Oligonucleotide loading determines cellular uptake of DNA-modified gold nanoparticles

In vitro transcription and translation inhibition via DNA functionalized gold nanoparticles

The use of gold nanoparticles (AuNPs) has been gaining momentum as vectors for gene silencing strategies, combining the AuNPs' ease of functionalization with DNA and/or siRNA, high loading capacity and fast uptake by target cells. Here, we used AuNP functionalized with thiolated oligonucleotides to specifically inhibit transcription in vitro, demonstrating the synergetic effect between AuNPs and a specific antisense sequence that blocks the T7 promoter region. Also, AuNPs efficiently protect the antisense oligonucleotide against nuclease degradation, which can thus retain its inhibitory potential. In addition, we demonstrate that AuNPs functionalized with a thiolated oligonucleotide complementary to the ribosome binding site and the start codon, effectively shut down in vitro translation. Together, these two approaches can provide for a simple yet robust experimental set up to test for efficient gene silencing of AuNP-DNA conjugates. What is more, these results show that appropriate functionalization of AuNPs can be used as a dual targeting approach to an enhanced control of gene expression-inhibition of both transcription and translation.

Tailoring DNA structure to increase target hybridization kinetics on surfaces

We report a method for increasing the rate of target hybridization on DNA-functionalized surfaces using a short internal complement DNA (sicDNA) strand. The sicDNA causes up to a 5-fold increase in association rate by inducing a conformational change that extends the DNA away from the surface, making it more available to bind target nucleic acids. The sicDNA-induced kinetic enhancement is a general phenomenon that occurred with all sequences and surfaces investigated. Additionally, the process is selective and can be used in multicomponent systems to controllably and orthogonally "turn on" specific sequences by the addition of the appropriate sicDNA. Finally, we show that sicDNA is compatible with systems used in gene regulation, intracellular detection, and microarrays, suggesting several potential therapeutic, diagnostic, and bioinformatic applications.

Scavenger receptors mediate cellular uptake of polyvalent oligonucleotide-functionalized gold nanoparticles

Mammalian cells have been shown to internalize oligonucleotide-functionalized gold nanoparticles (DNA-Au NPs or siRNA-Au NPs) without the aid of auxiliary transfection agents and use them to initiate an antisense or RNAi response. Previous studies have shown that the dense monolayer of oligonucleotides on the nanoparticle leads to the adsorption of serum proteins and facilitates cellular uptake. Here, we show that serum proteins generally act to inhibit cellular uptake of DNA-Au NPs. We identify the pathway for DNA-Au NP entry in HeLa cells. Biochemical analyses indicate that DNA-Au NPs are taken up by a process involving receptor-mediated endocytosis. Evidence shows that DNA-Au NP entry is primarily mediated by scavenger receptors, a class of pattern-recognition receptors. This uptake mechanism appears to be conserved across species, as blocking the same receptors in mouse cells also disrupted DNA-Au NP entry. Polyvalent nanoparticles functionalized with siRNA are shown to enter through the same pathway. Thus, scavenger receptors are required for cellular uptake of polyvalent oligonucleotide functionalized nanoparticles.

Cellular response of polyvalent oligonucleotide-gold nanoparticle conjugates

Nanoparticles are finding utility in myriad biotechnological applications, including gene regulation, intracellular imaging, and medical diagnostics. Thus, evaluating the biocompatibility of these nanomaterials is imperative. Here we use genome-wide expression profiling to study the biological response of HeLa cells to gold nanoparticles functionalized with nucleic acids. Our study finds that the biological response to gold nanoparticles stabilized by weakly bound surface ligands is significant (cells recognize and react to the presence of the particles), yet when these same nanoparticles are stably functionalized with covalently attached nucleic acids, the cell shows no measurable response. This finding is important for researchers studying and using nanomaterials in biological settings, as it demonstrates how slight changes in surface chemistry and particle stability can lead to significant differences in cellular responses.

Visualizing light-triggered release of molecules inside living cells

The light-triggered release of deoxyribonucleic acid (DNA) from gold nanoparticle-based, plasmon resonant vectors, such as nanoshells, shows great promise for gene delivery in living cells. Here we show that intracellular light-triggered release can be performed on molecules that associate with the DNA in a DNA host-guest complex bound to nanoshells. DAPI (4',6-diamidino-2-phenylindole), a bright blue fluorescent molecule that binds reversibly to double-stranded DNA, was chosen to visualize this intracellular light-induced release process. Illumination of nanoshell-dsDNA-DAPI complexes at their plasmon resonance wavelength dehybridizes the DNA, releasing the DAPI molecules within living cells, where they diffuse to the nucleus and associate with the cell's endogenous DNA. The low laser power and irradiation times required for molecular release do not compromise cell viability. This highly controlled co-release of nonbiological molecules accompanying the oligonucleotides could have broad applications in the study of cellular processes and in the development of intracellular targeted therapies.

