Spectrally tunable leakage-free gold nanocontainers

Multifunctional compact hybrid Au nanoshells: a new generation of nanoplasmonic probes for biosensing, imaging, and controlled release

Gold nanoshells (AuNSs) with tunable localized surface plasmon resonance (LSPR) peaks in the near-infrared (NIR) region possess unique optical properties-particularly that soft tissues are "transparent" at these wavelengths-making them of great interest in cancer diagnosis and treatment. Since 1998 when Halas and co-workers invented the first generation of AuNS, with a silica core and Au shell, researchers have studied and designed AuNSs for theranostic-individualized, combination diagnosis and therapy-nanomedicine. As demand has increased for more powerful and practical theranostic applications, so has demand for the next generation of AuNSs-compact yet complex multifunctional AuNSs with finely integrated plasmonic and nonplasmonic inorganic components. For in vivo biomedical applications, such a hybrid AuNS offers the desirable optical properties of NIR LSPR. Size, however, has proved a more challenging parameter to control in hybrid AuNSs. The ideal size of therapeutic NPs is 10-100 nm. Larger particles have limited diffusion in the extracellular space, while particles less than 5 nm are rapidly cleared from the circulation through extravasation or renal clearance. Conventional methods of preparing AuNS have failed to obtain small-sized hybrid AuNSs with NIR LSPR responses. In this Account, we present a new class of multifunctional hybrid AuNSs with ultrathin AuNSs and varied, functional (nonplasmonic) core components ranging from "hard" semiconductor quantum dots (QDs), to superparamagnetic NPs, to "soft" liposomes made using poly-l-histidine as a template to direct Au deposition. The resultant hybrid AuNSs are uniform and compact (typically 15-60 nm) but also preserve the optical properties and shell-type NIR response necessary for biomedical use. We also demonstrate these particles' innovative plasmonic applications in biosensing, multimodal imaging and controlled release. More importantly, the magnetic-plasmonic Fe3O4/Au core-shell NP enables a new biological imaging method-magnetomotive photoacoustic (mmPA) imaging, which suppresses the nonmagnetomotive background and therefore offers remarkable contrast enhancement and improved specificity compared with photoacoustic images using conventional NP contrast agents. The advantages of our AuNSs are obvious: they are monodisperse, small (<100 nm), highly integrated, and have tunable visible-NIR plasmonic responses. All of these properties are crucial for in vitro or in vivo biological/biomedical studies and many applications, especially for studies of single cells or molecules which require particle monodispersity and tight size control. The plasmonic fluorescent QD/Au and the magnetic plasmonic Fe3O4/Au core-shell NPs may also reveal new physical phenomena that may lead to useful applications, owing to their well-defined core-shell nanoarchitectures and underlying nanoscale physical interactions.

Synthesis of various supramolecular hybrid nanostructures based on pillar[6]arene modified gold nanoparticles/nanorods and their application in pH- and NIR-triggered controlled release

Organic/inorganic supramolecular hybrid micelles, onion-like disks and vesicles were obtained by the self-assembly of water-soluble pillar[6]arene stabilized gold nanoparticles/nanorods with different amounts of a hydrophobic chain functionalized paraquat derivative in water.

Construction of thermal- and light-responsive liposomes noncovalently decorated with gold nanoparticles

GNP–DPPC, a gold nanoparticle-decorated DPPC liposome complex, can release encapsulated dyes upon heating or illumination. GNP–DPPC also has a faster thermal response and higher critical leakage temperature than liposomes.

Controlled polymerization of histidine and synthesis of well-defined stimuli responsive polymers. Elucidation of the structure–aggregation relationship of this highly multifunctional material

Synthesis of multifunctional poly(l-histidine) containing polypeptides and hybrid polymers for controlled drug delivery applications.

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.

