Scanning Microwave Microscopy for Biological Applications: Introducing the State of the Art and Inverted SMM

Often, a student comes in excited by a revolutionary idea. When this happens, we invite the student to check the literature carefully and, moreover, to extend the search way back, for more than a century, in fact. For example, encouraged by Albert Einstein, Edward H. Synge introduced the concept of a near-field scanning microscope in the 1928 paper "A Suggested Method for Extending Microscopic Resolution Into the Ultramicroscopic Region" [1]. He claimed to have overcome the "...axiom in microscopy, that the only way to extend resolving power lies in the employment of light of smaller wavelength." For subwavelength resolution of a biological sample, Synge proposed to place an opaque screen with a 10-nm diameter pinhole within 10 nm of the sample (Figure 1). Light passing through the pinhole and the sample is focused on a photodetector. By moving the screen laterally in 10-nm steps, the sample is imaged with 10-nm resolution, regardless of the wavelength of the light. Later, what he proposed became known as a scanning near-field optical microscope (SNOM).