Development of a Silicon-based Gas Chromatographic Microsystem in Clinical Diagnostics

Systematically screening in medicine has great importance to perform early diagnoses, but in many cases it requires high costs. In this context, portable, cost effective miniaturized systems realized with microfabrication technologies are suitable to perform reliable, fast and real time analyses. In particular, it could be of great interest to have a portable device to perform in-field screening of parameters related to neuroblastoma tumor that, if not early detected, can cause mortality in the first year of life. The detection of neuroblastoma tumor can be accomplished by monitoring urinary levels of homovanillic acid (HVA) and vanilmandelic acid (VMA) that are end-products of dopamine and norepinephrine metabolism, respectively. Several methods have been described to detect HVA and VMA by means of chromatographic techniques. This work presents a cost-effective silicon-based miniaturised gas-chromatograph for clinical diagnoses. The miniaturized system consists of two main components: i.) a micromachined separation capillary column and ii.) a metal oxide semiconductor gas detector. A system approach has been pursued for the development of the whole device. In this aim, the capillary column has been fabricated by means of a deep reactive ion etching (DRIE) process of a silicon wafer and the resulting microchannels have been plugged by means of a wafer-to-wafer fusion bonding. The microchamber for gas sensor positioning and the inlets/outlets have been obtained by a wet etching (TMAH) process on the backside of the micromachined wafer. The microchannel walls have been coated with a stationary phase according to standard procedures for gas-chromatography. Finally, a detector consisting of a thick film gas sensor with a polysilicon microheather has been bonded on the top of the outlet. In order to test the microsystem performances, preliminary tests with homovannilic acid (HVA) and vanilmandelic acid (VMA) vapour solutions have been performe