Analysis of biomarkers in living cells is crucial for deciphering the dynamics of cells as well as for precise diagnosis of diseases. DNA biosensors employ DNA sequences as probes to offer insights into living cells, and drive progress in disease diagnosis and drug development. In this review, we present recent advances in DNA biosensors for detecting biomarkers in living cells. The basic structural components of DNA biosensors and the signal output method are presented. The strategies of DNA biosensors crossing the cell membrane are also described, including coincubation, nanocarriers, and nanoelectroporation techniques. Based on biomarker categorization, we detail recent applications of DNA biosensors for detecting small molecules, RNAs, proteins, and integrated targets in living cells. Furthermore, the future development directions of DNA biosensors are summarized to encourage further research in this growing field.