The Nanonest2Sense project aims at developing a low cost technology that could provide affordable devices for point-of-care detection of molecules of interest for health monitoring or pre-diagnostics. The proposed technological building block has the additional advantage of being intrinsically versatile and compatible with CMOS technology. For demonstration, two types of applications will be targeted: the detection of extracted molecules or DNA samples that circulate in body fluids and breath analysis.
One example of the first application is the detection of free-circulating micro-ribonucleic acid (m-RNA) strands which are released by cancerous tumours during treatment. Point-of-care monitoring of such molecules could allow a more reactive follow-up of tumour evolution, more personalized treatments, the use of smaller doses, and hopefully lead to a better care for the patients. Specific detection can be obtained by using relevant DNA probes and by detecting their hybridization with the target m-RNA.
Presently available biosensors are based on a labelling technique where DNA molecules of the biosample under test are firstly tagged by fluorescent labels so that their immobilization with a given probe can be visualized. However, the labelling step is costly, time consuming, and can drastically change the binding properties of the molecules. For this reason, R&D activities are now focusing on label-free methods, where the interaction between the target and the probe molecules is directly sensed through the modification of electronic, optical or mechanical properties of the transducer. However, the detection of the optical or electromechanical response is still raising implementation issues, such as the integration of a laser source for Surface Plasmon Resonance (SPR) or viscosity issues for MEMS/NEMS. This adds to their cost and makes them better suited to centralized use in hospitals for instance than to point-of-care applications.
On the other hand, breath tests are becoming popular as non-invasive method of disease diagnoses, due to their quick results and ease of use. Exhaled breath consists of many different molecular species, and some of them are typical of diseases. With diabetes, acetone content increases significantly in breath as fatty acids are metabolized for energy during periods of glucose deficiency, and it is thus a useful biomarker of type I diabetes. Unfortunately, portable devices for exhaled acetone measurements remain currently unavailable.
The Nanonets2Sense project aims at addressing these needs. It proposes a structured effort to deliver a low-cost technology for the fabrication of fully integrated sensor where the active sensing device is processed above the CMOS conditioning and read-out circuit.
The active device takes advantage of the sensitivity of nanowires electrical properties to surface effects. However, we use networks of randomly positioned nanowires instead of single nanowires or controlled arrangements of nanowires. The fabrication process is then mostly independent of the material used (here, silicon for biosensing and zinc oxide for breath analysis). The sensing device can be processed using standard microelectronic techniques and can be integrated above any kind of substrate, including CMOS circuits, using a 3D integration scheme. The process is especially well suited to the integration of matrices of sensing pixels above CMOS, providing the ability to test several molecules at the same time, with the potential of improving specificity and reliability by processing and correlating the responses of several sensing pixels.