Team:Peking/Project/3D/2D

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Summary

Having obtained the E.coli strain BL21 transformed with the optimized light sensor and GFP reporter, a series of plate assays were carried out as a graphic visual depiction of our LexA-VVD device.

Through blue light exposure on a lawn of bacteria, light-induced spatial control of gene expression in E.coli is achieved in our experiment, which might be used to 'print' complex biological materials[1] and to control metabolic pathways in a cheaper and more precise way in the future.

The right image shows that the bacteria did not die or flee, for they evenly distribute in the plate.

Prepare the Plate

The strain we used is BL21 transformed with Overnight cultures are grown in 5 mL of LB broth + appropriate antibiotics in 30oC and irradiated by blue LED (465nm,6-10μW/cm2). 1 mL suspension culture (OD600~0.9-1.6) is added into 100mL LB solid medium (0.6g agarose and appropriate antibiotics added). Pour the mixture into culture dishes.

Printer Design

After several attempts, a simple printer (Figure 2) is put into use for printing experiments. A single blue LED serves as the light source and is put at the focal point of a convex lens. Both the LED and the convex lens are fixed on an opaque cylinder which is aimed at shielding stray light. Through this device, parallel light is obtained. A photomask is then sticked to the bottom of the plate and fixed on the tube. The whole device is wrapped in black fabric and grown in 30oC. As it is easy to produce the photomask, images could be printed conveniently.

Fig. 2 (a)The printer that uses photomask. The blue LED is put at the focal point of the convex lens.(b)(c)Complex Chinese character is printed. The line width is about 1 mm. This character means illumination or sunshine.

Furthermore, another printer is designed to serve as an interface between cellular and electronic components[2] (Figure 3a). iPad serves as a light source. We make use of the image formation property of convex lens to form image directly on the plate. The tube is adjustable to form a sharper image on the plate.

Fig. 3 (a) The printer that uses iPad. The tube is adjustable to form a sharper image on the plate. (b)(c) An apple logo is printed.

Discuss: How to get sharper image

Three key points is supposed to be considered in printing: dark room, parallel light or clear image formation, thin plate.

As the LexA-VVD is highly sensitive, it is vital to shield stray light. The device needs to be separated from the indoor lighting environment, or it might sense the room light and the imaging would be disturbed.

For the device that uses parallel light, it's important to keep the light parallel, which requires carefully measurement of the focal length. (Figure 4 a-c)

A thinner plate produces sharper edge, though the contrast ratio would become lower, for less bacteria exists in the plate. (Figure 4 d-f)

Fig.4 (a)-(c) This three figure show why parallel light produces sharper image. (d)-(f) This three figure show why thinner plate produces sharper image.

Reference

  • 1. Christopher A. Voigt.et al. Nature 438; 441-442 (2005).
  • 2. Christopher A. Voigt Nature 481; 33 (2012)

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