Analysis of Serotonin Molecules on Silver Nanocolloids—A Raman Computational and Experimental Study

Abstract

Combined theoretical and experimental analysis of serotonin by quantum chemical density functional calculations and surface-enhanced Raman spectroscopy, respectively, is presented in this work to better understand phenomena related to this neurotransmitter’s detection and monitoring at very low concentrations specific to physiological levels. In addition to the successful ultrasensitive analyte detection on silver nanoparticles for concentrations as low as 10−11 molar, the relatively good agreement between the simulated and experimentally determined results indicates the presence of all serotonin molecular forms, such as neutral, ionic, and those oxidized through redox reactions. Obvious structural molecular deformations such as bending of lateral amino chains are observed for both ionic and oxidized forms. Not only does this combined approach reveal more probable adsorption of serotonin into the silver surface through hydroxyl/oxygen sites than through NH/nitrogen sites, but also that it does so predominantly in its neutral (reduced) form, somewhat less so in its ionic forms, and much less in its oxidized forms. If the development of opto-voltammetric biosensors and their effective implementation is envisioned for the future, this study provides some needed scientific background for comprehending changes in the vibrational signatures of this important neurotransmitter.

The highly sensitive determination of serotonin by using gold nanoparticles (Au NPs) with a localized surface plasmon resonance (LSPR) absorption wavelength in the visible region

“…76 Specic to the SERS spectrum, the ring H 23 -C 9 , H 22 -C 8 , and H 20 -C 5 out-of-plane rocking vibrations at around 840 cm À1 , the twisting deformation of H 16 -C 2 -H 17 at around 1360 cm À1 , the wagging deformation of H 16 -C 2 -H 17 and H 18 -C 3 -H 19 at about 1433 cm À1 , and the scissoring deformation of H 16 -C 2 -H 17 at around 1582 cm À1 have stronger vibrations than the standard serotonin powder. 77,78 The spectrum of serotonin powder was analyzed for the conrmation of 5-HT detection using our substrate via Raman spectroscopy. 79 The specic uctuations of serotonin found in this paper are shown in Table 1.…”

Comparative Computational and Experimental Detection of Adenosine Using Ultrasensitive Surface-Enhanced Raman Spectroscopy

“…Such modifications also imply anticipated changes in the positions and intensities of vibrational lines that are indeed observed. For instance, when the overall induced molecular dipole moment results from the normal component of the electric field associated with the light excitation, dominantly in-plane vibrations are expected [ 41 , 42 ], such as those observed in Figure 2 b, which are mostly associated with adenine ring bending. On the other hand, if the tangential field component induces the molecular dipole moment, out of plane vibrations such as those seen in Figure 2 d are likely.…”

“…Another point worth considering is the greater complexity of the analyte’s redox reaction than those of other neurotransmitters such as dopamine and serotonin [ 23 , 25 , 41 , 43 ]. Also, in view of the fact that current sample preparation involves dilution of adenosine in ultrapure water, oxidized forms of adenosine are very likely to occur and to contribute to Raman experimental results.…”

A Preliminary Investigation on Human Tears by Means of Surface Enhanced Raman Spectroscopy

“…However, pathological status can alter fluid composition equilibrium, changing the amino acid relative concentrations and the concerned SERS response. For instance, an increase of the branched-chain amino acids Isoleucine, Leucine and Valine levels, potentially detectable by SERS, can be the mark of neuronal diseases [21]. Table 1).…”