A nanoscale, visible-light, self-sensing stress probe would be highly desirable in a variety of biological, imaging, and materials engineering applications, especially a device that does not alter the mechanical properties of the material it seeks to probe. Here we present the CdSe-CdS tetrapod quantum dot, incorporated into polymer matrices via electrospinning, as an in situ luminescent stress probe for the mechanical properties of polymer fibers. The mechanooptical sensing performance is enhanced with increasing nanocrystal concentration while causing minimal change in the mechanical properties even up to 20 wt % incorporation. The tetrapod nanoprobe is elastic and recoverable and undergoes no permanent change in sensing ability even upon many cycles of loading to failure. Direct comparisons to side-by-side traditional mechanical tests further validate the tetrapod as a luminescent stress probe. The tetrapod fluorescence stress-strain curve shape matches well with uniaxial stress-strain curves measured mechanically at all filler concentrations reported.
Microscale mechanical forces can determine important outcomes ranging from the site of material fracture to stem cell fate. However, local stresses in a vast majority of systems cannot be measured due to the limitations of current techniques. In this work, we present the design and implementation of the CdSe-CdS core-shell tetrapod nanocrystal, a local stress sensor with bright luminescence readout. We calibrate the tetrapod luminescence response to stress and use the luminescence signal to report the spatial distribution of local stresses in single polyester fibers under uniaxial strain. The bright stress-dependent emission of the tetrapod, its nanoscale size, and its colloidal nature provide a unique tool that may be incorporated into a variety of micromechanical systems including materials and biological samples to quantify local stresses with high spatial resolution.nanoscience | semiconductor nanocrystals | fluorescence | luminescent stress gauge L ocal microscale stresses play a crucial role in inhomogeneous mechanical processes from cell motility to material failure. Stress is a tensor representing force per unit area and is directly related to strain-a tensor that represents change in size and/or shape-via the stiffness constants of a material. Contact-probe techniques that measure stiffness such as atomic force microscopy (1, 2), indentation testing (3), and optical coherence elastography (4), and noncontact techniques that measure stress such as micro-Raman spectroscopy (5), electron backscatter diffraction (6), and polymeric post arrays (7) have been used to quantify local mechanical behavior with high spatial resolution. However, these techniques remain limited to studies in specific material systems due to spectroscopic and geometric constraints. For example, although the mechanical behavior of cells can be indicative of significant aspects of their biology, including metastatic potential (8), the stresses exerted by cells in physiologic threedimensional culture systems cannot currently be quantified. A luminescent nanocrystal probe, with its small size, bright and narrow emission, and colloidal processability is ideally suited to measure local stresses in a variety of systems without spectroscopic requirements from or excessive perturbations to the material of interest.We present here the design and implementation of a luminescent nanocrystal stress gauge, the CdSe-CdS core-shell tetrapod. The tetrapod, with a CdSe quantum dot at its core, has the same advantages as its widely used quantum dot predecessor, including tunable quantum confinement and high fluorescence quantum yields (9). Four CdS arms protruding from the CdSe core confer a branched, three-dimensional structure on the tetrapod; these arms can act as dynamic levers to torque the CdSe core and alter its optical response. The tetrapod can be incorporated into many materials, yielding a local stress measurement through optical fluorescence spectroscopy of the electronically confined CdSe core states. In this report, we calibrate the stress...
Recent advances in the synthesis of multicomponent nanocrystals have enabled the design of nanocrystal molecules with unique photophysical behavior and functionality. Here we demonstrate a highly luminescent nanocrystal molecule, the CdSe/CdS core/shell tetrapod, which is designed to have weak vibronic coupling between excited states and thereby violates Kasha's rule via emission from multiple excited levels. Using single particle photoluminescence spectroscopy, we show that in addition to the expected LUMO to HOMO radiative transition, a higher energy transition is allowed via spatially indirect recombination. The oscillator strength of this transition can be experimentally controlled, enabling control over carrier behavior and localization at the nanoscale.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.