On-chip mass spectrometric analysis in non-polar solvents by liquid beam infrared matrix-assisted laser dispersion/ionization

Interrogating Matrix Stiffness and Metabolomics in Pancreatic Ductal Carcinoma Using an Openable Microfluidic Tumor-on-a-Chip

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a dense fibrotic stroma that contributes to aggressive tumor biology and therapeutic resistance. Current in vitro PDAC models lack sufficient optical and physical access for fibrous network visualization, in situ mechanical stiffness measurement, and metabolomic profiling. Here, we describe an openable multilayer microfluidic PDAC-on-a-chip platform that consists of pancreatic tumor cells (PTCs) and pancreatic stellate cells (PSCs) embedded in a 3D collagen matrix that mimics the stroma. Our system allows fibrous network visualization via reflected light confocal (RLC) microscopy, in situ mechanical stiffness testing using atomic force microscopy (AFM), and compartmentalized hydrogel extraction for PSC metabolomic profiling via mass spectrometry (MS) analysis. In comparing cocultures of gel-embedded PSCs and PTCs with PSC-only monocultures, RLC microscopy identified a significant decrease in pore size and corresponding increase in fiber density. In situ AFM indicated significant increases in stiffness, and hallmark characteristics of PSC activation were observed using fluorescence microscopy. PSCs in coculture also demonstrated localized fiber alignment and densification as well as increased collagen production. Finally, an untargeted MS study putatively identified metabolic contributions consistent with in vivo PDAC studies. Taken together, this platform can potentially advance our understanding of tumor-stromal interactions toward the discovery of novel therapies.

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 (o₁/w/o₂) 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. A microfluidic two-step emulsification process is developed to generate the (o₁/w/o₂) double-emulsion droplets. In this first example of microfluidic double-emulsion MS coupling, we show in proof-of-concept experiments that the chemical composition of the water layer can be read online using ESI–MS. Double-emulsion droplets were further employed as two-phase micro-reactors for the hydrolysis of the lipophilic ester p-nitrophenyl palmitate catalyzed by the Candida antarctica lipase B (CalB). Finally, the formation of the hydrophilic reaction product p-nitrophenol within the double-emulsion droplet micro-reactors is verified by subjecting the double-emulsion droplets to online ESI–MS analysis.

Identification of a Two‐Coordinate Iron(I)–Oxalate Complex

Exotic oxidation states of the first‐row transition metals have recently attracted much interest. In order to investigate the oxidation states of a series of iron–oxalate complexes, an aqueous solution of iron(III) nitrate and oxalic acid was studied by infrared free liquid matrix‐assisted laser desorption/ionization as well as ionspray mass spectrometry. Here, we show that iron is not only detected in its common oxidation states +II and +III, but also in its unusual oxidation state +I, detectable in both positive‐ion and in negative‐ion modes, respectively. Vibrational spectra of the gas phase anionic iron oxalate complexes [Fe^III(C₂O₄)₂]⁻, [Fe^II(C₂O₄)CO₂]⁻, and [Fe^I(C₂O₄)]⁻ were measured by means of infrared photodissociation spectroscopy and their structures were assigned by comparison to anharmonic vibrational spectra based on second‐order perturbation theory.