Please tell us about yourself

Girish Kulkarni, a graduate student in the Electrical Engineering Program at University of Michigan, received a U-M Rackham Predoctoral Fellowship to support his dissertation research on Carbon Nanoelectronic Heterodyne Sensors for Chemical and Biological Detection. This fellowship is awarded to outstanding doctoral candidates in the final stages of their program who are unusually creative, ambitious and risk-taking.

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By taking a novel approach to sensing, Girish’s research has resulted in a new paradigm in sensor technology that promises both high-speed and highly-sensitive detection, which are critical for practical applications. He has built sensors that can be used not only to detect hazardous chemical leaks in a lab or chemical attacks on a battlefield, but also in point-of-care diagnostics for example measuring PSA levels and other biomarkers in blood; he believes that one day these sensors can detect health irregularities by breath alone.

“And our devices are so small they can be put almost anywhere,” Girish added.

What did you study?

Girish did his Bachelors of Engineering (B.E.) in Electronics & Electrical Engineering from Punjab Engineering College. He subsequently did his Masters and PhD in Electrical Engineering from University of Michigan.

Tell us about your work

“Nanoelectronic sensors typically depend on detecting charge transfer between the sensor and a molecule in air or in solution,” explained Girish. “It is well known that charge transfer is a rate limiting step for molecular detection leading to extremely slow response and recovery. Moreover, conventional charge-based detection techniques fail in solution due to ionic screening effect, which can be overcome only through time-consuming steps like desalting, making them impractical for real-time sensing.”

“We use a technique called heterodyne mixing,” Girish continued. “Instead of detecting molecular charge, we look at the interaction between the dipoles associated with these molecules and the nanosensor at high frequencies.”

Kulkarni’s approach gives sub-second response times and parts-per-billion level sensitivity simultaneously. The technique has been demonstrated on carbon nanotubes and graphene, though it can also be used on any nanoelectronic sensor platform and works both for solution and gas phase detection.

And because his devices are less than a micron-by-micron is size, they are conducive for multiplexed detection. The graphene heterodyne sensor has been shown to detect 20 different volatile organic compounds on one small device, with many more possible.

Girish Kulkarni is advised by Prof. Zhaohui Zhong, who has done pioneering work in graphene. Girish came to Michigan in 2008, the same year as his advisor; he was attracted by the opportunities Prof. Zhong offered to new students joining his group.

Those opportunities have only increased for Girish, who plans to continue investigating and perhaps one day commercializing this technology

How does your research benefit the community?

Researchers, including Girish are developing a new wearable vapour sensor that could offer continuous disease monitoring for patients with diabetes, high blood pressure, anemia or lung disease.

The new sensor, being developed at the University of Michigan, can detect airborne chemicals either exhaled or released through the skin.

It would likely be the first wearable to pick up a broad array of chemical, rather than physical, attributes, researchers said.

“Each of the diseases has its own biomarkers that the device would be able to sense. For diabetes, acetone is a marker, for example,” said Sherman Fan, a professor of biomedical engineering.

Other chemicals it could detect include nitric oxide and oxygen, abnormal levels of which can point to conditions such as high blood pressure, anemia or lung disease.

Fan is developing the sensor with Zhaohui Zhong, an associate professor of electrical and computer engineering, and Girish Kulkarni, a doctoral candidate in electrical engineering.

The researchers said their device is faster, smaller and more reliable than its counterparts, which today are much too big to be wearable.

Beyond disease monitoring, the sensor has other applications. It would be able to register the presence of hazardous chemical leaks in a lab, or elsewhere, or provide data about air quality.

To create their technology, the researchers took a unique approach to detecting molecules.

“Nanoelectronic sensors typically depend on detecting charge transfer between the sensor and a molecule in air or in solution,” Kulkarni said.

However, these previous techniques typically led to strong bonds between the molecules being detected and the sensor itself. That binding leads to slow detection rates.

“Instead of detecting molecular charge, we use a technique called heterodyne mixing, in which we look at the interaction between the dipoles associated with these molecules and the nanosensor at high frequencies,” Kulkarni said.

This technique, made possible through the use of graphene, results in extremely fast response times of tenths of a second, as opposed to the tens or hundreds of seconds typical in existing technology.

It also dramatically increases the device’s sensitivity. The sensor can detect molecules in sample sizes at a ratio of several parts per billion.

These nanoelectronic graphene vapour sensors can be completely embedded in a microgas chromatography system, which is the gold standard for vapour analysis, the researchers said.