Spectrally tunable leakage-free gold nanocontainers

Nanogold-based materials in medicine: from their origins to their future

The properties of gold-based materials have been explored for centuries in several research fields, including medicine. Multiple published production methods for gold nanoparticles (AuNPs) have shown that the physicochemical and optical properties of AuNPs depend on the production method used. These different AuNP properties have allowed exploration of their usefulness in countless distinct biomedical applications over the last few years. Here we present an extensive overview of the most commonly used AuNP production methods, the resulting distinct properties of the AuNPs and the potential application of these AuNPs in diagnostic and therapeutic approaches in biomedicine.

Drug -driven self-assembly of pH-sensitive nano-vesicles with high loading capacity and anti-tumor efficacy

The in vivo delivery of nanomedicine is severely hampered by the limited enhanced permeability and retention effect (EPR) in tumors. Aiming at overcoming this limitation and achieving high anti-tumor effect of chemotherapeutics, we specially addressed an available strategy from a viewpoint of increasing the drug loading of nano-carriers. Here, we constructed a novel pH-responsive polymersome based on the drug-driven self-assembly of amphiphilic polyphosphazenes PAP containing the ortho ester group ABD and mPEG2000. Due to the non-covalent attractive forces between PAP and doxorubicin hydrochloride (DOX·HCl), DOX·HCl can induce the self-assembly of PAP via embedding itself in the lamella to form vesicles and the subsequent location in the center aqueous chamber of the resultant nano-vesicles, which resulted in the high drug loading content of 35.77 wt%. In addition, with the incorporation of cholesteryl hemisuccinate (CholHS), the premature leakage of DOX·HCl was significantly inhibited under physiological conditions. Meanwhile, the pH-sensitive drug release occurred at pH 5.5 by the advantage of the pH-sensitive biodegradation of ABD in PAP. Consequently, this CholHS-incorporated DOX·HCl-driven PAP vesicle achieved excellent anti-tumor effect with tumor growth inhibition up to 82.4% in S180 tumor-bearing mice. Taken together, our newly developed drug-driven vesicles may promote the development of efficient drug delivery systems for application in cancer therapy.

Plasmonic carriers responsive to pulsed laser irradiation: a review of mechanisms, design, and applications

This review focuses on interactions which govern release from plasmonic carrier systems including liposomes, polymersomes, and nanodroplets under pulsed irradiation.

Hybrid nanocapsules for in situ TEM imaging of gas evolution reactions in confined liquids

Liquid cell transmission electron microscopy (TEM) enables the direct observation of dynamic physical and chemical processes in liquids at the nanoscale. Quantitative investigations into reactions with fast kinetics and/or multiple reagents will benefit from further advances in liquid cell design that facilitate rapid in situ mixing and precise control over reagent volumes and concentrations. This work reports the development of inorganic-organic nanocapsules for high-resolution TEM imaging of nanoscale reactions in liquids with well-defined zeptoliter volumes. These hybrid nanocapsules, with 48 nm average diameter, consist of a thin layer of gold coating a lipid vesicle. As a model reaction, the nucleation, growth, and diffusion of nanobubbles generated by the radiolysis of water is investigated inside the nanocapsules. When the nanobubbles are sufficiently small (10-25 nm diameter), they are mobile in the nanocapsules, but their movement deviates from Brownian motion, which may result from geometric confinement by the nanocapsules. Gases and fluids can be transported between two nanocapsules when they fuse, demonstrating in situ mixing without using complex microfluidic schemes. The ability to synthesize nanocapsules with controlled sizes and to monitor dynamics simultaneously inside multiple nanocapsules provides opportunities to investigate nanoscale processes such as single nanoparticle synthesis in confined volumes and biological processes such as biomineralization and membrane dynamics.

