Analysis of Proteins at the Single Cell Level

Proteins bring a consequent additional level of information in comparison with nucleic acids on a cell’s state as proteins are dynamically processed and chemically modified in the cell as a function of the cell life. Yet, the analysis of proteins is challenging as no amplification step is possible as is the case for nucleic acids, and another difficulty lies in the dynamic range of protein expression in a single sample (e.g. a single cell). While the same challenges are still found for microfluidic-based analysis of proteins, microsystems bring about enhanced analytical performance and novel analysis opportunities. This is illustrated here for two different strategies that can be adopted for protein analysis in a chip format. A first strategy consists of transposing the standard proteomic protocol in miniaturized analytical tools, and this provides a number of advantages and enhancement for the analysis: an overall improvement is expected when using smaller systems whose capacity matches better the size of the samples; sample manipulation is minimized when using LOC technology,and this goes together with a decrease in sample loss and contamination; enhanced analytical performance in terms of analysis time and detection sensitivity is ensured by micro- and nano-scale features; last, the use of microfabricated structures guarantees higher analysis reproducibility. In a second strategy, the analysis is actually performed at the single cell level. This strategy does not enable protein mapping anymore, but the investigation focuses on given proteins (a single protein of a small number thereof) which are specifically targeted. For that purpose, innovative microfluidic-based protocols have been developed, and we classify them in three categories of fully destructive, partially invasive and non invasive protocols. Ongoing developments in the area of nanotechnology would enable truly protein mapping at the single cell level, with the use of nanofabricated tools in a LOC platform.