Immobilization of gold nanoparticles on living cell membranes upon controlled lipid binding

Cell-membrane engineering strategies for clinic-guided design of nanomedicine

Cells are the fundamental units of life. The cell membrane primarily composed of two layers of phospholipids (a bilayer) structurally defines the boundary of a cell, which can protect its interior from external disturbances and also selectively exchange substances and conduct signals from the extracellular environment. The complexity and particularity of transmembrane proteins provide the foundation for versatile cellular functions. Nanomedicine as an emerging therapeutic strategy holds tremendous potential in the healthcare field. However, it is susceptible to recognition and clearance by the immune system. To overcome this bottleneck, the technology of cell membrane coating has been extensively used in nanomedicines for their enhanced therapeutic efficacy, attributed to the favorable fluidity and biocompatibility of cell membranes with various membrane-anchored proteins. Meanwhile, some engineering strategies of cell membranes through various chemical, physical and biological ways have been progressively developed to enable their versatile therapeutic functions against complex diseases. In this review, we summarized the potential clinical applications of four typical cell membranes, elucidated their underlying therapeutic mechanisms, and outlined their current engineering approaches. In addition, we further discussed the limitation of this technology of cell membrane coating in clinical applications, and possible solutions to address these challenges.

Putting Hybrid Nanomaterials to Work for Biomedical Applications

Hybrid nanomaterials have found use in many biomedical applications. This article provides a comprehensive review of the principles, techniques, and recent advancements in the design and fabrication of hybrid nanomaterials for biomedicine. We begin with an introduction to the general concept of material hybridization, followed by a discussion of how this approach leads to materials with additional functionality and enhanced performance. We then highlight hybrid nanomaterials in the forms of nanostructures, nanocomposites, metal-organic frameworks, and biohybrids, including their fabrication methods. We also showcase the use of hybrid nanomaterials to advance biomedical engineering in the context of nanomedicine, regenerative medicine, diagnostics, theranostics, and biomanufacturing. Finally, we offer perspectives on challenges and opportunities.

Direct Visualization and Identification of Membrane Voltage-Gated Sodium Channels from Human iPSC-Derived Neurons by Multiple Imaging and Light Enhanced Spectroscopy

In this study, transmission electron microscopy atomic force microscopy, and surface enhanced Raman spectroscopy are combined through a direct imaging approach, to gather structural and chemical information of complex molecular systems such as ion channels in their original plasma membrane. Customized microfabricated sample holder allows to characterize Na_v channels embedded in the original plasma membrane extracted from neuronal cells that are derived from healthy human induced pluripotent stem cells. The identification of the channels is accomplished by using two different approaches, one of them widely used in cryo-EM (the particle analysis method) and the other based on a novel Zernike Polynomial expansion of the images bitmap. This approach allows to carry out a whole series of investigations, one complementary to the other, on the same sample, preserving its state as close as possible to the original membrane configuration.

Enhancement of Radiosensitization by Silver Nanoparticles Functionalized with Polyethylene Glycol and Aptamer As1411 for Glioma Irradiation Therapy

Background

The efficacy of radiotherapy for glioma is often limited by the radioresistance of glioma cells. The radiosensitizing effects of silver nanoparticles (AgNPs) on glioma were found in the previous studies of our group. In order to enhance the radiosensitivity of tumor cells and selectively kill them while reducing the side effects of irradiation therapy, targeted modification of AgNPs is urgently needed.

Materials and methods

In the present study, AgNPs functionalized with polyethylene glycol (PEG) and aptamer As1411 (AsNPs) were synthesized and subsequently characterized by transmission electron microscopy, ultraviolet-visible spectroscopy and Fourier transform infrared spectroscopy. Then the targeting property of AsNPs was evaluated by dark-field imaging, confocal microscopy and in vivo imaging. Both colony formation assay and glioma-bearing mouse model were employed to study the radiosensitizing effect of AsNPs.