Growing a Nucleotide/Lanthanide Coordination Polymer Shell on Liposomes

Coating liposomes with a shell is a useful strategy to increase membrane stability and prevent leakage or fusion. Nucleotide/lanthanide coordination nanoparticles (NPs) are formed by a simple mixing at ambient conditions. Because some lipid headgroups contain lanthanide binding ligands, they may direct the growth of such coordination NPs. Herein, a gadolinium/adenosine monophosphate (Gd³⁺/AMP) shell was formed on liposomes (liposome@Gd³⁺/AMP) using lipids containing phosphoserine (PS) or cholinephosphate (CP) headgroups, while phosphocholine liposomes did not support the shell. Liposome binding Gd³⁺ is confirmed by transmission electron microscopy (TEM). The negatively charged CP and PS liposomes reversed to positive upon Gd³⁺ binding, while other metals such as Ca²⁺ and Zn²⁺ did not reverse the charge. Binding of Gd³⁺ did not leak the PS liposomes. Then, AMP was further added to cross-link Gd³⁺ on the liposome surface. A shell was formed as indicated by TEM, and the content inside the liposome remained for the PS liposomes. While adding Triton X-100 still induced leakage of the encapsulated liposomes, the shell protected the liposomes from leakage induced by ZnO NPs, suggesting a porous structure of the Gd³⁺/AMP shell which allowed penetration of Triton X-100 but not the larger ZnO NPs. This work provides a simple method to coat liposomes, and also offers a fundamental understanding of liposome adsorption of lanthanide ions.

Photochemical preparation of gold nanoparticle decorated cyclodextrin vesicles with tailored plasmonic properties

We report a photochemical strategy for the preparation of plasmonic vesicles by the in situ formation of gold nanoparticles at the surface of cyclodextrin host vesicle templates decorated with photoactive guest polymers. Upon irradiation with UV light, these carefully designed polymer shells undergo a Norrish type I reaction to generate reducing radicals for the in situ reduction of gold salts and simultaneously provide a stabilizing matrix allowing for a dense decoration with discrete gold seeds. In a highly controlled growth procedure the gold particle size can be adjusted between 3 and 28 nm resulting in an increasing interparticle plasmonic coupling as revealed by a pronounced redshift of the surface plasmon resonance (SPR) band and an enhanced absorption at wavelengths above 600 nm. This unique combination of cyclodextrin vesicles capable of specifically recognizing guest molecules with a plasmonic particle shell displaying multiple interparticle gaps acting as electromagnetic hotspots shows great potential for surface-enhanced Raman scattering (SERS) applications.

On demand synthesis of hollow fullerene nanostructures

Hollow nanostructures are widely used in chemistry, materials, bioscience, and medicine, but their fabrication remains a great challenge. In particular, there is no effective strategy for their assembly and interconnection. We bring pottery, the oldest and simplest method of fabricating hollow containers, into the nanoscale. By exploiting the liquid nature of the xylene template, fullerene hollow nanostructures of tailored shapes, such as bowls, bottles, and cucurbits, are readily synthesized. The liquid templates permit stepwise and versatile manipulation and hence, modular assembly of nodes and junctions leads to interconnected hollow systems. As a proof-of-concept, we create multi-compartment nano-containers, with different nanoparticles isolated in the separate pockets. This methodology expands the synthetic freedom for hollow nanostructures, building a bridge from isolated hollow units to interconnected hollow systems.

At nanoscale, it is synthetically very difficult to increase the structural complexity of hollow structures. Here, the authors use a stepwise liquid templating strategy to build, assemble, and interconnect fullerene hollow nanostructures, just like the synthetic freedom one could have with pottery.

Nanoparticles and intracellular applications of surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectrocopy (SERS) offers ultrasensitive vibrational fingerprinting at the nanoscale. Its non-destructive nature affords an ideal tool for interrogation of the intracellular environment, detecting the localisation of biomolecules, delivery and monitoring of therapeutics and for characterisation of complex cellular processes at the molecular level. Innovations in nanotechnology have produced a wide selection of novel, purpose-built plasmonic nanostructures capable of high SERS enhancement for intracellular probing while microfluidic technologies are being utilised to reproducibly synthesise nanoparticle (NP) probes at large scale and in high throughput. Sophisticated multivariate analysis techniques unlock the wealth of previously unattainable biomolecular information contained within large and multidimensional SERS datasets. Thus, with suitable combination of experimental techniques and analytics, SERS boasts enormous potential for cell based assays and to expand our understanding of the intracellular environment. In this review we trace the pathway to utilisation of nanomaterials for intracellular SERS. Thus we review and assess nanoparticle synthesis methods, their toxicity and cell interactions before presenting significant developments in intracellular SERS methodologies and how identified challenges can be addressed.

