Ultrasensitive determination of exosomes by tyramine-assisted colorimetric sensors for tumor diagnosis

Exosomes, which are recognized as a kind of valuable liquid biopsy biomarker, exhibit significant application potential in cancer diagnosis. Therefore, it is crucial to establish a reliable detection method for their clinical application. In this study, we presented an ultrasensitive aptasensor for the visual detection of exosomes by employing tyramine-assisted dual signal amplification technology. Firstly, we utilized magnetic beads modified with the nucleolin aptamer (MNPs-Aptnucleolin) to capture exosomes. This modification not only enhanced specificity, but also reduced interference of complex sample components. The captured exosomes as a rich source of proteins could bind with the multiple biotinyl-tyramide (Bio-TR) through a catalytic reaction involving horseradish peroxidase (HRP) and H2O2. Secondly, streptavidin-HRP complex-modified gold nanoparticles (GNPs-Str-HRP) as signal amplification probe was introduced to further enhance the detection signal by binding to Bio-TR. Lastly, the addition of 3,3',5,5'-tetramethylbenzidine (TMB) solution induced a visible color change, enabling the quantification of exosome concentration. This dual signal amplification strategy resulted in a low limit of detection (LOD) of 63 particles/μL, and also demonstrated accurate visual diagnosis capabilities for clinical samples. The successful implementation of this approach suggests its potential as a promising tool for point-of-care testing (POCT) in cancer diagnostics.