Light-induced release of DNA from plasmon-resonant nanoparticles: Towards light-controlled gene therapy

Plasmonic-Driven Regulation of Biomolecular Activity In Situ

Selective and remote manipulation of activity for biomolecules, including protein, DNA, and lipids, is crucial to elucidate their molecular function and to develop biomedical applications. While advances in tool development, such as optogenetics, have significantly impacted these directions, the requirement for genetic modification significantly limits their therapeutic applications. Plasmonic nanoparticle heating has brought new opportunities to the field, as hot nanoparticles are unique point heat sources at the nanoscale. In this review, we summarize fundamental engineering problems such as plasmonic heating and the resulting biomolecular responses. We highlight the biological responses and applications of manipulating biomolecules and provide perspectives for future directions in the field.

Smaller Gold Nanoparticles Release DNA More Efficiently During fs Laser Pulsed Optical Heating

This work investigates the effect of plasmonic gold nanoparticle (AuNP) size on the rate of thermal release of single-stranded oligonucleotides under femtosecond (fs)-pulsed laser irradiation sources. Contrary to the theoretical predictions that larger AuNPs (50-60 nm diameter) would produce the most solution heating and fastest DNA release, it is found that smaller AuNP diameters (25 nm) lead to faster dsDNA denaturation rates. Controlling for the pulse energy fluence, AuNP concentration, DNA loading density, and the distance from the AuNP surface finds the same result. These results imply that the solution temperature increases around the AuNP during fs laser pulse optical heating may not be the only significant influence on dsDNA denaturation, suggesting that direct energy transfer from the AuNP to the DNA (phonon-phonon coupling), which is increased as AuNPs decrease in size, may play a significant role.

Electron-Induced Damage by UV Photolysis of DNA Attached to Gold Nanoparticles

Photolysis of DNA attached to gold nanoparticles (AuNPs) with ultraviolet (UV) photons induces DNA damage. The release of nucleobases (Cyt, Gua, Ade, and Thy) from DNA was the major reaction (99%) with an approximately equal release of pyrimidines and purines. This reaction contributes to the formation of abasic sites in DNA. In addition, liquid chromatography-mass spectrometry/MS (LC-MS/MS) analysis revealed the formation of reduction products of pyrimidines (5,6-dihydrothymidine and 5,6-dihydro-2'-deoxyuridine) and eight 2',3'- and 2',5'-dideoxynucleosides. In contrast, there was no evidence of the formation of 5-hydroxymethyluracil and 8-oxo-7,8-dihydroguanine, which are common oxidation products of thymine and guanine, respectively. Using appropriate filters, the main photochemical reactions were found to involve photoelectrons ejected from AuNPs by UV photons. The contribution of "hot" conduction band electrons with energies below the photoemission threshold was minor. The mechanism for the release of free nucleobases by photoelectrons is proposed to take place by the initial formation of transient molecular anions of the nucleobases, followed by dissociative electron attachment at the C1'-N glycosidic bond connecting the nucleobase to the sugar-phosphate backbone. This mechanism is consistent with the reactivity of secondary electrons ejected by X-ray irradiation of AuNPs attached to DNA, as well as the reactions of various nucleic acid derivatives irradiated with monoenergetic very-low-energy electrons (∼2 eV). These studies should help us to understand the chemistry of nanoparticles that are exposed to UV light and that are used as scaffolds and catalysts in molecular biology, curative agents in photodynamic therapy, and components of sunscreens and cosmetics.

Controlled Release of DNA Binding Anticancer Drugs from Gold Nanoparticles with Near-Infrared Radiation

Traditional chemotherapies target rapidly developing cells in the human body resulting in harsh side effects including fatigue, immune system suppression, and nausea, among others. Delivery systems to focus the active pharmaceutical ingredients (APIs) to the diseased tissue can diminish the negative side effects while improving treatment outcomes. Gold nanoparticles (AuNP) offer many unique advantages as drug delivery vehicles, including being biologically inert, easily adaptable to various shapes and sizes, able to create a strong Au-thiol bond, and able to generate heat upon the absorption of near-infrared light. To this end, a AuNP delivery vehicle was engineered to load and release two DNA binding anti-cancer drugs, mithramycin and doxorubicin, in a controlled fashion. The drugs were loaded onto the surface of the AuNP with temperature sensitive linkages. The amount of heat generated, and subsequent release of the drugs was controlled by the irradiation time with a near-infrared laser. By modulating the linkage used to load the drugs three different release profiles were able to be achieved, indicating the feasibility of such a system for combinational therapy requiring sequential release of APIs.

