Carbon nanotubes have attracted interest as contrast agents for biomedical imaging because they strongly absorb electromagnetic\nradiation in the optical and microwave regions. This study applies thermoacoustic (TA) imaging and spectroscopy to measure the\nfrequency-dependent absorption profile of single-walled carbon nanotubes (SWNT) in the ranges of 2.7ââ?¬â??3.1GHz and 7ââ?¬â??9GHz\nusing two tunable microwave sources. Between 7 and 9GHz, the peak TA signal for solutions containing semiconducting and\nmetallic SWNTs increased monotonically with a slope of 1.75AU/GHz (R2 = 0.95) and 2.8AU/GHz (R2 = 0.93), respectively, relative\nto a water baseline. However, after compensating for the background signal from water, it was revealed that the TA signal from\nmetallic SWNTs increased exponentially within this frequency band. Results suggest that TA imaging and spectroscopy could be a\npowerful tool for quantifying the absorption properties of SWNTs and optimizing their performance as contrast agents for imaging\nor heat sources for thermal therapy.
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