Mass-Produced Microscopic Sensors Transmit Data from Living Tissue

Cornell University researchers who build nanoscale electronics have developed microsensors so tiny, they can fit 30,000 on one side of a penny. They are equipped with an integrated circuit, solar cells and light-emitting diodes (LEDs) that enable them to harness light for power and communication. And because they are mass fabricated, with up to one million sitting on an eight-inch wafer, each device costs a fraction of that same penny.

A voltage-sensing OWIC as it fits inside the Lincoln Memorial on the back of a penny, and a schematic of an OWIC’s components. (Source: A. Cortese, Cornell U.)

The sensors can be used to measure inputs like voltage and temperature in hard-to-reach environments, such as inside living tissue and microfluidic systems. For example, when rigged with a neural sensor, they would be able to noninvasively record nerve signals in the body and transmit findings by blinking a coded signal via the LED. As a proof of concept, the team successfully embedded a sensor in brain tissue and wirelessly relayed the results.

The collaboration is led by Paul McEuen, professor of physical science, and Alyosha Molnar, associate professor of electrical and computer engineering. Working with the paper’s lead author, Alejandro Cortese, a Cornell presidential postdoctoral fellow, they devised a platform for parallel production of their optical wireless integrated circuits (OWICs) – sensors the size of 100 microns.

The OWICS are essentially paramecium-size smartphones that can be specialized with apps. But rather than rely on cumbersome radio frequency technology, as cellphones do, the researchers looked to light as a potential power source and communication medium.

Placing tiny circuits on a silicon wafer is relatively easy in the nanotech arena, McEuen said, but adding LEDs is a special challenge as they are made with gallium arsenide. In order to transfer the LEDs to a wafer with the electrical components and integrate them, the researchers developed a complicated assembly method that involved more than 15 layers of photolithography, 30 different materials and more than 100 steps.

This collection of OWICs is barely visible to the naked eye. (Source: A. Cortese, Cornell U.)

Once the OWICs are freed from their substrate of silicon, they can be used to measure inputs like voltage and temperature in hard-to-reach environments, such as inside living tissue and microfluidic systems. For example, an OWIC rigged with a neural sensor would be able to noninvasively record nerve signals in the body and transmit its findings by blinking a coded signal via the LED.

McEuen, Molnar and Cortese have launched their own company, OWiC Technologies, to commercialize the microsensors. A patent application has been filed through the Center for Technology Licensing. The first application is the creation of e-tags that can be attached to products to help identify them.

The tiny, low-cost OWICs could potentially spawn generations of microsensors that use less power while tracking more complicated phenomena. (Source: Cornell U.)

Reference: A. J. Cortese et al.: Microscopic sensors using optical wireless integrated circuits, PNAS 117 (17) 9173-9179; first published April 17, 2020; DOI: 10.1073/pnas.1919677117

Link: McEuen Group, Laboratory of Atomic and Solid State Physics (LASSP), Cornell University, Ithaca, NY, USA

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