A fabrication method of gold coated colloidosomes and their application as targeted drug carriers

Colloidosomes have attracted considerable attention in recent years because of their potential applications in a range of industries, such as food, bioreactors and medicine. However, traditional polymer shell colloidosomes leak low molecular weight encapsulated materials due to their intrinsic shell permeability. Here, we report aqueous core colloidosomes coated with a gold shell, which make the capsules impermeable. The shells can be ruptured using ultrasound. The gold coated colloidosomes are prepared by making an aqueous core capsule with a polymer shell and then adding HAuCl4, surfactant and l-ascorbic acid to form a second shell. We propose to use the capsules as drug carriers. The gold coated colloidosomes demonstrate a low cytotoxicity and after triggering, both encapsulated doxorubicin and broken gold fragments kill cancer cells. In addition, we set up a targeting model by modifying the gold shell colloidosomes using 4,4'-dithiodibutyric acid and crosslinking them with proteins-rabbit immunoglobulin G (IgG). Label-free surface plasmon resonance was used to test the specific targeting of the functional gold shells with rabbit antigen. The results demonstrate that a new type of functional gold coated colloidosome with non-permeability, ultrasound sensitivity and immunoassay targeting could be applied to many medical applications.

Synthesis of Hybrid-Polypeptides m-PEO-b-poly(His-co-Gly) and m-PEO-b-poly(His-co-Ala) and Study of Their Structure and Aggregation. Influence of Hydrophobic Copolypeptides on the Properties of Poly(L-histidine)

The highly diverse and sophisticated action of proteins results from their equally diverse primary structure, which along with the nature of interactions between the amino acids, defines the higher self-assembly of proteins. The interactions between amino acids can be very complicated, and their understanding is necessary in order to elucidate the protein structure-properties relationship. A series of well-defined hybrid-polypeptidic diblock copolymers of the type m-PEO-b-poly(His-co-Gly) and m-PEO-b-poly(His-co-Ala) was synthesized through the ring opening polymerization of the N-carboxyanhydrides of the corresponding amino acids, with a molar ratio of the hydrophobic peptide to histidine at 10%, 20% and 40%. The excellent purity of the monomers combined with the high vacuum techniques resulted in controlled polymerization with high molecular and compositional homogeneity. FT-IR, as well as circular dichroism, were employed to investigate the secondary structure of the polymers, while DLS, SLS and ζ-potential were utilized to study the aggregates formed in aqueous solutions, as well as their pH responsiveness. The results revealed that the randomly distributed monomeric units of glycine or alanine significantly influence L-histidine’s structure. Depending on the pH, aggregates with a different structure, different molecular characteristics and a different surface charge are formed, potentially leading to very interesting bioapplications.

Novel Liposome-Based Surface-Enhanced Raman Spectroscopy (SERS) Substrate

Although great strides have been made in recent years toward making highly enhancing surface-enhanced Raman spectroscopy (SERS) substrates, the biological compatibility of such substrates remains a crucial problem. To address this issue, liposome-based SERS substrates have been constructed in which the biological probe molecule is encapsulated inside the aqueous liposome compartment, and metallic elements are assembled using the liposome as a scaffold. Therefore, the probe molecule is not in contact with the metallic surfaces. Herein we report our initial characterization of these novel nanoparticle-on-mirror substrates, both experimentally and theoretically, using finite-difference time-domain calculations. The substrates are shown to be structurally stable to laser irradiation, the liposome compartment does not rise above 45 °C, and they exhibit an analytical enhancement factor of 8 × 10⁶ for crystal violet encapsulated in 38 liposomes sandwiched between a 40 nm planar gold mirror and 80 nm gold colloid.

