Advancing the science of dynamic airborne nanosized particles using Nano-DIHM

Abstract

In situ and real-time characterization of aerosols is vital to several fundamental and applied research domains including atmospheric chemistry, air quality monitoring, or climate change studies. To date, digital holographic microscopy is commonly used to characterize dynamic nanosized particles, but optical traps are required. In this study, a novel integrated digital in-line holographic microscope coupled with a flow tube (Nano-DIHM) is demonstrated to characterize particle phase, shape, morphology, 4D dynamic trajectories, and 3D dimensions of airborne particles ranging from the nanoscale to the microscale. We demonstrate the application of Nano-DIHM for nanosized particles (≤200 nm) in dynamic systems without optical traps. The Nano-DIHM allows observation of moving particles in 3D space and simultaneous measurement of each particle’s three dimensions. As a proof of concept, we report the real-time observation of 100 nm and 200 nm particles, i.e. polystyrene latex spheres and the mixture of metal oxide nanoparticles, in air and aqueous/solid/heterogeneous phases in stationary and dynamic modes. Our observations are validated by high-resolution scanning/transmission electron microscopy and aerosol sizers. The complete automation of software (Octopus/Stingray) with Nano-DIHM permits the reconstruction of thousands of holograms within an hour with 62.5 millisecond time resolution for each hologram, allowing to explore the complex physical and chemical processes of aerosols.

Novel Dynamic Technique, Nano-DIHM, for Rapid Detection of Oil, Heavy Metals, and Biological Spills in Aquatic Systems

“…The nano-DIHM resolved the size and shape of the stationary metal oxide particles and clusters, which typically ranged in size from 1 up to 100 μm (Table S1). The technique has been shown to be capable of observing nano-sized particles in water, which is shown in Figure S6. The size statistics for all types of particles measured in this work are given in Table S1.…”

“…A more detailed description of the digital nano-DIHM with a flow tube system setup, method of operation, and process of hologram reconstruction are provided in a previous publication by Pal et al A brief description is provided in the current work here. DIHM, as a method, is composed of two main processes.…”

“…The light wave passing through the pinhole then illuminates the sample placed in the holder. To observe the submicron-sized particles, the sample must be within a few micrometers of the pinhole, yet can be millimeters away from the pinhole when looking at larger particles or groups of particles . Once the light wave has interacted with the object, it produces a magnified diffraction pattern on the screen (photosensitive matrix, model MV1-D2048-96-G2-10, Photonfocus AG 00140622, version 2.1).…”

“…This provides a good approximate starting point for training the software and can be adjusted in various iterations to optimize the results. For example, a low threshold value would allow too many pixels to be detected and hinder differentiating different particles, and a high threshold value would cause too few pixels to be detected and may prevent the desired particle from even being detected …”

“…In this work, we use a newly developed application of digital in-line holographic microscopy (nano-DIHM) designed for airborne particles and adapt it for applications in water, allowing measurement of the size, shape, intensity, phase, and interactions of significant nano-/microparticle contaminants of global natural water systems. This methodology provides an edge over S/TEM (scanning/transmission electron microscopy) for imaging water-suspended particulates as it allows for liquid (stationary) and in situ dynamic measurements (flowing water).…”