Evaluation of wheat and maize seeds by photoacoustic microscopy

In this study photoacoustic microscopy (PAM) was used to evaluate the deterioration of wheat and maize seeds. The analyzed seeds were obtained from different productive cycles. In the PAM experimental setup a modulated focused laser beam impinges on the sample. Due to the periodic heating it is possible to obtain a photoacoustic signal (PA) by using a microphone sensor; from this sensor an electrical signal is obtained due to the temperature variation in the sample. Since there are local differences in seed structure, the optical absorption of the laser beam and thermal properties are inhomogeneous, which produces a different PA signal in each point of the sample. By taking the set of the obtained PA signals as a function of their positions, it is possible to obtain a PA image. The image resolution was 50 μm for each seed. Therefore, the main objective of the present study was to obtain PA images of wheat and maize seeds, from different productive cycles (i.e., from different annual cycles). The analysis has shown that PAM is an alternative technique to evaluate seed deterioration. Also, the optical absorption spectra of these seeds were obtained by PA spectroscopy.