Accurate distance control between a probe and a surface using a microcantilever

We demonstrate a method to accurately control the distance between a custom probe and a sample on a {\mu}m to nm scale. The method relies on the closed-loop feedback on the angular deflection of an in-contact AFM microcantilever. High performance in stability and accuracy is achieved in this method by taking advantage of the small mechanical feedback path between surface and probe. We describe how internal error sources that find their origin in the microcantilever and feedback can be minimized to achieve an accurate and precise control up to 3 nm. In particular, we investigated how hysteresis effects in the feedback caused by friction forces between tip and substrate, can be minimized. By applying a short calibration procedure, distance control from contact to several micrometers probe-sample distance can be obtained with an absolute nanometer-scale accuracy. The method presented is compatible with any probe that can be fixed on a microcantilever chip and can be easily built into existing AFM systems

Direct Integration of Micromachined Pipettes in a Flow Channel for Single DNA Molecule Study by Optical Tweezers

We have developed a micromachined flow cell consisting of a flow channel integrated with micropipettes. The flow cell is used in combination with an optical trap setup (optical tweezers) to study mechanical and structural properties of λ-DNA molecules. The flow cell was realized using silicon micromachining including the so-called buried channel technology to fabricate the micropipettes, the wet etching of glass to create the flow channel,\ud and the powder blasting of glass to make the fluid connections. The volume of the flow cell is 2 µl. The pipettes have a length of 130 m, a width of 5–10 µm, a round opening of 1 um and can be processed with different shapes. Using this flow cell we stretched single molecules (λ-DNA) showing typical force-extension curves also found with conventional techniques. These pipettes can be\ud also used for drug delivery, for injection of small gas bubbles into a liquid flow to monitor the streamlines, and for the mixing of liquids to study diffusion effects. The paper describes the design, the fabrication and testing of the flow cell

Micromachined pipettes integrated in a flow channel for single DNA molecule study by optical trapping

We have developed a micromachined flow cell consisting of a flow channel integrated with micropipettes. The flow cell is used in combination with an optical trap set-up (optical tweezers) to study mechanical and structural properties of λ-DNA molecules. The flow cell was realized using silicon micromachining including the so-called buried channel technology to fabricate the micropipettes, the wet etching of glass to create the flow channel, and the powder blasting of glass to create the fluid connections. The volume of the flow cell is 2 µl. The pipettes have a length of 130 µm, a width of 5-10 µm, a round opening of 1 micron and can be processed with different shapes. Using this flow cell we stretched single molecules (λ-DNA) showing typical force-extension curves also found with conventional techniques