A new microscopic shape-shifting probe capable of sensitive, high-resolution remote biological sensing has been developed by scientists at the National Institute of Standards and Technology (NIST) and the National Institutes of Health (NIH). If eventually put into widespread use, the design could have a major impact on research in medicine, chemistry, biology, and engineering and ultimately used in clinical diagnostics, according to the researchers. To date, most efforts to image highly localized biochemical conditions such as abnormal pH* and ion concentration — critical markers for many disorders — rely on various types of nanosensors that are probed using light at optical frequencies. But the light doesn’t reach far into the body, so the sensitivity and resolution of the resulting optical signals decrease rapidly with increasing depth into the body. That has limited most applications to more optically accessible regions.
Fluorescent and plasmonic labels and sensors have revolutionized molecular biology, helping visualize cellular and biomolecular processes. Increasingly, such probes are now being designed to respond to wavelengths in the near-infrared region, where reduced tissue autofluorescence and photon attenuation enable subsurface in vivo sensing. But even in the near-infrared region, optical resolution and sensitivity decrease rapidly with increasing depth. A team of scientists now presents a sensor design that obviates the need for optical addressability by operating in the nuclear magnetic resonance (NMR) radio-frequency spectrum, where signal attenuation and distortion by tissue and biological media are negligible, where background interferences vanish, and where sensors can be spatially located using standard magnetic resonance imaging (MRI) equipment.
The radio-frequency-addressable sensor assemblies presented here comprise pairs of magnetic disks spaced by swellable hydrogel material; they reversibly reconfigure in rapid response to chosen stimuli, to give geometry-dependent, dynamic NMR spectral signatures. The sensors can be made from biocompatible materials, are themselves detectable down to low concentrations, and offer potential responsive NMR spectral shifts that are close to a million times greater than those of traditional magnetic resonance spectroscopies. Inherent adaptability should allow such shape-changing systems to measure numerous different environmental and physiological indicators, thus providing broadly generalizable, MRI-compatible, radio-frequency analogues to optically based probes for use in basic chemical, biological, medical and engineering research.