Anchoring Hollow Nanoneedles in a Free-Standing Plate for Integration in a Microfluidic System

Inhalt:
Small needles can be used for various biomedical, intracellular applications of electrical or fluidic nature. Here, we analyze and optimize the anchoring of hollow nanoneedles in a plate suspended above a fluidic channel. Good anchoring is required for achieving a leakage-free fluidic connection between nanoneedles and channels while also ensuring sufficient mechanical stability for cell interfacing. To align the diameters of the nanoneedles and the corresponding holes in the plate, different parameters of the fabrication method are scrutinized. Namely, the exposure doses during lithography, the photomask dimensions, and the etch processes as well as their respective effects on the nanoneedle anchoring are examined. Using a geometrical model and extensive scanning electron microscopy analyses, the aforementioned parameters were adjusted to achieve adequate anchoring for different nanoneedle sizes. For instance, between the two separate patterning steps, diameter differences in the resist of 20 nm, 270 nm, and 360 nm were required to fabricate well anchored nanoneedles with heights of 2 µm and diameters of 500 nm, 1000 nm, and 2000 nm, respectively. With the eventually fabricated and stable geometry, liquids may be transported through the nanoneedles from the backside with good spatiotemporal control. As the novel fabrication method also enables high-density electrical integration, a new combination of capabilities and intracellular applications may become possible with this device.