Near-Infrared Responsive Gold-Layersome Nanoshells

Anionic liposomes coated with cationic polyelectrolyte poly-l-lysine (PLL), or layersomes, were used as soft, self-assembled templates for synthesizing gold nanoshells that absorb near-infrared radiation. The gold nanoshells were formed using two techniques: (a) direct reduction of tetrachloroauric acid on the layersomes and (b) the reduction of a tetrachloroauric acid/potassium carbonate "growth" solution on nanosized gold seeds bound to the surface of layersomes. The resulting structures were characterized by transmission and scanning electron microscopy and visible-near-infrared spectroscopy. Direct reduction produced discrete gold nanoparticles on the layersomes. The slower reduction from the growth solution on the gold seeds resulted in more complete shells. The absorption spectra of these suspensions were sensitive to the synthesis method. The morphology of the gold shells was tuned for absorption at biologically safe and tissue-penetrating NIR wavelengths, and laser irradiation at 810 nm produced significant heat. These gold-layersome nanoshells have the potential to be used for photothermal therapy, photothermally mediated drug delivery, and biomedical imaging.

Biomedical Applications of Multifunctional Gold-Based Nanocomposites

Active application of gold nanoparticles for various diagnostic and therapeutic purposes started in recent decades due to the emergence of new data on their unique optical and physicochemical properties. In addition to colloidal gold conjugates, growth in the number of publications devoted to the synthesis and application of multifunctional nanocomposites has occurred in recent years. This review considers the application in biomedicine of multifunctional nanoparticles that can be produced in three different ways. The first method involves design of composite nanostructures with various components intended for either diagnostic or therapeutic functions. The second approach uses new bioconjugation techniques that allow functionalization of gold nanoparticles with various molecules, thus combining diagnostic and therapeutic functions in one medical procedure. Finally, the third method for production of multifunctional nanoparticles combines the first two approaches, in which a composite nanoparticle is additionally functionalized by molecules having different properties.

Leakage-free polypyrrole–Au nanostructures for combined Raman detection and photothermal cancer therapy

A novel PPy–Au nanostructure with the bifunctionality of Raman detection and photothermal therapy of cancer is reported.

Near-Infrared-Triggered Azobenzene-Liposome/Upconversion Nanoparticle Hybrid Vesicles for Remotely Controlled Drug Delivery to Overcome Cancer Multidrug Resistance

Overcoming multidrug resistance is achieved by developing a novel drugdelivery-system paradigm based on azobenzene liposome and phosphatidylcholine-modified upconversion nanoparticle (UCNP) hybrid vesicles for controlled drug release using a nearinfrared (NIR) laser. Upon 980 nm light irradiation, the reversible photoisomerization of the azobenzene derivatives by simultaneous UV and visible light emitted from the UCNPs makes it possible to realize NIR-triggered release of the chemotherapeutic drug doxorubicin.

Multifunctional gold-based nanocomposites for theranostics

Although Au-particle potential in nanobiotechnology has been recognized for the last 15 years, new insights into the unique properties of multifunctional nanostructures have just recently started to emerge. Multifunctional gold-based nanocomposites combine multiple modalities to improve the efficacy of the therapeutic and diagnostic treatment of cancer and other socially significant diseases. This review is focused on multifunctional gold-based theranostic nanocomposites, which can be fabricated by three main routes. The first route is to create composite (or hybrid) nanoparticles, whose components enable diagnostic and therapeutic functions. The second route is based on smart bioconjugation techniques to functionalize gold nanoparticles with a set of different molecules, enabling them to perform targeting, diagnostic, and therapeutic functions in a single treatment procedure. Finally, the third route for multifunctionalized composite nanoparticles is a combination of the first two and involves additional functionalization of hybrid nanoparticles with several molecules possessing different theranostic modalities. This last class of multifunctionalized composites also includes fluorescent atomic clusters with multiple functionalities.

Recent Advances of Using Hybrid Nanocarriers in Remotely Controlled Therapeutic Delivery

The development of hybrid biomaterials has been attracting great attention in the design of materials for biomedicine. The nanosized level of inorganic and organic or even bioactive components can be combined into a single material by this approach, which has created entirely new advanced compositions with truly unique properties for drug delivery. The recent advances in using hybrid nanovehicles as remotely controlled therapeutic delivery carriers are summarized with respect to different nanostructures, including hybrid host-guest nanoconjugates, micelles, nanogels, core-shell nanoparticles, liposomes, mesoporous silica, and hollow nanoconstructions. In addition, the controlled release of guest molecules from these hybrid nanovehicles in response to various remote stimuli such as alternating magnetic field, near infrared, or ultrasound triggers is further summarized to introduce the different mechanisms of remotely triggered release behavior. Through proper chemical functionalization, the hybrid nanovehicle system can be further endowed with many new properties toward specific biomedical applications.