Liposome-Tethered Gold Nanoparticles Triggered by Pulsed NIR Light for Rapid Liposome Contents Release and Endosome Escape

Remote triggering of contents release with micron spatial and sub-second temporal resolution has been a long-time goal of medical and technical applications of liposomes. Liposomes can sequester a variety of bioactive water-soluble ions, ligands and enzymes, and oligonucleotides. The bilayer that separates the liposome interior from the exterior solution provides a physical barrier to contents release and degradation. Tethering plasmon-resonant, hollow gold nanoshells to the liposomes, or growing gold nanoparticles directly on the liposome exterior, allows liposome contents to be released by nanosecond or shorter pulses of near-infrared light (NIR). Gold nanoshells or nanoparticles strongly adsorb NIR light; cells, tissues, and physiological media are transparent to NIR, allowing penetration depths of millimeters to centimeters. Nano to picosecond pulses of NIR light rapidly heat the gold nanoshells, inducing the formation of vapor nanobubbles, similar to cavitation bubbles. The collapse of the nanobubbles generates mechanical forces that rupture bilayer membranes to rapidly release liposome contents at the preferred location and time. Here, we review the syntheses, characterization, and applications of liposomes coupled to plasmon-resonant gold nanostructures for delivering a variety of biologically important contents in vitro and in vivo with sub-micron spatial control and sub-second temporal control.

Mechanistic Understanding of DNA Denaturation in Nanoscale Thermal Gradients Created by Femtosecond Excitation of Gold Nanoparticles

There is significant interest in developing photothermal systems that can precisely control the structure and function of biomolecules through local temperature modulation. One specific application is the denaturation of double-stranded (ds) DNA through femtosecond (fs) laser pulse optical heating of gold nanoparticles (AuNPs); however, the mechanism of DNA melting in these systems is not fully understood. Here, we utilize 55 nm AuNPs with surface-tethered dsDNA, which are locally heated using fs laser pulses to induce DNA melting. By varying the dsDNA distance from the AuNP surface and the laser pulse energy fluence, this system is used to study how the nanosecond duration temperature increase and the steep temperature gradient around the AuNP affect dsDNA dehybridization. Through modifying the distance between the dsDNA and AuNP surface by 3.8 nm in total and the pulse energy fluence from 7.1 to 14.1 J/m², the dehybridization rates ranged from 0.002 to 0.05 DNA per pulse, and the total amount of DNA released into solution was controlled over a range of 26-93% in only 100 s of irradiation. By shifting the dsDNA position as little as ∼1.1 nm, the average dsDNA dehybridization rate is altered up to 30 ± 2%, providing a high level of control over DNA melting and release. By comparing the theoretical temperature around the dsDNA to the experimentally derived temperature, we find that maximum or peak temperatures have a greater influence on the dehybridization rate when the dsDNA is closer to the AuNP surface and when lower laser pulse fluences are used. Furthermore, molecular dynamics simulations mimicking the photothermal heat pulse around a AuNP provide mechanistic insight into the stochastic nature of dehybridization and demonstrate increased base pair separation near the AuNP surface during laser pulse heating when compared to steady-state heating. Understanding how biological materials respond to the short-lived and non-uniform temperature increases innate to fs laser pulse optical heating of AuNPs is critical to improving the functionality and precision of this technique so that it may be implemented into more complex biological systems.

Photothermal-triggered system for oligonucleotides delivery from cationic gold nanorods surface: A molecular dynamic investigation

Bioconjugate gold-based nanostructures combining the plasmonic photothermal effect with photothermal-triggered DNA delivery are appealing materials for medical diagnostic and therapy for cell-based disease. In this study, we demonstrate the use of surface hybridization to prepare DNA-modified gold nanorods to be used as photo-delivery system for single stranded oligonucleotides. The as prepared DNA modified gold nanorods have strong absorption bands in the visible and near-infrared regions in which the absorbed light through photothermal effect, induces a surface temperature increasing up to the melting temperature with consequent DNA release. No evident DNA release was observed below the melting temperature. The experimental data were supported by molecular dynamic simulation investigation, showing the kinetics aspect of dsDNA de-hybridization at gold nanorods surface at temperature below (298 K) and above (333 K) the melting temperature of sequence investigated. We demonstrate that the cationic charges of surfactant, localized at nanorods surface, induce a remarkable de-hybridization of strands DNA, as confirmed by an increasing of hybridization enthalpy value of about 7 kcal/mol and by a faster de-hybridization process, respect the model of gold nanorods without positive charges. These data were corroborated by the increasing of the root mean square deviation value (about 4.4 Å, calculated at 333 K) indicating that the presence of cationic headgroup at gold surface induce separation of the double strand. This finding data paving the way for the development of nanostructured material for photothermal-triggered delivery systems of DNA for gene therapy application.

Gold Nanoparticles in Glioma Theranostics

Despite many endeavors to treat malignant gliomas in the last decades, the median survival of patients has not significantly improved. The infiltrative nature of high-grade gliomas and the impermeability of the blood-brain barrier to the most therapeutic agents remain major hurdles, impeding an efficacious treatment. Theranostic platforms bridging diagnosis and therapeutic modalities aim to surmount the current limitations in diagnosis and therapy of glioma. Gold nanoparticles (AuNPs) due to their biocompatibility and tunable optical properties have widely been utilized for an assortment of theranostic purposes. In this Review, applications of AuNPs as imaging probes, drug/gene delivery systems, radiosensitizers, photothermal transducers, and multimodal theranostic agents in malignant gliomas are discussed. This Review also aims to provide a perspective on cancer theranostic applications of AuNPs in future clinical trials.

