High-resolution micro-magnetometer based on novel nano-junction oxide SQUIDs

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This Phase II project will develop a general purpose magnetic microscope and evaluate its utility in biomedical sciences. The microscope will detect the magnetic field using high-transition temperature (high-Tc) sensors based on the superconducting quantum interference device (SQUID) developed during the Phase I. UC Riverside (UCR) has developed a novel high-Tc SQUID fabrication technique that gives a junction noise comparable to that of low-Tc SQUIDs. Their approach uses a focused helium ion beam to make the Josephson junction with 0.5 nm precision, resulting in reliable, reproducible SQUIDs with high yields. During Phase I we have designed three magnetometers based on this SQUID. We found the direct injection magnetometer to produce a junction noise of 6 µΦo/√Hz comparable with a low-Tc SQUID noise. We mounted the best one just below the window of a microscope stage in an inverted microscope and determined its field sensitivity at 13oK to be 1 pT/√Hz for an effective detector area of 62 µm radius. In Aim 1, UCR will improve the noise level further by optimizing the dimensions of the junction, the SQUID loop and the coupling efficiency with the pickup loop. UCR will construct 1x3 SQUID chips and deliver them to Tristan in year 1. Tristan, meanwhile, will design and construct an inverted SQUID microscope (iSM) based on their previous iSM. It will be equipped with an up-right fluorescent microscope above and micromanipulators for stimulator and recording electrodes on the sides. The window in the microscope stage will have a micro-channel etched inside to achieve a distance of 10-25 µm between a sample and the SQUID array for single nanoparticle and neuron detection. This very short gap is possible because the SQUIDs are high-Tc superconductors and thus they operate at >10oK. They will mount two of the test SQUID chips into a 2x3 array and evaluate their sensitivities. Once a working iSM is constructed, it will be shipped to Boston for evaluating its utility in biomedical sciences by the beginning of year 2. After shipping the iSM, UCR will continue to improve their SQUID chips. Once they achieve a significant reduction in detector noise, Boston will ship the iSM back to Tristan and Tristan will test the iSM with the improved SQUID chips. Tristan will ship back the improved iSM to Boston for continuing the evaluation. In Aim 2, Dr. Okada of Moment and Dr. Lin of Boston University (BU) will use an isolated crayfish giant axon during year 1 to develop the method for magnetic field detection from single neurons. Dr. Man of BU will develop cultured hippocampal neurons from fetal rats. In year 2, Drs. Okada and Lin will evaluate the iSM for measuring intracellular currents from single neurons. In Aim 3, Dr. Okada and Dr. Medarova of the Martinos Center at Massachusetts General Hospital will construct nanoparticles and fluorescent dye conjugated with avidin and biotin. They will magnetize the nanoparticles using an AC method and test whether the iSM can detect single complexes. This will serve as the proof of concept for future applications. The fluorescent signals from the same complex will be measured with the optical microscope for comparative studies. Phase II deliverables – the iSM, a performance report, publications.