Abstract
We describe the synthesis and characterization of melanin-like nanoparticles (MNP) as novel contrast agents for optoacoustic tomography. Good dispersion stability of high concentration MNPs in different biological media was achieved with thiol-terminated methoxy-poly(ethylene glycol), which can be used for further functional conjugation. MNP-PEG were found biocompatible with human MCF-7 and 3T3 cells. Cell toxicity of MNPs was found lower than that of gold nanorods for concentrations that provide equal optical absorbance. Optoacoustic tomography images were obtained with Laser Optoacoustic Imaging System (LOIS-3D) from tubes filled with contrast agents and live mice. Imaging of tubes permitted verification of the system resolution <300μm and sensitivity Δμa=0.03/cm under safe laser fluence of 20mJ/cm2. Water suspensions of MNP demonstrated optoacoustic efficiency that is about equal to that of gold nanorods under conditions of equal optical absorption. We conclude that MNPs have the potential for biomedical imaging applications as optoacoustic contrast agents.
Highlights
Optoacoustic tomography (OAT) is a biomedical imaging modality that combines the spectral selectivity and the high optical contrast based on variation of optical absorption with the high resolution based on detection of ultrasound generated in tissues with nanosecond laser pulses [1,2]
After overnight synthesis (12 hours) the melanin-like nanoparticles (MNP) were purified through several centrifugation/redispersion cycles in deionized water to increase the uniformity of the MNP fraction
Formation of melanin nanoparticles synthesized by neutralization of dopamine hydrochloride with sodium hydroxide, or with oxidation DOPA with KMnO4, has been verified by transmission electron microscopy (TEM) and NIR spectroscopy
Summary
Optoacoustic tomography (OAT) is a biomedical imaging modality that combines the spectral selectivity and the high optical contrast based on variation of optical absorption with the high resolution based on detection of ultrasound generated in tissues with nanosecond laser pulses [1,2]. The signal amplitude emitted by a contrast agent is proportional to its volume accumulated at the target site. Nanoparticles, such as gold nanorods, having their volume and the optical absorption coefficient much larger than those of any molecular probe, are thought to be of especially significant value as contrast agents for optoacoustic imaging [11]. Two of the biggest advantages of using endogenous contrast agents for imaging applications are safety and the possibility of revealing the true physiological conditions, because the physiological parameters are not altered during optoacoustic image acquisition
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