Fig. 2
a Excitation wavelength of AuNPs and AuNSs (left) and the T-junction demonstration of the microfluidic nanovalve device with PNIPAAm/AuNPs and AuNSs hydrogels comprising 100-µM-wide channels. (Reproduced with permission from Ref. [35], © 2005, WILEY–VCH Verlag GmbH & Co. KGaA, Weinheim). b Schematic of the AuNPs and AuNSs modified with PNIPAAm, and confocal laser scanning microscopy (CLSM) images of light-controlled shape changes in three-strata AuNSs300–AuNPs300–AuNSs300 cubes upon irradiation using wavelengths at 546 nm (1.1 W/cm2) and 785 nm (2 W/cm2). (Reproduced with permission from Ref. [42], © 2012 American Chemical Society). c Schematic of the volume shrinking of the hydrogels with AuNPs under light irradiation (top), actuation mechanism responding to visible light, and optical photos of the PNIPAAm-AuNPs/PAAm actuator without light irradiation (left panel) and with light irradiation (150 mW/cm2, right panel) for 25 s. Images of the photo-thermal hydrogel actuator performing a precise finger-like one-by-one bending via light (bottom). (Reproduced with permission from Ref. [36], © 2017, WILEY–VCH Verlag GmbH & Co. KGaA, Weinheim)