Ag2S quantum dots loaded dendritic mesoporous silica nanospheres as signal amplification labels for ultrasensitive electrochemical immuno-biosensor for Staphylococcus aureus

Developing novel signal amplification labels in electrochemical immuno-biosensors for ultrasensitive, fast and selective detection of foodborne pathogen is urgent and significant for people's health and life safety. Herein, dendritic mesoporous silica nanospheres (DMSNs) loaded with silver sulfide quantum dots (Ag2S QDs) were fabricated and employed as signal amplification labels for highly sensitive electrochemical detection of Staphylococcus aureus (S. aureus). DMSNs were treated with 3-aminopropyltrioxysilane to introduce amino group on surfaces to facilitate the immobilization of Ag2S QDs. Benefiting from the highly accessible surface areas and large pore channels characteristics given by the unique radial flower-like structure of DMSNs, large amount of Ag2S QDs were loaded into the surfaces and pores of the DMSNs to form Ag2S/DMSNs. To specifically recognize S. aureus cells, Ag2S/DMSNs were modified by anti-S. aureus antibody (Ab) to form Ab-Ag2S/DMSNs. When the sandwich-type electrochemical immuno-biosensor operated, Ag(Ⅰ) ions were released from the Ag2S/DMSNs label by HNO3 leaching, and the detection of S. aureus was realized by the differential pulse voltammetry. The electrochemical signal of the prepared immuno-biosensor was substantially magnified when compared to the immuno-biosensor employing Ag2S QDs as signal label, since much more Ag2S QDs were labeled to each bacterial cell due to the high loading of Ag2S QDs on the DMSNs. As a consequence, the developed immuno-biosensor was capable of detecting S. aureus cells down to a limit of 2 colony forming units per mL (CFU mL−1) and exhibited a wide linear detection range from 10 CFU mL−1 to 108 CFU mL−1. In addition, the immuno-biosensor showed excellent selectivity and stability for the detection of S. aureus, and was successfully applied to detected S. aureus in milk samples.