pH-Dependent aggregation and pH-independent cell membrane adhesion of monolayer-protected mixed charged gold nanoparticles

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.

Ligand Lipophilicity Determines Molecular Mechanisms of Nanoparticle Adsorption to Lipid Bilayers

The interactions of ligand-functionalized nanoparticles with the cell membrane affect cellular uptake, cytotoxicity, and related behaviors, but relating these interactions to ligand properties remains challenging. In this work, we perform coarse-grained molecular dynamics simulations to study how the adsorption of ligand-functionalized cationic gold nanoparticles (NPs) to a single-component lipid bilayer (as a model cell membrane) is influenced by ligand end group lipophilicity. A set of 2 nm diameter NPs, each coated with a monolayer of organic ligands that differ only in their end groups, was simulated to mimic NPs recently studied experimentally. Metadynamics calculations were performed to determine key features of the free energy landscape for adsorption as a function of the distance of the NP from the bilayer and the number of NP-lipid contacts. These simulations revealed that NP adsorption is thermodynamically favorable for all NPs due to the extraction of lipids from the bilayer and into the NP monolayer. To resolve ligand-dependent differences in adsorption behavior, string method calculations were performed to compute minimum free energy pathways for adsorption. These calculations revealed a surprising nonmonotonic dependence of the free energy barrier for adsorption on ligand end group lipophilicity. Large free energy barriers are predicted for the least lipophilic end groups because favorable NP-lipid contacts are initiated only through the unfavorable protrusion of lipid tail groups out of the bilayer. The smallest free energy barriers are predicted for end groups of intermediate lipophilicity which promote NP-lipid contacts by intercalating within the bilayer. Unexpectedly, large free energy barriers are also predicted for the most lipophilic end groups which remain sequestered within the ligand monolayer rather than intercalating within the bilayer. These trends are broadly in agreement with past experimental measurements and reveal how subtle variations in ligand lipophilicity dictate adsorption mechanisms and associated kinetics by influencing the interplay of lipid-ligand interactions.

Using Aggregation to Chaperone Nanoparticles Across Fluid Interfaces

Nanoparticles (NPs) transfer is usually induced by adding ligands to modify NP surfaces, but aggregation of NPs oftentimes hampers the transfer. Here, we show that aggregation during NP phase transfer does not necessarily result in transfer failure. Using a model system comprising gold NPs and amphiphilic polymers, we demonstrate an unusual mechanism by which NPs can undergo phase transfer from the aqueous phase to the organic phase via a single-aggregation-single pathway. Our discovery challenges the conventional idea that aggregation inhibits NP transfer and provides an unexpected pathway for transferring larger-sized NPs (>20 nm). The charged amphiphilic polymers effectively act as chaperons for the NP transfer and offer a unique way to manipulate the dispersion and distribution of NPs in two immiscible liquids. Moreover, by intentionally jamming the NP-polymer assembly at the liquid/liquid interface, the transfer process can be inhibited.

A Comparable icELISA and Lateral Flow Immunoassay for the Sensitive and Rapid Detection of 4,4'-Dinitrocarbanilide in Chicken

4,4'-dinitrocarbanilide (DNC) is a key component and marker residue of nicarbazin, which forms residues in edible tissue and then causes nephrotoxicity and hepatotoxicity in humans if used excessively. To simplify sample preparation and monitor the DNC rapidly and accurately, a comparable icELISA and lateral flow immunoassay (LFIA) was developed in this study. Briefly, the reaction parameters were explored for improving the sensitivity of icELISA and LFIA. Under the optimal conditions, methanol was selected as the extracting solvent for DNC in chicken, and 20- and 10-fold dilutions of sample extraction eliminated the matrix effect for icELISA and LFIA, separately. After sample pretreatment, the analysis properties of icELISA and LFIA were compared. The limit of detection of icELISA for DNC was 0.8 μg/kg, and the visual and quantitative limits of detection of LFIA were 8 and 2.5 μg/kg. Compared with icELISA, LFIA showed lower sensitivity but obvious advantages in terms of matrix tolerance and detection time (within 15 min). The sensitivity, specificity, and accuracy of the developed assays satisfied the detection requirement even if using simple sample pretreatment. This comparable icELISA and LFIA provided mutual verifiability methods for the accurate detection of DNC in chicken.

Understanding Molecular Aggregation of Ligand-Protected Atomically-Precise Metal Nanoclusters

Monolayer-protected atomically precise nanoclusters (MPCs) are an important class of molecules due to their unique structural features and diverse applications, including bioimaging, sensors, and drug carriers. Understanding the atomistic and dynamical details of their self-assembly process is crucial for designing system-specific applications. Here, we applied molecular dynamics and on-the-fly probability-based enhanced sampling simulations to study the aggregation of Au₂₅(pMBA)₁₈ MPCs in aqueous and methanol solutions. The MPCs interact via both hydrogen bonds and π-stacks between the aromatic ligands to form stable dimers, oligomers, and crystals. The dimerization free energy profiles reveal a pivotal role of the ligand charged state and solvent mediating the molecular aggregation. Furthermore, MPCs' ligands exhibit suppressed conformational flexibility in the solid phase due to facile intercluster hydrogen bonds and π-stacks. Our work provides unprecedented molecular-level dynamical details of the aggregation process and conformational dynamics of MPCs ligands in solution and crystalline phases.

