A selective off–on fluorescent aptasensor for alpha-fetoprotein determination based on N-carbon quantum dots and oxidized nanocellulose

• Development of a sensitive and selective method for determination of AFP. • Apt@NCQDs as a molecular recognition probe, and oxidized NCs as a quencher. • Apt@NCQDs & oxidized NCs as a selective aptasensor for quantification of AFP. • Application of designed aptasensor for direct determination of AFP in human serum samples. • An off–on aptasensor for the determination of AFP based on fluorescence resonance energy transfer. A selective off–on aptasensor was designed to measure tumor marker alpha-fetoprotein (AFP). Nitrogen carbon quantum dots modified with aptamer was synthesized. The addition of oxidized nanocellulose to this system causes quenching of the fluorescence intensity. But in the presence of AFP, the aptamers bind strongly with AFP, resulting in the release of oxidized nanocellulose and an increase in the fluorescence intensity of Apt@N-CQDs. The important parameters on AFP determination were optimized through response surface methodology and central composite design. Under optimized conditions, the fluorescence intensity enhanced linearly with AFP concentration in the range of 0.03–7.0 µg L −1 with a detection limit of 0.008 µg L −1 and relative standard deviations of 2.2 and 3.8% (at 4.0 µg L −1 of AFP; for n = 6) for intra- and inter-day assays. The method was successfully applied for the determination of AFP in human serum samples.