Molecular "robots" have been developed by chemists to explore the unmapped chemical environments of living cells and transmit back the results.
The new molecules encrypt measurements of two different chemical features of cell membranes into light signals to be decoded by the British and Japanese chemists that built them. One measurement is encoded in the light's intensity, and the other in its wavelength, or colour.
Being able to map the variables they measure could help biochemists probe the mechanisms by which cells generate energy, or how signals travel through nerve cells.
"Concepts of nanorobotic vehicles and of mapping out nanospaces have emerged from science fiction into experimental science for the first time," lead researcher A. Prasanna de Silva at Queen’s University, Belfast, UK, told New Scientist.
Phone home
de Silva's "robots" are molecules sensitive to two features of their chemical environment. The first variable is proton – hydrogen ion – concentration. Mapping it is important because cells use gradients of proton concentration to store and generate energy.
The second variable is polarity, the degree to which electrons in an area are shared out evenly, or held in negatively charged clumps by some molecules. Polarity is used in cells to shape the structure of membranes, and to bring molecules together or keep them apart.
The new molecular probes are made from a proton-sensitive section linked to a polarity-sensitive fluorescent region. When the proton receptor detects a hydrogen ion, it releases energy that makes the fluorescent section emit light. The more protons there are around, the more light is emitted.
But because the glowing fluorescent section is sensitive to changes in polarity, the wavelength of light emitted encodes the polarity around the molecule. The more polarised the environment, the longer the wavelength of light.
Proton maps
de Silva and colleagues developed 18 different versions of these molecular probes and tested them on artificial cell-like membrane capsules made using soap-like chemicals and water. The different versions varied in how hydrophobic (water-hating) or hydrophilic (water-loving) they were, which meant that they naturally travelled to various different positions around the membrane structures.
By monitoring the intensity and wavelength of the emitted light, de Silva and colleagues could create detailed maps of the electrochemical environments around the membranes.
"This is the first time that the proton distribution near a membrane has been mapped in such detail," says de Silva. "This is also the first time that a family of sensor molecules have delivered two separate kinds of information simultaneously from a series of locations."
This work represents "significant progress in the design of molecular sensors", says Luigi Fabbrizzi, a molecular chemist at the University of Pavia, Italy.
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