Ultrafast Photothermal Release of DNA from Gold Nanoparticles

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.

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.

Femtosecond Laser Pulse Excitation of DNA-Labeled Gold Nanoparticles: Establishing a Quantitative Local Nanothermometer for Biological Applications

Femtosecond (fs) laser pulsed excitation of plasmonic nanoparticle (NP)-biomolecule conjugates is a promising method to locally heat biological materials. Studies have demonstrated that fs pulses of light can modulate the activity of DNA or proteins when attached to plasmonic NPs; however, the precision over subsequent biological function remains largely undetermined. Specifically, the temperature the localized biomolecules "experience" remains unknown. We used 55 nm gold nanoparticles (AuNPs) displaying double-stranded (ds) DNA to examine how, for dsDNA with different melting temperatures, the laser pulse energy fluence and bulk solution temperature affect the rate of local DNA denaturation. A universal "template" single-stranded DNA was attached to the AuNP surface, and three dye-labeled probe strands, distinct in length and melting temperature, were hybridized to it creating three individual dsDNA-AuNP bioconjugates. The dye-labeled probe strands were used to quantify the rate and amount of DNA release after a given number of light pulses, which was then correlated to the dsDNA denaturation temperature, resulting in a quantitative nanothermometer. The localized DNA denaturation rate could be modulated by more than threefold over the biologically relevant range of 8-53 °C by varying pulse energy fluence, DNA melting temperature, and surrounding bath temperature. With a modified dissociation equation tailored for this system, a "sensed" temperature parameter was extracted and compared to simulated AuNP temperature profiles. Determining actual biological responses in such systems can allow researchers to design precision nanoscale photothermal heating sources.

Advances on non-invasive physically triggered nucleic acid delivery from nanocarriers

Nucleic acids (NAs) have been considered as promising therapeutic agents for various types of diseases. However, their clinical applications still face many limitations due to their charge, high molecular weight, instability in biological environment and low levels of transfection. To overcome these drawbacks, therapeutic NAs should be carried in a stable nanocarrier, which can be viral or non-viral vectors, and released at specific target site. Various controllable gene release strategies are currently being evaluated with interesting results. Endogenous stimuli-responsive systems, for example pH-, redox reaction-, enzymatic-triggered approaches have been widely studied based on the physiological differences between pathological and normal tissues. Meanwhile, exogenous triggered release strategies require the use of externally non-invasive physical triggering signals such as light, heat, magnetic field and ultrasound. Compared to internal triggered strategies, external triggered gene release is time and site specifically controllable through active management of outside stimuli. The signal induces changes in the stability of the delivery system or some specific reactions which lead to endosomal escape and/or gene release. In the present review, the mechanisms and examples of exogenous triggered gene release approaches are detailed. Challenges and perspectives of such gene delivery systems are also discussed.

Temperature-Dependent Plasmonic Responses from Gold Nanoparticle Dimers Linked by Double-Stranded DNA

DNA is a powerful tool to assemble gold nanoparticles into discrete structures with tunable plasmonic properties for photonic or biomedical applications. Because of their photothermal properties or their use in biological media, these nanostructures can experience drastic modifications of the local temperature that can affect their morphology and, therefore, their optical responses. Using single-nanostructure spectroscopy, we demonstrate that, even with a fully stable DNA linker, gold particle dimers can undergo substantial conformational changes at temperatures larger than 50 °C and aggregate irreversibly. Such temperature-dependent resonant optical properties could find applications in imaging and in the design of nonlinear photothermal sources. Inversely, to provide fully stable DNA-templated plasmonic nanostructures at biologically relevant temperatures, we show how passivating the gold nanoparticles using amphiphilic surface chemistries renders the longitudinal plasmon resonance of gold particle dimers nearly independent of the local temperature.

