Near-infrared-II
fluorescence imaging (NIR-II FI) has become a
powerful imaging technique for disease diagnosis owing to its superiorities,
including high sensitivity, high spatial resolution, deep imaging
depth, and low background interference. Despite the widespread application
of conjugated polymer nanoparticles (CPNs) for NIR-II FI, most of
the developed CPNs have quite low NIR-II fluorescence quantum yields
based on the energy gap law, which makes high-sensitivity and high-resolution
imaging toward deep lesions still a huge challenge. This work proposes
a nanoengineering strategy to modulate the size of CPNs aimed at optimizing
their NIR-II fluorescence performance for improved NIR-II phototheranostics.
By adjusting the initial concentration of the synthesized conjugated
polymer, a series of CPNs with different particle sizes are successfully
prepared via a nanoprecipitation approach. Results show that the NIR-II
fluorescence brightness of CPNs gradually amplifies with decreasing
particle size, and the optimal CPNs, NP0.2, demonstrate up to a 2.05-fold
fluorescence enhancement compared with the counterpart nanoparticles.
With the merits of reliable biocompatibility, high photostability,
and efficient light–heat conversion, the optimal NP0.2 has
been successfully employed for NIR-II FI-guided photothermal therapy
both in vitro and in vivo. Our work highlights an effective strategy
of nanoengineering to improve the NIR-II performance of CPNs, advancing
the development of NIR-II FI in life sciences.