Session: Rising Stars of Mechanical Engineering Celebration & Showcase

Paper Number: 150508

150508 - Optical Super-Resolution Nanothermometry via Stimulated Emission Depletion Imaging of Upconverting Nanoparticles 

Modern electronic, data storage, and energy conversion devices increasingly combine nanoscale dimensions with challenging operating conditions, including extreme temperatures, high pressures, large electromagnetic fields, and harsh chemical environments. In tandem, thermal properties play an outsize role in determining the overall performance of these technologies. Engineering improved performance thus requires the ability to visualize heat flow using non- invasive thermometry techniques with nanoscale spatial resolution. Conventional far-field optical techniques enable non-contact measurements, but such approaches fundamentally lack the spatial resolution required to resolve nanoscale temperature heterogeneities. Upconverting nanoparticles (UCNPs) are popular luminescent thermometers with Boltzmann-distributed emission intensity that facilitates thermometry via temperature-dependent spectral peak intensity ratios, an approach known as “ratiometric” thermometry. UCNP coatings have been applied for temperature mapping with diffraction limited spatial resolution. Additionally, single-UCNP measurements have been used to circumvent the diffraction limit, but this approach only allows for single-point nanothermometry. Recently, heavily (~10%) Tm-doped UCNPs were shown to enable a super-resolution imaging method called stimulated emission depletion (STED) that has been widely used in biological imaging to circumvent the optical diffraction limit. Compared with other common STED imaging probes, UCNPs require much lower STED laser powers. Separately, this same UCNP composition, but with a much lower Tm concentration of ~1%, has been used for diffraction-limited ratiometric thermometry, suggesting the possibility of adapting STED imaging for far-field optical temperature mapping with sub-diffraction limited spatial resolution.

Here, we demonstrate an optical super-resolution nanothermometry technique based on temperature-dependent STED imaging and spectroscopy of heavily Tm-doped UCNPs [1]. First, we show that individual heavily Tm-doped UCNPs allow for both ratiometric thermometry and STED imaging. We then measure temperature-dependent emission spectra of individual UCNPs and identify peak intensity ratios that show sensitive, repeatable temperature dependence with good particle-to-particle uniformity. Using a custom-built STED imaging and spectroscopy system, we also demonstrate single-UCNP spectroscopic depletion. We further show that the sub-diffraction limited imaging resolution of our system is maintained from room temperature up to 400 K. Using an interfacial self-assembly method, we create uniform UCNP monolayers that can subsequently be placed on a sample surface. By scanning the surface of a monolayer-coated substrate at different uniform temperatures, we can record temperature-dependent ratios at each pixel and generate temperature maps. We also measure a Joule-heated microstructure and show that STED nanothermometry can resolve a temperature gradient that is undetectable with diffraction limited thermometry. These results indicate that temperature-dependent STED imaging of heavily Tm-doped UCNPs has excellent potential to enable optical super-resolution thermometry of structures with nanoscale temperature heterogeneities.

[1] Z. Ye, B. Harrington, and A.D. Pickel, “Optical Super-Resolution Nanothermometry via Stimulated Emission Depletion Imaging of Upconverting Nanoparticles,” accepted at Science Advances.

Presenting Author: Andrea Pickel University of Rochester

Presenting Author Biography: Andrea Pickel joined the Department of Mechanical Engineering at the University of Rochester as an Assistant Professor in July 2019. She received her Ph.D. in Mechanical Engineering from the University of California, Berkeley in May 2019, where she was supported by a National Science Foundation (NSF) Graduate Research Fellowship and a UC Berkeley Chancellor’s Fellowship. She received her B.S. in Mechanical Engineering with University and College Honors from Carnegie Mellon University in 2014. Her current research focuses on harnessing the unique properties of luminescent materials to develop nanothermometry techniques for challenging operating environments. Andrea is the recipient of an American Chemical Society Petroleum Research Fund (ACS PRF) Doctoral New Investigator Award (2020), a University of Rochester Furth Fund Award (2021), and an NSF CAREER Award (2022), and she was named a Scialog Fellow for Automating Chemical Laboratories (2024). Her teaching contributions have been recognized with the G. Graydon Curtis ’58 and Jane W. Curtis Award for Non-Tenured Faculty Teaching (2023).

Authors:

Andrea Pickel University of Rochester