Surface Enhanced Raman Spectroscopy for Quantitative Analysis: Results of a Large-Scale European Multi-Instrument Interlaboratory Study

Abstract

Surface-enhanced Raman scattering (SERS) is a powerful and sensitive technique for the detection of fingerprint signals of molecules and for the investigation of a series of surface chemical reactions. Many studies introduced quantitative applications of SERS in various fields, and several SERS methods have been implemented for each specific application, ranging in performance characteristics, analytes used, instruments, and analytical matrices. In general, very few methods have been validated according to international guidelines. As a consequence, the application of SERS in highly regulated environments is still considered risky, and the perception of a poorly reproducible and insufficiently robust analytical technique has persistently retarded its routine implementation. Collaborative trials are a type of interlaboratory study (ILS) frequently performed to ascertain the quality of a single analytical method. The idea of an ILS of quantification with SERS arose within the framework of Working Group 1 (WG1) of the EU COST Action BM1401 Raman4Clinics in an effort to overcome the problematic perception of quantitative SERS methods. Here, we report the first interlaboratory SERS study ever conducted, involving 15 laboratories and 44 researchers. In this study, we tried to define a methodology to assess the reproducibility and trueness of a quantitative SERS method and to compare different methods. In our opinion, this is a first important step toward a “standardization” process of SERS protocols, not proposed by a single laboratory but by a larger community.

Nanoparticles Engineering by Pulsed Laser Ablation in Liquids: Concepts and Applications

“…We have participated in a very recent collaboration, in which NPs, produced by laser ablation at our lab, were tested in 15 laboratories around Europe in an experiment coordinated by the University of Trieste within a COST action (Raman4clinics). The results were very satisfactory and show that, in particular with the Au NPs, a linear relationship between signals and analyte concentration was obtained with appropriate reproducibility and trueness [179]. These experiments also made it possible to use NPs for photothermal therapy of the tumor, evidencing an increase of the tumor far field measured temperature, after 10 min of irradiation, by 8 degrees which is considered sufficient to start the apoptosis mechanism for the tumor cells.…”

“…We have participated in a very recent collaboration, in which NPs, produced by laser ablation at our lab, were tested in 15 laboratories around Europe in an experiment coordinated by the University of Trieste within a COST action (Raman4clinics). The results were very satisfactory and show that, in particular with the Au NPs, a linear relationship between signals and analyte concentration was obtained with appropriate reproducibility and trueness [179].…”

“…NPs synthesized by LAL are of particular interest because of their clean surface, which allows functional molecules to reach easily the NP surface [179,180]. Antigen cell targeting [171][172][173][180][181][182], direct or indirect analytical sensors [177,179,183] and multimodal contrast agent in vivo [182] are examples of recent results obtained in our laboratories with plasmonic nanostructures for biotechnology applications.…”

From Raman to SESORRS: moving deeper into cancer detection and treatment monitoring

“…One of the limiting factors in the clinical application of Raman spectroscopy, particularly SERS, is that a standard method is yet to be adopted and results can sometimes be considered irreproducible. Large inter-laboratory studies have recently been undertaken in an effort to overcome these issues, 88,89 and recommendations have been published on the key parameters that should be considered to improve comparability of results across laboratories. 90 These considerations are essential for clinical translation of the techniques and collaborative studies should continue such that standardised methods can be developed.…”

Chemometric Tools to Point Out Benchmarks and Chromophores in Pigments through Spectroscopic Data Analyses

“…Pre-treatments and data fusion are quite important: dataset are submitted to peak alignment [ 2 ], normalization processes or a band area selection and processed with regression analysis [ 20 ], observing the separation through PCA, linear discriminant analysis or cluster analysis [ 21 ].…”