Experimental set-up and absorption spectra. a, Perspective view: The linear transducer array is mounted on the translation stage, which is attached to a rotation stage. Both the sample and the optical fibers are fixed. The optical fibers are mounted on a supporting holder and the laser beam is directed towards the sample to obtain a homogeneous illumination. For acoustic coupling, the sample and ultrasonic transducer were immersed in water; b, Top view of the experimental setup; c, Absorption spectra of the gold nanorods (AuNR) formulation (orange) and the fluorescent agent (IRDye CW800CW) in green. The spectra were normalized by their maximum value. The vertical lines and markers indicate, for each contrast agent, the wavelengths used for optical excitation during the multispectral acquisition.