Signal amplification surface-enhanced Raman scattering immunosorbent assay of human chorionic gonadotrophin based on repeated enzyme biocatalytic precipitation

Abstract

A novel surface-enhanced Raman scattering (SERS) immunoassay method based on tyramine signal amplification (TSA) technology triggering the formation of enzyme repeats on an enzyme-linked immunosorbent assay (ELISA) was designed for...

Highly Sensitive Measurement of Horseradish Peroxidase Using Surface-Enhanced Raman Scattering of 2,3-Diaminophenazine

“…Although we have claimed that our main goal is the optimization of SERS measurements of DAP, this procedure is dependent on the conditions of the preceding enzymatic reaction. SERS spectra with AgNPs were previously reported for both oPD [ 15 , 27 , 37 , 38 ] and DAP [ 15 , 27 , 31 , 32 ], implying that they both have some affinity for the silver surface, so during the SERS measurements, they compete for binding to the metal. Thus, our goal could be refined as a search for conditions that favor the binding of small quantities of enzymatically formed DAP over the excess of unreacted oPD.…”

“…Surface-enhanced Raman scattering (SERS) is also a promising candidate that meets the requirement of high sensitivity. Indeed, a SERS-based ELISA is a growing area in analytical chemistry that is gradually accumulating a range of available approaches as well as a number of successful applications [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ] (see also reviews [ 21 , 22 ]).…”

“…In other words, the product should have both a high Raman scattering cross-section and a high affinity for the metal surface used for enhancement. Several substrates have been tested up to date: o -phenylenediamine (oPD) [ 14 , 15 , 23 , 24 , 25 , 26 , 27 , 28 ], 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) [ 16 ], 3,3′,5,5′-tetramethylbenzidine (TMB) [ 17 , 18 , 19 ], and leuco dyes [ 11 ]. Among these, oPD appears to be the most promising.…”

“…Secondly, this reaction is not a simple oxidation, but rather, an oxidative dimerization, leading to substantial differences in the chemical structures, and hence, in the vibrational spectra of the substrate and the product. It has also been previously shown that all forms of DAP (neutral DAP, protonated DAPH + , and doubly-protonated DAPH 2 2+ ) exhibit intense SERS spectra with silver nanoparticles [ 15 , 27 , 31 , 32 ]. Finally, both oPD and DAP are commercially available, which is not relevant for the assay but greatly simplifies the research, as model solutions of both substances and their mixtures may be easily prepared and studied.…”

“…In order to achieve a high sensitivity, the conditions for both steps should be optimized. While several examples of enzymatic reaction optimization have been described previously for colorimetric- [ 33 , 34 , 35 ] and SERS-based measurements [ 15 ] of HRP with the oPD substrate, no studies have focused on understanding and refining the SERS detection procedure. For the first time, the current paper addresses this issue.…”