Smart Nanostructures for Cargo Delivery: Uncaging and Activating by Light

Solvent Magic for Organic Particles

Organic particles have attracted extensive attention due to their broad scientific and industrial applications. Solvents play important roles in producing organic particles with fine-tuned sizes, shapes, and surface morphologies, thus the advancement of microfluidic devices with a thorough understanding of solvent miscibility offers additional opportunities to fabricate organic particles in large quantities. In this issue of ACS Nano, Chen et al. report that solvents could play a seemingly magical role in switching both reaction directions and particle morphologies from the same starting materials. Through monitoring the particle formulation kinetics, both social self-sorting and narcissistic self-sorting mechanisms have been proposed, which offer powerful methods to yield organic particles with desirable shapes and compositions.

Two-Dimensional and Three-Dimensional Single Particle Tracking of Upconverting Nanoparticles in Living Cells

Lanthanide-doped upconversion nanoparticles (UCNPs) are inorganic nanomaterials in which the lanthanide cations embedded in the host matrix can convert incident near-infrared light to visible or ultraviolet light. These particles are often used for long-term and real-time imaging because they are extremely stable even when subjected to continuous irradiation for a long time. It is now possible to image their movement at the single particle level with a scale of a few nanometers and track their trajectories as a function of time with a scale of a few microseconds. Such UCNP-based single-particle tracking (SPT) technology provides information about the intracellular structures and dynamics in living cells. Thus far, most imaging techniques have been built on fluorescence microscopic techniques (epifluorescence, total internal reflection, etc.). However, two-dimensional (2D) images obtained using these techniques are limited in only being able to visualize those on the focal planes of the objective lens. On the contrary, if three-dimensional (3D) structures and dynamics are known, deeper insights into the biology of the thick cells and tissues can be obtained. In this review, we introduce the status of the fluorescence imaging techniques, discuss the mathematical description of SPT, and outline the past few studies using UCNPs as imaging probes or biologically functionalized carriers.

Reversible Shielding between Dual Ligands for Enhanced Tumor Accumulation of ZnPc-Loaded Micelles

Herein, we report a ligand-reversible-shielding strategy based on the mutual shielding of dual ligands tethered to the surface of nanoparticles. To exemplify this concept, phenylboronic acid-functionalized poly(ethylene glycol)- b-poly(ε-caprolactone) (PBA-PEG-PCL) and galactose-functionalized diblock polymer (Gal-PEG-PCL) were mixed to form dual-ligand micelles (PBA/Gal). PBA and Gal residues could form a complex at pH 7.4 and mutually shield their targeting function. At pH 6.8, the binding affinity between PBA and Gal weakened, and PBA preferred to bind with the sialic acid residues on the tumor cell surface rather than to Gal on the micellar surface; furthermore, the unbound Gal recovered its targeting ability toward the asialoglycoprotein receptor. When the pH decreased from 7.4 to 6.8, enzyme-linked immunosorbent assays exhibited that the percentage of exposed Gal on the micellar surface increased 1.9-fold, and flow cytometry showed that HepG2 cellular uptake increased 4.3-fold. More importantly, this process was reversible, confirming the reversible shielding and deshielding of dual ligands. With the encapsulation of a photosensitizer, zinc phthalocyanine (ZnPc), the reversible-shielding micelles showed a 48% improvement in the half-life ( t_1/2) in blood circulation, a 54% decrease in liver capture, a 40% increase in tumor accumulation, and a 10.3% improvement in the tumor inhibition rate compared to the Gal-coated irreversible micelles. This dual-ligand mutual-shielding strategy provides a new perspective on reversible tumor targeting.

Activatable near-infrared emission-guided on-demand administration of photodynamic anticancer therapy with a theranostic nanoprobe

Development of theranostic probes that can be used to identify tumors and direct the on-demand drug administration to cancers is ongoing but remains challenging. Herein, we report a theranostic platform composed of a H2S-activated imaging probe and a light-sensitive drug. The designed probe affords advantages of H2S-activated NIR emission light-up and efficient 1O2 generation, enabling the selective visualization of H2S-rich cancers and the subsequent imaging-directed on-demand light exposure to the detected cancers while leaving normal tissues untouched. Such controllable administration of photodynamic anticancer therapy maximizes the therapeutic efficiency and minimizes side effects. This work should facilitate significant advances toward precise diagnosis and treatment of cancer.

Photodegradable coumarin-derived amphiphilic dendrons for DNA binding: Self-assembly and phototriggered disassembly in water and air-water interface

In this article, we demonstrate the self-assembly and photoresponive behavior of a novel coumarin-based amphiphilic dendron in both aqueous solution and air-water interface. The dendritic structure, namely C-IG₁, was composed of a lipophilic cholesterol and hydrophilic poly(amido amine) (PAMAM) dendron, and the amphiphilic counterpart is interconnected by a photolabile coumarin carbonate ester, enabling the photoinduced degradation of the amphiphiles in protic solvents via S_N1-like mechanism. A Nile red solubilization fluorescence assay suggests a low critical aggregation concentration for the micelle formation of C-IG₁ in aqueous solutions (3.9 × 10^-5 M); the Langmuir analysis further indicates that C-IG₁ possesses significant compressibility in air-water interface, eventually forming homogeneous monolayers with a final molecular area (A₀) of 36 Ų. Notably, the micelles and Langmuir monolayer are quite stable until photo-triggered dissociation based on the photocleavage of C-IG₁ amphiphile activated by 365-nm incident light. Moreover, the transition in interfacial morphology of the Langmuir monolayer during the assembly and photodegradation processes also can be visually analyzed by incorporating Nile red probes with in situ monitoring through fluorescence microscopy. The thin film deposited on a glass substrate by the Langmuir-Blodgett technique also shows a photoresponsive behavior based on the change in the contact angles of a water droplet on the surface upon light stimulation. The binding affinity of C-IG₁ and cyclic DNA determined by the fluorescence quenching analysis of the coumarin reporter suggests a ground-state macromolecular complexation process occurring through polyvalent interactions between the pseudodendrimers and biomacromolecules. The ethidium bromide displacement assay further indicates thus dendriplex formation at low nitrogen-to-phosphorous value (N/P < 1) and confirms that the decomplexation accompanied by DNA release can be achieved through an active phototriggered route under spatiotemporal control.

