A capacitance biosensor for prostate cancer detection via normalised urinary extracellular vesicles

Extracellular vesicles (EVs), and in particular exosomes, play an important role in intercellular communication and can be found in biological fluids. Inevitably, EVs have emerged as promising biomarkers for cancer diagnosis. Detecting EVs in urine is less invasive than blood. However, reliable EV quantitation in urine is still challenging due to low EV concentration and lack of standardisation. Herein, we introduce a capacitance-based electrochemical biosensor for two EV markers, CD63 and prostate-specific membrane antigen (PSMA) - the former being a generic marker present in all exosomes and the latter a prostate cancer (PCa) marker. Integrating a capacitance technique (non-Faradaic impedance) provides highly sensitive and reagent-free technique capabilities ideal for point-of-care diagnosis. For the sensor fabrication, both thiolated CD63 and PSMA aptamers were self-assembled on reduced graphene oxide and molybdenum disulfide (rGO/MoS₂) modified screen-printed carbon electrodes (SPCE). The results can be obtained in 10 min using 10 μL from EVs isolated sample. Under optimal conditions, the associated PSMA and CD63 detection limits are 4.83 × 10² and 1.47 × 10³ EV/μL, respectively, without any additional signal amplification steps. To validate the sensor, urinary EV samples were analysed using the sensor. The results showed a strong correlation with a commercial PSMA ELISA. Additionally, the PSMA/urine creatinine (uCRE) level can differentiate between PCa patients from healthy controls, indicating its applicability as a non-invasive diagnosis tool. Overall, the developed sensor provides a simple, fast, reagent-free, and more reliable detection technique for urinary EVs detection to improve PCa diagnosis.