2.5. Calculation of Fluorescence Quenching and Fluorescence Quenching Efficiency

The fluorescence intensity of samples containing Cd²⁺ or interferences was recorded as F. F₀ was assigned to the fluorescence intensity of a blank containing FAM-aptamer and MOPS only, where 10 μL aqueous sample containing Cd²⁺ was replaced by 10 μL ultrapure water. Fluorescence quenching (∆F) was defined as the difference between F₀ and F, which can be calculated as ∆F = F₀ − F; thus, fluorescence quenching efficiency (∆F/F₀) can be calculated as ∆F/F₀ = (F₀ − F)/F₀.