Plasmonic MoO3-x nanoparticles incorporated in Prussian blue frameworks exhibit highly efficient dual photothermal/photodynamic therapy

Development of near infrared (NIR) light-responsive nanomaterials for high performance multimodal phototherapy within a single nanoplatform is still challenging in technology and biomedicine. Herein, a new phototherapeutic nanoagent based on FDA-approved Prussian blue (PB) functionalized oxygen-deficient molybdenum oxide nanoparticles (MoO_3-x NPs) is strategically designed and synthesized by a facile one-pot size/morphology-controlled process. The as-prepared PB-MoO_3-x nanocomposites (NCs) with a uniform particle size of ∼90 nm and high water dispersibility exhibited strong optical absorption in the first biological window, which is induced by plasmon resonance in an oxygen-deficient MoO_3-x semiconductor. More importantly, PB-MoO_3-x NCs not only exhibited a high photothermal conversion efficiency of ∼63.7% and photostability but also offered a further approach for the generation of reactive oxygen species (ROS) upon singular NIR light irradiation which significantly improved the therapeutic efficiency of the PB agent. Furthermore, PB-MoO_3-x NCs showed a negligible cytotoxic effect in the dark, but an excellent therapeutic effect toward two triple-negative breast cancer (TNBC) cell lines at a low concentration (20 μg mL^-1) of NCs and a moderate NIR laser power density. Additionally, efficient tumor ablation and metastasis inhibition in a 4T1 TNBC mouse tumor model can also be realized by synergistic photothermal/photodynamic therapy (PTT/PDT) under a single continuous NIR wave laser. Taken together, this study paved the way for the use of a single nanosystem for multifunctional therapy.

Chemiluminescence-initiated and in situ-enhanced photoisomerization for tissue-depth-independent photo-controlled drug release

Tissue-penetration-depth-independent self-luminescence is highly expected to perform photoisomerization-related bioapplications in vivo to overcome the limitation of shallow tissue-penetration from external photoexcitation. However, it remains extremely challenging because of lacking a target-specific high-intensity self-luminescence to precisely and effectively drive the photoisomerization. Here, we first report a target-specific tissue-depth-independent photoisomerization in vivo by developing a target-specific initiated and in situ-enhanced chemiluminescence (one of self-luminescence) strategy that overcomes the limitation of lacking target-specific high-intensity self-luminescence. Considering that photoisomerization shows boundless glamour in drug-controlled release for disease-specific chemotherapy, we demonstrated applicability of our strategy to apply it in tumor-specific self-luminescence-controlled drug chemotherapy. Specifically, a chemiluminescence substrate and chemiluminescence fluorophore (antitumor drug, CPT) were co-encapsulated in host-guest carriers composed of cyclodextrin and the photoisomerization molecule azobenzene. Tumor-specific H2O2-induced chemiluminescence preliminarily isomerizes azobenzene, triggering the partial dissociation of host-guest carriers and CPT release. Particularly, the initially released CPT again functions as a chemiluminescence enhancer to achieve in situ enhanced chemiluminescence, assuring target-specific enhanced isomerization and CPT release. With high tumor-inhibition-rate (73%) and no obvious therapy-side-effect in vivo indicates the good efficiency and target-specificity of our chemiluminescence-driven photoisomerization. Although we only demonstrated one example of a photoisomerization-related bioapplication, namely photoisomerization-controlled drug chemotherapy, our work provides guidelines to design various target-specific tissue-depth-independent photoisomerization for bioapplications.

Förster Resonance Energy Transfer-Activated Processes in Smart Nanotheranostics Fabricated in a Sustainable Manner

Multilayer nanocarriers loaded with optically activated payloads are gaining increasing attention due to their anticipated crucial role for providing new mechanisms of energy transfers in the health-oriented applications, as well as for energy storage and environmental protection. The combination of careful selection of optical components for efficient Förster resonance energy transfer, and surface engineering of the nanocarriers, allowed us to synthesize and characterize novel theranostic nanosystems for diagnosis and therapy of deep-seated tumors. The cargo, constrained within the oil core of the nanocapsules, composed of NaYF₄ :Tm⁺³ , Yb⁺³ up-converting nanoparticles together with a second-generation porphyrin-based photosensitizing agent-Verteporfin, assured requisite diagnostic and therapeutic functions under near-IR laser excitation. The outer polyaminoacid shell of the nanocapsules was functionalized with a ligand-poly(l-glutamic acid) functionalized by PEG-ylated folic acid-to ensure both a "stealth" effect and active targeting towards human breast cancer cells. The preparation criteria of all nanocarrier building blocks meet the requirements for sustainable and green chemistry practices. The multifunctionality of the proposed nanocarriers is a consequence of both the surface-functionalized organic exterior part, which was accessible for selective accumulation in cancer cells, and the hydrophobic optically active interior, which shows phototoxicity upon irradiation within the first biological window.

