On the stability of microwave-fabricated SERS substrates – chemical and morphological considerations

Abstract

The stability of surface-enhanced Raman spectroscopy (SERS) substrates in different organic solvents and different buffer solutions was investigated. SERS substrates were fabricated by a microwave-assisted synthesis approach and the morphological as well as chemical changes of the SERS substrates were studied. It was demonstrated that the SERS substrates treated with methanol, ethanol, or N,N-dimethylformamide (DMF) were comparable and showed overall good stability and did not show severe morphological changes or a strong decrease in their Raman activity. Toluene treatment resulted in a strong decrease in the Raman activity whereas dimethyl sulfoxide (DMSO) treatment completely preserved or even slightly improved the Raman enhancement capabilities. SERS substrates immersed into phosphate-buffered saline (PBS) solutions were observed to be rather instable in low and neutral pH buffer solutions. Other buffer systems showed less severe influences on the SERS activity of the substrates and a carbonate buffer at pH 10 was found to even improve SERS performance. This study represents a guideline on the stability of microwave-fabricated SERS substrates or other SERS substrates consisting of non-stabilized silver nanoparticles for the application of different organic solvents and buffer solutions.

In Situ and Ex Situ Raman Studies of Cysteine’s Behavior on a Titanium Surface in Buffer Solution

“…It should be noted that the preparation of samples for measurements has a significant impact on the spectral information obtained. Parameters such as the sample's condition [35], type of solvent [48], buffer solutions [49], and pH [30,33,50] can influence the recorded spectra.…”

“…It should be noted that the preparation of samples for measurements has a significant impact on the spectral information obtained. Parameters such as the sample's condition [35], type of solvent [48], buffer solutions [49], and pH [30,33,50] can influence the recorded spectra. The reference Raman spectra for Cys (10 −1 M/PBS) were obtained in solution at a pH from 1 to 7.4 and do not differ significantly from each other.…”

“…The in situ SERS spectra (Figure 1B) obtained under these conditions drastically differ from the respective reference Raman spectra of Cys at the same pH (Figure 1A). At pH 3, 5, and 7.4 the appearance of bands at ~1175 cm −1 and ~1056 cm −1 can be mainly assigned to vibrations due to phosphate groups from the buffer solution [49,51,52]. Moulton et.…”

Surface-Enhanced Raman Spectroscopy Substrate Time Stability Improvement Using an External Oxygen Barrier Method

“…[13][14][15][16] To enhance the stability of the spectra, the core-shell structure is commonly used, in which the substrate is usually covered with a thin protective layer to isolate it from oxygen. 17,18 For instance, Liu et al 19 prepared Ag-titanium (Ti) alloy nanorods using the oblique angle deposition (OAD) method, utilizing the higher chemical activity of Ti to create a Ti oxide film on the surface of Ag and protecting the inner Ag. This approach improved the time stability of the SERS substrate, with experimental results demonstrating that the 2% Ti (atomic) substrate not only had high SERS sensitivity but also remained stable for over a month in air.…”

A Three-Dimensional Hydrophobic Surface-Enhanced Raman Scattering Sensor via a Silver-Coated Polytetrafluoroethylene Membrane for the Direct Trace Detection of Molecules in Water

“…The target molecules in the solution are easily diffused into the non-excited region, resulting in a decreased number of molecules for detection and reducing both the sensitivity and the homogeneity of the device. The construction of a three-dimensional (3D) hydrophobic SERS substrate is more meaningful in the condensation of target molecules [17][18][19][20][21]. Moreover, the 3D structure can expand the interaction volume and total surface area between the local field and the target molecules [22], improving the SERS performance substantially.…”