Use of dye sensitizers for increased photoacoustic mechanosensation

The photoacoustic effect refers to the generation of pressure waves in matter stimulated by light[1]. In the context of radiology (i.e., photoacoustic imaging) waves generated by pulsed laser light are detected by an ultrasound transducer[2-4]. It has been shown that photoacoustic waves produce a mechanical, tactile sensation in humans on bare skin[5]. In a series of psychophysical experiments, performed with both medical grade and off-the-shelf pulsed light systems, participants could detect, categorically describe, and discern the direction of travel of pulsed optical stimuli with the use of a dye as an optical absorber on the skin. To a large extent, the sensations were perceived as localized vibration on the glabrous surface of the fingers, when sensitized with the thin film of dye. This form of sensory stimulation demonstrates an enhanced non-contact, non-optogenetic, in situ activation of the mechanosensory system. This modality of sensation may provide a tool that leads to new insights in psychology, neuroscience, mechanobiology, and the health sciences. Finally, it has many advantageous characteristics for human interaction with artificial environments, as optical signals can be projected onto the skin across distances.