Remotely controlled opening of delivery vehicles and release of cargo by external triggers

Tremendous efforts have been devoted to the development of future nanomedicines that can be specifically designed to incorporate responsive elements that undergo modification in structural properties upon external triggers. One potential use of such stimuli-responsive materials is to release encapsulated cargo upon excitation by an external trigger. Today, such stimuli-response materials allow for spatial and temporal tunability, which enables the controlled delivery of compounds in a specific and dose-dependent manner. This potentially is of great interest for medicine (e.g. allowing for remotely controlled drug delivery to cells, etc.). Among the different external exogenous and endogenous stimuli used to control the desired release, light and magnetic fields offer interesting possibilities, allowing defined, real time control of intracellular releases. In this review we highlight the use of stimuli-responsive controlled release systems that are able to respond to light and magnetic field triggers for controlling the release of encapsulated cargo inside cells. We discuss established approaches and technologies and describe prominent examples. Special attention is devoted towards polymer capsules and polymer vesicles as containers for encapsulated cargo molecules. The advantages and disadvantages of this methodology in both, in vitro and in vivo models are discussed. An overview of challenges associate with the successful translation of those stimuli-responsive materials towards future applications in the direction of potential clinical use is given.

siRNA Delivery Using Dithiocarbamate-Anchored Oligonucleotides on Gold Nanorods

We present a robust method for loading small interfering RNA (siRNA) duplexes onto the surfaces of gold nanorods (GNRs) at high density, using near-infrared laser irradiation to trigger their intracellular release with subsequent knockdown activity. Citrate-stabilized GNRs were first coated with oleylsulfobetaine, a zwitterionic amphiphile with low cytotoxicity, which produced stable dispersions at high ionic strength. Amine-modified siRNA duplexes were converted into dithiocarbamate (DTC) ligands and adsorbed onto GNR surfaces in a single incubation step at 0.5 M NaCl, simplifying the charge screening process. The DTC anchors were effective at minimizing premature siRNA desorption and release, a common but often overlooked problem in the use of gold nanoparticles as oligonucleotide carriers. The activity of GNR-siRNA complexes was evaluated systematically against an eGFP-producing ovarian cancer cell line (SKOV-3) using folate receptor-mediated uptake. Efficient knockdown was achieved by using a femtosecond-pulsed laser source to release DTC-anchored siRNA, with essentially no contributions from spontaneous (dark) RNA desorption. GNRs coated with thiol-anchored siRNA duplexes were less effective and also permitted low levels of knockdown activity without photothermal activation. Optimized siRNA delivery conditions were applied toward the targeted knockdown of transglutaminase 2, whose expression is associated with the progression of recurrent ovarian cancer, with a reduction in activity of >80% achieved after a single pulsed laser treatment.

Photothermally Triggered Endosomal Escape and Its Influence on Transfection Efficiency of Gold-Functionalized JetPEI/pDNA Nanoparticles

Plasmonic nanoparticles for drug delivery have attracted increasing interest over the last few years. Their localized surface plasmon resonance causes photothermal effects on laser irradiation, which allows for delivering drugs in a spatio-temporally controlled manner. Here, we explore the use of gold nanoparticles (AuNP) as carriers for pDNA in combination with pulsed laser irradiation to induce endosomal escape, which is currently considered to be one of the major bottlenecks in macromolecular drug delivery on the intracellular level. In particular, we evaluate nanocomplexes composed of JetPEI (polyethylenimine)pDNA and 10 nm AuNP, which do not exhibit endosomal escape by themselves. After incubating HeLa cells with these complexes, we evaluated endosomal escape and transfection efficiency using low- and high-energy laser pulses. At low laser energy heat is produced by the nanocomplexes, while, at higher laser energy, explosive vapour nanobubbles (VNB) are formed. We investigated the ability of heat transfer and VNB formation to induce endosomal escape and we examine the integrity of pDNA cargo after inducing both photothermal effects. We conclude that JetPEI/pDNA/AuNP complexes are unable to induce meaningful transfection efficiencies because laser treatment causes either dysfunctionality of the cargo when VNB are formed or forms too small pores in the endosomal membrane to allow pDNA to escape in case of heating. We conclude that laser-induced VNB is the most suitable to induce effective pDNA endosomal escape, but a different nanocomplex structure will be required to keep the pDNA intact.

