3 The Ideal Microfluidic System for POC Sensor Design
The ideal prototyping material is a tunable material that can provide structural
stability and external interface, such as manifold integration. It has to be chemically
inert, compatible with chemical and biological samples without absorbing them,
and allows stable and patternable surface modifications to be employed to control
the wetting and biological functionalization properties of the device. Finally, the
material must allow for biocompatible bonding to a wide range of substrates. These
properties are concretized in the list below:
1.Tunable mechanical properties: The mechanical properties of an ideal
prototyping material are somewhat contradictory. On one hand, it must mirror
the stiffness of commercial thermoplastics to produce geometrically stable
microfluidic devices with robust external chip-to-world interfaces. On the
other hand, it must be soft enough to allow for the pneumatically actuated valves
and pumps to operate, commonly used in PDMS.
2.Chemical inertness and low interaction with the sample: To be able to analyze
low concentration samples, the ideal material must not absorb small molecules,
such as proteins or DNA from the sample, react with the sample, or leach
uncured components that may interact with the sample or the sensor.
3.Solvent resistance: Critical to many chemical reactions and separation processes
is the use of harsh solvents. The ideal material must not dissolve or swell in the
presence of these solvents.
4.Direct,patternable,and stable surface modifications: The spatial control of
surface properties is instrumental for controlling liquids and immobilizing
biological receptors on the chip. The ideal material allows for spatial control
of surface modifications, preferably without the need to first activate the polymer
surface by plasma or solvents.
5.Fast, scalable, and utilizing inexpensive materials and processes: The
prototyping method has a fast-curing micro-structuring step and uncomplicated
back-end processes, which enables rapid device development. To be useful in
academic research, the ideal prototyping method relies on inexpensive materials
and does not require access to expensive/technically-complicated facilities. To
allow a fast transition to commercial production, the method is possible to scale
up to medium or large-scale production.
6.Three-dimensional microfluidics: Advanced lab-on-chips must be able to handle
multiple liquids, something that often requires 3D microfluidic channels with
under- and overpasses. The ideal prototyping method therefore allows for
efficient fabrication of multiple vertical interconnections between channel
layers.
7.Biocompatible bonding: Essential for labs-on-chip is a simple and biocompatible
bonding method to surfaces that are functionalized with proteins and DNA. The
ideal prototyping method must form a strong bond to a wide number of materials
under biocompatible conditions.
6 Materials and Surfaces in Microfluidic Biosensors 161