Scanning Aperture Approach for Spatially Selective ATR-FTIR Spectroscopy: Application to Microfluidics

Abstract

We present a novel spectroscopy accessory that can easily convert any Fourier transform infrared (FTIR) spectrometer into a fully automated mapping and assaying system. The accessory uses a multiridge attenuated total reflection (ATR) wafer as the sensing element coupled with a moving aperture that is used to select the regions of interest on the wafer. In this demonstration, the accessory is combined with a series of parallel micropatterned channels, which are positioned co-linear with the light-coupling ridges on the opposite side of the ATR wafer. The ATR spectroscopy microfluidic assay accessory (ASMAA) was used in continuous mapping mode to scan perpendicular to the ATR ridges, revealing complex but repeatable oscillations in the spectral intensities. To understand this behavior, the light path through the optical components was simulated with consideration of the aperture position, ridge-to-channel alignment, and excitation beam profile. With this approach, the simulation reproduced the experimental mapping results and provided evidence that the measurement position and area changed with the aperture position. To demonstrate the assay mode, we obtained spectra along the centerline of individual microchannels and determined noise baselines and limits of detection.

SpectIR-fluidics: completely customizable microfluidic cartridges for high sensitivity on-chip infrared spectroscopy with point-of-application studies on bacterial biofilms

“…This feature did not block the light path, but it increased the effective thickness of the sealing layer, which can undermine the precision in spatial selection of the measurement region by an aperture. 20 Therefore, the protruding meniscus was typically removed with a blade. The ATR sensing side featured a nearly continuous, planar PDMS/ATR surface for bonding to the microfluidic feature side (ESI, † section S3).…”

“…19 To reduce the system cost and expand applications, our group has demonstrated a simple method for generating linear maps or "x-scans" via a moving aperture that admits light into different locations of such multi-ridge ATR-coupled devices, with detection handled by a standard single-element detector. 20 Despite their potential, the trend in multi-ridge ATR crystals in lab-on-a-chip applications has largely remained the same: open microchannels are constructed using a pattered photoresist on top of the ATR sensing surface, with the latter forming the bottom wall. 16,20,21 The channels usually remain open because spin-coated photoresists on the small (ca.…”

“…20 Despite their potential, the trend in multi-ridge ATR crystals in lab-on-a-chip applications has largely remained the same: open microchannels are constructed using a pattered photoresist on top of the ATR sensing surface, with the latter forming the bottom wall. 16,20,21 The channels usually remain open because spin-coated photoresists on the small (ca. 1 cm 2 ) multi-ridge ATR crystals are dominated by edge beading, which complicates sealing of the top side.…”

Chemical Imaging of Mass Transport Near the No-Slip Interface of a Microfluidic Device using Attenuated Total Reflection–Fourier Transform Infrared Spectroscopy

“…However, the imaging field of view in that study was limited due to multiple beam paths through the multigrooved IRE. Greener and co-workers opted to aperture the relatively large beam from the source of a conventional FTIR spectrometer to collect chemical line scans of biofilms in microfluidic channels supported on a relatively large germanium IRE and subsequently on commercially available microgrooved IREs . The power of ATR–FTIR imaging for microfluidic applications has been demonstrated most convincingly by coupling a macrosized IRE with an FPA. , In the so-called macro-ATR technique, , larger field of view imaging is generally prioritized over maximum spatial resolution using commercial ATR accessories with little to no magnification of the approximately millimeter-sized beam spot.…”

In‐line monitoring of protein concentration with MIR spectroscopy during UFDF

“…Alternatively, cost‐effective ATR silicon crystals can be used. These ATR crystals have micromechanical structuring on the underside, produced through MEMS processing, in which a single internal reflection can occur [ 26 , 27 ]. Due to the thinness of the silicon ATR crystal (0.5 mm), the full spectral range, including the fingerprint region.…”