Coupling Droplet Microfluidics with Ion Mobility Spectrometry for Monitoring Chemical Conversions at Nanoliter Scale

Abstract

We introduce the coupling of droplet microfluidics and ion mobility spectrometry (IMS) to address the challenges of label-free and chemical-specific detection of compounds in individual droplets. In analogy to the established use of mass spectrometry, droplet−IMS coupling can be also achieved via electrospray ionization but with significantly less instrumental effort. Because IMS instruments do not require high-vacuum systems, they are very compact, cost-effective, and robust, making them an ideal candidate as a chemical-specific end-of-line detector for segmented flow experiments. Herein, we demonstrate the successful coupling of droplet microfluidics with a custom-built high-resolution drift tube IMS system for monitoring chemical reactions in nL-sized droplets in an oil phase. The analytes contained in each droplet were assigned according to their characteristic ion mobility with limit of detections down to 200 nM to 1 μM and droplet frequencies ranging from 0.1 to 0.5 Hz. Using a custom sheath flow electrospray interface, we have further achieved the chemical-specific monitoring of a biochemical transformation catalyzed by a few hundred yeast cells, at single droplet level.

Ion Mobility-Mass Spectrometry Coupled to Droplet Microfluidics for Rapid Protein Structure Analysis and Drug Discovery

“…Sample droplets can range from femtoliter to nanoliter in volume, where each droplet can be manipulated and treated like an individual microreactor. Droplet-MS provides a robust way to rapidly introduce hundreds or even thousands of individual picoliter to nanoliter samples into MS. − Droplet microfluidics have also been coupled to IMS and IM-MS. , While this platform has been primarily used for small molecule analysis, droplet-MS can be used for intact protein analysis. , Recently sample introduction rates of 33 Hz have been achieved for protein analysis by droplet-MS . This seminal work droplet-MS of proteins has been focused on protein detection without more in-depth analysis.…”

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

“…[30] To achieve this goal, future studies will explore the in situ generation of diastereomeric adducts [31] as well as the use of pseudoenatiomeric compounds [32] to enable enantioselective mass spectrometric determination in single droplets. Given the recent advances in the analysis of isomers using ion mobility spectrometry (IMS), [33] the combination of the technology presented here with droplet IMS [34] is another avenue now paved toward enantioselective catalytic transformation studies at the single-species level. Our results now allow detailed studies of the minimal catalytic unit, an isolated single cell, to better understand reaction heterogeneity, reaction mechanisms, metabolism, and biochemical network functions determining the selectivities and efficiencies of whole-cell biocatalysts.…”

Quantifizierung biokatalytischer Umwandlungen durch einzelne mikrobielle Zellen mittels maßgeschneiderter Integration von Tröpfchenmikrofluidik und Massenspektrometrie

“…[30] Um dieses Ziel zu erreichen, werden künftige Studien die in-situ-Erzeugung von diastereomeren Addukten [31] sowie die Verwendung von pseudoenatiomeren Verbindungen [32] untersuchen, um eine enantioselektive massenspektrometrische Bestimmung in einzelnen Tröpfchen zu ermöglichen. Angesichts der jüngsten Fortschritte bei der Analyse von Isomeren mittels Ionenmobilitätsspektrometrie (IMS) [33] ist die Kombination der hier vorgestellten Technologie mit der Tröpfchen-IMS [34] ein weiterer vielversprechender Weg zu enantioselektiven katalytischen Transformationsstudien auf der Ebene einzelner Spezies. Unsere Ergebnisse ermöglichen nun detaillierte Studien der minimalen katalytischen Einheit, einer isolierten Einzelzelle, um die Reaktionsheterogenität, die Reaktionsmechanismen, den Stoffwechsel und die biochemischen Netzwerkfunktionen, welche die Selektivitäten und Effizienzen von Ganzzell-Biokatalysatoren bestimmen, besser zu verstehen.…”