Evaluating the Mechanisms of Light-Triggered siRNA Release from Nanoshells for Temporal Control Over Gene Regulation

The ability to regulate intracellular gene expression with exogenous nucleic acids such as small interfering RNAs (siRNAs) has substantial potential to improve the study and treatment of disease. However, most transfection agents and nanoparticle-based carriers that are used for the intracellular delivery of nucleic acids cannot distinguish between diseased and healthy cells, which may cause them to yield unintended widespread gene regulation. An ideal delivery system would only silence targeted proteins in diseased tissue in response to an external stimulus. To enable spatiotemporal control over gene silencing, researchers have begun to develop nucleic acid-nanoparticle conjugates that keep their nucleic acid cargo inactive until it is released from the nanoparticle on-demand by externally applied near-infrared laser light. This strategy can overcome several limitations of other nucleic acid delivery systems, but the mechanisms by which these platforms operate remain ill understood. Here, we perform a detailed investigation of the mechanisms by which silica core/gold shell nanoshells (NSs) release conjugated siRNA upon excitation with either pulsed or continuous wave (CW) near-infrared (NIR) light, with the goal of providing insight into how these nanoconjugates can enable on-demand gene regulation. We demonstrate that siRNA release from NSs upon pulsed laser irradiation is a temperature-independent process that is substantially more efficient than siRNA release triggered by CW irradiation. Contrary to literature, which suggests that only pulsed irradiation releases siRNA duplexes, we found that both modes of irradiation release a mixture of siRNA duplexes and single-stranded oligonucleotides, but that pulsed irradiation results in a higher percentage of released duplexes. To demonstrate that the siRNA released from NSs upon pulsed irradiation remains functional, we evaluated the use of NSs coated with green fluorescent protein (GFP)-targeted siRNA (siGFP-NS) for on-demand knockdown of GFP in cells. We found that GFP-expressing cells treated with siGFP-NS and irradiated with a pulsed laser experienced a 33% decrease in GFP expression compared to cells treated with no laser. Further, we observed that light-triggered gene silencing mediated by siGFP-NS is more potent than using commercial transfection agents to deliver siRNA into cells. This work provides unprecedented insight into the mechanisms by which plasmonic NSs release siRNA upon light irradiation and demonstrates the importance of thoroughly characterizing photoresponsive nanosystems for applications in triggered gene regulation.

Non-viral Gene Delivery

Although viral vectors comprise the majority of gene delivery vectors, their various safety, production, and other practical concerns have left a research gap to be addressed. The non-viral vector space encompasses a growing variety of physical and chemical methods capable of gene delivery into the nuclei of target cells. Major physical methods described in this chapter are microinjection, electroporation, and ballistic injection, magnetofection, sonoporation, optical transfection, and localized hyperthermia. Major chemical methods described in this chapter are lipofection, polyfection, gold complexation, and carbon-based methods. Combination approaches to improve transfection efficiency or reduce immunological response have shown great promise in expanding the scope of non-viral gene delivery.

Plasmon-actuated nano-assembled microshells

We present three-dimensional microshells formed by self-assembly of densely-packed 5 nm gold nanoparticles (AuNPs). Surface functionalization of the AuNPs with custom-designed mesogenic molecules drives the formation of a stable and rigid shell wall, and these unique structures allow encapsulation of cargo that can be contained, virtually leakage-free, over several months. Further, by leveraging the plasmonic response of AuNPs, we can rupture the microshells using optical excitation with ultralow power (<2 mW), controllably and rapidly releasing the encapsulated contents in less than 5 s. The optimal AuNP packing in the wall, moderated by the custom ligands and verified using small angle x-ray spectroscopy, allows us to calculate the heat released in this process, and to simulate the temperature increase originating from the photothermal heating, with great accuracy. Atypically, we find the local heating does not cause a rise of more than 50 °C, which addresses a major shortcoming in plasmon actuated cargo delivery systems. This combination of spectral selectivity, low power requirements, low heat production, and fast release times, along with the versatility in terms of identity of the enclosed cargo, makes these hierarchical microshells suitable for wide-ranging applications, including biological ones.

Near-infrared remotely triggered drug-release strategies for cancer treatment

Remotely controlled, localized drug delivery is highly desirable for potentially minimizing the systemic toxicity induced by the administration of typically hydrophobic chemotherapy drugs by conventional means. Nanoparticle-based drug delivery systems provide a highly promising approach for localized drug delivery, and are an emerging field of interest in cancer treatment. Here, we demonstrate near-IR light-triggered release of two drug molecules from both DNA-based and protein-based hosts that have been conjugated to near-infrared-absorbing Au nanoshells (SiO2 core, Au shell), each forming a light-responsive drug delivery complex. We show that, depending upon the drug molecule, the type of host molecule, and the laser illumination method (continuous wave or pulsed laser), in vitro light-triggered release can be achieved with both types of nanoparticle-based complexes. Two breast cancer drugs, docetaxel and HER2-targeted lapatinib, were delivered to MDA-MB-231 and SKBR3 (overexpressing HER2) breast cancer cells and compared with release in noncancerous RAW 264.7 macrophage cells. Continuous wave laser-induced release of docetaxel from a nanoshell-based DNA host complex showed increased cell death, which also coincided with nonspecific cell death from photothermal heating. Using a femtosecond pulsed laser, lapatinib release from a nanoshell-based human serum albumin protein host complex resulted in increased cancerous cell death while noncancerous control cells were unaffected. Both methods provide spatially and temporally localized drug-release strategies that can facilitate high local concentrations of chemotherapy drugs deliverable at a specific treatment site over a specific time window, with the potential for greatly minimized side effects.

