Identification of Mycoplasma pneumoniae by DNA-modified gold nanomaterials in a colorimetric assay.

Mycoplasma pneumoniae is a highly infectious bacterium and the major cause of pneumonia especially in school-going children. Mycoplasma pneumoniae affects the respiratory tract, and 25% of patients experience health-related problems. It is important to have a suitable method to detect M. pneumoniae, and gold nanoparticle (GNP)-based colorimetric biosensing was used in this study to identify the specific target DNA for M. pneumoniae. The color of GNPs changes due to negatively charged GNPs in the presence of positively charged monovalent (Na+ ) ions from NaCl. This condition is reversed in the presence of a single-stranded oligonucleotide, as it attracts GNPs but not in the presence of double-stranded DNA. Single standard capture DNA was mixed with optimal target DNA that cannot be adsorbed by GNPs; under this condition, GNPs are not stabilized and aggregate at high ionic strength (from 100 mM). Without capture DNA, the GNPs that were stabilized by capture DNA (from 1 µM) became more stable under high ionic conditions and retaining their red color. The GNPs turned blue in the presence of target DNA at concentrations of 1 pM, and the GNPs retained a red color when there was no target in the solution. This method is useful for the simple, easy, and accurate identification of M. pneumoniae target DNA at higher discrimination and without involving sophisticated equipment, and this method provides a diagnostic for M. pneumoniae.

Evaluation of Fe3O4-MnO2@RGO magnetic nanocomposite as an effective persulfate activator and metal adsorbent in aqueous solution.

A reduced graphene oxide (RGO) supported Fe3O4-MnO2 nanocomposite (Fe3O4-MnO2@RGO) was successfully prepared for catalytic degradation of oxytetracycline (20 mg/L) by potassium persulfate (PS) and adsorption removal of mixture of Pb2+, Cu2+, and Cd2+ ions (each 0.2 mM) in the synchronous scenario. The removal efficiencies of oxytetracycline, Pb2+, Cu2+, and Cd2+ ions were observed as high as 100%, 99.9%, 99.8%, and 99.8%, respectively, under the conditions of [PS]0 = 4 mM, pH0 = 7.0, Fe3O4-MnO2@RGO dosage = 0.8 g/L, reaction time = 90 min. The ternary composite exhibited higher oxytetracycline degradation/mineralization efficiency, greater metal adsorption capacity (Cd2+ 104.1 mg/g, Pb2+ 206.8 mg/g, Cu2+ 70.2 mg/g), and better PS utilization (62.6%) than its unary and binary counterparts including RGO, Fe3O4, Fe3O4@RGO, and Fe3O4-MnO2. More importantly, the ternary composite had good magnetic recoverability and excellent reusability. Notably, Fe, Mn, and RGO could play a synergistic role in the improvement of pollutant removal. Quenching results indicate that surface bounded SO4•- was the major contributor to oxytetracycline decomposition, and the -OH groups on the composite surface shouldered a significant role in PS activation. The results indicate that the magnetic Fe3O4-MnO2@RGO nanocomposite has a good potential for removing organic-metal co-contaminants in waterbody.