Permeation of nanoparticles through a model membrane: CG-MD Simulations Studies

How nanoparticles interact with biological membranes and the structural and mechanical properties of membranes during the nanoparticle permeation are of significant importance in determining the toxicity of nanoparticles as well as their potential applications in phototherapy, imaging and gene/drug delivery. In this work, coarse-grained molecular dynamics (CG-MD) simulations are carried out to explore the permeation characteristics of nanoparticles through a model membrane as well as the structural and mechanical properties of the membrane. We study gold nanoparticles as our model nanoparticles and a self-assembled DPPC lipid bilayer as our model membrane. A series of simulations are performed to validate the coarse-grained model for nanoparticles and lipid membrane. We start with various sizes of nanocrystals (bare nanoparticles) and then compare the differences in permeation behaviors between bare nanoparticles with ligand-coated nanoparticles with various ligand lengths to provide insights into how the ligands affect the permeation process. After that, CG-MD is applied to investigate the water penetration, ion transport and lipid molecule flip-flop phenomenon during nanoparticle permeation. The effect of ion concentration, pressure differential across the membrane, nanoparticle size and permeation velocity have been examined in this work. Finally, CG-MD is implemented to explore a method for the calculation of membrane compressibility. Membrane behavior for conditions not studied experimentally is also predicted by our method. The findings described in our work will lead to a better understanding of nanoparticle permeation process, nanoparticle-lipid membrane interactions, membrane deformation and should help in developing more efficient nanocarrier drug delivery systems while avoiding cell cytotoxicity

Accurate second Kerr virial coefficient of rare gases from the state-of-the-art <i>ab initio</i> potentials and (hyper)polarizabilities

The second Kerr virial coefficient of rare gases is studied in this work using the best ab initio potentials and (hyper)polarizabilities in the literature. The second Kerr virial coefficient of helium-4, helium-3, neon, argon, and krypton and its polarizability component of xenon are computed by the semi-classical method together with the Padé approximant over a wide temperature range. In addition, the uncertainty of second Kerr virial coefficient is estimated from the uncertainties of the ab initio interaction-induced properties. The experimental and theoretical data in the literature is compared with our calculated values to examine the quality of this work. It is shown that our computed values in the supplementary materials are as accurate as the literature data at medium and high temperatures and are more reliable at low temperatures.</p

Contact Angles of Surface Nanobubbles on Mixed Self-Assembled Monolayers with Systematically Varied Macroscopic Wettability by Atomic Force Microscopy

The dependence of the properties of so-called “surface nanobubbles” at the interface of binary self-assembled monolayers (SAMs) of octadecanethiol (ODT) and 16-mercaptohexadecanoic acid (MHDA) on ultraflat template-stripped gold and water on the surface composition was studied systematically by in situ atomic force microscopy (AFM). The macroscopic water contact angle (θmacro) of the SAMs spanned the range between 107° ± 1° and 15° ± 3°. Surface nanobubbles were observed on all SAMs by intermittent contact-mode AFM; their size and contact angle were found to depend on the composition of the SAM. In particular, nanoscopic contact angles θnano nano calculated from these data were found to change from 167° ± 3° to 33° ± 58°, when θmacro decreased from 107° ± 1° to 37° ± 3°. While the values for θnano significantly exceeded those of θmacro for hydrophobic SAMs, which is fully in line with previous reports, this discrepancy became less pronounced and finally vanished for more hydrophilic surfaces

Optimized Model Surfaces for Advanced Atomic Force Microscopy Studies of Surface Nanobubbles