Characterizing the localized surface plasmon resonance behaviors of Au nanorings and tracking their diffusion in bio-tissue with optical coherence tomography

The characterization results of the localized surface plasmon resonance (LSPR) of Au nanorings (NRs) with optical coherence tomography (OCT) are first demonstrated. Then, the diffusion behaviors of Au NRs in mouse liver samples tracked with OCT are shown. For such research, aqueous solutions of Au NRs with two different localized surface plasmon resonance (LSPR) wavelengths are prepared and characterized. Their LSPR-induced extinction cross sections at 1310 nm are estimated with OCT scanning of solution droplets on coverslip to show reasonably consistent results with the data at individual LSPR wavelengths and at 1310 nm obtained from transmission measurements of Au NR solutions and numerical simulations. The resonant and non-resonant Au NRs are delivered into mouse liver samples for tracking Au NR diffusion in the samples through continuous OCT scanning for one hour. With resonant Au NRs, the average A-mode scan profiles of OCT scanning at different delay times clearly demonstrate the extension of strong backscattering depth with time. The calculation of speckle variance among successive OCT scanning images, which is related to the local transport speed of Au NRs, leads to the illustrations of downward propagation and spreading of major Au NR motion spot with time.

Phagocytosis of biocompatible gold nanoparticles

We report the evidence for the cellular uptake of gold nanoparticles via the phagocytosis mechanism in murine macrophage cells strongly supported by TEM and optical microscopy. Nanoparticles were prepared using several biocompatible molecules of choice (5-aminovaleric acid, l-DOPA, melatonin, and serotonin hydrochloride) as stabilizers for gold colloids. Their surface chemistry was fully characterized by UV-vis, ATR-FTIR, (1)H NMR, and HR-MAS (1)H NMR spectroscopies, and size distribution was determined by CPS disc centrifuge and TEM. Differences in coatings were evaluated against cellular uptake, and a preferential movement of macrophages toward 5-aminovaleric acid-modified gold nanoparticles was shown, leading to the fast accumulation of nanoparticles in the cytosol.

Functionalized gold nanoparticles for the binding, stabilization, and delivery of therapeutic DNA, RNA, and other biological macromolecules

Nanotechnology has virtually exploded in the last few years with seemingly limitless opportunity across all segments of our society. If gene and RNA therapy are to ever realize their full potential, there is a great need for nanomaterials that can bind, stabilize, and deliver these macromolecular nucleic acids into human cells and tissues. Many researchers have turned to gold nanomaterials, as gold is thought to be relatively well tolerated in humans and provides an inert material upon which nucleic acids can attach. Here, we review the various strategies for associating macromolecular nucleic acids to the surface of gold nanoparticles (GNPs), the characterization chemistries involved, and the potential advantages of GNPs in terms of stabilization and delivery.

Laser ablation-based one-step generation and bio-functionalization of gold nanoparticles conjugated with aptamers

Background

Bio-conjugated nanoparticles are important analytical tools with emerging biological and medical applications. In this context, in situ conjugation of nanoparticles with biomolecules via laser ablation in an aqueous media is a highly promising one-step method for the production of functional nanoparticles resulting in highly efficient conjugation. Increased yields are required, particularly considering the conjugation of cost-intensive biomolecules like RNA aptamers.

Results

Using a DNA aptamer directed against streptavidin, in situ conjugation results in nanoparticles with diameters of approximately 9 nm exhibiting a high aptamer surface density (98 aptamers per nanoparticle) and a maximal conjugation efficiency of 40.3%. We have demonstrated the functionality of the aptamer-conjugated nanoparticles using three independent analytical methods, including an agglomeration-based colorimetric assay, and solid-phase assays proving high aptamer activity. To demonstrate the general applicability of the in situ conjugation of gold nanoparticles with aptamers, we have transferred the method to an RNA aptamer directed against prostate-specific membrane antigen (PSMA). Successful detection of PSMA in human prostate cancer tissue was achieved utilizing tissue microarrays.

