Tuning the interactions of PEG-coated gold nanorods with BSA and model proteins through insertion of amino or carboxylate groups

Optimizing Plasmonic Gold Nanorod Deposition on Glass Surfaces for High-Sensitivity Refractometric Biosensing

Owing to high surface sensitivity, gold nanorods (AuNRs) are widely used to construct surface-based nanoplasmonic biosensing platforms for label-free molecular diagnostic applications. A key fabrication step involves controlling AuNR deposition onto the target surface, which requires maximizing surface density while minimizing inter-particle aggregation, and is often achieved by surface functionalization with a self-assembled monolayer (SAM) prior to AuNR deposition. To date, existing studies have typically used a fixed concentration of SAM-forming organic molecules (0.2-10% v/v) while understanding how SAM density affects AuNR deposition and resulting sensing performance would be advantageous. Herein, we systematically investigated how controlling the (3-aminopropyl)triethoxysilane (APTES) concentration (1-30% v/v) during SAM preparation affects the fabrication of AuNR-coated glass surfaces for nanoplasmonic biosensing applications. Using scanning electron microscopy (SEM) and UV-visible spectroscopy, we identified an intermediate APTES concentration range that yielded the highest density of individually deposited AuNRs with minimal aggregation and also the highest peak wavelength in aqueous solution. Bulk refractive index sensitivity measurements indicated that the AuNR configuration had a strong effect on the sensing performance, and the corresponding wavelength-shift responses ranged from 125 to 290 nm per refractive index unit (RIU) depending on the APTES concentration used. Biosensing experiments involving protein detection and antigen-antibody interactions further demonstrated the high surface sensitivity of the optimized AuNR platform, especially in the low protein concentration range where the measurement shift was ~8-fold higher than that obtained with previously used sensing platforms.

Cationic Liposome/DNA Complexes Mediate Antitumor Immunotherapy by Promoting Immunogenic Tumor Cell Death and Dendritic Cell Activation

Immunotherapy has been successfully used in the treatment of multiple malignancies, but clinical studies revealed low response rates. Thus, the development of new effective immunotherapeutic modalities is urgently needed. Successfully inducing tumor cell death with enhanced antigenicity is important for the expansion and differentiation of tumor-specific CD8⁺ cytotoxic T lymphocytes. Cationic liposome/DNA complexes (CLN/DNA), which usually have obvious cytotoxic effects, may improve the antitumor immunity through enhancing the immunogenicity of dying tumor cells. Herein, we report that a plasmid DNA-encapsulated cationic lipid nanoparticle formulated with cholesterol, DOTAP, and DSPE-mPEG₂₀₀₀ significantly increases the tumor cell death with high antigenicity in vitro. Furthermore, the cationic liposome/DNA complex (CLN/DNA) treatment promotes the activation of dendritic cells (DCs). We also find that the intratumorally injected CLN/DNA successfully promoted the activation of DCs in the tumor-draining lymph node. Importantly, both local tumor growth and distant tumor formation were significantly inhibited by T cell-dependent antitumor immune responses after intratumoral injection of CLN/DNA. This study presents a simple and effective strategy for improving the cancer immunotherapy.

Impact of Kapitza resistance on the stability and efficiency of photoacoustic conversion from gold nanorods

Plasmonic particles have been proposed for a broad variety of optical and hybrid applications, including the photothermal ablation and photoacoustic imaging of cancer, or their integration in photonic sensors. Here, we address the effect of thermal resistance at the gold-water interface, or Kapitza resistance, on the performance of photoacoustic conversion of gold nanorods. Our findings point to possible strategies for the optimization of plasmonic particles as contrast agents for imaging, or even as transducers for biosensing. We perform numerical simulations that project a simultaneous increase of efficiency and stability of photoacoustic conversion with a decrease of Kapitza resistance. We suggest an effective approach to modulate Kapitza resistance by including underresolved features as roughness or the presence of adsorbates. Inspired by this idea, we synthesize a rough variant of gold nanorods by the deposition and galvanic replacement of a silver shell, where roughness provides higher photoacoustic signals by about 70% and damage thresholds by 120%. In addition, we coat our particles with a protein corona and find a decrease of photoacoustic signals with shell thickness, which may inspire new solutions for biosensors based on a mechanism of photoacoustic transduction. Both our findings are consistent with an effective modulation of Kapitza resistance, which decreases upon roughening, due to an underlying increase of specific surface area, and increases upon coating with a protein shell that may act as a thermal insulation. We discuss possible directions to gain more advantage of our concept for topical applications at the crossroads of plasmonics, biomedical optics and biosensing.

