Detection of Polymer Deposition on Hydroxyapatite Disks by Fluorescence EEM Spectroscopy

Objectives: Deposition of polymer films on enamel surfaces can provide protection for teeth. As the interaction between enamel; i.e.., hydroxyapatite (HAP), and the polymer is non-covalent and the deposition time limited by contact time between the dental surface and polymer, the amount of material deposited may be very small. As such, relatively sensitive methods are required to detect and monitor the presence of film. The objective of the work described here was to detect polymer deposition on hydroxyapatite (HAP) using the fluorescence excitation – emission matrix (EEM) to detect directly the presence of polymer and quantitate how much is present on the disk. The advantages of the use of a fast fluorescence EEM method will be discussed.
Methods: Polymer covalently labelled with fluorescein was deposited onto HAP by soaking in a 2% solution of labelled polymer for five minutes, after which the HAP was dipped ten times into and out of 250 ml of distilled water. The polymer film was detected by acquiring the fluorescence excitation emission matrix. In this method, the excitation monochromator was scanned across wavelength and the emission is dispersed by a grating onto an array detector, which permitted the entire emission spectrum at a given wavelength to be collected in a single exposure interval (typically 0.1 sec – 1.0 sec). Excitation wavelengths ranged from 300 nm to 600 nm, with emission monitored to 556 nm.
Results: A primary emission feature arising from the deposited film was observed near 480 nm and emission maximum near 500 nm. A weaker, secondary feature was observed with excitation and emission maxima near 380 nm and 450 nm, respectively.
Conclusions: Non-covalent films of polymer deposited on HAP by soaking followed by rinsing can be detected and monitored using fluorescence EEM spectroscopy. Future work will involve use of different types of polymers and optimization of deposition conditions.