High resolution and high sensitivity near-field optical microscope

We have built a multi-purpose optical microscope by integrating a conventional confocal laser microscope (CLM) and a state of the art scanning near-field optical microscope (SNOM) with a conventional inverted optical microscope. The setup is designed for fluorescence imaging of delicate samples at very low signal levels as found in applications in the Life Sciences. An active-feedback closed-loop x-y-scanner with a scan range of 100 x 100 mu m enables the instrument to rapidly record large area scans using confocal microscopy. Interesting areas of the samples identified by such a scan can subsequently be investigated with sub-diffraction limited resolution. The near-field part of the instrument is based on standard optical fibre probes and a non-optical, tuning fork shear-force technique for maintaining the probe-sample distance. An extremely sensitive feedback working on the phase rather than the amplitude of the tuning fork response is used in order not to damage delicate biological samples. First results on mu-contact printed rabbit IgG and single molecule fluorescence are reported.