Shuttling gold nanoparticles into tumoral cells with an amphipathic proline-rich peptide

Long-Term Intracellular Tracking of Label-Free Nanoparticles in Live Cells and Tissues with Confocal Microscopy

The label-free imaging of inorganic nanoparticles (NPs) using confocal laser scanning microscopy (CLSM) provides a powerful and versatile tool for studying interactions between NPs and biological systems. Without the need for exogenous labels or markers, it simply benefits from the differential scattering of visible photons between biomaterials and inorganic NPs. Validation experiments conducted on fixed and living cells in real-time, as well as mouse tissue sections following parenteral administration of NPs. Additionally, by incorporating reporter fluorophores and utilizing both reflectance and fluorescence imaging modalities, the method enables high-resolution multiplex imaging of cellular structures and NPs. Different sizes and concentrations of Au NPs are tested as for Ag, Fe3O4, and CeO2 NPs, all with biological interest. Overall, the comprehensive study of NP imaging by confocal microscopy in reflectance mode provides valuable insights and tools for researchers interested in monitoring the nano-bio interactions.

Exploiting endocytosis for transfection of mRNA for cytoplasmatic delivery using cationic gold nanoparticles

Introduction

Gene therapy holds promise to cure various diseases at the fundamental level. For that, efficient carriers are needed for successful gene delivery. Synthetic 'non-viral' vectors, as cationic polymers, are quickly gaining popularity as efficient vectors for transmitting genes. However, they suffer from high toxicity associated with the permeation and poration of the cell membrane. This toxic aspect can be eliminated by nanoconjugation. Still, results suggest that optimising the oligonucleotide complexation, ultimately determined by the size and charge of the nanovector, is not the only barrier to efficient gene delivery.

Methods

We herein develop a comprehensive nanovector catalogue comprising different sizes of Au NPs functionalized with two different cationic molecules and further loaded with mRNA for its delivery inside the cell.

Results and Discussion

Tested nanovectors showed safe and sustained transfection efficiencies over 7 days, where 50 nm Au NPs displayed the highest transfection rates. Remarkably, protein expression was increased when nanovector transfection was performed combined with chloroquine. Cytotoxicity and risk assessment demonstrated that nanovectors are safe, ascribed to lesser cellular damage due to their internalization and delivery via endocytosis. Obtained results may pave the way to design advanced and efficient gene therapies for safely transferring oligonucleotides.

Characterization of Charge States in Conducting Organic Nanoparticles by X-ray Photoemission Spectroscopy

The metallic and semiconducting character of a large family of organic materials based on the electron donor molecule tetrathiafulvalene (TTF) is rooted in the partial oxidation (charge transfer or mixed valency) of TTF derivatives leading to partially filled molecular orbital-based electronic bands. The intrinsic structure of such complexes, with segregated donor and acceptor molecular chains or planes, leads to anisotropic electronic properties (quasi one-dimensional or two-dimensional) and morphology (needle-like or platelet-like crystals). Recently, such materials have been synthesized as nanoparticles by intentionally frustrating the intrinsic anisotropic growth. X-ray photoemission spectroscopy (XPS) has emerged as a valuable technique to characterize the transfer of charge due to its ability to discriminate the different chemical environments or electronic configurations manifested by chemical shifts of core level lines in high-resolution spectra. Since the photoemission process is inherently fast (well below the femtosecond time scale), dynamic processes can be efficiently explored. We determine here the fingerprint of partial oxidation on the photoemission lines of nanoparticles of selected TTF-based conductors.