Conclusions

In comparison to the conventional generation of bio-conjugated gold nanoparticles using chemical synthesis and subsequent bio-functionalization, the laser-ablation-based in situ conjugation is a rapid, one-step production method. Due to high conjugation efficiency and productivity, in situ conjugation can be easily used for high throughput generation of gold nanoparticles conjugated with valuable biomolecules like aptamers.

Transfection of pancreatic islets using polyvalent DNA-functionalized gold nanoparticles

BACKGROUND

Transplantation of pancreatic islets is an effective treatment for select patients with type 1 diabetes. Improved cellular therapy results may be realized by altering the gene expression profile of transplanted islets. Current viral and nonviral vectors used to introduce nucleic acids for gene regulation hold promise, but safety and efficacy shortcomings motivate the development of new transfection strategies. Polyvalent gold nanoparticles (AuNPs) densely functionalized with covalently immobilized DNA oligonucleotides (AuNP-DNA) are new single entity transfection and gene regulating agents (ie, not requiring lipids, polymers, or viral vectors for cell entry) able to enter cells with high efficiency and no evidence of toxicity. We hypothesize that AuNP-DNA conjugates can efficiently transfect pancreatic islets with no impact on viability or functionality, and can function to regulate targeted gene expression.

METHODS

AuNPs were surface-functionalized with control and antisense DNA oligonucleotides. Purified murine and human islets were exposed to AuNP-DNA conjugates for 24 hours. Islet AuNP-DNA uptake, cell viability, and functionality were measured. Furthermore, the ability of antisense AuNP-DNA conjugates to regulate gene expression was measured using murine islets expressing eGFP.

RESULTS

Collectively, fluorescent confocal microscopy, transmission electron microscopy, mass spectrometry, and flow cytometry revealed substantial penetration of the AuNP-DNA conjugates into the inner core of the islets and within islet cells. No change in cellular viability occurred and the insulin stimulation index was unchanged in treated versus untreated islets. Transplantation of AuNP-DNA treated islets cured diabetic nude mice. Functionally, antisense eGFP AuNP-DNA conjugates reduced eGFP expression in MIP-eGFP islets.

CONCLUSION

Polyvalent AuNP-DNA conjugates may represent the next generation of nucleic acid-based therapeutic agents for improving pancreatic islet engraftment, survival, and long-term function.

Tailored design of Au nanoparticle-siRNA carriers utilizing reversible addition-fragmentation chain transfer polymers

The facile synthesis of polymer-stabilized Au nanoparticles (AuNPs) capable of forming neutral, sterically stable complexes with small interfering RNA (siRNA) is reported. The amine-containing cationic block of poly(N-2-hydroxypropyl methacrylamide(70)-block-N-[3-(dimethylamino)propyl] methacrylamide(24)) [P(HPMA(70)-b-DMAPMA(24))] was utilized to promote the in situ reduction of Au(3+) to AuNPs and subsequently bind small interfering RNA, while the nonimmunogenic, hydrophilic block provided steric stabilization. The ratio of [DMAPMA](0)/[Au(3+)](0) utilized in the reduction reaction was found to be critical to the production of polymer-stabilized AuNPs capable of complexing siRNA. Significant protection ( approximately 100 times) against nucleases was demonstrated by enzymatic tests, while gene down-regulation experiments indicated successful delivery of siRNA to cancerous cells.

Hairpin DNA-functionalized gold colloids for the imaging of mRNA in live cells

A strategy is presented for the live cell imaging of messenger RNA using hairpin DNA-functionalized gold nanoparticles (hAuNP). hAuNP improve upon technologies for studying RNA trafficking by their efficient internalization within live cells without transfection reagents, improved resistance to DNase degradation, low cytotoxicity, and the incorporation of hairpin DNA molecular beacons to confer high specificity and sensitivity to the target mRNA sequence. Furthermore, the targeted nanoparticle-beacon construct, once bound to the target mRNA sequence, remains hybridized to the target, enabling spatial and temporal studies of RNA trafficking and downstream analysis. Targeted hAuNP exhibited high specificity for glyceraldehyde 3-phosphate dehydrogenase (GADPH) mRNA in live normal HEp-2 cells and respiratory syncytial virus (RSV) mRNA in live RSV-infected HEp-2 cells with high target to background ratios. Multiplexed fluorescence imaging of distinct mRNAs in live cells and simultaneous imaging of mRNAs with immunofluorescently stained protein targets in fixed cells was enabled by appropriate selection of molecular beacon fluorophores. Pharmacologic analysis suggested that hAuNP were internalized within cells via membrane-nanoparticle interactions. hAuNP are a promising approach for the real-time analysis of mRNA transport and processing in live cells for elucidation of biological processes and disease pathogenesis.