Polymer Amphiphiles for Photoregulated Anticancer Drug Delivery

We report the synthesis of amphiphilic polymers featuring lipophilic stearyl chains and hydrophilic poly(ethylene glycol) polymers that are connected through singlet oxygen-cleavable alkoxyanthracene linkers. These amphiphilic polymers assembled in water to form micelles with diameters of ∼20 nm. Reaction of the alkoxyanthracene linkers with light and O₂ cleaved the ether C-O bonds, resulting in formation of the corresponding 9,10-anthraquinone derivatives and concomitant disruption of the micelles. These micelles were loaded with the chemotherapeutic agent doxorubicin, which was efficiently released upon photo-oxidation. The drug-loaded reactive micelles were effective at killing cancer cells in vitro upon irradiation at 365 nm, functioning through both doxorubicin release and photodynamic mechanisms.

Eco-friendly porous iron(iii) oxide micromotors for efficient wastewater cleaning

Eco-friendly porous iron(iii) oxide micromotors obtained by calcining octahedral PB microcrystals are used for efficient adsorption of organic pollutants in water.

Photo-controlled release of paclitaxel and model drugs from RNA pyramids

Stimuli-responsive release of drugs from a nanocarrier in spatial-, temporal-, and dosage-controlled fashions is of great interest in the pharmaceutical industry. Paclitaxel is one of the most effective and popular chemotherapeutic drugs against a number of cancers such as metastatic or nonmetastatic breast cancer, non-small cell lung cancer, refractory ovarian cancer, AIDS-related Kaposi's sarcoma, and head and neck cancers. Here, by taking the advantage of RNA nanotechnology in biomedical and material science, we developed a three-dimensional pyramid-shaped RNA nanocage for a photocontrolled release of cargo, using paclitaxel as a model drug. The light-triggered release of paclitaxel or fluorophore Cy5 was achieved by incorporation of photocleavable spacers into the RNA nanoparticles. Upon irradiation with ultraviolet light, cargos were rapidly released (within 5 min). In vitro treatment of breast cancer cells with the RNA nanoparticles harboring photocleavable paclitaxel showed higher cytotoxicity as compared to RNA nanoparticles without the photocleavable spacer. The methodology provides proof of concept for the application of the light-triggered controlled release of drugs from RNA nanocages.

Achieving traceless ablation of solid tumors without recurrence by mild photothermal-chemotherapy of triple stimuli-responsive polymer–drug conjugate nanoparticles

We put forward an innovative strategy to leverage hyperthermia and a high drug-loading capacity for mild PT-CT, which achieved traceless ablation of solid MCF-7 tumors without recurrence within 50 days.

External stimulus responsive inorganic nanomaterials for cancer theranostics

Cancer is a highly intelligent system of cells, that works together with the body to thrive and subsequently overwhelm the host in order for its survival. Therefore, treatment regimens should be equally competent to outsmart these cells. Unfortunately, it is not the case with current therapeutic practices, the reason why it is still one of the most deadly adversaries and an imposing challenge to healthcare practitioners and researchers alike. With rapid nanotechnological interventions in the medical arena, the amalgamation of diagnostic and therapeutic functionalities into a single platform, theranostics provides a never before experienced hope of enhancing diagnostic accuracy and therapeutic efficiency. Additionally, the ability of these nanotheranostic agents to perform their actions on-demand, i.e. can be controlled by external stimulus such as light, magnetic field, sound waves and radiation has cemented their position as next generation anti-cancer candidates. Numerous reports exist of such stimuli-responsive theranostic nanomaterials against cancer, but few have broken through to clinical trials, let alone clinical practice. This review sheds light on the pros and cons of a few such theranostic nanomaterials, especially inorganic nanomaterials which do not require any additional chemical moieties to initiate the stimulus. The review will primarily focus on preclinical and clinical trial approved theranostic agents alone, describing their success or failure in the respective stages.

Nanopharmaceuticals and nanomedicines currently on the market: challenges and opportunities

There has been a revolution in nanotechnology and nanomedicine. Since 1980, there has been a remarkable increase in approved nano-based pharmaceutical products. These novel nano-based systems can either be therapeutic agents themselves, or else act as vehicles to carry different active pharmaceutical agents into specific parts of the body. Currently marketed nanostructures include nanocrystals, liposomes and lipid nanoparticles, PEGylated polymeric nanodrugs, other polymers, protein-based nanoparticles and metal-based nanoparticles. A range of issues must be addressed in the development of these nanostructures. Ethics, market size, possibility of market failure, costs and commercial development, are some topics which are on the table to be discussed. After passing all the ethical and biological assessments, and satisfying the investors as to future profitability, only a handful of these nanoformulations, successfully obtained marketing approval. We survey the range of nanomedicines that have received regulatory approval and are marketed. We discuss ethics, costs, commercial development and possible market failure. We estimate the global nanomedicine market size and future growth. Our goal is to summarize the different approved nanoformulations on the market, and briefly cover the challenges and future outlook.

Development of organic semiconducting materials for deep-tissue optical imaging, phototherapy and photoactivation

Recent progress in developing organic semiconducting materials (OSMs) for deep-tissue optical imaging, cancer phototherapy and biological photoactivation is summarized.

Singlet oxygen partition between the outer-, inner- and membrane-phases of photo/chemotherapeutic liposomes

Herein, we developed a strategy to quantify the fraction of singlet oxygen lifetime spent in the three distinct local liposomal environments through the combination of direct and indirect singlet oxygen detection approaches.

Positively charged helical chain-modified stimuli-responsive nanoassembly capable of targeted drug delivery and photoacoustic imaging-guided chemo-photothermal synergistic therapy

Tumor targeted size-switchable CPT/IR780@H30-PCL-PPI(L−)/PEI(–COOH/FA) nanoassembly with a “pomegranate” construction was designed, which could efficiently expand the penetration depth and accelerate the cell internalization.

