Detection of Hg(II) at Part-Per-Quadrillion Levels by Fiber Optic Plasmonic Absorption Using DNA Hairpin and DNA-Gold Nanoparticle Conjugates

Mercury ion (Hg2+) is extremely toxic even at very low concentrations and its detection mainly relies on bulky and high-cost analytical instruments. Here, we introduce a fast and ultrasensitive biosensing method developed by the integration of fiber optic particle plasmon resonance and a highly selective molecular beacon with a stem-loop DNA structure immobilized on the unclad surface of an optical fiber. In the presence of Hg2+ ions and a free assisting DNA probe, the stem-loop opens and forms thymine-Hg2+-thymine complexes. A DNA reporting probe conjugated to gold nanoparticles is used as a label to interrogate the recognition event by binding with the terminal DNA binding domain of the opened stem-loop. The method provides a wide linear range of at least 5 orders from 10(-14) to 10(-9) M and an extremely low detection limit of 4.37 fM (0.876 ppq). It takes less than 15 min to analyze the concentration of Hg2+ ions in aqueous samples. The method is desirable for point-of-use applications because of its low-cost instrumentation and sensor chips, easy operation, and portability.

Automated summary

The introduced fast and ultrasensitive biosensing method for detecting highly toxic mercury ions relies on fiber optic particle plasmon resonance and a selective molecular beacon. It offers a wide linear range and an extremely low detection limit. The method is suitable for point-of-use applications due to its low-cost instrumentation, ease of use, and portability.