Preparation of colorimetric aptasensor for CAP detection

The immobilization of CAP Apt onto Au MNPs was carried out according to LDE225 procedure as previously reported with some modification [29]. One millilitre of Au MNPs and 4 μL of 10% (v/v) Tween 80 in water were mixed and reacted for 30 min at room temperature. The mixture was then placed in 0.1 M PBS buffer (pH 7.4). Next, thiol-Apt thiolated 40 mer Apt [30], 5′ (CH2)6-ACT TCA GTG AGT TGT CCC ACG GTC GGC GAG TCG GTG GTAG; was added to the above solution to ensure the eventual DNA concentration of 1 μM and the adequate response 2.5 h at a constant temperature. All the experiments were carried out at 50 °C for Tween 80-mediated conjugation reactions. Unconjugated DNA was removed by magnetic separation and rinsed with 0.1 M buffer (pH 7.4) (10 mM phosphate, 0.1 M NaCl, 0.05% Tween 20, pH 7.4) three times. Finally, the conjugations were distributed in a solution of 0.1 M PBS buffer (pH 7.4). Then the mixture is reserved in 4 °C before use.