Ultrasonic resonator technology as a new quality control method evaluating gelatin nanoparticles

Nanomedicine is a quickly evolving field where more and more possible applications become evident and start entering clinical trials or even the market. However, the analytic methods are not always able to keep pace with the new formulations' demands. One example of a promising medical implementation is oligodeoxynucleotide (ODN) delivery by gelatin nanoparticles (GNPs). Currently, quality control is dependent on either some time consuming or destructive spectrometric, chromatographic or electrophoretic methods. A possible enlargement of the portfolio by Ultrasonic Resonator Technology (URT) is investigated here by subjecting plain GNPs in various sizes and concentrations as well as ODN-loaded GNPs to URT analysis. If calibrated by photon correlation spectroscopy (PCS) and other spectroscopy methods for each single nanoparticle system parameter, URT is an efficient and non-destructive technique and serves as a broad characterization method. URT is emphasized to play a possible future part in the size, concentration and ODN loading monitoring, e.g. of gelatin nanoparticles in the course of formulation development.

Delivery of shRNA using gold nanoparticle-DNA oligonucleotide conjugates as a universal carrier

The efficient delivery of nucleic acids into mammalian cells is a central aspect of research involving cell biology and medical applications, including the clinical treatment of genetic disorders. We report an efficient small hairpin RNA (shRNA) delivery system that utilizes a single species of gold nanoparticle-DNA oligonucleotide conjugate (AuNP-DNA oligo) as a universal carrier. In vitro synthesized shRNA that is specific to the p53 gene was efficiently delivered into HEK293 and HeLa human cell lines using an AuNP-DNA oligo. The delivery resulted in an 80-90% knockdown of p53 expression. The same AuNP-DNA oligo was also efficient for the delivery of another shRNA, which is specific to the Mcl-1 gene, as well as the repression of MCL-1 expression. The knockdown efficiency of shRNA that was delivered using an AuNP-DNA oligo was comparable with that of a liposome-based shRNA delivery method. Our results offer an alternate delivery system for shRNA that can be used on any gene of interest.

The Polyvalent Gold Nanoparticle Conjugate-Materials Synthesis, Biodiagnostics, and Intracellular Gene Regulation

Advances in nanoscale directed assembly strategies have enabled researchers to analogize atomic assembly via chemical reactions and nanoparticle assembly, creating a new nanoscale "periodic table." We are just beginning to realize the nanoparticle equivalents of molecules and extended materials and are currently developing the ground rules for creating programmable nanometer-scale coordination environments. The ability to create a diverse set of nanoscale architectures from one class of nanoparticle building blocks would allow for the synthesis of designer materials, wherein the physical properties of a material could be predicted and controlled a priori. Our group has taken the first steps toward this goal and developed a means of creating tailorable assembly environments using DNA-nanoparticle conjugates. These nanobioconjugates combine the discrete plasmon resonances of gold nanoparticles with the synthetically controllable and highly selective recognition properties of DNA. Herein, we elucidate the beneficial properties of these materials in diagnostic, therapeutic, and detection capabilities and project their potential use as nanoscale assembly agents to realize complex three-dimensional nanostructures.

Synthesis of gelatin-stabilized gold nanoparticles and assembly of carboxylic single-walled carbon nanotubes/Au composites for cytosensing and drug uptake

Gelatin-stabilized gold nanoparticles (AuNPs-gelatin) with hydrophilic and biocompatible were prepared with a simple and "green" route by reducing in situ tetrachloroauric acid in gelatin. The nanoparticles showed the excellent colloidal stability. UV-vis spectra, transmission electron microscopy (TEM), and atomic force microscopy revealed the formation of well-dispersed AuNPs with different sizes. By combination of the biocompatibility of AuNPs and excellent conductivity of carboxylic single-walled carbon nanotubes (c-SWNTs), a novel nanocomposite was designed for the immobilization and cytosensing of HL-60 cells at electrodes. The immobilized cells showed sensitive voltammetric response, good activity, and increased electron-transfer resistance. It can be used as a highly sensitive impedance sensor for HL-60 cells ranging from 1 x 10(4) to 1 x 10(7) cell mL(-1) with a limit of detection of 5 x 10(3) cell mL(-1). Moreover, the nanocomposite could effectively facilitate the interaction of adriamycin (ADR) with HL-60 cells and remarkably enhance the permeation and drug uptake of anticancer agents in the cancer cells, which could readily lead to the induction of the cell death of leukemia cells.