Recent advances in applying nanotechnologies for cancer immunotherapy

Cancer immunotherapy aimed at boosting cancer-specific immunoresponses to eradicate tumor cells has evolved as a new treatment modality. Nanoparticles incorporating antigens and immunomodulatory agents can activate immune cells and modulate the tumor microenvironment to enhance anti-tumor immunity. The nanotechnology approach has been demonstrated to be superior to standard formulations in in-vivo settings. In this article, we focus on recent advances made within the last 5 years in nanoparticle-based cancer immunotherapy, including peptide- and nucleic acid-based nanovaccines, nanomedicines containing an immunoadjuvant to activate anti-tumor immunity, nanoparticle delivery of immune checkpoint inhibitors and the combination of the above approaches. Encouraging results and new emerging nanotechnologies in drug delivery promise the continuous growth of this field and ultimately clinical translation of enhanced immunotherapy of cancer.

Near-Infrared Photothermal Release of siRNA from the Surface of Colloidal Gold-Silver-Gold Core-Shell-Shell Nanoparticles Studied with Second-Harmonic Generation

Photothermal release of oligonucleotides from the surface of plasmonic nanoparticles represents a promising platform for spatiotemporal controlled drug delivery. Here we demonstrate the use of novel gold-silver-gold core-shell-shell (CSS) nanoparticles to study the photothermal cleaving and release of micro-RNA (miRNA) mimics or small interfering RNA (siRNA) under nearinfrared (NIR) irradiation. The furan-maleimide-based Diels-Alder adduct cleaves thermally above 60 °C and is used to bind siRNA to the colloidal nanoparticle surface in water. We investigate the photothermal cleaving kinetics of siRNA under different NIR laser powers using surface-sensitive time-dependent second-harmonic generation (SHG) spectroscopy. The photothermal release of siRNA from the surface of CSS nanoparticles is significantly higher than that from the surface of gold nanoparticles (GNPs) under similar experimental conditions. These results demonstrate that plasmonic CSS nanoparticles with photothermal cleaving linkers have important potential applications for nanoparticle-based NIR-mediated drug-delivery systems.

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.

Plasmon-Enhanced Photocleaving Dynamics in Colloidal MicroRNA-Functionalized Silver Nanoparticles Monitored with Second Harmonic Generation

The photocleaving dynamics of colloidal microRNA-functionalized nanoparticles are studied using time-dependent second harmonic generation (SHG) measurements. Model drug-delivery systems composed of oligonucleotides attached to either silver nanoparticles or polystyrene nanoparticles using a nitrobenzyl photocleavable linker are prepared and characterized. The photoactivated controlled release is observed to be most efficient on resonance at 365 nm irradiation, with pseudo-first-order rate constants that are linearly proportional to irradiation powers. Additionally, silver nanoparticles show a 6-fold plasmon enhancement in photocleaving efficiency over corresponding polystyrene nanoparticle rates, while our previous measurements on gold nanoparticles show a 2-fold plasmon enhancement compared to polystyrene nanoparticles. Characterizations including extinction spectroscopy, electrophoretic mobility, and fluorimetry measurements confirm the analysis from the SHG results. The real-time SHG measurements are shown to be a highly sensitive method for investigating plasmon-enhanced photocleaving dynamics in model drug delivery systems.

Synergistic nanomedicine by combined gene and photothermal therapy

To date, various nanomaterials with the ability for gene delivery or photothermal effect have been developed in the field of biomedicine. The therapeutic potential of these nanomaterials has raised considerable interests in their use in potential next-generation strategies for effective anticancer therapy. In particular, the advancement of novel nanomedicines utilizing both therapeutic strategies of gene delivery and photothermal effect has generated much optimism regarding the imminent development of effective and successful cancer treatments. In this review, we discuss current research progress with regard to combined gene and photothermal therapy. This review focuses on synergistic therapeutic systems combining gene regulation and photothermal ablation as well as logically designed nano-carriers aimed at enhancing the delivery efficiency of therapeutic genes using the photothermal effect. The examples detailed in this review provide insight to further our understanding of combinatorial gene and photothermal therapy, thus paving the way for the design of promising nanomedicines.

