Detection Limit for Sodium Fluorescein
We now have a linear standard curve for sodium fluorescein (Na-F) in clear 24-well plates. What is the detection limit?
The detection limit is defined as the lowest background-corrected concentration that is 3 standard deviations above the noise of the background. The background here is HBSS with 10mM HEPES.
I measured the dilutions a four times in the same plate, calculated the standard deviation of the HBSS/HEPES well and found the lowest concentration that was 3x higher than this deviation. Here is the blank-reduced standard curve (so y-intercept = 0) with n=4 trials. Small deviations and nice R2 value.
I calculated the detection limit to be ~ 400 pM Na-F! The Tecan manual claims a detection limit of <= 100 pM for fluorescein. However, this was calculated in a black 96-well plate to minimize cross talk and maximize fluorescent signal. I think our detection limit of 400 pM is quite good, especially since we are at a low gain (88) and could push this limit even lower with a higher gain.