Kelvin probes provide non-contact measurements of variations of surface potential. This tool can be used to map either of the two components contributing to surface potentials – one due to work function and another due to trapped charge. Charge distribution on the wall acquired during manufacturing or in routine operation, can impact the function and behavior of the fluid in the channel. For example, it has been linked to cell adhesion and clotting of red blood cells on artificial surfaces. A Kelvin probe can be used to map the charge embedded in the wall by scanning the outside of the fluidic channel, using the electrolyte in the channel as an electrode. A macroscale Kelvin probe has been used to measure surface potentials, however no micromachined devices are available for sensing in liquids.
Researchers at the University of Michigan have developed a novel micromachined probe apparatus that can be used to characterize liquid in a fluidic channel and map embedded charge in a sample on a substrate. Non-invasive probe apparatus includes an integrated scanning tip and a dither actuation mechanism. The device is fabricated by a modified micro electro-discharge machining process, which allows electrical isolation within the micromachined structure using an epoxy plug. The apparatus may be used to measure changes in the external surface potential of a microfluidic channel as a function of varying pH of liquid inside the channel. It may also be used to map embedded charge in a thin layer on a substrate, showing it to be suitable for monitoring microelectronics manufacturing processes.
Applications and Advantages
- Mapping surface charge and surface-nl-potential difference
- Measuring the pH of liquids in a microchannel-nl-(through changes in surface potential,-nl-which are correlated to pH)
- Micromachined for use in microfluidic devices
- Provides non-invasive, non-contact measurements