[Study on MSO/GO-based determination method for trace amount of aqueous Hg2+].

OBJECTIVE: To establish a highly sensitive fluorometric nanobiosensor for determination of aqueous mercury ions (Hg(2+)) using optimized mercury-specific oligonucleotide (MSO) probes and graphene oxide (GO). METHODS: The nanobiosensor was assembled by attaching the self-designed MSO(1) (5' end labeled with fluorophore carboxyfluorescein (FAM), denoted as FAM-MSO(1)) and MSO(2) to the surface of GO through strong non-covalent bonding forces. Upon the addition of Hg(2+), the formation of the T-Hg(2+)-T configuration desorbed the FAM-MSO(1) and MSO(2) from the surface of GO, resulting in a restoration of the fluorescence of FAM-MSO(1). Using the specific mispairing of T-Hg(2+)-T and the changes in fluorescent signals in solutions, quantitative analysis of Hg(2+) could be performed. RESULTS: The average thickness of the prepared GO sheets was only 1.4 nm. For the Hg(2+) nanobiosensor, the optimum concentrations of FAM-MSO(1) and MSO(2) were both 1 µmol/L, the optimum volume of 0.5 g/L GO was 5 µL, and the limit of detection was 10 pmol/L; it had low cross-reactivity with 10 other kinds of non-specific metal ions; the fluorescence recovery efficiency was up to 65% in the re-determination of Hg(2+) after addition of Na(2)S(2)O(3). CONCLUSION: The MSO/GO-based nanobiosensor is convenient to operate, highly sensitive, highly specific, highly accurate, and reusable. It can be applied to determine trace amount of Hg(2+) in aqueous solutions.

Aptasensors for rapid detection of Escherichia coli O157:H7 and Salmonella typhimurium.

Herein we reported the development of aptamer-based biosensors (aptasensors) based on label-free aptamers and gold nanoparticles (AuNPs) for detection of Escherichia coli (E. coli) O157:H7 and Salmonella typhimurium. Target bacteria binding aptamers are adsorbed on the surface of unmodified AuNPs to capture target bacteria, and the detection was accomplished by target bacteria-induced aggregation of the aptasensor which is associated as red-to-purple color change upon high-salt conditions. By employing anti-E. coli O157:H7 aptamer and anti-S. typhimurium aptamer, we developed a convenient and rapid approach that could selectively detect bacteria without specialized instrumentation and pretreatment steps such as cell lysis. The aptasensor could detect as low as 105colony-forming units (CFU)/ml target bacteria within 20 min or less and its specificity was 100%. This novel method has a great potential application in rapid detection of bacteria in the near future.

[Detection of mercury (II) ions (Hg(2+)) in water by a nanobiosensor].

OBJECTIVE: To develop a nanobiosensor for rapid colorimetric detecting Mercury (II) Ions (Hg(2+)) in water by mercury-specific oligonucleotides (MSOs) probe and gold nanoparticles. METHODS: The nanobiosensor was assembled by adsorbing the optimized MSOs on the surface of gold nanoparticles. A direct colorimetric probe of Hg(2+) which relied on the T-T mismatches in DNA duplexes was used to selectively and strongly capture Hg(2+). Hg(2+) induces the aggregation of gold nanoparticles with appropriate amount of salts, resulting the color change (red to blue). RESULTS: The diameter and concentration of the gold nanoparticle preparation were 15 nm and 2.97 nmol/L, respectively. Truncated MSOs (9 bp) showed the similar Hg(2+)-binding activity. The optimum concentration of the NaNO3 solution was 0.5 mol/L. The nanobiosensor could detect Hg(2+)in a range of 10 ∼ 1000 µmol/L within few minutes and the specificity was 100%. CONCLUSION: A new nanobiosensor is developed successfully for rapid colorimetric detecting Hg(2+) in water, avoiding either MSOs labeling or gold nanoparticles modification. This technique is simple, convenient and rapid detecting method with high sensitivity and specificity.