Zeolite based microconcentrators for volatile organic compounds sensing at trace-level: fabrication and performance

Abstract

A novel 6-step microfabrication process is proposed in this work to prepare microfluidic devices with integrated zeolite layers. In particular, microfabricated preconcentrators designed for volatile organic compounds (VOC) sensing applications are fully described. The main novelty of this work is the integration of the pure siliceous MFI type zeolite (silicalite-1) polycrystalline layer, i.e 4.0 ± 0.5 µm thick, as active phase, within the microfabrication process just before the anodic bonding step. Following this new procedure, Si microdevices with an excellent distribution of the adsorbent material, integrated resistive heaters and Pyrex caps have been obtained. Firstly, the microconcentrator performance has been assessed by means of the normal hexane breakthrough curves as a function of sampling and desorption flowrates, temperature and micropreconcentrator design. In a step further, the best preconcentrator device has been tested in combination with downstream Si based microcantilevers deployed as VOC detectors. Thus, a preliminar evaluation of the improvement on detection sensitivity by silicalite-1 based microconcentrators is presented.

Cu-BTC Functional Microdevices as Smart Tools for Capture and Preconcentration of Nerve Agents

“…The microfluidic channel, 2.5cm length and 20 µm depth, on un-doped <100>-oriented, polycrystalline 500 ± 20 µm Si wafer is fabricated as previously described. 22 Channel depth has been confirmed by profilometry.…”

Recent developments and trends in miniaturized gas preconcentrators for portable gas chromatography systems: A review

“…In the last decades, MEMS technology has been widely used for the fabrication of PCs [1,5,20,26,27,[33][34][35][36][37][38][39][40]; therefore, most of these devices are made of materials related to the electronics industry. So far, silicon has been the most employed material due to its relatively high thermal conductivity and the variety of existing micromachining techniques.…”

“…Wet etching techniques involve the use of liquid chemicals such as hydrofluoric acid or potassium hydroxide to remove the exposed surfaces of the substrate. These techniques played an important role in the early stages of MEMS development to create microfluidic cavities and channels in silicon at a relatively low cost compared to other etching techniques [29,39]. Wet chemical etching is isotropic and produces rounded side wall microchannels.…”

“…Therefore, high aspect ratio features are hard to build using these methods. For that reason, their use in PC fabrication has been limited [39]. On the contrary, dry etching techniques offers the possibility to create high aspect ratio structures.…”

“…Due to the narrowness of the microchannels altogether with the flow resistance added by the adsorbent particles, some of the one-single channel designs often shows relatively high pressure drops. Therefore, designs leading to lower pressure drop, such as a wide rectangular cavity connected to inlet and outlet channels [6,10,22,39] are usually preferred. In these microdevices, prior to fabrication, flow simulations are frequently conducted to estimate the pressure drop and optimize the distribution of the gas flow.…”