pH-Sensitive assembly/disassembly gold nanoparticles with the potential of tumor diagnosis and treatment

Stimuli-triggered Self-Assembly of Gold Nanoparticles: Recent Advances in Fabrication and Biomedical Applications

Gold nanoparticles have been widely used in engineering, material chemistry, and biomedical applications owing to their ease of synthesis and functionalization, localized surface plasmon resonance (LSPR), great chemical stability, excellent biocompatibility, tunable optical and electronic property. In recent years, the decoration and modification of gold nanoparticles with small molecules, ligands, surfactants, peptides, DNA/RNA, and proteins have been systematically studied. In this review, we summarize the recent approaches on stimuli-triggered self-assembly of gold nanoparticles and introduce the breakthrough of gold nanoparticles in disease diagnosis and treatment. Finally, we discuss the current challenge and future prospective of stimuli-responsive gold nanoparticles for biomedical applications.

Hill-type pH probes

Sensitive detection of the minute and yet pathologically significant pH variation is important and in fact challenging for the conventional pH probes following the Henderson-Hasselbalch equation, i.e., HH-type probes. A paradigm shift to Hill-type pH probes is ongoing. Bestowed by their positive cooperative acid-base chemistry, their pH-responsive profile follows the Hill equation, which exhibits a narrower acid/base transition width than HH-type probes and warrants a higher detection sensitivity. A polymer-based Hill-type pH-responsive material was first developed. More recently, there emerged several distinct small-molecular approaches to achieve Hill-type pH-responsive profiles. They complement the polymer-based sensing materials in applications where membrane permeability is a concern. In this trends article, we rationalize the molecular origins of their positive cooperativity in pH sensing and highlight some interesting proof-of-concept applications. We also discussed future directions of this dynamic research area.

Tumor acid microenvironment-activated self-targeting & splitting gold nanoassembly for tumor chemo-radiotherapy

Low accumulation and penetration of nanomedicines in tumor severely reduce therapeutic efficacy. Herein, a pH-responsive gold nanoassembly is designed to overcome these problems. Polyethylene glycol linked raltitrexed (RTX, target ligand and chemotherapy drug) and two tertiary amine molecules (1-(2-aminoethyl) pyrrolidine and N,N-dibutylethylenediamine) are modified on the surface of the 6-nm gold nanoparticles by lipoic acid to form gold nanoassembly defined as Au-NNP(RTX). The Au-NNP (RTX) nanoassembly could remain at about 160 nm at the blood circulation (pH 7.4), while split into 6-nm gold nanoparticles due to tertiary amine protonation at tumor extracellular pH (pH 6.8). This pH-responsive disassembly behavior endows Au-NNP(RTX) better tumor tissue permeability through the better diffusion brought by the size reduction. Meanwhile, after disassembly, more RTXs on the surface of gold nanoparticles are exposed from the shielded state of assembly along with 2.25-fold augment of cellular uptake capability. Most importantly, the results show that Au-NNP(RTX) possesses of high tumor accumulation and effective tumor penetration, thereby enhancing the tumor chemo-radiotherapy efficiency.

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A pH-responsive self-targeting & splitting gold nanoassembly is fabricated.

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The nanoassembly holds better tumor tissue permeability by the size reduction.

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The nanoassembly enhances targeting capability by ligand shielding and exposure.

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Clever design endows the system synergistic effect of chemo-radiotherapy.

A Titanium Nitride Nanozyme for pH-Responsive and Irradiation-Enhanced Cascade-Catalytic Tumor Therapy

Nanozyme-based catalytic tumor therapy is an emerging therapeutic method with high reactivity in response to tumor microenvironments (TMEs). To overcome the current limitations of deficient catalytic activity of nanozymes, we studied the contributing factors of enzymatic activity based on non-metallic-atom doping and irradiation. Nitrogen doping significantly enhanced the peroxidase activity of Ti-based nanozymes, which was shown experimentally and theoretically. Based on the excellent NIR-adsorption-induced surface plasmon resonance and photothermal effect, the enzymatic activity of TiN nanoparticles (NPs) was further improved under NIR laser irradiation. Hence, an acidic TME-responsive and irradiation-mediated cascade nanocatalyst (TLGp) is presented by using TiN-NP-encapsulated liposomes linked with pH-responsive PEG-modified glucose oxidase (GOx). The integration of pH-responsive GOx-mediated H₂ O₂ self-supply, nitrogen-doping, and irradiation-enhanced enzymatic activity of TiN NPs and mild-photothermal therapy enables an effective tumor inhibition by TLGp with minimal side effects in vivo.

Construction of a pH/TGase "Dual Key"-Responsive Gold Nano-radiosensitizer with Liver Tumor-Targeting Ability

The method of tumor microenvironment (TME)-responsive aggregation has become a promising approach to enhance treatment effect by improving the accumulation of nanoparticles in tumors. The enzymatic cross-linking strategy has widely attracted attention owing to its good aggregation stability and biocompatibility. However, the enzymes in nontumor tissue can also catalyze the cross-linking reaction and reduce accumulation of nanoparticles in tumor. In this work, a "dual key"-responsive strategy is utilized to construct a transglutaminase (TGase)/pH-responsive radiosensitizer (Au@TAcoGal) with specific aggregation behavior in hepatic tumor cells. Au@TAcoGal can retain its stability in blood circulation (pH 7.4) even in the presence of TGase in plasma. On reaching tumor sites, it can be endocytosed by hepatoma cells by the active targeting of phenylboronic acid (PBA) and aggregated under acidity and overexpression of TGase in cells. Due to its specific accumulation in hepatoma cells, radiotherapy can be operated under a lower dose of X-ray. The results show that the cellular accumulation of Au@TAcoGal increases by 30-70%, and the cell survival rate is less than 25% under X-ray irradiation. The antineoplastic results show that Au@TAcoGal exhibits a higher therapeutic effect, and the tumor inhibition rate can reach 84.21%.

