Comparative study of the surface enhanced near infrared Raman spectra of adenine and NAD+ on a gold electrode

Electrochemical TERS Elucidates Potential‐Induced Molecular Reorientation of Adenine/Au(111)

“…[26,27,29] Thefirst peak can be attributed to an increase in capacitance as ar esult of the molecular reorientation from ap hysisorbed tilted arrangement to av ertical geometry around the potential of zero charge, [37] such that more Au surface is exposed to the adenine-free electrolyte,i na greement with previous studies. [25,27,38] Thes econd peak at around 0.6 Vr esults from deprotonation and partial charge transfer from adenine to the Au electrode (around 0.68 electrons per molecule as determined by Aldaz and coworkers [39] ). [25,27,38] Note that oxidation of adenine to its oxo forms occurs at potentials higher than 1.2 Voutside our potential window.…”

“…[25,27,38] Thes econd peak at around 0.6 Vr esults from deprotonation and partial charge transfer from adenine to the Au electrode (around 0.68 electrons per molecule as determined by Aldaz and coworkers [39] ). [25,27,38] Note that oxidation of adenine to its oxo forms occurs at potentials higher than 1.2 Voutside our potential window. [40,41] Importantly,the CV was identical before and after the EC-TERS experiment, that is,a fter ramping up to 1.2 Vs everal times,i ndicating that (partial) Au oxidation does not alter the behavior of adenine at the electrode (Supporting Information, Section 2).…”

“…Thesignificant blue-shift from 245 to 274 cm À1 can be attributed to as trengthening of the Au À Nb ond with increasing potential, that is,anincreasing interaction between the Nlone pairs and the metal d*-band that results in aplanar orientation of adenine.C oordination of neutral adenine through the amino group N10 and N1 at potentials above the anodic peaks in the CV is consistent with all observed trends.T he lack of the Au À Nmode at potentials below 0.6 V is in line with weakly physisorbed adenine in which the monolayer is stabilized by p-d* adsorbate-substrate or p-p intermolecular interactions at potentials below or around 0.3 V, respectively. [25,30,32] Figure 4summarizes the adsorption/ reaction model of the potential-dependent, reversible adenine (de)protonation and reorientation as deduced from our EC-TERS results.…”

“…Given the importance of understanding the interactions between DNA bases and noble metals for biosensing applications and for the development of biocompatible materials, [22,23] it is surprising that the DNAbase orientation with respect to the Au surface (for example,upright, tilted, or flat) and the chemical state of the DNAb ase (for example,( de)protonated or anionic) has remained ap oint of controversy,d espite extensive efforts to characterize the system with traditional cyclo-voltammetric (CV) approaches in combination with SPM or (ensemble) spectro-electrochemistry. [24][25][26][27][28][29][30][31][32] EC-TERS offers the unique advantage of placing the near-field probe at alocation of interest chosen according to the SPM topographic information gathered simultaneously,in contrast to EC-SERS and EC-SEIRAS studies in which substrate roughness leads to an inherent variation of the geometry of the surface adsorption sites and thus to ab road distribution of probed molecular adsorption geometries.Our approach thus enables selective monitoring of potentialdependent TER spectral changes from less than 100 adenine molecules adsorbed onto aA u(111) terrace with uniform adsorption geometry in which an averaging effect from different substrate/adsorbate geometries is limited. We complement the experimental EC-TERS results with density funcitonal theory (DFT) gas-phase approximations for data analysis and interpretation.…”

Silver-Based SERS Pico-Molar Adenine Sensor

“…In most reported cases, adenine molecules adsorb on silver metal at a tilted angle to the surface [ 11 ]. Some planar adsorption was also reported [ 12 ]. The signal strength of a specific SERS vibration mode and frequency depends on the alignment of the molecular structure with the exciting electromagnetic fields.…”