Shao Ning Pei

Light-actuated digital microfluidics for large-scale, parallel manipulation of arbitrarily sized droplets

We report on a new light-actuated digital microfluidics device which is capable of using on demand, ‘virtual’ electrodes formed by a data projector to enable large-scale, parallel manipulation of arbitrarily sized droplets. The device features a thin, high-quality Al2O3 film deposited via atomic layer deposition (ALD) which allows aggressive scaling of the dielectric thickness, while maintaining high device reliability. We demonstrate the splitting, merging and parallel manipulation of droplets at high actuation speeds (2 cm/s). Due to the thin ALD dielectric layer, this high actuation speed is achieved at 85x lower optical power and 5x lower voltage than our previous device.

Distributed Circuit Model for Multi-Color Light-Actuated Opto-Electrowetting Microfluidic Device

We report on a distributed circuit model for multi-color light-actuated optoelectrowetting devices. The model takes into consideration the large variation of absorption coefficient (15×) of photoconductors in the visible spectrum and the nonuniform distribution of photogenerated carriers. With the help of this model, we designed opto-electrowetting devices with optimum thickness of photoconductors. This leads to significant improvement in performance compared with prior reports, including 200× lower optical power, 5× lower voltage, and 20× faster droplet moving speed. This enables the use of commercial projectors to create on-demand “virtual” electrodes for large-scale parallel manipulation of droplets. We have achieved simultaneous manipulation of 96-droplet array. Finally, we have demonstrated parallel on chip detection of Herpes Simplex Virus Type 1 within 45 min using a real-time isothermal polymerase chain reaction assay.

Quantifying heat transfer in DMD-based optoelectronic tweezers with infrared thermography

Optoelectronic tweezers (OET) have emerged in recent years as a powerful form of optically-induced dielectrophoresis for addressing single cells and trapping individual nanostructures with DMD-based virtual-electrodes. In this technique an alternating electric field is used to induce a dipole within structures of interest while very low-intensity optical images are used to produce local electric field gradients that create dynamic trapping potentials. Addressing living cells, particularly for heat-sensitive cell lines, with OETs optical virtual-electrodes requires an in-depth understanding of heating profiles within OET devices. In this work we present quantitative measurements of the thermal characteristics of single-crystalline-silicon phototransistor based optoelectronic tweezers (PhOET). Midwave infrared (3 - 5 micron) thermographic imaging is used to determine relative heating in PhOET devices both with and without DMD-based optical actuation. Temperature increases of approximately 2°C from electrolyte Joule-heating are observable in the absence of DMD-illumination when glass is used as a support for PhOET devices. An additional temperature increase of no more than 0.2°C is observed when DMD-illumination is used. Furthermore, significantly reduced heating can be achieved when devices are fabricated in direct contact with a metallic heat-sink.

Open-access phototransistor-based optoelectronic tweezers for long-term single cell heterogeneity study

We demonstrate, for the first-time, long-term culturing of single cells under continuous phototransistor-based optoelectronic tweezers (Ph-OET) trapping. A new device configuration, open-access Ph-OET, is presented to integrate the trapping functionality of Ph-OET with culturing capabilities in a Petri dish. Maintenance of human leukemia cell lines (K562, Jurkat) under optical manipulation for up to five cell generation has been achieved.

Thermo-sensitive microgels as in-situ sensor for temperature measurement in optoelectronic tweezers

We report on the application of thermo-sensitive microgels as in situ temperature sensor for phototransistor-based optoelectronic tweezers (Ph-OET) device. The thermo-sensitive microgels are cross-linked polymeric particles that swell or shrink reversibly in response to changes in the surrounding temperature. The technique has an accuracy of 0.054°C and a spatial resolution of 25µm. Temperature rise in Ph-OET is measured under various operating conditions, and the maximum temperature increase is measured at 2.6°C. The results show cell damage can be prevented with adequate heat sink. When physiological temperature is required, the applied bias should be kept low (10V}inpp}), or smaller optical patterns should be used. The technique demonstrated here can be extended to other microfluidic devices.

Novel electrode shape to reduce heating in light-actuated digital microfluidics

A novel, ring-shaped optical electrode is employed to reduce heating in light-actuated digital microfluidics. Using thermo-sensitive hydrogel microspheres, the temperature rise is measured to be 0.35°C, about 15× lower than those using square electrodes.

An integrated single cell optofluidic platform based on phototransistor optoelectronic tweezers

We present a novel single cell manipulation platform based on phototransistor optoelectronic tweezers. This new platform integrates the functionalities of phOET for parallel cell manipulation in highly conductive culture media with a commercial microfluidic device.