Computational Image Analysis of Guided Acoustic Waves Enables Rheological Assessment of Sub-nanoliter Volumes.

Muhammad Arslan Khalid,Andriejus Demčenko,Derek Tseng,Steve Cohen,Aydogan Ozcan,Aniruddha Ray,Manlio Tassieri,Julien Reboud,Jonathan M Cooper

doi:10.1021/acsnano.9b03219

Muhammad Arslan Khalid, Andriejus Demčenko + Show 7 more

Open Access

https://doi.org/10.1021/acsnano.9b03219

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Abstract

We present a method for the computational image analysis of high frequency guided sound waves based upon the measurement of optical interference fringes, produced at the air interface of a thin film of liquid. These acoustic actuations induce an affine deformation of the liquid, creating a lensing effect that can be readily observed using a simple imaging system. We exploit this effect to measure and analyze the spatiotemporal behavior of the thin liquid film as the acoustic wave interacts with it. We also show that, by investigating the dynamics of the relaxation processes of these deformations when actuation ceases, we are able to determine the liquid’s viscosity using just a lens-free imaging system and a simple disposable biochip. Contrary to all other acoustic-based techniques in rheology, our measurements do not require monitoring of the wave parameters to obtain quantitative values for fluid viscosities, for sample volumes as low as 200 pL. We envisage that the proposed methods could enable high throughput, chip-based, reagent-free rheological studies within very small samples.

Highlights

The visualization and characterization of acoustic waves as they propagate in media have previously been used to elucidate material properties and gain a deeper understanding of physical phenomena, including the RamanNath effect and Brillouin scattering.[1,2] For example, it has previously been shown that wave propagation through solid media can reveal valuable information about the mechanical properties of materials[3] such as local stresses, densities, and elastic moduli.[4]
Guided acoustic waves have previously been used in rheological applications[13,14] by measuring their attenuation. Such mechanical excitations, including those using surface acoustic waves (SAWs) and Lamb-type waves, have been used to drive liquid actuation in microfluidic systems.[15−18] In this work, we make use of the capability of acoustic waves to deform a subnanoliter-scale liquid volume and monitor the dynamics of its relaxation when the actuation is turned off
It was designed to generate a set of subpixel shifted images, which were used to digitally synthesize images with subpixel resolution.[26−28] The disposable biochip was coupled to the interdigitated transducer (IDT) using a thin layer of polyethylene glycol (PEG 400) which we found to be a stable coupling agent

Summary

Introduction

The visualization and characterization of acoustic waves as they propagate in media have previously been used to elucidate material properties and gain a deeper understanding of physical phenomena, including the RamanNath effect and Brillouin scattering.[1,2] For example, it has previously been shown that wave propagation through solid media can reveal valuable information about the mechanical properties of materials[3] such as local stresses, densities, and elastic moduli.[4]. We present a simple optical method for imaging small amplitude guided waves of wavelength λ in plates coated by a thin fluid layer of thickness 2a (with 2a ≪ λ) and demonstrate its application for measuring the viscosity of liquid samples with subnanoliter volumes, without monitoring wave parameters.

Results

Conclusion