Biomedical applications of the peptide decorated gold nanoparticles

Currently, peptide-nanoparticle (NP) conjugates have been demonstrated to be efficient and powerful tools for the treatment and the diagnosis of various diseases as well as in the bioimaging application. Several bioconjugation strategies have been adopted to formulate the peptide-NP conjugates. In this review, we discuss the exciting applications of peptide-gold (Au) NP conjugates in the area of drug delivery, targeting, cancer therapy, brain diseases, vaccines, immune modulation, biosensor, colorimetric detection of heavy metals, and bio-labeling in vitro and in vivo models. Within this framework, various approaches such as radiotherapy, photothermal therapy, photodynamic therapy and chemo-photothermal therapy have been demonstrated for the treatment of several diseases. Moreover, we highlight how the morphology, size, density of peptide and the protein corona influence the biological activity, biodistribution and biological fate of peptide-AuNP conjugates. In the end, we discuss the future outlook and the challenges being faced in the clinical translation of the peptide-AuNP conjugates. Overall, this review emphasizes that the peptide-AuNP conjugates might be used as potential theranostic agents for the treatment of life-threatening diseases in an economical fashion in the future.

Gold Nanoparticles in Conjunction with Nucleic Acids as a Modern Molecular System for Cellular Delivery

Development of nanotechnology has become prominent in many fields, such as medicine, electronics, production of materials, and modern drugs. Nanomaterials and nanoparticles have gained recognition owing to the unique biochemical and physical properties. Considering cellular application, it is speculated that nanoparticles can transfer through cell membranes following different routes exclusively owing to their size (up to 100 nm) and surface functionalities. Nanoparticles have capacity to enter cells by themselves but also to carry other molecules through the lipid bilayer. This quality has been utilized in cellular delivery of substances like small chemical drugs or nucleic acids. Different nanoparticles including lipids, silica, and metal nanoparticles have been exploited in conjugation with nucleic acids. However, the noble metal nanoparticles create an alternative, out of which gold nanoparticles (AuNP) are the most common. The hybrids of DNA or RNA and metal nanoparticles can be employed for functional assemblies for variety of applications in medicine, diagnostics or nano-electronics by means of biomarkers, specific imaging probes, or gene expression regulatory function. In this review, we focus on the conjugates of gold nanoparticles and nucleic acids in the view of their potential application for cellular delivery and biomedicine. This review covers the current advances in the nanotechnology of DNA and RNA-AuNP conjugates and their potential applications. We emphasize the crucial role of metal nanoparticles in the nanotechnology of nucleic acids and explore the role of such conjugates in the biological systems. Finally, mechanisms guiding the process of cellular intake, essential for delivery of modern therapeutics, will be discussed.

Nanotechnological Strategies for Protein Delivery

The use of therapeutic proteins plays a fundamental role in the treatment of numerous diseases. The low physico-chemical stability of proteins in physiological conditions put their function at risk in the human body until they reach their target. Moreover, several proteins are unable to cross the cell membrane. All these facts strongly hinder their therapeutic effect. Nanomedicine has emerged as a powerful tool which can provide solutions to solve these limitations and improve the efficacy of treatments based on protein administration. This review discusses the advantages and limitations of different types of strategies employed for protein delivery, such as PEGylation, transport within liposomes or inorganic nanoparticles or their in situ encapsulation.

Peptide Mediated Brain Delivery of Nano- and Submicroparticles: A Synergistic Approach

The brain is a complex, regulated organ with a highly controlled access mechanism: The Blood-Brain Barrier (BBB). The selectivity of this barrier is a double-edged sword, being both its greatest strength and weakness. This weakness is evident when trying to target therapeutics against diseases within the brain. Diseases such as metastatic brain cancer have extremely poor prognosis due to the poor permeability of many therapeutics across the BBB. Peptides can be designed to target BBB receptors and gain access to the brain by transcytosis. These peptides (known as BBB-shuttles) can carry compounds, usually excluded from the brain, across the BBB. BBB-shuttles are limited by poor loading of therapeutics and degradation of the peptide and cargo. Likewise, nano- submicro- and microparticles can be fine-tuned to limit their degradation and with high loading of therapeutics. However, most nano- and microparticles' core materials completely lack efficient targeting, with a few selected materials able to cross the BBB passively. Combining the selectivity of peptides with the high loading potential of nano-, microparticles offers an exciting strategy to develop novel, targeted therapeutics towards many brain disorders and diseases. Nevertheless, at present the field is diverse, in both scope and nomenclature, often with competing or contradictory names. In this review, we will try to address some of these issues and evaluate the current state of peptide mediated nano,-microparticle transport to the brain, analyzing delivery vehicle type and peptide design, the two key components that must act synergistically for optimal therapeutic impact.