Nanocarriers for delivery of siRNA and co-delivery of siRNA and other therapeutic agents

A major problem in cancer treatment is the multidrug resistance. siRNA inhibitors have great advantages to solve the problem, if the bottleneck of their delivery could be well addressed by the various nanocarriers. Moreover, co-delivery of siRNA together with the various anticancer agents in one nanocarrier may maximize their additive or synergistic effect. This review provides a comprehensive summary on the state-of-the-art of the nanocarriers, which may include prodrugs, micelles, liposomes, dendrimers, nanohydrogels, solid lipid nanoparticles, nanoparticles of biodegradable polymers and nucleic acid nanocarriers for delivery of siRNA and co-delivery of siRNA together with anticancer agents with focus on synthesis of the nanocarrier materials, design and characterization, in vitro and in vivo evaluation, and prospect and challenges of nanocarriers.

Delivery and cytotoxicity of doxorubicin and temozolomide to primary glioblastoma cells using gold nanospheres and gold nanorods

Nanoparticles with coating entrapping a chemotherapeutic drug for delivery have not been tested for their cytotoxic effects in in-vitro glioblastoma cell cultures to increase treatment efficacy. Therefore, we synthesized silica-coated gold nanorods and gold nanospheres that were loaded with doxorubicin or temozolomide. The morphology of the nanoparticles was characterized using transmission electron microscopy (TEM), the molecular structure was characterized using infrared spectroscopy and in vitro efficacy was determined using glioblastoma cell cultures. TEM analysis showed that gold nanorods had a length of 49–65 nm and a diameter of 8.5–14 nm whereas gold nanospheres had a diameter of 9.5–37 nm. Infrared spectroscopy of doxorubicin and temozolomide and the silica coating revealed molecular fingerprints such as bending, stretching and vibrations of chemical bonds that confirmed the presence of silica coating and drug loading of the gold nanoparticles. In the biological assessment of the effects of drug-loaded gold nanoparticles on primary glioblastoma cell cultures, cytotoxicity, viability and the ratio of cyototoxicity and viability were used as parameters to analyze the effects on the cells of drug delivery via gold nanoparticles on the cells. Our data suggest that doxorubicin in the concentration range of 0.12–3.16 μM when delivered using both gold nanorods and nanospheres induced a 3.8–5.5-fold increased cytotoxicity in comparison to direct delivery. Temozolomide in the concentration range of 4.6–115 μM when delivered by either type of gold nanoparticles induced a 2–4-fold increased cytotoxicity in comparison to direct delivery. Nanospheres were more effective in delivery and cytotoxicity of doxorubicin and temozolomide to glioblastoma cells than gold nanorods. Our data suggest that gold nanoparticles and in particular gold nanospheres are more effective in delivery of doxorubicin and temozolomide to primary glioblastoma cells in culture than direct delivery.

In vitro controlled release of cisplatin from gold-carbon nanobottles via cleavable linkages

Carbon nanotubes' (CNTs) hollow interior space has been explored for biomedical applications, such as drug repository against undesirable inactivation. To further devise CNTs as smart material for controlled release of cargo molecules, we propose the concept of "gold-carbon nanobottles". After encapsulating cis-diammineplatinum(II) dichloride (cisplatin, CDDP) in CNTs, we covalently attached gold nanoparticles (AuNPs) at the open-tips of CNTs via different cleavable linkages, namely hydrazine, ester, and disulfide-containing linkages. Compared with our previous study in which more than 80% of CDDP leaked from CNTs in 2 hours, AuNPs were found to significantly decrease such spontaneous release to <40%. In addition, CDDP release from AuNP-capped CNTs via disulfide linkage was selectively enhanced by twofolds in reducing conditions (namely with 1 mM dithiothreitol [DTT]), which mimic the intracellular environment. We treated human colon adenocarcinoma cells HCT116 with our CDDP-loaded gold-carbon nanobottles and examined the cell viability using lactate dehydrogenase assay. Interestingly, we found that our nanobottles with cleavable disulfide linkage exerted stronger cytotoxic effect in HCT116 compared with normal human fetal lung fibroblast cells IMR-90. Therefore, we infer that our nanobottles strategy with inbuilt disulfide linkage could attain selective release of payload in highly reductive tumor tissues while avoiding collateral damage to normal tissues.

