Supporting Information

PDMS-Film Coatedon PCB for AC Impedance Sensing of Biological Cells

Jinhong Guo1, Chang Ming Li2and Yuejun Kang*1

1School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459

2Institute for Clean Energy &Advanced Materials, Southwest University, Beibei, Chongqing 400715, P. R. China

Model:

Figure S1. (a) The schematic view of the 3-D model; (b) The cross-sectional view of the device geometry for the simulation

As Fig.S1 shows, the model is composed of four components. The dimension of microfluidic channel is 300 μm in width and 60μm in height. The aperture dimension is 202020 μm3. The diameter of the polystyrene bead is 15 μm. The simulation parameters are summarized in TableS1.

Table S1: major parameters used in the simulation:[1,2]

Dielectric Constant / Electrical Conductivity
PDMS / 2.55 / 1x10-12 s/m
PBS solution / 80 / 1.6 s/m
PCB / 4 / 1x10-12 s/m
Polystyrene Bead / 2.5 / 1x10-14 s/m

Numerical Simulation:

The simulation and optimization is performed by a commercial Finite Element Method package COMSOL Multiphysics 4.3b (COMSOL, CA, USA). The COMSOL AC/DC module can compute the electrical field by solving the following equation:

(S1)

where Vis the electrical potential, E is the electrical field strength. The electric current density can be written as:

(S2)

Where σ is the electrical conductivity,J is the current density, D is the electrical displacement field, ω is the angular frequency. Jeis the excitation current density.

The boundary conditionsat the electrodes are given by

Excitation electrode: V=1 V (S3)

Grounded electrode: V=0 V (S4)

The particle surface and the outer wall are assumed non-conducting:

(S5)

An adaptive mesh set was applied to the model. In the sensing aperture region, ultra-fine mesh was used with maximum mesh size of 0.5μm, and minimum mesh size of0.1 μm.For the rest of the computation domain, fine mesh was employed with maximum mesh size of 10 μm, and minimum mesh size of 1 μm.

The total electric current is given by

(S6)

The impedance is expressed as

(S7)

The impedance modulation is then calculated as

(S8)

The AC voltage excitation has magnitude 1V and frequency sweep range is from 200KHz to 1MHz; PDMS film thickness changes from 10 μm to 100 μm.

References:

[1]J. Mark, Polymer Data Handbook. Oxford University Press, 1999.

[2]S. Emaminejad, M. Javanmard, R. W. Dutton, R. W. Davis, Microfluidic diagnostic tool for the developing world: contactless impedance flow cytometry, Lab Chip, 12, 4499, 2012.

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