Cell-Free DNA Circuits as the Safer Injectable: A Design Study of a Marker-Activated Molecular System Without Living Cells

Design study of an injectable diagnostic and therapeutic-logic system made only of DNA strands, with no living cells. The circuit circulates inert and activates only inside cells presenting a two-marker disease signature via toehold exchange. Computed budgets cover activation (0.510 in a diseased cell, 3.66% total false activation in a healthy cell), clearance (4.36 h half-life, 14.5 h working window), and payload (35,075 copies per target cell against a 10,000-copy requirement), together with a quantitative safety comparison against living engineered-cell products and the costs of giving up replication, migration, and memory. SIMULATED, NOT MEASURED. Nothing described has been built, synthesized, or tested.