ZnO-functionalized mesoporous inner-empty nanotheranostic platform: upconversion imaging guided chemotherapy with pH-triggered drug delivery

Here we report a novel drug delivery system using mesoporous inner-empty upconversion microspheres carrying drugs with ZnO quantum dots (UCMPS@ZnO) acting as a 'door-keeper' for pH-triggered drug release. Compared to other upconversion drug delivery systems, it is smarter, simpler, more efficient and more biocompatible. In particular, the UCMPS@ZnO microspheres show low cytotoxicity, are simple to produce and have a high drug loading rate (15%). Promisingly, a mice treatment experiment demonstrated that the multifunctional nanoparticles have efficient inhibition of tumor growth after a 14-day treatment. This makes UCMPS@DOX-ZnO microspheres a promising theranostic candidate in cancer treatment and clinical trials.

Reversible encapsulations and stimuli-responsive biological delivery from a dynamically assembled cucurbit[7]uril host and nanoparticle guest scaffold

The positive outcome of any therapeutic molecule requires control over its delivery rate. When delivered without control, administration of large doses is required to stimulate a therapeutic effect, frequently leading to increased toxicity or undesirable side effects. Recent advances introduced "smart" materials that actively release drugs in response to environmental stimuli. Although a variety of endogenous and exogenous triggers are reported, they are either difficult to control or lack tissue penetration depth. We report here a dynamic drug delivery scaffold based on a cucurbit[7]uril (CB[7]) host and benzylammonium functionalized gold nanoparticle (AuNP) guest that utilizes a bioorthogonal small molecule to achieve therapeutic control. In addition to their ability to reach deep tissue, small molecule activation is benefitted by their external controllability. Through cell culture studies we demonstrate that the host-guest supramolecular scaffold provides a nontoxic platform that effectively encapsulates a variety of therapeutic molecules and controls the payload release upon exposure to a high-affinity competitive guest molecule. This study presents a new strategy for controlling drug release rate through the use of competitive interactions of orthogonally presented guest molecules with immediate advantages in dosage control.

Hydrogen-bonded six-component assembly for capsule formation based on tetra(4-pyridyl)cavitand and isophthalic acid linker and its application to photoresponsive capsule

Two molecules of tetra(4-pyridyl)cavitand 1 and four molecules of isophthalic acid linker 2a with a triethylene glycol monomethyl ether (TEG) group self-assembled into a six-component capsule 1₂·2a₄ through eight pyNHO₂C hydrogen bonds, which encapsulates one molecule of guest G such as bis(4-acetoxyphenyl)acetylene and hexakis(4-iodophenyl)benzene to form G@(1₂·2a₄). Guest-encapsulation ability and selectivity of 1₂·2a₄ were revealed. trans-5-(p-Substituted-phenylazo)isophthalic acid with two dichotomous branching TEG groups trans-2b serves as a photoresponsive linker to form 1₂·(trans-2b)₄, which moderately reduced guest-encapsulation ability upon photoisomerization (at the photostationary state, 10% guest release upon subunit-trans-2b/subunit-cis-2b = 18 : 82).

Recent progress in the engineering of multifunctional colloidal nanoparticles for enhanced photodynamic therapy and bioimaging

This up-to-date review summarizes the design and current fabrication strategies that have been employed in the area of mono- and multifunctional colloidal nanoparticles - nanocarriers well suited for photodynamic therapy (PDT) and diagnostic purposes. Rationally engineered photosensitizer (PS)-loaded nanoparticles may be achieved via either noncovalent (i.e., self-aggregation, interfacial deposition, interfacial polymerization, or core-shell entrapment along with physical adsorption) or covalent (chemical immobilization or conjugation) processes. These PS loading approaches should provide chemical and physical stability to PS payloads. Their hydrophilic surfaces, capable of appreciable surface interactions with biological systems, can be further modified using functional groups (stealth effect) to achieve prolonged circulation in the body after administration and/or grafted by targeting agents (such as ligands, which bind to specific receptors uniquely expressed on the cell surface) or stimuli (e.g., pH, temperature, and light)-responsive moieties to improve their action and targeting efficiency. These attempts may in principle permit efficacious PDT, combination therapies, molecular diagnosis, and - in the case of nanotheranostics - simultaneous monitoring and treatment. Nanophotosensitizers (nano-PSs) should possess appropriate morphologies, sizes, unimodal distributions and surface processes to be successfully delivered to the place of action after systemic administration and should be accumulated in certain tumors by passive and/or active targeting. Additionally, physically facilitating drug delivery systems emerge as a promising approach to enhancing drug delivery, especially for the non-invasive treatment of deep-seated malignant tissues. Recent advances in nano-PSs are scrutinized, with an emphasis on design principles, via the promising use of colloid chemistry and nanotechnology.

Self-Assembly of Metallacages into Multidimensional Suprastructures with Tunable Emissions

Cubic metallacages were arranged into multidimensional (one-, two-, and three-dimensional) suprastructures via multistep assembly. Four new shape-controllable, hybrid metallacages with modified substituents and tunable electronic properties were prepared using dicarboxylate ligands with various substituents (sodium sulfonate, nitro, methoxyl, and amine), tetra-(4-pyridylphenyl) ethylene, and cis-(PEt3)2Pt(OTf)2. The as-prepared metallacages were used as building blocks for further assembly. Diverse suprastructures with tunable emissions (λmax from 451 to 519 nm) and various substituents (-SO3Na, -NO2, -OCH3, and -NH2) were prepared depending on the substituents and solvents used.

