Final Report Summary - BIOMAGSENS (Ultra sensitive magnetic sensors for medical applications) The aim of the project was to develop a new generation of ultra-sensitive magnetic sensors with very low noise based on magnetic tunnel junctions for diagnosis and healthcare applications. These elements will first be used to develop hybrid sensors able to detect femtoTesla fields for magnetic imaging of the human body, mainly heart and brain, from these were to be developed the next generation of magnetic based biochips. Finally the project aimed to explore a new approach for biochips based on fluctuating particles localised in space by dipolar reconstruction. The consortium is composed of three research and development institutes, two small and medium enterprises and a large scale industry. It was expected that the main outputs of this project will be reliable, highly sensitive magnetic sensors for very different applications, hybrid sensors for femtoTesla field detection, a magneto-cardiographic (MCG) device, a new generation of magnetic based biochips and quantitative evaluation of dipolar reconstruction methods at the micron length scale. The first objective targeted the building of highly sensitive magnetic tunnel junctions based sensors in order to implement them in various applications. Micron size TMR sensors must be designed in a way quite different from existing TMR elements in magnetic random access memories (MRAMs). For the medical applications, the critical issue is to maximise the field sensitivity while the magnetic noise of the sensor is as low as possible. The high frequency behaviour is less critical. The main issue is to greatly reduce the low frequency 1/f noise created by the tunnel barrier of the sensor and by the soft magnetic layer. The second objective dealt with the coupling of a TMR element with a flux to field transformer allows us obtaining hybrid sensors with sensitivity comparable to low-Tc superconducting quantum interference devices (SQUIDs) which are the most sensitive magnetic sensors presently used. These sensors will be implemented for low-cost and highly sensitive magnetic imaging medical systems. With GMR sensors, a sensitivity of 30 fT/sqrt(Hz) has been recently obtained by CEA, TCD and Neuromag and resolution as high as 3 fT/sqrt(Hz) could be obtained by flux-to-field transformer optimization at 4 K. With very low 1/f noise TMR sensors, an order of magnitude more sensitive hybrid sensors could be fabricated with a resolution of about 4 fT/sqrt(Hz). This will open the possibility of producing low cost medical magnetic imaging systems. The output of this objective is the production of a magneto-cardiographic (MCG) imager based on hybrid sensors as a device showing the feasibility of that approach. Lastly they investigated the sensor/detection-specific progress that can be achieved with optimised TMR sensors: the limits of detection, the feasibility of different detection strategies and the reduction of noise in such systems. In this way, BIOMAGSENS looked at a generation ahead of the bio-related Integrated Projects that are currently under development which integrate first generation spin-valve based sensors. The project produced micron size MgO based TMR sensors with MR ratio of more than 250 % at room temperature (40 % were targeted in the project). This is among the best results worldwide. Al2Ox based TMR sensors requiring no annealing, or low annealing temperatures (~180 C) have been also produced. The flexibility of the TMR materials (barrier resistance, magnetic response) allows us incorporating them in the different devices targeted. For the 1/f noise, several techniques based on the modulation of super-current or flux guide vibration have been developed and several patents are pending. TMR biochips have been successfully fabricated and tested in an integrated platform. The platform developed allows multiplexing the sensors of the biochip, generating a DC and AC field to magnetise the magnetic particles and acquiring and processing the signal coming from the sensors. Furthermore, the software calibrates the DC external field in order to obtain the best particle detection signal. The platform can perform continuous recognition assays during eight hours when powered by a 1300 mA/h battery. Experimental results show noise levels one order of magnitude lower than the presented by the previously used measurement apparatus. Finally, a micro-fluidic channel is incorporated in the platform in order to have a fully integrated platform and to improve the reproducibility and the speed of the experiments. Related documents Final Report - BIOMAGSENS (Ultra sensitive magnetic sensors for medical applications)
