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E. M. Rodriguez Celis, M. Tourigny, A. Blain, L. W. Jones; Elemental Analysis of Hydrogel Contact Lenses Using Laser-Induced Breakdown Spectroscopy (LIBS). Invest. Ophthalmol. Vis. Sci. 2010;51(13):3411.
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To determine the feasibility of using Laser-Induced Breakdown Spectroscopy (LIBS), an atomic emission instrumental technique, for rapid elemental characterization of hydrogel contact lenses.
Seven different polyHEMA-based and silicone hydrogel lens materials (nelfilcon A, etafilcon A, galyfilcon A, senofilcon A, lotrafilcon A, lotrafilcon B, and balafilcon A) were analyzed by LIBS (PharmaLIBSTM250). No sample preparation was required, and the laser was directly focused onto the surface of the hydrogel materials. Each lens was analyzed at 121 sites, requiring less than 2 minutes per lens. Instrumental parameters and experimental conditions were carefully addressed to ensure reproducibility and confidence in the selected method and results obtained. The Si emission line at 390.6 nm was monitored for all materials to determine its presence or absence, surface uniformity and its variation with respect of drying time. Si uniformity in the lenses was assessed by reporting the %RSD (relative standard deviation = [SD/average Si intensity]*100) and two-dimensional plots. The potential effect of water content and influence of the packaging solution in the results was also addressed. The ablation efficiency (crater size and shape) was characterized by atomic force microscopy (AFM).
As predicted, no Si signal was detected for the polyHEMA-based materials nelfilcon A and etafilcon A, All five silicone hydrogel materials exhibited a strong Si signal, with a high signal to noise ratio. For the non-surface treated lenses, galyfilcon A and senofilcon A, an increase in the Si signal was observed with drying time (up to 12 hours). This behaviour was not observed in the plasma-coated lotrafilcon A and lotrafilcon B materials.
This is the first study to report on the use of LIBS to provide direct elemental analysis of hydrogel contact lenses. In less than two minutes and with no sample preparation, materials were analyzed for the presence of Si, surface changes over time, and homogeneity of Si across the lens surface. LIBS is a new analytical tool that provides much promise in the characterization of hydrogel biomaterials.
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