Sensitive Plasmonic ELISA Assay Based on Butyrylcholinesterase Catalyzed Hydrolysis for the Detection of Staphylococcus Aureus

Enzyme-linked immunosorbent assay (ELISA) is one of the most powerful techniques for biomolecule detection, but suffers from insufficient sensitivity and relatively tedious operation. In this paper, we present a highly sensitive ELISA approach for Staphylococcus aureus (S. aureus) determination. S. aureus is first captured by vancomycin (Van) and butyrylcholinesterase (BChE) co-functionalized magnetic beads (MBs), and then immo-bilized on a 96-well plate through the binding with the precoated IgG. Afterwards, gold nanoparticles (AuNPs) and butyrylthiocholine (BTCh) are added, allowing BChE to catalyze BTCh into thiocholine (TCh). The presence of TCh triggers the aggregation of AuNPs, resulting in distinct color change from red to purple. Therefore, a sensitive quantification method for S. aureus can be developed based on the correlation between the amount of S. aureus and the color change of AuNPs. Under optimal conditions, naked eye detection can be realized at S. aureus down to 100 CFU mL(-1). A limit of detection of 5 CFU mL(-1) can be reached with microplate reader measurement, along with a dynamic range of 5-102 CFU mL(-1) and 10(2)-10(7) CFU mL(-1). The system is selective towards S. aureus and shows resistance to other bacteria. By taking advantage of the high sensitivity of enzymatic reaction and AuNPs-based colorimetric method, this method greatly improves the dynamic range and sensitivity, providing alternative approach for the sensitive detection of S. aureus.