The formation of self-assembled monolayers (SAMs) of binary mixtures of 16-mercaptohexadecanoic acid (MHDA) and 1-octadecanethiol (ODT) on ultraflat template-stripped gold (TSG) surfaces was systematically investigated to clarify the assembly behavior, composition, and degree of possible phase segregation in light of atomic force microscopy (AFM) studies of surface nanobubbles on these substrates. The data for SAMs on TSG were compared to those obtained by adsorption on rough evaporated gold, as reported in a previous study. Quartz crystal microbalance and surface plasmon resonance data acquired <i>in situ</i> on TSG indicate that similar to SAM formation on conventional evaporated gold substrates ODT and MHDA form monolayers and bilayers, respectively. The second layer on MHDA, whose formation is attributed to hydrogen bonding, can be easily removed by adequate rinsing with water. The favorable agreement of the grazing incidence reflection Fourier transform infrared (GIR FTIR) spectroscopy and contact angle data analyzed with the Israelachvili–Gee model suggests that the binary SAMs do <i>not</i> segregate laterally. This conclusion is fully validated by high-resolution friction force AFM observations down to a length scale of 8–10 nm, which is much smaller than the typical observed surface nanobubble radii. Finally, correspondingly functionalized TSG substrates are shown to be valuable supports for studying surface nanobubbles by AFM in water and for addressing the relation between surface functionality and nanobubble formation and properties

Simulations of the thermodynamic properties of the helium fluid from the state-of-the-art <i>ab initio</i> potentials and their uncertainty estimation

The molecular dynamics simulation method is used to study the internal energy, pressure, isochoric heat capacity, and sound speed of helium based on the state-of-the-art ab initio potentials. The simulations cover a wide temperature and density range of (20–2000) K and (0.0005–70) molL−1. The uncertainty of simulation data are evaluated based on the uncertainty of the potential and the uncertainty of the simulation method. At temperatures below 300 K, the quantum Feynman-Hibbs modified potential and the Wigner-Kirkwood modified potential are introduced and the results are almost the same as those by the original ab initio potential. The modified potentials can not reasonably describe the quantum effects for the helium fluid at low temperatures, which become obvious below 200 K. The two-body ab initio potential is combined with the three-body ab initio potential to evaluate the influence of multi-body interactions at high densities. When the density is lower than 45 molL−1, the contribution of the three-body term to our simulation data is not significant. As a result, the three-body potential is omitted in our calculations to improve the overall computational efficiency. The thermodynamic property data of this work show agreement with the experimental data in the literature as well as the NIST Refprop 10.0 data at temperatures above 200 K and densities below 45 molL−1.</p

Microcontact Printing of Monodiamond Nanoparticles: An Effective Route to Patterned Diamond Structure Fabrication

By combining microcontact printing with a nanodiamond seeding technique, a precise micrometer-sized chemical vapor deposition (CVD) diamond pattern have been obtained. On the basis of the guidance of basic theoretical calculations, monodisperse detonation nanodiamonds (DNDs) were chosen as an “ink” material and oxidized poly(dimethylsiloxane) (PDMS) was selected to serve as a stamp because it features a higher interaction energy with the DNDs compared to that of the original PDMS. The adsorption kinetics shows an approximately exponential law with a maximum surface DND density of 3.4 × 1010 cm–2 after 20 min. To achieve a high transfer ratio of DNDs from the PDMS stamp to a silicon surface, a thin layer of poly(methyl methacrylate) (PMMA) was spin coated onto the substrates. A microwave plasma chemical vapor deposition system was used to synthesize the CVD diamond on the seeded substrate areas. Precise diamond patterns with a low expansion ratio (3.6%) were successfully prepared after 1.5 h of deposition. Further increases in the deposition time typically lead to a high expansion rate (∼0.8 μm/h). The general pattern shape, however, did not show any significant change. Compared with conventional diamond pattern deposition methods, the technique described here offers the advantages of being simple, inexpensive, damage-free, and highly compatible, rendering it attractive for a broad variety of industrial applications

Turn-On Fluorescent Probe for BSA Detection Constructed by Supramolecular Assembly

