Sensors 2020, 20, 5634; doi:10.3390/s20195634 www.mdpi.com/journal/sensors
Letter
Raman Signal Enhancement Tunable by
Gold-Covered Porous Silicon Films with
Different Morphology
Svetlana N. Agafilushkina
1,†
, Olga Žukovskaja
2,3,4,†
, Sergey A. Dyakov
5
, Karina Weber
2,3,4
,
Vladimir Sivakov
4,
*, Jürgen Popp
2,3,4
, Dana Cialla-May
2,3,4
and Liubov A. Osminkina
1,6,
*
1
Physics Department, Lomonosov Moscow State University, 119991 Moscow, Russia;
shevchenko.svetlana@physics.msu.ru
2
Institute of Physical Chemistry and Abbe Center of Photonics, Friedrich Schiller University Jena,
Helmholtzweg 4, 07745 Jena, Germany; Olga.Zukovskaja@leibniz-ipht.de (O.Ž.); karina.weber@leibniz-
ipht.de (K.W.); juergen.popp@ipht-jena.de (J.P.); dana.cialla-may@leibniz-ipht.de (D.C.-M.)
3
Research Campus InfectoGnostics, Philosophenweg 7, 07743 Jena, Germany
4
Leibniz Institute of Photonic Technology, Member of the Leibniz Research Allicance, Leibniz Health
Technologies, Albert-Einstein-Straße 9, 07745 Jena, Germany
5
Skolkovo Institute of Science and Technology, Nobel Street 3, 143025 Moscow, Russia;
s.dyakov@skoltech.ru
6
Institute for Biological Instrumentation of Russian Academy of Sciences, 142290 Pushchino, Russia
* Correspondence: vladimir.sivakov@leibniz-ipht.de (V.S.); osminkina@physics.msu.ru (L.A.O.)
†
These authors contributed equally to this work.
Received: 1 September 2020; Accepted: 29 September 2020; Published: 2 October 2020
Abstract: The ease of fabrication, large surface area, tunable pore size and morphology as well
surface modification capabilities of a porous silicon (PSi) layer make it widely used for sensoric
applications. The pore size of a PSi layer can be an important parameter when used as a matrix for
creating surface-enhanced Raman scattering (SERS) surfaces. Here, we evaluated the SERS activity
of PSi with pores ranging in size from meso to macro, the surface of which was coated with gold
nanoparticles (Au NPs). We found that different pore diameters in the PSi layers provide different
morphology of the gold coating, from an almost monolayer to 50 nm distance between
nanoparticles. Methylene blue (MB) and 4-mercaptopyridine (4-MPy) were used to describe the
SERS activity of obtained Au/PSi surfaces. The best Raman signal enhancement was shown when
the internal diameter of torus-shaped Au NPs is around 35 nm. To understand the role of plasmonic
resonances in the observed SERS spectrum, we performed electromagnetic simulations of Raman
scattering intensity as a function of the internal diameter. The results of these simulations are
consistent with the obtained experimental data.
Keywords: porous silicon; gold; surface-enhanced Raman scattering; plasmonics; sensorics
1. Introduction
Raman spectroscopy is a traditional sensing technique to detect the presence of chemical
substances, pollutants, toxins etc. Surface-enhanced Raman scattering (SERS) offers an effective
technique to improve the efficiency of Raman detection [1,2]. The signal enhancement is mainly
attributed to the electromagnetic or/and chemical mechanism which provide a significant SERS
enhancement up to 10
14
[2–4]. The sensitivity of SERS analysis allows to “fingerprint” even single
molecules [5]. This advantage makes SERS a unique tool for detection and diagnostic assays. As
