The Flamingo is a modular, shareable light sheet microscope suited to a new model of scientific collaboration. Each microscope is customized for a given application, equipped to travel from lab to lab and providing widespread access to advanced microscopy. It is a compact selective plane illumination microscope (SPIM) that can be turned upright for multi-view imaging of hanging samples or turned on its side for samples in a dish. Rapid multi-color imaging is achieved via sCMOS cameras and several possible laser lines. With its selective sheet illumination, the Flamingo is well suited for fast and gentle imaging of developing organisms.
Using optical tweezers for micro-rheological investigations of a surrounding fluid has been routinely demonstrated. In this work, we will demonstrate that rheological measurements of the bulk and surface properties of aerosol particles can be made directly using optical tweezers, providing important insights into the phase behavior of materials in confined environments and the rate of molecular diffusion in viscous phases. The use of holographic optical tweezers to manipulate aerosol particles has become standard practice in recent years, providing an invaluable tool to investigate particle dynamics, including evaporation/ condensation kinetics, chemical aging and phase transformation. When combined with non-linear Raman spectroscopy, the size and refractive index of a particle can be determined with unprecedented accuracy <+/- 0.05%). Active control of the relative positions of pairs of particles can allow studies of the coalescence of particles, providing a unique opportunity to investigate the bulk and surface properties that govern the hydrodynamic relaxation in particle shape. In particular, we will show how the viscosity and surface tension of particles can be measured directly in the under-damped regime at low viscosity. In the over-damped regime, we will show that viscosity measurements can extend close to the glass transition, allowing measurements over an impressive dynamic range of 12 orders of magnitude in relaxation timescale and viscosity. Indeed, prior to the coalescence event, we will show how the Brownian trajectories of trapped particles can yield important and unique insights into the interactions of aerosol particles.
Holographic aerosol optical tweezers can be used to trap arrays of aerosol particles allowing detailed studies of
particle properties and processes at the single particle level. Recent observations have suggested that secondary
organic aerosol may exist as ultra-viscous liquids or glassy states at low relative humidity, potentially a
significant factor in influencing their role in the atmosphere and their activation to form cloud droplets. A
decrease in relative humidity surrounding a particle leads to an increased concentration of solute in the droplet
as the droplet returns to equilibrium and, thus, an increase in the bulk viscosity. We demonstrate that the
timescales for condensation and evaporation processes correlate with particle viscosity, showing significant
inhibition in mass transfer kinetics using ternary sucrose/sodium chloride/water droplets as a proxy to
atmospheric multi-component aerosol. We go on to study the fundamental process of aerosol coagulation in
aerosol particle arrays, observing the relaxation of non-spherical composite particles formed on coalescence.
We demonstrate the use of bright-field imaging and elastic light scattering to make measurements of the
timescale for the process of binary coalescence contrasting the rheological properties of aqueous sucrose and
sodium chloride aerosol over a range of relative humidities.
The use of optical tweezers for the analysis of aerosols is valuable for understanding the dynamics of atmospherically
relevant particles. However to be able to make accurate measurements that can be directly tied to real-world phenomena
it is important that we understand the influence of the optical trap on those processes. One process that is seemingly
straightforward to study with these techniques is binary droplet coalescence, either using dual beam traps, or by particle
collision with a single trapped droplet. This binary coalescence is also of interest in many other processes that make use
of dense aerosol sprays such as spray drying and the use of inhalers for drug delivery in conditions such as asthma or hay
fever. In this presentation we discuss the use of high speed (~5000 frames per second) video microscopy to track the
dynamics of particles as they approach and interact with a trapped aqueous droplet and develop this analysis further by
considering elastic light scattering from droplets as they undergo coalescence. We find that we are able to characterize
the re-equilibration time of droplets of the same phase after they interact and that the trajectories taken by airborne
particles influenced by an optical trap are often quite complex. We also examine the role of parameters such as the salt
concentration of the aqueous solutions used and the influence of laser wavelength.
Aerosols play a crucial role in many areas of science, ranging from atmospheric chemistry and physics, to
drug delivery to the lungs, combustion science and spray drying. The development of new methods to
characterise the properties and dynamics of aerosol particles is of crucial importance if the complex role that
particles play is to be more fully understood. Optical tweezers provide a valuable new tool to address
fundamental questions in aerosol science. Single or multiple particles 1-15 μm in diameter can be
manipulated over indefinite timescales using optical tweezing. Linear and non-linear Raman and fluorescence
spectroscopies can be used to probe a particle's composition and size. In this paper we will report on the latest
developments in the use of holographic optical trapping (HOT) to study aerosols. Although widely used to
trap and manipulate arrays of particles in the condensed phase, the application of HOT to aerosols is still in its
infancy. We will explore the opportunities provided by the formation of complex optical landscapes for
controlling aerosol flow, for comparing the properties of multiple particles, for performing the first ever
digital microfluidic operations in the aerosol phase and for examining interparticle interactions that can lead
to coalescence/coagulation. Although aerosol coagulation is the primary process driving the evolution of
particle size distributions, it remains very poorly understood. Using HOT, we can resolve the time-dependent
motion of trapped particles and the light scattering from particles during the coalescence process.