Science Tokyo reports nanosensors whose stiffness changes how they detect water pressure

The Institute of Science Tokyo announced on October 5 that its researchers had developed nanoscale polymer capsules whose membrane stiffness changes how they signal water pressure through fluorescence. The team reports strong sensitivity across 0.1 to 50 megapascals, a range relevant to the high-pressure environments it hopes eventually to study. The announcement describes laboratory measurements; it does not report pressure measurements inside living tissue.

The announcement says the underlying study appeared in ACS Applied Nano Materials on August 15. A later Phys.org article, published October 9, was provided by the institute. Those are distinct dates: the October report did not mark publication of a new experiment. The institute identifies the study as ‘A Programmable Nanovesicle Platform for Megapascal Pressure Sensing,’ with DOI 10.1021/acsanm.6c02728.

How membrane stiffness changes the pressure signal

The researchers used polyionic complex vesicles, polymer capsules that form in water, and attached fluorescent pyrene molecules to their membranes. They changed the degree of chemical crosslinking to make the membranes softer or stiffer while keeping the capsules approximately 100 nanometres across. This let them compare the effect of membrane stiffness on the optical response without making capsule size the intended variable.

According to the institute, pressure changes the arrangement of pyrene molecules in the membrane. When neighboring molecules move closer together, they produce more of a combined fluorescent emission called an excimer. The researchers compared that emission with light from individual pyrene molecules. A change in the ratio of the two signals gives a way to track pressure without relying on one fluorescence intensity alone.

Stiffer membranes offered a different readout. The institute says their fluorescence lifetime changed more noticeably with pressure. Fluorescence lifetime measures how long a molecule continues to emit light after excitation. The researchers propose using that timing difference in fluorescence-lifetime imaging microscopy, which can distinguish a sensor signal from some background fluorescence in biological material.

What the researchers tested in water-based media

The institute says the capsules remained intact and did not aggregate in salty seawater or protein-rich cell-culture medium. That is relevant because a sensor designed for marine or biological use must continue working in more complex liquids than purified water. Stability in those media, however, is a different test from measuring pressure inside a living cell, tissue or deep-sea organism.

The proposed uses include studying pressure around deep-sea microorganisms and within small biological spaces. The institute describes adding molecules to the capsule surface to target particular cells or tissues as future work. Its account does not establish that the present formulation can reach a selected site in a living system or provide a real-time microscopic pressure map there.

How this compares with an earlier fluorescent pressure sensor

Fluorescent sensing of hydrostatic pressure has an earlier precedent. In a 2013 PLOS ONE study, a separate research team inserted glycines into yellow fluorescent protein to make its light output more responsive to pressure. That team reported testing the modified protein in E. coli in a high-pressure chamber. Its device was a protein-based sensor, rather than a polymer capsule with stiffness-adjustable membranes.

The PLOS ONE researchers reported that one variant, YFP-3G, responded more strongly than unmodified yellow fluorescent protein at pressures of 100 and 300 megapascals. They also identified temperature sensitivity and the need for further improvement. Their cell experiment shows that fluorescent pressure sensing in living cells has been explored before, but it does not test or independently validate Science Tokyo’s newer nanovesicles.

For the new platform, the central result is the ability to select different optical responses by adjusting membrane stiffness, according to the institute. The practical question remains whether those responses can be measured reliably in the intended biological and marine settings. The available announcement describes possible applications and planned targeting work, while the underlying ACS article was unavailable for direct examination during preparation of this report.