Ternary-Responsive Drug Delivery with Activatable Dual Mode Contrast-Enhanced in Vivo Imaging

Designing a smart nanotheranostic system has recently attracted tremendous attention and is highly desirable for realizing targeted cancer therapy and early diagnosis. Herein we report the fabrication of smart nanotheranostic system using multiresponsive gatekeeping protocol of mesoporous silica nanoparticles (MSN). Acid, oxidative stress and redox sensitive manganese oxide (MnO _x) coated superparamagnetic iron oxide nanoparticle (SPION) were employed as nanolids to regulate the camptothecin drug release from the channels of mesoporous silica and achieve responsive dual-mode MRI contrast. The nonvehicle showed high magnetization and T2 contrast in magnetic resonance imaging (MRI) due to the significant density of SPION onto the surface of MSN, and at the same time the MnO _x shell degradation release Mn²⁺ which enhanced the T1MRI visualization. The efficacy of responsive drug delivery system was investigated on pancreatic cancer cells and tumor-bearing mice, and results reinforced that MnO _x-SPION@MSN@CPT nonvehicle is efficacious against cancer cells. We envision that our unique and multiresponsive nanoplatform may find applications in effective delivering of imaging and therapeutic agents to wide range of diseases besides cancer.

Multifunctional and self-propelled spherical Janus nano/micromotors: recent advances

Recent progress in autonomous self-propelled multifunctional Janus nano/micromotors, which are able to convert chemical or light energy into mechanical motion, is presented. This technology of moving micro- and nanodevices is at the forefront of materials research and is a promising and growing technology with the possibility of using these motors in both biomedical and environmental applications. The development of novel multifunctional Janus motors together with their motion mechanisms is discussed. Different preparation and synthesis routes are compared. The effects of the size, interfacial structures and porosity on the directional motion and the speed of Janus micromotors are discussed. For light-derived Janus micromotors, newly developed techniques that are able to observe directly the interfaces' charge distribution on a nanometer scale are presented in order to clarify the underlying electrophoresis motion mechanism. This review aims to encourage further research in the field of micromotors using new and facile methodologies for obtaining novel Janus motors with enhanced motion and activity.

Cell Membrane Coated Semiconducting Polymer Nanoparticles for Enhanced Multimodal Cancer Phototheranostics

Phototheranostic nanoagents are promising for early diagnosis and precision therapy of cancer. However, their imaging ability and therapeutic efficacy are often limited due to the presence of delivery barriers in the tumor microenvironment. Herein, we report the development of organic multimodal phototheranostic nanoagents that can biomimetically target cancer-associated fibroblasts in the tumor microenvironment for enhanced multimodal imaging-guided cancer therapy. Such biomimetic nanocamouflages comprise a near-infrared (NIR) absorbing semiconducting polymer nanoparticle (SPN) coated with the cell membranes of activated fibroblasts. The homologous targeting mechanism allows the activated fibroblast cell membrane coated SPN (AF-SPN) to specifically target cancer-associated fibroblasts, leading to enhanced tumor accumulation relative to the uncoated and cancer cell membrane coated counterparts after systemic administration in living mice. As such, AF-SPN not only provides stronger NIR fluorescence and photoacoustic signals to detect tumors but also generates enhanced cytotoxic heat and singlet oxygen to exert combinational photothermal and photodynamic therapy, ultimately leading to an antitumor efficacy higher than that of the counterparts. This study introduces an organic phototheranostic system that biomimetically targets the component in the tumor microenvironment for enhanced multimodal cancer theranostics.

Near-infrared-triggered antibacterial and antifungal photodynamic therapy based on lanthanide-doped upconversion nanoparticles

An alarming worldwide increase in microbial resistance to traditional drugs and classical pharmacophores has spurred the search for new antimicrobial compounds. Antimicrobial photodynamic therapy (aPDT) has recently emerged as an effective modality for the selective destruction of bacteria and other pathogenic microorganisms. However, some of the factors, including the aggregation of the hydrophobic photosensitizer (PS) in aqueous media and the inefficient biodistribution of PS limit its expansion to clinical conditions. In addition, the photoactivation under visible-light irradiation limits the therapeutic effect of aPDT for deep-tissue infection. To overcome these limitations, a PS (β-carboxyphthalocyanine zinc, CPZ) delivery system with lanthanide-doped upconversion nanoparticles (UCNPs, LiYF4:Yb/Er) and polyvinylpyrrolidone (PVP) was prepared and its antimicrobial (antibacterial and antifungal) activities were investigated. Such a near-infrared (NIR) triggered UCNPs-CPZ-PVP system significantly reduced the aggregation of CPZ and presented a high anti-infectious activity against multi-drug resistant (MDR) bacteria (methicillin-resistant Staphylococcus aureus by 4.7 log10 and MDR Escherichia coli by 2.1 log10) post aPDT (at 50 μg mL-1 UCNPs-CPZ-PVP with 0.5 W cm-2 980 nm light). In particular, UCNPs-CPZ-PVP showed high antifungal efficacy against Candida albicans. In vivo aPDT experiments were further carried out using an MDR bacterial infection murine model in the presence of 5 mm thick tissue specimens, demonstrating the great potential of UCNPs-CPZ-PVP against infections in deep tissue. Altogether, we reveal an efficient NIR-triggered nano-photosensitizer with promising antifungal and antibacterial efficacy for clinical antimicrobial therapy.

