Synthesis of On-Demand Gold Nanoparticles with Precision Morphologies through an Automatic Feedback Control Quenching System

Gold nanoparticles (Au NPs) with diverse morphologies have attracted considerable interest due to their unique optical and catalytic properties. Here, we present a Cuvette-based Absorbance Real-time Tracking and Quenching (CART-Q) system for synthesizing Au NPs with precise morphologies via closed-loop feedback control based on ultraviolet–visible (UV–vis) absorbance. By finely tuning the injection of ascorbic acid (AA) as a reducing agent, we observed distinct shifts in UV–vis spectra corresponding to morphological changes in the Au NPs, evident through color transitions from pink to purple, blue, and gray. The CART-Q system comprises two key components: an in situ detection unit for real-time absorbance monitoring and an automated quenching unit, where a solenoid actuator dispenses the quenching solution in response to algorithmic commands. In seed-mediated synthesis, Au NPs evolve from spherical to star-like shapes, accompanied by absorbance shifts from 520 to 860 nm. CART-Q continuously tracks the absorbance peak and halts nanoparticle growth at the target wavelength by introducing a quenching solution, enabling the desired morphology to be achieved in a single experiment. We further evaluated the catalytic activity of the synthesized Au NPs in the reduction of 4-nitrophenol, finding that those with longer spikes exhibited superior performance, completing the reaction in just 98 s. The CART-Q platform thus enables efficient, high-precision synthesis of nanomaterials.