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3 Vision

For accurate vision and analysis, the brain moves the eyes to scan an area with a lot

of micromovements [5]. These micromovements in scanning were mimicked by another

group using a very basic artificial sensor (tiny lens, two digital pixels) [6]. The resulting

sensor is more sensitive than related sensors since it detects contrast via movement on

top of the number of photons. It was also able to locate a much smaller object than the

lens should allow for by looking for contrast. The authors are currently refining this

technology so that it can also be used in robotics. It would be powerful to combine both

technologies, but nothing to that effect has been reported so far.

Modified rhodopsin can also be used to measure voltage or ions instead of light. To

image voltage in life cells in real time, a genetically modified rhodopsin was expressed

in neurons or muscle cells in Caenorhabditis elegans, a common animal model in neuro

and cell biology (Figure 3.3) [7]. It was possible to measure voltage, and with that muscle

and neuron activity, in-vivo.

Figure 3.3: All-trans retinal (ATR) is used to image intrinsic muscle

activity of the pharyngeal muscle under a fluorescence microscope [7].

Iterative directed evolution coupled with protein structure modeling created a rho-

dopsin variant that measures chloride concentration instead of light (Figure 3.4) [8].

The variant was expressed in E. coli cells that now function as life, in-vivo chloride

sensors.

Figure 3.4: Confocal fluorescence microscopy is used to measure chloride in-vivo in E. coli cells: (A) 0 mM

and (B) 400 mM sodium chloride. For each panel, the emission from a control (red, left) and from the mod-

ified resorcinol (cyan, right) are compared (scale bar = 5 µm). (C) Boxplots show the normalized emission

response (FGR2/FCFP) of each cell analyzed from four biological replicates (with permission from [8]).