Professor Peter So's Laboratory
BEAM group (Bioinstrumentation Engineering And Microanalysis)
Standing-Wave Total Internal Reflection Microscopy (SW-TIRM)

Investigators: Euiheon Chung, Peter So

Light microscopy is widely used in biomedical research to study living biological systems. A major limitation of optical imaging is its inability to resolve objects with separation below several hundred nanometers. Even though there are several scanning-probe methods with higher resolution such as atomic force microscopy, there is significant resolution degradation in soft biological specimens and this method is inherently slow due to point-by-point scanning. Thus there is a need to develop a wide-field optical imaging method with below 100nm resolution.

The use of Standing evanescent wave imaging in a total internal reflection geometry have shown that lateral resolution better than 1/6 of excitation wavelength can be achieved. The enhanced image results from the high-spatial frequency modulation to the conventional point-spread function.


Figure 1: 3D point-spread function of SW-TIRM which has narrower PSF in the direction of standing wave.


Figure 2: A schematic diagram of SW-TIRM which shows the basic idea of generating standing evanescent wave and imaging.



If this development is successful, the technology should have interesting applications in cell biology, single molecular level detection, protein studies and the examination of pathological specimens.

1 - So P.T.C. et al. (2001) Resolution enhancement in standing-wave total internal reflection microscopy: a point-spread function engineering approach. J. Opt. Soc. Am.A, 18, No.11: 2833-2845.
2 - Cragg G.E. et al. (2000) Lateral resolution enhancement with standing evanescent waves. Optics Letters, 25: 46-48.
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