A nanocrystal strain gauge for luminescence detection of mechanical forces

Local microscale stresses play a crucial role in inhomogeneous mechanical processes from cell motility to material failure. However, it remains difficult to spatially resolve stress at these small length scales. While contact-probe and non-contact based techniques have been used to quantify local mechanical behavior in specific systems with high stiffness or stress and spatial resolution, these methods cannot be used to study a majority of micromechanical systems due to spectroscopic and geometrical constraints. We present here the design and implementation of a luminescent nanocrystal strain gauge, the CdSe/CdS core/shell tetrapod. The tetrapod can be incorporated into many materials, yielding a local stress measurement through optical fluorescence spectroscopy of the electronically confined CdSe core states. The stress response of the tetrapod is calibrated and utilized to study mechanical behavior in single polymer fibers. We expect that tetrapods can be used to investigate local stresses in many other mechanical systems.