DNA-incorporating nanomaterials in biotechnological applications

The recently developed ability to controllably connect biological and inorganic objects on a molecular scale opens a new page in biomimetic methods with potential applications in biodetection, tissue engineering, targeted therapeutics and drug/gene delivery. Particularly in the biodetection arena, a rapid development of new platforms has largely been stimulated by a spectrum of novel nanomaterials with physical properties that offer efficient, sensitive and inexpensive molecular sensing. Recently, DNA-functionalized nano-objects have emerged as a new class of nanomaterials that can be controllably assembled in predesigned structures. Such DNA-based nanoscale structures might provide a new detection paradigm due to their regulated optical, electrical and magnetic responses, chemical heterogeneity and high local biomolecular concentration. The specific biorecognition DNA and its physical-chemical characteristics allows for an exploitation of DNA-functionalized nanomaterials for sensing of nucleic acids, while a broad tunability of DNA interactions permits extending their use for detection of proteins, small molecules and ions. We discuss the progress that was achieved in the last decade in the exploration of new detection methods based on DNA-incorporating nanomaterials as well as their applications to gene delivery. The comparison between various detection platforms, their sensitivity and selectivity, and specific applications are reviewed.

DNA-mediated control of metal nanoparticle shape: one-pot synthesis and cellular uptake of highly stable and functional gold nanoflowers

The effects of different DNA molecules of the same length on the morphology of gold nanoparticles during synthesis are investigated. While spherical nanoparticles (AuNS) are observed in the presence of 30-mer poly T, like that in the absence of DNA, 30-mer poly A or poly C induces formation of the flower-shaped gold nanoparticle (AuNF). Detailed mechanistic studies indicate that the difference in DNA affinity to the AuNP plays a major role in the different morphology control processes. The DNA adsorbed on the AuNS surface could act as template to mediate the formation of flower-like gold nanoparticles. The formation of the AuNF can result from either selective deposition of the reduced gold metal on AuNS templated by surface bound DNA or uneven growth of the AuNS due to the binding of DNA to the surface. Furthermore, DNA functionalization with high stability was realized in situ during the one-step synthesis while retaining their biorecognition ability, allowing programmable assembly of new nanostructures. We have also shown that the DNA-functionalized nanoflowers can be readily uptaken by cells and visualized under dark-field microscopy.

A functionalized gold nanoparticles-assisted universal carrier for antisense DNA

In this study, single-stranded DNA functionalized gold nanoparticles (AuNP GDS) were proved to be efficient gene delivery systems for oligo antisense DNAs specific to any gene of interest without affecting normal cell physiology.

Interaction of multi-functional silver nanoparticles with living cells

Silver nanoparticles (AgNPs) are widely used in household products and in medicine due to their antibacterial and to wound healing properties. In recent years, there is also an effort for their use in biomedical imaging and photothermal therapy. The primary reason behind the effort for their utility in biomedicine and therapy is their unique plasmonic properties and easy surface chemistry for a variety of functionalizations. In this study, AgNPs modified with glucose, lactose, oligonucleotides and combinations of these ligands are investigated for their cytotoxicity and cellular uptake in living non-cancer (L929) and cancer (A549) cells. It is found that the chemical nature of the ligand strongly influences the toxicity and cellular uptake into the model cells. While the lactose-and glucose-modified AgNPs enter the L929 cells at about the same rate, a significant increase in the rate of lactose-modified AgNPs into the A549 cells is observed. The binding of oligonucleotides along with the carbohydrate on the AgNP surfaces influences the differential uptake rate pattern into the cells. The cytotoxicity study with the modified AgNPs reveals that only naked AgNPs influence the viability of the A549 cells. The findings of this study may provide the key to developing effective applications in medicine such as cancer therapy.

DNA nanomedicine: Engineering DNA as a polymer for therapeutic and diagnostic applications

Nanomedicine, the application of nanotechnology to medicine, encompasses a broad spectrum of fields including molecular detection, diagnostics, drug delivery, gene regulation and protein production. In recent decades, DNA has received considerable attention for its functionality and versatility, allowing it to help bridge the gap between materials science and biological systems. The use of DNA as a structural nanoscale material has opened a new avenue towards the rational design of DNA nanostructures with different polymeric topologies. These topologies, in turn, possess unique characteristics that translate to specific therapeutic and diagnostic strategies within nanomedicine.