Nanoparticles for Improving Cancer Diagnosis

Despite the progress in developing new therapeutic modalities, cancer remains one of the leading diseases causing human mortality. This is mainly attributed to the inability to diagnose tumors in their early stage. By the time the tumor is confirmed, the cancer may have already metastasized, thereby making therapies challenging or even impossible. It is therefore crucial to develop new or to improve existing diagnostic tools to enable diagnosis of cancer in its early or even pre-syndrome stage. The emergence of nanotechnology has provided such a possibility. Unique physical and physiochemical properties allow nanoparticles to be utilized as tags with excellent sensitivity. When coupled with the appropriate targeting molecules, nanoparticle-based probes can interact with a biological system and sense biological changes on the molecular level with unprecedented accuracy. In the past several years, much progress has been made in applying nanotechnology to clinical imaging and diagnostics, and interdisciplinary efforts have made an impact on clinical cancer management. This article aims to review the progress in this exciting area with emphases on the preparation and engineering techniques that have been developed to assemble "smart" nanoprobes.

A facile and general preparation of high-performance noble-metal-based free-standing nanomembranes by a reagentless interfacial self-assembly strategy

As a simple and flexible 2D platform, the water-air interface is envisioned as an environmentally-friendly approach to prepare ultrathin free-standing nanomembranes (FNMs) of monolayered nanoparticles of interest via interfacial self-assembly. However, attempts so far have been rather rare due to the lack of efficient methods. In this article, we report on a facile and general strategy for fabrication of a family of noble metal-based FNMs by a simple and reagentless interfacial self-assembly tactics to prepare functional (plasmonic or catalytic) FNMs, such as Au, Ag, Pd, Pt-FNMs and their bimetallic hybrids, Ag/Au-FNMs and Pd/Pt-FNMs. The organic solvent-free process, varying somewhat from metal to metal only in precursors, reducing agents and dosage of reagents used, is found to be a general phenomenon and ligand-independent (irrespective of the monolayer quality of the resulting FNMs), allowing the growth of high-quality noble metal-based FNMs with well-defined nanoparticulate and monolayer morphology as large as several square centimeters. Heat treatment (boiling) is performed to accelerate the formation of FNMs within 15 min. More significantly, the as-prepared plasmonic Au-FNMs acting as a SERS substrate show a superior activity; whereas the resulting catalytic Pd-FNMs, except for their excellent ethanol electrooxidation performance, exhibit higher electrocatalytic activity for formic acid oxidation than commercial catalysts.

Shape transformation and visible region plasmonic modulation of silver nanoplates by graphene oxide

The plasmon band of Ag nanoplates can be continuously tuned over the visible region by simply stirring with graphene oxide (GO) nanosheets, accompanied with the shape transformation from triangle to round. The ability of GO to competitively adsorb ligands (from Ag nanoplates) has been considered to response for this interesting change. Through the protection of sufficient citrate ions, the resultant Ag nanoplates exhibit the excellent stability over a long time without noticeable change of their optical properties.

Light-activated content release from liposomes

Successful integration of diagnostic and therapeutic actions at the level of individual cells requires new materials that combine biological compatibility with functional versatility. This review focuses on the development of liposome-based functional materials, where payload release is activated by light. Methods of sensitizing liposomes to light have progressed from the use of organic molecular moieties to the use of metallic plasmon resonant structures. This development has facilitated application of near infrared light for activation, which is preferred for its deep penetration and low phototoxicity in biological tissues. Presented mechanisms of light-activated liposomal content release enable precise in vitro manipulation of minute amounts of reagents, but their use in clinical diagnostic and therapeutic applications will require demonstration of safety and efficacy.

Engineering plasmonic gold nanostructures and metamaterials for biosensing and nanomedicine

The fields of biosensing and nanomedicine have recently witnessed an explosion of interest and progress in the design and study of plasmonic Au nanostructures (p-AuNSs) or metamaterials geared towards a broad range of biological and biomedical applications. Due to their tunable and versatile plasmonic properties, such artificially engineered p-AuNSs and materials have the potential to push biosensor sensitivity towards the single-molecule detection limit, enabling new bioimaging modalities and new analytical techniques and tools capable of single-molecule detection, analysis and manipulation, and to revolutionize the diagnosis and treatment of many diseases, including cancers. This report summarizes and highlights recent major advances in the emerging field of bioapplication-oriented engineering of p-AuNSs and hybrids, focusing on design considerations and ways to carry them out. A brief overview of the optical properties of p-AuNSs is introduced, and then the importance of plasmonic engineering and future promising research directions and challenges in the field are discussed.

