Lightvalve for Controlling Microfluids

A new optofluidic platform for biological sample processing and optical analysis is made of polydimethylsiloxane (PDMS) and features tunable optics and novel lightvalves (Source: C. Lagattuta / UCSC)

A new optofluidic platform for biological sample processing and optical analysis is made of polydimethylsiloxane (PDMS) and features tunable optics and novel lightvalves (Source: C. Lagattuta / UCSC)

For well over a decade, electrical engineer Holger Schmidt has been develo­ping devices for optical analysis of samples on integrated chip-based platforms, with appli­­cations in areas such as bio­lo­gical sensors, virus detection, and chemical analysis. The latest device from his lab is based on novel techno­­logy that combines high-perfor­mance micro­­fluidics for sample proces­sing with dynamic optical tuning and switching, all on a low-cost chip made of a flexible silicone material.

In previous devices from Schmidt’s lab, optical functions were built into silicon chips using the same fabri­cation techno­logy used to make computer chips. The new device is made entirely of poly­­dimethyl­­siloxane (PDMS), a soft, flexible material used in microfluidics as well as in products such as contact lenses and medical devices. “We can use this fabri­cation method now to build an all-in-one device that allows us to do bio­logical sample proces­sing and optical detection on one chip,” said Schmidt, the Kapany Professor of Opto­­electronics and director of the W. M. Keck Center for Nano­scale Opto­­fluidics at UC Santa Cruz.

The flexi­bility of PDMS allows for novel ways of controlling both light and fluids on the chip. Using multi­layer soft litho­graphy techniques, senior graduate student Joshua Parks built chips containing both solid-core and hollow-core wave­guides for guiding light signals, as well as fluidic microvalves to control the movement of liquid samples. Schmidt and Parks also developed a special micro­valve that functions as a light­valve, controlling the flow of both light and fluids. “That opens up a whole new set of functions that we couldn’t do on a silicon chip,” Schmidt said. “The light­valve is the most exciting element. In additional to a simple on-off switch, we built a moveable optical trap for analysis of bio­logical particles such as viruses or bacteria.”

In a previous study, Schmidt, Parks, and colleagues at BYU and UC Berkeley demon­strated a hybrid device in which a PDMS micro­fluidic chip for sample pre­paration was integrated with a silicon-based opto­fluidic chip for optical detection of viral pathogens. The new device combines both functions on the same chip. In addition, Schmidt said, the materials are relatively inexpensive, allowing rapid proto­typing of devices. “We can do the full chain of fabri­cation here in our lab, and we can make new devices very quickly,” he said.

Schmidt said the potential appli­cations for this techno­logy include a wide range of bio­logical sensors and ana­lytical devices. For viral diagnostic assays, for example, fluores­cently labeled anti­bodies can be used to tag specific viral strains for optical detection. In a recent paper, Schmidt and colleagues demonstrated detec­tion and iden­tification of different flu strains using fluores­cence detection in a multi-mode inter­ference (MMI) wave­guide. With the new device, they showed that they can actively tune an MMI waveguide on the chip.

The dynamic tuning of the opto­fluidic device is achieved by applying pressure to the opto­fluidic channel, changing its dimensions and thereby altering its photonic pro­perties. “We can actually tune the spot pattern made in the channel by the inter­ference waveguide, which we couldn’t do with the silicon chip,” Schmidt said. (Source: UCSC)

Reference: J. W. Parks & H. Schmidt: Flexible optofluidic waveguide platform with multi-dimensional reconfigurability, Sci. Rep. 6, 33008 (2016); DOI: 10.1038/srep33008

Link: W. M. Keck Center for Nanoscale Optofluidics, University of California Santa Cruz, Santa Cruz, USA

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