Laser-Ablative Engineering of ZrN-Based Nanoparticles for Photothermal Therapy and SERS-Based Biological Imaging

Zirconium nitride (ZrN) nanoparticles (NPs) can offer appealing plasmonic properties for biomedical applications, but the synthesis of nontoxic, water-dispersible nanoformulations exhibiting plasmonic features in the biotransparency window presents a great challenge. Here, we report the synthesis, by methods of laser ablation, of small ZrN-based NPs, which are unique in combining photothermal heating and near-field enhancement in the transparency window. Depending on the synthesis environment, the formed ZrN-based NPs exhibit plasmonic absorption bands with maxima around 660-670 and 610-630 nm, which are largely red-shifted compared to what is expected from pure ZrN NPs. The observed shift is explained by the inclusion of zirconium oxide ZrO_x (1 < x < 2) into NP composition and NP coating by naturally formed ZrO_x. We then explored biophotonic applications of ZrN NPs. While pure NPs demonstrate their nontoxicity in vitro, their conjugation with anti-HER1 affibody Z_HER1:1907 and subsequent photothermal heating with NIR-I laser cause 100% cancer cell death. In addition, profiting from the field enhancement, we demonstrate bioimaging functionality using a designed surface-enhanced Raman scattering probe based on an NP-conjugated azobenzene-CN-OH molecule as a Raman reporter. Combining a strong photothermal effect and the imaging option, laser-synthesized ZrN/ZrO_x NPs promise a major advancement of theranostic modalities based on plasmonic nanomaterials.