Making a hybrid microfluidic platform compatible for in situ imaging by vacuum-based techniques

Abstract

A self-contained microfluidic-based device was designed and fabricated for in situ imaging of aqueous surfaces using vacuum techniques. The device is a hybrid between a microfluidic poly(dimethyl siloxane) block and external accessories, all portable on a small platform (10 × 8 cm2). The key feature is that a small aperture with a diameter of 2-3 μm is opened to the vacuum, which serves as a detection window for in situ imaging of aqueous surfaces. Vacuum compatibility and temperature drop due to water vaporization are the two most important challenges in this invention. Theoretical calculations and fabrication strategies are presented from multiple design aspects. In addition, results from the time-of-flight secondary ion mass spectrometry and scanning electron microscopy of aqueous surfaces are presented.

Improving the Molecular Ion Signal Intensity for In Situ Liquid SIMS Analysis

“…The details of SALVI fabrication have been extensively described in our previous publications [11,12,16]. In brief, a microfluidic channel with a cross-section of 200 × 300 μm 2 was prepared on a PDMS block.…”

“…In situ liquid SIMS was developed in the last several years and one of its unique capabilities is the analysis of liquid-solid and liquid-vacuum interfaces [11][12][13][14][15][16][17][18]. To enable in situ liquid SIMS measurement, a vacuum-compatible device named system for analysis at the liquid-vacuum interface (SALVI) was developed [11,12], where a liquid of interest can be sealed in a microfluidic channel under a thin (e.g., 100 nm) silicon nitride (SiN) membrane. The key to in situ liquid SIMS measurements is the use of a~2 μm diameter aperture on the thin SiN membrane, through which the liquid interface and the liquid itself can be analyzed.…”

“…The key to in situ liquid SIMS measurements is the use of a~2 μm diameter aperture on the thin SiN membrane, through which the liquid interface and the liquid itself can be analyzed. Because the aperture size is small, surface tension can hold the liquid beneath the SiN membrane, and the evaporation of the liquid from the aperture does not cause any unacceptable problem to the vacuum system of the SIMS instrument [12]. The SiN membrane surface can be modified and the liquid in the cell can be changed, allowing various liquid-solid interfaces to be studied.…”

“…However, initial studies reported detection of only negative molecular ions [11][12][13][14][15][16][17] because the signals of the positive ion spectra were too weak to be meaningful. In addition, although negative molecular ions could be successfully analyzed, their signal intensity was not strong [16,17].…”

Through a Window, Brightly: A Review of Selected Nanofabricated Thin-Film Platforms for Spectroscopy, Imaging, and Detection

“…9c). 197 A custom-designed vacuum compatible microfluidic electrochemical device was created with a thin-film SiN x cover. By forming a $2 mm hole in that cover, the authors were able to then use in situ liquid secondary ion mass spectrometry (SIMS) to probe the electrochemistry, including the electrode-solution interface.…”