Fig. 4.

Representative normalized cellular TPEF images of NADH and FAD taken (a, b) after 5-minute acetic acid treatments, and (c, d) after 5-minute acetic acid treatment followed by 5-minute washout. Images labeled with (i) to (iii) are taken at different acetic acid concentrations from 0% to 1.2% (pH 7.56 - 3.86) for treatment and washout conditions, respectively. Note the excitation power used on the samples was less than 5 mW, and a total integration time of 60s per image was used. Image sizes are 50 μm x 50 μm.