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 have presented an ultrasensitive aptasensor for the visual detection of exosomes by employing tyramine-assisted dual-signal amplification technology. First, we utilized magnetic beads modified with the nucleolin aptamer (MNPs-Apt_nucleolin) 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 can bind with multiple biotinyl-tyramide (Bio-TR) molecules through a catalytic reaction involving horseradish peroxidase (HRP) and H₂O₂. Second, streptavidin-HRP complex-modified gold nanoparticles (GNPs-Str-HRP) as a 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 quantification of the exosome concentration. This dual-signal amplification strategy resulted in a low limit of detection (LOD) of 63 particles per μL, and it 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.