A Demonstration of Le Chatelier's Principle on the Nanoscale

Photothermal desorption of molecules from plasmonic nanoparticles is an example of a light-triggered molecular release due to heating of the system. However, this phenomenon ought to work only if the molecule-nanoparticle interaction is exothermic in nature. In this study, we compare protein adsorption behavior onto gold nanoparticles for both endothermic and exothermic complexation reactions, and demonstrate that Le Chatelier's principle can be applied to predict protein adsorption or desorption on nanomaterial surfaces. Polyelectrolyte-wrapped gold nanorods were used as adsorption platforms for two different proteins, which we were able to adsorb/desorb from the nanorod surface depending on the thermodynamics of their interactions. Furthermore, we show that the behaviors hold up under more complex biological environments such as fetal bovine serum.

Utilizing light-triggered plasmon-driven catalysis reactions as a template for molecular delivery and release

Due to the facile manipulation and non-invasive nature of light-triggered release, it is one of the most potent ways to selectively and remotely deliver a molecular target. Among the various carrier platforms, plasmonic nanoparticles possess advantages such as enhanced cellular uptake and easy loading of "cargo" molecules. Two general strategies are currently utilized to achieve light-induced molecule release from plasmonic nanoparticles. The first uses femtosecond laser pulses to directly break the bond between the nanoparticle and the loaded target. The other requires significant photo-thermal effects to weaken the interaction between the cargo molecules and nanoparticle-attached host molecules. Different from above mechanisms, herein, we introduce a new light-controlled molecular-release method by taking advantage of a plasmon-driven catalytic reaction at the particle surface. In this strategy, we link the target to a plasmon responsive molecule, 4-aminobenzenethiol (4-ABT), through the robust and simple EDC coupling reaction and subsequently load the complex onto the particles via the strong Au-thiol interaction. Upon continuous-wave (CW) laser illumination, the excited surface plasmon catalyzes the formation of 4,4'-dimercaptoazobenzenethiol (DMAB) and simultaneously releases the loaded molecules with high efficiency. This method does not require the use of high-power pulsed lasers, nor does it rely on photo-thermal effects. We believe that plasmon-driven release strategies open a new direction for the designing of next-generation light-triggered release processes.

Gold Nanorods as Nanodevices for Bioimaging, Photothermal Therapeutics, and Drug Delivery

Gold nanorods are promising metals in several biomedical applications such as bioimaging, thermal therapy, and drug delivery. Gold nanorods have strong absorption bands in near-infrared (NIR) light region and show photothermal effects. Since NIR light can penetrate deeply into tissues, their unique optical, chemical, and biological properties have attracted considerable clinical interest. Gold nanorods are expected to act not only as on-demand thermal converters for photothermal therapy but also as mediators of a controlled drug-release system responding to light irradiation. In this review, we discuss current progress using gold nanorods as bioimaging platform, phototherapeutic agents, and drug delivery vehicles.

Optically Triggered Melting of DNA on Individual Semiconducting Carbon Nanotubes

Optical excitation of nanostructures is known to induce local heating, a phenomenon that has been intensely exploited for drug release, gene delivery, cancer thermotherapy, and energy harvesting. However, the effect is typically small requiring collective heating of a large concentration or aggregates of particles. Herein, we show that optical excitation of individual semiconducting single-walled carbon nanotubes triggers strongly localized heating adequate to melt non-covalently attached double-stranded oligonucleotides in solution. In contrast to conventional thermal dehybridization, this optically triggered DNA melting occurs at a solution temperature that is 22 °C lower than the DNA melting temperature. This unexpectedly large localized optical heating effect provides important new insights to design selective optical nanoheaters at the single particle level.

Gold nanoparticle-mediated photothermal therapy: applications and opportunities for multimodal cancer treatment

Photothermal therapy (PTT), in which nanoparticles embedded within tumors generate heat in response to exogenously applied laser light, has been well documented as an independent strategy for highly selective cancer treatment. Gold-based nanoparticles are the main mediators of PTT because they offer: (1) biocompatibility, (2) small diameters that enable tumor penetration upon systemic delivery, (3) simple gold-thiol bioconjugation chemistry for the attachment of desired molecules, (4) efficient light-to-heat conversion, and (5) the ability to be tuned to absorb near-infrared light, which penetrates tissue more deeply than other wavelengths of light. In addition to acting as a standalone therapy, gold nanoparticle-mediated PTT has recently been evaluated in combination with other therapies, such as chemotherapy, gene regulation, and immunotherapy, for enhanced anti-tumor effects. When delivered independently, the therapeutic success of molecular agents is hindered by premature degradation, insufficient tumor delivery, and off-target toxicity. PTT can overcome these limitations by enhancing tumor- or cell-specific delivery of these agents or by sensitizing cancer cells to these additional therapies. All together, these benefits can enhance the therapeutic success of both PTT and the secondary treatment while lowering the required doses of the individual agents, leading to fewer off-target effects. Given the benefits of combining gold nanoparticle-mediated PTT with other treatment strategies, many exciting opportunities for multimodal cancer treatment are emerging that will ultimately lead to improved patient outcomes. WIREs Nanomed Nanobiotechnol 2017, 9:e1449. doi: 10.1002/wnan.1449 For further resources related to this article, please visit the WIREs website.

