Laser-Ablative Engineering\nof ZrN-Based Nanoparticles\nfor Photothermal Therapy and SERS-Based Biological Imaging

Zirconium nitride (ZrN) nanoparticles (NPs) can offer\nappealing\nplasmonic properties for biomedical applications, but the synthesis\nof nontoxic, water-dispersible nanoformulations exhibiting plasmonic\nfeatures in the biotransparency window presents a great challenge.\nHere, we report the synthesis, by methods of laser ablation, of small\nZrN-based NPs, which are unique in combining photothermal heating\nand near-field enhancement in the transparency window. Depending on\nthe synthesis environment, the formed ZrN-based NPs exhibit plasmonic\nabsorption bands with maxima around 660–670 and 610–630\nnm, which are largely red-shifted compared to what is expected from\npure ZrN NPs. The observed shift is explained by the inclusion of\nzirconium oxide ZrO<sub><i>x</i></sub> (1 < <i>x</i> < 2) into NP composition and NP coating by naturally formed ZrO<sub><i>x</i></sub>. We then explored biophotonic applications\nof ZrN NPs. While pure NPs demonstrate their nontoxicity in vitro,\ntheir conjugation with anti-HER1 affibody Z<sub>HER1:1907</sub> and\nsubsequent photothermal heating with NIR-I laser cause 100% cancer\ncell death. In addition, profiting from the field enhancement, we\ndemonstrate bioimaging functionality using a designed surface-enhanced\nRaman scattering probe based on an NP-conjugated azobenzene-CN-OH\nmolecule as a Raman reporter. Combining a strong photothermal effect\nand the imaging option, laser-synthesized ZrN/ZrO<sub><i>x</i></sub> NPs promise a major advancement of theranostic modalities\nbased on plasmonic nanomaterials.