Fig. 3: Scope of photothermal approach, and shape modulation.

a, b Comparison of the photothermally synthesized nanoparticle with conventional heating showing a, for a particular size (≈5 nm at 180 °C, n = 131; ≈10 nm at 200 °C, n = 122 with SD as error bar, as described in Fig. 2a, and Supplementary Fig. 5) or b, shape of nanoparticle (yellow with black outline), photothermal heating is much more efficient compared to conventional heating (≈30–100 °C). c–e TEM images of (c), triangular iron oxide nanoparticle (≈6–8 nm, synthesized photothermally at 180 °C, as described in Fig. 1a), (d), spherical iron oxide nanoparticle (≈2–4 nm; synthesized photothermally at 200 °C, reference ³⁹), and e, nanoplate of iron oxide (≈15 nm; synthesized photothermally at 200 °C, reference ⁴²). c–e Photothermal heating (red outline), and (f–h): conventional heating (blue outline), demonstrating almost intact morphology of the nanoparticles synthesized utilizing photothermal activation at a lower temperature (≈180–200 °C) compared to conventional heating at ≈210–300 °C (f, 210 °C, and g–h, 300 °C). Scale bars 50 nm. Inset showing the magnetic response of the nanoparticles in the presence of a laboratory-based bar magnet. Scale bar 1 cm. Source data are provided as a Source Data file.