An highlighted paper by Dr Y. Roupioz :”Plasmonic Nanohole Array Biosensor for Label-Free and Real-Time Analysis of Live Cell Secretion”

With the aim of getting more and better insights into living systems, the real time follow-up of protein secretion remains an important objective. Several issues have to be simultaneously addressed to real this holly Graal. First, the transducing method should enable the real-time analysis. Often, real-monitoring precludes the use of labels such as fluorophores, nanoparticles, electroactive species… Then, optical methods based on plasmonic effects are interesting approaches to fix this problem. Second, the entire device should enable ‘long incubation times’, i.e. between few hours to several days as usual cytokine secretion levels and kinetics are low by comparison to other secreting events such as insulin or neuro-transmitters. On a technological point of view, it underlies designs compatible with medium refreshing, temperature and CO2 pressure control and surface chemistries ensuring low fouling processes. Last but not least, the transducing method should enable the specific detection of the relevant targets present at very low levels (generally between few tens to several hundreds of picomolar), and diluted in highly complex fluids (culture media, often combined to mammalians sera).

In a recent paper published earlier in Lab on a Chip, Li et al. published an interesting paper addressing several key issues in the efficient follow-up of protein secretion. The authors describe a system combining two modules, with one part enabling the cell culture of Hela cells for up to 10 hours and another part, where the liquid media release in the cell culture module is injected. This latter part is a nanostructured surface enabling the plasmonic monitoring of molecular interaction occurring on immobilized probes, similarly to an immuno-assay. On the contrary to most surface plasmon resonance (SPR) biosensors which are relying on a Kretschmann configuration, the present set up is based on light transmission and plasmonic effects through nanoholes manufactured on flat devices. Such array thus enables optical detection with a regular microscope and reaches outstanding sensitivity. Indeed, in the specific case of vascular endothelial growth factor (VEGF) detection, the authors managed to detect as low as picomolar levels after 5 to 6 hours. Although this proof of concept relies on data produced with cell lines (Hela cells) and not primary cells, and the fact that only one target is monitored, this approach looks promising for application on several relevant targets released from human cells. This two-parts system is an original possibility to avoid background signal often monitored when analysis are directly carried in the culture medium, although we may expect some delay between the cytokine extracellular release and its flowing on the sensing module.

 

Plasmonic Nanohole Array Biosensor for Label-Free and Real-Time Analysis of Live Cell Secretion

 

Dr Yoann Roupioz is Research Director at CNRS, Deputy director of the laboratory SyMMES, UMR 5819 CNRS-CEA-Univ. Grenoble-Alpes.