Continuous and Scalable Production of Uniform Au Nanocrystals Capped by Citrate Species in Flow Reactors for Lateral Flow Tests

Gold (Au) nanocrystals with uniform sizes and shapes are critical for enhancing the sensitivity and reliability of lateral flow tests (LFTs). Herein, a modular platform based on flow reactors for continuous and scalable production of uniform Au nanocrystals, including clusters, small spheres, cubes, and large spheres is reported. It is demonstrated that the one-shot injection method commonly used with batch reactors can be readily adapted for continuous flow reactors, which also allow for on-line monitoring of growth kinetics using UV-vis spectroscopy. The uniform Au nanospheres exhibit narrower localized surface plasmon resonance peaks, greatly enhancing their mass-to-signal conversion ratio and diagnostic sensitivity relative to the Au nanoparticles currently used for commercial LFTs. Upon surface modification with citric acid in a flow reactor, the Au nanospheres show excellent colloidal stability, highlighting their promise for further functionalization and point-of-care diagnostics based on LFTs.