An easy and sensitive sandwich assay for detection of Mycobacterium tuberculosis Ag85B antigen using quantum dots and gold nanorods

• Fluorescence quenching detection system using quantum dots and gold nanorods.
• Sandwich Ag-Ab interaction to detect active Tuberculosis (TB) antigen.
• Sensitive detection of secretory antigen, Ag85B, from Mycobacterium tuberculosis.
• The limit of TB detection was 13 pg mL−1 within 1 h in patient urine samples.

Mycobacterium tuberculosis is a serious global infectious pathogen causing tuberculosis (TB). The development of an easy and sensitive method for the detection of M. tuberculosis is in urgent need due to complex and low specificity of the current assays. Herein, we present a novel method for M. tuberculosis detection based on a sandwich assay via antigen-antibody interaction using silica-coated quantum dots (SiQDs) and gold nanorods (AuNRs). A genetically engineered recombinant antibody (GBP-50B14 and SiBP-8B3) was bound to surfaces of AuNRs and SiQDs respectively, without any surface modification. The antigen-antibody interaction was revealed using M. tuberculosis-specific secretory antigen, Ag85B. Two biocomplexes showed a quenching effect in the presence of the target antigen through a sandwich assay. The assay response was in the range of 1×10−3–1×10−10 μg mL−1 (R=0.969) and the limit of detection for Ag85B was 13.0 pg mL−1. The Ag85B was selectively detected using three different proteins (CFP10, and BSA), and further specifically confirmed by the use of spiked samples. Compared with existing methods, a highly sensitive and selective method for Ag85B-expressing M. tuberculosis detection has been developed for better diagnosis of TB.