Multispectral photoacoustic bioimaging using low power continuous wave lasers

We have developed a low-cost, non-contact, multispectral photoacoustic microscope system to study the functional parameters of cellular choromophores. The system uses low power continuous wave lasers and a photoacoustic sensor made of a kHz microphone coupled to a resonant chamber. Methemoglobin has relatively high optical absorption at 500 nm and 630 nm. Moreover, it has an almost the same optical absorption as hemoglobin at the isosbestic point of 525 nm. Photoacoustic data collected from methemoglobin using our system at wavelengths of 473 nm, 533 nm, and 633 nm show the similar trends as the methemoglobin optical absorption spectrum. The PA amplitude at 473 nm is about 1.03 times greater than at 533 nm and about 2.4 times greater than at 633 nm. Similarly, it possesses optical absorption of about 1.08 greater than at 533 nm and 1.34 times greater than at 633 nm. The developed system can be used as a differential photoacoustic microscope.