improved sensitivity in comparison to conventional methods. Analysis of complex
biological samples such as blood is possible with microfluidics, and is best handled
by pressure-driven flow due to the more stringent requirement of electric force-
based and capillary-driven systems on the composition and viscosity of the sample.
On the other hand, more complex capillary circuits with novel elements have been
demonstrated, allowing for precisely controlled sequence of fluid operation
performed in full automation with minimal requirement for instrumentation and
power. Bead-based heterogeneous assays have experienced significant progress,
particularly in the development of novel encoded beads for multiplexing.
Whereas microfluidic immunoassays progress significantly in the last decades,
the potential for more advancement remains very high. In particular, multiple fluid
handling modalities would be applied in synergy and integrated within a single
platform, hence more complex fluid operation can be carried out with enhanced
precision and reliability. Integration of novel transducers and detection methods
with microfluidic would further improve the specificity and sensitivity of the assay,
and facilitate multiplexing.
There are still challenges to be overcome. New strategies for reagents
pre-loading and their long-term storage on-chip need to be developed. The issue
of reagent stability is particularly important for immunoassays as most biological
reagents, such as antibodies, are perishable and require specific storage environ-
ments. Whereas polymeric substrates such as PDMS are the preferred materials for
prototype fabrication at the laboratory level, materials with similar properties but
having capabilities for mass production such as injection molding are in great
demand for practical applications and commercialization. The ultimate goal of
microfluidic system development is to provide fully integrated, packaged, robust,
user-friendly, low-cost and disposable devices. Given the active research and
continual progress in the field, and the increasing number of innovations, it is
envisioned that this goal can be achieved in the near future.
References
- Rossier JS, Girault HH (2001) Enzyme linked immunosorbent assay on a microchip with
electrochemical detection. Lab Chip 1:153–157 - Sia SK, Whitesides GM (2003) Microfluidic devices fabricated in poly(dimethylsiloxane) for
biological studies. Electrophoresis 24:3563–3576 - Hatch A, Kamholz AE, Hawkins KR, Munson MS, Schilling EA, Weigl BH, Yager P (2001)
A rapid diffusion immunoassay in a T-sensor. Nat Biotechnol 19:461–465 - Lim TK, Ohta H, Matsunaga T (2003) Microfabricated on-chip-type electrochemical flow
immunoassay system for the detection of histamine released in whole blood samples. Anal
Chem 75:3316–3321 - Reichmuth DS, Wang SK, Barrett LM, Throckmorton DJ, Einfeld W, Singh AK (2008) Rapid
microchip-based electrophoretic immunoassays for the detection of swine influenza virus.
Lab Chip 8:1319–1324 - Meagher RJ, Hatch AV, Renzi RF, Singh AK (2008) An integrated microfluidic platform for
sensitive and rapid detection of biological toxins. Lab Chip 8:2046–2053
240 A. Ng