Conformational Plasticity of the Cell-Penetrating Peptide SAP As Revealed by Solid-State 19F-NMR and Circular Dichroism Spectroscopies

The cell-penetrating peptide SAP, which was designed as an amphipathic poly-l-proline helix II (PPII), was suggested to self-assemble into regular fibrils that are relevant for its internalization. Herein we have analyzed the structure of SAP in the membrane-bound state by solid-state ¹⁹F-NMR, which revealed other structural states, in addition to the expected surface-aligned PPII. Trifluoromethyl-bicyclopentyl-glycine (CF₃-Bpg) and two rigid isomers of trifluoromethyl-4,5-methanoprolines (CF₃-MePro) were used as labels for ¹⁹F-NMR analysis. The equilibria between different conformations of SAP were studied and were found to be shifted by the substituents at Pro-11. Synchrotron-CD results suggested that substituting Pro-11 by CF₃-MePro governed the coil-to-PPII equilibrium in solution and in the presence of a lipid bilayer. Using CD and ¹⁹F-NMR, we examined the slow kinetics of the association of SAP with membranes and the dependence of the SAP conformational dynamics on the lipid composition. The peptide did not bind to lipids in the solid ordered phase and aggregated only in the liquid ordered "raft"-like bilayers. Self-association could not be detected in solution or in the presence of liquid disordered membranes. Surface-bound amphipathic SAP in a nonaggregated state was structured as a mixture of nonideal extended conformations reflecting the equilibrium already present in solution, i.e., before binding to the membrane.

Characterization of the cell penetrating properties of a human salivary proline-rich peptide

Saliva contains hundreds of small proline-rich peptides most of which derive from the post-translational and post-secretory processing of the acidic and basic salivary proline-rich proteins. Among these peptides we found that a 20 residue proline-rich peptide (p1932), commonly present in human saliva and patented for its antiviral activity, was internalized within cells of the oral mucosa. The cell-penetrating properties of p1932 have been studied in a primary gingival fibroblast cell line and in a squamous cancer cell line, and compared to its retro-inverso form. We observed by mass-spectrometry, flow cytometry and confocal microscopy that both peptides were internalized in the two cell lines on a time scale of minutes, being the natural form more efficient than the retro-inverso one. The cytosolic localization was dependent on the cell type: both peptide forms were able to localize within nuclei of tumoral cells, but not in the nuclei of gingival fibroblasts. The uptake was shown to be dependent on the culture conditions used: peptide internalization was indeed effective in a complete medium than in a serum-free one allowing the hypothesis that the internalization could be dependent on the cell cycle. Both peptides were internalized likely by a lipid raft-mediated endocytosis mechanism as suggested by the reduced uptake in the presence of methyl-ß-cyclodextrin. These results suggest that the natural peptide may play a role within the cells of the oral mucosa after its secretion and subsequent internalization. Furthermore, lack of cytotoxicity of both peptide forms highlights their possible application as novel drug delivery agents.

TAT and HA2 facilitate cellular uptake of gold nanoparticles but do not lead to cytosolic localisation

The methods currently available to deliver functional labels and drugs to the cell cytosol are inefficient and this constitutes a major obstacle to cell biology (delivery of sensors and imaging probes) and therapy (drug access to the cell internal machinery). As cell membranes are impermeable to most molecular cargos, viral peptides have been used to bolster their internalisation through endocytosis and help their release to the cytosol by bursting the endosomal vesicles. However, conflicting results have been reported on the extent of the cytosolic delivery achieved. To evaluate their potential, we used gold nanoparticles as model cargos and systematically assessed how the functionalisation of their surface by either or both of the viral peptides TAT and HA2 influenced their intracellular delivery. We evaluated the number of gold nanoparticles present in cells after internalisation using photothermal microscopy and their subcellular localisation by electron microscopy. While their uptake increased when the TAT and/or HA2 viral peptides were present on their surface, we did not observe a significant cytosolic delivery of the gold nanoparticles.

