Hi Tom,

Apart from the data of the low concentrations, blank injections are also needed to calculate to S/N and LOD of an established analytical method.

As I am working in environmental chemistry, we usually prefer to use "method detection limit (MDL)" to describe these things, and you can visit "https://www.epa.gov/cwa-methods/method-detection-limit-frequent-questions" for more information.

This set of data indicates your sensor has "no meaningful" response under 0.5 and it is linear from 0.5 to 10. You can do a regression from 0.5 to 10, then use the regression equation to calculate the "concentration" for your response reading at 0.5. You have standard derivation for the data. You must have more than 3 reading for each point. Then you should get more than 3 concentration number at "0.5". You can calculate the standard derivation for the concentration number you just get. 3xof the SD is your estimated LOD.

Good luck!

Hello Tom, as you have mentioned that LOD is 3 x std LOB, but if you calculate the LOD according to the IUPAC standard which is ( S.D/slop)*3 that would be more accurate for your fluorescence sensor. Slop value you can get from typical calibration carve (Conc Vs FL intensity). For more details here is a link for you: https://www.sciencedirect.com/topics/nursing-and-health-professions/limit-of-detection.

Hope it will help you.