Self-assembled plasmonic vesicles of SERS-encoded amphiphilic gold nanoparticles for cancer cell targeting and traceable intracellular drug delivery

We report the development of bioconjugated plasmonic vesicles assembled from SERS-encoded amphiphilic gold nanoparticles for cancer-targeted drug delivery. This new type of plasmonic assemblies with a hollow cavity can play multifunctional roles as delivery carriers for anticancer drugs and SERS-active plasmonic imaging probes to specifically label targeted cancer cells and monitor intracellular drug delivery. We have shown that the pH-responsive disassembly of the plasmonic vesicle, stimulated by the hydrophobic-to-hydrophilic transition of the hydrophobic brushes in acidic intracellular compartments, allows for triggered intracellular drug release. Because self-assembled plasmonic vesicles exhibit significantly different plasmonic properties and greatly enhanced SERS intensity in comparison with single gold nanoparticles due to strong interparticle plasmonic coupling, disassembly of the vesicles in endocytic compartments leads to dramatic changes in scattering properties and SERS signals, which can serve as independent feedback mechanisms to signal cargo release from the vesicles. The unique structural and optical properties of the plasmonic vesicle have made it a promising platform for targeted combination therapy and theranostic applications by taking advantage of recent advances in gold nanostructure based in vivo bioimaging and photothermal therapy and their loading capacity for both hydrophilic (nucleic acids and proteins) and hydrophobic (small molecules) therapeutic agents.

Interaction of liposome-encapsulated cisplatin with biomolecules

We prepared liposomes by hydrating 1,2-dioleoyl-sn-glycero-3-phosphocholine lipid with aqueous solutions of three "probe" molecules-cis-diamminedichloroplatinum(II) (cis-[Pt(II)(NH(3))(2)Cl(2)], cisplatin), guanosine 5'-monophosphate (5'-GMP), and 9-ethylguanine (9-EtG)-in phosphate-buffered saline as well as N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid buffer. The positively charged hydrolysis product of cisplatin, [Pt(II)(NH(3))(2)Cl(H(2)O)](+), is in the inner core of the liposomes and negatively charged 5'-GMP embeds in the lipid bilayer of liposomes. In the presence of cisplatin, the size of the liposomes remains unchanged, and for 5'-GMP-embedded liposomes the size increases significantly compared with that of empty or control liposomes. In contrast, the neutral biomolecule 9-EtG was found to be dispersed in the exterior bulk water and the size of the liposomes remained the same as that of empty or control liposomes. When cisplatin-containing liposomes mix with 5'-GMP-embedded liposomes or liposomes with 9-EtG, the N7 nitrogen atom of 5'-GMP or 9-EtG binds the cisplatin, thus replacing the "leaving groups" and forming a bisadduct. After 48 h of mixing, the size of the liposomes changes for the mixture of 5'-GMP-embedded liposomes and cisplatin-containing liposomes. We used (1)H and (31)P NMR spectroscopic techniques to monitor incorporation or association of cisplatin and biomolecules with liposomes and their subsequent reactions with each other. The dynamic light scattering technique provided the size distribution of the liposomes in the presence and absence of probe molecules.

The golden age: gold nanoparticles for biomedicine

Gold nanoparticles have been used in biomedical applications since their first colloidal syntheses more than three centuries ago. However, over the past two decades, their beautiful colors and unique electronic properties have also attracted tremendous attention due to their historical applications in art and ancient medicine and current applications in enhanced optoelectronics and photovoltaics. In spite of their modest alchemical beginnings, gold nanoparticles exhibit physical properties that are truly different from both small molecules and bulk materials, as well as from other nanoscale particles. Their unique combination of properties is just beginning to be fully realized in range of medical diagnostic and therapeutic applications. This critical review will provide insights into the design, synthesis, functionalization, and applications of these artificial molecules in biomedicine and discuss their tailored interactions with biological systems to achieve improved patient health. Further, we provide a survey of the rapidly expanding body of literature on this topic and argue that gold nanotechnology-enabled biomedicine is not simply an act of 'gilding the (nanomedicinal) lily', but that a new 'Golden Age' of biomedical nanotechnology is truly upon us. Moving forward, the most challenging nanoscience ahead of us will be to find new chemical and physical methods of functionalizing gold nanoparticles with compounds that can promote efficient binding, clearance, and biocompatibility and to assess their safety to other biological systems and their long-term term effects on human health and reproduction (472 references).

