Exosomes are cell-derived nanovesicles that have recently gained popularity as potential biomarkers in liquid biopsies due to the large amounts of molecular cargo they carry, such as nucleic acids and proteins. However, most existing exosome-based analytical sensing methods struggle to achieve high sensitivity and high selectivity simultaneously.
Researchers from Duke University have developed an electrochemical micro-aptasensor for the highly sensitive detection of exosomes by integrating a micropatterned electrochemical aptasensor and a hybridization chain reaction (HCR) signal amplification method. Specifically, exosomes are enriched on CD63 aptamer-functionalized electrodes and then recognized by HCR products with avidin-horseradish peroxidase (HRP) attached using EpCAM aptamers as bridges. Subsequently, the current signal that is generated through the enzyme reaction between the HRP enzyme and 3,3’,5,5’-tetramethylbenzidine (TMB)/H2O2 directly correlates to the amount of bound HRP on the HCR products and thus to the number of target exosomes. By introducing anti-EpCAM aptamers, micro-aptasensors can detect cancerous exosomes with high specificity. Due to the micropatterned electrodes and HCR dual-amplification strategy, the micro-aptasensors achieve a linear detection response for a wide range of exosome concentrations from 2.5×103 to 1×107 exosomes/mL, with a detection limit of 5×102 exosomes/mL. Moreover, this method successfully detects lung cancer exosomes in serum samples of early-stage and late-stage lung cancer patients, showcasing the great potential for early cancer diagnosis.
Schematics illustrating the mechanism of electrochemical micro-aptasensors
based on hybridization chain reaction (HCR)
a Procedures for preparing biotin-labeled HCR exosomes. b, top Modification of microelectrodes with CD63. b, bottom A photo of a fabricated electrochemical micro-aptasensor with CD63-modified electrodes and a microfluidic chamber. c The working mechanism of electrochemical micro-aptasensors.