Fluorescence mapping and photobleaching of dye-labeled latex-particles dispersed in poly(vinyl alcohol) matrices with a near-field optical microscope

Polymer composite films consisting of fluorescent nanometric dye-labeled latex particles dispersed in poly(vinyl alcohol) matrices were imaged with a near-field scanning optical microscope (NSOM). Films with a thickness of ∼10 μm and of ∼25 nm containing latex particles with a diameter of 103 ± 9 nm with low particle density were studied. During image acquisition with the NSOM the particles were excited by an argon ion laser at the maximum or at the red edge of the excitation band at the excitation wavelength, λ, of λ = 458 nm or of λ = 488 nm, respectively. Maximum fluorescence contrast occurred in the first case. Fluorescence spots with FWHM diameters of <λ/2 could be found. In the case of the ∼10 μm thick films particles could only be imaged by mapping their fluorescence if they were located at the polymer-air interface. Subinterface particles could be detected as well. Additionally, photobleaching of a single fluorescent latex particle with a NSOM was performed, demonstrating a controlled photochemical reaction on a submicrometer length scale.