Subdiffraction, Luminescence-Depletion Imaging of Isolated, Giant, CdSe/CdS Nanocrystal Quantum Dots

Subdiffraction spatial resolution luminescence depletion imaging was performed with giant CdSe/14CdS nanocrystal quantum dots (g-NQDs) dispersed on a glass slide. Luminescence depletion imaging used a Gaussian shaped excitation laser pulse overlapped with a depletion pulse, shaped into a doughnut profile, with zero intensity in the center. Luminescence from a subdiffraction volume is collected from the central portion of the excitation spot, where no depletion takes place. Up to 92% depletion of the luminescence signal was achieved. An average full width at half-maximum of 40 ± 10 nm was measured in the lateral direction for isolated g-NQDs at an air interface using luminescence depletion imaging, whereas the average full width at half-maximum was 450 ± 90 nm using diffraction-limited, confocal luminescence imaging. Time-gating of the luminescence depletion data was required to achieve the stated spatial resolution. No observable photobleaching of the g-NQDs was present in the measurements, which allowed imaging with a dwell time of 250 ms per pixel to obtain images with a high signal-to-noise ratio. The mechanism for luminescence depletion is likely stimulated emission, stimulated absorption, or a combination of the two. The g-NQDs fulfill a need for versatile, photostable tags for subdiffraction imaging schemes where high laser powers or long exposure times are used.