Parinaz Fathi1 Indu Tripathi1 Santosh Kumar Misra1 Fatemeh Ostadhossein1 Aaron Schwartz-Duval1 Dipanjan Pan1

1, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States

Biliverdin is a naturally-occurring pigment in bile that exhibits high UV-Vis absorbance in the near-IR region, providing a potential platform for photoacoustic imaging with minimal background interference from biological tissue. Biliverdin nanoparticles (BVNPs) were synthesized in a variety of solvents, and were characterized using transmission electron microscopy (TEM), UV-Vis spectroscopy, Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy / Energy Dispersive X-Ray Spectroscopy (SEM/EDS), zeta potential measurements, fluorescence spectroscopy, fluorescence imaging, and photoacoustic imaging. The nanoparticles exhibited high absorbance at 365 nm and 680 nm, fluorescence when excited at 365 nm, and photoacoustic properties when excited at 680 nm. Nanoparticles were shown to form as early as ten minutes into the synthesis, and their properties varied based on the synthesis solvent. Nanoparticles synthesized in water and 0.9% NaCl solution were found to exhibit higher absorbance and lower fluorescence compared to the nanoparticles synthesized in MES. Additionally, nanoparticles synthesized in MES exhibited a red-shifted fluorescence over time compared to the other nanoparticles. The potential of these nanoparticles for use as photoacoustic agents in lymph node imaging was demonstrated in nude mice.