Microfluidic electrochemical immunoassay systems

There is a continuing demand for fast and simple analytical methods for the determination of many clinical, biochemical and environmental analytes. In this respect, immunoassays and immunosensors that rely on antibody-antigen interactions provide a promising means of analysis owing to their specificity and sensitivity. High specificity 

ELECTROCHEMICAL SENSORS, BIOSENSORS AND THEIR BIOMEDICAL APPLICATIONS 

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FIGURE 5.2 Schematic representation of (a) competitive and (b) non-competitive immunoassay formats. 

FIGURE 5.3 A schematic illustrating a competitive immunoassay format used for the detection of estradiol. (Reprinted from [11] with permission from Elsevier.) 

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Heinemann et al. pioneered electrochemical immunoassays prior to the nanoparticle era [25]. His team s systems involve sandwich immunoassays using the enzyme label alkaline phosphatase which produces electroactive products that are transported by a chromatographic or fluidic system to an electrode detector [26,27]. Recent advances have interfaced this approach into microfluidic devices [28]. Interdigitated electrodes have provided the highest sensitivity [29]. 

Electrochemical immunoassays were pioneered in the 1980s by Heineman, Halsall, and coworkers.23-29 Early in their studies, they employed voltammetric and amperometric techniques to measure proteins and small biologically important molecules, such as hormones, via competitive and sandwich-type immunoassays. Heineman and Halsall and other researchers explored many different measurement techniques and incorporated microfluidics, - reagent delivery systems, interdigitated electrode arrays, b34-36 magnetic beads ° b33,35-37 various designs to improve... 

The use of ELISA is broad and it finds applications in many biological laboratories over the last 30 years many tests have been developed and vahdated in different domains such as clinical diagnostics, pharmaceutical research, industrial control or food and feed analytics for instance. Our work has been to redesign the standard ELISA test to fit in a microfluidic system with disposable electrochemical chips. Many applications are foreseen since the biochemical reagents are directly amenable from a conventional microtitre plate to our microfluidic system. For instance, in the last 5 years, we have reported previous works with this concept of microchannel ELISA for the detection of thromboembolic event marker (D-Dimer) [4], hormones (TSH) [18], or vitamin (folic acid) [24], It is expected that similar technical developments in the future may broaden the use of electroanalytical chemistry in the field of clinical tests as has been the case for glucose monitoring. This work also contributes to the novel analytical trend to reduce the volume and time consumption in analytical labs using lab-on-a-chip devices. Not only can an electrophoretic-driven system benefit from the miniaturisation but also affinity assays and in particularly immunoassays with electrochemical detection. 

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