Biomolecules and nanostructures
The Optical Sciences group studies the interaction of light and matter. Our current focus is on detection and sensing/imaging with an emphasis on the development of integrated photonics. We are part of Twente University's Department of Science and Technology and member of the MESA+ institute.
In Near-field optics, a sample is illuminated through a sub-wavelength aperture. This aperture is typically a pulled, coated optical fiber. From the illuminated area, optical information like transmission or fluorescence can be detected. For correct operation, the sample needs to be in the near field of the aperture, i.e. within a few nanometers. This is achieved by mounting the fiber on a quartz tuning fork. The tuning fork is mechanically excited at its resonance frequency. When the fiber tip is within several nanometers from the sample, the resonance frequency of the tuning fork with fiber shifts resulting in a drop in amplitude and a phase shift of the piezoelectric tuning fork signal. The aperture is kept in the near field by adjusting the tip-sample-distance to keep the tuning fork signal constant (tuning fork based shear-force feedback). If the sample is mounted on a x-y-z-scanner, the sample can be scanned under the aperture and an optical image can be reconstructed. Recording the adjustments to keep the tip-sample-distance constant, also a topographic image of the sample can be reconstructed.
The main advantages of NSOM are the high optical resolution (~50 nm) and the combined topography. In several fields of biology, like cell biology and molecular biology, NSOM would be a powerful tool. However, the requirement of a liquid environment has been a major obstacle for tuning fork based shear force feedback. This has prevented many applications for NSOM in biology to emerge.
The goal of this project is to overcome the limitations put forward by the presence of a liquid environment. A NSOM dedicated to biology will be developed and applied in the field of cell biology.
The following articles have been published regarding this project:
Imaging soft samples in liquid with tuning fork based shear force microscopy(abstract) (full pdf)
Rensen WHJ, van Hulst NF, Kammer SB
APPLIED PHYSICS LETTERS
vol 77 issue 10: p1557-p1559 SEP 4 2000
Atomic steps with tuning-fork-based noncontact atomic force microscopy(abstract) (full pdf)
Rensen WHJ, van Hulst NF, Ruiter AGT, West PE
APPLIED PHYSICS LETTERS
vol 75 issue 11: p1640-p1642 SEP 13 1999