Self-assembled protein-enzyme nanoflower-based fluorescent sensing for protein biomarker.

Multi-protein (or enzyme) conjugates play a vital role in biosensing due to the integrated function of each component, such as biological recognition and signal amplification. In this work, a green self-assembled method for the synthesis of multi-functional protein-enzyme nanoflowers has been developed, in which no chemical modification and coupling reaction is needed to fabricate the fluorescent signal probe. The self-assembled protein-enzyme conjugates streptavidin (SA) -β-galactosidase (β-Gal)-CaHPO4 nanoflowers load sufficient enzymes without damaging their activity, which meets the requirements of signal tags for biosensing. Through integrated multi-function of biorecognition (SA) and signal amplification (β-Gal), the SA-β-Gal-CaHPO4 hybrid nanoflower-based fluorescent sensor exhibited an ultrasensitive detection of protein biomarker alpha-fetoprotein (AFP), with limits of detection at the fM level. The presented self-assembled strategy can be extensively applied to develop on-demand protein-enzyme conjugates according to the specific requirements in a variety of applications including biosensors, bioimaging, and biomedicine. Graphical abstract A self-assembled method has been presented for the facile and green synthesis of SA-β-Gal-CaHPO4 nanocomplexes with flower-like shape and high activity, and further employed as signal tag for fluorescent sensing of protein biomarker.