Heterogemini surfactant assisted synthesis of monodisperse icosahedral gold nanocrystals and their applications in electrochemical biosensing

Icosahedral nanocatalysts (NCs) have shown very interesting physical and chemical properties owing to their multiply twinned nanostructures. Herein, we introduce a novel heterogemini surfactant (C₁₀OhpNC₈) assisted seed mediated growth approach for the synthesis of monodisperse icosahedral gold (Au) NCs in aqueous solution at room temperature. Very small shape impurities were observed in the resultant icosahedral Au NCs. Significantly improved monodispersity (relative standard deviation (RSD) of <10%) has been achieved by using a binary mixture of C₁₀OhpNC₈ and PVP as structure directing agents. Interestingly, the size of icosahedral Au NCs can be tuned ranging from 40 nm to 190 nm, which guides the surface plasmon resonance (SPR) peak to be tuned throughout the whole visible region and even to the near infrared (NIR) region. Furthermore, the developed icosahedral Au NCs specific probe has been designed to be applied as an easy electrochemical biosensor and successfully used to detect the bacteria Escherichia coli O157:H7 (E. coli O157:H7) with a detection limit of ∼10 colony forming units (CFU) mL^-1. Notably, a much higher sensitivity of these icosahedral Au NCs probes has been achieved compared to the traditional colloidal gold immunochromatography (detection limit ∼10³ CFU mL^-1).