We looked into various sources of radiation to test our engineered yeast’s resistance. One method was to irradiate yeast with ionizing radiation in the form of x-ray or beta radiation and the alternative was to use UV-C light. We chose to proceed with UV-C light, because the safety precautions for UV-C were much simpler to implement. Thus, we constructed a safe device to carry out controlled UV-C light exposure to yeast cultures. The inspiration for our device was driven by the laminar hood that uses UV-C to sterilize the working surfaces. The laminar hood itself was not used due to high risk of contaminating the work area with yeast that could potentially be resistant to UV radiation.

The primary purpose of the hardware designed here is to irradiate yeast in safe confinement which has safety measures in place in order to protect eyesight of curious fellow researchers by interrupting the UV exposure in case the chamber is breached (i.e. door opened). The device could be used in any lab in order to sterilize various items, such as lab coats, pipettes and plastics. Additionally, the lamp can be utilized as a portable UV-C light source to decontaminate surfaces in the lab.

The list of required components is presented in Table 1 and the link to the code repository is below.

Table 1. List of components. All prices are referenced without delivery.

Code respository

Hardware description and calculations

The device is a chamber with a UV lamp controlled by a relay which is in turn controlled by the esp8266 that has Internet access and communicates with the end user via a telegram bot. There are two modes of operation: safe and hazardous. In safe mode the exposure is interrupted if the door is open and the hall sensor does not sense the magnet that is on the door. In hazardous mode, however, the radiation is not interrupted if the door is opened. The radiation timer can be set manually and can be set at a desired dose and distance from source to target. The device photo (Fig. 1), assembly schematic (Fig. 5) and the 3d model (Fig. 6) of the assembled device can be seen lower.

The UV intensity provided by the seller is 45 μW/cm^² at the distance of 1 meter. The radiation dose required to kill Saccharomyces cerevisiae is around 130 mJ/cm^² (Uvcbyefsen.com). Further literature research confirmed that 100 mJ/cm^² (Malayeri et al., 2016) is required to kill 99.9% of the cells. To calculate the dose absorbed by the yeast we assumed that we have a point source of radiation. In this case, UV intensity drops according to the inverse square law, whereby twice bigger distance brings four times drop in radiation intensity. So, at 10 cm distance, which is 10 times smaller than one meter distance, the intensity is 4.5 mW/cm^². 10-fold (Malayeri et al., 2016) decrease of yeast viability requires 42mJ/cm^² radiation, which is merely 10 seconds of exposure at 10 cm distance. Interestingly, the radiation intensity in our device for 1 second exposure at 10 cm distance surpasses the radiation that is required to inactivate SARS-CoV-2 virus by 1000 times (Biasin et al., 2021).

Figure 1. Photo of the device.

In order to ensure that the bulb produces the UV-C we measured it using the thorlabs ccs200 spectrometer and obtained the following data (Fig. 2).

Figure 2. The spectrum of the purchased UV bulb. The leftmost peak is around 254 nm, as expected.

We compared it to Stratalinker 1800 UV DNA crosslinker and it produced similar but more powerful spectrum (Fig. 3), but the price of this particular device is over 700 dollars (acmerevival.com).

Figure 3. Stratalinker 1800 UV DNA crosslinker spectrum. The leftmost peak is around 254 nm with high intensity.

Reference graphs of yeast survival under different dosages of UV-C radiation are presented on Figure 4 (Birrell et al., 2001).

Figure 4. Surviving fraction of cells depending on the UV-C dose.

Shematic:

Further developments:

The device could be further upgraded and used in order to sterilize lab equipment, including lab coats, pipettes, and lab plastics. The required dosage to kill most microorganisms is 100-200 mJ/cm² (Malayeri et al., 2016). To improve the current setup, more UV bulbs can be used to provide a higher dose and more even coverage in a shorter period of time. Hence, with two lamps used at the same time (intensity would become 2*4.5 mW/cm^², at the distance of 10 cm), it would require 200 mJ/cm^²/(9 mW/cm^²)=22 seconds to sterilize the surface. The same setup with the timer could also be utilized to sterilize lab benche

Biasin, M., Bianco, A., Pareschi, G., Cavalleri, A., Cavatorta, C., Fenizia, C., Galli, P., Lessio, L., Lualdi, M., Tombetti, E., Ambrosi, A., Redaelli, E. M. A., Saulle, I., Trabattoni, D., Zanutta, A., & Clerici, M. (2021). UV-C irradiation is highly effective in inactivating SARS-CoV-2 replication. Scientific Reports 2021 11:1, 11(1), 1–7. https://doi.org/10.1038/s41598-021-85425-w

Birrell, G. W., Giaever, G., Chu, A. M., Davis, R. W., & Brown, J. M. (2001). A genome-wide screen in Saccharomyces cerevisiae for genes affecting UV radiation sensitivity. Proceedings of the National Academy of Sciences of the United States of America, 98(22), 12608. https://doi.org/10.1073/PNAS.231366398

Uvcbyefsen.com - David Ivarsson. (n.d.). UVC for disinfection of surfaces - EFSEN UV & EB TECHNOLOGY. Retrieved October 11, 2022, from https://uvcbyefsen.com/uvc-for-disinfection-of-surfaces/

Malayeri, A. H., Mohseni, M., Cairns, B., Bolton, J. R., Barbeau, B., Wright, H., & Linden, K. G. (2016). Fluence (UV Dose) Required to Achieve Incremental Log Inactivation of Bacteria, Protozoa, Viruses and Algae With earlier contributions by Gabriel Chevrefils (2006) 4 and Eric Caron (2006) 4 With peer review by. www.iuva.org.