Near-Field Optical Microscopy, Spectroscopy, and Chemical Sensors

Abstract

Introduction Optical microscopy and spectroscopy have long been key techniques in medicine, biology, chemistry, and materials science. Among their advantages are: 1. Universality. All materials and samples attenuate light and have spectroscopic states. 2. Noninvasiveness. Most often the sample is not altered in a microscopic and/or spectroscopic investigation. Moreover, biological samples usually can be studied in their native environment. Most chemical reactions are not perturbed by light of long enough wavelength. 3. Real-time observation. Biological phenomena, chemical reactions, crystallization, and so on can be observed under the microscope as they happen in situ (even with one's eyes); spectroscopic measurements can be performed on line in an industrial process or other setting. 4. Energy and chemical state resolution. The obvious advantages of spectroscopy and photochemistry, at ambient temperature, can be trivially added to the optical methods mentioned above. By contrast, this is not easily accomplished with other techniques such as electron microscopy or x-ray crystallography. 5. Safety. Optical and spectroscopic analyses usually are very safe, and precautions are mostly limited to wearing optically protective eyeglasses. 6. Low price. Optical microscopy is much cheaper than, say, electron microscopy; optical spectroscopy is usually a bargain compared with, say, NMR instruments. Obviously, there are exceptions. 7. Speed, zoom, and human factors. Optical techniques are usually fast and can be extended even into the femtosecond time domain. They can be used from astronomical to microscopic distances. Preliminary or concomitant observations can be made using our most developed sense—sight, and in living color—even without the brokerage services of an analog or digital interface.