Results

The characterization results revealed a spherical shape of AgNPs with an average diameter of 18 nm and the successful construction of AsNPs. AsNPs were confirmed to specifically target C6 glioma cells, but not normal human microvascular endothelial cells. Moreover, AsNPs could not only internalize into tumor cells, but also penetrate into the core of tumor spheroids. In vitro experiments showed that AsNPs exhibited a better radiosensitizing effect than AgNPs and PEGylated AgNPs (PNPs), inducing a higher rate of apoptotic cell death. In vivo imaging demonstrated that Cy5-AsNPs preferentially accumulated at the tumor site, and the ratio of fluorescence intensity of Cy5-AsNPs to that of Cy5-PNPs reached the maximum at 6 h post-systemic administration. Furthermore, the combination of AsNPs with irradiation significantly prolonged the median survival time of C6 glioma-bearing mice.

Conclusion

Our results indicated that AsNPs could be an effective nano-radiosensitizer for glioma targeting treatment.

Membrane fusogenic high-density lipoprotein nanoparticles

Membrane fusion under mildly acidic pH occurs naturally during viral infection in cells and has been exploited in the field of nanoparticle-mediated drug delivery to circumvent endosomal entrapment of the cargo. Herein, we aimed to confer virus-like fusogenic activity to HDL in the form of a ca. 10-nm disc comprising a discoidal lipid bilayer and two copies of a lipid-binding protein at the edge. A series of HDL mutants were prepared with a mixture of three lipids and a cell-penetrating peptide (TAT, penetratin, or Arg8) fused to the protein. In a lipid-mixing assay with anionic liposomes at pH 5.5, one HDL mutant showed the fusogenic activity higher than known fusogenic liposomes. In live mammalian cells, this HDL mutant showed high plasma membrane-binding activity in the presence of serum independent of pH. In the absence of serum, a mildly acidic pH dependency for binding to the plasma membrane and the subsequent lipid mixing between them was observed for this mutant. We propose a novel strategy to develop HDL-based drug carriers by taking advantage of the HDL lipid/protein composite structure.

Nano-bio-computing lipid nanotablet

Using nanoparticles as substrates for computation enables algorithmic and autonomous controls of their unique and beneficial properties. However, scalable architecture for nanoparticle-based computing systems is lacking. Here, we report a platform for constructing nanoparticle logic gates and circuits at the single-particle level on a supported lipid bilayer. Our "lipid nanotablet" platform, inspired by cellular membranes that are exploited to compartmentalize and control signaling networks, uses a lipid bilayer as a chemical circuit board and nanoparticles as computational units. On a lipid nanotablet, a single-nanoparticle logic gate senses molecules in solution as inputs and triggers particle assembly or disassembly as an output. We demonstrate a set of Boolean logic operations, fan-in/fan-out of logic gates, and a combinational logic circuit such as a multiplexer. We envisage that our approach to modularly implement nanoparticle circuits on a lipid bilayer will create new paradigms and opportunities in molecular computing, nanoparticle circuits, and systems nanoscience.

Intracellular localization of nanoparticle dimers by chirality reversal

The intra- and extracellular positioning of plasmonic nanoparticles (NPs) can dramatically alter their curative/diagnostic abilities and medical outcomes. However, the inability of common spectroscopic identifiers to register the events of transmembrane transport denies their intracellular vs. extracellular localization even for cell cultures. Here we show that the chiroptical activity of DNA-bridged NP dimers allows one to follow the process of internalization of the particles by the mammalian cells and to distinguish their extra- vs intra-cellular localizations by real-time spectroscopy in ensemble. Circular dichroism peaks in the visible range change from negative to positive during transmembrane transport. The chirality reversal is associated with a spontaneous twisting motion around the DNA bridge caused by the large change in electrostatic repulsion between NPs when the dimers move from interstitial fluid to cytosol. This finding opens the door for spectroscopic targeting of plasmonic nanodrugs and quantitative assessment of nanoscale interactions. The efficacy of dichroic targeting of chiral nanostructures for biomedical applications is exemplified here as photodynamic therapy of malignancies. The efficacy of cervical cancer cell elimination was drastically increased when circular polarization of incident photons matched to the preferential absorption of dimers localized inside the cancer cells, which is associated with the increased generation of reactive oxygen species and their preferential intracellular localization.

The ability to spectroscopically pinpoint whether nanoparticles are located inside or outside of cells represents an overarching need in biology and medicine. Here, the authors show that the chirality of DNA-bridged particle dimers reverses when they cross the cell membrane, providing a real-time chiroptical signature of their intra- or extracellular location.

Enhanced cellular uptake of iron oxide nanoparticles modified with 1,2-dimyristoyl-sn-glycero-3-phosphocholine

DMPC greatly enhanced the cellular uptake of SPIONs, resulting in remarkable amounts of accumulated nanoparticles in PC-12 cells.

