New, shape-shifting sensor to report internal body conditions

A team of scientists has devised and demonstrated new shape-shifting probe devices that will be able to detect and measure localized conditions on the molecular scale deep within tissues.

National Institute of Standards and Technology (NIST) and the National Institutes of Health (NIH) scientists' new, shape-shifting probe is about 5 to 10 times smaller than a single red blood cell, one of the smallest human cells and is capable of sensitive, high-resolution remote biological sensing that is not possible with current technology.

Lead author Gary Zabow said that instead of optically based sensing, the shape-changing probes are designed to operate in the radio frequency (RF) spectrum, specifically to be detectable with standard nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI) equipment. In these RF ranges, signals are, for example, not appreciably weakened by intervening biological materials. As a result, they can get strong, distinctive signals from very small dimensions at substantial depths or in other locations impossible to probe with optically based sensors.

The novel devices, called geometrically encoded magnetic sensors (GEMs), are microengineered metal-gel sandwiches and each consists of two separate magnetic disks that range from 0.5 to 2 micrometers (millionths of a meter) in diameter and are just tens of nanometers (billionths of a meter) thick.

Scientists tested the sensors in solutions of varying pH, in solutions with ion concentration gradients and in a liquid growth medium containing living canine kidney cells as their metabolism went from normal to nonfunctional in the absence of oxygen. That phenomenon caused the growth medium to acidify and the change over time was sensed by the GEMs and recorded through real-time shifting in resonant frequencies. Even for the un-optimized, first-generation probes used, the frequency shifts resulting from changes in pH were easily resolvable and orders of magnitude larger than any equivalent frequency shifting observed through traditional magnetic resonance spectroscopy approaches.

One of the most significant features of GEMs is that they can be "tuned" in fabrication to respond to different biochemical states and to resonate in different parts of the RF spectrum by altering the gel composition and the magnet shapes and materials, respectively. So placing two different populations of GEMs at the same site makes it possible to track changes in two different variables at the same time.

Zabow added that they think that these sensors can potentially be adapted to measure a variety of different biomarkers, possibly including things such as glucose, local temperatures, various ion concentrations, possibly the presence or absence of various enzymes and so forth.

The study appears online in the journal Nature.