Cancer, a life-threatening disease, has become a global pandemic. Targeted tumor imaging using near-infrared (NIR) light is the key to improve the penetration depth and it is highly promising for clinical tumor diagnostics. Driven by this need, in this Letter we have reported aptamer conjugated graphene oxide-based two-photon imaging of breast tumor cells selectively. Reported data indicate that there is an extremely high two-photon absorption from aptamer conjugated graphene oxide (σ2PA = 46890 GM). Experimental data show that two-photon luminescence signal remains almost unchanged even after 2 h of illuminations. Reported results show that S6 RNA aptamers conjugated graphene oxide-based two-photon fluorescence can be used for selective two-photon imaging of SK-BR-3 breast tumor cell in second biological transparency windows using 1100 nm wavelength. Experimental data demonstrate that it is highly capable of distinguishing targeted breast cancer SK-BR-3 cells from other nontargeted MDA-MB-231 breast cancer cells.

Development of novel tumor-targeted theranostic nanoparticles activated by membrane-type matrix metalloproteinases for combined cancer magnetic resonance imaging and therapy

A major drawback with current cancer therapy is the prevalence of unrequired dose-limiting toxicity to non-cancerous tissues and organs, which is further compounded by a limited ability to rapidly and easily monitor drug delivery, pharmacodynamics and therapeutic response. In this report, the design and characterization of novel multifunctional "theranostic" nanoparticles (TNPs) is described for enzyme-specific drug activation at tumor sites and simultaneous in vivo magnetic resonance imaging (MRI) of drug delivery. TNPs are synthesized by conjugation of FDA-approved iron oxide nanoparticles ferumoxytol to an MMP-activatable peptide conjugate of azademethylcolchicine (ICT), creating CLIO-ICTs (TNPs). Significant cell death is observed in TNP-treated MMP-14 positive MMTV-PyMT breast cancer cells in vitro, but not MMP-14 negative fibroblasts or cells treated with ferumoxytol alone. Intravenous administration of TNPs to MMTV-PyMT tumor-bearing mice and subsequent MRI demonstrates significant tumor selective accumulation of the TNP, an observation confirmed by histopathology. Treatment with CLIO-ICTs induces a significant antitumor effect and tumor necrosis, a response not observed with ferumoxytol. Furthermore, no toxicity or cell death is observed in normal tissues following treatment with CLIO-ICTs, ICT, or ferumoxytol. These findings demonstrate proof of concept for a new nanotemplate that integrates tumor specificity, drug delivery and in vivo imaging into a single TNP entity through attachment of enzyme-activated prodrugs onto magnetic nanoparticles. This novel approach holds the potential to significantly improve targeted cancer therapies, and ultimately enable personalized therapy regimens.

Smart drug delivery systems: from fundamentals to the clinic

Smart materials can endow implantable depots, targetable nanocarriers and insertable medical devices with activation-modulated and feedback-regulated control of drug release.

Aptamer-modified magnetic nanoprobe for molecular MR imaging of VEGFR2 on angiogenic vasculature

Nucleic acid-based aptamers have been developed for the specific delivery of diagnostic nanoprobes. Here, we introduce a new class of smart imaging nanoprobe, which is based on hybridization of a magnetic nanocrystal with a specific aptamer for specific detection of the angiogenic vasculature of glioblastoma via magnetic resonance (MR) imaging. The magnetic nanocrystal imaging core was synthesized using the thermal decomposition method and enveloped by carboxyl polysorbate 80 for water solubilization and conjugation of the targeting moiety. Subsequently, the surface of the carboxylated magnetic nanocrystal was modified with amine-functionalized aptamers that specifically bind to the vascular growth factor receptor 2 (VEGFR2) that is overexpressed on angiogenic vessels. To assess the targeted imaging potential of the aptamer-conjugated magnetic nanocrystal for VEGFR2 markers, the magnetic properties and MR imaging sensitivity were investigated using the orthotopic glioblastoma mouse model. In in vivo tests, the aptamer-conjugated magnetic nanocrystal effectively targeted VEGFR2 and demonstrated excellent MR imaging sensitivity with no cytotoxicity.