Self-healable and reversible liposome leakage by citrate-capped gold nanoparticles: probing the initial adsorption/desorption induced lipid phase transition

We herein report that the adsorption/desorption of citrate-capped gold nanoparticles (AuNPs) transiently causes leakage in fluid phase DOPC liposomes, while the liposomes do not leak with AuNPs capped with mercaptopropionic acid (MPA). Leakage also fails to occur for gel phase DPPC liposomes. Citrate-capped (but not MPA-capped) AuNPs raise the phase transition temperature of DPPC. We conclude that citrate-capped AuNPs interact with the PC liposomes very strongly, inducing a local fluid-to-gel lipid phase transition for DOPC. Leakage takes place during this transition, and the membrane integrity is resumed after the transition. Citrate-capped AuNPs allow stronger van der Waals forces than MPA-capped AuNPs with PC liposomes, since the latter are separated from the liposome surface by the ∼0.3 nm MPA layer.

The impact of surface chemistry on the performance of localized solar-driven evaporation system

This report investigates the influence of surface chemistry (or wettability) on the evaporation performance of free-standing double-layered thin film on the surface of water. Such newly developed evaporation system is composed of top plasmonic light-to-heat conversion layer and bottom porous supporting layer. Under solar light illumination, the induced plasmonic heat will be localized within the film. By modulating the wettability of such evaporation system through the control of surface chemistry, the evaporation rates are differentiated between hydrophilized and hydrophobized anodic aluminum oxide membrane-based double layered thin films. Additionally, this work demonstrated that the evaporation rate mainly depends on the wettability of bottom supporting layer rather than that of top light-to-heat conversion layer. The findings in this study not only elucidate the role of surface chemistry of each layer of such double-layered evaporation system, but also provide additional design guidelines for such localized evaporation system in applications including desalination, distillation and power generation.

Supramolecular free radicals: near-infrared organic materials with enhanced photothermal conversion

A novel kind of supramolecular free radical with significantly improved free radical yield and enhanced near-infrared (NIR) photothermal conversion has been fabricated. Perylene diimide (PDI) can undergo chemical reduction to generate PDI radical anions. Cucurbit[7]uril (CB[7]), a bulky hydrophilic head, was utilized to encapsulate the two end groups of the PDI derivative via host-guest interactions, thus hindering its aggregation and suppressing the dimerization and quenching of PDI radical anions in aqueous solution. Due to the increased concentration of radical anions and their absorption above 800 nm, the efficiency of NIR photothermal conversion was significantly improved. Compared with free radicals fabricated by covalent chemistry, the supramolecular free radicals established here could provide a facile approach for the promoted formation of aromatic free radicals, thus opening up a new strategy for the design of NIR photothermal materials with enhanced photothermal conversion.

Unexpected high photothemal conversion efficiency of gold nanospheres upon grafting with two-photon luminescent ruthenium(II) complexes: A way towards cancer therapy?

The design and development of functional hybrid nanomaterials is currently a topic of great interest in biomedicine. Herein we investigated the grafting of Ru(II) polypyridyl complexes onto gold nanospheres (Ru@AuNPs) to improve the particles' near infrared (NIR) absorption, and ultimately allow for application in photothermal cancer therapy. As demonstrated in this article, these ruthenium(II) complexes could indeed significantly enhance gold nanospheres' two-photon luminescence (PTL) intensity and photothermal therapy (PTT) efficiency. The best dual functional nanoparticles of this study were successfully used for real-time luminescent imaging-guided PTT in live cancer cells. Furthermore, in vivo tumor ablation was achieved with excellent treatment efficacy under a diode laser (808 nm) irradiation at the power density of 0.8 W/cm(2) for 5 min. This study demonstrates that the coupling of inert Ru(II) polypyridyl complexes to gold nanospheres allows for the enhancement of two-photon luminescence and for efficient photothermal effect.

