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. 2024 May 23;15(20):5428-5435.
doi: 10.1021/acs.jpclett.4c00806. Epub 2024 May 14.

Variable Non-Gaussian Transport of Nanoplastic on Supported Lipid Bilayers in Saline Conditions

Diyali Sil  1 , Edin Osmanbasic  1 , Sasthi Charan Mandal  2 , Atanu Acharya  2   3 , Chayan Dutta  1
Affiliations

Variable Non-Gaussian Transport of Nanoplastic on Supported Lipid Bilayers in Saline Conditions

Diyali Sil et al. J Phys Chem Lett. .

Abstract

Nanoplastic-lipid interaction is vital to understanding the nanoscale mechanism of plastic adsorption and aggregation on a lipid membrane surface. However, a single-particle mechanistic picture of the nanoplastic transport process on a lipid surface remains unclear. Here, we report a salt-dependent non-Gaussian transport mechanism of polystyrene particles on a supported 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) lipid bilayer surface. Particle stickiness on the POPC surface increases with salt concentration, where the particles stay longer at the surface and diffuse to shorter distances. Additionally, a non-Gaussian diffusion state dominates the transport process at high salt concentrations. Our current study provides insight into the transport mechanism of polystyrene (PS) particles on supported lipid membranes, which is essential to understanding fundamental questions regarding the adsorption mechanisms of nanoplastics on lipid surfaces.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Two types of transport modes for PS on POPC bilayers. (A) An experimental model system showing a carboxy functionalized PS bead (100 nm) on a supported POPC bilayer surface. (B) Representative trajectory showing a random diffusion with longer displacement and confined diffusion for PS beads.
Figure 2
Figure 2
A higher number of particles are adsorbed on the POPC supported lipid bilayer surface at high salt concentrations. (A and B) Representative raw data showing PS beads on a supported POPC bilayer at 10 uM and 1000 uM NaCl, respectively. (C) Total number of PS particles on the lipid bilayer surface as a function of salt (NaCl) concentration. Here the number of particles at each concentration is calculated as an average from at least 10 different data sets, and the error bar represents the standard deviations from all measurements.
Figure 3
Figure 3
Displacement modulation for long and short displacements of PS particles from single-particle trajectories at varying salt concentrations. (A) Single-frame displacement distribution for carboxy-functionalized PS beads on the supported POPC surface under varying NaCl salt concentrations from 10 to 1000 μM. Two different populations of displacements are observed in all conditions. Each single-frame displacement distribution curve (dotted lines with filled circles) represents at least 3000 single-particle events. Dotted lines with black triangles represent the MCMC approximation of the distribution. (B) Long and short populations at each concentration obtained from MCMC analysis are plotted as a function of NaCl. As concentration increases, the long displacement is decreased, while the short population increases. Here each point is the average of 10 different data sets, and the error bar represents the standard deviation.
Figure 4
Figure 4
Particles stay longer at the lipid surface at high NaCl concentration. (A) Cumulative SRT probability distributions are plotted at 10, 100, and 1000 μM NaCl concentrations. The dotted lines represent the fittings at each concentration. (B) Average surface residence times (formula image) as a function of NaCl concentration. Each data point is an average of 10 different data sets, and the error bars represent the standard deviations in each measurement.
Figure 5
Figure 5
Non-Gaussian diffusion at high NaCl concentration. (A) Self-part of the van Hove distribution for representative particle trajectories at 10, 100, and 1000 μM NaCl concentration. A central peak at short displacements (0.5 μm) are observed at all conditions. (B) Self-part of the van Hove distributions at only buffer and (C) 1000 μM NaCl concentrations at different time lags. In both cases, the central peak broadens with time lag (data presented at insets for clarity), showing confined diffusion. The broad Gaussian peak at the buffer condition broadens with time, typical for surface-mediated transport processes. Also, the long-tailed distribution for the 1000 μM NaCl broadens with time. (D) The non-Gaussian parameter (α2) calculated at different time lags shows increasing non-Gaussian behavior for all conditions.
Scheme 1
Scheme 1. Salt-Dependent Transport Model of Carboxy Modified PS on Supported POPC Surface
Debye length decreases with increasing salt concentration, so at low ionic strength there is lower electrostatic interaction between the negatively charged PS beads and the zwitterionic surface head groups of the POPC lipids leading to longer displacement and lower surface adsorption. At higher salt concentration, stronger electrostatic interactions lead to higher adsorption, shorter displacement, and confined diffusion.
Figure 6
Figure 6
(A) The number density profile of the lipid headgroups, formula image (magenta) and formula image (cyan) along the z-axis of the simulation box. (B) The density profile for Na+(blue) and Cl– (red) ions. Representative snapshots show Na+ ions are bound to the formula image groups (C) and Cl– ions bound to the formula image groups (D). The lipid tails are shown in yellow.
See this image and copyright information in PMC

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