LEGO Blocks as "Standard" Samples for Evaluation of Fluorescence Avoidance and Mitigation in Raman Spectroscopy

Fluorescence interference in Raman spectroscopy is a well-known problem and is especially significant in portable instruments where the availability of a variety of exciting wavelengths is unlikely. Several fluorescence avoidance and mitigation schemes are described in the literature, and implemented by Raman spectrometer manufacturers, but there is no standard method for evaluating the accuracy and repeatability of these schemes. Some test samples shown in instrument descriptions, such as "dark rum" and "sesame seed oil" are not reproducible. Therefore, we propose a set of colored LEGO blocks as "standard" samples for this purpose; they have the attractive properties of being very low cost, rugged, non-toxic, easy to transport and store, and appear to be manufactured using a standard process. This paper shows the Raman spectra of a set of these blocks at different excitation wavelengths, acquired on laboratory instruments, along with their visible-near-infrared spectra. The goal is to qualitatively understand the origins of the observed fluorescence and lay the groundwork for exploring the effectiveness of methods currently implemented on handheld Raman instruments.