We decided to measure the light intensity at various optic fiber cable lengths, for each of the LEDs representative and isolated GFP of different bioluminescent wavelengths. This gave the following results:

Figure 1: Light intensity measured for different LEDs representatives and isolated GFP at different optic fiber cable lengths.

Figure 2: Scatter plots of a. The recorded signal of the orange LED light for each of the optical fiber lengths, b. The recorded signal of the cyan LED light for each of the optical fiber lengths ad c. The recorded signal of the GFP for each of the optical fiber lengths.

The signal for LED lights was much stronger than GFP. However, we were able to measure the fluorescence of GFP upon excitation. Notably, the measured light intensity was higher for the 23 and 29 cm cable lengths. This was very likely an error. However, upon further investigation it did seem like a legitimate intensity read. Further investigations and repeats should be conducted to find the underlying cause of this result. 

Our experiments were aimed at addressing the capability of the sensor to quantify Green Fluorescent Protein (GFP) and Red Fluorescent Protein (RFP). However, owing to the absence of complete data and the lack of calibration for the light sensor, we are unable to definitively ascertain the precise measurements. Nevertheless, we can affirm that the sensor registers variations in measurements when distinguishing between empty or water-filled PCR tubes and those containing GFP and RFP. Notably, values recorded for PCR tubes containing fluorescent proteins are consistently lower. This reduction in recorded values can probably be attributed to the fact that fluorescent proteins absorb a portion of incident light energy and emit light at a reduced intensity. Conversely, higher values measured are primarily attributable to light reflection from tube surfaces and the method employed.

Tubes filled with GFP surprisingly registered lower light emission than their empty counterparts. This observation led to the following hypothesis: GFP potentially absorbs the UV light, while its emitted light propagates nearly isotropically, contrasting with the empty tubes’ UV reflection, which tends to direct more light toward the photoresistor. Navigating further, we identified additional variables, such as the photoresistor’s non-uniform spectral sensitivity, unknown precision, and the asymmetric absorption/emission intensities of GFP, which could have contributed to the intriguing observed behavior.

Given these results, further research could go into testing more sensitive photoresistors in combination with higher quality UV lasers. These could then be used to further investigate the dynamics of fluorescence of different fluorescent proteins as compared to e.g. LED lights. However, our results show that even a simple, relatively cheap light sensor setup can generate usable and interpretable data. This sensor can be built and used as is, or it can be expanded to perform more specific and sensitive measurements.