Gold nanoparticles for biology and medicine

Gold colloids have fascinated scientists for over a century and are now heavily utilized in chemistry, biology, engineering, and medicine. Today these materials can be synthesized reproducibly, modified with seemingly limitless chemical functional groups, and, in certain cases, characterized with atomic-level precision. This Review highlights recent advances in the synthesis, bioconjugation, and cellular uses of gold nanoconjugates. There are now many examples of highly sensitive and selective assays based upon gold nanoconjugates. In recent years, focus has turned to therapeutic possibilities for such materials. Structures which behave as gene-regulating agents, drug carriers, imaging agents, and photoresponsive therapeutics have been developed and studied in the context of cells and many debilitating diseases. These structures are not simply chosen as alternatives to molecule-based systems, but rather for their new physical and chemical properties, which confer substantive advantages in cellular and medical applications.

Polyvalent oligonucleotide iron oxide nanoparticle "click" conjugates

We have utilized the copper-catalyzed azide-alkyne reaction to form a dense monolayer of oligonucleotides on a superparamagnetic nanoparticle core. These particles exhibit the canonical properties of materials densely functionalized with DNA, which can be controlled by modulating the density of oligonucleotides on the surface of the particles. Furthermore, like their Au analogues, these particles can easily cross HeLa (cervical cancer) cell membranes without transfection agents due to their dense DNA shell. Importantly, this approach should be generalizable to other azide-functionalized particles.

Regulating immune response using polyvalent nucleic acid-gold nanoparticle conjugates

The immune response of macrophage cells to internalized polyvalent nucleic acid-functionalized gold nanoparticles has been studied. This study finds that the innate immune response (as measured by interferon-beta levels) to densely functionalized, oligonucleotide-modified nanoparticles is significantly less (up to a 25-fold decrease) when compared to a lipoplex carrying the same DNA sequence. The magnitude of this effect is inversely proportional to oligonucleotide density. It is proposed that the enzymes involved in recognizing foreign nucleic acids and triggering the immune response are impeded due to the local surface environment of the particle, in particular high charge density. The net effect is an intracelluar gene regulation agent that elicits a significantly lower cellular immune response than conventional DNA transfection materials.

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.

Polyvalent oligonucleotide gold nanoparticle conjugates as delivery vehicles for platinum(IV) warheads

Amine-functionalized polyvalent oligonucleotide gold nanoparticles (DNA-Au NPs) were derivatized with a cisplatin prodrug, and the resulting DNA-Au NP conjugates were used to internalize multiple platinum centers. A platinum(IV) complex, c,c,t-[Pt(NH(3))(2)Cl(2)(OH)(O(2)CCH(2)CH(2)CO(2)H)], was tethered to the surface of DNA-Au NPs through amide linkages. The platinum-tethered gold nanoparticles were taken into several cancer cells. The drop in intracellular pH facilitated reductive release of cisplatin from the prodrug, which then formed 1,2-d(GpG) intrastrand cross-links in the cell nuclei, as confirmed by an antibody specific for this adduct. The cytotoxicity of the platinum(IV) complex increases significantly in several cancer cell lines when the complex is attached to the surface of the DNA-Au NPs and in some instances exceeds that of cisplatin.

Effect of surface properties on nanoparticle-cell interactions

The interaction of nanomaterials with cells and lipid bilayers is critical in many applications such as phototherapy, imaging, and drug/gene delivery. These applications require a firm control over nanoparticle-cell interactions, which are mainly dictated by surface properties of nanoparticles. This critical Review presents an understanding of how synthetic and natural chemical moieties on the nanoparticle surface (in addition to nanoparticle shape and size) impact their interaction with lipid bilayers and cells. Challenges for undertaking a systematic study to elucidate nanoparticle-cell interactions are also discussed.

Directed evolution of gold nanoparticle delivery to cells

A newly selected anti-receptor (anti-EGFR) aptamer was conjugated to gold nanoparticles via a facile hybridization method and was found to specifically and quantitatively direct the delivery of gold nanoparticles to cells expressing EGFR through receptor-mediated endocytosis.