Red blood cell membrane-mediated fusion of hydrophobic quantum dots with living cell membranes for cell imaging

Nanoparticle fusion with cell membranes is an interesting phenomenon that may have crucial implications for their biomedical applications. Here, we proposed a biomimetic and controlled route to fusion of hydrophobic quantum dots (QDs) with the cell membranes of living cells, while preserving their sensing and optical properties and thus their capability of membrane imaging and single-nanoparticle tracking. Red blood cell (RBC) membrane lipids were extracted to phase transfer hydrophobic QDs and the resulting RBC-encapsulated QDs (RBC-QDs) can be well fused within cell membranes as membrane markers. The fusion was validated through single-nanoparticle imaging and different movement behaviours were reliably discriminated. RBC-QDs possessed some novel features, such as controllable selective membrane staining, no invasion, and high photobleaching resistance, which allowed for long-term imaging, and single-nanoparticle tracking. This approach provides a versatile platform for controlled hydrophobic QD-based fluorescence investigation of living cell membranes.

Optical Nanoparticle Sorting Elucidates Synthesis of Plasmonic Nanotriangles

We investigate the optical and morphological properties of gold nanoparticles grown by reducing a gold salt with Na2S. Lasers are tuned to the observed plasmon resonances, and the optical forces exerted on the nanoparticles are used to selectively print individual nanoparticles onto a substrate. This enables us to combine dark-field spectroscopy and scanning electron microscopy to compare the optical properties of single nanoparticles with their morphology. By arresting the synthesis at different times, we are able to investigate which type of nanoparticle is responsible for the respective resonances. We find that thin Au nanotriangles are the source of the observed near infrared (NIR) resonance. The initial lateral growth of these triangles causes the plasmon resonance to redshift into the NIR, whereas a subsequent thickening of the triangles and a concomitant truncation lead to a blueshift of the resonance. Furthermore, we find that the nanotriangles produced have extremely narrow line widths (187 ± 23 meV), show nearly isotropic scattering, and are stable for long periods of time. This shows their vast potential for applications such as in vivo imaging and bio(chemical) sensing. The method used here is generally applicable to other syntheses, and shows how complex nanostructures can be built up on substrates by selectively printing NPs of varying plasmonic resonances.

Fabrication of plasmon length-based surface enhanced Raman scattering for multiplex detection on microfluidic device

The length of bioreceptors plays an important role in signal enhancement of surface-enhanced Raman scattering (SERS) due to amplification of electromagnetic fields generated by the excitation of localized surface plasmons. Herein, intact antibodies (IgG) and Fab fragments conjugated onto gold nanostar were used to fabricate two kinds of immunosensors for measurement of their SERS signals. Using CA125 as the antigen and Rhodamine-6G (R6G)-conjugated immunogolds, a SERS immunosensor was self-assembled by antigen-antibody interaction. The results showed that the SERS signal from the Fab immunosensor was 2.4 times higher than that of the IgG immunosensor. Furthermore, increased hot-spots by silver atom deposition onto the IgG and Fab immunosensor showed 2.1 and 1.4 times higher signals than before enhancement, respectively. For application, based on the Fab immunosensor, a SERS-compatible microfluidic system was designed for multiplex assays to overcome the drawbacks of conventional assays. This system can measure biological specimens directly from bio fluids instead of using a complex microfluidic device containing separation and detection elements. Four approved biomarkers of breast cancer, including cancer antigen (CA125), HER2, epididymis protein (HE4), and Eotaxin-1, were detected from patient-mimicked serum with limits of 15 fM, 17 fM, 21 fM, and 6.5 fM, respectively. The results indicated that the lengths and geometry of the bioreceptors determined the intensity of SERS signal from the interface and cavity of the sandwich immunosensor. Silver atom deposition at the cavity of the immunosensor increased the SERS signal. Finally, the SERS immunosensor built-in microfluidic system improved the performance of multiplex diagnostics.

