A microfluidic chip capable of switching W/O droplets to vertical laminar flow for electrochemical detection of droplet contents

Xingyu Lin; Xianqiao Hu; Zeqing Bai; Qiaohong He; Hengwu Chen; Yangzhi Yan; Zhihua Ding

doi:10.1016/j.aca.2014.04.023

A microfluidic chip capable of switching W/O droplets to vertical laminar flow for electrochemical detection of droplet contents

Anal Chim Acta. 2014 May 30:828:70-9. doi: 10.1016/j.aca.2014.04.023. Epub 2014 Apr 15.

Authors

Xingyu Lin¹, Xianqiao Hu¹, Zeqing Bai¹, Qiaohong He¹, Hengwu Chen², Yangzhi Yan³, Zhihua Ding³

Affiliations

¹ The Institute of Microanalytical Systems, Chemistry Department, Zhejiang University, Zijin'gang Campus, Hangzhou 310058, China.
² The Institute of Microanalytical Systems, Chemistry Department, Zhejiang University, Zijin'gang Campus, Hangzhou 310058, China. Electronic address: hwchen@zju.edu.cn.
³ State Key Lab of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027, China.

PMID: 24845817
DOI: 10.1016/j.aca.2014.04.023

Abstract

Analysis of droplet contents is a key function involved in droplet-based microfluidic systems. Direct electrochemical detection of droplet contents suffers problems such as relatively poor repeatability, interference of capacitive current and relatively poor detectability. This paper presents a novel hybrid polydimethylsiloxane-glass chip for highly sensitive and reproducible amperometric detection of droplet contents. By wettability-patterning of the channel surface of the hybrid chip, water in oil droplets generated in the upstream part of the central channel can be switched to a two-phase vertical laminar flow (i.e., a continuous oil stream flowing atop a continuous aqueous stream) in the downstream part of the channel. The vertical laminar flow keeps the analyte in the underneath-flowing aqueous stream in direct contact with the sensing electrodes located on the bottom surface of the channel. Therefore, steady-state current signals with high sensitivity (1.2AM(-1)cm(-2) for H2O2), low limit of detection (0.12μM, S/N=2), and good reproducibility (RSD 1.1% at 0.3mM H2O2) were obtained. The methods for patterning of the inner channel surface are presented, and the behaviors of the microchip in flow profile switching and amperometric detection are discussed. The application of the developed microchip to enzyme kinetics study is also demonstrated.

Keywords: Droplets; Electrochemical detection; Enzyme kinetics; Glucose; Microfluidic chip; Vertical laminar flow.