Compatibility of organic solvents for electrochemical measurements in PDMS-based microfluidic devices

Abstract

possesses their drawbacks and advantages. Historically, the first materials for microfluidic device fabrication were glass and silicon, and the chips were made by wet etching and then fusion bonding procedures. Because of the stiffness and chemical resistivity of these materials, processing usually requires the use of dangerous chemicals like hydrofluoric acid (in the wet etching step) and super clean environments together with high temperature and pressure conditions (in the fusion bonding step). These factors increase the overall cost of microfluidic chips fabrication and limit the broader use of these materials.Over the last few years, devices made from paper where the liquid solutions are moved along the chip by capillary forces have become increasingly popular (Martinez et al. 2007). Since the channels are open to air and there is a cellulose matrix in the channel area, the number of analytical methods that can be integrated with these devices is also limited. So far, the most commonly used method is colorimetry, whose application to paper chips seems to be the main strategy for their commercial applications, mainly due to minimum requirements of the equipment needed for analysis (Martinez et al. 2008). Another drawback of the paper chips is that they cannot be integrated with small size valves which are used for precise control and manipulation of the flowing liquids.For laboratory research-where one needs to compromise the ease of fabrication and the performance of the device-the most commonly used materials are elastomers, and among these, poly(dimethylsiloxane) (PDMS) is the most popular one (McDonald and Whitesides 2002). The main advantage of PDMS is the convenience in fabrication-it can be cast with high resolution in a relatively simple and fast photolithography process (Wu et al. 2003). Due to PDMS elasticity, it is possible to fabricate microvalves which can act like on-demand filters (Unger et al. 2000). AbstractWe have investigated the compatibility of some organic solvents commonly used in electrochemistry with microfluidic channels based on poly(dimethylsiloxane) (PDMS) and compared the stability of electrochemical measurements over several hours with how much PDMS swells when immersed in these solvents. Lee et al. (Anal Chem 75: 6544-6554. doi:10.1021/ac0346712, 2003 have shown that there is a good correlation between swelling of PDMS and the solubility parameter (δ H ) of the various solvents and suggested that δ H can function as an indication of PDMS compatibility. We show that solvents with a very high swelling ratio can give stable voltammetry over several hours, and thus, we do not find that swelling is a good measure for compatibility with PDMS in electrochemical experiments.

Simple Isopropanol-Assisted Direct Soft Imprint Lithography for Residue-Free Microstructure Patterning

“…The probable increase in contact angle after isopropanol treatment may be attributed to the surface swelling after being permeated by isopropanol. 22 The swelling effect during isopropanol treatment causes a slightly curved surface, resulting in an increase in the contact angle. θ values of Si/SiO 2 , glass, PI, and IGZO on Si/SiO 2 were 18.4, 25.8, 15.2, and 11.9°, respectively.…”

“…The range of θ for five untreated PDMS samples was 30.1–42.9°, while that of isopropanol-treated PDMS was 37.6–46.6°. The probable increase in contact angle after isopropanol treatment may be attributed to the surface swelling after being permeated by isopropanol . The swelling effect during isopropanol treatment causes a slightly curved surface, resulting in an increase in the contact angle.…”

Toward Achieving Highly Ordered Fluorinated Surfaces of Spin-Coated Polymer Thin Films by Optimizing the Air/Liquid Interfacial Structure of the Casting Solutions

“…The other two solvents (i.e., toluene and trifluorotoluene) were employed in the studies. The solubility parameters (δ) of cyclohexanone, toluene, and trifluorotoluene are 9.9, 8.9, and 8.3 cal 1/2 ·cm –3/2 , respectively, corresponding to the order of solubility toward FMA: trifluorotoluene > toluene > cyclohexanone. The DLS data of FMA 1 - ec -PMMA 65 - ec -FMA 1 in toluene and trifluorotoluene solution are shown in Figure S3.…”

Design of Electrochemical Microfluidic Detectors: A Review

“…to its chemical inertness, PDMS is compatible with most of the solvents and electrolytes, [106] However, if online physical characterization methods are needed, PDMS will generate undesirable background signals reducing the accuracy of the optical technique, as reported in online mass spectrometry (MS) studies. [6] Also, a great expansion of PDMS in all dimensions when swelled with various organic solvents were repeatedly measured by Adamiak et al [107] , which shows that its use as microfluidic building blocks is subject to the property of solvents. PDMS is also permeable by oxygen, which may be a disadvantage in some experiments.…”