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1. Thermodynamics of Protein-Surface Binding- the Model Makes all the Difference

   Nicholas C. Fitzkee, Kayla D (February 2020, Biophysical journal)

   null (Ed.)

   Gold nanoparticles (AuNPs) are now being used in such areas as diagnostics, drug delivery, and biological sensing. In these applications, AuNPs are frequently exposed to biological fluids. These fluids contain many different proteins, any of which may interfere with the intended function of the nanoparticle. In this work, we examine the thermodynamic consequences of proteinnanoparticle binding using a combined spectroscopic and calorimetric approach. We monitored binding using UV-Vis spectroscopy, differential scanning calorimetry (DSC), and isothermal titration calorimetry (ITC). Six proteins were studied based on their differing chemical properties, and both 15 nm and 30 nm citrate-coated AuNPs were investigated. We interpreted the UV-Vis data using two different models: the commonly-used Langmuir isotherm model and a more complex mass transport model. Both models can be used to determine Kd values for the 30 nm AuNP data; however, the mass transport model is more appropriate for 15 nm AuNPs. This is because, when fitting the Langmuir model, it is commonly assumed that most proteins are not surface-associated, and this assumption fails for 15 nm AuNPs. The DSC thermograms show two transitions for a globular protein adsorbed to a 15 nm AuNP: one high-temperature transition that is similar to global protein unfolding (68 C), and one low-temperature transition that may correspond to unfolding at the surface (56 C). Conversely, ITC experiments show no net heat of adsorption for GB3, even at high protein/AuNP concentrations. Together, the spectroscopic and calorimetric data suggest a complex, multi-step process for protein-nanoparticle adsorption. Moreover, for the proteins studied, both AuNP curvature and protein chemistry contribute to protein adsorption, with proteins generally binding more weakly to the larger nanoparticles. In the future, this work may lead to principles for improving the design of AuNPbased therapeutics and sensors. 

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2. The role of polymer coatings in lipid membrane penetration by graphene oxide dots

   https://doi.org/10.1039/D5NR00838G  

   Frigerio, Giulia; Siani, Paulo; Donadoni, Edoardo; Cui, Qiang; Di_Valentin, Cristiana (August 2025, Nanoscale)

   Understanding the cell membrane penetration process of biomedical nanosystems and its dependence on nanomaterial properties and surface functionalization is crucial for the rational design of safe and efficient cellular internalization strategies. Computer simulations are powerful tools to evaluate the thermodynamic aspects of the process and to elucidate its underlying molecular mechanisms. In this work, the interaction between uncoated or polymer-coated graphene oxide (GO) dots and lipid bilayer models is investigated by coarse-grained (CG) molecular dynamics (MD) simulations. We first validate the coarse-grained model against all-atom MD simulations (AAMD). Then, we perform CGMD simulations and free energy calculations to assess the effect of the polymeric coating and of its features (grafting density, polymer end-group charge and polymer hydrophilic/hydrophobic character) on the interaction between GO dots of realistic size and lipid membranes. We find that the membrane penetration of GO dots is spontaneous when coated with a low-density polyethylene glycol (PEG) layer, while a high-density PEG coating prevents the penetration, and a mixed PEG/polyethylene (PE) coating excessively stabilizes the nanosystem in the inner membrane region. These findings will help to fine-tune how GO dots interact with cellular membranes. 

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3. Anionic nanoparticle-induced perturbation to phospholipid membranes affects ion channel function

   https://doi.org/10.1073/pnas.2004736117  

   Foreman-Ortiz, Isabel U.; Liang, Dongyue; Laudadio, Elizabeth D.; Calderin, Jorge D.; Wu, Meng; Keshri, Puspam; Zhang, Xianzhi; Schwartz, Michael P.; Hamers, Robert J.; Rotello, Vincent M.; et al (October 2020, Proceedings of the National Academy of Sciences)

   Understanding the mechanisms of nanoparticle interaction with cell membranes is essential for designing materials for applications such as bioimaging and drug delivery, as well as for assessing engineered nanomaterial safety. Much attention has focused on nanoparticles that bind strongly to biological membranes or induce membrane damage, leading to adverse impacts on cells. More subtle effects on membrane function mediated via changes in biophysical properties of the phospholipid bilayer have received little study. Here, we combine electrophysiology measurements, infrared spectroscopy, and molecular dynamics simulations to obtain insight into a mode of nanoparticle-mediated modulation of membrane protein function that was previously only hinted at in prior work. Electrophysiology measurements on gramicidin A (gA) ion channels embedded in planar suspended lipid bilayers demonstrate that anionic gold nanoparticles (AuNPs) reduce channel activity and extend channel lifetimes without disrupting membrane integrity, in a manner consistent with changes in membrane mechanical properties. Vibrational spectroscopy indicates that AuNP interaction with the bilayer does not perturb the conformation of membrane-embedded gA. Molecular dynamics simulations reinforce the experimental findings, showing that anionic AuNPs do not directly interact with embedded gA channels but perturb the local properties of lipid bilayers. Our results are most consistent with a mechanism in which anionic AuNPs disrupt ion channel function in an indirect manner by altering the mechanical properties of the surrounding bilayer. Alteration of membrane mechanical properties represents a potentially important mechanism by which nanoparticles induce biological effects, as the function of many embedded membrane proteins depends on phospholipid bilayer biophysical properties. 

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4. Ligand Lipophilicity Determines Molecular Mechanisms of Nanoparticle Adsorption to Lipid Bilayers

   https://doi.org/10.1021/acsnano.3c11854  

   Huang-Zhu, Carlos A.; Sheavly, Jonathan K.; Chew, Alex K.; Patel, Samarthaben J.; Van Lehn, Reid C. (February 2024, ACS Nano)

   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 non-monotonic 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. 

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5. Silver Nanoparticles Stable to Oxidation and Silver Ion Release Show Size-Dependent Toxicity In Vivo

   https://doi.org/10.3390/nano11061516  

   Cunningham, Brittany; Engstrom, Arek M.; Harper, Bryan J.; Harper, Stacey L.; Mackiewicz, Marilyn R. (June 2021, Nanomaterials)

   null (Ed.)

   Silver nanoparticles (AgNPs) are widely used in commerce, however, the effect of their physicochemical properties on toxicity remains debatable because of the confounding presence of Ag+ ions. Thus, we designed a series of AgNPs that are stable to surface oxidation and Ag+ ion release. AgNPs were coated with a hybrid lipid membrane comprised of L-phosphatidylcholine (PC), sodium oleate (SOA), and a stoichiometric amount of hexanethiol (HT) to produce oxidant-resistant AgNPs, Ag–SOA–PC–HT. The stability of 7-month aged, 20–100 nm Ag–SOA–PC–HT NPs were assessed using UV–Vis, dynamic light scattering (DLS), and inductively coupled plasma mass spectrometry (ICP-MS), while the toxicity of the nanomaterials was assessed using a well-established, 5-day embryonic zebrafish assay at concentrations ranging from 0–12 mg/L. There was no change in the size of the AgNPs from freshly made samples or 7-month aged samples and minimal Ag+ ion release (<0.2%) in fishwater (FW) up to seven days. Toxicity studies revealed AgNP size- and concentration-dependent effects. Increased mortality and sublethal morphological abnormalities were observed at higher concentrations with smaller nanoparticle sizes. This study, for the first time, determined the effect of AgNP size on toxicity in the absence of Ag+ ions as a confounding variable. 

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