Indefinite and Bidirectional Near Infrared Nanocrystal Photoswitching

TL;DR

This paper introduces a novel NIR bidirectional photoswitching nanoparticle system that enables indefinite, reversible control of luminescence for advanced imaging and data storage applications.

Contribution

The study demonstrates for the first time bidirectional, indefinite NIR photoswitching of colloidal nanoparticles with full optical control, surpassing limitations of previous photoswitchable materials.

Findings

Achieved >1000 switching cycles without degradation

Enabled sub-Å superresolution imaging of nanoparticles

Demonstrated 2D and 3D rewritable optical patterning

Abstract

Materials whose luminescence can be switched by optical stimulation drive technologies ranging from superresolution imaging1-4, nanophotonics5, and optical data storage6-8, to targeted pharmacology, optogenetics, and chemical reactivity9. These photoswitchable probes, including organic fluorophores and proteins, are prone to photodegradation, and often require phototoxic doses of ultraviolet (UV) or visible light. Colloidal inorganic nanoparticles have significant stability advantages over existing photoswitchable materials, but the ability to switch emission bidirectionally, particularly with NIR light, has not been reported with nanoparticles. Here, we present 2-way, near-infrared (NIR) photoswitching of avalanching nanoparticles (ANPs), showing full optical control of upconverted emission using phototriggers in the NIR-I and NIR-II spectral regions useful for subsurface imaging. Employing single-step photodarkening10-13 and photobrightening12,14-18, we demonstrate indefinite photoswitching of individual nanoparticles (>1000 cycles over 7 h) in ambient or aqueous conditions without measurable photodegradation. Critical steps of the photoswitching mechanism are elucidated by modeling and by measuring the photon avalanche properties of single ANPs in both bright and dark states. Unlimited, reversible photoswitching of ANPs enables indefinitely rewritable 2D and 3D multi-level optical patterning of ANPs, as well as optical nanoscopy with sub-{\AA} localization superresolution that allows us to distinguish individual ANPs within tightly packed clusters.