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Fast and Reproducible iSERS Microscopy of Single HER2-positive Breast Cancer Cells using Gold Nanostars as SERS Nanotags

Abstract

Speed is often a bottleneck in conventional Raman microscopy on biological specimen. In immuno-Raman microspectroscopy, or short iSERS microscopy, acquisition times per pixel have been reduced by more than one order of magnitude over the past decade since its proof of concept. Typically rather high laser power densities are employed with the intention to compensate for the shorter acquisition times, without checking the reproducibility of the results in repeated experiments on the same sample. Here, we systematically analyze this aspect at the single-cell level since it forms the basis of quantification and is very important for the reinspection of the same specimen. Specifically, we investigate experimentally the role of laser power density in conjunction with acquisition times per pixel in a series of repeated iSERS experiments on the same single cell overexpressing the breast cancer tumor marker human epidermal growth factor receptor 2 (HER2). Confocal iSERS mapping experiments were guided by wide-field fluorescence microscopy for selecting regions of interest. We demonstrate that the combination of ca. 1-2 mW laser power (40x objective, NA 0.6), 50 msec acquistion time per pixel and a high EM-CCD signal gain yields highly reproducible iSERS images in a series of four repeated experiments on the same single cell. In contrast, longer acquisition times (0.8 sec, no EM gain) and in particular higher laser power (4 mW up to 18 mW) densities lead to non-reproducible iSERS results due to signal degradation. Finally, we point out to several issues which in our opinion are important for future developments: (i) Are ultra-bright and ultra-uniform SERS nanotags mutually exclusive? (ii) How to compare the performance of SERS nanotags across different laboratories? (iii) What is the value of SERS cuvette experiments if we do not know the composition and in particular the aggregation state of the colloid?

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Publication details

The article was received on 15 Apr 2017, accepted on 02 Jun 2017 and first published on 09 Jun 2017


Article type: Paper
DOI: 10.1039/C7FD00135E
Citation: Faraday Discuss., 2017, Accepted Manuscript
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    Fast and Reproducible iSERS Microscopy of Single HER2-positive Breast Cancer Cells using Gold Nanostars as SERS Nanotags

    X. Wang, B. Walkenfort, L. König, S. Kasimir-Bauer and S. Schlücker, Faraday Discuss., 2017, Accepted Manuscript , DOI: 10.1039/C7FD00135E

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