Experimental parameters for the SERS of nitrate ion for label‐free semi‐quantitative detection of proteins and mechanism for proteins to form SERS hot sites: a SERS study

Abstract

We have explored the effects of the experimental parameters on the surface-enhanced Raman scattering (SERS) intensities of NO 3 − and proteins observed by a heat-induced SERS method developed by our group. The results have shown that a strong SERS signal can be obtained at pH 4.0, using an Ag colloid prepared with the reduction time of 15 min (the average size of Ag nanoparticle is 56.5 nm) dilution prepared Ag colloid by a factor of 2 by use of a 5 mM citrate buffer, using 6 mM NaNO 3 and drying the sample at 100 • C, respectively. Based on the results, two possible mechanisms for proteins to form SERS hot sites during the sample preparations are proposed. A semi-quantitative SERS detection of ribonuclease B has been investigated. Also, NaNO 2 , Mg (NO 3 ) 2 , MgSO 4 and Na 2 SO 4 have been found to be suitable for the heat-induced SERS method. Importantly, samples prepared by the heat-induced SERS method are so stable that these samples can be used as a standard and transferred to different laboratories for direct comparison. Namely, it can overcome uncontrollable aggregation of Ag colloids in a solution sample. All these advantages and the simplicity of experimental setup have demonstrated that the heat-induced SERS method using NaNO 3 as an electrolyte is very promising for label-free routine and quantitative detection of proteins.

Suitability of Ag‐agar gel for the micro‐extraction of organic dyes on different substrates: the case study of wool, silk, printed cotton and a panel painting mock‐up

“…With respect to the previous work, no red shift of the absorption spectrum was noticed after the addition of EDTA and after the heating of the gel/nanoparticles system by microwave. This experimental result might be explained by the fact that the chelating agent EDTA stabilizes the silver nanoparticles so that they do not further nucleate after the heating process . More specifically, EDTA, coating the AgNps, is chemisorbed onto the surface by means of carboxylate groups.…”

“…In brief, 0.2 g of agar–agar in flakes (analytical grade) were mixed in a beaker with 0.1 g of EDTA (Fisher Scientific) and 10 ml of silver colloid. The colloidal solution used for the synthesis of Ag‐agar gel was prepared according to the Lee–Meisel procedure . In particular, after a reduction time of 60 min, the flask containing the colloid was put into an ice‐bath to cool down, instead of being cooled at room temperature.…”

Influence of applied potential on bradykinin adsorption onto Ag, Au, and Cu electrodes

“…This information could be obtained through the use of surface‐enhanced Raman spectroscopy (SERS). The SERS technique has been applied across a wide spectrum of research areas, including electrochemistry, surface science, technology, biological, and biomedical sciences, to successfully detect and identify different biological molecules, such as nucleic acids, amino acids, peptides, and proteins, under physiological conditions (i.e. aqueous environments, low sample concentrations, and a pH of approximately 7).…”

SERS detection of red organic dyes in Ag‐agar gel

“…Due to the dependence of nanoparticles size on the reduction time of Ag + , both the UV–Vis absorption spectra and the TEM images of the Ag‐colloid were acquired (Fig. a–b) to evaluate the size of the nanoparticles obtained.…”

“…In particular, after a reduction time of 60 min, the flask containing the colloidal solution was placed in an ice bath to cool. This prompt cooling process of the colloidal dispersion has been adopted in order to obtain a wider distribution of nanoparticle sizes having an average diameter of about 40 nm . Prior to being used for the gel synthesis, no aggregation salts have been added to the colloid.…”