Sensitive Detection of Monoamine Oxidase B Based on Localized Surface Plasmon Resonance Induced by Silver Deposited Gold Nanostar

Human monoamine oxidase (MAO) plays an important role in maintaining the balance of the homeostasis of neurotransmitters and other biogenic amines. Monoamine oxidase B (MAO-B) is one of the isoforms of MAO and its aberrant expression is associated to neurodegenerative diseases closely. Thus, a dual-mode strategy for the detection of MAO-B with dark-field scattering technique and colorimetry was designed by using gold nanostars (AuNSs) as plasmonic nanosensor. In the presence of MAO-B, the substrate benzylamine was oxidized to benzaldehyde. Then the added Tollens’ reagent was reduced to silver by benzaldehyde, and silver deposited on the surface of AuNSs to form AuNSs@Ag. The gradual increase of silver shell changed the morphology of AuNSs, which resulted in strong localized surface plasmon resonance (LSPR) effect. Therefore, with the increase of MAO-B concentration, the scattering light color of individual AuNS varied from red to yellow, and finally to green under the dark-field microscope (DFM). MAO-B was sensitively quantified at the single-particle level based on the obvious blue shift of LSPR scattering peak. Furthermore, as the MAO-B activity increased, the color of the solution changed from blue to purple, and then to yellow, which could be identified by the naked eye, accompanied by the blue shift of the UV absorption peak. Both of the proposed methods could be applied for detecting MAO-B in human serum samples with satisfactory recovery, which holds promising prospects in clinical diagnosis of neurodegenerative diseases.