Systematic investigation of the effects of PEG and tween on nanoparticle mobility using total internal reflective fluorescence microscopy

Introduction: Respiratory diseases, including chronic obstructive pulmonary disease and asthma, are major global health concerns and traditional drug delivery methods often fail to reach concentrations at target sites due to limited drug penetration. Nanoparticle-based drug delivery systems offer a promising approach to overcome these barriers by enhancing the drug’s bioavailability and delivery efficiency. Here, varying concentrations and types of PEG and Tween were investigated as part of a suspension media to observe their effect on the diffusion of fluorescence-labelled polystyrene nanoparticles.

Methods: Nanoparticle suspensions were prepared using fluorescence carboxylate-modified nanoparticles of different sizes, and the suspension media was made of varying concentrations and types of PEG and Tween. The nanoparticle suspensions were characterised using total internal reflective fluorescence microscopy (TIRFM). The particles’ Mean Square Displacement (MSD) and diffusion coefficients were analysed using the TrackMate plugin in Fiji ImageJ and customised MATLAB scripts.

Results: Figure 1 shows the MSD tracking of nanoparticles using TIRFM and Trackmate plugin, where the background and particle fluorescence thresholds were automatically adjusted, allowing simultaneous monitoring of multiple particles. Custom MATLAB scripts were successfully developed and used to verify the accuracy of the X and Y coordinates. Nanoparticle traces with less than 200 data points were excluded due to loss of focus. MSD analysis showed that smaller particles and the presence of Tween 60 significantly enhanced diffusion, while larger particles and the presence of surfactants with greater molecular weight (MW), such as PEG 4K and 8K, reduced diffusion, consistent with the classical diffusion theory. High MW PEG also reduced the microviscosity of the surrounding environment, while minimal changes were observed in any of the other conditions tested.

Conclusions: Tween 60 and PEG 2K and small particle sizes are identified as the key surfactants to improve their diffusion across various biohydrogel barriers significantly. Future research will focus on developing this static MSD setup into a high throughput setting using 96-well plates and automated TIRFM functions.