Ultrasensitive Nucleic Acid Testing: From Foundational Research to Clinical Translation

The ability to detect nucleic acids at ever-lower detection limits is crucial in molecular science, enabling disease management to shift from reactive response to proactive prediction and personalized medicine. This review synthesizes the technological landscape, which is organized into three strategies. First, we examine amplification-dependent platforms, charting their evolution from the quantitative polymerase chain reaction (PCR) to the absolute quantification of digital PCR (dPCR) and the rapid point-of-care utility of isothermal methods. Second, we explore amplification-free paradigms, where technologies such as clustered regularly interspaced short-palindromic repeat (CRISPR)-based diagnostics and nanopore sequencing achieve sensitivity through signal generation mechanisms that directly interrogate native target molecules. Finally, we detail the emergence of nanotechnology-based biosensors, which employ the physicochemical properties of nanomaterials to transduce molecular recognition events into measurable optical or electronic signals. The clinical and scientific translation of these platforms is very useful, enabling noninvasive cancer monitoring via liquid biopsy, real-time infectious disease surveillance, and the reconstruction of past ecosystems from trace environmental DNA. However, realizing the full potential of these technologies is contingent on overcoming significant translational hurdles. Critical challenges include the standardization of preanalytical workflows to ensure sample integrity and the engineering of fully integrated, cost-effective "sample-in, answer-out" systems suitable for widespread deployment. The future trajectory of the field points toward the convergence of these molecular tools with microfluidics, automation, and artificial intelligence, thus promoting decentralized and predictive healthcare.