Interference Confocal Reflectance Microscopy for Collagen Fibril Diameter Measurement

Collagen fibrils provide an interesting challenge for traditional optical microscopy due to being large enough to visualize (>20nm) but usually below the Abbe diffraction limit point spread function. Confocal reflectance microscopy has been used previously to visualize collagen fibrils without fluorescent tags or other lethal methods (e.g, electron microscopy), but still cannot break the fundamental diffraction limit. We explore a sub-category of confocal reflectance known most commonly as interference reflectance microscopy, and more specifically confocal interference reflectance microscopy. The previous literature and the working principle for both mono and multi-wavelength systems are examined, finite difference time domain (FDTD) simulation results are presented, and initial imaging results of Type I collagen fibrils are shown. We believe this method has untapped potential for imaging collagen fibrils and could provide another non-lethal, no stain live imaging method to qualitatively measure collagen fibril diameters.