Interaction of an anti-cancer photosensitizer with a genomic DNA: From base pair specificity and thermodynamic landscape to tuning the rate of detergent-sequestered dissociation

A detailed characterization of the binding interaction of a potent cancer cell photosensitizer, norharmane (NHM) with a genomic DNA (herring sperm; hsDNA) is undertaken with particular emphasis on deciphering the strength, mode, dynamics, energetics and kinetics of binding. A major focus of the study underlies a successful exploration of the concept of detergent-sequestered dissociation of drug from the drug-DNA complex. Biophysical techniques such as absorption, steady-state and time-resolved fluorescence spectroscopy, circular dichroism, DNA helix melting, stopped-flow fluorescence kinetics and calorimetry have been used. A primarily intercalative mode of binding of NHM with DNA is shown. However, the overall interaction is governed by more than one type of binding forces. We demonstrate that the essential prerequisite of a slower dissociation rate of drug from DNA helix is achieved by tenable choice surfactants. Our results also highlight an effective tunability of the rate of dissociation of the DNA-intercalated drug via detergent-sequestration. A detailed isothermal titration calorimetric study unveils the key role of hydrophobic force underlying NHM-hsDNA association. This is further substantiated by the enthalpy-entropy compensation behavior. The major entropic contribution in detergent-induced dissociation of NHM from NHM-hsDNA complex is also demonstrated. Our results present not only a comprehensive structural and thermodynamic profile, base pair specificity, association kinetics for binding of NHM with DNA but also explore the thermodynamic and kinetic aspects of dissociation of bound drug. Characterization and tuning of the essential prerequisites for a drug to be efficient in anti-cancer functionality bear direct and widespread significance in contemporary global research.

Fe3O4 nanoparticles as robust photothermal agents for driving high barrier reactions under ambient conditions

Magnetite nanoparticles (MNPs) show remarkable stability during extreme photothermal heating (≥770 K), displaying no change in size, crystallinity, or surfactants. The heat produced is also shown as chemically useful, driving the high-barrier thermal decomposition of polypropylene carbonate. This suggests MNPs are better photothermal agents (compared to gold nanoparticles), for photothermally driving high-barrier chemical transformations.

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.

Gold nanoparticle mediated cancer immunotherapy

Significant progress has been made in the field of cancer immunotherapy, where the goal is to activate or modulate the body's immune response against cancer. However, current immunotherapy approaches exhibit limitations of safety and efficacy due to systemic delivery. In this context, the use of nanotechnology for the delivery of cancer vaccines and immune adjuvants presents a number of advantages such as targeted delivery to immune cells, enhanced therapeutic effect, and reduced adverse outcomes. Recently, gold nanoparticles (AuNP) have been explored as immunotherapy carriers, creating new AuNP applications that merit a critical overview. This review highlights recent advances in the development of AuNP mediated immunotherapies that harness AuNP biodistribution, optical properties and their ability to deliver macromolecules such as peptides and oligonucleotides. It has been demonstrated that the use of AuNP carriers can improve the delivery and safety of immunotherapy agents, and that AuNP immunotherapies are well suited for synergistic combination therapy with existing cancer therapies like photothermal ablation.

FROM THE CLINICAL EDITOR

Cancer immunotherapy approaches are rapidly evolving and are some of the most promising avenues to approach malignancies. This review summarizes the role of gold nanoparticles in immunotherapy agent delivery, and in the development of synergistic therapies such as photothermal ablation.

