Oxygen Vacancy-Rich Amorphous BiVO₄ Nanoparticles for Colorimetric Sensing

Defects in crystalline nanozymes play a critical role in enhancing their performances and related catalytic events. However, creating a high concentration of active and robust defects in well-explored crystalline metal oxides to achieve high-performance single-enzymatic activity is challenging. Herein, amorphous BiVO₄ beyond traditional crystalline nanozymes is prepared via a facile solution-processed coprecipitation method favorable to large-scale manufacturing to mimic enzymatic properties. As expected, the specially designed amorphous material without any post-treatments has sufficient and robust oxygen vacancies, which are highly active in converting oxygen to reactive radicals (O₂^–•). Simultaneously, the negatively charged surface has a high affinity for the substrate, facilitating charge transfer between materials and substrates and, in turn, providing higher catalytic efficiency compared to the crystalline counterparts. Most importantly, the sample can only mimic oxidase-like activity rather than the multienzyme-like activity generally observed in most reported crystalline metal oxides, which is a step forward in the development of nanozymes. This amorphous BiVO₄-based system is also evaluated for the sensitive and selective detection of l-cysteine. The study provides insight into nanozyme development and highlights the great potential of amorphous materials in addition to amorphous BiVO₄.