In Situ Growth Strategy to Integrate Up-Conversion Nanoparticles with Ultrasmall CuS for Photothermal Theranostics

In the theranostic field, a near-infrared (NIR) laser is located in the optical window, and up-conversion nanoparticles (UCNPs) could be potentially utilized as the imaging agents with high contrast. Meanwhile, copper sulfide (CuS) has been proposed as a photothermal agent with increased temperature under a NIR laser. However, there is still no direct and effective strategy to integrate the hydrophobic UCNPs with CuS until now. Herein, we propose an in situ growth routine based on the hydrophobic core/shell UCNPs combined with ultrasmall water-soluble CuS triggered by single 808 nm NIR irradiation as the theranostic platform. Hydrophobic NaYF₄:Yb,Er@NaYF₄,Nd,Yb could be turned hydrophilic with highly dispersed and biocompatible properties through conjunction with transferred dopamine. The as-synthesized ultrasmall CuS (3 and 7 nm) served as a stable photothermal agent even after several laser-on/off cycles. Most importantly, comparing with the mix routine, the in situ growth routine to coat UCNPs with CuS is meaningful, and the platform is uniform and stable. Green luminescence-guided hyperthermia could be achieved under a single 808 nm laser, which was evidenced by in vitro and in vivo assays. This nanoplatform is applicable as a bioimaging and photothermal antitumor agent, and the in situ growth routine could be spread to other integration processes.