Nanooncology: the future of cancer diagnosis and therapy

In recent years, there has been an unprecedented expansion in the field of nanomedicine with the development of new nanoparticles for the diagnosis and treatment of cancer. Nanoparticles have unique biological properties given their small size and large surface area-to-volume ratio, which allows them to bind, absorb, and carry compounds such as small molecule drugs, DNA, RNA, proteins, and probes with high efficiency. Their tunable size, shape, and surface characteristics also enable them to have high stability, high carrier capacity, the ability to incorporate both hydrophilic and hydrophobic substances and compatibility with different administration routes, thereby making them highly attractive in many aspects of oncology. This review article will discuss how nanoparticles are able to function as carriers for chemotherapeutic drugs to increase their therapeutic index; how they can function as therapeutic agents in photodynamic, gene, and thermal therapy; and how nanoparticles can be used as molecular imaging agents to detect and monitor cancer progression.

Selecting improved peptidyl motifs for cytosolic delivery of disparate protein and nanoparticle materials

Cell penetrating peptides facilitate efficient intracellular uptake of diverse materials ranging from small contrast agents to larger proteins and nanoparticles. However, a significant impediment remains in the subsequent compartmentalization/endosomal sequestration of most of these cargoes. Previous functional screening suggested that a modular peptide originally designed to deliver palmitoyl-protein thioesterase inhibitors to neurons could mediate endosomal escape in cultured cells. Here, we detail properties relevant to this peptide's ability to mediate cytosolic delivery of quantum dots (QDs) to a wide range of cell-types, brain tissue culture and a developing chick embryo in a remarkably nontoxic manner. The peptide further facilitated efficient endosomal escape of large proteins, dendrimers and other nanoparticle materials. We undertook an iterative structure-activity relationship analysis of the peptide by discretely modifying key components including length, charge, fatty acid content and their order using a comparative, semiquantitative assay. This approach allowed us to define the key motifs required for endosomal escape, to select more efficient escape sequences, along with unexpectedly identifying a sequence modified by one methylene group that specifically targeted QDs to cellular membranes. We interpret our results within a model of peptide function and highlight implications for in vivo labeling and nanoparticle-mediated drug delivery by using different peptides to co-deliver cargoes to cells and engage in multifunctional labeling.

Targeted quantum dots fluorescence probes functionalized with aptamer and peptide for transferrin receptor on tumor cells

Quantum dots (QDs) fluorescent probes based on oligonucleotide aptamers and peptides with specific molecular recognition have attracted much attention. In this paper, CdSe/ZnS QDs probes for targeted delivery to mouse and human cells using aptamer GS24 and peptide T7 specific to mouse/human transferrin receptors were developed. Capillary electrophoresis analyses indicated that the optimal molar ratios of QDs to aptamer or peptide were 1:5. Fluorescence and confocal microscope imaging revealed QD-GS24 and QD-T7 probes were able to specifically recognize B16 cells and HeLa cells respectively. Quantitative flow cytometry analysis indicated the transportation of QD-GS24 or QD-T7 into cells could be promoted by corresponding free transferrin. Transmission electron microscopy confirmed the uptake of probes in cells and the effective intracellular delivery. MTT assay suggested the cytotoxicity of probes was related to the surface ligand, and aptamer GS24 (or peptide T7) could reduce the cytotoxicity of probes to a certain degree. The study has great significance for preparing QDs fluorescent probes using non-antibody target molecules.

