Detection and Characterization of Nodularin by Using Label-Free Surface-Enhanced Spectroscopic Techniques

Abstract

Nodularin (NOD) is a potent toxin produced by Nodularia spumigena cyanobacteria. Usually, NOD co-exists with other microcystins in environmental waters, a class of cyanotoxins secreted by certain cyanobacteria species, which makes identification difficult in the case of mixed toxins. Herein we report a complete theoretical DFT-vibrational Raman characterization of NOD along with the experimental drop-coating deposition Raman (DCDR) technique. In addition, we used the vibrational characterization to probe SERS analysis of NOD using colloidal silver nanoparticles (AgNPs), commercial nanopatterned substrates with periodic inverted pyramids (KlariteTM substrate), hydrophobic Tienta® SpecTrimTM slides, and in-house fabricated periodic nanotrenches by nanoimprint lithography (NIL). The 532 nm excitation source provided more well-defined bands even at LOD levels, as well as the best performance in terms of SERS intensity. This was reflected by the results obtained with the KlariteTM substrate and the silver-based colloidal system, which were the most promising detection approaches, providing the lowest limits of detection. A detection limit of 8.4 × 10−8 M was achieved for NOD in solution by using AgNPs. Theoretical computation of the complex vibrational modes of NOD was used for the first time to unambiguously assign all the specific vibrational Raman bands.

Solvent-driven biotoxin into nano-units as a versatile and sensitive SERS strategy

“…6 The NOD toxin has been shown to cause hepatotoxicity through inhibition of phosphoproteins 1A and 2A (PP1 and PP2A), leading to a signicant use of important cellular proteins, and is therefore considered a potential tumour promoter and carcinogen. 1,7,8 Thus, to ensure the marine environment and food safety, it is important to develop highly sensitive and reliable method of quick detection of biotoxins. High performance liquid chromatography (HPLC) 9 and liquid chromatography/mass spectrometry (LC-MS) 10 provide accurate and sensitive analytical methods for the identication and quantication of toxins, but their instruments are expensive and require specialist personnel to operate them, and the memory effect of the mass spectrometry ion source reduces the accuracy and sensitivity of subsequent determinations of toxins.…”