The detection and quantification of a biological agent or entity has become paramount to anticipate a possible health threat (epidemic or pandemic) or environmental threat (water pollutions) or to combat other contextual threats as bioterrorism. Consequently, developing a portable cost effective device that could detect and quantify such threats is the research focus of the joint project between RWTH Aachen and Université Pierre et Marie Curie (UPMC). The design and fabrication of such systems is very challenging because it involves interdisciplinary knowledge ranging from electromagnetic modeling, multiphysics simulations and fine measurement techniques, microfluidics design, simulation and fabrication, physics and chemistry of magnetic particle synthesis, characterization and functionalization, and finally immunological validation aspects.
The multidisciplinary aspects of an electromagnetic microsystem for immunologic detection based on magnetic nanoparticles (MNP) in a microfluidic lab-on-chip (LoC) have been studied. A comprehensive summary of the state of the art of the various aspects of lab-on-chip components and corresponding challenges is given with an emphasis on detection.
Because of their extractability and sortability, magnetic nanoparticles are adapted for examination of biological samples, serving as markers for biochemical reactions. So far, the final detection step is mostly achieved by well-known immunochemical or fluorescence-based techniques. Optical detection has a limited dynamic range and requires transparent, non-fluorescent media. Standard enzymatic detection as used in ELISA exhibits a limited sensitivity and is time-consuming. Because of regulations for radiation protection, radioactive markers are also problematic. Therefore, magnetic immunoassays detecting the analyte by means of magnetic markers constitute a promising alternative. MNP covered with biocompatible surface coating can be specifically bound to analytes, cells, viruses or bacteria. They can also be used for separation and for concentration enhancement.
The novel frequency mixing magnetic detection method allows quantifying MNP with a very large dynamic measurement range. By observation of amplitudes and phases of higher order frequency mixing components, specific non-linear signatures of different types of MNP can be discriminated. In this study, emphasis is put on the miniaturized implementation of this detection scheme.
Following the development using analytical and multiphysics simulations tools for optimization of both excitation frequencies and detection planar coils, a first multilayered printed circuit board (PCB) prototype integrating all three different coils along with an adapted microfluidic chip has been designed and realized. The prototype structures have been tested and characterized with respect to their performance for limit of detection (LOD) of MNP, linear response and validation of theoretical concepts. Using the frequency mixing magnetic detection technique, a LOD of 15ng/mL of 20 nm core sized MNP has been achieved without any shielding with a sample volume of 14 L corresponding to a drop of blood.
For biosensing, the microfluidic chip has been functionalized with specific antibodies using an appropriate surface functionalization method. For immunoassay validation and assessment tests, C-reactive protein (CRP) has been chosen for proof of concept validation as it plays an important role in inflammatory reactions, and serves as a biological marker for these. This first realized magnetic immunodetection system along with the developed analytical and simulations tools will serve as groundwork for a further improved fully integrated device for the detection of other relevant infectious disease biomarkers such as Procalcitonin (PCT) for immunoassays.
Hamid Kokabi is currently a professor of the faculty of engineering, University of Pierre and Marie Curie (UPMC) at Sorbonne University in Paris, France. He is a member of the laboratory of Electronics and Electromagnetism (L2E) at UPMC and in charge of the research theme on biomedical applications at L2E. His research interests have been passive electronic components and integrated piezoelectric sensors, microwave superconductivity, NDE using high Tc RF SQUIDs and other magnetic sensors for non magnetic metals, magnetic immunoassay using magnetic nanoparticles, microwave percutaneous biological tissues characterisation for diagnostic and hyperthermia for therapy and wireless medical embedded microsystems. Professor Kokabi received his Dipl. Ing. degree in electrical engineering from ENSICAEN in France in 1989, his MSc and PhD degrees in material sciences for electronics from Caen University in 1990 and 1993 respectively. After he spent one year (1993/1994) in Japan as a guest researcher working on piezoelectric thin films for embedded strain sensors. He joined then UPMC in 1994 first as an assistant professor (94-96) and then associate professor (1996-2005) and obtained his Habilitation in 2003 and full professor position in 2005. He has already achieved more than hundred and ten publications in different journals, international and national conferences and is a co-author of a patent on wireless communicating endoprosthesis. He is currently vice chair of IEEE EMBS (France section), the responsible for international relations at the Master of Electrical Engineering of UPMC and also at L2E laboratory and responsible since 2014 of the research council of the Health Engineering Institute (IUIS) of Sorbonne University.