Enhancing the Cellular Delivery of Nanoparticles using Lipo-Oligoarginine Peptides

Nanoparticles have great potential as nanotherapeutics, delivery vectors, and molecular imaging agents due to their flexible properties. Although intracellular and nuclear delivery of nanoparticles is desirable for therapeutic applications, it remains a challenge. Cell penetrating peptides (CPPs) are a powerful tool for the intracellular delivery of various cargoes. Here we report that functionalization of nanoparticles with a myristoylated oligoarginine CPP promoted cellular uptake without increased toxicity. It was evidenced that the myristoylated CPP is much more effective in transporting nanoparticles than the unmodified CPPs.

Detoxifying antitumoral drugs via nanoconjugation: the case of gold nanoparticles and cisplatin

Nanoparticles (NPs) have emerged as a potential tool to improve cancer treatment. Among the proposed uses in imaging and therapy, their use as a drug delivery scaffold has been extensively highlighted. However, there are still some controversial points which need a deeper understanding before clinical application can occur. Here the use of gold nanoparticles (AuNPs) to detoxify the antitumoral agent cisplatin, linked to a nanoparticle via a pH-sensitive coordination bond for endosomal release, is presented. The NP conjugate design has important effects on pharmacokinetics, conjugate evolution and biodistribution and results in an absence of observed toxicity. Besides, AuNPs present unique opportunities as drug delivery scaffolds due to their size and surface tunability. Here we show that cisplatin-induced toxicity is clearly reduced without affecting the therapeutic benefits in mice models. The NPs not only act as carriers, but also protect the drug from deactivation by plasma proteins until conjugates are internalized in cells and cisplatin is released. Additionally, the possibility to track the drug (Pt) and vehicle (Au) separately as a function of organ and time enables a better understanding of how nanocarriers are processed by the organism.

Facile preparation of cationic gold nanoparticle-bioconjugates for cell penetration and nuclear targeting

The present work faces the rising demand of cationic particles of different sizes for biological applications, especially in gene therapies and nanotoxicology studies. A simple phase-transfer methodology has been developed for the functionalization of gold nanoparticles (Au NPs) with a variety of ligands, both cationic and anionic in aqueous solution, employing different nanocrystal sizes with narrow size distributions. Successful functionalization has been demonstrated by UV-vis spectroscopy, DLS, ζ-potential, and FTIR spectroscopy characterization of the particles before and after the phase transfer. The intracellular uptake of the differently charged Au NPs functionalized with peptidic biomolecules was investigated with human fibroblasts (1BR3G) by ICP-MS analysis of the digested cells and confocal fluorescence microscopy, which showed increased internalization of the cationic bioconjugates. Nuclear targeting could be observed by TEM, suggesting that the cationic peptidic biomolecule is acting as a nuclear localization signal.

Synthesis and in vitro inhibition properties of oligonucleotide conjugates carrying amphipathic proline-rich peptide derivatives of the sweet arrow peptide (SAP)

In this study, a series of derivatives of the amphipathic proline-rich sweet arrow peptide (SAP) were covalently linked to antisense oligonucleotides designed to inhibit Renilla luciferase gene. Oligonucleotide-peptide conjugates carrying lysine (Lys) and ornithine (Orn) residues were prepared using the stepwise approach by assembling first the peptide sequence followed by the assembly of the DNA molecule. The resulting Lys, Orn-conjugates were transformed to the corresponding arginine and homoarginine oligonucleotide-peptide conjugates by reaction with O-methylisourea. The introduction of the SAP at 3'-termini of a phosphorothioate oligonucleotide did not affect the ability to inhibit gene expression when transfected with lipofectamine. However, these conjugates were not able to enter cells without transfecting agent. Further studies using SAP as a transfection agent showed promising results for the conjugates carrying the Orn-SAP. All conjugates showed high duplex stabilities.

