Disposable spectrofluidic devices for attenuated total reflection infrared spectroscopy: characterization sensitivity, spatial resolution and generally applicable to multiple device types

Abstract

In this paper, we present a generalizable method for the fabrication of disposable spectrofluidic devices for solution characterization by attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy. A major design feature is the integration of an ATR element into the device rather than the fabrication of the microchannels on its sensing surface. This alleviates spatial limitations, due to small element footprint and dominance of edge-beading, enabling arbitrarily complex microfluidic circuitry and complex world-to-chip interfaces while leaving the entire ATR element available for sensing. An optimized optical interface maximizes light transfer into the on-chip sensing chamber. This promotes low limits of detection, fast measurements and/or designs featuring multiple sensing sub regions. To demonstrate the approach, we conducted measurements on complex flow profiles generated from four separate proof-of-concept spectrofluidic devices. A high sensitivity device detected glucose and sodium phosphate dibasic(Na2HPO4) at concentrations as low as 3 mM and 1 mM, respectively or and for time-lapse results with second-scale time resolution from single-scan measurements. We also demonstrated spatial selectivity for assays in parallel channels, measurements of concentration gradients in a multi-laminar co-flow device, and monitored fast kinetics of the protonation of a pH buffer in a microfluidic reactor.

A spectIR-fluidic reactor for monitoring fast chemical reaction kinetics with on-chip attenuated total reflection Fourier transform infrared spectroscopy

“…For further details, the reader is referred elsewhere. 30 The test analyte used in this study were sodium phosphate dibasic (Na2HPO4) (84486-300, Anachemia, Canada), which is a major component of the popular biological sodium phosphate buffer. A stock solution of 0.2 M was prepared by dissolving 2.84 g of Na2HPO4 in 100 mL of deionized water.…”

“…27,29 Recently, we have demonstrated a versatile microfabrication approach called spectIR-fluidics, for the integration of a multiridge silicon ATR wafer (Si-ATR) into microfluidic devices with virtually no limit on channel geometry. 30 Coupling this with an aperture-based scanning system for low-cost chemical mapping 31 opens the door to multi-point measurements for kinetic studies. Moreover, the approach allows the ATR element to be refocused as a sensor, boosting signal quality, rather than dedicating valuable surface area to world-to-chip connectors and mixers.…”