Dual Ratiometric electrochemical sensor based on one-step electrodeposited CuNi-NPs modified flexible graphite paper electrode for the detection of adenine in human serum

Adenine, a key purine base in DNA/RNA, is closely associated with diseases like gout, hyperuricemia, and tumors. Herein, a novel dual-ratiometric electrochemical sensor (CuNi-Gp) was fabricated for rapid adenine quantification in human serum via one-step electrodeposition of copper‑nickel nanoparticles (CuNi-NPs) on flexible graphite paper (Gp). CuNi-NPs enhanced adenine accumulation and electron transfer and acted as an internal reference for dual-ratiometric quantification. Two signals were used: a 0.2 V signal from adenine-CuNi-NPs coordination and a 0.9 V signal from adenine oxidation to 2-hydroxyadenine. Both were normalized against Cu 2+ intrinsic signal (j₀) to form j 1 /j 0 and j 2 /j 0 for self-calibration. The sensor showed excellent performance with 6–110 μM linear range, 4.2 μM detection limit (3σ/slope), strong anti-interference, and high selectivity. Spiked human serum tests yielded 97.8 %–102.8 % recoveries and 1.82 %–4.14 % RSDs, confirming accuracy. This work provides a simple, cost-effective sensor with one-step fabrication, dual-ratiometric self-calibration, and serum compatibility, promising clinical use in early diagnosis of adenine metabolism-related diseases.