New Tool for Microscopic Temperature Mapping

Temperature plays a critical role in countless biological processes at the cellular level. However, precisely measuring temperature fluctuations within living cells remains a significant challenge. Conventional temperature measurement techniques often lack the spatial resolution needed to detect subtle temperature changes in complex microscopic environments.

Moreover, many existing molecular thermometers suffer from limitations in sensitivity, resolution, and applicability, highlighting the need for innovative solutions.

A Novel Molecular Thermometer Using Solvatochromic Fluorescent Dye

A research team from the Institute of Science Tokyo, Japan, led by Associate Professor Gen-ichi Konishi, has developed a groundbreaking molecular thermometer utilizing a newly designed solvatochromic fluorescent dye. Their findings, published in the Journal of the American Chemical Society, demonstrate how this novel compound enables highly precise temperature measurements by altering its fluorescence characteristics.

Using a π-extended fluorene structure, the researchers engineered donor−π–acceptor (D−π–A) fluorophores. These molecules are specifically designed to change their fluorescence behavior in response to the polarity of their environment.

As temperature increases, the polarity of the solvent decreases slightly, causing these dyes to emit light at different wavelengths and intensities. By measuring the ratio of fluorescence intensities at two specific wavelengths, researchers can accurately determine temperature fluctuations.

This "ratiometric" method eliminates variables such as dye concentration and excitation light intensity, allowing for exceptionally precise detection of even the smallest temperature changes within microscopic environments, such as cellular organelles.

Unprecedented Sensitivity and Resolution

The newly developed dyes exhibit remarkable solvatochromic properties, with emission wavelengths extending into the red region (701–828 nm) and shifts exceeding 200 nm between different solvents. Notably, the researchers achieved a temperature resolution of less than 0.1 °C and an impressive relative sensitivity of up to 3.0%/°C.

“These results represent the highest sensitivity and resolution ever reported for small organic single-fluorophore ratiometric fluorescence thermometers dispersed in solution—an ideal advancement for bioimaging,” says Associate Professor Gen-ichi Konishi.

The team furthered the design of future molecular thermometers by conducting additional mechanistic analysis, uncovering the underlying principles responsible for the dyes’ extraordinary solvatochromic properties.

Real-World Applications in Live Cells

To demonstrate the practical applications of their molecular thermometer, the team introduced one of the dyes into live human cell cultures. Using ratiometric confocal microscopy, they confirmed its effectiveness as a temperature sensor within cellular environments—particularly in cellular droplets, where local temperature variations may influence crucial biological processes.

“This molecular thermometer, based on a solvatochromic fluorescent dye, is expected to significantly expand the capabilities of fluorescence thermometry, enabling the discovery of previously unknown biological phenomena,” says Professor Konishi.

Future Directions and Broader Implications

Beyond biological research, this novel molecular thermometer has potential applications in material science, such as studying temperature-dependent properties of polymeric materials. The research team aims to develop a comprehensive library of fluorescence thermometers tailored for diverse environments and scientific applications.

By providing unprecedented insights into microscopic temperature fluctuations, these innovative dyes may revolutionize research in fields ranging from cell biology and chemistry to materials science, enabling scientists to explore temperature-dependent biological phenomena with unparalleled precision.