Excitons in two-dimensional (2D) materials are tightly bound and exhibit rich physics. So far, the optical excitations in 2D semiconductors are dominated by Wannier-Mott excitons, but molecular systems can host Frenkel excitons (FE) with unique properties. Here, we report a strong optical response in a class of monolayer molecular J-aggregates. The exciton exhibits giant oscillator strength and absorption (over 30% for monolayer) at resonance, as well as photoluminescence quantum yield in the range of 60–100%. We observe evidence of superradiance (including increased oscillator strength, bathochromic shift, reduced linewidth and lifetime) at room-temperature and more progressively towards low temperature. These unique properties only exist in monolayer owing to the large unscreened dipole interactions and suppression of charge-transfer processes. Finally, we demonstrate light-emitting devices with the monolayer J-aggregate. The intrinsic device speed could be beyond 30 GHz, which is promising for next-generation ultrafast on-chip optical communications.
Targeted delivery
of enzyme-activatable probes into cancer cells
to facilitate accurate imaging and on-demand photothermal therapy
(PTT) of cancers with high spatiotemporal precision promises to advance
cancer diagnosis and therapy. Here, we report a tumor-targeted and
matrix metalloprotease-2 (MMP-2)-activatable nanoprobe (T-MAN) formed
by covalent modification of Gd-doping CuS micellar nanoparticles with
cRGD and an MMP-2-cleavable fluorescent substrate. T-MAN displays
a high r
1 relaxivity (∼60.0 mM–1 s–1 per Gd3+ at 1 T)
and a large near-infrared (NIR) fluorescence turn-on ratio (∼185-fold)
in response to MMP-2, allowing high-spatial-resolution magnetic resonance
imaging (MRI) and low-background fluorescence imaging of gastric tumors
as well as lymph node (LN) metastasis in living mice. Moreover, T-MAN
has a high photothermal conversion efficiency (PCE, ∼70.1%)
under 808 nm laser irradiation, endowing it with the ability to efficiently
generate heat to kill tumor cells. We demonstrate that T-MAN can accumulate
preferentially in gastric tumors (∼23.4% ID%/g at 12 h) after
intravenous injection into mice, creating opportunities for fluorescence/MR
bimodal imaging-guided PTT of subcutaneous and metastatic gastric
tumors. For the first time, accurate detection and laser irradiation-initiated
photothermal ablation of orthotopic gastric tumors in intraoperative
mice was also achieved. This study highlights the versatility of using
a combination of dual biomarker recognition (i.e., αvβ3 and MMP-2) and dual modality imaging (i.e., MRI
and NIR fluorescence) to design tumor-targeting and activatable nanoprobes
with improved selectivity for cancer theranostics in vivo.
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