Functional-Group Effect of Ligand Molecules on the Aggregation of Gold Nanoparticles: A Molecular Dynamics Simulation Study

In this paper, atomistic molecular dynamics simulations are performed for the systems consisting of functionalized gold nanoparticles (NPs) in a toluene medium. Gold NPs are coated with ligand molecules that have different terminal groups, that is, polar carboxyl (COOH), hydroxyl (OH), amine (NH₂), and nonpolar methyl (CH₃). These functional groups are selected to understand the relation between the aggregation behavior of functionalized gold NPs in toluene and the polarity of terminal groups of ligand molecules. The center-of-mass distances between NP pairs, the radial distribution functions, the mean square displacements, the radius of gyration, and the number of hydrogen bonds (H-bond) between ligand molecules are computed. Our simulation results indicate that functionalized gold NPs exhibit different aggregation/dispersion behaviors depending upon the terminal group of ligands.

Biosynthetic gold nanoparticles of Hibiscus syriacus L. callus potentiates anti-inflammation efficacy via an autophagy-dependent mechanism

Biological applications of gold nanoparticles (AuNps) have potentially explored an efficient agent attributed to their biocompatibility and high efficiency in drug delivery. Our study applied an extract of Hibiscus syriacus L. callus (HCE) with a pioneer implementation on the induction of mass production. Bioactive compounds present in HCE were identified by Gas chromatography-mass spectrometry (GC-MS) and Liquid chromatography MS (LC-MS), wherein, the Denatonium was exclusively identifiable in HCE. Next, AuNps were synthesized and optimized using HCE (HCE-AuNps), and the comparison was conducted to evaluate the anti-inflammatory effect in lipopolysaccharide (LPS)-stimulated macrophages. As per result, HCE-AuNps was reported to show a prominent reduction of pro-inflammatory cytokines and renovate the mitochondrial function through restoring the mitochondrial membrane potential changes, decreasing reactive oxygen species (ROS) accumulation, and recovering ATP contents, respectively. Furthermore, the immunoblotting of LC3b/a accumulation, and p62 rapid degradation revealed that HCE-AuNps could induce the autophagy as an intracellular response to reinforce alleviation of pro-inflammatory cytokines and mitochondria dysfunction. Besides, 740 Y-P (PI3K agonist) was used to verify that inhibiting autophagy could partially reverse HCE-AuNps suppressed mitochondrial dysfunction, and thus exacerbated inflammation, supporting a causal role for autophagy in the anti-inflammatory effect of HCE-AuNps. Taken together, we strongly anticipate that HCE-AuNps would act as a potential autophagy inducer for LPS-triggered macrophage's inflammation, providing a novel insight for biosynthetic nanoparticles in the treatment of mitochondria dysfunction and inflammation related diseases.

Engineering the Interface between Inorganic Nanoparticles and Biological Systems through Ligand Design

Nanoparticles (NPs) provide multipurpose platforms for a wide range of biological applications. These applications are enabled through molecular design of surface coverages, modulating NP interactions with biosystems. In this review, we highlight approaches to functionalize nanoparticles with "small" organic ligands (Mw < 1000), providing insight into how organic synthesis can be used to engineer NPs for nanobiology and nanomedicine.

Membrane poration, wrinkling, and compression: deformations of lipid vesicles induced by amphiphilic Janus nanoparticles

Building upon our previous studies on interactions of amphiphilic Janus nanoparticles with glass-supported lipid bilayers, we study here how these Janus nanoparticles perturb the structural integrity and induce shape instabilities of membranes of giant unilamellar vesicles (GUVs). We show that 100 nm amphiphilic Janus nanoparticles disrupt GUV membranes at a threshold particle concentration similar to that in supported lipid bilayers, but cause drastically different membrane deformations, including membrane wrinkling, protrusion, poration, and even collapse of entire vesicles. By combining experiments with molecular simulations, we reveal how Janus nanoparticles alter local membrane curvature and collectively compress the membrane to induce shape transformation of vesicles. Our study demonstrates that amphiphilic Janus nanoparticles disrupt vesicle membranes differently and more effectively than uniform amphiphilic particles.

Atomistic insight into the aggregation of [Au25(SR)18] q nanoclusters

Atomically precise nanoclusters have been proven to give solid state aggregates with intriguing optical properties. However, the mechanism that regulates this aggregation remains unclear. Here, the aggregation of two Au₂₅ nanoclusters in solution is investigated through enhanced sampling molecular dynamics simulations. To understand how the free energy of the systems depends on the nanocluster features, calculations were performed on three nanocluster pairs which differ in charge states and substituent nature and dimension. Our results show that the choice of the ligands heavily affects the free energy profile of the systems when the structures are nearby and, in some cases, the formation of a dimeric phase is observed. This phase is particularly stable in long-chain substituted nanoclusters, where the long alkane chains can generate bundles and the gold cores are closer compared to the short-chain ligands. We found a remarkable agreement between our calculations and the literature-available solid-state structures, especially for the orientation of the interacting nanoclusters. Moreover, some of the dimeric structures are prodromal to the formation of the aurophilic intercluster bond observed in the crystal structures, meaning that the dimer can act as a precursor and can drive the whole crystallization mechanism toward the formation of stable crystal species.

An amphiphilic-ligand-modified gold nanoflower probe for enhancing the stability of lateral flow immunoassays in dried distillers grains

An amphiphilic ligand-capped gold nanoflower (AuNF) was proposed as a novel lateral flow immunoassay (LFA) reporter for zearalenone (ZEN) detection in distillers dried grains solubles (DDGS).