Optical microscopes, structure, types and limitations. Considerations in choosing and constructing optical microscopes for biomedical imaging. Label-free microscopy (darkfield microscopy, phase microscopy, digital holographic microscopy). Label-based microscopy (fluorescence microscopy, using nano-particles in biological cells). Sectioning and specificity in microscopic imaging (confocal microscopy, fluorescence resonance energy transfer (FRET) microscopy, total internal reflection fluorescence (TIRF) microscopy, second harmonic generation (SHG) microscopy, two-photon and multi-photon microscopy, deconvolution microscopy, optical coherence microscopy). Resolution improvement in microscopy, optical nanoscopy (near-field microscopy, structured illumination and super resolution, advance methods for breaking the resolution limit).