Hydrothermal vent nanostructures can imitate life processes, guide ions and generate energy, aiding origin of life theories and blue energy technology. A team of scientists has discovered inorganic nanostructures around deep-sea hydrothermal vents that bear striking resemblance to the molecules of life as we know it. These nanostructures are self-organized and function as selective ion channels that can generate energy and harness it in the form of electricity. This discovery could not only impact our understanding of the origin of life, but could also have applications in industrial blue energy harvesting.

The research, led by Ryuhei Nakamura of RIKEN's Center for Sustainable Resource Science (CSRS) and Tokyo Institute of Technology's Earth Life Sciences Institute (ELSI), was recently published in Nature Communications.

a) Photo of high-pressure sediment collected from the Xinhai seepage field. b) Cross-polarized optical microscope image of a cross-section of the precipitate. c, d) Scanning electron images showing layers inside the precipitate.

geoenergy system

As seawater seeps deep into the Earth through cracks in the ocean floor, it is heated by magma, rises back to the surface, and is released back into the ocean through cracks called hydrothermal vents. The rising hot water contains dissolved minerals obtained from deep within the earth, and when it encounters cool seawater, chemical reactions force mineral ions out of the water, forming solid structures called sediments around the vents.

Schematic showing the development of osmotic forces upon contact with potassium chloride (KCl). The overlapping electrical double layers within the nanopore create a shielding barrier that is permeable only to ions with a specific charge. Source: RIKEN

Osmotic energy conversion in nature

Hydrothermal vents are considered the birthplace of life on Earth because they provide the necessary conditions: stable, rich in minerals and a source of energy. Most life on Earth depends on osmotic energy, which is generated by ionic gradients (differences in salt and proton concentrations) inside and outside living cells.

RIKEN CSRS researchers studied serpentine-hosted hydrothermal vents because the mineral deposits from these vents have a very complex layered structure formed from metal oxides, hydroxides and carbonates.

"We unexpectedly discovered that osmotic energy conversion, an important function of modern plant, animal and microbial life, can occur abiotically in geological environments," Nakamura said.

Experimental Observation of Ion Channels

Researchers are studying samples collected from a new sea seepage field located at a depth of 5,743 meters in the Mariana Trench in the Pacific Ocean. Optical microscopy and micron-scale X-ray scanning show that the lapis lazuli crystals are arranged in continuous columns and are nanochannels for the spout fluid.

The researchers noticed that the surface of the precipitate was charged, with the magnitude and direction of the charge - positive or negative - varying across the surface. The researchers knew that structured nanopores with variable charge were a hallmark of osmotic energy conversion, so they next tested whether osmotic energy conversion indeed occurs naturally in inorganic deep-sea rocks.

ion transport mechanism

The team used electrodes to record the current and voltage of the sample. When the sample is exposed to high concentrations of potassium chloride, the conductance is proportional to the salt concentration at the nanopore surface. However, at lower concentrations, the conductance is constant rather than proportional and is determined by the local charge on the precipitated surface. This charge-governed ion transport is very similar to the voltage-gated ion channels observed in living cells such as neurons.

By testing the samples with chemical gradients found in the deep ocean, the researchers were able to show that the nanopores functioned as selective ion channels. Where carbonate is attached to the surface, the nanopores allow positive sodium ions to flow through. However, in nanopores with calcium attached to the surface, the pores only allow negative chloride ions to pass through.

Ryuhei Nakamura said: "The spontaneous formation of ion channels discovered in deep-sea hydrothermal vents has direct implications for the origin of life on Earth and elsewhere. In particular, our study shows how osmotic energy conversion, an important function of modern life, occurs abiotically in geological environments."

Impact on blue energy harvesting

Industrial power plants exploit the salinity gradient between seawater and river water to generate energy, a process known as blue energy harvesting. Nakamura said understanding how nanopore structures arise spontaneously in hydrothermal vents could help engineers design better synthesis methods to use osmotic conversion to generate electricity.

Compiled from/SciTechDaily