Sodium Lauryl Sulfate-Conjugated Cationic Gemini-Surfactant-Capped Gold Nanoparticles as Model System for Biomolecule Recognition

Abstract

Surfactant-based nanostructures are promising materials for designing novel colorimetric biosensors based on aggregation/disaggregation phenomena. In this work, a colorimetric sensor based on the plasmonic shift of surfactant-capped gold nanoparticles via the disaggregation mechanism was developed. To perform this, the optimum SDS concentration was firstly determined in order to form Au@16-s-16/SDS complex aggregates with a well-defined SPR band in the blue region. Once the optimal SDS concentration for Au@16-s-16 aggregation was established, the sensing method depended on the nature of the electrostatic charge of the biopolymer studied where both the strength of the biopolymer/SDS and biopolymer/Au@16-s-16 interactions and the cationic gold nanoparticles play a key role in the disaggregation processes. As a result, an instantaneous color change from blue to red was gradually observed with increasing biopolymer concentrations. The response of the sensor was immediate, avoiding problems derived from time lapse, and highly dependent on the order of addition of the reagents, with a detection limit in the nanomolar and picomolar range for DNA and Lysozyme sensing, respectively. This behavior can be correlated with the formation of different highly stabilized Au@16-s-16/biopolymer/SDS complexes, in which the particular biopolymer conformation enhances the distance between Au@16-s-16 nanoparticles among the complexes.