Nucleic acid sensors in vivo: challenges and opportunities

Nucleic acid biosensors, integrated with functional nucleic acids, have drawn extensive attention for diverse biomedical applications. In particular, many nucleic acid probes have been developed for biosensing and imaging of tumor-associated species, including pH, small molecules, RNAs, metal ions, proteins, and cells. Despite the progress made, these sensors are mainly performed at the level of test tube assays or live cells for disease diagnosis and pathological studies. In recent years, increasing research works are pushing the limit of nucleic acid sensors in preclinical applications and imaging-guided therapy. However, the applicability of current nucleic acid sensors in vivo is largely hindered by the complexity of living animals. Herein, we review recent advances in the design and applications of nucleic acid biosensors in vivo, in which the key factors for the fabrication of eligible sensors are highlighted. Additionally, given the inherent shortcomings of nucleic acid, we will also describe the challenges of the current in vivo nucleic acid biosensors and some new strategies that may significantly accelerate the development of biosensors.