Raman spectroscopic monitoring of droplet polymerization in a microfluidic device

Abstract

Microfluidic methodologies are becoming increasingly important for rapid formulation and screening of materials, and development of analytical tools for multiple sample screening is a critical step in achieving a combinatorial 'lab on a chip' approach. This work demonstrates the application of Raman spectroscopy for analysis of monomer composition and degree of conversion of methacrylate-based droplets in a microfluidic device. Droplet formation was conducted by flow focusing on the devices, and a gradient of component composition was created by varying the flow rates of the droplet-phase fluids into the microchannels. Raman data were collected using a fiber optic probe from a stationary array of the droplets/particles on the device, followed by partial least squares (PLS) calibration of the first derivative (1600 cm 21 to 1550 cm 21 ) allowing successful measurement of monomer composition with a standard error of calibration (SEC) of ¡1.95% by volume. Following photopolymerization, the percentage of double bond conversion of the individual particles was calculated from the depletion of the normalized intensity of the CLC stretching vibration at 1605 cm 21 . Raman data allowed accurate measurement of the decrease in double bond conversion as a function of increasing crosslinker concentration. The results from the research demonstrate that Raman spectroscopy is an effective, on-chip analytical tool for screening polymeric materials on the micrometre scale.

Recent advances in surface‐enhanced Raman scattering detection technology for microfluidic chips

“…In this work, the CRM was successfully utilized for rapid, on-line analysis and reaction condition screening of the catalytic oxidation of IPA. Barnes et al [80] used fiber optic Raman spectroscopy for the quantitative analysis of monomer composition and degree of conversion of methacrylate-based droplets in a microfluidic device. Raman data allowed accurate measurement of the decrease in the C=C bond conversion as a function of increasing cross-linker concentration.…”

Mikrotröpfchen in Mikrofluidiksystemen: eine Technik für Entdeckungen in der Chemie und Biologie

“…[9,120] Ein parallelisiertes Mikrotröpf-chenverfahren [121] [127] Die räumlich auflösende RamanSpektroskopie ermöglicht es auch, das Mischen von zwei Lösungen im Inneren von Tröpfchen zu verfolgen. [127,128] Sarrazin et al [128] [129] Bei der oberflächenverstärkten Raman-Spektroskopie (surface-enhanced Raman spectroscopy, SERS) erhöhen Kolloide mit Oberflächenplasmonen das Raman-Signal. Die Zugabe solcher Kolloide kann die Messgenauigkeit deutlich steigern, in herkömmlichen Küvetten und auch in Flusszellen kann es aber zur Abscheidung der Kolloide und der Analyte an den Innenwänden, und folglich zu Artefakten, kommen.…”

Basic Technologies for Droplet Microfluidics

“…Various methods have been employed for the detection and characterization of droplet contents. Since most microfluidic devices are fabricated using transparent materials such as PDMS and glass, optical systems, including fluorescence microscopy [53,68,69] and Raman spectroscopy [70], can be directly used to detect the reaction products inside droplets. Up until now, fluorescence measurement has been the most successful and prevalent method to detect the droplet contents.…”

“…Later on theoretical interests arose on the characterization and exploration of complex dynamic phenomena involved in droplet generation and trafficking within microfluidic channel networks [3,4]. Meanwhile, a wealth of technologies for improved droplet generation, intra-droplet content manipulation, and methods for controlled trafficking, all enabled a wide range of appealing applications [5][6][7][8] from chemical kinetics [9] and protein 70 S. Zeng et al crystallization [10,11] to material synthesis [12,13], single cell analysis [14,15], polymerase chain reaction (PCR) [16], protein engineering, and high throughput screening technologies [17]. This review will discuss the recent advances in technologies that enable droplets as microreactors with complete functions and the applications of droplets in chemistry and biology.…”