Near-Infrared Photothermally Activated DNAzyme-Gold Nanoshells for Imaging Metal Ions in Living Cells

DNAzymes have enjoyed success as metal ion sensors outside cells. Their susceptibility to metal-dependent cleavage during delivery into cells has limited their intracellular applications. To overcome this limitation, a near-infrared (NIR) photothermal activation method is presented for controlling DNAzyme activity in living cells. The system consists of a three-stranded DNAzyme precursor (TSDP), the hybridization of which prevents the DNAzyme from being active. After conjugating the TSDP onto gold nanoshells and upon NIR illumination, the increased temperature dehybridizes the TSDP to release the active DNAzyme, which then carries out metal-ion-dependent cleavage, resulting in releasing the cleaved product containing a fluorophore. Using this construct, detecting Zn2+ in living HeLa cells is demonstrated. This method has expanded the DNAzyme versatility for detecting metal ions in biological systems under NIR light that exhibits lower phototoxicity and higher tissue penetration ability.

Nanostructures for NIR light-controlled therapies

In general, effective clinical treatment demands precision medicine, which requires specific perturbation to disease cells with no damage to normal tissue. Thus far, guaranteeing that selective therapeutic effects occur only at targeted disease areas remains a technical challenge. Among the various endeavors to achieve such an outcome, strategies based on light-controlled therapies have received special attention, mostly due to their unique advantages, including the low-invasive property and the capability to obtain spatial and temporal precision at the targeted sites via specific wavelength light irradiation. However, most conventional light-mediated therapies, especially those based on short-wavelength UV or visible light irradiation, have potential issues including limited penetration depth and harmful photo damage to healthy tissue. Therefore, the implemention of near-infrared (NIR) light illumination, which can travel into deeper tissues without causing obvious photo-induced cytotoxcity, has been suggested as a preferable option for precise phototherapeutic applications in vitro and in vivo. In this article, an overview is presented of existing therapeutic applications through NIR light-absorbed nanostructures, such as NIR light-controlled drug delivery, NIR light-mediated photothermal and photodynamic therapies. Potential challenges and relevant future prospects are also discussed.

Surfactant-Free Preparation of Au@Resveratrol Hollow Nanoparticles with Photothermal Performance and Antioxidant Activity

Nanocomposites based on hollow Au nanostructures have gained considerable attention in theranostics applications because of their unique plasmonic structures and attractive physicochemical properties. The exploration of feasible and facile methods for constructing multifunctional nanocomposites combined with bioactive molecules is greatly needed for the development of multifunctional theranostics platforms. In this work, resveratrol, a natural polyphenol with antioxidant activity and cancer-chemopreventive propertyies is employed as the reducing agent cum coating agent for the surfactant-free preparation of Au@resveratrol hollow NPs (Au@Res HNPs). The as-prepared Au@Res HNPs were found to present good photothermal performance and chemical inhibition for cancer therapy. In vitro experiments indicated that the Au@Res HNPs can block cell cycles to inhibit cell division and lead to cell apoptosis after 808-nm laser irradiation. Because no toxic surfactants are introduced, the current protocol avoids the tedious surfactant separation and surface modification processes that are necessary for most theranostics materials.

Understanding Resonant Light-Triggered DNA Release from Plasmonic Nanoparticles

Nanoparticle-based platforms for gene therapy and drug delivery are gaining popularity for cancer treatment. To improve therapeutic selectivity, one important strategy is to remotely trigger the release of a therapeutic cargo from a specially designed gene- or drug-laden near-infrared (NIR) absorbing gold nanoparticle complex with NIR light. While there have been multiple demonstrations of NIR nanoparticle-based release platforms, our understanding of how light-triggered release works in such complexes is still limited. Here, we investigate the specific mechanisms of DNA release from plasmonic nanoparticle complexes using continuous wave (CW) and femtosecond pulsed lasers. We find that the characteristics of nanoparticle-based DNA release vary profoundly from the same nanoparticle complex, depending on the type of laser excitation. CW laser illumination drives the photothermal release of dehybridized single-stranded DNA, while pulsed-laser excitation results in double-stranded DNA release by cleavage of the Au-S bond, with negligible local heating. This dramatic difference in DNA release from the same DNA-nanoparticle complex has very important implications in the development of NIR-triggered gene or drug delivery nanocomplexes.