Controlled delivery of antisense oligonucleotides: a brief review of current strategies

Antisense therapy has been investigated extensively over the past two decades, either experimentally for gene functional research or clinically as therapeutic agents owing to the conceptual simplicity, ease of design and low cost. The concept of this therapeutic approach is promising because short antisense oligonucleotides (ASOs) can be delivered into target cells for specific hybridisation with target mRNA, resulting in the inhibition of the expression of pathogenic genes. However, the efficient delivery of the ASO molecules into target cells remains challenging; this bottleneck together with several other technical hurdles need to be overcome before this approach becomes effective and widely adopted. A variety of vectors such as lipids, polymers, peptides and nanoparticles have been explored. This review outlines the recent advances of the non-viral ASO delivery strategies. Several recent scientific studies, including authors' contributions, have been selected to highlight the technical aspects of ASO delivery.

Aptamer nano-flares for molecular detection in living cells

We demonstrate a composite nanomaterial, termed an aptamer nano-flare, that can directly quantify an intracellular analyte in a living cell. Aptamer nano-flares consist of a gold nanoparticle core functionalized with a dense monolayer of nucleic acid aptamers with a high affinity for adenosine triphosphate (ATP). The probes bind selectively to target molecules and release fluorescent reporters which indicate the presence of the analyte. Additionally, these nanoconjugates are readily taken up by cells where their signal intensity can be used to quantify intracellular analyte concentration. These nanoconjugates are a promising approach for the intracellular quantification of other small molecules or proteins, or as agents that use aptamer binding to elicit a biological response in living systems.

Nano-flares for mRNA regulation and detection

We build off the previously described concept of a nanoflare to develop an oligonucleotide gold nanoparticle conjugate that is capable of both detecting and regulating intracellular levels of mRNA. We characterize the binding rate and specificity of these materials using survivin, a gene associated with the diagnosis and treatment of cancer, as a target. The nanoconjugate enters cells and binds mRNA, thereby decreasing the relative abundance of mRNA in a dose- and sequence-dependent manner, resulting in a fluorescent response. This represents the first demonstration of a single material capable of both mRNA regulation and detection. Further, we investigate the intracellular biochemistry of the nanoconjugate, elucidating its mechanism of gene regulation. This work is important to the study of biologically active nanomaterials such as the nanoflare and is a first step toward the development of an mRNA responsive "theranostic".

Multiple alignment modes for nematic liquid crystals doped with alkylthiol-capped gold nanoparticles

The ability of alkylthiol capped gold nanoparticles (Au NPs) to tune, alter, and reverse the alignment of nematic liquid crystals (LCs) has been investigated in detail. Adjusting the concentration of the suspended Au NPs in the nematic LC host, optimizing the sample preparation protocol, or providing different sample substrates (untreated glass slides, rubbed polyimide-coated LC test cell, or ITO-coated glass slides) results in several LC alignment scenarios (modes) including vertical alignment, planar alignment, and a thermally controlled alignment switch between these two alignment modes. The latter thermal switch between planar and homeotropic alignment was observed particularly for lower concentrations (i.e., around 1 to 2 wt %) of suspended NPs in the size regime of 1.5-2 nm and was found to be concentration-dependent and thermally reversible. Different scenarios are discussed that could explain these induced alignment modes. In one scenario, the NP-induced alignment is related to the temperature-dependent change of the order parameter, S, of the nematic phase (ordering in the bulk). In the second scenario, a change of the ordering of the nematic molecules around the NPs that reside at the interfaces is described. We also started to test spin coating as an alternative way of preparing nematic thin films with well-separated Au NPs on the substrate and found this to be a possible method for manufacturing of future NP-doped LC devices, as this method produced evenly distributed NPs on glass substrates. Together the presented findings continue to pave the way for LC display-related applications of Au NP-doped nematic LCs and provide insights for N-LC sensor applications.

Laser-Activated Gene Silencing via Gold Nanoshell-siRNA Conjugates

The temporal and spatial control over the delivery of materials such as siRNA into cells remains a significant technical challenge. We demonstrate the pulsed near-infrared (NIR) laser-dependent release of siRNA from coated 40 nm gold nanoshells. Tat-lipid coating mediates the cellular uptake of the nanomaterial at picomolar concentration, while spatiotemporal silencing of a reporter gene (green fluorescence protein) was studied using photomasking. The NIR laser-induced release of siRNA from the nanoshells is found to be power- and time-dependent, through surface-linker bond cleavage, while the escape of the siRNA from endosomes occurs above a critical pulse energy attributed to local heating and cavitation. NIR laser-controlled drug release from functional nanomaterials should facilitate more sophisticated developmental biology and therapeutic studies.

