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The control of nanoparticle morphology can effectively change their properties. Adjusting the aggregation state of bovine serum albumin-coated gold nanoclusters (BSA-Au NCs) can regulate the enzyme-mimicking catalytic activity. Hyaluronic acid (HA) induces the aggregation of BSA-Au NCs, leading to the shielding of the catalytic active sites and a decrease in activity; this feature has been utilized to design a multicolor biosensor for hyaluronidase (HAase). The presence of HAase can hydrolyze the glycosidic bonds in HA, causing the aggregated BSA-Au NCs to disperse and express their catalytic activity, which in turn catalyzes the etching of Au nanobipyramids (Au-NBPs) in the presence of 3,3′,5,5′-tetramethylbenzidine (TMB), resulting in a morphological transition from bipyramidal to ellipsoidal and spherical shapes, while the solution displays a variety of colors. Visual recognition of these multicolor changes establishes a relationship between the enzyme activity and color. Based on the controlled aggregation and dispersion of BSA-Au NCs and the etching of Au-NBPs, a simple multicolor HAase biosensor was designed. The proposed biosensor shows a linear response to HAase concentrations in the range of 5–80 U/mL, with clear color changes under optimized conditions. The limit of detection (LOD) of the sensor was determined to be 1.98 U/mL (LOD = 3s/k). This method successfully applies the changing of enzyme-mimicking catalytic activity nanoparticles for colorimetric analysis detection. [ABSTRACT FROM AUTHOR]

11-Mercaptoundecanoic acid-protected gold nanoclusters (Au@MUA NCs) were synthesized and investigated as a model to understand the photoluminescence (PL) properties of water-soluble, structurally unknown Au NCs. Surface engineering, including ligand exchange where the length of the alkane chain was changed, ligand conjugation where the charged terminal carboxyl group of the ligands was blocked, and effects of external chemical reducing and oxidizing agents, was carried out. PL profiles were monitored to reveal the impact of surface engineering on the PL. We found that surface ligands, especially the ligand's length and ligand functionalities, play a significant role in the PL properties of Au@MUA NCs. The results also show interesting properties of these NCs as a tunable PL sensor. [ABSTRACT FROM AUTHOR]