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New tricks for nanosensors

Lithium atom via Flickr.

Lithium atom via Flickr.

Perhaps by now you’ve heard of Heather Clark’s work developing nanosensors to monitor biological states for both clinical and research applications. Maybe you read the story in Wired magazine about her nanosensor tattoo that, combined with a simple iPhone app, helps diabetic patients determine their real-time blood sugar level. Clark’s nanosensors have shown promise in neurological and cardiac settings alike. But one of the main limitations to the current technology, according to post-doctoral researcher Kevin Cash, is the team’s current inability to read sensor outputs that are embedded deep within the body.

To address that challenge, Cash was recently awarded a Ruth L. Kirschstein National Research Service Award from the National Institute for Biomedical Imaging and Bioengineering. In April 2011, Lihong Wang delivered a lecture at the bioengineering seminar that piqued Cash’s interest. “We make things that need to be imaged,” said Cash. “[Wang’s lab] makes  awesome imaging techniques–and it’s a match made in heaven.”

The particular awesome imaging technique he’s referring to is called photoacoustic imaging, and it is just as cool as Cash would have you believe. Today, Clark’s nanosensors work by absorbing a beam of light and emitting a fluorescent response that corresponds to the concentration of whatever the nanosensor was designed to interact with–neurotransmitters, calcium ions and glucose being a few examples. In this scenario, the nanosensor must reside pretty close to the skin, because otherwise the fluorescent signal would never make it back out and thus it no detection device would be able to read it.

Photoacoustic imaging works analogously, but instead of ultraviolet light, a laser beam is shone on the particle of interest. And instead of a fluorescence signal, the particle heats up and expands, emitting an acoustic signal that can be detected with ultrasound technology. “Ultrasound can get through inches of tissue, no problem,” said Cash.

While coupling the two techniques–nansensors and photoacoustic imaging–could significantly expand the research areas available to Clark’s lab, it must first go through a “proof-of-concept” phase.”No one has done it before, so we have no idea what problems we’ll run into,” said Cash.

With the grant, Cash will design and test a new class of nanosensors intended to track lithium levels in the body. Lithium is one of the main treatments for bipolar disorder, which affects nearly 2.6% of the population. But its narrow therapeutic window means that the difference between an optimum dose and a toxic dose is very small. Like the glucose sensors developed previously, Cash’s lithium sensors will provide continuous monitoring of lithium concentrations. “This will give you a better feel for what’s happening in the body and how it’s being processed,” said Cash. For patients new to lithium treatment, this kind of pharmacokinetic profile can allow for more appropriate dosing information.

“Five years from now, who knows what this will lead to,” said Cash. “Because no one has been there before.”