Abstract
Optoelectronic tweezers (OET) has advanced within the past decade to become a promising tool for cell and microparticle manipulation. Its incompatibility with high conductivity media and limited throughput remain two major technical challenges. Here a novel manipulation concept and corresponding platform called Self-Locking Optoelectronic Tweezers (SLOT) are proposed and demonstrated to tackle these challenges concurrently. The SLOT platform comprises a periodic array of optically tunable phototransistor traps above which randomly dispersed single cells and microparticles are self-aligned to and retained without light illumination. Light beam illumination on a phototransistor turns off the trap and releases the trapped cell, which is then transported downstream via a background flow. The cell trapping and releasing functions in SLOT are decoupled, which is a unique feature that enables SLOT’s stepper-mode function to overcome the small field-of-view issue that all prior OET technologies encountered in manipulation with single-cell resolution across a large area. Massively parallel trapping of more than 100,000 microparticles has been demonstrated in high conductivity media. Even larger scale trapping and manipulation can be achieved by linearly scaling up the number of phototransistors and device area. Cells after manipulation on the SLOT platform maintain high cell viability and normal multi-day divisibility.
Highlights
Most conventional Optoelectronic tweezers (OET) devices cannot operate in high conductivity media, including regular physiological buffers, due to the fact that only limited photocurrents can be generated in the aforementioned photoconductive materials
Since a lens with a large FOV typically comes with a low numerical aperture (NA), it cannot provide the light beam a resolution required for single-cell manipulation
Since the fabrication of Self-Locking Optoelectronic Tweezers (SLOT) chips requires only two photolithography steps and micron scale feature sizes, they can be reproduced in an academic lab or mass-produced in any entry-level semiconductor manufacture foundry for low cost
Summary
The demonstrated SLOT manipulation mechanism can be scaled up for single-cell manipulation across a much larger area and higher throughput than what has been demonstrated in the manuscript. Assuming the tolerable temperature rise at the SLOT surface in contact with liquid is 2.5 °C, and the silicon substrate thickness is 0.5 mm, the heat dissipation rate is 74.5 W/cm[2], which is more than 10 times larger than the 6 W/cm[2] heat generation rate for SLOT operation in regular physiological buffer. This means the approximate temperature rise in the current SLOT chip is less than ~0.25 °C for media of electrical conductivity less than 1 S/m. Potential applications of SLOT are broad, including tissue engineering[28,29,30], drug screening[31], cell-to-cell communication, rare cell sorting, in vitro fertilization[32] and beyond
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