Probing endogenous molecular profiles is of fundamental importance to understand cellular function and processes. Despite the promise of programmable nucleic‐acid‐based aptasensors across the breadth of biomolecular detection, target‐responsive aptasensors enabling intracellular detection are as of yet infrequently realized. Several challenges remain, including the difficulties in quantification/normalization of quencher‐based intensiometric signals, stability issues of the probe architecture, and complex sensor operations often necessitating extensive structural modeling. Here, the biomimetic crystallization‐empowered self‐assembly of a tumor‐targetable DNA–inorganic hybrid nanocomposite aptasensor is presented, which enables Förster resonance energy transfer (FRET)‐based quantitative interpretation of changes in the cellular target abundance. Leveraging the design programmability and high‐throughput fabrication of rolling circle amplification‐driven DNA nanoarchitecture, this designer platform offers a method to self‐assemble a robust nanosensor from a multifunctionality‐encoded template that includes a cell‐targeting aptamer, a ratiometric aptasensor, and a cholesterol‐decorating element. Taking prostate cancer cells and intracellular adenosine triphosphate molecules as a model system, a synergistic effect in the targeted delivery by cholesterol and aptamers, and the feasibility of quantitative intracellular aptasensing are demonstrated. It is envisioned that this approach provides a highly generalizable strategy across wide‐ranging target systems toward a biologically deliverable nanosensor that enables quantitative monitoring of the abundance of endogenous biomolecules.