Microfluidic encapsulation of soluble reagents with large-scale concentration gradients in a sequence of droplets for comparative analysis

Abstract

Concentration gradient is important for comparative analysis in the fields of biomedicine and chemistry, especially with the in-depth research of material synthesis, enzyme kinetic analysis and cell biology. In this work, we reported a simple coaxial injection microfluidic device for encapsulation of soluble reagents with large-scale concentration gradients in a sequence of nanoliter-scale water-in-oil(W/O) droplets for comparative analysis. The concentration gradients can be adjusted straightforwardly by changing the flow rates of phases in two coaxial channels. The concentration gradients of the components can reach the order of 105. As proofs of this concept, acid-base reaction, L-Ascorbic acid redox reaction and synthesis of metal organic frameworks(MOFs) are conducted using this concentration gradient generator. Nanoliter-grade reagents preparation, reactions and analyses with higher concentration gradients and less sample consumption can be achieved without stopping experiments and changing solutions by using this simple microfluidics concentration gradient generator.