Rational Synthesis of Uniform Au Nanospheres under One-Shot Injection: From Mechanistic Understanding to Experimental Control

Gold nanospheres with uniform sizes greater than 30 nm are essential to quantitative lateral flow immunoassays for the rapid detection of pathogens such as viruses, bacteria, and fungi. However, scaling up their synthesis for commercial applications remains challenging due to the necessity to introduce the precursor dropwise. Herein, we report the synthesis of Au cubes with an edge length of 30 nm using one-shot injection of the precursor, followed by aging to transform the cubes into uniform spheres of 35 nm in diameter. Our mechanistic study based on qualitative and quantitative analyses using surface-enhanced Raman scattering and inductively coupled plasma mass spectrometry, respectively, suggests that Br^- desorption from the surface of Au nanocubes at an elevated temperature was responsible for the shape transformation by inducing oxidative etching and atomic migration in the outermost layer. By eliminating the need for dropwise addition, this protocol is well-suited for the mass production of Au nanospheres in a continuous flow reactor for future incorporation into quantitative point-of-care sensors.