Recent Advances of Using Hybrid Nanocarriers in Remotely Controlled Therapeutic Delivery

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

Gold Nanoantenna-Mediated Photothermal Drug Delivery from Thermosensitive Liposomes in Breast Cancer

In this work, we demonstrate controlled drug delivery from low-temperature-sensitive liposomes (LTSLs) mediated by photothermal heating from multibranched gold nanoantennas (MGNs) in triple-negative breast cancer (TNBC) cells in vitro. The unique geometry of MGNs enables the generation of mild hyperthermia (∼42 °C) by converting near-infrared light to heat and effectively delivering doxorubicin (DOX) from the LTSLs in breast cancer cells. We confirmed the cellular uptake of MGNs by using both fluorescence confocal Z-stack imaging and transmission electron microscopy (TEM) imaging. We performed a cellular viability assay and live/dead cell fluorescence imaging of the combined therapeutic effects of MGNs with DOX-loaded LTSLs (DOX-LTSLs) and compared them with free DOX and DOX-loaded non-temperature-sensitive liposomes (DOX-NTSLs). Imaging of fluorescent live/dead cell indicators and MTT assay outcomes both demonstrated significant decreases in cellular viability when cells were treated with the combination therapy. Because of the high phase-transition temperature of NTSLs, no drug delivery was observed from the DOX-NTSLs. Notably, even at a low DOX concentration of 0.5 μg/mL, the combination treatment resulted in a higher (33%) cell death relative to free DOX (17% cell death). The results of our work demonstrate that the synergistic therapeutic effect of photothermal hyperthermia of MGNs with drug delivery from the LTSLs can successfully eradicate aggressive breast cancer cells with higher efficacy than free DOX by providing a controlled light-activated approach and minimizing off-target toxicity.

Local temperature variation measurement by anti-Stokes luminescence in attenuated total reflection geometry

Strong temperature dependence of anti-Stokes luminescence intensity from Rhodamine 101 is used to probe local temperature variation at a surface region in the attenuated total reflection geometry (ATR), when heating with laser light. In this method, the measured region can be limited by observing evanescent luminescence. The near-field depth (penetration depth) was changed by the observation angle θ_out of the evanescent luminescence and the spatial temperature variation was observed.

Optically controlled release of DNA based on nonradiative relaxation process of quenchers

Optically controlled release of a DNA strand based on a nonradiative relaxation process of black hole quenchers (BHQs), which are a sort of dark quenchers, is presented. BHQs act as efficient energy sources because they relax completely via a nonradiative process, i.e., without fluorescent emission-based energy losses. A DNA strand is modified with BHQs and the release of its complementary strand is controlled by excitation of the BHQs. Experimental results showed that up to 50% of the target strands were released, and these strands were capable of inducing subsequent reactions. The controlled release was localized on a substrate within an area of no more than 5 micrometers in diameter.

Partially PEGylated dendrimer-entrapped gold nanoparticles: a promising nanoplatform for highly efficient DNA and siRNA delivery

Partially PEGylated dendrimer-entrapped gold nanoparticles can be used as a promising nanoplatform for highly efficient pDNA and siRNA delivery.

[The Increase of Oligonucleotides--Gold Nanoparticles Conjugates Stability]

For today the reagents based on oligonucleotides--gold nanoparticles conjugates and used for specific nucleic acids detection are actively being developed. Such molecular structures are stabilized through the bonds between thiol group in oligonucleotides and gold atoms in nanoparticle. The durability of oligonucleotides--gold nanoparticles binding affects directly on the stability of conjugates and on the possibility of further manipulations. In this paper, a method for the strengthening of oligonucleotides attachment on the gold nano-particles surface by means of anchor groups with dithiolane residues is proposed. A comparative study of the anchors molecular structure influence on the conjugates stability at conditions that typical for oligonucleotide probes was carried out.

Photoresponsive nanoparticles for drug delivery

Externally triggerable drug delivery systems provide a strategy for the delivery of therapeutic agents preferentially to a target site, presenting the ability to enhance therapeutic efficacy while reducing side effects. Light is a versatile and easily tuned external stimulus that can provide spatiotemporal control. Here we will review the use of nanoparticles in which light triggers drug release or induces particle binding to tissues (phototargeting).

Stimuli-responsive cancer therapy based on nanoparticles

Nanoparticles (NPs) have recently been well investigated for cancer therapy. Among them, those that are responsive to internal or external stimuli are promising due to their flexibility. In this feature article, we provide an overview on stimuli-sensitive cancer therapy, using pH- and reduction-sensitive NPs, as well as light- and magnetic field-responsive NPs.

Thermoplasmonic ssDNA Dynamic Release from Gold Nanoparticles Examined with Advanced Fluorescence Microscopy

Plasmon excitation of spherical gold nanoparticles carrying a fluorescent labeled 30 bp dsDNA cargo, with one chain covalently attached through two S-Au bonds to the surface, results in release of the complementary strand as ssDNA that can be examined in situ using high-resolution fluorescence microscopy. The release is dependent on the total energy delivered, but not the rate of delivery, an important property for plasmonic applications in medicine, sensors, and plasmon-induced PCR.

