Sol–gel derived urease-based optical biosensor for the rapid determination of heavy metals Original Research Article

A urease optical biosensor for the determination of heavy metals based on sol–gel immobilization technique was developed. A fluorescent dye, FITC-dextran, was encapsulated and parameters including optical properties of the probe, relative enzyme activity, initial pH value and the buffer concentration for substrate preparation were investigated. In sol–gel immobilization, 1 mM Tris–HCl at pH 7.1 provided a sufficient buffer capacity for metal ion analysis as well as the enzyme activity maintenance. Also, two analytical procedures, incubated and un-incubated systems, were compared to understand the sensitivity and applicability to heavy metal analysis. The developed optical biosensor showed high reproducibility and the relative standard deviation (R.S.D.) of 5.1% (n=10) was obtained. Also, eight measurements can be completed automatically within 36 min. The biosensor has high sensitivity to Cu(II) and Cd(II) and an analytical range of 10–230 μM with a detection limit of 10 μM was achieved. Moreover, biological and environmental samples were examined to evaluate the applicability of the developed biosensor. A 19–82% of inhibition was observed when 20–45 μM metal ions were amended into tested samples, revealing that the developed system has the potential for the determination of heavy metals in real samples.