A novel nanovesicle-based platform developed at Institute of Science Tokyo can measure hydrostatic pressure by converting pressure-induced molecular changes into fluorescence signals. The researchers developed pyrene-modified polyionic complex vesicles and demonstrated that variations in the vesicles’ membrane stiffness regulate their pressure sensitivity. Softer vesicles showed strong sensitivity in the 0.1–50 MPa range, while stiffer vesicles showed pressure-dependent changes in fluorescence lifetime. These findings enable the investigation of hydrostatic pressure-dependent phenomena in diverse inaccessible environments.
Hydrostatic pressure is the compressive pressure exerted on an object from all directions by a surrounding fluid at rest. It can influence many physical, chemical, and biological processes, making its measurement important in diverse environments, ranging from the deep ocean to living tissues. Despite its importance, measuring this parameter at microscopic scales remains challenging, particularly in aqueous and biological environments. Existing molecular sensors face limitations such as poor water solubility, insufficient sensitivity in the megapascal range, or operational difficulties in biological settings.
Against this backdrop, a research team led by Assistant Professor Hayato L. Mizuno and Associate Professor Yasutaka Anraku from Institute of Science Tokyo, Japan, along with Professor Gaku Fukuhara from Kyushu University, Japan, developed a nanovesicle platform for hydrostatic pressure sensing. Their study introduces pyrene-modified polyionic complex vesicles, or Pyr-PICsomes, whose membrane stiffness directly regulate their fluorescence response to pressure. The study was made available online on August 15, 2026, and was published in Volume 9, Issue 36 of the journal ACS Applied Nano Materials on September 11, 2026.
“An important aspect of our platform is that it does not rely on a single sensing mechanism,” says Mizuno. “By changing the membrane stiffness, we can access different fluorescence readouts, providing flexibility in how the pressure is measured.”
PICsomes are polymer-based vesicles that self-assemble in water from oppositely charged polymers. The researchers chemically crosslinked PICsome membranes using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). The EDC concentration was used to adjust the membrane stiffness while maintaining the vesicle size at approximately 100 nm in diameter. They then incorporated pyrene molecules into the membrane, which act as pressure-sensitive fluorescent probes.
When the pyrene molecules are separated, they fluoresce mainly as individual monomers at around 380 nm. Under hydrostatic pressure, neighboring pyrene molecules are brought closer together, allowing them to form temporary pairs called excimers that emit fluorescent signals at around 500 nm. The change in the excimer-to-monomer fluorescence ratio, therefore, provides a measure of the hydrostatic pressure.
Additionally, the researchers found that the stiffness of the Pyr-PICsome membrane strongly affected how the vesicles responded to pressure. The softest vesicles, with a stiffness of 7.3 pN/nm, showed the largest change in the fluorescence ratio between excimers and monomers across the 0.1–50 MPa range. Their sensitivity was 0.28 MPa⁻¹, compared with 0.02 MPa⁻¹ for the stiffest vesicles, which had a stiffness of 39 pN/nm. The amount of pyrene also affected the response, with more pyrene molecules leading to greater excimer formation and higher pressure-detection sensitivity.
While investigating the influence of pyrene on the excited-state dynamics of Pyr-PICsomes, the researchers identified another way to detect pressure by measuring fluorescence lifetime, or how long a fluorescent molecule remains in an excited state. In this case, the stiffer vesicles showed stronger fluorescence lifetime changes as pressure increased. The stiffest vesicles showed a lifetime sensitivity of −0.09 ns/MPa between 0.1 and 50 MPa. These properties make them a good candidate for fluorescence lifetime imaging microscopy (FLIM) probes. These finding suggest that membrane stiffness should be tailored depending on whether the hydrostatic pressure is measured through fluorescence intensity or FLIM.
“This tunability allows the sensing mode to be tailored to different environments and measurement methods, opening possibilities for studying pressure in complex aqueous systems,” notes Mizuno.
Furthermore, the researchers tested the platform's suitability for complex environments. Interestingly, the covalent crosslinking helps the vesicles maintain their structure in saline conditions, while their hydrophilic outer layer helps protect the membrane environment in biological fluids. Based on this, the authors propose that Pyr-PICsomes could eventually be used to investigate localized pressure in tissues, cell cultures, ex vivo samples, and deep-sea organisms.
This study establishes a materials-design strategy in which membrane mechanics can be used to program optical response behavior. The researchers developed a versatile, water-soluble, biocompatible, robust, and tunable platform capable of detecting hydrostatic pressure in complex inaccessible environments. This strategy lays the foundation for smart materials with varied applications across diverse disciplines.
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About Institute of Science Tokyo (Science Tokyo)
Institute of Science Tokyo (Science Tokyo) was established on October 1, 2024, following the merger between Tokyo Medical and Dental University (TMDU) and Tokyo Institute of Technology (Tokyo Tech), with the mission of “Advancing science and human wellbeing to create value for and with society.”
ACS Applied Nano Materials
Experimental study
Not applicable
A Programmable Nanovesicle Platform for Megapascal Pressure Sensing
11-Sep-2026
The authors declare no competing interests.