## 3 Results and Discussion
### Examination of Thrombin Load by Aptamer-Functionalized DNA Hydrogel
It could be explained when the content of TB exceeded that of the aptamer, the aptamers in the hydrogel were consumed completely. The results showed that when the molar ratio of TB to aptamers was kept at 1:1, the hydrogels reached saturation capture and capture equilibrium. In addition, an obvious change in the normalized capture with the different concentrations of thrombin was found in the range of 8 nM to 1 \(\upmu\)M in both the buffer and human urine-spiked samples. The limit of detection is as low as 80 pM. It is anticipated that our thrombin capture system could be a promising tool for the clinical diagnosis of thrombin in human urine. Another important factor that influenced the capture capacity of the hydrogel was the S-DNA concentration. As shown in Figure 3D, with the increase of the aptamer assembling into the hydrogel,  
Figure 3: **(A)** The thrombin (TB) capture capabilities of hydrogels (X-DNA 400 \(\upmu\)M, L-DNA 800 \(\upmu\)M) with or without aptamers at different incubation time. The concentration of S-DNA was fixed at 200 \(\upmu\)M (the volume is 1 \(\upmu\)L). The molar ratio of TB to aptamers was kept at 2:1. (**B**) The capture capability of two building blocks at different concentrations. For normalization, the capture capability of 800 \(\upmu\)M of X-DNA and 1600 \(\upmu\)M of L-DNA (the control) is regarded as one. The concentration of S-DNA was fixed at 200 \(\upmu\)M (the volume is 1 \(\upmu\)L) in the hydrogel. The molar ratio of TB to aptamers was kept at 1:1. (**C**) The influence of the thrombin amount in the absorption medium on the TB capture capability of the hydrogel (X-DNA 400 \(\upmu\)M, L-DNA 800 \(\upmu\)M). When the molar ratio of TB to aptamers was 0.25:1, the capture capability was regarded as one. The concentration of S-DNA was fixed at 200 \(\upmu\)M (the volume is 1 \(\upmu\)L). (**D**) Relationship between the aptamer concentrations and the capture capability of the hydrogels. The hydrogel’s capture capability without an aptamer (aptamer 0 nmol) was represented as one (X-DNA 400 \(\upmu\)M, L-DNA 800 \(\upmu\)M). The concentration of TB was fixed at 7.5 \(\upmu\)M (the volume is 100 \(\upmu\)L). The samples with obviously higher normalized capture than the control group (the normalized capture = one) were noted with \({}^{\star}\) (\(p<0.05\)). the protein-capture capability was raised obviously. The normalized capture of the hydrogel without aptamers was regard as one. As the aptamers concentration increased from 0.19 nmol to 0.75 nmol, the normalized capture was enhanced from 4.16 \(\pm\) 0.31 to 14.48 \(\pm\) 0.52. Since the amount of TB was fixed at 0.75 nmol, with the amount of aptamer continuously increasing from 0.75 nmol to 0.92 nmol, the normalized capture of the hydrogel was basically changeless. The thrombin in the loading medium had been entirely loaded into the hydrogel. The results suggest that the specific bind of the aptamers and thrombin was the primary impetus for thrombin capture. Thus, by adjusting the three parameters, the thrombin-capture capability could be controlled accurately, and it was better than a large proportion of the conventional protein carriers with low and uncontrolled protein-loading efficiency [40; 41].