Measurement of the amount and number of pollen particles of Cryptomeria japonica (Taxodiaceae) by imaging with a photoacoustic microscope

A photoacoustic microscope (PAM), which includes a condenser microphone and a pair of linear-motor-driven pulse stages, was specially designed for spectroscopic applications. The PAM was applied to measure the amount and number of pollen particles of Cryptomeria japonica (CJ), which is known for its allergic function against eyes and nose. The advantage of photoacoustic (PA) imaging is both its high sensitivity and its counting ability up to high concentrations of the specimen. The CJ pollen particles were fixed on a piece of adhesive tape or on albumen (egg white) on a glass slide set in a PA cell. The PA image showed the ability of this method to count CJ pollen from the several-hundred-milligram region to even a single particle. The PA signal obtained was integrated over the specimen surface. The dependence of the PA signal on the amount or number of the pollen particles was measured. The resulting coefficients of correlation of the calibration curves for the amount and the number of pollen particles were 0.94 and 0.97, respectively.