The development of early diagnosis techniques, both rapid and sensitive, is a real challenge in fields as varied as defence, environment and health. These techniques often involve the use of antibodies which are specific enough to allow the detection of very small concentrations of target molecules in a biological fluid. For the earliest possible detection, it is necessary to have tools that, coupled with antibodies, are able to provide the required sensitivity.
The approach we propose in the MAGDIAG project is very innovative in this respect. This approach is based on the use of magnetic nanoparticles, functionalized by monoclonal antibodies which are produced in the JOLIOT/LERI laboratory and directed against target biological objects. The dynamic detection of the latter, after interaction with magnetic nanoparticles, is carried out using giant magnetoresistance sensors (GMR sensors), developed at SPEC/LNO, through which biological objects can be marked one by one. LNO has extensive expertise in the design and use of these highly sensitive sensors based on spin electronics. These sensors advantages are : high detectivity, in the range of 50 to 200 pT/√Hz, inexpensiveness and easiness to integrate into a lab-on-a-chip. Therefore, fast, sensitive, low-cost and field transportable diagnostic tests would be achievable thanks to this technique.
A first proof of concept of this type of test based on GMR sensors integrated in a biochip (Figure 1) was performed on Eurokaryotic cells (murine myeloma NS1). The criteria to be met by diagnostic methods, such as sensitivity, specificity and robustness, but also speed and ease of use, were assessed for the first time with this type of device. Although capable of detecting the marked biological objects one by one, the detection limit is currently equal to 104 cells/ml. This is mainly due to false positive signals caused by magnetic bead aggregates forming in the absence of cells, which are detected by magnetic sensors as marked biological targets. Despite these obstacles, this sensitivity is already similar to that of commercial tests used routinely (flow cytometry ELISA test). To improve our system, we have therefore developed a new lab-on-a-chip based on GMR sensors (subject of a patent application), with sensors placed on either side of the microfluidic channel. This system will allow us to differentiate biological objects marked magnetically from magnetic bead aggregates. On the other hand, the use of magnetic nanoparticles, synthesized specifically for this project by the PHENIX laboratory (UMR 8234) should considerably reduce the number of aggregates.
We are also adapting our device to the high microbiological safety L2 laboratory of the LERI, for preliminary tests on salmonella, the bacterial model we have chosen and which presents a real challenge in terms of public health.
The work carried out within the framework of DIM ELICIT has been published and patented.
Evaluation of In-Flow Magnetoresistive Chip Cell-Counter as a Diagnostic Tool, M. Giraud, F.D. Delapierre, A. Wijkhuisen,P. Bonville, M. Thévenin, G. Cannies, M. Plaisance, E. Paul, E. Ezan , S. Simon , C. Fermon , C. Féraudet- Tarisse and G. Jasmin-Lebras, Biosensors 2019, 9(3), 105; https://doi.org/10.3390/bios9030105
French patent n° 1855217 (application : 14/06/2018). Invention Title : dispositif et procédé de détection magnétique d’objets biologiques microscopiques