With the aim of treating effluent containing Cd2+, a low-cost and efficient technique has been established in this work. By a combination of sulfate-reducing bacteria (SRB), carboxymethyl konjac glucomannan (CMKGM), and nickel–iron bimetallic (Ni/Fe) nanoparticles, we greatly enhanced Cd2+ removal and bacteria resistance to metals toxicity. Furthermore, it had much higher removal efficiencies (99.72%) than SRB (57.38%), CMKGM (52.46%), and Ni/Fe (58.91%) systems after 48 h in the treat processes. The parameters effecting Cd2+ removal of this system were obtained: the initial Cd2+ concentrations 150 mg/L, optimum pH 7.0, optimum temperature 37 °C, optimum time 48 h, respectively. CMKGM and SRB played significant roles in Cd2+ adsorption as they contained many functional groups on their surfaces. In addition, SRB promoted the degeneration of inorganic contaminants. The mechanism of adsorption was clarified by a serious of analysis. Overall, this study provided a highly efficient activated biomaterial for the practical treatment of Cd2+ in wastewater.

•More than 97 % of heavy metals removal was achieved by the proposed biological methods.•Camellia oleifera cake degradation promoted by B. cereus created an anoxic•environment that supports SRB.•Both of SRB and B. cereus functioned as decomposers for Camellia oleifera cake and sweepers for heavy metals.•Camellia oleifera cake was either as sorbent or culture medium for bacteria.•Biomass particulates could be reused for metal biosorption to reduce the cost of production.To decontaminate heavy metal-containing waste water, a microbial biotechnology was developed by using the synergy between Sulfate reducing bacteria (SRB), Bacillus cereus (B. cereus) and Camellia oleifera cake (COC). In this process the COC degradation assisted by B.cereus, created an anoxic environment and provided energy and nutrition for SRB. Both of B. cereus and SRB played significant roles through biosorption, bioaccumulation and biosurfactant production. Meanwhile, a flotation technology commonly used in many effluent treatments has been led into this system for increasing the efficiency as well. After desorption and regeneration with acid and deionized water, the biosorbents could be reused to adsorb metal ions. 97% of heavy metals removal was achieved by the proposed technology. For multiple heavy metals-containing solutions, the capacities are in the order of Cd2+ > Zn2+ > Cu2+.

This article describes a sensitive and selective fluorometric method for the determination of Salmonella enteritidis by exploiting the polymerase activity of the Klenow fragment and dual fluorescence. First, one end of a target-selective aptamer was labeled with the fluorophore 6-carboxyfluorescein (FAM). Once the labeled aptamer binds to graphene oxide (GO) via π-stacking interaction, the fluorescence of FAM is quenched. However, the addition of target (16S rRNA) leads to the restoration of fluorescence due to the binding of probe and target which shifts the FAM fluorophore away from the quenching GO. By using the Klenow fragment and by exploiting the synergistic effect of FAM and the DNA probe SYBR Green I (which is strongly fluorescent in presence of dsDNA only), fluorescence is strongly amplified and sensitivity improved. The analyte 16SrRNA can be determined by this method in the 60 pM to 100 nM concentration range, and the detection limit is 60 pM. It is also shown that Salmonella enteritidis can be determined in milk samples by this method in concentrations between 102 to 105 cfu⋅mL‾1, with a detection limit of 300 cfu⋅mL‾1. This assay displays high sensitivity and selectivity and may possess wide applications in pathogen detection.

Outbreaks of Salmonella paratyphi A (S. paratyphi A) infection continue to occur worldwide and have drawn close attention. A useful practical detection platform is essential to the early rapid diagnosis of the infection. In this study, a simple and cost-effective DNA aptasensor was constructed, which was composed of a designed aptamer (DA) and two short carboxyfluorescein (FAM)-modified sequences (probe 1 and probe 2) for fluorimetric determination of S. paratyphi A. In the absence of a target, the two-FAM aptasensor (the aptasensor) was bound to graphene oxide (GO) and the fluorescence of FAM was quenched. In the presence of a target, however, the aptasensor was released from the surface of GO due to specific binding of the aptasensor to the target and a strong fluorescence signal could subsequently be detected. More importantly, the fluorescence signal could be substantially amplified by a DNase I-mediated target recycling process. Under the optimized conditions, the fluorescence intensity increased linearly with the target concentrations ranging from 1 × 102 to 1 × 1011 cells per mL with a detection limit of 1 × 102 cells per mL. These results demonstrated that this detection platform exhibited high sensitivity and specificity for the detection of S. paratyphi A, and it might even be a potential alternative approach for the detection of other bacteria.