Supported lipid bilayers as dynamic platforms for tethered particles

Nanoparticle tethering to lipid bilayers enables the observation of hundreds of diffusing particles that are confined within a single field of view. A wide variety of materials ranging from plasmonic metals to soft matter can be stably tethered to the surface of a fluid bilayer by covalent or non-covalent means. The controlled environment of this experimental platform allows direct control over surface compositions and accurate tracking of nanoparticle interactions. This minireview will cover studies that use bilayer-tethered nanoparticles to investigate physical properties related to lipid mobility, biomolecule sensing, and surface interactions, as well as experiments to reversibly manipulate tethered nanoparticles by electric fields.

Interaction of mixed-ligand monolayer-protected Au₁₄₄ clusters with biomimetic membranes as a function of the transmembrane potential

Understanding the interaction of nanoparticles with cell membranes is a high-priority research area for possible biomedical applications. We describe our findings concerning the interaction of Au144 monolayer-protected clusters (MPCs) with biomimetic membranes and their permeabilizing effect as a function of the transmembrane potential. We synthesized Au144(SCH2CH2Ph)60 and modified the capping monolayer with 8-mercaptooctanoic acid (Au144OctA) or thiolated trichogin (Au144TCG), a channel-forming peptide. The interactions of these MPCs with mercury-supported lipid mono- and bilayers were studied with a combination of electrochemical techniques specifically sensitive to changes in the properties of biomimetic membranes and/or charge-transfer phenomena. Permeabilization effects were evaluated through the influence of MPC uptake on the reduction of cadmium(II) ions. The nature and properties of the Au144 capping molecules play a crucial role in controlling how MPCs interact with membranes. The native MPC causes a small effect, whereas both Au144OctA and Au144TCG interact significantly with the lipid monolayer and show electroactivity. Whereas Au144OctA penetrates the membrane, Au144TCG pierces the membrane with its peptide appendage while remaining outside of it. Both clusters promote Cd(2+) reduction but with apparently different mechanisms. Because of the different way that they interact with the membrane, Au144OctA is more effective in Cd(2+) reduction when interacting with the lipid bilayer and Au144TCG performs particularly well when piercing the lipid monolayer.

Revisiting 30 years of biofunctionalization and surface chemistry of inorganic nanoparticles for nanomedicine

In the last 30 years we have assisted to a massive advance of nanomaterials in material science. Nanomaterials and structures, in addition to their small size, have properties that differ from those of larger bulk materials, making them ideal for a host of novel applications. The spread of nanotechnology in the last years has been due to the improvement of synthesis and characterization methods on the nanoscale, a field rich in new physical phenomena and synthetic opportunities. In fact, the development of functional nanoparticles has progressed exponentially over the past two decades. This work aims to extensively review 30 years of different strategies of surface modification and functionalization of noble metal (gold) nanoparticles, magnetic nanocrystals and semiconductor nanoparticles, such as quantum dots. The aim of this review is not only to provide in-depth insights into the different biofunctionalization and characterization methods, but also to give an overview of possibilities and limitations of the available nanoparticles.

Protein coronas on gold nanorods passivated with amphiphilic ligands affect cytotoxicity and cellular response to penicillin/streptomycin

We probe how amphiphilic ligands (ALs) of four different types affect the formation of protein coronas on gold nanorods (NRs) and their impact on cellular response. NRs coated with cetyltrimethylammonium bromide were ligand exchanged with polyoxyethylene[10]cetyl ether, oligofectamine, and phosphatidylserine (PS). Protein coronas from equine serum (ES) were formed on these NR-ALs, and their colloidal stability, as well as cell uptake, proliferation, oxidative stress, and gene expression, were examined. We find that the protein corona that forms and its colloidal stability are affected by AL type and that the cellular response to these NR-AL-coronas (NR-AL-ES) is both ligand and corona dependent. We also find that the presence of common cell culture supplement penicillin/streptomycin can impact the colloidal stability and cellular response of NR-AL and NR-AL-ES, showing that the cell response is not necessarily inert to pen/strep when in the presence of nanoparticles. Although the protein corona is what the cells see, the underlying surface ligands evidently play an important role in shaping and defining the physical characteristics of the corona, which ultimately impacts the cellular response. Further, the results of this study suggest that the cellular behavior toward NR-AL is mediated by not only the type of AL and the protein corona it forms but also its resulting colloidal stability and interaction with cell culture supplements.

