Microfluidic Enabling Platform for Cell-based Assays

Allergen screening bioassays: recent developments in lab-on-a-chip and lab-on-a-disc systems

Allergies occur when a person's immune system mounts an abnormal response with or without IgE to a normally harmless substance called an allergen. The standard skin-prick test introduces suspected allergens into the skin with lancets in order to trigger allergic reactions. This test is annoying and sometimes life threatening. New tools such as lab-on-a-chip and lab-on-a-disc, which rely on microfabrication, are designed for allergy testing. These systems provide benefits such as short analysis times, enhanced sensitivity, simplified procedures, minimal consumption of sample and reagents and low cost. This article gives a summary of these systems. In particular, a cell-based assay detecting both the IgE- and non-IgE-type triggers through the study of degranulation in a centrifugal microfluidic system is highlighted.

Micro/nanoscale well and channel fabrication on organic polymer substrates via a combination of photochemical and alkaline hydrolysis etchings

With the utilization of photomasks, micro/nanoscale wells and channels with depths ranging from nanometers to several micrometers were fabricated on a poly(ethylene terephthalate) (PET) surface by a simple combination of photochemical and alkaline hydrolysis etching. The PET surface region could be directly and photochemically etched by UV light and N,N-dimethylformamide (DMF) to create 125-350 nm etching depths (step 1). In step 2, the depth could be further enlarged to 250-1400 nm by potassium hydroxide (KOH) developing. More importantly, when this combination etching was repeated with the same photomask, the depth increased with increasing etching times. For instance, the depth reached approximately 6 microm after a series of three combination etchings. The cross-sectional shape of the final structure was trapezoidal with smooth corners. No obvious widening effect in lateral size was observed after one combination etching, whereas the top width of the microfabricated channels was enlarged from 50 microm (the designed feature of the photomask used) to 100 microm after two or three combination etchings. Even more interesting was that step 1 resulted in the formation of a kind of aminated surface in the channel (6.5% amine content), but when step 2 was conducted, the aminated surface was erased. This process could be reversibly carried out by repeating step 1 (amination) and step 2 (erasing). Electrostatical self-assembly of an antibody, fluorescein isothiocyanate-labeled immunoglobulin G (FITC-IgG, goat anti-rabbit), was achieved on the aminated surface of the etched channels, which demonstrated that by this combination strategy, micro/nanoscale channels or wells featuring tunable depths and functional channel surfaces could be readily fabricated. Undoubtedly, these functionalized channels or wells onto organic substrates could provide a potential platform for microchips toward various functions such as microarrays, heterogeneous immunoassays, biosensors, concentrations, filtrations, and microanalysis.