Pulsed photoacoustic measurements of suspensions: in case study of mitochnodrial NADH and its phantom

Abstract

The laser photoacoustic spectroscopy (LPAS) can be applied analytically to determine the concentration of an analyte in samples and its absorption variation as a function of time. The LPAS has advantages of higher detection sensitivity, pure absorption measurement and much less interference by background scattering in comparison with traditional optical spectroscopy. On the other hand, the apparatus is simpler and more generally useful than that of fluorescent spectroscopy. In this study, we built a photoacoustic setup of a Q-switched Nd:YAG laser excited at the third harmonic wavelength and a wideband piezoelectric transducer clamped to the side of a cuvette. The samples included NADH solutions, mitochondrial suspensions and Intralipid-ink mixtures. The experiment results show that the lowest detectable absorption of the setup is in the order of 10-5 cm-1; the detectable concentration of NADH in a buffer is as low as 1.67 μM. When monitoring mitochondrial suspensions, the minimal concentration that can be detected is lower than 0.1 mg/mL and the absorption variation caused by full reduction of NAD+ to NADH in mitochondria can be detected.