Synthesis and Characterization of Elongated-Shaped Silver Nanoparticles as a Biocompatible Anisotropic SERS Probe for Intracellular Imaging: Theoretical Modeling and Experimental Verification.

Carlos Caro,David Pozo,Manuel Pernia Leal,Ana Zaderenko,Pedro Quaresma,Jose Oliva-Montero,Jaime Franco,Eulália Pereira,Ricardo Franco,Jose Royo,Maria García-Martín,Patrick Merkling

doi:10.3390/nano9020256

Abstract

Progress in the field of biocompatible SERS nanoparticles has promising prospects for biomedical applications. In this work, we have developed a biocompatible Raman probe by combining anisotropic silver nanoparticles with the dye rhodamine 6G followed by subsequent coating with bovine serum albumin. This nanosystem presents strong SERS capabilities in the near infrared (NIR) with a very high (2.7 × 107) analytical enhancement factor. Theoretical calculations reveal the effects of the electromagnetic and chemical mechanisms in the observed SERS effect for this nanosystem. Finite element method (FEM) calculations showed a considerable near field enhancement in NIR. Using density functional quantum chemical calculations, the chemical enhancement mechanism of rhodamine 6G by interaction with the nanoparticles was probed, allowing us to calculate spectra that closely reproduce the experimental results. The nanosystem was tested in cell culture experiments, showing cell internalization and also proving to be completely biocompatible, as no cell death was observed. Using a NIR laser, SERS signals could be detected even from inside cells, proving the applicability of this nanosystem as a biocompatible SERS probe.

Highlights

In recent years, Raman spectroscopy has been studied extensively, given its wide range of applications especially those based on the Surface Enhanced Raman Scattering (SERS) effect [1,2,3,4,5,6,7,8], by which Raman-active compounds can be detected at very low concentrations
Energy-dispersive X-ray spectroscopy (EDX) results show a clear peak for Ag, Cu and C elements corresponding to the grid, while Si and O indicate are related to minor associated impurities (Figure 1B)
With an surface plasmon resonance (SPR) band in the near-IR zone (~800 nm) and bovine serum albumin (BSA) capping for biocompatibility, the newly synthesized aggregates of thiol-immobilized silver-based NPs (AgNPs) have potential uses as bioprobes, since living tissues do not absorb light energy in near-IR-zone

Summary

Introduction

Raman spectroscopy has been studied extensively, given its wide range of applications especially those based on the Surface Enhanced Raman Scattering (SERS) effect [1,2,3,4,5,6,7,8], by which Raman-active compounds can be detected at very low concentrations. In SERS, to obtain an efficient amplification, the organic compound should be near the surface of metallic nanoparticles (NPs), especially those based on the reduced form of metals such as copper, gold or silver, where the Raman signals can be amplified by factors as high as 1014–1015 [9,10,11] In this manner, the ultimate detection limit could be a single analyte molecule [12,13,14]. According to the latest findings, Raman spectroscopy parallel to the SERS effect can be considered as one of the most powerful techniques currently available for sensing applications [22,23,24,25,26,27]

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