Using functional nanomaterials to target and regulate the tumor microenvironment: diagnostic and therapeutic applications

Malignant tumors remain a major health burden throughout the world and effective therapeutic strategies are urgently needed. Cancer nanotechnology, as an integrated platform, has the potential to dramatically improve cancer diagnosis, imaging, and therapy, while reducing the toxicity associated with the current approaches. Tumor microenvironment is an ensemble performance of various stromal cells and extracellular matrix. The recent progress in understanding the critical roles and the underlying mechanisms of the tumor microenvironment on tumor progression has resulted in emerging diagnostic and therapeutic nanomaterials designed and engineered specifically targeting the microenvironment components. Meanwhile, the bio-physicochemical differences between tumor and normal tissues have recently been exploited to achieve specific tumor-targeting for cancer diagnosis and treatment. Here, the major players in the tumor microenvironment and their biochemical properties, which can be utilized for the design of multifunctional nanomaterials with the potential to target and regulate this niche, are summarized. The recent progress in engineering intelligent and versatile nanomaterials for targeting and regulating the tumor microenvironment is emphasized. Although further investigations are required to develop robust methods for more specific tumor-targeting and well-controlled nanomaterials, the applications of tumor microenvironment regulation-based nanotechnology for safer and more effective anticancer nanomedicines have been proven successful and will eventually revolutionize the current landscape of cancer therapy.

Remotely Triggered Drug Release from Gold Nanoparticle-based Systems

Nanoparticles are attractive drug carriers that can combine drug molecules and targeting moieties in order to improve treatment efficacy and reduce unwanted side effects. In addition, activatable nanoparticles may enable drug release in the target sites at accurate timings or conditions, in which drug discharge can be controlled by specific stimuli. Especially, gold nanoparticles provide a great opportunity as drug carriers because of the following advantageous features: i) simple formulation with various sizes and shapes and non-toxicity; ii) easy incorporation of targeting molecules, drugs or other therapeutic molecules on them; iii) triggered drug release by means of external or internal stimuli. In this chapter, we describe relevant examples of the preparation techniques and the performance of various types of gold nanoparticles for drug delivery as well as theranostics.

Carbon Nanotube-Patterned Surface-Based Recognition of Carcinoembryonic Antigens in Tumor Cells for Cancer Diagnosis

It has been of high significance to devise a biochemical analytical tool kit enabling the detection of few circulating tumor cells (CTCs) for early diagnosis of cancer. Despite recent effort made to detect few CTCs, it is still challenging to sense such cells with their low concentration and/or the minute amount of marker proteins expressed on few CTCs. In this work, we report the label-free recognition of carcinoembryonic antigens (CEAs) expressed on few CTCs by using a carbon nanotube (CNT) sensor coupled with scanning probe microscopy imaging for cancer diagnosis. It is shown that a CNT-patterned surface is able to specifically capture the CEA molecules in the whole cell lysate of CTCs with their concentration even up to 10(-3) cells/mL. Our work sheds light on our bioassay based on a CNT-patterned surface for highly sensitive, label-free detection of marker proteins expressed on few tumor cells, which may open a new avenue in early diagnosis of cancer by providing a novel biochemical analysis tool kit.

Efficient CD44-targeted magnetic resonance imaging (MRI) of breast cancer cells using hyaluronic acid (HA)-modified MnFe2O4 nanocrystals

Targeted molecular imaging with hyaluronic acid (HA) has been highlighted in the diagnosis and treatment of CD44-overexpressing cancer. CD44, a receptor for HA, is closely related to the growth of cancer including proliferation, metastasis, invasion, and angiogenesis. For the efficient detection of CD44, we fabricated a few kinds of HA-modified MnFe2O4 nanocrystals (MNCs) to serve as specific magnetic resonance (MR) contrast agents (HA-MRCAs) and compared physicochemical properties, biocompatibility, and the CD44 targeting efficiency. Hydrophobic MNCs were efficiently phase-transferred using aminated polysorbate 80 (P80) synthesized by introducing spermine molecules on the hydroxyl groups of P80. Subsequently, a few kinds of HA-MRCAs were fabricated, conjugating different ratios of HA on the equal amount of phase-transferred MNCs. The optimized conjugation ratio of HA against magnetic content was identified to exhibit not only effective CD44 finding ability but also high cell viability through in vitro experiments. The results of this study demonstrate that the suggested HA-MRCA shows strong potential to be used for accurate tumor diagnosis.