Gold, poly(beta-amino ester) nanoparticles for small interfering RNA delivery

The safe and effective delivery of RNA therapeutics remains the major barrier to their broad clinical application. Here we develop a new nanoparticulate delivery system based on inorganic particles and biodegradable polycations. First, gold nanoparticles were modified with the hydrophilic polymer poly(ethylene glycol) (PEG), and then small interfering RNA (siRNA) was conjugated to the nanoparticles via biodegradable disulfide linkages, with approximately 30 strands of siRNA per nanoparticle. The particles were then coated with a library of end-modified poly(beta-amino ester)s (PBAEs), previously identified as capable of facilitating intracellular DNA delivery. Nanoparticulate formulations developed here facilitate high levels of in vitro siRNA delivery, facilitating delivery as good or better than the commercially available lipid reagent, Lipofectamine 2000.

Colloidal nanocarriers: a review on formulation technology, types and applications toward targeted drug delivery

Colloidal nanocarriers, in their various forms, have the possibility of providing endless opportunities in the area of drug delivery. The current communication embodies an in-depth discussion of colloidal nanocarriers with respect to formulation aspects, types, and site-specific drug targeting using various forms of colloidal nanocarriers with special insights to the field of oncology. Specialized nanotechnological approaches like quantum dots, dendrimers, integrins, monoclonal antibodies, and so forth, which have been extensively researched for targeted delivery of therapeutic and diagnostic agents, are also discussed. Nanotechnological patents, issued by the U.S. Patent and Trademark Office in the area of drug delivery, are also included in this review to emphasize the importance of nanotechnology in the current research scenario.

FROM THE CLINICAL EDITOR

Colloidal nanocarriers provide almost endless opportunities in the area of drug delivery. While the review mainly addresses potential oncological applications, similar approaches may be applicable in other conditions with a requirement for targeted drug delivery. Technologies including quantum dots, dendrimers, integrins, monoclonal antibodies are discussed, along with US-based patents related to these methods.

Toxicity of therapeutic nanoparticles

A total of six nanotherapeutic formulations are already approved for medical use and more are in the approval pipeline currently. Despite the massive research effort in nanotherapeutic materials, there is relatively little information about the toxicity of these materials or the tools needed to assess this toxicity. Recently, the scientific community has begun to respond to the paucity of information by investing in the field of nanoparticle toxicology. This review is intended to provide an overview of the techniques needed to assess toxicity of these therapeutic nanoparticles and to summarize the current state of the field. We begin with background on the toxicological assessment techniques used currently as well as considerations in nanoparticle dosing. The toxicological research overview is divided into the most common applications of therapeutic nanoparticles: drug delivery, photodynamic therapy and bioimaging. We end with a perspective section discussing the current technological gaps and promising research aimed at addressing those gaps.

Layer-by-layer assembled gold nanoparticles for siRNA delivery

Although uptake into cells is highly complex and regulated, heterogeneous particle collectives are usually employed to deliver small interfering RNA (siRNA) to cells. Within these collectives, it is difficult to accurately identify the active species, and a decrease in efficacy is inherent to such preparations. Here, we demonstrate the manufacture of uniform nanoparticles with the deposition of siRNA on gold in a layer-by-layer approach, and we further report on the cellular delivery and siRNA activity as functions of surface properties.

Asymmetric charge renormalization for nanoparticles in aqueous media

The effective renormalized charge of nanoparticles in an aqueous electrolyte is essential to determine their solubility. By using a molecular model for the supporting aqueous electrolyte, we find that the effective renormalized charge of the nanoparticles is strongly dependent on the sign of the bare charge. Negatively charged nanoparticles have a lower effective renormalized charge than positively charged nanoparticles. The degree of asymmetry is a nonmonotonic function of the bare charge of the nanoparticle. We show that the effect is due to the asymmetric charge distribution of the water molecules, which we model using a simple three-site molecular structure of point charges.

Curvature effects in DNA:Au nanoparticle conjugates

DNA-coated Au nanoparticles have myriad applications as versatile building blocks in nanomaterials assembly, powerful amplification tags for bioanalysis, and promising new approaches to medical therapeutics. Characterization, control, and a thorough understanding of the DNA surface interface are essential in the development of these conjugates. A new paper in this issue explores the impact of nanosphere diameter on DNA adsorption and demonstrates that particle curvature plays an important role in controlling the DNA surface density. The study proposes a model that can be used to predict DNA packing on nonspherical particles and validates it using Au nanorods. This work paves the way for improved understanding of the DNA:Au interface in these versatile bioconjugates.