Strategies and challenges to improve the performance of tumor-associated active targeting

Over the past decade, nanoparticle-based drug delivery systems have been extensively explored. However, the average tumour enrichment ratio of passive targeting systems corresponds to only 0.7% due to the nonspecific uptake by normal organs and poor selective retention in tumours. The therapeutic specificity and efficacy of nano-medicine can be enhanced by equipping it with active targeting ligands, although it is not possible to ignore the recognition and clearance of the reticuloendothelial system (RES) caused by targeting ligands. Given the complexity of the systemic circulation environment, it is necessary to carefully consider the hydrophobicity, immunogenicity, and electrical property of targeting ligands. Thus, for an active targeting system, the targeting ligands should be shielded in blood circulation and de-shielded in the tumour region for enhanced tumour accumulation. In this study, strategies for improving the performance of active targeting ligands are introduced. The strategies include irreversible shielding, reversible shielding, and methods of modulating the multivalent interactions between ligands and receptors. Furthermore, challenges and future developments in designing active ligand targeting systems are also discussed.

Stimuli-Responsive Plasmonic Assemblies and Their Biomedical Applications

Among the diverse development of stimuli-responsive assemblies, plasmonic nanoparticle (NP) assemblies functionalized with responsive molecules are of a major interest. In this review, we outline a comprehensive and up-to-date overview of recently reported studies on in vitro and in vivo assembly/disassembly and biomedical applications of plasmonic NPs, wherein stimuli such as enzymes, light, pH, redox potential, temperature, metal ions, magnetic or electric field, and/or multi-stimuli were involved. Stimuli-responsive assemblies have been applied in various biomedical fields including biosensors, surfaced-enhanced Raman scattering (SERS), photoacoustic (PA) imaging, multimodal imaging, photo-activated therapy, enhanced X-ray therapy, drug release, stimuli-responsive aggregation-induced cancer therapy, and so on. The perspectives on the use of stimuli-responsive plasmonic assemblies are discussed by addressing future scientific challenges involving assembly/disassembly strategies and applications.

Encapsulation and release of drug nanoparticles in functional polymeric vesicles

We investigated the co-assembly of amphiphilic diblock copolymers in solutions containing drugs and functional nanoparticles using the dissipative particle dynamics (DPD) method. By controlling the size and the concentration of the functional nanoparticles, the length of the hydrophobic blocks, and the interaction parameters between the hydrophobic block/solvent and the functional nanoparticles, we obtained the desired aggregates to load drugs. The aggregates loaded with drugs can be disk-like micelles, sphere-like micelles and vesicles with functional nanoparticles on the surface. When the solvent environment changes, the drugs loaded in the functional vesicles can release into the solvent. The release content is critically dependent on the repulsive interaction between the drugs and the solvent. The dynamic curve of drug release is obtained. The result is in agreement with the experiments about drug release. Our studies showed that we can precisely control the formation of functional vesicles to load and release drugs. Loading drugs in the process of self-assembly and controlling the release have broad potential in the field of clinical medicine and adding functional nanoparticles can be of great help in drug delivery and medical diagnosis.

Metal-Organic Framework-Integrated Enzymes as Bioreactor for Enhanced Therapy against Solid Tumor via a Cascade Catalytic Reaction

Emerging natural-enzyme-based nanocatalytic tumor therapy depending on the high catalytic performance of natural enzymes has inspired great research interest in clinical applications. Nevertheless, the natural-enzyme-based catalytic therapy efficiency is seriously hampered by the low operational stability, poor delivery efficiency, and the short lifetime of enzymes. Herein, a bioreactor based on zeolitic imidazolate framework-8 (ZIF-8) was fabricated through one-pot embedding horseradish peroxidase (HRP) and glucose oxidase (Gox) strategy (ZIF-8@Gox/HRP) for synergistic cancer therapy. Notably, the obtained ZIF-8@Gox/HRP can efficiently consume endogenous glucose to generate gluconic acid and H₂O₂ for starving tumors, and subsequently, H₂O₂ was decomposed by encapsulated HRP to release high-toxic ^•OH radicals, inducing cancer cell apoptosis for oxidation therapy. Importantly, in vivo results showed that ZIF-8@Gox/HRP had an impressive tumor-suppression rate based on cascade catalytic reaction. Therefore, this work paves a new avenue to design smart enzyme-based platforms for safe and efficient cancer therapy.

Self-Assembly of Ultrathin Nanocrystals to Multidimensional Superstructures

The self-assembly of ultrathin nanocrystals (UTNCs) into well-organized multidimensional superstructures is one of the key topics in material chemistry and physics. Highly ordered nanocrystal assemblies also known as superstructures or synthetic structures have remained a focus for researchers over the past few years due to synergy in their properties as compared to their components. Here, we aim to present the recent progress being made in this field with highlights of our research group endeavors in the engineering of self-assembled complex multidimensional superstructures of various inorganic materials, including polyoxometalates. The driving forces for the assembly process and its kinetics along with the potential applications associated with these unique ordered and spatially complex superstructures are also discussed.

One-pot synthesis of acid-induced in situ aggregating theranostic gold nanoparticles with enhanced retention in tumor cells

In this work, we took advantage of a one-pot reaction to prepare tumor-targeting nanoparticles (Au@T), which could respond to the intracellular acidic environment and form aggregates to enhance the retention effect of nanoparticles in tumor cells, for tumor dual-mode diagnose and photothermal therapy.