Figure 2.

Multicontrast and multiscale PAT. (a) Absorption spectra of endogenous molecules at normal concentrations in vivo [27]. Bilirubin: 12 mg L^-1 in blood; DNA/RNA: 1 g L^-1 in cell nuclei; HbO₂: oxyhemoglobin; HbR: deoxyhemoglobin, 2.3 mM in blood; MbO₂: oxymyoglobin; MbR: reduced myoglobin, 0.5% mass concentration in skeletal muscle; melanin: 14.3 g L^-1 in the skin; lipid: 20% volume concentration in tissue; water: 80% volume concentration in tissue. (b) Noise equivalent molar concentrations of some widely used exogenous contrast agents, based on reported values from the literature [27]. Illumination fluence is not compensated. EB: evens blue [45]; EGFP: enhanced green fluorescent protein [46]; GNB: gold nanobeacon [47]; GNC: gold nanocage [48]; GNR: gold nanorod [49]; ICG: indocyanine green [50]; IRDye800: near-infrared Dye800 [51]; iRFP: near-infrared red fluorescent protein [52]; MB: methylene blue [53]; mCherry: monomeric cherry protein [46]; microbubble [54]; RFP: red fluorescent protein [52]; SWNT: single-walled nanotube [55]. The dashed curve is power function fitting $y=0.1x^{-1}$, where $y$ is the noise equivalent concentration in molars and $x$ the molar extinction coefficient in cm^-1 M^-1. (c) Multiscale PAT and representative images. Organelles and PA nanoscopy of a single mitochondrion (scale bar, 500 nm) [37]. Single cells, optical-resolution PAM of red blood cells (scale bar, 20 μm) [38]. Tissues, acoustic-resolution PAM of human skin (scale bar, 500 μm) [25]. Whole-body small animals and whole-body PACT of a nude mouse in vivo (scale bar, 4 mm) [39].