measuring OD at 750 nm

[scaralbi]

Hi !

I would like to measure the optical density of my cultures of cyanobacteria at 750 nm. At 650 nm there is overlap with emission of chlorophylls and so not very ideal to estimate cell growth.
Is there any easy way of doing that instead of using the 650 nm built-in laser ?
Is it doable to change the laser if I am not familiar with electronics ?

Thanks in advance for your help and your great work,#

Best
Albi

[harrison]

Hello Albi,

Probably the easiest way would be to de-solder the laser diode that is in there at the moment and attach a laser at approximately the right wavelength you wish for.
In principle this is not so difficult – what you need to do is look at the schematics/part numbers for Chi.Bio (available on thhis site) to get the part number for the laser diode; then look up the datasheet to see what each of the three “pins” on the diode correspond to, and then find a replacement IR laser with the same “pins” and approximately the same output power.
Off the top of my head there should be quite a few options for laser diodes of ~700-800nm with 5mW power maximum (this is all you need, in fact less is fine) which you could be for $10 or less.
You could then solder in the laser onto the circuit board and use the exact same control circuit and all that which would control it (turn on/off etc).
Hope this makes sense!

[scaralbi]

Awesome ! Thanks for the help

[Pratham_K]

Hey Albi, I just wanted to check in and ask what you ended up doing with this in the end. Did you go the full DIY route and build the Chi.Bio yourself, or did you buy one from Labmaker and then swap out the OD laser diode? I’m considering doing something similar for 750 nm OD/illumination work with Synechocystis, so I’d be really interested to hear how it worked out for you in practice.

Did the diode replacement work cleanly with the existing control board and optics, or did you run into any issues with pinout, power, calibration, or wavelength compatibility? Also, if you’ve got any newer recommendations or updates since the original 2022 post, especially for far-red / 750 nm setups, that would be super helpful.

Best,
Pratham

[Author]

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