The fluorescent probe method has attracted significant research attention due to its high sensitivity and reproducibility in detecting bovine serum albumin (BSA). In this study, we constructed a fluorescent probe for BSA detection by assembling an amphiphilic organic fluorescent molecule, termed 2-(2’-hydroxyphenyl) benzothiazole (HBT-11), with BSA. In an aqueous solution, HBT-11 exhibited a weak fluorescence emission at 501 nm. However, the addition of BSA substantially enhanced the fluorescence emission at 501 nm, indicating that the assembly was driven by electrostatic interactions between HBT-11 and BSA. HBT-11, serving as a fluorescent probe for BSA detection, demonstrated a limit of detection (LOD) as low as 3.92 nmol L–1, excellent photostability, high selectivity, and robust anti-interference capability. Notably, we successfully applied HBT-11 for detecting BSA in fetal bovine serum and selectively imaging BSA in HeLa cells

Mitochondria Targetable Time-Gated Luminescence Probe for Singlet Oxygen Based on a β‑Diketonate–Europium Complex

Singlet oxygen (¹O₂) plays a key role in the photodynamic therapy (PDT) technique of neoplastic diseases. In this work, by using a 9,10-dimethyl-2-anthryl-containing β-diketone, 1,1,1,2,2-pentafluoro-5-(9′,10′-dimethyl-2′-anthryl)-3,5-pentanedione (Hpfdap), as a ¹O₂-recognition ligand, a novel β-diketonate–europium­(III) complex that can act as a luminescence probe for ¹O₂, [Eu­(pfdap)₃(tpy)] (tpy = 2,2′,2″-terpyridine), has been designed and synthesized for the time-gated luminescence detection of ¹O₂ in living cells. The complex is weakly luminescent due to the quenching effect of 9,10-dimethyl-2-anthryl groups. After reaction with ¹O₂, accompanied by the formation of endoperoxides of 9,10-dimethyl-2-anthryl groups, the luminescence quenching disappears, so that the long-lived luminescence of the europium­(III) complex is switched on. The complex showed highly selective luminescence response to ¹O₂ with a remarkable luminescence enhancement. Combined with the time-gated luminescence imaging technique, the complex was successfully used as a luminescent probe for the monitoring of the time-dependent generation of ¹O₂ in 5-aminolevulinic acid (a PDT drug) loaded HepG2 cells during the photodynamic process. In addition, by coloading the complex and a mitochondrial indicator, Mito-Tracker Green, into HepG2 cells, the specific localization of [Eu­(pfdap)₃(tpy)] molecules in mitochondria of HepG2 cells was demonstrated by confocal fluorescence imaging measurements

A Europium(III) Complex as an Efficient Singlet Oxygen Luminescence Probe

A new europium(III) complex, [4‘-(10-methyl-9-anthryl)-2,2‘:6‘,2‘ ‘-terpyridine-6,6‘ ‘-diyl]bis(methylenenitrilo) tetrakis(acetate)−Eu3+, was designed and synthesized as a highly sensitive and selective time-gated luminescence probe for singlet oxygen (1O2). The new probe is highly water soluble with a large stability constant of ∼1021 and a wide pH available range (pH 3−10), and can specifically react with 1O2 to form its endoperoxide (EP-MTTA−Eu3+) with a high reaction rate constant at 1010 M-1 s-1, accompanied by the remarkable increases of luminescence quantum yield from 0.90% to 13.8% and lifetime from 0.80 to 1.29 ms, respectively. The wide applicability of the probe was demonstrated by detection of 1O2 generated from a MoO42-/H2O2 system, a photosensitization system of 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate) (TMPyP), and a horseradish peroxidase catalyzed aerobic oxidation system of indole-3-acetic acid (IAA). In addition, it was found that the new probe could be easily transferred into living HeLa cells by incubation with TMPyP. A time-gated luminescence imaging technique that can fully eliminate the short-lived background fluorescence from TMPyP and cell components has been successfully developed for monitoring the time-dependent generation of 1O2 in living cells