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Title: Upconverting Nanoparticles as Optical Sensors of Nano- to Micro-Newton Forces

Mechanical forces affect a myriad of processes, from bone growth to material fracture to touch-responsive robotics. While nano- to micro-Newton forces are prevalent at the microscopic scale, few methods have the nanoscopic size and signal stability to measure them in vivo or in situ. Here, we develop an optical force-sensing platform based on sub-25 nm NaYF 4 nanoparticles (NPs) doped with Yb 3+, Er 3+, and Mn 2+. The lanthanides Yb 3+ and Er 3+ enable both photoluminescence and upconversion, while the energetically coupled d-metal Mn 2+ adds force tunability through its crystal field sensitivity. IN using a diamond anvil cell to exert up to 3.5 GPa pressure or ~10 μN force per particle, we track stress-induced spectral responses. The red (660 nm) to green (520, 540 nm) emission ratio varies linearly with pressure, yielding an observed color change from orange to red for α-NaYF 4 and from yellow–green to green for d-metal optimized β-NaYF 4 when illuminated in the near infrared. We record consistent readouts over multiple pressure cycles and hours of illumination. With the nanoscopic size, a dynamic range of 100 nN to 10 μN, and photostability, these nanoparticles lay the foundation for visualizing dynamic mechanical processes, suchmore » as stress propagation in materials and force signaling in organisms.« less
ORCiD logo [1] ;  [2] ;  [2] ;  [2] ; ORCiD logo [3] ;  [4] ;  [5] ;  [2]
  1. Stanford Univ., CA (United States). Dept. of Applied Physics
  2. Stanford Univ., CA (United States). Dept. of Materials Science and Engineering
  3. Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
  4. Stanford Univ., CA (United States). Dept. of Molecular and Cellular Physiology
  5. Stanford Univ., CA (United States). Dept. of Geological Sciences
Publication Date:
Grant/Contract Number:
FG02-99ER45775; SC0001293; 2013156180; AC02-06CH11357; AC02-76SF00515; NA0001974
Accepted Manuscript
Journal Name:
Nano Letters
Additional Journal Information:
Journal Volume: 17; Journal Issue: 7; Journal ID: ISSN 1530-6984
American Chemical Society
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE National Nuclear Security Administration (NNSA); National Science Foundation (NSF)
Country of Publication:
United States
36 MATERIALS SCIENCE; crystal field theory; d-metal; diamond anvil cell; force sensor; lanthanides; upconversion; 77 NANOSCIENCE AND NANOTECHNOLOGY; crystal field theory, d-metal, diamond anvil cell, force sensor, lanthanides, upconversion
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1440363