Organic nanoparticles with ultrahigh stimulated emission depletion efficiency for low-power STED nanoscopy

Abstract

We prepared a STED probe with ultrahigh stimulated emission depletion efficiency for low-power STED nanoscopy.

Shedding New Lights Into STED Microscopy: Emerging Nanoprobes for Imaging

“…For example, SiNPs doped with the Atto647N dye showed STED power requirement (100∼400 MW/cm 2 ) similar to that of the bare dyes (Tavernaro et al, 2017). Meanwhile, SiNPs doped with specially designed fluorophores (non-SOC (Liang et al, 2020) or non-ACQ (Man et al, 2019)) showed an ultralow I sat of ∼10 -1 MW/cm 2 .…”

“…For SiNPs, their surficial Si-OH groups are not very reactive with most linkage groups (carboxyl, amine, etc.). Therefore, the functionalization of SiNPs is mostly performed through silane linkers like APTES before further modification with functional molecules by amidation (Schubbe et al, 2010;Schübbe et al, 2012;Man et al, 2019). This might lead to an increase in particle size during the modification, altering the biodistribution of these probes, especially for smaller particles.…”

“…Furthermore, inorganic emitters like UCNPs and QDots typically have a longer PL lifetime (×10 ns), which also contribute to their low saturation intensity values. To this day, nanoprobes like UCNPs (Liu et al, 2017;Liang and Liu, 2017), QDots (Ye et al, 2020;Ye et al, 2018), CDots (Li et al, 2019), and SiNPs (Liang et al, 2020;Man et al, 2019) have been reported with an ultralow saturation intensity of 10 -1 MW/cm 2 , which are 2∼3 magnitude lower than that of typical molecular STED probes. For FNDs, the lowest reported saturation intensity for N-V and N-V-N defects was 1 MW/cm 2 (Han et al, 2009) and 2.5 MW/cm 2 (Laporte and Psaltis, 2016), respectively, slightly lower than that of molecular probes.…”

“…Another success in improving resolution and reducing the STED power requirement was achieved by introducing a nonplanar twist intramolecular charge transfer (TICT) compound DAPF as the emitting core (Man et al, 2019). As a result, a stable and highly efficient STED nanoprobe was fabricated, which achieved a lateral resolution of 60 nm at <1 MW/cm 2 STED intensity (∼3 mW in power scale) for cell imaging.…”

“…This particularly limits the usage of bare SiNPs and FNDs, as their surface composition is hydrophobic and might form agglomerates under physiological conditions (Schubbe et al, 2010;Tzeng et al, 2011). Meanwhile, inorganic nanoparticles like QDots, UCNPs, and LPR hybrids Schübbe et al (2012), Peuschel et al (2015), Tavernaro et al (2017), Man et al (2019) LPR hybrids \ ∼0.9 ns 10∼100 μs Yes Sonnefraud et al (2014), Cortés et al (2016), Urban et al (2018), Gao et al (2020) contain heavy metal elements, resulting in potential long-term toxicity, especially for in vivo imaging. Fortunately, since the toxicity of inorganic nanoparticles can be largely alleviated by bioconjugation and the dosages required for imaging are generally low, the toxicity of these materials for cellular imaging has proved acceptable (Gao et al, 2005).…”