Tunable loading of single-stranded DNA on gold nanorods through the displacement of polyvinylpyrrolidone

A quantitative and tunable loading of single-stranded (ss-DNA) molecules onto gold nanorods was achieved through a new method of surfactant exchange. This new method involves the exchange of cetyltrimethylammonium bromide surfactants for an intermediate stabilizing layer of polyvinylpyrrolidone and sodium dodecylsulfate. The intermediate layer of surfactants on the anisotropic gold particles was easily displaced by thiolated ss-DNA, forming a tunable density of single-stranded DNA molecules on the surfaces of the gold nanorods. The success of this ligand exchange process was monitored in part through the combination of extinction, X-ray photoelectron, and infrared absorption spectroscopies. The number of ss-DNA molecules per nanorod for nanorods with a high density of ss-DNA molecules was quantified through a combination of fluorescence measurements and elemental analysis, and the functionality of the nanorods capped with dense monolayers of DNA was assessed using a hybridization assay. Core-satellite assemblies were successfully prepared from spherical particles containing a probe DNA molecule and a nanorod core capped with complementary ss-DNA molecules. The methods demonstrated herein for quantitatively fine tuning and maximizing, or otherwise optimizing, the loading of ss-DNA in monolayers on gold nanorods could be a useful methodology for decorating gold nanoparticles with multiple types of biofunctional molecules.

Selective dehybridization of DNA-Au nanoconjugates using laser irradiation

Plasmonic heating to trigger release of oligonucleotides from nanoconjugates is potentially useful for therapeutic purposes and designed assembly of DNA nanostructures. In the past, great controllability has been achieved by introducing distinctive absorption nanoparticle centers, where the anchoring bond (e.g., sulfur-gold bond) has been selectively broken. Instead of releasing the surface-bound duplex DNA via breakage of the gold-sulphur anchor bond, selective and non-destructive dehybridization of DNA under a "mild" condition on different gold nanoconjugates is demonstrated in this work. This finding will permit sequential dehybridization/release of DNA at specific regions of a complex system; thus it can be extended to control gene expression and to manipulate an assembly of highly organized DNA constructs. Particularly we show herein the feasibility of selectively dehybridizing DNA-Au nanoconjugates via localized plasmonic heating, which is accomplished by controlling the laser wavelength, power, and irradiation time.

Photonic gene circuits by optically addressable siRNA-Au nanoantennas

The precise perturbation of gene circuits and the direct observation of signaling pathways in living cells are essential for both fundamental biology and translational medicine. Current optogenetic technology offers a new paradigm of optical control for cells; however, this technology relies on permanent genomic modifications with light-responsive genes, thus limiting dynamic reconfiguration of gene circuits. Here, we report precise control of perturbation and reconfiguration of gene circuits in living cells by optically addressable siRNA-Au nanoantennas. The siRNA-Au nanoantennas fulfill dual functions as selectively addressable optical receivers and biomolecular emitters of small interfering RNA (siRNA). Using siRNA-Au nanoantennas as optical inputs to existing circuit connections, photonic gene circuits are constructed in living cells. We show that photonic gene circuits are modular, enabling subcircuits to be combined on-demand. Photonic gene circuits open new avenues for engineering functional gene circuits useful for fundamental bioscience, bioengineering, and medical applications.

Controlled release of Rituximab from gold nanoparticles for phototherapy of malignant cells

Releasing drug molecules at their targets with high spatial and temporal accuracy could aid numerous clinical applications which require low systemic damage and low side effects. Nano-carriers of drugs are an attractive solution for such task, allowing specific accumulation in tumors and gradual release of their payload. Here, we utilize gold nanospheres conjugated to Rituximab, an anti-CD20 monoclonal antibody-based drug, for carrying and releasing the drug upon irradiation of specifically tailored femtosecond laser pulses. The released anti-CD20 molecules retain their functionality and ability of triggering the complement-dependent cytotoxicity. This effect comes in addition to cell necrosis caused by the plasmonic nanometric shock waves emanating from the nanospheres and rupturing the plasma membranes. Main advantages of the presented technique include high spatial and temporal resolution, low toxicity and high repeatability and consistency due to the morphological stability of the nanospheres.