Scanning near-field infrared microscopy for biomedical imaging with a subwavelength spatial resolution

This work addresses the need to spectrally analyze of the absorption of middle-infrared (mid-IR) radiation in single living cells, with subwavelength spatial resolution, to identify molecular groups in them. The challenge is considerable, no lens can be used, so to realize such a device, a near-field probe was developed, from an optical fiber that is transparent in the mid-IR, non soluble in water, non-toxic and mechanically suitable. Incorporation of this probe in a scanning microscope, and use on a specially contained single living cell in water, allowed to achieve subwavelength imaging. Our fiber-material of choice is silver halides, i.e. AgClxBr1-x, made in the Applied Phyics Group of Tel-Aviv University. In spite of being bulky they were mechanically adapted to scanning microscopy. Theoretical and experimental investigations into the dampening of the motion of the probe in water were performed. A grid-like holder for containing living-cells for near-field microscopy has been introduced. The operating principle of this grid is based on sinking the cells inside the holes of the grid and letting them only negligibly protrude out of the holes (compared to the height-range of motion of the tip), in air and water. The result is a demonstration of the operation of the SNIM on different types of objects, including yeast cells, in water.