Slide turns microscope into thermometer
Image: New thermo-sensitive microscope slide [University at Buffalo].
US-based researchers have developed a cheap, microscope slide that supports real-time temperature mapping as well as conventional microscopic imaging.
By depositing a novel, polymer-based coating to a standard coverslip, Professor Ruogang Zhao from Biomedical Engineering at the University of Buffalo, and colleagues, have combined microscale thermal imaging with microscopy, an achievement that has evaded researchers for decades.
“We have instruments that magnify incredibly small objects, and we have tools that measure heat, like infrared thermometers. But we haven’t been able to combine them in a low-cost and reliable manner," highlights Zhao. "This new coating takes a big step in that direction.”
The new coating comprises a layer of polymethyl methacrylate sandwiched between two layers of 20 nm-thick, transparent gold.
Zhao and colleagues fabricated the coating so that so-called 'exceptional points' - spectral singularities that exhibit unusual light behaviour - could develop within the tri-layered structure.
This Au-PMMA-Au structure was deposited onto a silica glass slide that was then mounted to a standard epi-fluorescent microscope, equipped with a helium-neon laser, ready for thermal imaging.
a Microscope system with the glass slide. While the white light source is for conventional microscopic imaging, the He–Ne laser (labeled by red arrow) is used as the incidence for thermal mapping. Inset: zoom-in of the glass slide in the microscope system. b Schematic drawing of the thermo-sensitive glass slide engineered at an exceptional point. c Transparency of the thermo-sensitive glass slide. [Zhao et al, Nature Communications, 9, 1764 (2018)]
"While maintaining transmitted-light imaging mode, a monochromatic laser light at the exceptional point wavelength [was] applied to map the reflection variation," says Zhao. "The He–Ne laser... can be seamlessly integrated with most microscopes, and was chosen in our work to probe the optical-thermal signal transduction."
"Despite the coating of the multilayer structure, the glass slide is transparent under white light... [so] in addition to the new function of temperature detection, the glass slide maintains the conventional topography-type imaging function of a microscope with transmitted light," he adds.
Experiments revealed the slide could efficiently monitor temperature with enhanced thermal sensitivity and microscale spatial resolution.
Thermal mapping of hot water injection. a Microscope slide with a bonded water reservoir for hot water injection. b Microscope image of the top right corner of the water reservoir by transmitted white light. The boundary divides the water and PDMS regions, demonstrating transmitted light imaging capacity of the glass slide. c Thermal mapping of the reservoir edge area when the reservoir is filled with room temperature water as a control experiment. d–g Transient thermal mappings at different times using forward reflection of the He–Ne laser beam, after injection of 43 °C hot water. Dashed lines in c–g represent the boundary of water and PDMS. Scale bars in b–g, 100 μm [Zhao et al, Nature Communications, 9, 1764 (2018)]
According to the researcher, the set-up also has high temporal-resolution for real-time monitoring of temperature distribution and evolution in samples.
"The thermo-sensitive microscope slide successfully enables real-time monitoring of the dynamic evolution of a heat transfer process, promising in-situ control of temperature in the applications where temperature monitoring is necessary," says Zhao. "It could play an important role in protein biosynthesis where enzyme activities are affected by heat generation."
Research is published in Nature Communications.