A Microfluidic Device to Realize Electrochemically Controlled SERS Detection in HPLC.

Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for vibrational spectroscopy, but analyzing mixtures in solution remains challenging due to spectral overlap. Integrating SERS with a separation method, such as high-performance liquid chromatography (HPLC), offers a promising solution. However, online coupling has been limited by the compatibility issues between the SERS process and flow-based systems, which can result in either irreversible analyte adsorption on the SERS substrate or insufficient interaction.

High-spatial-resolution mass spectrometry imaging of biological tissues using a microfluidic probe.

Nanospray desorption electrospray ionization (nano-DESI) is a liquid extraction-based ambient ionization mass spectrometry imaging (MSI) technique that enables quantitative molecular mapping of biological samples in their native state with high spatial resolution. To facilitate the wider adoption of nano-DESI MSI by the scientific community, we have developed a robust and user-friendly microfluidic probe (MFP). The probe has been used to achieve high spatial resolution of 8-10 µm and up to 10-fold improvement in the experimental throughput, enabling imaging of large tissue sections with cellular resolution.

Modular Chip-Based nanoSFC-MS for Ultrafast Separations.

This study presents the development of a miniaturized device for supercritical fluid chromatography coupled with mass spectrometry. The chip-based, modular nanoSFC approach utilizes a particle-packed nanobore column embedded between two monolithically structured glass chips. A microtee in the pre-column section ensures picoliter sample loads onto the column, while a microcross chip structure fluidically controls the column backpressure.

Coupling of droplet-on-demand microfluidcs with ESI/MS to study single-cell catalysis.

Droplet microfluidics provides an efficient method for analysing reactions within the range of nanoliters to picoliters. However, the sensitive, label-free and versatile detection with ESI/MS poses some difficulties. One challenge is the difficult association of droplets with the MS signal in high-throughput droplet analysis.

A monolithic microfluidic probe for ambient mass spectrometry imaging of biological tissues.

Ambient mass spectrometry imaging (MSI) is a powerful technique that allows for the simultaneous mapping of hundreds of molecules in biological samples under atmospheric conditions, requiring minimal sample preparation. We have developed nanospray desorption electrospray ionization (nano-DESI), a liquid extraction-based ambient ionization technique, which has proven to be sensitive and capable of achieving high spatial resolution. We have previously described an integrated microfluidic probe, which simplifies the nano-DESI setup, but is quite difficult to fabricate.

Surface-Enhanced Raman Spectroscopic Probing in Digital Microfluidics through a Microspray Hole.

We report a novel approach for surface-enhanced Raman spectroscopy (SERS) detection in digital microfluidics (DMF). This is made possible by a microspray hole (μSH) that uses an electrostatic spray (ESTAS) for sample transfer from inside the chip to an external SERS substrate. To realize this, a new ESTAS-compatible stationary SERS substrate was developed and characterized for sensitive and reproducible SERS measurements.

Analysis of double-emulsion droplets with ESI mass spectrometry for monitoring lipase-catalyzed ester hydrolysis at nanoliter scale.

Microfluidic double-emulsion droplets allow the realization and study of biphasic chemical processes such as chemical reactions or extractions on the nanoliter scale. Double emulsions of the rare type (o/w/o) are used here to realize a lipase-catalyzed reaction in the non-polar phase. The surrounding aqueous phase induces the transfer of the hydrophilic product from the core oil phase, allowing on-the-fly MS analysis in single double droplets.

On-the-Fly Mass Spectrometry in Digital Microfluidics Enabled by a Microspray Hole: Toward Multidimensional Reaction Monitoring in Automated Synthesis Platforms.

We report an approach for the online coupling of digital microfluidics (DMF) with mass spectrometry (MS) using a chip-integrated microspray hole (μSH). The technique uses an adapted electrostatic spray ionization (ESTASI) method to spray a portion of a sample droplet through a microhole in the cover plate, allowing its chemical content to be analyzed by MS. This eliminates the need for chip disassembly or the introduction of capillary emitters for MS analysis, as required by state-of-the-art.

Quantification of Biocatalytic Transformations by Single Microbial Cells Enabled by Tailored Integration of Droplet Microfluidics and Mass Spectrometry.

Improving the performance of chemical transformations catalysed by microbial biocatalysts requires a deep understanding of cellular processes. While the cellular heterogeneity of cellular characteristics, such as the concentration of high abundant cellular content, is well studied, little is known about the reactivity of individual cells and its impact on the chemical identity, quantity, and purity of excreted products. Biocatalytic transformations were monitored chemically specific and quantifiable at the single-cell level by integrating droplet microfluidics, cell imaging, and mass spectrometry.

Integration of segmented microflow chemistry and online HPLC/MS analysis on a microfluidic chip system enabling enantioselective analyses at the nanoliter scale.

In this work, we introduce an approach to merge droplet microfluidics with an HPLC/MS functionality on a single chip to analyze the contents of individual droplets. This is achieved by a mechanical rotor-stator interface that precisely positions a microstructured PEEK rotor on a microfluidic chip in a pressure-tight manner. The developed full-body fused silica chip, manufactured by selective laser-induced etching, contained a segmented microflow compartment followed by a packed HPLC channel, which were interconnected by the microfluidic PEEK rotor on the fused silica lid with hair-thin through-holes.