Abstract
Single-cell analysis is essential to understand the physical and functional characteristics of cells. The basic knowledge of these characteristics is important to elucidate the unique features of various cells and causative factors of diseases and determine the most effective treatments for diseases. Recently, acoustic tweezers based on tightly focused ultrasound microbeam have attracted considerable attention owing to their capability to grab and separate a single cell from a heterogeneous cell sample and to measure its physical cell properties. However, the measurement cannot be performed while trapping the target cell, because the current method uses long ultrasound pulses for grabbing one cell and short pulses for interrogating the target cell. In this paper, we demonstrate that short ultrasound pulses can be used for generating acoustic trapping force comparable to that with long pulses by adjusting the pulse repetition frequency (PRF). This enables us to capture a single cell and measure its physical properties simultaneously. Furthermore, it is shown that short ultrasound pulses at a PRF of 167 kHz can trap and separate either one red blood cell or one prostate cancer cell and facilitate the simultaneous measurement of its integrated backscattering coefficient related to the cell size and mechanical properties.
Highlights
The basic knowledge of physical and functional characteristics of cells is essential for understanding the unique features of various cells and the causative factors of diseases and determining the most effective treatments for diseases
As the transducer was moved to the right while delivering ultrasound microbeams at a pulse repetition frequency (PRF) of 167 kHz, the captured microsphere was moved in the same direction (Fig. 2(c) and (d)), which indicated that the short ultrasound pulses successfully trapped and separated one microsphere
We demonstrated that acoustic trapping force of short ultrasound pulses can be controlled by PRF; it is possible to capture a single cell and measure its integrated backscattering (IB) coefficient simultaneously
Summary
The basic knowledge of physical and functional characteristics of cells is essential for understanding the unique features of various cells and the causative factors of diseases and determining the most effective treatments for diseases. Fluorescent dyes tagged for FACS and particular antibodies for MACS may influence normal cellular physiology and functions[18,19] For these reasons, label-free single-cell analysis techniques have attracted considerable attention because the complexity of sample preparation and analysis procedures is relatively low and intrinsic physical cell properties such as cell size, shape, compressibility, and polarizability can be measured while minimizing the effect on cell physiology and function[19,20,21]. After cell sorting in microfluidic systems, additional processing may be required to eliminate unwanted cells from the sorted group of cells, manipulate a single cell, and measure the physical and functional characteristics of a single cell As another label-free single-cell analysis technique, it was demonstrated that an acoustic tweezer exhibits the ability to grab a single cell or measure physical cell properties such as size, stiffness, and backscattering coefficient[33,34,35].
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