An oriented self-assembly biosensor with built-in error-checking for precise midkine detection in cancer diagnosis and prognosis evaluation.

Midkine (MDK) is a neurotrophic growth factor highly expressed during embryogenesis, currently recognized as a multifaceted factor in cancer progression and drug resistance. MDK has demonstrated greater accuracy than existing biomarkers. Serum MDK is a valuable indicator for the non-invasive early detection of tumors. It dynamically changes following surgical tumor excision and prior to recurrence, facilitating prognosis and treatment response evaluation. However, existing methods struggle to achieve the sensitivity required for clinical applications. Herein, we developed a triple-mode biosensor with oriented self-construction and built-in error-checking for rapid, sensitive, and convenient MDK detection. The sensor construction adhered to the principle of achieving oriented and strong covalent connections to ensure high sensitivity. Biosynthesized quantum dots (BQDs) were introduced to orient antibodies, enhancing the exploration of active binding sites and significantly increasing antibody-capturing ability. To further enhance sensitivity and signal amplification, Au@Pt nanorods-Ab2 (MF-Probe) were used as multifunctional probes, incorporating an error-checking mechanism to minimize false results. Detection was feasible using an electrochemical workstation, a microplate reader, and even a mobile phone. The sensor exhibited a wide linear range from 5 fg/mL to 100 ng/mL and a low limit of detection (LOD) of 1.620 fg/mL. It accurately distinguished MDK levels in the serum of healthy donors and cancer patients. Compared to existing ELISA kits, it exhibited a lower LOD and a more sensitive response to trace MDK, suggesting it is a promising tool for cancer diagnosis and prognostic evaluation.