Integrated nanocatalysts

Despite significant advancements in catalysis research, the prevailing catalyst technology remains largely an art rather than a science. Rapid development in the fields of nanotechnology and materials chemistry in the past few decades, however, provides us with a new capacity to re-examine existing catalyst design and processing methods. In recent years, "nanocatalysts" has become a term often used by the materials chemistry and catalysis community. It refers to heterogeneous catalysts at nanoscale dimensions. Similar to homogeneous catalysts, freestanding (unsupported) nanocatalysts are difficult to separate after use. Because of their small sizes, they are also likely to be cytotoxic and pose a threat to the environment and therefore may not be practical for industrial use. On the other hand, if they are supported on ordinary catalyst carriers, the nanocatalysts would then revert to act as conventional heterogeneous catalysts, since chemists have known active metal clusters or oxide particles in the nanoscale regime long before the nanotechnology era. To resolve this problem, we need new research directions and synthetic strategies. Important advancements in catalysis research now allow chemists to prepare catalytic materials with greater precision. By controlling particle composition, structure, shape, and dimension, researchers can move into the next phase of catalyst development if they can bridge these old and new technologies. In this regard, one way seems to be to integrate active nanostructured catalysts with boundary-defined catalyst supports that are "not-so-nano" in dimension. However, these supports still have available hierarchical pores and cavity spaces. In principle, these devices keep the essence of traditional "catalyst-plus-support" type systems. They also have the advantages of nanoscale engineering, which involves both high level design and integration processes in their fabrication. Besides this, the active components in these devices are small and are easy to integrate into other systems. For these reasons, we refer to the final catalytic devices as integrated nanocatalysts (INCs). In this Account, we describe the current status of nanocatalyst research and introduce the various possible forms of design and types of integration for INC fabrication with increasing compositional and structural complexities. In addition, we discuss present difficulties and urgent issues of this research and propose the integration of the INCs into even more complex "supracatalysts" for future research.

Activatable near-infrared fluorescent probe for in vivo imaging of fibroblast activation protein-alpha

Fibroblast activation protein-alpha (FAPα) is a cell surface glycoprotein which is selectively expressed by tumor-associated fibroblasts in malignant tumors but rarely on normal tissues. FAPα has also been reported to promote tumor growth and invasion and therefore has been of increasing interest as a promising target for designing tumor-targeted drugs and imaging agents. Although medicinal study on FAPα inhibitors has led to the discovery of many FAPα-targeting inhibitors including a drug candidate in a phase II clinical trial, the development of imaging probes to monitor the expression and activity of FAPα in vivo has largely lagged behind. Herein, we report an activatable near-infrared (NIR) fluorescent probe (ANP(FAP)) for in vivo optical imaging of FAPα. The ANP(FAP) consists of a NIR dye (Cy5.5) and a quencher dye (QSY21) which are linked together by a short peptide sequence (KGPGPNQC) specific for FAPα cleavage. Because of the efficient fluorescence resonance energy transfer (FRET) between Cy5.5 and QSY21 in ANP(FAP), high contrast on the NIR fluorescence signal can be achieved after the cleavage of the peptide sequence by FAPα both in vitro and in vivo. In vitro assay on ANP(FAP) indicated the specificity of the probe to FAPα. The in vivo optical imaging using ANP(FAP) showed fast tumor uptake as well as high tumor to background contrast on U87MG tumor models with FAPα expression, while much lower signal and tumor contrast were observed in the C6 tumor without FAPα expression, demonstrating the in vivo targeting specificity of the ANP(FAP). Ex vivo imaging also demonstrated ANP(FAP) had high tumor uptake at 4 h post injection. Collectively, these results indicated that ANP(FAP) could serve as a useful NIR optical probe for early detection of FAPα expressing tumors.