In this work, a dynamic terminus-regulated fabric of DNA hydrogel was invented in debt to the reiterative catalysis of terminal deoxynucleotidyl transferase (TdT). It extended free 3'-OH end to an overhang of homopolymeric adenosine base pair, and alternated with branching from the frayed complementary seed oligo T20G5. The cycle of this template-independent and isothermal amplification resulted in a microscale dendritic DNA fractal at first, which then gelatinized into a cohesive and intricate 3D network. Details of the complex were elucidated with gel electrophoresis, confocal and atomic force microscopy. Its well hydrated inner space could further provide plenty of biocompatible chambers for enzymatic transducers fused along the elongation. Taking merits of this neat and flexible setup, an in situ hydrogelation strategy was developed and utilized in the signal cascade of a miRNA biomarker detector on an electrode microarray, thus accomplished an ultrasensitive, selective and high-throughput sensing even for real samples. This collective manipulation of DNA-protein hydrogel ensemble on interface demonstrates its potency as a general scheme of sensitization in bioanalytical applications.