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Optical calorimetry in microfluidic droplets

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Abstract

A novel microfluidic calorimeter that measures the enthalpy change of reactions occurring in 100 μm diameter aqueous droplets in fluoropolymer oil has been developed. The aqueous reactants flow into a microfluidic droplet generation chip in separate fluidic channels, limiting contact between the streams until immediately before they form the droplet. The diffusion-driven mixing of reactants is predominantly restricted to within the droplet. The temperature change in droplets due to the heat of reaction is measured optically by recording the reflectance spectra of encapsulated thermochromic liquid crystals (TLC) that are added to one of the reactant streams. As the droplets travel through the channel, the spectral characteristics of the TLC represent the internal temperature, allowing optical measurement with a precision of ≈6 mK. The microfluidic chip and all fluids are temperature controlled, and the reaction heat within droplets raises their temperature until thermal diffusion dissipates the heat into the surrounding oil and chip walls. Position resolved optical temperature measurement of the droplets allows calculation of the heat of reaction by analyzing the droplet temperature profile over time. Channel dimensions, droplet generation rate, droplet size, reactant stream flows and oil flow rate are carefully balanced to provide rapid diffusional mixing of reactants compared to thermal diffusion, while avoiding thermal “quenching” due to contact between the droplets and the chip walls. Compared to conventional microcalorimetry, which has been used in this work to provide reference measurements, this new continuous flow droplet calorimeter has the potential to perform titrations ≈1000-fold faster while using ≈400-fold less reactants per titration.

Graphical abstract: Optical calorimetry in microfluidic droplets

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Publication details

The article was received on 27 Nov 2017, accepted on 04 May 2018 and first published on 04 May 2018


Article type: Paper
DOI: 10.1039/C7LC01266G
Citation: Lab Chip, 2018, Advance Article
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    Optical calorimetry in microfluidic droplets

    J. Chamoun, A. Pattekar, F. Afshinmanesh, J. Martini and M. I. Recht, Lab Chip, 2018, Advance Article , DOI: 10.1039/C7LC01266G

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