Directed self-assembly of Ag + -deposited MoS 2 quantum dots for colorimetric, fluorescent and fluorescence-lifetime sensing of alkaline phosphatase

We developed a triple-readout probe for colorimetric, fluorescent, and fluorescence-lifetime sensing of alkaline phosphatase (ALP) through the hydrolyzed ascorbic acid phosphate (AAP)–mediated formation of silver nanoparticles (AgNPs) on Ag + -deposited MoS 2 quantum dots (QDs). Ag + ions were self-assembled on a monolayer MoS 2 QD surface through the formation of Ag–S bonds. When ALP hydrolyzed AAP in an alkaline buffer, the resultant ascorbic acid (AA) triggered the reduction of the bound Ag + ions into AgNPs on the MoS 2 QD surface. The resultant AgNPs induced an efficient fluorescence quenching of the MoS 2 QDs through simultaneous static and dynamic quenching processes, generated an intense surface plasmon resonance peak, and triggered a reduction in the fluorescence lifetime of the MoS 2 QDs. Electron microscopy and spectroscopic techniques revealed the successful fabrication of Ag + -deposited MoS 2 QDs and the ALP-mediated formation of AgNPs on the MoS 2 QD surface. The linear quantification ranges for ALP were 0.05–2.5, 0.1–4, and 1–4 units L −1 in the fluorescent, colorimetric, and fluorescence-lifetime detection modes, respectively. In addition, the proposed probe integrated with an ALP-linked sandwich immunoassay exhibited high sensitivity and selectivity for the fluorescence sensing of rabbit immunoglobulin G with a detection limit of 8 pg mL −1 and linear range of 25–1000 pg mL −1 . The sensitivity of the probe is comparable to those of previously reported immunoassays involving ultrasensitive electrochemical detection, hydrogen evolution reactions, or electron spin resonance. The probe integrated with the sandwich assay serves as a promising platform for the detection of target proteins in clinical samples. Graphical abstract