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Temperature measurement for a nanoparticle suspension by detecting the Brownian motion using optical serial sectioning microscopy (OSSM)

A concept of nonintrusive thermometry is presented based on the correlation of the Brownian motion of suspended nanoparticles with the surrounding fluid temperature. Detection of fully three-dimensional Brownian motion is possible by the use of optical serial sectioning microscopy (OSSM). This technique measures optically diffracted particle images, the so-called point spread function (PSF), and determines the defocusing or line-of-sight location of the imaged particle measured from the focal plane. A dry objective lens (40×, 0.75 NA) is used to detect the diffraction patterns of 500 nm polystyrene fluorescent (505/515) nanoparticles suspended in water at a volume concentration of 4 × 10−6, for a range of temperatures from 5 to 70 °C. The measured mean square displacement (MSD) data (figure 8, table 1) agree fairly well with the well-known Einstein predictions. Differentials of 5.54%, 4.26% and 3.19% were found for the 1D, 2D and 3D cases, respectively. In summary, the line-of-sight Brownian motion detection using the OSSM technique is proposed in lieu of the more cumbersome two-dimensional Brownian motion tracking on the imaging plane as a potentially more effective tool to nonintrusively map the temperature fields for nanoparticle suspension fluids.