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

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

Photocontrolled nanoparticle delivery systems for biomedical applications

"Smart" stimuli-responsive nanomaterials are becoming popular as targeted delivery systems because they allow the use of internal or external stimuli to achieve spatial or temporal control over the delivery process. Among the stimuli that have been used, light is of special interest because it is not only noninvasive but also controllable both spatially and temporally, thus allowing unprecedented control over the delivery of bioactive molecules such as nucleic acids, proteins, drugs, etc. This is particularly advantageous for biomedical applications where specificity and selectivity are highly desired. Several strategies have evolved under the umbrella of light based delivery systems and can be classified into three main groups. The first strategy involves "caging" of the bioactive molecule using photolabile groups, loading these caged molecules onto a carrier and then "uncaging" or activating them at the targeted site upon irradiation with light of a particular wavelength. The second strategy makes use of nanocarriers that themselves are made photoresponsive either through modification with photosensitive groups or through the attachment of photolinkers on the carrier surface. These nanoparticles upon irradiation dissociate, releasing the cargo encapsulated within, or the photolinkers attaching the cargo to the surface get cleaved, resulting in release. The third approach makes use of the surface plasmon resonance of noble metal based nanoparticles. Upon irradiation with light at the plasmon resonant frequency, the resulting thermal or nonthermal field enhancement effects facilitate the release of bioactive molecules loaded onto the nanoparticles. In addition, other materials, certain metal sulfides, graphene oxide, etc., also exhibit photothermal transduction that can be exploited for targeted delivery. These approaches, though effective, are constrained by their predominant use of UV or visible light to which most photolabile groups are sensitive. Near infrared (NIR) excitation is preferred because NIR light is safer and can penetrate deeper in biological tissues. However, most photolabile groups cannot be excited by NIR light directly. So light conversion from NIR to UV/visible is required. Nanomaterials that display upconversion or two-photon-excitation properties have been developed that can serve as nanotransducers, converting NIR to UV/visible light to which the aforementioned photoresponsive moieties are sensitive. This Account will review the existing light-based nanoparticle delivery systems, their applications, the limitations they face, and the technologies that have emerged in an effort to overcome these limitations.

Nanoparticles for photothermal therapies

The current status of the use of nanoparticles for photothermal treatments is reviewed in detail. The different families of heating nanoparticles are described paying special attention to the physical mechanisms at the root of the light-to-heat conversion processes. The heating efficiencies and spectral working ranges are listed and compared. The most important results obtained in both in vivo and in vitro nanoparticle assisted photothermal treatments are summarized. The advantages and disadvantages of the different heating nanoparticles are discussed.

Photothermally targeted thermosensitive polymer-masked nanoparticles

The targeted delivery of therapeutic cargos using noninvasive stimuli has the potential to improve efficacy and reduce off-target effects (toxicity). Here, we demonstrate a targeting mechanism that uses a thermoresponsive copolymer to mask a peptide ligand that binds a widely distributed receptor (integrin β1) on the surface of silica core-gold shell nanoparticles. The nanoparticles convert NIR light into heat, which causes the copolymer to collapse, exposing the ligand peptide, allowing cell binding. The use of NIR light could allow targeting of plasmonic nanoparticles deep within tissues. This approach could be extended to a variety of applications including photothermal therapy and drug delivery.

Light-activatable gold nanoshells for drug delivery applications

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

Emerging advances in nanomedicine with engineered gold nanostructures

Gold nanostructures possess unique characteristics that enable their use as contrast agents, as therapeutic entities, and as scaffolds to adhere functional molecules, therapeutic cargo, and targeting ligands. Due to their ease of synthesis, straightforward surface functionalization, and non-toxicity, gold nanostructures have emerged as powerful nanoagents for cancer detection and treatment. This comprehensive review summarizes the progress made in nanomedicine with gold nanostructures (1) as probes for various bioimaging techniques including dark-field, one-photon and two-photon fluorescence, photothermal optical coherence tomography, photoacoustic tomography, positron emission tomography, and surface-enhanced Raman scattering based imaging, (2) as therapeutic components for photothermal therapy, gene and drug delivery, and radiofrequency ablation, and (3) as a theranostic platform to simultaneously achieve both cancer detection and treatment. Distinct from other published reviews, this article also discusses the recent advances of gold nanostructures as contrast agents and therapeutic actuators for inflammatory diseases including atherosclerotic plaque and arthritis. For each of the topics discussed above, the fundamental principles and progress made in the past five years are discussed. The review concludes with a detailed future outlook discussing the challenges in using gold nanostructures, cellular trafficking, and translational considerations that are imperative for rapid clinical viability of plasmonic nanostructures, as well as the significance of emerging technologies such as Fano resonant gold nanostructures in nanomedicine.