1.7 Sensor Elements and Testing on the Nanoscale

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Figure 1.59: The AFM can measure forces on the nanoscale by comparing the adhesion and retraction

forces of the tip while keeping track of distances in the z-direction accurately.

There is another method I need to mention when talking about measuring in the

nanoscale: microfluidics. When working with solutions in very small diameter tubes,

the flow will be laminar, unless the system includes specifically designed intersections

that will mix the new solvent/compound in the channel (Figure 1.60). Microfluidics can

be used for very precise sequential synthesis, but it is mostly used to detect specific

compounds with, e. g., a fluorescent label. With that you can detect, i. e., cancer cells or

infectious bacteria, in very low concentrations or identify a specific protein within a

cell.

Figure 1.60: Example for a microfluidic testing system. A) Solution with labeled cells is flowing through

a very narrow tube with laminar flow. B) The crossing with a junction of a channel containing solvent will

dilute the solution and force the cells to flow in a line. C) A laser beam excites the fluorescent label of the

cell; the fluorescence will then be measured.