Biomedical applications of gold nanomaterials: opportunities and challenges

In the past few years, there has been an unprecedented development of gold nanomaterials (AuNMs) for potential clinical applications. Owing to their advantageous physical, chemical, and biological properties, AuNMs have attracted great attention in the nanomedicine arena for applications in biological sensing, biomedical imaging, drug delivery, and photothermal therapy. Their tunable size, shape, and surface characteristics coupled with excellent biocompatibility render them ideal candidates for translation from bench-top to bedside. This review summarizes the recent research on the applications of AuNM with a focus on biomedical diagnostics and therapeutics. The bio-interaction of these NM with cells and their in vivo responses are presented. After reviewing these potential applications, future challenges and prospects are discussed and the suitability of how AuNMs are used as effective tools in clinical medicine is assessed.

Light induced cytosolic drug delivery from liposomes with gold nanoparticles

Externally triggered drug release at defined targets allows site- and time-controlled drug treatment regimens. We have developed liposomal drug carriers with encapsulated gold nanoparticles for triggered drug release. Light energy is converted to heat in the gold nanoparticles and released to the lipid bilayers. Localized temperature increase renders liposomal bilayers to be leaky and triggers drug release. The aim of this study was to develop a drug releasing system capable of releasing its cargo to cell cytosol upon triggering with visible and near infrared light signals. The liposomes were formulated using either heat-sensitive or heat- and pH-sensitive lipid compositions with star or rod shaped gold nanoparticles. Encapsulated fluorescent probe, calcein, was released from the liposomes after exposure to the light. In addition, the pH-sensitive formulations showed a faster drug release in acidic conditions than in neutral conditions. The liposomes were internalized into human retinal pigment epithelial cells (ARPE-19) and human umbilical vein endothelial cells (HUVECs) and did not show any cellular toxicity. The light induced cytosolic delivery of calcein from the gold nanoparticle containing liposomes was shown, whereas no cytosolic release was seen without light induction or without gold nanoparticles in the liposomes. The light activated liposome formulations showed a controlled content release to the cellular cytosol at a specific location and time. Triggering with visual and near infrared light allows good tissue penetration and safety, and the pH-sensitive liposomes may enable selective drug release in the intracellular acidic compartments (endosomes, lysosomes). Thus, light activated liposomes with gold nanoparticles are an attractive option for time- and site-specific drug delivery into the target cells.

Plasmonic giant quantum dots: hybrid nanostructures for truly simultaneous optical imaging, photothermal effect and thermometry

A new compact and multifunctional hybrid semiconductor–metal nanostructure is elucidated and demonstrated for real-time optical imaging, photothermal heating, and in situ thermometry.

Hybrid semiconductor–metal nanoscale constructs are of both fundamental and practical interest. Semiconductor nanocrystals are active emitters of photons when stimulated optically, while the interaction of light with nanosized metal objects results in scattering and ohmic damping due to absorption. In a combined structure, the properties of both components can be realized together. At the same time, metal–semiconductor coupling may intervene to modify absorption and/or emission processes taking place in the semiconductor, resulting in a range of effects from photoluminescence quenching to enhancement. We show here that photostable ‘giant’ quantum dots when placed at the center of an ultrathin gold shell retain their key optical property of bright and blinking-free photoluminescence, while the metal shell imparts efficient photothermal transduction. The latter is despite the highly compact total particle size (40–60 nm “inorganic” diameter and <100 nm hydrodynamic diameter) and the very thin nature of the optically transparent Au shell. Importantly, the sensitivity of the quantum dot emission to local temperature provides a novel internal thermometer for recording temperature during infrared irradiation-induced photothermal heating.

Synthesis and characterization of cell-microenvironment-sensitive leakage-free gold-shell nanoparticles with the template of interlayer-crosslinked micelles

Novel pH-GSNPs exhibit drug leakage-free behavior in a physiological environment, while achieving rapid drug release and remarkable nanogold interlayer aggregation in the intracellular microenvironment.

