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1Laser nanostructuring of thin films for magnetic biosensing
application
I.O. Dzhun1*, D.V. Shuleiko2, A.V. Nazarov1, N.N. Perova2, V.Yu. Nesterov2, D.E. Presnov2, I.L.
Romashkina1, M.G. Kozin1, N.G. Chechenin1,2, S.V. Zabotnov2
1- Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 1/2 Leninskie Gory, Moscow,
119991, Russia
2- Faculty of Physics, Lomonosov Moscow State University, 1/2 Leninskie Gory, Moscow, 119991, Russia
Health monitoring and early diagnostics of diseases require portable point-of-care devices. For this purpose, lab-on-chips techniques that perform coin-size chips combining the functions of diagnostic laboratory are developed. Along with common optical methods magnetic biosensors that detect magnetically labeled cells and biomolecules are also of interest due to their high sensitivity, low energy consumption and low background noise. However, their detection limit and fabrication cost are still the subjects to improve.
Here we suggest the applying of laser nanostructuring technologies as a helpful tool in this area and perform the results of our pilot experiments. Laser technologies were applied in two paths: fabrication of magnetic nanoparticles via pulsed laser ablation in liquid (PLAL) and creation of sensors surface relief via femtosecond laser induced periodical surface structures (LIPSS) formation. At the first part MNPs colloids were produced by ablation of thin 250 nm magnetron sputtered on the glass substrate Fe films instead of commonly used bulk target. PLAL of such film in acetone leaded to creation of Fe@FeO core shell MNPs with mean size of 90 nm and thickness of oxide shell of about 20 nm as follows from our transmission and scanning electron microscopies. The presence of crystalline a-Fe core and FeO shell was indicated by Mossbauer spectroscopy and Raman scattering data. At the second part to form the surface relief of Si/Ta30nm/NiFe10nm/IrMn10nm/Ta15nm exchange biased layer stack the deposition of multilayer on the previously structured Si wafer was used to avoid undesirable thermal effects such as melting and layer intermixing. The magneto-optical Kerr effect microscopy investigation has shown the appearance of the out-of-plane magnetization of NiFe layer that is completely in plane in unstructured area and the remanence of exchange bias of about 150 Oe that makes the sensor more sensitive to MNPs stray fields. That is also confirmed by appearance of periodical contrast in magnetic force microscopy image with period equal to that of LIPSS. In final part the obtained MNPs colloid was dropped onto the multilayer structure. The scanning electron microscopy revealed the crowding of MNPs in relief area and inside the grooves. Thus obtained MNPs and relief-surface multilayer structures could be prospective elements for magnetic biosensors with improved detection limit.
