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

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 an 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 10 8 due to a combination of the 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 cells nucleic acids/proteins/lipids. Specifically, the bSi/Au SERS-active substrate offers a unique opportunity to investigate the living cells' malignant transformation using characteristics 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 the lab-on-a-chip SERS biosensors that can be integrated into silicon-based photonics device.

Intracellular Biosynthesis of Gold Nanoparticles for Monitoring Microalgal Biomass via Surface-Enhanced Raman Spectroscopy

“…zofingiensis-0.5Au were small and isolated, which resulted in relatively weak SERS “hot spots” among the AuNSs, while the AuNPs in C. zofingiensis-1.0Au grew into large AuHNs, leading to a coupled electromagnetic effect that is responsible for a significant SERS activity. , In terms of the SERS substrates applied in complex biological samples, the enhancement effect of AuHNs (9.7 folds) in this study is still compelling compared to other reported nanostructures (Table S3), such as the liquid-state interfacial AuNP array (16 folds) and the nickel-based functionalized nanoprobe (5–7 folds). , Coupled with the rapid sample preparation of intracellular AuHNs, this microalgae-mediated AuHN would be a powerful Raman substrate to monitor the change of microalgal biomass composition.…”

Stable and Reusable Lace-like Black Silicon Nanostructures Coated with Nanometer-Thick Gold Films for SERS-Based Sensing

“…The calculated EF for BSi/Au has a magnitude of 10 6 , indicating that the major impact on the SERS signal comes from the EM mechanism. However, CT could not be excluded as its possibility was demonstrated previously in ref by DFT simulations for similar structures.…”

“…The created structures demonstrate high Raman signal enhancement with excitation in the NIR region (785 nm), with an EF of around 10 6 . A significant advantage of the produced bSi is the reduced thickness of the gold layer as compared with other gold-based structures used in SERS-based analyses. , The high surface density of vertically aligned gold nanostructures ensures the shift of the absorption cross-section to the NIR range and the high magnitude of electromagnetic field enhancement, as demonstrated in several studies. , …”

“…30,31 The high surface density of vertically aligned gold nanostructures ensures the shift of the absorption cross-section to the NIR range and the high magnitude of electromagnetic field enhancement, as demonstrated in several studies. 32,65 The bSi/Au substrate is characterized by the high reproducibility of the results and low signal variation within 6% over a 100 × 100 μm 2 area. Substrate storage in the air atmosphere and under normal ambient conditions results in less than 3% signal decrease over 4 months and around 40% decrease over 20 months of storage, which is, according to our knowledge, the longest term of SERS substrate storage, which offers good SERS signal enhancement.…”

“…In comparison with recently proposed gold−bSi structures, 30,31 which contain 100−600 nm thick gold layers, we significantly reduce the amount of gold needed by creating a mosaic distribution of plasmonic hemispheres on the rich Si relief having a quasiperiodic lace-like structure. Moreover, the enhanced nanoroughness of the bSi surface enables plasmonic core− shell Si-Au nanostructures, 32 rendering the buffer layer (e.g., Ti thin film), conventionally used to improve the adhesion of plasmonic nanoparticles, unnecessary. 29 Analysis of the reliability, durability, stability, and reusability of Au-coated black Si-based SERS-active (bSi/Au) substrates reveals the beneficial "lace-type" bSi and mosaic gold geometries.…”