Miniaturised platforms

Consideration of sample preparation also leads to the question of whether for some applications at least sensors would be more effectively constructed as a collection of modules each with a different function (sample preparation, transduction, detection, data collection) on a platform, large, small or miniaturised, rather than the old ideal of a small, self-contained device with intimately appressed layers which could return a rapid answer from a bucket of slime or some other spectacularly heterogeneous matrix. It is accepted that those with a taxonomic bent... 

The hrst pTAS devices were based on GC. Soon after, HPLC-based pTAS platforms began to appear and then CE followed. In chip CE, an injection was performed and an electrophoretic separation of a sample mixture (different fluorescent dyes) and all liquid handling was achieved using electro-osmotic flow. Since then, electrophoresis and electrokinetic fluid handling have been the cornerstones of many miniaturised analytical devices. 

Due to the compactness of LOC systems, extensive integration of functionality and the small volumes involved, many parts must now be made available in a miniaturised form. Hence there are many components and tools to aid the fitting together of all the components onto such a small platform. These include ... 

Hybridisation of matching strands of ssDNA is the underlying prinoiple of DNA arrays. Modern array platforms, such as that developed by Affymetrix Corp., are extremely miniaturised and allow massively parallel analysis for DNA sequencing and comparative studies of DNA samples. 

Exposure of the sensor layer to the analyte induces a change in its optical properties, which is monitored by a detector such as a photodiode, spectrometer, or CCD camera. The optical signal is then converted into an electrical one for quantification. The sensor layer may be inserted into a bench-top spectrophotometer or, alternatively, the platform components may be partially or completely integrated within a stand-alone miniaturised device. For in situ work the sensor element may be spatially separated from both excitation source and detector, or added as a component to the sample under investigation as in fluorescence microscopy. 

Vidigal, S. S. M. R, I. V. Toth, and A. O. S. S. Rangel. 2013. Sequential injection lab-on-valve platform as a miniaturisation tool for solid phase extraction. Anal. Methods 5 585-597. 

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