Potential Regulation for Surface-Enhanced Raman Scattering Detection and Identification of Carotenoids

Abstract

Surface-enhanced Raman scattering (SERS) is often impaired by the limited affinity of molecules to plasmonic substrates. Here, we use carbon fiber microelectrodes modified with silver nanoparticles as a plasmonic microsubstrate with tunable affinity for enrichment and molecular identification by SERS. The silver nanoparticles self-assemble by electrostatic interaction with diamine molecules that are electrochemically grafted onto the surface of the microelectrodes. β-carotene and trans-β-Apo-8′-carotenal, producing similar resonant SERS spectra, are employed as model molecules to study the effect of electroenrichment and SERS screening for different electrode potentials. The data show that at a characteristic electrode potential, the low affinity of polyene chains without hydrophilic groups to the substrate can be overcome. Different potentials were applied to recognize the two types of carotenoids by their typical SERS signal, and the applicability of this strategy was further confirmed in the environment of a real cell culture. The results indicate that by regulating the potential, carotenoid molecules with a similar molecular structure can be selectively quantified and identified by SERS. The developed SERS-active microelectrode is expected to help the development of portable, miniaturized point-of-care diagnostic SERS sensors.

Electrodeposition of Silver Nanostructures in Ethanol for Sensitive Electrochemical SERS Detection

“…In our sample, the bands in the SERS spectra of the CFME can be attributed to the narrow symmetric G peak at 1608 cm –1 , the D band at 1396 cm –1 , and other typical vibrations assigned to amorphous carbon at 1128 cm –1 , at 926 cm –1 , indicating sp 2 hybridization, and at 854 cm –1 . − The spectra of the two carotenoid molecules were collected at an electrode potential of 0 V (Figure a black and purple trace). Both spectra display three typical Raman bands of carotenoid molecules, the band at 1525 cm –1 of the CC stretching vibration, the C–C stretching vibration at 1160 cm –1 , and the methyl rocking vibration at 1007 cm –1 , supporting our results obtained with silver nanoparticles that we immobilized on the CFME by linker molecules previously …”

“…Both spectra display three typical Raman bands of carotenoid molecules, the band at 1525 cm −1 of the C�C stretching vibration, the C−C stretching vibration at 1160 cm −1 , and the methyl rocking vibration at 1007 cm −1 , 14 supporting our results obtained with silver nanoparticles that we immobilized on the CFME by linker molecules previously. 12 In agreement with the changes in density and morphology of the deposited silver nanostructures for different electrodeposition times (cf. Figures 1a−e and 2a), the SERS signal of trans-β-Apo-8′-carotenal (10 −7 M) at the same applied potential varies by a factor of ∼14 for the different samples, with the optimum signal being obtained for 2 min (Figure S6a).…”

“…Therefore, it could become the basis of fabrication technologies to control silver nanoparticle electrodeposition. Different from previous systems that involve the grafting of preprepared silver nanostructures by additional molecules onto the CFME, 12 leading to potential interference and impairment of stability of the nanostructures, the high stability of the plasmonic sensor and the high signal enhancement provide improved optical detection with metal-functionalized microelectrodes. CFME-dAg provide a high enhancement of resonant Raman signals of carotene species.…”

“…15 In previous work, we have demonstrated the possibility to immobilize ex situ produced silver nanoparticles by molecules that we grafted electrochemically onto the CFME surface. 12 Nevertheless, avoiding potential interference by the additional molecular species that act as linkers of silver nanoparticles 12 would be highly desirable, in order to obtain a very pure twocomponent composite electrode.…”

“…CFMEs have many unique features, such as outstanding chemical inertness, and mechanical and electrical properties that make them the ideal base electrodes for use in analytical applications . In previous work, we have demonstrated the possibility to immobilize ex situ produced silver nanoparticles by molecules that we grafted electrochemically onto the CFME surface . Nevertheless, avoiding potential interference by the additional molecular species that act as linkers of silver nanoparticles would be highly desirable, in order to obtain a very pure two-component composite electrode.…”