PEGylated hydrazided gold nanorods for pH-triggered chemo/photodynamic/photothermal triple therapy of breast cancer

Integration of multimodal therapies into one nanoplatform holds great promise to overcome the drawbacks of conventional single-modal therapy and pursues enhanced anticancer efficacy. Herein, we developed a PEGylated gold nanorods (GNRs)-based nanoplatform (GNRs-MPH^-ALA/DOX-PEG) with pH-responsive drug release property for triple-combined chemotherapy (CT), photodynamic therapy (PDT) and photothermal therapy (PTT) of breast cancer. GNRs were first decorated with mercaptopropionylhydrazide (MPH) and thiol-terminated monomethoxyl poly(ethylene glycol) (mPEG-SH) via Au-thiol linkage, and subsequently conjugated with chemotherapeutant doxorubicin (DOX) and pro-photosensitizer 5-aminolevulinic acid (ALA) through acid-liable hydrazone bonds between drugs and MPH molecules. The resulting nanoplatform GNRs-MPH^-ALA/DOX-PEG exhibited excellent stability in physiological solutions and pH-responsive DOX and ALA release behaviors. In vitro studies showed that GNRs-MPH^-ALA/DOX-PEG could efficiently enter human breast cancer MCF-7 cells and release DOX and ALA into cytoplasm. Furthermore, DOX could locate in the cell nucleus and ALA was productively metabolized into protoporphyrin IX (PpIX). Upon near-infrared (NIR) irradiation, PpIX produced enough reactive oxygen species for PDT and meanwhile GNRs could efficiently induce hyperthermia for PTT. Compared with single CT and dual-modal CT/PDT or CT/PTT treatment, the triple-combined CT/PDT/PTT treatment could more efficiently kill MCF-7 cells via a superadditive antitumor effect. Furthermore, the circulation half-life of GNRs-MPH^-ALA/DOX-PEG in the blood was as long as approximately 52 min and it exhibited a tumor accumulation of 3.3%. The triple-combined CT/PDT/PTT treatment could completely suppress tumor growth without obvious systemic toxicity. Our study paves a new avenue for multimodal therapy of breast cancer. STATEMENT OF SIGNIFICANCE: The development of a simple but effective strategy to construct a versatile nanoplatform for multi-combined therapy still remains an enormous challenge. In this work, we developed a novel and simple nanoplatform GNRs-MPH^-ALA/DOX-PEG with pH-responsive drug release for triple-combined chemotherapy (CT), photodynamic therapy (PDT) and photothermal therapy (PTT) of breast cancer. The nanoplatform could be efficiently internalized by MCF-7 cells. The intracellular GNRs-MPH^-ALA/DOX-PEG could release DOX for CT, induce hyperthermia for PTT and generate high levels of ROS for PTT. Compared with single CT and dual-modal CT/PDT or CT/PTT treatments, the triple-combined CT/PDT/PTT treatment could more efficiently kill MCF-7 cells via a superadditive antitumor effect. Furthermore, upon triple-combined CT/PDT/PTT treatment, the tumor growth was completely suppressed without obvious systemic toxicity.

CE Separation and ICP-MS Detection of Gold Nanoparticles and Their Protein Conjugates

A full understanding and mediation of nanoparticle-serum protein interactions is key to design nanoparticles with vivid functions within the body, and to solve this problem one needs to differentiate and characterize individual nano-protein conjugates. In this paper, the authors applied capillary electrophoresis combined with inductively coupled plasma mass spectrometry detection to study the behavior of gold nanoparticles of different geometry, size and surface functionalization upon interacting with serum proteins and their mixtures. Due to high-resolution and -sensitivity benefits of this combined technique baseline separations were attained for free nanoparticles (at real-life doses) and different protein conjugates, and the conversion into the protein-bound form was scrutinized in terms of reaction time.

Electrophoretic Interpretation of PEGylated NP Structure with and without Peripheral Charge

Anchoring poly(ethylene glycol) (PEG) to inorganic nanoparticles (NPs) permits control over NP properties for a variety of technological applications. However, the core-shell structure tremendously complicates the interpretation of the ubiquitous ζ-potential, as furnished by electrophoretic light-scattering, capillary electrophoresis or gel electrophoresis. To advance the ζ-potential-and the more fundamental electrophoretic mobility-as a quantitative diagnostic for PEGylated NPs, we synthesized and characterized Au NPs bearing terminally anchored 5 kDa PEG ligands with univalent carboxymethyl end groups. Using the electrophoretic mobilities, acquired over a wide range of ionic strengths, we developed a theoretical model for the distributions of polymer segments, charge, electrostatic potential, and osmotic pressure that envelop the core: knowledge that will help to improve the performance of soft NPs in fundamental research and technological applications.