Optical trapping and manipulation of plasmonic nanoparticles: fundamentals, applications, and perspectives

This feature article discusses the optical trapping and manipulation of plasmonic nanoparticles, an area of current interest with potential applications in nanofabrication, sensing, analytics, biology and medicine. We give an overview over the basic theoretical concepts relating to optical forces, plasmon resonances and plasmonic heating. We discuss fundamental studies of plasmonic particles in optical traps and the temperature profiles around them. We place a particular emphasis on our own work employing optically trapped plasmonic nanoparticles towards nanofabrication, manipulation of biomimetic objects and sensing.

pH-responsive gold nanoparticles-in-liposome hybrid nanostructures for enhanced systemic tumor delivery

We report a pH-responsive gold nanoparticles-in-liposome hybrid nanostructure, which effectively combines the pH-responsive assembly and surface plasmon property changes of 'smart' gold nanoparticles and enhanced systemic circulation and tumor accumulation of the PEG-grafted liposomes.

Photoacoustic recovery after photothermal bleaching in living cells

We present an innovative method, photoacoustic recovery after photothermal bleaching (PRAP), for studying particle dynamics at micron scale via photoacoustic imaging. As an intuitive way to visualize and quantify dynamic processes, PRAP is demonstrated first in a simple phantom study and then in a more complex measurement involving live cells. Compared with the conventional fluorescence-based approach, PRAP provides high signal-to-noise ratio (SNR) imaging with minimal bleaching-induced artifacts during the recovery stage, ideal for monitoring the diffusive and kinetic processes inside a cell.

Lipid bilayer-integrated optoelectronic tweezers for nanoparticle manipulations

Remotely manipulating a large number of microscopic objects is important to soft-condensed matter physics, biophysics, and nanotechnology. Optical tweezers and optoelectronic tweezers have been widely used for this purpose but face critical challenges when applied to nanoscale objects, including severe photoinduced damages, undesired ionic convections, or irreversible particle immobilization on surfaces. We report here the first demonstration of a lipid bilayer-integrated optoelectronic tweezers system for simultaneous manipulation of hundreds of 60 nm gold nanoparticles in an arbitrary pattern. We use a fluid lipid bilayer membrane with a ~5 nm thickness supported by a photoconductive electrode to confine the diffusion of chemically tethered nanoparticles in a two-dimensional space. Application of an external a.c. voltage together with patterned light selectively activates the photoconducting electrode that creates strong electric field localized near the surface. The field strength changes most significantly at the activated electrode surface where the particles tethered to the membrane thus experience the strongest dielectrophoretic forces. This design allows us to efficiently achieve dynamic, reversible, and parallel manipulation of many nanoparticles. Our approach to integrate biomolecular structures with optoelectronic devices offers a new platform enabling the study of thermodynamics in many particle systems and the selective transport of nanoscale objects for broad applications in biosensing and cellular mechanotransductions.

Interfacing engineered nanoparticles with biological systems: anticipating adverse nano-bio interactions

The innovative use of engineered nanomaterials in medicine, be it in therapy or diagnosis, is growing dramatically. This is motivated by the current extraordinary control over the synthesis of complex nanomaterials with a variety of biological functions (e.g. contrast agents, drug-delivery systems, transducers, amplifiers, etc.). Engineered nanomaterials are found in the bio-context with a variety of applications in fields such as sensing, imaging, therapy or diagnosis. As the degree of control to fabricate customized novel and/or enhanced nanomaterials evolves, often new applications, devices with enhanced performance or unprecedented sensing limits can be achieved. Of course, interfacing any novel material with biological systems has to be critically analyzed as many undesirable adverse effects can be triggered (e.g. toxicity, allergy, genotoxicity, etc.) and/or the performance of the nanomaterial can be compromised due to the unexpected phenomena in physiological environments (e.g. corrosion, aggregation, unspecific absorption of biomolecules, etc.). Despite the need for standard protocols for assessing the toxicity and bio-performance of each new functional nanomaterial, these are still scarce or currently under development. Nonetheless, nanotoxicology and relating adverse effects to the physico-chemical properties of nanomaterials are emerging areas of the utmost importance which have to be continuously revisited as any new material emerges. This review highlights recent progress concerning the interaction of nanomaterials with biological systems and following adverse effects.

