Imaging 'intact' myofibrils with a near-field scanning optical microscope.

Fluorescently labelled myofibrils were imaged in physiological salt solution by near-field scanning optical microscopy and shear-force microscopy. These myofibrils were imaged in vitro, naturally adhering to glass while retaining their ability to contract. The Z-line protein structure of the myofibrils was antibody labelled and easily identified in the near-field fluorescence images. The distinctive protein banding structure of the myofibril was also seen clearly in the shear-force images without any labelling requirement. With the microscope in the transmission mode, resolution of the fluorescence images was degraded significantly by excessive specimen thickness (> 1 micron), whereas the shear-force images were less affected by specimen thickness and more affected by poor adherence to the substrate. Although the exact mechanism generating contrast in the shear-force images is still unknown, shear-force imaging appears to be a promising new imaging modality.