(131c) Fabric Microfluidics for Low-Cost Protein Separations

Introduction: Point-of-care diagnostic tests (POCTs) are
necessary to screen for disease and monitor treatment at the site of patient
care. By this definition, a POC device must be standalone, consume minimum
laboratory resources and also be inexpensive [1]. For instance, the typical
paper-based POCT for pregnancy consists of a designated path for a small volume
of urine to flow along, complex with assay reagents and generate a result in
terms of a colored signal that can be interpreted by the lay user. However, the
manufacturing process involves multiple coating, drying and alignment steps
that can limit scalability and contribute to cost. In prior work, we
demonstrated a seamless, woven fabric-based microfluidics platform to address
this issue [2]. Weaving allows us to combine reagent patterning and device
assembly into a quasi-single step. Two main avenues will be discussed in the
context of fabric POCTs: a. Passive control of liquid flow in fabric b. Feasibility
of fabric as a platform for the electrophoretic separation of proteins from
biological samples.

Materials and Methods: Fabric samples were weaved on a handloom at
Achira Labs, Bangalore, India. The flow properties that are required to
maneuver medical samples such as serum or urine along a reagent-loaded pathway
are provided by controlled structural in-homogeneities in the fabric. To
manufacture the electrophoretic chip, Platinum wire electrodes were weaved into
a polyester flow path with absorbent cotton ends as buffer-reservoirs (Figure
1).  An Ohm's Law Plot was performed to
ensure that the system could withstand a minimum of 250V DC. In order to
discern diffusion effects from electrophoresis, dyes that can be tracked
visually were run on fabric with and without an applied voltage. After
confirming dye migration in an electric field, a dye-conjugated protein ladder
(ColorBurst^TM, Sigma) was resolved in
fabric at 250V and compared to a standard PAGE run.

Results and Discussion: Figure 2 shows a saw-toothed velocity
profile generated in a fabric where hydraulic resistance decreases in three
seamless steps.  This illustrates that
sample flow can be slowed in regions where time-sensitive reactions must take
place.  The colored
protein ladder was resolved by electrophoresis. Future work will attempt to
resolve fluorescent proteins for use with the more accurate and quantitative
detection of fluorescence.

Conclusions: From prior work ¹ and from the
electrophoretic separation achieved, fabric is a versatile platform
for a variety of analytical procedures. Added to the high manufacturing
throughput per-day on a standard industrial loom, fabric POCTs can be
disseminated at low costs to resource deprived medical laboratories.

References:

1. P. Yager, G. J. Domingo, J. Gerdes
(2008). Annu. Rev.
Biomed. Eng. 10: 107-144

2. P.Bhandari, T.Narahari, D.Dendukuri
(2011). Lab Chip 11(15):
2493-2499.