Ultrafast Photothermal Release of DNA from Gold Nanoparticles

We report results on ultrafast photothermal release of DNA from gold nanoparticles. We show that dehybridization of oligonucleotide duplex anchored on a gold nanoparticle surface occurs during a single laser pulse, leading to the release of single-strand DNA in solution. Breaking of the Au-S bond anchoring the duplex and the release of thiolated DNA are also evidenced. Our findings show that the size distribution of the nanoparticles plays a major role in the control of both phenomena. We establish a criterion regarding the size distribution of nanoparticles that allows full release of DNA without breaking of the anchoring thiol bonds.

Enzymatic plasmonic engineering of Ag/Au bimetallic nanoshells and their use for sensitive optical glucose sensing

Enzyme works for plasmonic nanostructure: an interesting enzyme-responsive hybrid Ag/Au-GOx bimetallic nanoshell (NS) system is reported, in which control over the enzyme reaction of glucose oxidase (GOx) can automatically fine-tune the morphology (from complete NS to porous NS) and optical properties of the hybrid nanostructure. The phenomenon is further exploited as a new platform for sensitive optical glucose sensing.

Mesoporous silica-coated gold nanorods as a light-mediated multifunctional theranostic platform for cancer treatment

Mesoporous silica-coated gold nanorods (Au@SiO(2)) are developed as a promising and versatile theranostic platform for cancer treatment. Intracellular localization of Au@SiO(2) is visualized through two-photon imaging. With doxorubicin hydrochloride loaded, Au@SiO(2)-DOX show two light-mediated therapeutic modes: low power density laser-triggered drug release for chemotherapy, and high power density laser-induced hyperthermia, which suggest the potential for in-vivo applications.

Novel Methods of Enhanced Retention in and Rapid, Targeted Release from Liposomes

Liposomes are single bilayer capsules with distinct interior compartments in which hydrophilic drugs, imaging agents, diagnostics, etc. can be sequestered from the exterior environment. The polar parts of the individual lipids face the water compartments, while the hydrophobic parts of the lipid provide a barrier in which hydrophilic or charged molecules are poorly soluble. Hydrophobic molecules can be dissolved within the bilayer. The bilayers are typically from 3 - 6 nm thick and the liposome can range from about 50 nm - 50 microns in diameter. The question asked in this review is if any one bilayer, regardless of its composition, can provide the extended drug retention, long lifetime in the circulation, active targeting to specific tissues and rapid and controllable drug release at the site of interest. As an alternative, we review methods of self-assembling multicompartment lipid structures that provide enhanced drug retention in physiological environments. We also review methods of externally targeting and triggering drug release via the near infrared heating of gold nanoshells attached to or encapsulated within bilayer vesicles.

Wavelength-Selective Light-Induced Release from Plasmon Resonant Liposomes

Biodegradable, spectrally tunable plasmon resonant nanocapsules are created via the deposition of gold onto the surface of 100 nm diameter thermosensitive liposomes. These nanocapsules demonstrate selective release of encapsulated contents upon illumination with light of a wavelength matching their distinct resonance bands, which correspond to 760 and 1210 nm in this study. Spectrally selective release is accomplished through the use of multiple, low intensity laser pulses delivered over a period of less than four minutes, ensuring that illumination affects only the gold-coated liposomes and avoids heating the surrounding media. The result of this illumination scheme for selective release using multiple wavelengths of light is a biologically safe mechanism for realizing drug delivery, microfluidic, and sensor applications.

Expeditious synthesis and assembly of sub-100 nm hollow spherical gold nanoparticle superstructures

Sub-100 nm hollow gold nanoparticle superstructures were prepared in a direct one-pot reaction. A gold-binding peptide conjugate, C(6)-AA-PEP(Au) (PEP(Au) = AYSSGAPPMPPF), was constructed and used to direct the simultaneous synthesis and assembly of gold nanoparticles. Transmission electron microscopy and electron tomography revealed that the superstructures are uniform and consist of monodisperse gold nanoparticles arranged into a spherical monolayer shell.