Platinum-doped carbon nanoparticles inhibit cancer cell migration under mild laser irradiation: Multi-organelle-targeted photothermal therapy

Tumor growth and metastasis are two main causes of cancer-related deaths. Here, we simultaneously investigated the effects of nanoparticles on cancer cell viability and migration using polyethylene glycol (PEG)-modified, platinum-doped (<4 mol %) carbon nanoparticles (denoted as PEG-PtCNPs). The bare PtCNPs were prepared by the facile one-step hydrothermal treatment of p-phenylenediamine and K₂PtCl₄ in aqueous solution. After PEGylation, the obtained PEG-PtCNPs can serve as an excellent photothermal nanoagent for cell migration inhibition, laser-triggered nuclear delivery, effective tumor accumulation, and imaging-guided tumor ablation with improved therapeutic efficacy and reduced side effects. In the absence of laser exposure, the positively charged PEG-PtCNPs with a hydrodynamic diameter of ∼19 nm easily entered the cells by endocytosis and were located in multiple organelles (including mitochondrion, endoplasmic reticulum, lysosome, and Golgi apparatus), causing a slight increase in the expression level of nuclear protein lamin A/C. Upon mild laser irradiation (0.3 W cm^-2), the fragmented cytoskeletal structures and overexpression of lamin A/C were observed, thus inhibiting cancer cell migration. Furthermore, hyperthermia induced by PEG-PtCNPs plus laser irradiation at a higher power density (1.0 W cm^-2) could cause irreversible damage to the nuclear membranes and then facilitate the nuclear delivery of the nanoagents without the introduction of nuclear targeting ligands. Taken together, this work develops a facile synthetic approach of platinum-based carbon nanoparticles with excellent photothermal properties, and demonstrates their potential applications for modulating tumor metastasis and realizing multi-organelle-targeted tumor ablation.

Mitochondria-Targeted Artificial "Nano-RBCs" for Amplified Synergistic Cancer Phototherapy by a Single NIR Irradiation

Phototherapy has emerged as a novel therapeutic modality for cancer treatment, but its low therapeutic efficacy severely hinders further extensive clinical translation and application. This study reports amplifying the phototherapeutic efficacy by constructing a near-infrared (NIR)-responsive multifunctional nanoplatform for synergistic cancer phototherapy by a single NIR irradiation, which can concurrently achieve mitochondria-targeting phototherapy, synergistic photothermal therapy (PTT)/photodynamic therapy (PDT), self-sufficient oxygen-augmented PDT, and multiple-imaging guidance/monitoring. Perfluorooctyl bromide based nanoliposomes are constructed for oxygen delivery into tumors, performing the functions of red blood cells (RBCs) for oxygen delivery ("Nano-RBC" nanosystem), which can alleviate the tumor hypoxia and enhance the PDT efficacy. The mitochondria-targeting performance for enhanced and synergistic PDT/PTT is demonstrated as assisted by nanoliposomes. In particular, these "Nano-RBCs" can also act as the contrast agents for concurrent computed tomography, photoacoustic, and fluorescence multiple imaging, providing the potential imaging capability for phototherapeutic guidance and monitoring. This provides a novel strategy to achieve high therapeutic efficacy of phototherapy by the rational design of multifunctional nanoplatforms with the unique performances of mitochondria targeting, synergistic PDT/PTT by a single NIR irradiation (808 nm), self-sufficient oxygen-augmented PDT, and multiple-imaging guidance/monitoring.

Near-infrared light triggered drug release from mesoporous silica nanoparticles

Stimuli triggered drug delivery systems enable controlled release of drugs at the optimal space and time, thus achieving optimal therapeutic effects. As one of the most important stimuli used in bioapplications, near-infrared (NIR) light possesses unique advantages such as deep tissue penetration with minimum auto-fluorescence & tissue scattering and high biosafety. Mesoporous silica nanoparticles (MSNs) are one of the most studied nanocarriers; apart from having a high surface area and large pore volume for loading of drugs, they can be easily functionalized with inorganic nanomaterials and stimuli responsive polymers or organic switch molecules, creating possibilities for designing complex stimuli triggered drug delivery systems. Considering the high tissue penetration depth of NIR light and the unique mesoporous structure of MSNs, NIR responsive inorganic nanoparticle functionalized MSNs can be further combined with stimuli responsive materials to form smart "nano-devices" for controlled drug delivery toward tumors, and to date much progress has been made. In this article, recent advances in the design of NIR triggered mesoporous silica drug delivery systems are systematically summarized and some outstanding studies are highlighted. We will also discuss the shortcomings, challenges and opportunities in the field.

A biodegradable polyphosphoester-functionalized poly(disulfide) nanocarrier for reduction-triggered intracellular drug delivery

Stimuli-responsive and biodegradable polymeric carriers are of great importance for safe delivery and efficient release of chemotherapeutic agents. In this work, given the unique advantages of poly(disulfide)s and biodegradable polyphosphoesters, we designed and constructed a reduction-sensitive amphiphilic triblock copolymer poly(ethyl ethylene phosphate)-b-poly(disulfide)-b-poly(ethyl ethylene phosphate) (PEEP-PDS-PEEP) by combining thiol-disulfide polycondensation and ring-opening polymerization (ROP). The thiol-disulfide polycondensation between 1,6-hexanedithiol and 2,2'-dithiodipyridine yielded the linear telechelic pyridyl disulfide-terminated poly(disulfide)s, followed by the treatment with 2-mercaptoethanol to quantitatively produce dihydroxyl-terminated poly(disulfide)s, which was used to initiate the ROP reaction of 2-ethoxy-2-oxo-1,3,2-dioxaphospholane, generating ABA-type amphiphilic triblock copolymers. The chemical structures of various polymers were thoroughly characterized and verified using nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy. The resultant amphiphilic PEEP-PDS-PEEP could self-assemble into spherical nanoparticles in aqueous solution as evidenced from dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses. Hydrophobic anti-tumor drug doxorubicin (DOX) was used to study the encapsulation capacity of nanoparticles, the drug loading content (DLC) and drug loading efficiency (DLE) values were determined to be 11.2% and 31.5%, respectively. In vitro release studies indicated that DOX was released much faster under reductive conditions compared to physiological conditions, confirming their reduction-responsive release behavior owing to the scission of the poly(disulfide) segment and subsequent disintegration of nanoparticles. The cellular uptake study using a live cell imaging system demonstrated that this DOX-loaded nanoparticle can be internalized into HeLa cells and release DOX over time. Methyl thiazolyl tetrazolium (MTT) assay revealed the favorable cytocompatibility of a bare triblock copolymer toward both L929 and HeLa cells, whereas the DOX-loaded copolymer nanoparticles exhibited the lower inhibitory ability against HeLa and HepG2 cell proliferation than free DOX. This finding presents a strategy for the construction of biocompatible and reduction-responsive polymeric drug carriers.

