The field of environmental DNA (eDNA) analysis has revolutionized our ability to detect and monitor biodiversity in aquatic and terrestrial ecosystems. However, traditional eDNA sampling methods often present limitations in terms of temporal and spatial coverage, resulting in a loss of resolution associated with infrequent events or those prohibitive to onsite fieldwork. In recent years, the emergence of autonomous eDNA sampling technology has provided researchers with a powerful tool for collecting high‐resolution genetic data, overcoming many of the challenges associated with manual sample acquisition. This review focuses exclusively on eDNA technologies designed for the collection and preservation of water samples, to provide a comprehensive overview of the current landscape of aquatic autonomous eDNA sampling technology and instrumentation. A new era of instrument development and capabilities is emerging; the result of knowledge gained through experience with long‐tested marine biological observation instrumentation. Lastly, we highlight current research to develop an in situ eDNA analytical capability, as well as explore the challenges and future prospects associated with this rapidly evolving field.

We have developed and tested a functionally integrated in situ analyzer, the IISA-ATP system, for microbial activity assays based on a quantitative determination of the total (particulate and dissolved) ATP in ocean environments. The IISA-ATP utilizes a PDMS–glass hybrid microfluidic device as its core functional element, which can perform cell lysis and total ATP quantification by a luciferin–luciferase bioluminescence assay in situ. Transparent heaters and a temperature sensor fabricated on a glass substrate provide temperature control. As a result of the evaluation using the microfluidic device with ATP standard solutions, the bioluminescence intensity was linearly correlated with 2 × 10⁻¹² to 2 × 10⁻⁸ M of ATP. A detection limit of 1.1 × 10⁻¹¹ M was determined using the completed IISA-ATP system, which includes a miniature pumping module and a control module. As a result of the evaluation using the environmental seawater sample collected from Tokyo Bay, Japan, 2.7 × 10⁻¹⁰ M of total ATP was successfully determined in the laboratory by the IISA-ATP. The system was operated at a shallow submarine hot spring area in Okinawa, Japan for an in situ trial. The result shows the system was successfully operated in situ and the total ATP was determined to be 3.4 × 10⁻¹⁰ M.

The oceans sustain the global environment and diverse ecosystems through a variety of biogeochemical processes and their complex interactions. In order to understand the dynamism of the local or global marine environments, multimodal combined observations must be carried out in situ. On the other hand, instrumentation of in situ measurement techniques enabling biological and/or biochemical combined observations is challenging in aquatic environments, including the ocean, because biochemical flow analyses require a more complex configuration than physicochemical electrode sensors. Despite this technical hurdle, in situ analyzers have been developed to measure the concentrations of seawater contents such as nutrients, trace metals, and biological components. These technologies have been used for cutting-edge ocean observations to elucidate the biogeochemical properties of water mass with a high spatiotemporal resolution. In this context, the contribution of lab-on-a-chip (LoC) technology toward the miniaturization and functional integration of in situ analyzers has been gaining momentum. Due to their mountability, in situ LoC technologies provide ideal instrumentation for underwater analyzers, especially for miniaturized underwater observation platforms. Consequently, the appropriate combination of reliable LoC and underwater technologies is essential to realize practical in situ LoC analyzers suitable for underwater environments, including the deep sea. Moreover, the development of fundamental LoC technologies for underwater analyzers, which operate stably in extreme environments, should also contribute to in situ measurements for public or industrial purposes in harsh environments as well as the exploration of the extraterrestrial frontier.