Summary : The development of rapid, sensitive, portable, and cost-effective methods for early diagnosis is now a major challenge for improving healthcare, particularly in emergency medicine and in areas with limited infrastructure. The rapid detection and management of infectious, chronic, and emerging diseases plays a central role in reducing mortality and controlling epidemics. Aware of these needs, in 2006 the World Health Organization (WHO) proposed a set of criteria known by the acronym REASSURED (Real-time connectivity, Ease of specimen collection, Affordable, Sensitive, Specific, User-friendly, Rapid and robust, Equipment-free, Deliverable to end-users), thereby defining the standards that point-of-care (POC) diagnostic tests must meet. To meet these needs, the rise of micro- and nanobiotechnologies in recent decades has paved the way for a new generation of miniaturized analytical platforms. Lab-on-a-chip technologies are a perfect example of this, as they enable functions that were once reserved for centralized and costly laboratories to be integrated into very small devices. These technologies open up new possibilities for accessible, reliable, and field-deployable testing.
In this context, a patented biochip based on giant magnetoresistance (GMR) sensors has been developed to magnetically detect biological targets. This approach is based on the magnetic labeling of biological targets using magnetic nanoparticles functionalized with antibodies specifically directed against the targets of interest. The dynamic detection of these targets, introduced into a microfluidic channel, is performed by GMR sensors, which are arranged face-to-face on either side of the microfluidic channel, allowing simultaneous detection of the labeled biological targets.
The first part of this thesis is devoted to a comprehensive and detailed preliminary study of cancer cells (murine NS1 myeloma cells) to evaluate the performance of the GMR biochip as a diagnostic tool. To this end, several criteria such as specificity, sensitivity, reproducibility, and robustness of detection were evaluated in a semi-complex matrix without sample pretreatment. The results obtained were promising, as the specificity and sensitivity of the measurements were demonstrated with an average detection limit of 500 cells/mL.
These results demonstrated the relevance and value of the GMR biochip as a detection tool, leading to a second study focusing on the detection of pathogenic bacteria involved in sepsis. In this second part of the study, work was carried out on different bacterial species (Salmonella, Enterobacter cloacae, and Escherichia coli), which differ from the cells studied previously in terms of their size (ten times smaller) and the antigens expressed on their surface. Numerous preliminary tests were therefore necessary to select the antibodies and magnetic nanoparticles best suited to the study of these new targets. The microfluidics of the biochip were also modified to enable the detection of magnetically labeled bacteria.
The results obtained are encouraging and prove that the detection of pathogenic bacteria is possible, but they also highlight the complexity of selecting new antibodies, the difficulties of labeling associated with the use of new nanoparticles, and the need for a comprehensive review due to the resizing of the microfluidic channels. In parallel with these tests, work has been carried out to miniaturize the experimental device with the aim of creating a lightweight, portable POC test.