Microfluidic Platform with Multiplexed Electronic Detection for Spatial Tracking of Particles

Summary

We demonstrate a microfluidic platform with an integrated surface electrode network that combines resistive pulse sensing (RPS) with code division multiple access (CDMA), to multiplex detection and sizing of particles in multiple microfluidic channels.

Abstract

Microfluidic processing of biological samples typically involves differential manipulations of suspended particles under various force fields in order to spatially fractionate the sample based on a biological property of interest. For the resultant spatial distribution to be used as the assay readout, microfluidic devices are often subjected to microscopic analysis requiring complex instrumentation with higher cost and reduced portability. To address this limitation, we have developed an integrated electronic sensing technology for multiplexed detection of particles at different locations on a microfluidic chip. Our technology, called Microfluidic CODES, combines Resistive Pulse Sensing with Code Division Multiple Access to compress 2D spatial information into a 1D electrical signal. In this paper, we present a practical demonstration of the Microfluidic CODES technology to detect and size cultured cancer cells distributed over multiple microfluidic channels. As validated by the high-speed microscopy, our technology can accurately analyze dense cell populations all electronically without the need for an external instrument. As such, the Microfluidic CODES can potentially enable low-cost integrated lab-on-a-chip devices that are well suited for the point-of-care testing of biological samples.

Introduction

Accurate detection and analysis of biological particles such as cells, bacteria or viruses suspended in liquid is of great interest for a range of applications^1,2,3. Well-matched in size, microfluidic devices offer unique advantages for this purpose such as high-sensitivity, gentle sample manipulation and well-controlled microenvironment^4,5,6,7. In addition, microfluidic devices can be designed to employ a combination of fluid dynamics and force fie....

Protocol

1. Design of Coding Electrodes

Note: Figure 1a shows the 3-D structure of the micropatterned electrodes.

1. Design a set of four 7-bit Gold codes for encoding the microfluidic channels²³.
   1. Construct two linear feedback shift-registers (LFSRs), each representing a primitive polynomial.
   2. Use the LFSRs to generate a preferred pair of 7-bit m-sequences.
   3. Cyclically shift the preferred pair of m-sequences and add them in mod 2 to generate four distinct Gold codes.
2. Design the layout of the coding electrodes (Figure 1b....

Results

A Microfluidic CODES device consisting of four sensors distributed over four microfluidic channels is shown in Figure 1b. In this system, the cross-section of each microfluidic channel was designed to be close to the size of a cell so that (1) multiple cells cannot pass over the electrodes in parallel and (2) cells remain close to the electrodes increasing the sensitivity. Each sensor is designed to generate a unique 7-bit digital code. The device was then tested using a .......

Discussion

Multiple resistive pulse sensors have previously been incorporated into microfluidic chips^{28,29,30,31,32}. In these systems, resistive pulse sensors were either not multiplexed^28,29,30,31 or they required individual sensors to be driv.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
98% Sulfuric Acid	BDH Chemicals	BDH3074-3.8LP
30% Hydrogen Peroxide	BDH Chemicals	BDH7690-3
Trichlorosilane	Aldrich Chemistry	235725-100G
NR9-1500PY Negative Photoresist	Furuttex
Resist Developer RD6	Furuttex
Acetone	BDH Chemicals	BDH1101-4LP
SU-8 2015 Negative Photoresist	Microchem	SU8-2015
SU-8 Developer	Microchem	Y010200
Polydimethylsiloxane (PDMS)	Dow Corning	3097358-1004	Sylgard 184 Silicone Elastomer Kit
Isopropyl Alcohol	BDH Chemicals	BDH1133-4LP
RPMI 1640	Corning Cellgro	10-040-CV
Fetal Bovine Serum (FBS)	Seradigm	1500-050
Penicillin-Streptomycin	Amresco	K952-100ML
Phosphate-Buffered Saline (PBS)	Corning Cellgro	21-040-CM
PHD 22/2000 Syringe Pump	Harvard Apparatus	70-2001
HF2LI Lock-in Amplifier	Zurich Instrument
HF2TA Current Amplifier	Zurich Instrument
Eclipse Ti-U Microscope	Nikon Corporation
DS-Fi2 High-Definition Color Camera	Nikon Corporation
v7.3 High-speed Camera	Phantom
PCIe-6361 Data Acquisition Board	National Instruments	781050-01
BNC-2120 Shielded Connector Block	National Instruments	777960-01
PX-250 Plasma Treatment System	Nordson MARCH