A New Label-Free Technique for Analysing Evaporation Induced Self-Assembly of Viral Nanoparticles Based on Enhanced Dark-Field Optical Imaging

Abstract

Nanoparticle self-assembly is a complex phenomenon, the control of which is complicated by the lack of appropriate tools and techniques for monitoring the phenomenon with adequate resolution in real-time. In this work, a label-free technique based on dark-field microscopy was developed to investigate the self-assembly of nanoparticles. A bio-nanoparticle with complex shape (T4 bacteriophage) that self-assembles on glass substrates upon drying was developed. The fluid flow regime during the drying process, as well as the final self-assembled structures, were studied using dark-field microscopy, while phage diffusion was analysed by tracking of the phage nanoparticles in the bulk solutions. The concentrations of T4 phage nanoparticles and salt ions were identified as the main parameters influencing the fluid flow, particle motion and, consequently, the resulting self-assembled structure. This work demonstrates the utility of enhanced dark-field microscopy as a label-free technique for the observation of drying-induced self-assembly of bacteriophage T4. This technique provides the ability to track the nano-sized particles in different matrices and serves as a strong tool for monitoring self-assembled structures and bottom-up assembly of nano-sized building blocks in real-time.

Continuous Optical Measurement of Internal Dynamics in Drying Colloidal Droplets

“…Finally, our fiber-based implementation can be incorporated into the existing characterization platforms such as drop profiling setups, including the ones based on the tracking florescent particles, , dark-field microscopy, or approaches where droplets are pinned on pillars in order to speed up the reaction assays. , The spatially resolved nature of an optical fiber-based instrumentation makes it possible to characterize even more complex situations where the solvent is either viscoelastic and/or heterogeneous or to study other dynamical aspects such as internal flows in conditions of quasi-stabilized evaporation …”

“…For such purpose, particle tracking-based approaches, that is, particle image velocimetry, , can be used but are limited to situations where the colloidal droplet is dilute (transparent) and the suspended particles are sufficiently large. Some implementations have been improved to construct, for instance, both the particles’ velocity and concentration fields, by using particles of different sizes that can fluoresce in different channels. , The tracking resolution can be further enhanced using variants of dark field microscopy . The main drawback of all these approaches is that they are limited to examine colloidal droplets in which the suspended particles serve only the purpose measurement beacons.…”

CLeANFIT – Contact‐Less Axial Nearfield‐Based Fluorescence Imaging Topography: A Method for 3D Micro‐ and Nanotopography Characterization

“…However, this method lacks axial resolution. [5] So far, no universal precise and low-price technique has been introduced to measure the micro-/nanotopography of thin films, nanostructures and nano-/biofeatures at the surfaces. [16] All micro-/nanotopography methods introduced so far have at least one of the three major drawbacks: (1) difficulty to obtain nanoscale resolution simultaneously in the axial and lateral directions, (2) intrusive contact mode, or (3) unsuitability for micro-/nanofeature measurement at the liquid/surface interface.…”

“…Surface nanostructures include thin/ultrathin films, whose precise characterization is important in semiconductors, optical components, and wear‐resistance coatings. Also, surface‐assembled and densely packed nanoparticle clusters such as viruses, [ 4,5 ] colloidal molecules, [ 6 ] DNA, [ 7 ] and supramolecules [ 8 ] form extended complex surface nanostructures which could be used to explore new paradigms in nanobiotechnology. Analyzing the surface bio‐nanotopography could open new possibilities of bio‐inspired system engineering.…”

“…However, this method lacks axial resolution. [ 5 ] So far, no universal precise and low‐price technique has been introduced to measure the micro‐/nanotopography of thin films, nanostructures and nano‐/biofeatures at the surfaces. [ 16 ]…”