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

A Microfluidic Design for Quantitative Measurements of Shear Stress-Dependent Adhesion and Motion of Dictyostelium discoideum Cells

Shear stress plays a crucial role in modulating cell adhesion and signaling. We present a microfluidic shear stress generator used to investigate the adhesion dynamics of Dictyostelium discoideum, an amoeba cell model organism with well-characterized adhesion properties. We applied shear stress and tracked cell adhesion, motility, and detachment using time-lapse videomicroscopy. In the precise shear conditions generated on-chip, our results show cell migration patterns are influenced by shear stress, with cells displaying an adaptive response to shear forces as they alter their adhesion and motility behavior. Additionally, we observed that DH1-10 wild-type D. discoideum cells exhibit stronger adhesion and resistance to shear-induced detachment compared to phg2 adhesion-defective mutant cells. We also highlight the influence of cell density on detachment kinetics.

Laminar Flow Infrared Spectroelectrochemistry

In this work, we advance lab-on-chip electrochemistry and spectroscopy by combining these capabilities onto a single platform, thereby achieving mid-infrared spectroelectrochemistry (SEC) for the first time. The key feature of this technique is the use of deterministic laminar flow patterns to precisely transport a reacted solution from upstream electrodes to a downstream spectral detection region. Laminar flow spectroelectrochemistry (LF-SEC) is therefore a completely new approach, which derives its distinction and advantage over traditional SEC by physically separating electrode and attenuated total reflection (ATR) elements. As such, these functional elements retain optimal properties, such as inert, highly conductive electrodes and a bare ATR element for sensitive Fourier transform infrared (FTIR) spectroscopy. By combining ATR-FTIR with a scanning aperture system, LF-SEC provides the additional advantage of spectroscopically monitoring reactions at individual electrodes. The LF-SEC system design is first optimized through a series of targeted experiments using a ferricyanide/ferrocyanide redox pair to validate electrochemical functionality, undertake spectroscopic calibration, optimize experimental parameters, and finally validate the quantitative relationship between FTIR results and the reaction rate under galvanostatic control. After optimization, we demonstrate the technique by monitoring the oxidation of the therapeutic compound ascorbic acid (vitamin C) in the presence of biomolecular interference from a molecule with an overlapping oxidation potential. We find that molecular availability causes the reaction to switch between reaction pathways, which we could finely monitor using LF-SEC. This work opens the door to future developments that take advantage of the microfluidic reactor setup, with benefits ranging from portability to high-throughput studies under precise reaction conditions.

Understanding Advanced Attenuated Total Reflection Correction: The Low Absorbance Assumption

We present an attenuated total reflection (ATR) correction scheme capable of rectifying ATR spectra while considering the polarization state for arbitrary angles of incidence, provided that this angle exceeds the critical angle for the entire ATR spectrum. Due to its reliance on the weak absorption approximation, it cannot achieve perfect correction of the ATR spectra. However, comprehending its functionality may offer valuable insights into the concept behind the weak absorption approximation. Depending on the specific polarization state of an instrument accessory combination, this correction scheme may outperform the proprietary advanced ATR correction authored by ThermoFisher while being as user-friendly, but in contrast to the latter completely transparent with regard to its functionality.

On-Chip Photonic Detection Techniques for Non-Invasive In Situ Characterizations at the Microfluidic Scale

Microfluidics has emerged as a robust technology for diverse applications, ranging from bio-medical diagnostics to chemical analysis. Among the different characterization techniques that can be used to analyze samples at the microfluidic scale, the coupling of photonic detection techniques and on-chip configurations is particularly advantageous due to its non-invasive nature, which permits sensitive, real-time, high throughput, and rapid analyses, taking advantage of the microfluidic special environments and reduced sample volumes. Putting a special emphasis on integrated detection schemes, this review article explores the most relevant advances in the on-chip implementation of UV-vis, near-infrared, terahertz, and X-ray-based techniques for different characterizations, ranging from punctual spectroscopic or scattering-based measurements to different types of mapping/imaging. The principles of the techniques and their interest are discussed through their application to different systems.

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

Microfluidics has emerged as a powerful technology with diverse applications in microbiology, medicine, chemistry, and physics. While its potential for controlling and studying chemical reactions is well recognized, the extraction and analysis of useful chemical information generated within microfluidic devices remain challenging. This is mainly due to the limited tools available for in situ measurements of chemical reactions. In this study, we present a proof-of-concept spectIR-fluidic reactor design that combines microfluidics with Fourier transform infrared (FTIR) spectroscopy for in situ kinetic studies of fast reactions. By integrating a multi-ridge silicon attenuated total reflection (ATR) wafer into the microfluidic device, we enable multi-point measurements for precise reaction time monitoring. As such, this work establishes a validated foundation for studying fast chemical reactions using on-chip ATR-FTIR spectroscopy in a microfluidic reactor environment, which enables simultaneous monitoring of reagents, intermediates, and products using a phosphate proton transfer reaction. The spectIR-fluidic reactor platform offers customizable designs, allowing for the investigation of reactions with various time scales, and has the potential to significantly advance studies exploring reaction mechanisms and optimization.