Defining the conditional basis of silicon phthalocyanine near-IR ligand exchange

Bond cleavage reactions initiated by long-wavelength light are needed to extend the scope of the caged-uncaged paradigm into complex physiological settings. Axially unsymmetrical silicon phthalocyanines (SiPcs) undergo efficient release of phenol ligands in a reaction contingent on three factors - near-IR light (690 nm), hypoxia, and a thiol reductant. These studies detail efforts to define the mechanistic basis for this unique conditionally-dependent bond cleavage reaction. Spectroscopic studies provide evidence for the formation of a key phthalocyanine radical anion intermediate formed from the triplet state in a reductant-dependent manner. Computational chemistry studies indicate that phenol ligand solvolysis proceeds through a heptacoordinate silicon transition state and that this solvolytic process is favored following SiPc radical anion formation. These results provide insight regarding the central role that radical anion intermediates formed through photoinduced electron transfer with biological reductants can play in long-wavelength uncaging reactions.

Bacterial components as naturally inspired nano-carriers for drug/gene delivery and immunization: Set the bugs to work?

Drug delivery is a rapidly growing area of research motivated by the nanotechnology revolution, the ideal of personalized medicine, and the desire to reduce the side effects of toxic anti-cancer drugs. Amongst a bewildering array of different nanostructures and nanocarriers, those examples that are fundamentally bio-inspired and derived from natural sources are particularly preferred. Delivery of vaccines is also an active area of research in this field. Bacterial cells and their components that have been used for drug delivery, include the crystalline cell-surface layer known as "S-layer", bacterial ghosts, bacterial outer membrane vesicles, and bacterial products or derivatives (e.g. spores, polymers, and magnetic nanoparticles). Considering the origin of these components from potentially pathogenic microorganisms, it is not surprising that they have been applied for vaccines and immunization. The present review critically summarizes their applications focusing on their advantages for delivery of drugs, genes, and vaccines.

Proton-Stabilized Photochemically Reversible E/ Z Isomerization of Spiropyrans

Spiropyrans undergo C_spiro-O bond breaking to their ring-open protonated E-merocyanine form upon protonation and irradiation via an intermediate protonated Z-merocyanine isomer. We show that the extent of acid-induced ring opening is controlled by matching both the concentration and strength of the acid used and with strong acids full ring opening to the Z-merocyanine isomer occurs spontaneously allowing its characterization by ¹H NMR spectroscopy as well as UV/vis spectroscopy, and reversible switching between Z/ E-isomerization by irradiation with UV and visible light. Under sufficiently acidic conditions, both E- and Z-isomers are thermally stable. Judicious choice of acid such that its p K_a lies between that of the E- and Z-merocyanine forms enables thermally stable switching between spiropyran and E-merocyanine forms and hence pH gating between thermally irreversible and reversible photochromic switching.

An upconverting nanotheranostic agent activated by hypoxia combined with NIR irradiation for selective hypoxia imaging and tumour therapy

A novel upconverting nanotheranostic agent, UCNP-CA_E-FDU/NO₂, activated by both hypoxia (internal stimuli) and NIR irradiation (external stimuli) was designed and synthesized for simultaneous imaging and chemotherapy of solid tumours. The devised theranostic agent consists of an active drug, floxuridine (FDU), upconverting nanoparticles (UCNP: NaYF₄:Yb³⁺/Tm³⁺, multifunctional carriers for upconverting 980 nm NIR light to 365 nm UV light and tumour-targeted drug delivery), (E)-o-hydroxycinnamic acid (CA_E, a UV-photo trigger and a fluorescence dye precursor), and a 4-nitrobenzyl group (a hypoxic trigger). In addition, FDU was modified by CA_E, and CA_E was modified by the 4-nitrobenzyl group; moreover, CA_E was conjugated to UCNPs by covalent bonds to form a novel UCNP-CA_E-FDU/NO₂ platform. In normal cells, the platform is "locked", whereas in tumour cells, hypoxia combined with NIR illumination (980 nm) "unlocks" the platform, based on a series of reactions including the reduction of UCNP-CA_E-FDU/NO₂ catalyzed by over-expression of nitroreductase (NTR), 1,6-rearrangement-elimination, the photo-isomerization of UCNP-CA_E-FDU caused by absorption of NIR irradiation and emission at 365 nm of UCNP-CA_E-FDU/NO₂, and intramolecular esterification, which initiate the fluorescent dye in conjugation with UCNP (UCNP-CM) formation and FDU release with high spatio-temporal control. The amounts of FDU and UCNP-CM released can be accurately tuned by controlling the NIR illumination time. UCNP-CA_E-FDU/NO₂ showed excellent selectivity for hypoxic cells, exhibited high cytotoxicity against cancer cells and almost no cytotoxicity to normal cells, presented significant inhibition of tumour growth in vivo, and displayed sensitive detection of the hypoxic status and the amount of FDU released. The excellent properties of UCNP-CA_E-FDU/NO₂ endow it with great potential applications for precise imaging of tumour cells and personalized solid tumour treatment.

