β-Lactoglobulin amyloid fibril-templated gold nanoclusters for cellular multicolor fluorescence imaging and colorimetric blood glucose assay

beta-Lactoglobulin amyloid fibril (BLGF)-capped gold nanoclusters (Au NCs) with red, green and blue emissions were fabricated via pH-dependent reduction strategy. The BLGF-Au NCs exhibited 3.2 times enhancement of fluorescence (lambda(ex) = 500 nm, lambda(em) = 684 nm), a significant 42 nm red shift, a 11.57% quantum yield and a 1.4 mu s decay time compared with native beta-lactoglobulin (BLG)-stabilized Au NCs. Meanwhile, the multicolor Au NCs were employed for cell imaging via incubation with A549 cells for 14 h. According to the Michaelis-Menten equation, the kinetic parameters of the BLGF-Au NCs showed a lower K-m value (66 mu mol L-1) for 3,3,5,5-tetramethylbenzidine (TMB) and a higher v(max) (3.74 x 10(-8) M s(-1)) for H2O2, which are comparable with other artificial nanoenzymes and natural peroxidases. Based on the highly intrinsic peroxidase-like activity of the BLGF-Au NCs, a colorimetric method was developed for glucose determination with a detection limit of 1.5 mu mol L-1 by determining the variation of the absorption at 652 nm, ranging from 5 to 100 mu mol L-1. In addition, the glucose assay method also revealed a 101.02 to 104.16% recovery in a real human serum sample.