Properties of cells through life and death – an acoustic microscopy investigation

Abstract

Current methods to evaluate the status of a cell are largely focused on fluorescent identification of molecular biomarkers. The invasive nature of these methods -requiring either fixation, chemical dyes, genetic alteration, or a combination of these -prevents subsequent analysis of samples. In light of this limitation, studies have considered the use of physical markers to differentiate cell stages. Acoustic microscopy is an ultrahigh frequency (>100 MHz) ultrasound technology that can be used to calculate the mechanical and physical properties of biological cells in realtime, thereby evaluating cell stage in live cells without invasive biomarker evaluation. Using acoustic microscopy, MCF-7 human breast adenocarcinoma cells within the G1, G2, and metaphase phases of the proliferative cell cycle, in addition to early and late programmed cell death, were examined. Physical properties calculated include the cell height, sound speed, acoustic impedance, cell density, adiabatic bulk modulus, and the ultrasonic attenuation. A total of 290 cells were measured, 58 from each cell phase, assessed using fluorescent and phase contrast microscopy. Cells actively progressing from G1 to metaphase were marked by a 28% decrease in attenuation, in contrast to the induction of apoptosis from G1, which was marked by a significant 81% increase in attenuation. Furthermore late apoptotic cells separated into 2 distinct groups based on ultrasound attenuation, suggesting that presently-unidentified sub-stages may exist within late apoptosis. A methodology has been implemented for the identification of cell stages without the use of chemical dyes, fixation, or genetic manipulation.

Photoacoustic F-Mode imaging for scale specific contrast in biological systems

“…Adherent cells tend to have a ʽfried-eggʼ appearance; with an increased thickness near the nucleus that tapers toward the cell periphery 49,50 . Traditional optical microscopy is the gold standard for 2D cell imaging; however, without the use of specialized techniques like confocal microscopy 51 , Raman Imaging 52 , or scanning acoustic microscopy 53 , no indication of cell thickness is typically obtained.…”

A Macro Lens-Based Optical System Design for Phototherapeutic Instrumentation

“…No stimuli were induced in the control group (n = 10) but the other groups were exposed to 460 nm LED or US transducer, and LED combined with the transducer for 30 min up to 3 days. Even though the thermal and mechanical effects caused by 460 nm LED and ultrasound are still under research, LED and ultrasound devices could effectively reduce cancer cell viability with signaling effects to the cells and cavitation effects [5,25]. For LED, light irradiation inhibits the signaling between cancer cells, thus inducing cell death without thermal increments [9].…”

“…The mechanical effects induced by ultrasound transducers can promote tumor necrosis by inducing the appropriate power and frequency of the transmitted sources [24][25][26][27]. Tumor cell structures and functions exposed to low-frequency ultrasound can be deformed, thus resulting in cell damage, necrosis, proliferation, migration, etc.…”

Methods for cell volume measurement

“…d). The speed of sound in the cells can be assumed to be 1,560–1,570 m/s , which is slightly higher than that in water (1,521 m/s) due to a high concentration of protein. Alternatively, one can use the echo reflected from the bare substrate in the vicinity of the cell, and use the speed of sound in water to calculate cell height.…”