Surface-Enhanced Raman Spectroscopy of Organic Molecules and Living Cells with Gold-Plated Black Silicon

Lena Golubewa,Algirdas Selskis,Polina Kuzhir,Dmitry Lyakhov,Ali Shah,Danielis Rutkauskas,Tatsiana Khlopina,Ieva Matulaitiene,Yuri Svirko,Renata Karpicz,Dominik Michels,Tatsiana Kulahava,Aliaksandr Pushkarchuk

doi:10.1021/acsami.0c13570

Abstract

Black silicon (bSi) refers to an etched silicon surface comprising arrays of microcones that effectively suppress reflection from UV to near-infrared (NIR) while simultaneously enhancing the scattering and absorption of light. This makes bSi covered with a nm-thin layer of plasmonic metal, i.e., gold, an attractive substrate material for sensing of bio-macromolecules and living cells using surface-enhanced Raman spectroscopy (SERS). The performed Raman measurements accompanied with finite element numerical simulation and density functional theory analysis revealed that at the 785 nm excitation wavelength, the SERS enhancement factor of the bSi/Au substrate is as high as 108 due to a combination of electromagnetic and chemical mechanisms. This finding makes the SERS-active bSi/Au substrate suitable for detecting trace amounts of organic molecules. We demonstrate the outstanding performance of this substrate by highly sensitive and specific detection of a small organic molecule of 4-mercaptobenzoic acid and living C6 rat glioma cell nucleic acids/proteins/lipids. Specifically, the bSi/Au SERS-active substrate offers a unique opportunity to investigate the living cells' malignant transformation using characteristic protein disulfide Raman bands as a marker. Our findings evidence that bSi/Au provides a pathway to the highly sensitive and selective, scalable, and low-cost substrate for lab-on-a-chip SERS biosensors that can be integrated into silicon-based photonics devices.

Highlights

Curing neurodegenerative diseases and stem cell therapies require effective biosensors for realtime in vivo controlling and monitoring the growth and functional activity of the cells
We suggest employing in SERS the substrates based on the black silicon, which has been proposed in 1997 to increase absorbance and suppress reflectivity of the silicon[22] by forming cone-shaped structures of micrometers height over the sample surface[23]
It consists of the hemisphere structures; their diameter distribution is presented in Fig. 1S, b

Summary

Introduction

Curing neurodegenerative diseases and stem cell therapies require effective biosensors for realtime in vivo controlling and monitoring the growth and functional activity of the cells. The sensitivity and specificity of Raman measurements can be drastically improved by using substrates enabling the surface-enhanced Raman scattering spectroscopy (SERS) This technique allows one to detect low bio-molecules concentrations[5,6,7] changes in cell metabolism[8] or cells viability[9], discriminate individual vesicles[10] as well as to realtime control of biochemical changes[11,12,13] by using so-called SERS-active substrates, which conventionally based on noble metal (Au, Ag, Cu) nanostructures[14,15,16]. This makes SERS signal very sensitive to the substrate morphology[18] and requires fabrication techniques providing fine control over the geometry and size of nanostructures/hot spots[19], which should be uniformly distributed over the entire substrate to be employed for biosensing

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Conclusion