Surface charge dependent nanoparticle disruption and deposition of lipid bilayer assemblies

Electrostatic interaction plays a leading role in nanoparticle interactions with membrane architectures and can lead to effects such as nanoparticle binding and membrane disruption. In this work, the effects of nanoparticles (NPs) interacting with mixed lipid systems were investigated, indicating an ability to tune both NP binding to membranes and membrane disruption. Lipid membrane assemblies (LBAs) were created using a combination of charged, neutral, and gel-phase lipids. Depending on the lipid composition, nanostructured networks could be observed using in situ atomic force microscopy representing an asymmetrical distribution of lipids that rendered varying effects on NP interaction and membrane disruption that were domain-specific. LBA charge could be localized to fluidic domains that were selectively disrupted when interacting with negatively charged Au nanoparticles or quantum dots. Disruption was observed to be related to the charge density of the membrane, with a maximum amount of disruption occurring at ∼40% positively charged lipid membrane concentration. Conversely, particle deposition was determined to begin at charged lipid concentrations greater than 40% and increased with charge density. The results demonstrate that the modulation of NP and membrane charge distribution can play a pivitol role in determining NP-induced membrane disruption and NP surface assembly.

Improved methodology for the preparation of water-soluble maleimide-functionalized small gold nanoparticles

Improved methodology to prepare maleimide-functionalized, water-soluble, small (<3 nm) gold nanoparticles using a retro-Diels-Alder strategy that we developed for similar organic-soluble AuNP's is described. Importantly, our results suggest that a recent paper by Zhu, Waengler, Lennox, and Schirrmacher describing a similar strategy gave results inconsistent with the formation of the titled maleimide-modified AuNP (Zhu, J.; Waengler, C.; Lennox, R. B.; Schirrmacher, R. Langmuir2012, 28, 5508) as the major product, but consistent with the major product being an adduct derived from the hydrolysis of maleimide formed under the conditions used for the required deprotection of the maleimide. Our methodology provides an efficient and accessible route to pure maleimide-modified small AuNP's that circumvents the formation of the hydrolysis product. The maleimide-modified small AuNP's are versatile because they are soluble in water and in a wide range of organic solvents and their reactivity can now be properly exploited as a reactive moiety in Michael addition for bioconjugation studies in aqueous solution.

Hybrid nanoparticles for detection and treatment of cancer

There is currently considerable effort to incorporate both diagnostic and therapeutic functions into a single nanoscale system for the more effective treatment of cancer. Nanoparticles have great potential to achieve such dual functions, particularly if more than one type of nanostructure can be incorporated in a nanoassembly, referred to in this review as a hybrid nanoparticle. Here we review recent developments in the synthesis and evaluation of such hybrid nanoparticles based on two design strategies (barge vs. tanker), in which liposomal, micellar, porous silica, polymeric, viral, noble metal, and nanotube systems are incorporated either within (barge) or at the surface of (tanker) a nanoparticle. We highlight the design factors that should be considered to obtain effective nanodevices for cancer detection and treatment.

Preparation of water-soluble maleimide-functionalized 3 nm gold nanoparticles: a new bioconjugation template

We present an efficient methodology to prepare maleimide-tethered, water-soluble gold nanoparticles (maleimide-AuNPs). The maleimide-AuNPs were prepared in the protected form and are readily recovered via a retro-Diels-Alder reaction. The maleimide-AuNPs were fully characterized by (1)H NMR, TGA, TEM, and XPS and were determined to have a gold core with an average size of 3.2 ± 0.8 nm; each core contains about 1000 gold atoms and is surrounded by 30 maleimide-terminated ligands and 60 thiolated PEG ligands. The maleimide-AuNPs efficiently react with rhodamine 123 and cysteine and are a promising template for biological applications.

Michael addition reactions for the modification of gold nanoparticles facilitated by hyperbaric conditions

The chemical interfacial modification of organic solvent soluble 2.4 ± 0.5 nm maleimide-modified monolayer protected gold nanoparticles (2-C(12)AuNPs) with primary or secondary amines via Michael addition reactions is demonstrated. Michael addition reactions between 2-C(12)AuNPs and primary or secondary amines at ambient temperature and pressure and under the conditions where the AuNP is soluble and stable are possible albeit sluggish, often taking days to weeks to go to completion. The rates and efficacies of the these same reactions are drastically increased at hyperbaric pressure conditions (11 000 atm) with no observed adverse effect to the gold nanoparticle stability. The resulting Michael addition adducts (3-C(12)AuNPs) formed from 2-C(12)AuNPs and the corresponding amines were characterized by TEM and by comparison of the (1)H NMR spectra of the 3-C(12)AuNPs with those of model reactions of the same amines with N-dodecylmaleimide, 2. The Michael addition reactions occur more readily with 2 rather than 2-C(12)AuNPs, consistent with the local environment of the latter imposing additional steric or other barriers to the reaction. The use of hyperbaric conditions makes the reaction of the organic solvent soluble 2-C(12)AuNP via Michael addition a viable interfacial modification process that is otherwise impractical. The results also suggest that it is a useful protocol for facilitating Michael addition reactions generally in solution at low temperatures.

