Addressing Cu2+ interference for accurate aptamer-based biomarker determinations of Alzheimer's disease

Aptamers are widely used as a recognition element for Alzheimer's disease (AD)-related biomarker determinations. Due to the existing Cu2+ in real samples, and its possible coordinations with aptamers and biomarkers, the aptamer-based biomarker determination could be seriously disturbed. In this work, taking A beta(40) oligomer (A beta O-40, a typical biomarker for AD) as a model, the interference of Cu2+ in the interaction between A beta O-40 and its aptamer (Apt) was investigated by surface plasmon resonance spectroscopy. The results demonstrated the binding of Cu2+ to Apt, resulting in significant changes on the original structure of Apt, and the affinity of Apt to A beta O-40. The affinity of Apt-Cu2+/A beta O-40-Cu2+ (K-d: 1.36 mu M) was 17 times weaker than that of Apt/A beta O-40 (K-d: 0.08 mu M), which induced a poor dynamic range in the Cu2+-involved A beta O-40 determination. The analysis of A beta O-40-spiked real samples revealed that the existing Cu2+ resulted in significant positive errors in CSF analysis, but also complicated errors in serum analysis that depended on the blood collection. Further studies confirmed that EDTA can completely chelate Cu2+ from Apt-Cu2+ and A beta O-40-Cu2+, eliminating the interference of Cu2+ on the A beta O-40/Apt system. Therefore, excess EDTA is highly recommended for Apt-based CSF and blood analysis, even if the samples are from EDTA- or other metal ion chelating agent-involved collection tubes. This work quantitatively revealed the interference of Cu2+ and provided a simple but effective approach to eliminate the interference, which will improve the existing method to achieve accurate Apt-based biomarker detection in real samples.

Automated summary

This study investigated the interference of Cu2+ in the interaction between A beta(40) oligomer (A beta O-40) and its aptamer (Apt) using surface plasmon resonance spectroscopy. The results showed that Cu2+ binding to Apt resulted in changes to its structure and affinity for A beta O-40. Real sample analysis revealed significant errors caused by Cu2+ in cerebrospinal fluid (CSF) and serum analysis. Further studies demonstrated that EDTA can eliminate the interference of Cu2+ on the A beta O-40/Apt system.