Issue 3, 2020

An optofluidic “tweeze-and-drag” cell stretcher in a microfluidic channel

Abstract

The mechanical properties of biological cells are utilized as an inherent, label-free biomarker to indicate physiological and pathological changes of cells. Although various optical and microfluidic techniques have been developed for cell mechanical characterization, there is still a strong demand for non-contact and continuous methods. Here, by combining optical and microfluidic techniques in a single desktop platform, we demonstrate an optofluidic cell stretcher based on a “tweeze-and-drag” mechanism using a periodically chopped, tightly focused laser beam as an optical tweezer to trap a cell temporarily and a flow-induced drag force to stretch the cell in a microfluidic channel transverse to the tweezer. Our method leverages the advantages of non-contact optical forces and a microfluidic flow for both cell stretching and continuous cell delivery. We demonstrate the stretcher for mechanical characterization of rabbit red blood cells (RBCs), with a throughput of ∼1 cell per s at a flow rate of 2.5 μl h−1 at a continuous-wave laser power of ∼25 mW at a wavelength of 1064 nm (chopped at 2 Hz). We estimate the spring constant of RBCs to be ∼14.9 μN m−1. Using the stretcher, we distinguish healthy RBCs and RBCs treated with glutaraldehyde at concentrations of 5 × 10−4% to 2.5 × 10−3%, with a strain-to-concentration sensitivity of ∼−1529. By increasing the optical power to ∼45 mW, we demonstrate cell-stretching under a higher flow rate of 4 μl h−1, with a higher throughput of ∼1.5 cells per s and a higher sensitivity of ∼−2457. Our technique shows promise for applications in the fields of healthcare monitoring and biomechanical studies.

Graphical abstract: An optofluidic “tweeze-and-drag” cell stretcher in a microfluidic channel

Supplementary files

Article information

Article type
Paper
Submitted
15 Oct 2019
Accepted
19 Dec 2019
First published
24 Dec 2019
This article is Open Access
Creative Commons BY-NC license

Lab Chip, 2020,20, 601-613

An optofluidic “tweeze-and-drag” cell stretcher in a microfluidic channel

Z. Yao, C. C. Kwan and A. W. Poon, Lab Chip, 2020, 20, 601 DOI: 10.1039/C9LC01026B

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