Spectroscopic Identification of Neurotoxin Tetramethylenedisulfotetramine (TETS) Captured by Supramolecular Receptor β-Cyclodextrin Immobilized on Nanostructured Gold Surfaces

Figure 1

We have demonstrated a supramolecular platform for detection of selective inclusion molecules by vibrational spectroscopy. Our experimental data show that functionalizing commercial Klarite SERS substrates with β-CD as a molecular receptor for TETS/HEXS was not effective for Raman spectroscopic detection, most likely due to the extremely weak differential cross section of these molecules at 633 nm excitation wavelength coupled with its relatively low surface concentration and discontinuous distribution on the surface. XPS confirms the surface of the Klarite was decorated with mono-thiol-β-CD, but the concentration was low, around 0.07 per unit formula per Au site (or 161 pmol cm⁻²) on the SERS-active area. Furthermore, the TETS/HEXS to CD ratio indicates only 1 in every 6.25 CD cavities is occupied by TETS/HEXS. On the other hand, we found that ATR-FTIR is able to detect these molecules most successfully when the surface is decorated with Au NPs. The NPs increase the number of self-assembled mono-thiol-β-CD molecules per unit area, giving a higher surface concentration of TETS/HEXS per unit measurement area for infrared detection. ATR-FTIR coupled with a NP-functionalized surface is therefore a viable alternative vibrational-based detection platform, as the absorption cross section of the molecules is always inherently much greater than the Raman scattering cross section. Comparison of the raw Raman spectra from powder sample of mono-thiol-β-CD (i) and TETS/HEXS (ii), those of mono-thiol-β-CD (self-assembled from 10 mM solution) on SERS-active Klarite surface (iii), drop-casted TETS/HEXS solution (6 sec integration time) on SERS-active Klarite surface (iv), and TETS/HEXS inclusion in mono-thiol-β-CD decorated SERS-active area of the Klarite surface (v).