Abstract
Radiation-damaged nanodiamonds (DNDs) are potentially ideal optical contrast agents for photoacoustic (PA) imaging in biological tissues due to their low toxicity and high optical absorbance. PA imaging contrast agents have been limited to quantum dots and gold particles, since most existing carbon-based nanoparticles, including fluorescent nanodiamonds, do not have sufficient optical absorption in the near-infrared (NIR) range. A new DND by He+ ion beam irradiation with very high NIR absorption was synthesized. These DNDs produced a 71-fold higher PA signal on a molar basis than similarly dimensioned gold nanorods, and 7.1 fmol of DNDs injected into rodents could be clearly imaged 3 mm below the skin surface with PA signal enhancement of 567% using an 820-nm laser wavelength.
Highlights
Photoacoustic (PA) imaging, a high-resolution noninvasive imaging technique, was recently proposed for biomedical applications
We have developed new radiation-damaged nanodiamonds (DNDs) with high optical absorbance in the NIR as a new contrast agent for PA imaging, and we compared optical absorption and imaging contrast capabilities of DNDs with those of AuNRs and single-wall carbon nanotubes (SWNT)
99% of the energy absorbed by the DND is released by nonradiative processes, e.g., vibration heating, which may contribute to the PA signal intensity
Summary
Photoacoustic (PA) imaging, a high-resolution noninvasive imaging technique, was recently proposed for biomedical applications. Tissue components or agents that absorb the laser energy undergo rapid microheating and generate ultrasonic waves due to transient thermoelastic expansion. These ultrasonic emissions are detected by a transducer and used to reconstruct a three-dimensional (3-D) image of the tissue structure based on optical absorption.[1] PA imaging provides better spatial resolution even in deep regions of biological tissues than pure optical imaging, such as optical coherence tomography and diffuse optical tomography, because scattering of ultrasonic energy is lower than optical energy in biological tissue. PA has provided excellent contrast and differentiation of breast malignancies compared to x-ray at depths of nearly 5 cm.[8]
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