Gold nanoprobes for theranostics

Gold nanoprobes have become attractive diagnostic and therapeutic agents in medicine and life sciences research owing to their reproducible synthesis with atomic level precision, unique physical and chemical properties, versatility of their morphologies, flexibility in functionalization, ease of targeting, efficiency in drug delivery and opportunities for multimodal therapy. This review highlights some of the recent advances and the potential for gold nanoprobes in theranostics.

Kinetically controlled seeded growth synthesis of citrate-stabilized gold nanoparticles of up to 200 nm: size focusing versus Ostwald ripening

Monodisperse citrate-stabilized gold nanoparticles with a uniform quasi-spherical shape of up to ∼200 nm and a narrow size distribution were synthesized following a kinetically controlled seeded growth strategy via the reduction of HAuCl(4) by sodium citrate. The inhibition of any secondary nucleation during homogeneous growth was controlled by adjusting the reaction conditions: temperature, gold precursor to seed particle concentration, and pH. This method presents improved results regarding the traditional Frens method in several aspects: (i) it produces particles of higher monodispersity; (ii) it allows better control of the gold nanoparticle size and size distribution; and (iii) it leads to higher concentrations. Gold nanoparticles synthesized following this method can be further functionalized with a wide variety of molecules, hence this method appears to be a promising candidate for application in the fields of biomedicine, photonics, and electronics, among others.

Negotiation of intracellular membrane barriers by TAT-modified gold nanoparticles

This paper contributes to the debate on how nanosized objects negotiate membrane barriers inside biological cells. The uptake of peptide-modified gold nanoparticles by HeLa cells has been quantified using atomic emission spectroscopy. The TAT peptide from the HIV virus was singled out as a particularly effective promoter of cellular uptake. The evolution of the intracellular distribution of TAT-modified gold nanoparticles with time has been studied in detail by TEM and systematic image analysis. An unusual trend of particles disappearing from the cytosol and the nucleus and accumulating massively in vesicular bodies was observed. Subsequent release of the particles, both by membrane rupture and by direct transfer across the membrane boundary, was frequently found. Ultimately, near total clearing of particles from the cells occurred. This work provides support for the hypothesis that cell-penetrating peptides can enable small objects to negotiate membrane barriers also in the absence of dedicated transport mechanisms.

Uptake of gold nanoparticles in healthy and tumor cells visualized by nonlinear optical microscopy

Understanding the mechanism underlying the interactions between inorganic nanostructures and biological systems is crucial for several rapidly growing fields that rely on nano-bio interactions. In particular, the further development of cell-targeted drug delivery using metallic nanoparticles (NP) requires new tools for understanding the mechanisms triggered by the contact of NPs with membranes in different cells at the subcellular level. Here we present a novel concept of multimodal microscopy, enabling three-dimensional imaging of the distribution of gold NPs in living, unlabeled cells. Our approach combines multiphoton induced luminescence (MIL) with coherent anti-Stokes Raman scattering (CARS) microscopy. Comparison with transmission electron microscopy (TEM) reveals in vivo sensitivity down to the single nanostructure. By monitoring the incorporation of NPs in human healthy epidermal keratinocytes and squamous carcinoma cells (SCC), we address the feasibility of noninvasive delivery of NPs for therapeutic purposes. While neutralizing PEG coating was confirmed to prevent NP integration in SCCs, an unexpectedly efficient integration of NPs into keratinocytes was observed. These results, independently validated using TEM, demonstrate the need for advanced surface modification protocols to obtain tumor selectivity for NP delivery. The CARS/MIL microscopy platform presented here is thus a promising tool for noninvasive study of the interaction between NPs and cell.

Design, synthesis and characterization of a new anionic cell-penetrating peptide: SAP(E)

Cell-penetrating peptides (CPPs) are powerful tools to transport cell-impermeable cargoes into the cytoplasm without damaging the cell membrane. The vast majority of these peptides described to date share several features, among others, they are positively charged at physiological pH. In several cases a clear correlation between an increasing number of positive charges and internalization properties has been reported. Here, we describe what, to the best of our knowledge, is the first anionic CPP. This new compound SAP(E) internalizes into a range of cell lines with good efficiency and it shows low toxicity. We also report on the internalization mechanism. The discovery of this new class of CPP opens the way to the intracellular delivery of new molecular cargoes.

