Microsphere-assisted microscopy: challenges and opportunities

Optical microscopy is one the oldest and most widely used techniques for sample inspection in life and material sciences. Microsphere-assisted microscopy (MAM) has emerged as a simple yet efficient approach to boost the spatial resolution. MAM uses a microsphere, placed in the immediate vicinity of the object, to enhance the numerical aperture and improve the resolution. MAM can be used in conjunction with white-light, wide-field, bright-field, dark-field, confocal, fluorescent, second harmonic generation, two-photon, interferometric, and digital holographic microscopies. It can be employed in reflection and transmission modes. There are several open questions and challenges associated with MAM, including the resolution limit, the mechanism behind resolution improvement, and the limited imaging field-of-view. Here, we present the progress in MAM in the past decade along with the associated opportunities and challenges.