Development of an Aptamer Based Luminescent Optical Fiber Sensor for the Continuous Monitoring of Hg(2+) in Aqueous Media

A fluorescent optical fiber sensor for the detection of mercury (Hg(2+)) ions in aqueous solutions is presented in this work. The sensor was based on a fluorophore-labeled thymine (T)-rich oligodeoxyribonucleotide (ON) sequence that was directly immobilized onto the tip of a tapered optical fiber. In the presence of mercury ions, the formation of T–Hg(2+)-T mismatches quenches the fluorescence emission by the labeled fluorophore, which enables the measurement of Hg(2+) ions in aqueous solutions. Thus, in contrast to commonly designed sensors, neither a fluorescence quencher nor a complementary ON sequence is required. The sensor presented a response time of 24.8 seconds toward 5 × 10(−12) M Hg(2+). It also showed both good reversibility (higher than the 95.8%) and selectivity: the I(0)/I variation was 10 times higher for Hg(2+) ions than for Mn(2+) ions. Other contaminants examined (Co(2+), Ag(+), Cd(2+), Ni(2+), Ca(2+), Pb(2+), Mn(2+), Zn(2+), Fe(3+), and Cu(2+)) presented an even lower interference. The limit of detection of the sensor was 4.73 × 10(−13) M Hg(2+) in buffer solution and 9.03 × 10(−13) M Hg(2+) in ultrapure water, and was also able to detect 5 × 10(−12) M Hg(2+) in tap water.