Aptamer-superparamagnetic nanoparticles capture coupling siderophore-Fe3+ scavenging actuated with carbon dots to confer an “off-on” mechanism for the ultrasensitive detection of Helicobacter pylori

The detection of Helicobacter pylori infection in human feces is an appropriate non-invasive diagnostic method. However, the antibody-dependent stool antigen immunoassay bears many challenges. Therefore, we developed an antibody-independent biosensing platform. The core of this platform was a triple-module biosensor. The first module was Ca2+-doped superparamagnetic nanoparticles modified with an H. pylori-specific aptamer, functioning to selectively capture H. pylori cells from samples. The second module was a bifunctional co-polymer of chloroprotoporphyrin IX iron (III)-polyethylene glycol-desferrioxamine, which could bind to H. pylori with high affinity and chelate Fe3+ from the third module of Fe3+-quenched carbon dots (CDs) solution. When the formed module 1-H. pylori-module 2 complexes reacted with module 3, a subsequent magnetic separation could scavenge Fe3+, causing fluorescence recovery from quenched CDs as the transducing mechanism. This transducer could respond to tiny changes in Fe3+ concentration with distinguishable fluorescence differences, thus conferring the biosensor with high sensitivity, a wide detection range of 10–107 CFU/mL and a limit of detection (LOD) as low as 1 CFU/mL. From simulated human stool samples, H. pylori was enriched with a centrifugal microfluidic plate to eliminate any interference from matrices, and the bacteria were subjected to detection using the biosensor. The actual LOD for the biosensing platform coupling microfluidics and the biosensor was 101, and the total time taken was 65 min. This work showcases an instant, accurate, and ultra-sensitive diagnosis of H. pylori in feces.