A photoacoustic (PA) imaging that utilizes acoustic detection of sound generated by a specimen due to the absorption of modulated light was applied to measure the amount of the pollen of the Cryptomeria japonica, Asian allergic plant. High-sensitivity PA imaging can measure pollen particles with a large dynamic range from single particle to several hundred micrograms. The PA signal dependence on the amount of the pollen showed good correlation with the amount of pollen.
Cryptomeria japonica (CJ) is one of an evergreen needle-leafed tree and indigenous race of Taxodiaceae, which is distributed among far-east Asia (China, Korea and Japan), and is famous for its allergic function against eyes and nose like hogweeds. Therefore, the counting of the amount of its pollen is important in the environmental science [
In order to achieve an automated pollen count, various methods including laser scattering have been introduced. However if optical detection such as CCD was adopted, it is difficult to achieve both high-sensitivity and wide dynamic range of detection because precise particle counting will be unavailable in the case of overlapping or stacking of pollen particles as shown in
The basic experimental setup of a PAM is similar to the previous publicatios [7,8] and shown in
The collected pollen particles were chosen to be specimens. Size of the CJ pollen of single particle is the about 30 µm in diameters. The pollen was collected and fixed on an adhesive tape on a slide-glass set in a PA cell. Exceptionally. CJ pollen particles ranging from one to ten were fixed on the albumen (egg white).
The optical and PA amplitude images of three pollen particles were shown in Figures 3(a) and (b), respectively. It was obtained at a modulation frequency of 90 Hz.
In
pollen amount of 0.03 to 0.70 mg was shown in
To reduce interfering PA noise that might be generated by other particles, differential absorption PA method [7,8] is favorable. Author’s group is developing a multi-pleco-lor LED and LD PA imaging system. The former [
For example, if we use diode-pumped solid-state lasers (DPSSL). Blue (457 nm) and green (532 nm) lights are easily available. As shown in
The optical and PA amplitude images of three pollen particles were shown in Figures 3(a) and (b), respectively. It was obtained at a modulation frequency of 90 Hz.
In
To reduce interfering PA noise that might be generated by other particles, differential absorption PA method [
For example, if we use diode-pumped solid-state lasers (DPSSL), blue (457 nm) and green (532 nm) lights are easily available. As shown in
A PAM was applied to the visualization, counting and measurement of pollen particles. Integration of PA amplitude signal over the specimen showed good agreement with pollen number or mass weight. The correlation coefficient of about 0.94 was obtained. Therefore, pollen measurement using the photoacoustic microscopy will be expected to be realized in the near future.