A mid-infrared lab-on-a-chip for dynamic reaction monitoring

Abstract

Mid-infrared spectroscopy is a sensitive and selective technique for probing molecules in the gas or liquid phase. Investigating chemical reactions in bio-medical applications such as drug production is recently gaining particular interest. However, monitoring dynamic processes in liquids is commonly limited to bulky systems and thus requires time-consuming offline analytics. In this work, we show a next-generation, fully-integrated and robust chip-scale sensor for online measurements of molecule dynamics in a liquid solution. Our fingertip-sized device utilizes quantum cascade technology, combining the emitter, sensing section and detector on a single chip. This enables real-time measurements probing only microliter amounts of analyte in an in situ configuration. We demonstrate time-resolved device operation by analyzing temperature-induced conformational changes of the model protein bovine serum albumin in heavy water. Quantitative measurements reveal excellent performance characteristics in terms of sensor linearity, wide coverage of concentrations, extending from 0.075 mg ml−1 to 92 mg ml−1 and a 55-times higher absorbance than state-of-the-art bulky and offline reference systems.

Beyond Karl Fischer titration: a monolithic quantum cascade sensor for monitoring residual water concentration in solvents

“…This gap hosts a tapered SiN/Au dielectric-loaded surface plasmon polariton (DLSPP) waveguide for mode confinement with simultaneous sensing capabilities. 48 To narrow down the spectral emission for addressing individual features of the broad liquid absorption bands, a weakly-coupled DFB grating is implemented into the QCLs. The spectral emission characteristics can be found in the ESI † material Fig.…”

“…This enables real-time monitoring of dynamic processes on millisecond timescales. 48 In this work we present the robustness and high performance of such a monolithic approach through realizing two compact liquid sensor designs. For this we either implement the QCLD chip (see Fig.…”

“…Based on this concept, (low) ppm values have already been realized when analyzing water 46 or proteins. 48 Due to the monolithic nature of such sensors, upscaling has minimal impact on the fabrication time or complexity. Another advantage is the much shorter data acquisition time of single wavelength measurements (<1 ms), compared to recording broadband spectra with an FTIR spectrometer (>1 s).…”

“…40,41 Further important milestones towards integrated sensors were the (photovoltaic) detector operation of unbiased QCL structures [42][43][44] and the combination of both devices into one single optimized QC active region (AR) for same-wavelength emission and detection (QCLD). 45 For improved sensor operation surface-sensitive mid-IR plasmonic waveguides can additionally be employed, 46,47 paving the way for miniaturized, on-chip devices, 46,48 which suppress beam distortions from standard ridge geometries. 49 The LOD can be adjusted to the investigated analyte by appropriate design of the waveguide length between the laser and detector.…”

Midinfrared Spectroscopic Analysis of Aqueous Mixtures Using Artificial-Intelligence-Enhanced Metamaterial Waveguide Sensing Platform

“…Although the MIR waveguide sensor can leverage the specific fingerprints of diverse molecules for analyte recognition, the quantitative analysis of complex liquid mixture components in the MIR remains challenging, as the superposition of absorption from multiple substances may affect the absorbance at the absorption peak of interest (Figure b), not to mention the strong water absorption background. Even though a MIR lab-on-a-chip is demonstrated for monitoring bovine serum albumin in heavy water (D 2 O) instead of in water (H 2 O) to evade the intrinsic strong water absorption, the water environment is still the most common and crucial sensing background that cannot be avoided and needs to be investigated. In recent years, metamaterials as a useful tool in designing various photonic devices with improved efficiency, including the tunable actuator, , metalens, and meta-waveguides, have also been applied to the waveguide gas sensor , due to the flexibility in controlling mode profile and effective RI for tuning sensitivity .…”