Growth of NIR-II-Responsive Gold Nanobipyramids with Improved Yield and a Study of Their Application in Cancer Therapy

Gold nanobipyramids (Au NBPs), as a novel and emerging plasmonic nanomaterial, have shown larger local electric field enhancements, larger optical cross-sections, and higher refractive index sensitivity compared to other plasmonic nanoparticles. Besides, their localized surface plasmon resonance (LSPR) absorption can be tailored to cover the entire NIR-II light region, which is crucial for clinical cancer treatment. However, strategies to synthesize Au NBPs with an NIR-II light response still have several disadvantages, such as tedious procedures and the use of hazardous chemical substances. In this work, we used a seed-mediated growth method and explored new strategies to synthesize high-yield Au NBPs with an NIR-II light response, especially in the region above 1030 nm, by regulating the conditions during Au seed growth. The yield of Au NBPs with a response at 1060 nm has been improved by 5-fold and 6-fold compared to previous seed-mediated growth methods when 230 μL of sodium citrate or a controlled temperature of 45 °C were used for Au seed growth with an Au seed solution containing 125 μL of NaBH₄. The influence mechanism of these factors on Au seed growth and the yield of Au NBPs has been explored in detail. Furthermore, the photodynamic and photothermal behaviors of Au NBPs with LSPR absorption at 1060 nm have been investigated, and the results indicate that Au NBPs have great potential in photothermal therapy. Besides, Au NBPs have been proven to induce immunogenic cell death (ICD), indicating their potential in immunotherapy. This work may provide a new idea for the synthesis and biomedical applications of Au NBPs with an NIR-II response.