Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectromicroscopy Using Synchrotron Radiation and Micromachined Silicon Wafers for Microfluidic Applications

Abstract

A custom-designed optical configuration compatible with the use of micromachined multigroove internal reflection elements (μ-groove IREs) for attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectroscopy and imaging applications in microfluidic devices is described. The μ-groove IREs consist of several face-angled grooves etched into a single, monolithic silicon chip. The optical configuration permits individual grooves to be addressed by focusing synchrotron sourced IR light through a 150 µm pinhole aperture, restricting the beam spot size to a dimension smaller than that of the groove walls. The effective beam spot diameter at the ATR sampling plane is determined through deconvolution of the measured detector response and found to be 70 µm. The μ-groove IREs are highly compatible with standard photolithographic techniques as demonstrated by printing a 400 µm wide channel in an SU-8 film spin-coated on the IRE surface. Attenuated total reflection FT-IR mapping as a function of sample position across the channel illustrates the potential application of this approach for rapid prototyping of microfluidic devices.

Probing Heterogeneity in Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy (ATR-SEIRAS) Response with Synchrotron Infrared Microspectroscopy

“…Figure 5b plots the S/N of the perchlorate absorption band and the absolute value of the detector signal as a function of position along the y-axis. The origin of the periodicity in the IR signal amplitude was previously reported 42 and is caused by off-reflection of the incident IR beam, when increasingly misaligned with a groove wall. Severe degradation of the S/N is observed when the beam is offset more than AE200 mm from a position of maximum intensity in the integrated detector amplitude.…”

“…We recently reported the development of a horizontal ATR microscope end station at the mid-IR beamline at the Canadian Light Source (CLS) that allows for the measurement of ATR spectra with a spot size of $150 mm. 42 We have used this beamline to chemically image H/D isotope exchange processes occurring in microfluidic devices printed directly onto a Si m-groove IREs. 43 In this study, the endstation was combined with the FcC 11 SH system in an effort to correlate the spatial distribution of the IR signal with structural heterogeneity on the electrodeposited Au@ITO layers on the Si m-groove IRE.…”

“…This demonstrates an appreciable synchrotron advantage caused by the greater geometric étendue of the synchrotron. 42 A series of mapping measurements were performed by translating the Si m-groove IRE in the y-axis direction (as indicated by the green arrow in Fig. 4b) in 100 mm increments.…”

Optimization of a Commercial Variable Angle Accessory for Entry Level Users of Electrochemical Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy (ATR-SEIRAS)

“…22,24–27 The reduced IR transparency of Si due to interference from Si–O vibrations and phonon modes can be overcome through the use of micromachined ATR wafers. 15,28–30 In practice, silicon hemispheres and hemicylinders dominate the electrochemical ATR-SEIRAS literature. Hemispheres and hemicylinders are potentially advantageous in home-built IR spectroelectrochemical optics as they can be used to collimate the incident IR radiation.…”

Surface enhanced infrared spectroelectrochemistry using a microband electrode

“…The ITO-modified µgroove IRE was assembled in the spectroelectrochemical cell and positioned at the horizontal ATR microscope endstation 22 at the mid-IR beamline of the CLS. The alignment procedure is described elsewhere.…”