New tricks for nanosensors

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.”