Insight into cell-entry mechanisms of CPPs by electron microscopy

Despite the quickly widening application of cell-penetrating peptides (CPP) for the cellular delivery of various macromolecules, the cell entry mechanisms of these peptides have remained elusive so far. The basic features of the translocation of CPPs into cells have been mapped by fluorescence microscopy and activity-based assays revealing that endocytotic mechanisms are mainly responsible for the uptake at physiological temperature. However, the high concentration of CPP or the lowering of the incubation temperature below 10°C (re)activates a nonvesicular cell entry mode. The fluorescence microscopy can hardly provide detailed information about the interaction of CPP molecules with the extracellular structures, the induced changes in the morphology of the plasma membrane, etc. Therefore, application of electron microscopy could help to shed light on the nature of nonvesicular uptake mechanism. Transmission electron microscopy (TEM) has been a valuable tool for the morphological characterization of biological material at high resolution. It can provide useful information at the ultrastructural level about the interaction and arrangement of CPPs on the cell surface, the entrapment in cellular organelles and the translocation to the cytoplasm. In this chapter, we present a method for the tagging of CPPs covalently with a 1.4 nm gold cluster and provide a flat-embedding protocol for the mapping of Nanogold™-labeled CPPs in cultured cells by TEM. This method enables to retain the cell monolayers in their in situ orientation. The Nanogold™ tag is putatively not interfering with the uptake of CPPs and enables the production of specimens with excellent morphology and good contrast.

Conjugation of peptides to the passivation shell of gold nanoparticles for targeting of cell-surface receptors

We report the preparation of gold nanoparticles (AuNPs) functionalized with the peptide-toxin conantokin-G and their selective binding to N-methyl-d-aspartate (NMDA) receptors recombinantly expressed by transfected HEK 293 cells. The AuNPs are passivated with a mixed self-assembled monolayer of ω-carboxy- and ω-amino-polyethylene glycol (PEG) thiols. We compare two different passivation systems: the alkyl-PEG600 system is characterized by a C(11)-alkyl chain between the thiol group and the PEG segment, whereas the PEG3000 system lacks this alkyl-chain. We show that only the alkyl-PEG600 passivation system allows selective conjugation of cysteine-terminated peptides to the periphery of the passivation layer via a heterobifunctional linker strategy. In contrast, using the PEG3000 passivation system, peptides are immobilized both on the passivation layer and directly on the gold surface via concurrent place-exchange reaction. We therefore recommend the use of the alkyl-PEG600 system to precisely control the number of immobilized peptides on AuNPs. In fact, we show that the number of conjugated peptides per particle can be varied with good control simply by varying the composition of the self-assembled monolayer. Finally, we demonstrate that conjugation of the conantokin-G peptide to the solvent-exposed interface of the passivation layer results in maximal binding interaction between the peptide-functionalized AuNPs and the targeted NMDA receptors on the cell surface. Conantokin G-coupled AuNP may be used to spatially restrict NMDA-receptor-blockade on neuronal surfaces.

Analysis of time-dependent conjugation of gold nanoparticles with an antiparkinsonian molecule by using curve resolution methods

In this work, the time-dependent conjugation process between a thiolated molecule (with anti-parkinsonian properties) and gold nanoparticles has been monitored and studied by the combined use of fast acquisition Ultra Violet-Visible (UV-Vis) spectra and the ability of Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) technique. From the highly informative kinetic profiles obtained it was possible to extract quantitative and qualitative information of the conjugation process which includes i) time-dependent concentration profiles and pure spectra of species involved on conjugation process, ii) estimation of molecule concentration necessary for the completeness of the conjugation reaction, iii) molecule footprint and iv) free energy of molecule adsorption.

