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Research Papers: Multiphase Flows

# A Digital Micro Magnetofluidic Platform For Lab-on-a-Chip Applications

[+] Author and Article Information
Wei Hang Koh

School of Mechanical and Aerospace Engineering,
Nanyang Technological University,
639798, Singapore
e-mail: KOHW0041@ntu.edu.sg

Khoi Seng Lok

National Institute of Education,
Nanyang Technological University,
639798, Singapore
e-mail: khoiseng@gmail.com

Nam-Trung Nguyen

Professor
Fellow ASME
Queensland Micro- andNanotechnology Centre,
Griffith University,
Brisbane, 4111, Australia
e-mail: nam-trung.nguyen@griffith.edu.au

1Corresponding author.

Manuscript received April 7, 2012; final manuscript received October 8, 2012; published online March 19, 2013. Assoc. Editor: Kendra Sharp.

J. Fluids Eng 135(2), 021302 (Mar 19, 2013) (6 pages) Paper No: FE-12-1175; doi: 10.1115/1.4023443 History: Received April 07, 2012; Revised October 08, 2012

## Abstract

This paper reports the design and investigation of a digital micro magnetofluidic platform for lab-on-a-chip applications. The platform allows a ferrofluid droplet to be driven along a preprogrammed path. The platform consists of a programmable x-y-positioning stage, a permanent magnet and a glass plate coated with a thin layer of Teflon. First, the actuation of a stand-alone water-based ferrofluid droplet was investigated. Circular, rectangular, triangular and number-eight-shape trajectories were tested and analyzed. The speed of the droplet is evaluated from the position data of the black ferrofluid using a customized MATLAB program. The results show that better positioning accuracy and steady movement can be achieved with smooth trajectories. Next, the ferrofluid droplet as the driving engine for a cargo of other diamagnetic liquid droplets is demonstrated. The characteristics of different cargo volumes are investigated. Due to the liquid/liquid cohesion, a large cargo of five times the volume of a 3-$μL$ ferrofluid droplet can be transported. If the cargo is larger than the driving ferrofluid droplet, the liquid system forms a long trail that faithfully follows the preprogrammed path. Various mixing experiments were carried out. The effectiveness of mixing in this system is demonstrated with a titration test as well as a chemiluminescence assay. The platform shows a robust, simple and flexible concept for implementing a complex analysis protocol with multiple reaction steps.

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## Figures

Fig. 1

The experimental setup of the digital magnetofluidic platform

Fig. 2

Preprogrammed paths and actual trajectories of a sessile ferrofluid droplet of 3-μL volume: (a) circular; (b) rectangular; (c) triangular; (d) number-8 shape

Fig. 3

Corresponding position components and speed of the droplet as functions of time: (a) circular; (b) rectangular; (c) triangular; (d) number-8 shape

Fig. 4

Time history of the speed of a 3-μL ferrofluid working as the engine for different cargo volumes (circular path with 10-mm diameter): (a) 3 μL; (b) 6 μL; (c) 9 μL; (d) 12 μL; (e) 15 μL; (f) 18 μL

Fig. 5

Mixing of a 9-μL water droplet with 3-μL ink droplet driven by a 3-μL ferrofluid droplet (circular path with 10-mm diameter): (a) snapshots of the mixing process; (b) time history of the tracked speed of the ferrofluid; (c) mixing index of the rear area of the merged droplet

Fig. 6

Titration experiment on the digital magnetofluidic platform driven by a 10-μL ferrofluid droplet (circular path with 10-mm diameter): (a) 10 μL 0.1 M NaOH droplet and 10 μL PR droplet; (b) 10 μL 0.1 M HCl droplet and 10 μL PR droplet; (c) 10 μL 0.1 M NaOH droplet, 10 μL 0.1 M HCl droplet and 10 μL PR droplet

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