In this work, the monodisperse spherical pure β-NaYF 4 :Yb 3+ ,Er 3+ core NCs with average size of 7.2 nm were synthesized by using NaOA as sodium source instead of the conventional NaOH, based on which the sub-20 nm β-NaYF 4 :Yb 3+ ,Er 3+ @NaGdF 4 core-shell NCs with magnetic-optical bifunctional properties were successfully obtained with seed-mediated growth method. The magnetization of the core-shell NCs enhanced proportionally with increased shell thickness, and the maximum upconversion intensity was three orders of magnitude increased in the 18.3 nm NaYF 4 : Yb 3+ ,Er 3+ @NaGdF 4 core-shell NCs compare with the corresponding core NCs. Besides, the upconversion mechanism for the core and core-shell NCs were discussed. This work may lead to an ideal platform for the preparation of sub-20 nm spherical NCs with magnetic and optical properties for application in biomedical imaging and drug delivery.
Nonlinear depletion of fluorescence states by stimulated emission constitutes the basis of stimulated emission depletion (STED) microscopy. Despite significant efforts over the past decade, achieving super-resolution at low saturation intensities by STED remains a major technical challenge. By harnessing the surface quenching effect in NaGdF 4 :Yb/Tm nanocrystals, we report here high-efficiency emission depletion through surface migration. Using a dual-beam, continuous-wave laser manipulation scheme (975-nm excitation and 730-nm de-excitation), we achieved an emission depletion efficiency of over 95% and a low saturation intensity of 18.3 kW cm −2 . Emission depletion by surface migration through gadolinium sublattices enables super-resolution imaging with sub-20 nm lateral resolution. Our approach circumvents the fundamental limitation of high-intensity STED microscopy, providing autofluorescence-free, re-excitation-background-free imaging with a saturation intensity over three orders of magnitude lower than conventional fluorophores. We also demonstrated super-resolution imaging of actin filaments in Hela cells labeled with 8-nm nanoparticles. Combined with the highly photostable lanthanide luminescence, surface-migration emission depletion (SMED) could provide a powerful mechanism for low-power, super-resolution imaging or biological tracking as well as super-resolved optical sensing/writing and lithography.
Xing Xing,Yao Zhou,Yelu Wei,Yuchen Zhang,Zaiqin Man,Weihua Zhang,Zhenda Lu
Precise patterning of molecules/ions in the nanometer scale is a crucial but challenging technique for the fabrication of advanced functional nanodevices. We developed a robust method to print molecules/ions into arbitrarily defined patterns with sub-20 nm precision assisted by reverse micelles. The reverse micelle, serving as a nano-sized vessel, can load molecules/ions and then be patterned onto the predefined positions by electrostatic attraction. The number of molecules/ions on each spot, the spot spacing, and pattern shapes can be flexibly adjusted, reaching 10 nm position accuracy, 30 nm spot size, and 100 nm spot spacing (>250,000 DPI). Then, water-soluble dye molecules, protein molecules, and chloroaurate ions were loaded in the micelles and successfully patterned into nanoarrays, which provides an important platform for the convenient, flexible, and robust fabrication of functional molecule/ion-based nanodevices, such as biochips, for high-throughput and ultrasensitive analysis.
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