Fine-tuning the LSPR response of gold nanorod–polyaniline core–shell nanoparticles with high photothermal efficiency for cancer cell ablation

Fine-tuning the LSPR response of Au nanorod–polyaniline core–shell nanoparticles can achieve high photothermal efficiency and stability for cancer cell ablation.

Design of hybrid nanovehicles for remotely triggered drug release: an overview

This review addresses the advantages of remote triggers, e.g. ultrasounds, near infrared light and alternating magnetic fields, the fabrication of the hybrid nanovehicles, the release mechanisms and the next challenges.

Plasmonic caged gold nanorods for near-infrared light controlled drug delivery

A new near-infrared light-controlled drug delivery system based on caged gold nanorods (CGNRs) is demonstrated. The loading and release process of drug payloads into/from CGNR nanocarriers were systematically investigated. The drug-loaded CGNR constructs could enable combined chemotherapy and photo-thermal effects in killing tumor cells upon light irradiation, therefore, enhance the killing efficiency. In conjunction with visibility under quenching-free dark-field imaging, CGNRs may serve as multifunctional theranostic reagents towards cancer diagnostics and therapeutics.

Free-standing alumina nanobottles and nanotubes pre-integrated into nanoporous alumina membranes

A novel interfacial structure consisting of long (up to 5 μm), thin (about 300 nm), highly-ordered, free-standing, highly-reproducible aluminum oxide nanobottles and long tubular nanocapsules attached to a rigid, thin (less than 1 μm) nanoporous anodic alumina membrane is fabricated by simple, fast, catalyst-free, environmentally friendly voltage-pulse anodization. A growth mechanism is proposed based on the formation of straight channels in alumina membrane by anodization, followed by neck formation due to a sophisticated voltage control during the process. This process can be used for the fabrication of alumina nanocontainers with highly controllable geometrical size and volume, vitally important for various applications such as material and energy storage, targeted drug and diagnostic agent delivery, controlled drug and active agent release, gene and biomolecule reservoirs, micro-biologically protected platforms, nano-bioreactors, tissue engineering and hydrogen storage.

Light-activatable gold nanoshells for drug delivery applications

Gold nanoshells (AuNSs) are currently being investigated as nanocarriers for drug delivery systems and have both diagnostic and therapeutic applications, including photothermal ablation, hyperthermia, drug delivery, and diagnostic imaging, particularly in oncology. AuNSs are valuable for their localized surface plasmon resonance, biocompatibility, low immunogenicity, and facile functionalization. AuNSs used for drug delivery can be spatially and temporally triggered to release controlled quantities of drugs inside the target cells when illuminated with a near-infrared (NIR) laser. Recently, many research groups have demonstrated that these AuNS complexes are able to deliver antitumor drugs (e.g., doxorubicin, paclitaxel, small interfering RNA, and single-stranded DNA) into cancer cells, which enhances the efficacy of treatment. AuNSs can also be functionalized with active targeting ligands such as antibodies, aptamers, and peptides to increase the particles' specific binding to the desired targets. This article reviews the current research on NIR light-activatable AuNSs used as nanocarriers for drug delivery systems and cancer theranostics.

Nanocontainers made of various materials with tunable shape and size

Nanocontainers have great potentials in targeted drug delivery and nanospace-confined reactions. However, the previous synthetic approaches exhibited limited control over the morphology, size and materials of the nanocontainers, which are crucial in practical applications. Here, we present a synthetic approach to multi-segment linear-shaped nanopores with pre-designed morphologies inside anodic aluminium oxide (AAO), by tailoring the anodizing duration after a rational increase of the applied anodizing voltage and the number of voltage increase during Al foil anodization. Then, we achieve nanocontainers with designed morphologies, such as nanofunnels, nanobottles, nano-separating-funnels and nanodroppers, with tunable sizes and diverse materials of carbon, silicon, germanium, hafnium oxide, silica and nickel/carbon magnetic composite, by depositing a thin layer of materials on the inner walls of the pre-designed AAO nanopores. The strategy has far-reaching implications in the designing and large-scale fabrication of nanocontainers, opening up new opportunities in nanotechnology applications.