Differential frequency-domain photoacoustic microscope for blood oxygen saturation measurements

We have developed a low-cost frequency domain differential photoacoustic microscope. The microscope uses a low-cost PA sensor made up of a kHz microphone, low power CW lasers and an optical chopper with 6/5 dual-slot disc. The system used dual-slot chopper disc to modulate two laser beams simultaneously and the corresponding PA signals were measured. This simultaneous modulation enabled a single scan instead of two scans required for two lasers in previous configurations, reducing the scanning time half. The configuration also enabled two PA interrogations at the same location of the sample whereas in the conventional sequential measuring system any backslash of the translation stage would alter the location of the interrogation area during the next measurement. The developed sensor is used to study the oxygen saturation of a single RBC. Two types of RBCs containing predominately oxy and methemoglobin were investigated using three different lasers of wavelengths 473 nm, 533 nm, and 633 nm. The single cell study showed that half of the oxy-RBC and meth-RBC exhibit oxygen saturation of about 90 % and 38.61 % respectively.