Dual Amplification Strategy: Exponential Amplification Reaction and Hybridization Chain Reaction‐Driven Electrochemical Biosensor for Ultrasensitive Pathogen Detection

The growth of nucleic acid‐based diagnostics integrated with electrochemical approaches has fundamentally transformed pathogen detection paradigms, with exponential amplification reaction (EXPAR) and hybridization chain reaction (HCR) emerging as next‐generation alternatives to conventional polymerase chain reaction methodologies. EXPAR and HCR have emerged as powerful tools, offering unique biochemical pathways to amplify detection signals for pathogen‐derived deoxyribonucleic acid (DNA) or ribonucleic acid (RNA). The key interest in this amplification strategy is due to improved detection signals without the use of sophisticated thermocycling equipment. EXPAR is a potent isothermal amplification technique that employs a mix of polymerases and nicking (specific single‐strand breaks) enzymes to rapidly cleave and extend short oligonucleotide sequences and, thereby it results in an exponential growth in the target DNA or RNA. This method is a perfect fit for field‐based and point‐of‐care applications, as it enables extremely quick detection. HCR, on the other hand, employs a regulated, enzyme‐free process in which metastable DNA hairpins self‐assemble upon hybridization with a target sequence, and resulting in an amplified signal. HCR's programmability and flexibility make it easier to integrate into microfluidic systems and biosensors for real‐time pathogen surveillance. Comparative studies suggest that EXPAR generally surpasses HCR in speed and sensitivity, whereas HCR excels in robustness, modularity, and ease of coupling with nanomaterials or aptamer‐functionalized probes. This review explores the fundamental principles of EXPAR and HCR, compares their efficiency, sensitivity, and applications in pathogen diagnostics, and discusses their integration with emerging electrochemical sensing technologies. Moreover, this review elaborates on the advances in the use of nanomaterials, aptamer‐functionalized probes, and the challenges of multiplexed detection strategies that further enhance their diagnostic potential. Finally, this review provides insights into future directions in next‐generation pathogen detection platforms, with an emphasis on their role in the design of rapid, low‐cost, and field‐deployable diagnostic assays.