Fig. 1. Physical mechanism and characteristics of the photothermal effect of metal nanoparticles. (a) Physical processes and characteristic timescales that occur when light is irradiated onto metal nanoparticles^[8]; (b) photothermal efficiency of gold nanorods under different irradiation wavelengths^[10]; (c) photothermal efficiency of metal nanoparticles with different shapes^[11]; (d) temperature profiles around metal nanoparticles under continuous laser and pulsed laser irradiation; (e)(f) distributions of temperature around metal nanoparticles in three-dimensional space under continuous laser and pulsed laser irradiation^[12]; (g) temperature evolution over time of metal nanoparticles with diameter of 100 nm under continuous laser and pulsed laser irradiation^[12]

Fig. 2. Characterization and detection techniques for the photothermal effect of nanoparticles. (a) Measurement of local temperature of Au nanoparticles through fluorescence polarization anisotropy of fluorescent molecules^[27]; (b) measuring temperature changes at the nanoscale using X-ray absorption spectroscopy^[31]; (c) monitoring changes in nanoscale temperature through changes in environmental physicochemical properties by photothermal microscopy^[32], refractive index (top), viscosity (middle), phase change (bottom); (d) scanning thermal probe measurement of the temperature of nanodevices^[34]; (e) resonant inelastic radiation detection of gold nanorod temperature^[35]; (f) anti-Stokes Raman detection of the temperature around gold nanorods, the excitation powers are 100, 70, 50, 35 μW from top to bottom lines in the left panel^[37]

Fig. 3. Plasmonic photothermal therapy (PPTT) and its applications. (a) Schematic illustration of the principle of using gold nanoparticles for various cancer treatments^[41]; (b) evaluation of the PPTT treatment effect of gold nanorods on breast cancer (this figure is adapted with permission from Dove Medical Press Ltd.)^[44]; (c) transmission electron microscope (TEM) images of gold core-shell pedal particles^[45]; (d) variation of the photothermal effect of different core-shell particles with power^[45]; (e) assessment of the cytotoxicity of different gold core-shell nanoparticles^[45]; (f) schematic diagram of octopus-shaped gold/dielectric composite Janus nanoparticles and their photothermal temperature change^[46]; (g) controllable release process of DOX anticancer drug with photothermal effect, the three curves from top to bottom correspond to the conditions of pH=5.1+NIR, pH=5.1, and pH=7.4^[46]; (h) overview chart of the tumor tissue killing effect of PPTT formulations with different structures^[46]

Fig. 4. Photothermal imaging and biosensing. (a) PIC experimental setup and results, differential interference contrast image of a mixed sample containing polystyrene microspheres and 10 nm and 80 nm gold nanoparticles (bottom left), photothermal image at a heating power of 30 kW/cm² (middle), and photothermal image at a heating power of 1.5 MW/cm² (bottom right)^[48]; (b) principle of PT CD imaging (left) and PT CD imaging of of chiral “swastika” shapes, scanning electron microscopy (SEM) imaging (top right), PT imaging (middle right), and PD CD imaging (bottom right)^[51]; (c) schematic of an improved LFA experimental setup using gold nanoparticles^[55]; (d) schematic of a new COVID-19 nucleic acid detection device that utilizes the synergistic effect of plasmonic photothermal effect and plasmonic sensing^[56]

Fig. 5. Applications of plasmonic photothermal effects in catalysis, energy, and seawater desalination. (a) Gold nanoparticle-assisted heterogeneous photothermal catalysis for methanol hydrogenation reaction, the three curves from top to bottom in the right graph correspond to CO₂, H₂, CO ,respectively^[61]; (b) Ru nanoparticle-composite Si nanowires catalyse the hydrogenation of CO₂ to methanol^[64]; (c) application of plasmonic photothermal effects in seawater desalination, schematic diagram of the Au/AAO composite structure (left), SEM image (right)^[66]; (d) seawater evaporation efficiency graph^[66]; (e) comparison of the thermoelectric conversion performance between gold nanoparticle/carbon nanotube composite devices and carbon nanotube devices^[67]; (f) performance comparison of photothermal electric output devices^[67]

Fig. 6. Photothermal manipulation techniques and its applications. (a) Optical manipulation mechanisms based on photothermal phoresis and photophoretic electrophoresis^[69]; (b) photothermal manipulation techniques based on material phase transitions^[84]; (c) photothermal boost based on interfacial melting^[87]; (d) surface elastic wave-driven mechanism^[86]; (e) photothermal crawling drive mechanism of gold nanowires on the surface of optical fibers^[87]; (f) directional rotational displacement of gold nanoplates on a taped optical fiber driven by Lamb waves^[88]; (g) chemically-assisted photothermal jetting of gold nanoparticle^[89]

Fig. 7. Applications of photothermal effect of metal nanoparticles in nanofabrication. (a) Application of bubble pen lithography in the patterning of colloidal particles^[91]; (b) photothermal and photomechanical synergistic driving of gold nanoparticle etching of polymer films^[92]; (c) in-situ growth of core-shell structured metal@semiconductor oxide nanoparticles induced by photothermal effect^[102]; (d) in-situ growth of core-shell structured metal@polymer nanoparticles induced by photothermal effect^[105]