I am using polymeric nanoparticles entrapping fluorescein and by placing these nanoparticles in a dialysis membrane placed in PBS from which i take samples at different time points. After calculating the amount released and dividing it by the amount entrapped the % Release is always more than 100%.
If you are using a fluorescence measurement to calculate the amount of released fluorescein, consider the following.
The entrapped fluorescein is probably quite concentrated and is self-quenching. When it is released, this quenching is relieved and the fluorescein quantum yield is increased. Therefore, the total fluorescence intensity of the dilute released fluorescein is greater than the total fluorescence intensity of the same amount of entrapped fluorescein.
The pH could also be a factor. Fluorescein fluorescence is reduced at acidic pH. If the vesicles are acidic inside but not outside, that would also reduce the fluorescence of the entrapped fluorescein relative to the released fluorescein.
If you are using a fluorescence measurement to calculate the amount of released fluorescein, consider the following.
The entrapped fluorescein is probably quite concentrated and is self-quenching. When it is released, this quenching is relieved and the fluorescein quantum yield is increased. Therefore, the total fluorescence intensity of the dilute released fluorescein is greater than the total fluorescence intensity of the same amount of entrapped fluorescein.
The pH could also be a factor. Fluorescein fluorescence is reduced at acidic pH. If the vesicles are acidic inside but not outside, that would also reduce the fluorescence of the entrapped fluorescein relative to the released fluorescein.
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