NIR-Triggered Crystal Phase Transformation of NiTi-Layered Double Hydroxides Films for Localized Chemothermal Tumor Therapy

Construction of localized drug-eluting systems with synergistic chemothermal tumor-killing abilities is promising for biomedical implants directly contacting with tumor tissues. In this study, an intelligent and biocompatible drug-loading platform, based on a gold nanorods-modified butyrate-inserted NiTi-layered double hydroxides film (Au@LDH/B), is prepared on the surface of nitinol alloy. The prepared films function as drug-loading "sponges," which pump butyrate out under near-infrared (NIR) irradiation and resorb drugs in water when the NIR laser is shut off. The stimuli-responsive release of butyrate is verified to be related with the NIR-triggered crystal phase transformation of Au@LDH/B. In vitro and in vivo studies reveal that the prepared films possess excellent biosafety and high efficiency in synergistic thermochemo tumor therapy, showing a promising application in the construction of localized stimuli-responsive drug-delivery systems.

Bioresponsive and near infrared photon co-enhanced cancer theranostic based on upconversion nanocapsules

Developing nanotheranostics responsive to tumor microenvironments has attracted tremendous attention for on-demand cancer diagnosis and treatment. Herein, a facile Mn-doping strategy was adopted to transform mesoporous silica coated upconversion nanoparticles (UCNPs) to yolk-like upconversion nanostructures which possess a tumor-responsive biodegradation nature. The huge internal space of the innovated nanocarriers is suitable for doxorubicin (DOX) storage, besides, the Mn-doped shell is sensitive to the intratumoral acidity and reducibility, which enables shell biodegradation and further accelerates the breakage of Si-O-Si bonds within the silica framework. This tumor-responsive shell degradation is beneficial for realizing tumor-specific DOX release. Subsequently, polyoxometalate (POM) nanoclusters that can enhance photothermal conversion in response to the tumor reducibility and acidity were modified on the surface of the silica shell, thereby achieving NIR-enhanced shell degradation and also preventing premature DOX leakage. The as-produced thermal effect of the POM couples with the chemotherapy effect of the released DOX to perform a synergetic chemo-photothermal therapy. Additionally, the shell degradation brings size shrinkage to the nanocarriers, allowing faster nanoparticle diffusion and deeper tumor penetration, which is significant for improving theranostic outcomes. Also, the drastic decline of the red/green (R/G) ratio caused by the DOX release can be used to monitor the DOX release content through a fluorescence resonance energy transfer (FRET) method. The MRI effect caused by Mn release together with the MRI/CT/UCL imaging derived from Gd3+/Yb3+/Nd3+/Er3+ co-doped UCNPs under 808 nm laser excitation endow the nanosystem with multiple imaging capability, thus realizing imaging-guided cancer therapy.

Semiconducting Polymer Nanoenzymes with Photothermic Activity for Enhanced Cancer Therapy

Regulation of enzyme activity is fundamentally challenging but practically meaningful for biology and medicine. However, noninvasive remote control of enzyme activity in living systems has been rarely demonstrated and exploited for therapy. Herein, we synthesize a semiconducting polymer nanoenzyme with photothermic activity for enhanced cancer therapy. Upon near-infrared (NIR) light irradiation, the activity of the nanoenzyme can be enhanced by 3.5-fold to efficiently digest collagen in the tumor extracellular matrix (ECM), leading to enhanced nanoparticle accumulation in tumors and consequently improved photothermal therapy (PTT). This study thus provides a promising strategy to remotely regulate enzyme activity for cancer therapy.

Photochromism into nanosystems: towards lighting up the future nanoworld

The ability to manipulate the structure and function of promising nanosystems via energy input and external stimuli is emerging as an attractive paradigm for developing reconfigurable and programmable nanomaterials and multifunctional devices. Light stimulus manifestly represents a preferred external physical and chemical tool for in situ remote command of the functional attributes of nanomaterials and nanosystems due to its unique advantages of high spatial and temporal resolution and digital controllability. Photochromic moieties are known to undergo reversible photochemical transformations between different states with distinct properties, which have been extensively introduced into various functional nanosystems such as nanomachines, nanoparticles, nanoelectronics, supramolecular nanoassemblies, and biological nanosystems. The integration of photochromism into these nanosystems has endowed the resultant nanostructures or advanced materials with intriguing photoresponsive behaviors and more sophisticated functions. In this Review, we provide an account of the recent advancements in reversible photocontrol of the structures and functions of photochromic nanosystems and their applications. The important design concepts of such truly advanced materials are discussed, their fabrication methods are emphasized, and their applications are highlighted. The Review is concluded by briefly outlining the challenges that need to be addressed and the opportunities that can be tapped into. We hope that the review of the flourishing and vibrant topic with myriad possibilities would shine light on exploring the future nanoworld by encouraging and opening the windows to meaningful multidisciplinary cooperation of engineers from different backgrounds and scientists from the fields such as chemistry, physics, engineering, biology, nanotechnology and materials science.

Household light source for potent photo-dynamic antimicrobial effect and wound healing in an infective animal model

Photodynamic antimicrobial chemotherapy (PACT) is considered a promising alternative to conventional antibiotic approach. We have previously developed a novel PS containing five lysine amino acids, pentalysine-β-carbonylphthalocyanine Zinc (ZnPc(Lys)₅), which in the presence of light, is highly toxic against a range of bacterial strains, including hospital isolated, drug resistant Acinetobacter baumannii. Here, we study the effect of light fluence of the two light sources on the PACT potency of ZnPc(Lys)₅. We observed that an exposure of E.coli to a red LED light for only 2 seconds (light fluence of 0.15 J/cm²) in the presence of ZnPc(Lys)₅ significantly eradicated 80% of the E.coli. We further demonstrated that a light fluence of 4.5 J/cm² from a household light source induced a noticeable photodynamic effect in vitro and in vivo animal model. This study points to a new research direction of reducing light illumination time by increasing potency of PS.