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Revision as of 20:33, 31 October 2017
Light Signalling in Gels
OPTIC MODEL
Introduction
Medusa aims at optically controlling bacteria immobilized in a gel by targetting them with two intersecting lasers. Two questions are important to address to achieve this goal:How far can a laser go in a gel?
What resolution can the laser achieve?
We present in this page our study of the optical properties of commonly used culture gels. We show that it is possible to obtain a clean light signal even at gel depths greater than 10cm.
Gel Choice
The optical properties of a gel depend on the gel type, its concentration and the nutrient source.| Alginate | Agar | Gelrite | |
|---|---|---|---|
| Key advantage | Solidifies at room temperature by adding calcium ion |
Most ubiquitous microbiology gel | Low absorbance |
| Recommended concentration | 1.75-4% | 1-1.5% | 0.15-0.25% |
| Melting-Gelling Point | NA | 0.5%:85-20C 1%:90-35C |
0.5%:65-15 1%:100-35C |
| Key disadvantage | Properties depend on calcium ion diffusion which is hard to control |
High absorbance | Melts less well than agar |
| Concentration studied | 1% with LB | 1% with LB | 1% & 0.5% with LB |
The optical properties of a gel depend on the gel type, its concentration and the nutrient source.
It is best to use a low gel concentration to reduce absorbance. Conveniently some gels have a higher melting point than solidifying point. This hysteresis phenomenon means that the gel concentration can be lowered and still be kept at in a solid state at 37C by pre-cooling them (to 6-8C) prior to warm incubation.
It is best to use a low gel concentration to reduce absorbance. Conveniently some gels have a higher melting point than solidifying point. This hysteresis phenomenon means that the gel concentration can be lowered and still be kept at in a solid state at 37C by pre-cooling them (to 6-8C) prior to warm incubation.
Alginate gelling is induced by calcium ions which crosslink gelling polymers at room temperature. To get a homogenous gel, calcium ions cannot be mixed with an Alginate solution but must diffuse from an underlying calcium source (1). Since the optical properties of Alginate depend on the amount of crosslinking, they ultimately depend on calcium diffusion which is a difficult parameter to control. It is important to note that keeping the same diffusion conditions (time, temperature, calcium source concentration etc.) is necessary to maintain identical alginate optical properties between experiments. In addition to the gelling agent, the nutrient source also impacts light absorbance. Conveniently, LB shows less absorbance than M9 media at most visible wavelengths and was therefore added to our gels for our study.
We initially attempted to extract the intensity landscape in the gel from a simple picture. The strong diffusion of light from the main laser beam observed on these pictures suggested that an important scattering was occurring in the gel (sfig xx).
Since the scattering observed on gel pictures was questioning the viability of Medusa, we further studied the light landscape with a different strategy. Briefly, we captured the light diffusion at various gels positions on the X-axis (X-axis represents gel depth) by scanning the light intensity along the Z-direction of the gel.
. The spread of this distribution represents the diameter of the laser beam. In contrast to what the gel pictures suggested, the laser diameter within the gel was actually close to its initial diameter, prior to entering the gel. The large light diffusion observed on gel pictures was probably caused by internal camera corrections which automatically balanced areas of high and low light intensity. In contrast, the low scattering that we recorded manually is very encouraging as it shows that a high targeting precision can be obtained within a gel which will give a high resolution to Medusa control. <br>
In addition, to scattering, the laser beam is also affected by absorbance when photons energy is absorbed by gel particles and converted into heat. As expected, the laser intensity followed an absorbance induced logarithmic decay which we modeled by rearranging Beer-Lambert’s law with the equation defining absorbance: <br>
<p> A(x)= εCx </p> and <p> A=Log(I<sub>0</sub>/I) </p>
</div>
</div>
<div class=text1>
<table>
<tr>
<th> </th>
<th>Absorption</th>
<th>Scattering</th>
</tr>
<tr>
<th> Profile </th>
<td><img src=)
ε: extinction coefficient
C: concentration of the absorptive medium.
z0: laser beam position (zero) on Z-axis, S: parameter controlling the spread of the distribution
RNA is a light cost nucleotide material in the cell,
We aim to recreate RNA agglomerations as formed
in mammalian cells with triple repeat disorders,
which show liquid phase separation, forming a
organelle-like vesicle, where local concentrations of
enzymes can be created.
RNA is a light cost nucleotide material in the cell,
We aim to recreate RNA agglomerations as formed
in mammalian cells with triple repeat disorders,
which show liquid phase separation, forming a
organelle-like vesicle, where local concentrations of
enzymes can be created.
RNA is a light cost nucleotide material in the cell,
We aim to recreate RNA agglomerations as formed
in mammalian cells with triple repeat disorders,
which show liquid phase separation, forming a
organelle-like vesicle, where local concentrations of
enzymes can be created.
THIRD MODEL
your text
RNA is a light cost nucleotide material in the cell,
We aim to recreate RNA agglomerations as formed
in mammalian cells with triple repeat disorders,
which show liquid phase separation, forming a
organelle-like vesicle, where local concentrations of
enzymes can be created.
RNA is a light cost nucleotide material in the cell,
We aim to recreate RNA agglomerations as formed
in mammalian cells with triple repeat disorders,
which show liquid phase separation, forming a
organelle-like vesicle, where local concentrations of
enzymes can be created.
RNA is a light cost nucleotide material in the cell,
We aim to recreate RNA agglomerations as formed
in mammalian cells with triple repeat disorders,
which show liquid phase separation, forming a
organelle-like vesicle, where local concentrations of
enzymes can be created.
RNA is a light cost nucleotide material in the cell,
We aim to recreate RNA agglomerations as formed
in mammalian cells with triple repeat disorders,
which show liquid phase separation, forming a
organelle-like vesicle, where local concentrations of
enzymes can be created.
Centre for Research and Interdisciplinarity (CRI)
Faculty of Medicine Cochin Port-Royal, South wing, 2nd floor
Paris Descartes University
24, rue du Faubourg Saint Jacques
75014 Paris, France
bettencourt.igem2017@gmail.com
bettencourt.igem2017@gmail.com 
