Electrical Detection of Pollen Allergen Using Electrode-Embedded-Micro-Channel

Hay fever is a disease that approximately 20 percent of the world population develop. Providing appropriate treatment for this plant-specific pollen allergy requires a method to identify various types of pollen. Here we introduce a technique that can be used for direct detections of single biological macromolecules such as pollen. Our method is based on two-probe current measurements using a microfluidic-channel-embedded-electrode system. A fabrication procedure of the device is as follows. First, we formed two gold nanoelectrodes by standard electron beam lithography and lift-off processes. The interelectrode gap distance was designed to be 500 nm. We then deposited a SiO₂ layer. After that, we fabricated Cr etching mask. Finally, we dry-etched the sample by reactive ion etching and obtained a microfluidic-channel-embedded-electrode structure. We flowed HEPES(2-[4-(2-Hydroxyethyl)-1-piperazinyl] ethanesulfonic acid) solution containing pollen of 500 nm size into the micro-channel and simultaneously measured current flowing through the two electrodes. Characteristic spike-like signals were observed; sharp rise of the current followed by a rather smooth decrease to the base current level. We exhibited control experiments in a HEPES solution wherein no pollen was added and observed only featureless current traces. We anticipate that the sharp current rise is associated with trapping of a single cedar pollen between the electrodes whereas the gradual current decrease represents the pollen detrapping. We propose the technique for identifying several kinds of pollens based on the height and the width of the current spikes.