Remotely triggerable drug delivery systems

Triggerable drug delivery systems enable on-demand controlled release profiles that may enhance therapeutic effectiveness and reduce systemic toxicity. Recently, a number of new materials have been developed that exhibit sensitivity to visible light, near-infrared (NIR) light, ultrasound, or magnetic fields. This responsiveness can be triggered remotely to provide flexible control of dose magnitude and timing. Here we review triggerable materials that range in scale from nano to macro, and are activated by a range of stimuli.

SERS-active gold lace nanoshells with built-in hotspots

Development of multifunctional drug delivery vehicles with therapeutic and imaging capabilities as well as in situ methods of monitoring of intracellular processes will greatly benefit from a simple method of preparation of plasmonic Au structures with nanometer scale gaps between sharp metallic elements where the so-called SERS hot spots can be formed. Here the synthesis of gold lace capsules with average diameters ca. 100 nm made of a network of metallic branches 3-5 nm wide and separated by 1-3 nm gaps is reported. Biocompatible amphiphilic polyurethanes (PUs) were used as template for these particles. The unusual topology of the produced gold lace shells somewhat reminiscent of Fabergé eggs is likely to reflect the network of hydrophobic and hydrophilic domains of PU globules. The gold lace develops from initial open weblike structures by gradual enveloping the PU template. The diameter of gold lace shell is determined by the size of PUs in water and can be adjusted by the molecular mass of PUs. The close proximity between branches makes them excellent supports for surface-enhanced Raman spectroscopy (SERS), which was demonstrated using 1-naphthalenethiol upon excitation with photons with different wavelengths. The loading and releasing of pyrene as a model of hydrophobic drugs and the use of SERS to monitor it were demonstrated.

Effect of surface charge on the cellular uptake and cytotoxicity of fluorescent labeled cellulose nanocrystals

Probing of cellular uptake and cytotoxicity was conducted for two fluorescent cellulose nanocrystals (CNCs): CNC-fluorescein isothiocyanate (FITC) and newly synthesized CNC-rhodamine B isothiocyanate (RBITC). The positively charged CNC-RBITC was uptaken by human embryonic kidney 293 (HEK 293) and Spodoptera frugiperda (Sf9) cells without affecting the cell membrane integrity. The cell viability assay and cell-based impedance spectroscopy revealed no noticeably cytotoxic effect of the CNC-RBITC conjugate. However, no significant internalization of negatively charged CNC-FITC was observed at physiological pH. Indeed, the effector cells were surrounded by CNC-FITC, leading to eventual cell rupture. As the surface charge of CNC played an important role in cellular uptake and cytotoxicity, facile surface functionalization together with observed noncytotoxicity rendered modified CNC as a promising candidate for bioimaging and drug delivery systems.

Plasmon resonant gold-coated liposomes for spectrally controlled content release

We recently demonstrated that liposome-supported plasmon resonant gold nanoshells are degradable into components of a size compatible with renal clearance, potentially enabling their use as multifunctional agents in applications in nanomedicine, including imaging, diagnostics, therapy, and drug delivery (Troutman et al., Adv. Mater. 2008, 20, 2604-2608). When illuminated with laser light at the wavelength matching their plasmon resonance band, gold-coated liposomes rapidly release their encapsulated substances, which can include therapeutic and diagnostic agents. The present research demonstrates that release of encapsulated agents from gold-coated liposomes can be spectrally controlled by varying the location of the plasmon resonance band; this spectral tuning is accomplished by varying the concentration of gold deposited on the surface of liposomes. Furthermore, the amount of laser energy required for release is qualitatively explained using the concept of thermal confinement (Jacques, Appl. Opt. 1993, 32(3), 2447-2454). Overlapping thermal confinement zones can be avoided by minimizing the laser pulse width, resulting in lower energy requirements for liposomal content release and less global heating of the sample. Control of heating is especially important in drug delivery applications, where it enables spatial and spectral control of delivery and prevents thermal damage to tissue.