Thermally triggered cellular uptake of quantum dots immobilized with poly(N-isopropylacrylamide) and cell penetrating peptide

Thermally sensitive quantum dots (TSQDs) that exhibit an "on-demand" cellular uptake behavior via temperature-induced "shielding/deshielding" of cell penetrating peptides (CPP) on the surface were fabricated. Poly(N-isopropylacrylamide) (PNIPAAm) (M(w) = 11.5K) and CPP were biotinylated at their terminal ends and co-immobilized on to the surface of streptavidin-coated quantum dots (QDs-Strep) through biotin-streptavidin interaction. The cellular contact of CPP was sterically hindered due to hydrated PNIPAAm chains below the lower critical solution temperature (LCST). In contrast, above the LCST, grafted PNIPAAm chains were collapsed to make CPP moieties resurfaced, leading to increased cellular uptake of QDs. The temperature-controlled "shielding/deshielding" of CPP was further applied for a thermally triggered siRNA delivery system, where biotinylated siRNA was additionally conjugated to the surface of TSQDs. The level of gene silencing was significantly enhanced by increasing temperature above the LCST due to the surface exposure of CPP.

Conjugating folic acid to gold nanoparticles through glutathione for targeting and detecting cancer cells

Gold nanoparticles (GNPs) were modified with glutathione (GSH) to form GSH-capped GNPs, which have carboxyl groups on the surface of these nanoparticles. Then folic acid (FA) was conjugated with GNPs through the reaction between amino group of FA and carboxyl group of GSH. These folic acid-conjugated nanoparticles (FA-GSH-GNPs) were stable in aqueous solution over a broad range of pH and ionic strength values. The targeting of FA-GSH-GNPs in human cervices carcinoma cells (HeLa cells) with high-level folate receptor expression was confirmed by transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM). No cellular uptake of these nanoparticles was observed in A549 cells lack of folate receptor. HeLa cells and mouse fibroblasts incubated with FA-GSH-GNPs were assayed by measuring the relative absorbance of the supernatant collected at low-speed centrifugation. Based on this simple spectroscopic method, HeLa cells have been detected with a detection limit of 10(2)cells/mL.

Intracellular delivery of a membrane-impermeable enzyme in active form using functionalized gold nanoparticles

Gold nanoparticles were coated with a short peptide to promote intracellular delivery of membrane-impermeable proteins. Through microscopy and enzyme assays, we demonstrated the particles were able to transport functional enzymes into a variety of cell lines. Significantly, the transported proteins were able to escape from endosomes. Moreover, these particles showed no apparent cytotoxicity.

Gold nanoparticles delivery in mammalian live cells: a critical review

Functional nanomaterials have recently attracted strong interest from the biology community, not only as potential drug delivery vehicles or diagnostic tools, but also as optical nanomaterials. This is illustrated by the explosion of publications in the field with more than 2,000 publications in the last 2 years (4,000 papers since 2000; from ISI Web of Knowledge, 'nanoparticle and cell' hit). Such a publication boom in this novel interdisciplinary field has resulted in papers of unequal standard, partly because it is challenging to assemble the required expertise in chemistry, physics, and biology in a single team. As an extreme example, several papers published in physical chemistry journals claim intracellular delivery of nanoparticles, but show pictures of cells that are, to the expert biologist, evidently dead (and therefore permeable). To attain proper cellular applications using nanomaterials, it is critical not only to achieve efficient delivery in healthy cells, but also to control the intracellular availability and the fate of the nanomaterial. This is still an open challenge that will only be met by innovative delivery methods combined with rigorous and quantitative characterization of the uptake and the fate of the nanoparticles. This review mainly focuses on gold nanoparticles and discusses the various approaches to nanoparticle delivery, including surface chemical modifications and several methods used to facilitate cellular uptake and endosomal escape. We will also review the main detection methods and how their optimum use can inform about intracellular localization, efficiency of delivery, and integrity of the surface capping.