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LASER DIAGNOSTICS AND SPECTROSCOPY
Ultrasensitive SERS active sensors based on leaning silver NWs bundles
E. Kozhina12, S. Bedin12, S. Andreev1, A. Naumov123
1-Lebedev Physical Institute RAS, 119991 Moscow, Russia 2- Moscow Pedagogical State University (MPGU), 119991 Moscow, Russia 3- Institute for Spectroscopy RAS, 108840 Moscow Troitsk, Russia Liza.kozhina.99@mail.ru
One of the most powerful techniques in analytical science is a Raman scattering. This method allows identifying the unique "fingerprints" of ultra-low analyte concentration, even to detect the infinitesimal angle deformation or elongation of the atomic bonds in the molecule. In addition, compared with the IR absorption spectroscopy the presence of water is not hindering its applicability. Within the years, Raman scattering was improved by developing the various plasmonic surfaces that allowed increasing the analyte signal intensity, leading to the formation of new spectroscopic methods such as the surface enhanced Raman scattering (SERS) and tip enhanced Raman scattering (TERS).
We offer a completely new approach to synthesis SERS-active substrates using track-etched membranes (TM) as a template. Due to significantly low pore density of TMs, we succeeded in achieving a NWs point contact and this is the key to a drastic increase in the SERS signal intensity/substrate sensitivity. Thanks to the variability of the surface pore density of the TM (may be varied from 105 to 109 cm-2), the spacing between the tips of the individual NWs in the array is also can be varied [1]. That makes possible optimization of NWs density on the surface of the substrate for the gap hot spots formation.
Our substrates with the leaning neighboring silver (may be a different galvanically deposited material as well) nanow-ires (Ag-NWs) amplify the signal due to the presence of a gap hot spot and the NWs leaning feature may be observed in the real-time mode even in the optical microscope.
Furthermore, it is possible to increase the impact of the NWs agglomeration into the SERS signal enhancement upon synthesis the layered magneto-plasmonic NWs with a ferromagnetic nickel layer in the middle of NWs length [2]. In that case applying the magnet to the substrate before SERS spectra measurements because of the nickel layer there will be a narrow point contact between leaning NWs tips where the local electric fields will be highly concentrated. That may give us an increase in SERS spectra intensity which is an order of magnitude higher comparing with SERS spectra without magnet application (Fig. 1).
Fig. 1 (a) 10-3 mol R6G SERS spectra with magnet application to the substrate before spectra recording; (b) 10-3 mol R6G SERS spectra without magnet application; (c) 10-3 mol R6G adsorbed on glass Raman spectra.
[1] E. Kozhina S. Bedin A., N. Nechaeva, S. Podoynitsyn, V. Tarakanov, S. Andreev, Y. Grigoriev, A. Naumov. Ag-Nanowire Bundles with Gap Hot Spots Synthesized in Track-Etched Membranes as Effective SERS-Substrates, Applied Sciences. Vol.11, pp. 1375, (2021)
[2] E. Kozhina, E. Kulesh, S. Bedin, I. Doludenko, A. Piryazev, I. Korolkov, A. Kozlovskiy, M. Zdorovets, A. Rogachev, A. Shumska-
ya One-Dimensional Magneto-Optical Nanostructures: Template Synthesis, Structure, Properties, and Application in Spectroscopy
Based on Plasmon Resonance, IEEE Magnetics Letters. Vol. 13. pp. 1-5 (2022)