Nanofabrication for the analysis and manipulation of membranes

Recent advancements and applications of nanofabrication have enabled the characterization and control of biological membranes at submicron scales. This review focuses on the application of nanofabrication towards the nanoscale observing, patterning, sorting, and concentrating membrane components. Membranes on living cells are a necessary component of many fundamental cellular processes that naturally incorporate nanoscale rearrangement of the membrane lipids and proteins. Nanofabrication has advanced these understandings, for example, by providing 30 nm resolution of membrane proteins with metal-enhanced fluorescence at the tip of a scanning probe on fixed cells. Naturally diffusing single molecules at high concentrations on live cells have been observed at 60 nm resolution by confining the fluorescence excitation light through nanoscale metallic apertures. The lateral reorganization on the plasma membrane during membrane-mediated signaling processes has been examined in response to nanoscale variations in the patterning and mobility of the signal-triggering molecules. Further, membrane components have been separated, concentrated, and extracted through on-chip electrophoretic and microfluidic methods. Nanofabrication provides numerous methods for examining and manipulating membranes for both greater understandings of membrane processes as well as for the application of membranes to other biophysical methods.

Liposomes: from a clinically established drug delivery system to a nanoparticle platform for theranostic nanomedicine

For decades, clinicians have used liposomes, self-assembled lipid vesicles, as nanoscale systems to deliver encapsulated anthracycline molecules for cancer treatment. The more recent proposition to combine liposomes with nanoparticles remains at the preclinical development stages; however, such hybrid constructs present great opportunities to engineer theranostic nanoscale delivery systems, which can combine simultaneous therapeutic and imaging functions. Many novel nanoparticles of varying chemical compositions are being developed in nanotechnology laboratories, but further chemical modification is often required to make these structures compatible with the biological milieu in vitro and in vivo. Such nanoparticles have shown promise as diagnostic and therapeutic tools and generally offer a large surface area that allows covalent and non-covalent surface functionalization with hydrophilic polymers, therapeutic moieties, and targeting ligands. In most cases, such surface manipulation diminishes the theranostic properties of nanoparticles and makes them less stable. From our perspective, liposomes offer structural features that can make nanoparticles biocompatible and present a clinically proven, versatile platform for further enhancement of the pharmacological and diagnostic efficacy of nanoparticles. In this Account, we describe two examples of liposome-nanoparticle hybrids developed as theranostics: liposome-quantum dot hybrids loaded with a cytotoxic drug (doxorubicin) and artificially enveloped adenoviruses. We incorporated quantum dots into lipid bilayers, which rendered them dispersible in physiological conditions. This overall vesicular structure allowed them to be loaded with doxorubicin molecules. These structures exhibited cytotoxic activity and labeled cells both in vitro and in vivo. In an alternative design, lipid bilayers assembled around non-enveloped viral nanoparticles and altered their infection tropism in vitro and in vivo with no chemical or genetic capsid modifications. Overall, we have attempted to illustrate how alternative strategies to incorporate nanoparticles into liposomal nanostructures can overcome some of the shortcomings of nanoparticles. Such hybrid structures could offer diagnostic and therapeutic combinations suitable for biomedical and even clinical applications.

Plasmonics: an emerging field fostered by Nano Letters

While studies of surface plasmons on metals have been pursued for decades, the more recent appearance of nanoscience has created a revolution in this field with "Plasmonics" emerging as a major area of research. The direct optical excitation of surface plasmons on metallic nanostructures provides numerous ways to control and manipulate light at nanoscale dimensions. This has stimulated the development of novel optical materials, deeper theoretical insight, innovative new devices, and applications with potential for significant technological and societal impact. Nano Letters has been instrumental in the emergence of plasmonics, providing its readership with rapid advances in this dynamic field.