A Critical Factor for Quantifying Proteins in Unmodified Gold Nanoparticles-Based Aptasensing: The Effect of pH

Abstract

Unmodified gold nanoparticles (AuNPs)-based aptasensing (uGA) assay has been widely implemented in the determination of many different targets, but there are few reports on protein detection using uGA. Here, we designed a uGA assay for protein detection including the elimination of interfering proteins. Positively charged protein can be absorbed directly on the surface of AuNPs to form “protein corona”, which results in the aggregation of AuNPs even without salt addition, thereby preventing target protein detection. To overcome this problem, we systematically investigated the effect of modifying the pH of the solution during the uGA assay. A probe solution with a pH slightly higher than the isoelectric points (pI) of the target protein was optimal for protein detection in the uGA assay, allowing the aptamer to selectively detect the target protein. Three proteins (beta-lactoglobulin, lactoferrin, and lysozyme) with different pI were chosen as model proteins to validate our method. Positively charged interfering proteins (with pIs higher than the optimal pH) were removed by centrifugation of protein corona/AuNPs aggregates before the implementation of actual sample detection. Most importantly, the limit of detection (LOD) for all three model proteins was comparable to that of other methods, indicating the significance of modulating the pH. Moreover, choosing a suitable pH for a particular target protein was validated as a universal method, which is significant for developing a novel, simple, cost-effective uGA assay for protein detection.

Localized Surface Plasmon Resonance as a Tool to Study Protein Corona Formation on Nanoparticles

“…Similar protective observations of proteins in culture media against the aggregation of the Au NPs were shown by Casals et al 22 where PC corona formation was found to be dependent on the size and surface chemistry of Au NPs. Recently, Lu et al 57 observed an influence of the pH of the media in relation to the isoelectric point of the protein on the aggregation of Au NPs following PC formation indicated by LSPR changes observed by UV/vis spectrophotometry. Interestingly, aspherical Au NPs such as Au nanorods (NRs) have two LSPR bands, transversal and longitudinal LSPR bands, that can be tuned on a wider wavelength scale.…”

Carbon Dots Fluorescence-Based Colorimetric Sensor for Sensitive Detection of Aluminum Ions with a Smartphone

“…To simplify the detection procedure, colorimetric sensors based on the nanoparticles have attracted considerable attention due to their instant, low-cost, and visual identification characteristics [6,7]. For example, Joshi et al reported a sensitive and selective colorimetric probe for Al 3+ by using indole-2-carboxylic acid capped sliver nanoparticles (AgNPs) [8].…”