In this study, we have developed a biosensor to detect adenosine triphosphate (ATP), based on fluorescence resonance energy transfer (FRET) and making use of the activities of exonuclease I (EXO I) and exonuclease III (EXO III). In the absence of ATP in the biosensor reaction system, the aptasensor is hydrolyzed by EXO I. When ATP is present, it conjugates with the aptasensor and protects it from hydrolysis by EXO I; the aptasensor can then hybridize with a fluorescent sequence linked to graphene oxide (GO). The dsDNA formed by the interaction between the aptasensor and the fluorescent sequence is then recognized and cleaved by EXO III. The increased distance between the fluorescent particle (FAM, 6-carboxyfluorescein) and the GO significantly hinders the FRET and increases the fluorescence of FAM. By incorporating EXO III into the process, the fluorescence signals of the biosensor are therefore greatly amplified and they were found to displayed a good linear relationship with ATP concentration, in the range from 0 to 3 μM. This system can be widely employed for the detection of other biological molecules.

•Convenience: The assay was performed within 2 h (including incubation time).•Environment friendly: We replaced the organic dyes with CNPs to fabricate molecule beacon.•Application: Our method has the potential for the detection of other molecules.Salmonella enteritidis (S. enteritidis) outbreaks continue to occur, and have increased public awareness of this pathogen. Nicking endonuclease Nb.BbvC I is widely used for the detection of biomolecules and displays activity for specific double-stranded DNA (dsDNA). In this study, we developed a biosensor to detect S. enteritidis based on fluorescence resonance energy transfer (FRET) using nicking enzyme and carbon nanoparticles (CNPs). Because of the quenching effect of black hole quencher 1 (BHQ 1), the CNPs do not fluoresce in the reaction system. When the target bacteria are added, the nicking enzyme recognizes and cleaves the dsDNA fabricated by the interaction between probe and target. As a result, the CNPs dissociate from BHQ 1and emit strong fluorescence. Using the nicking enzyme, the fluorescence signals of the biosensor are greatly amplified. The biosensor exhibited a linear relationship with the concentration of S. enteritidis ranging from 102 to 3×103 CFU/mL in water and from 1.5×102 to 3×103 CFU/mL in milk. The present results indicate that our FRET-based detection system can be widely employed for the effective detection of pathogens.

We report on an aptamer with high affinity against Salmonella typhimurium (S. typhimurium) and selected from an enriched oligonucleotide pool by a whole-cell SELEX process in a method for the fluorimetric determination of S. typhimurium using a graphene oxide platform. In the absence of target, the fluorescence was fairly weak as result of the FAM-labeled aptamer adjacent to graphene oxide. If, however, the fluorophore is released from the graphene oxide due to the formation of the target/aptamer complexes, fluorescence intensity is substantially increased. Under the optimum conditions, the assay displays a linear response to bacteria in the concentration range from 1 × 103 to 1 × 108 CFU·mL−1, with a detection limit of 100 CFU·mL−1. The method is selective in that fluorescence is not much enhanced in case of other bacteria. This aptasensor displays higher sensitivity and selectivity than others and is believed to possess a large potential with respect to the rapid detection of bacteria.

Nucleic acid aptamers have long demonstrated the capacity to bind cells with high affinity so that they have been utilized to diagnose various important pathogens. In this study, a DNA aptamer library was on initial efforts developed to act as a specific reporter for rapid detection of enter toxigenic Escherichia coli (ETEC) K88 combined with immuno-magnetic separation (IMS). During a Whole-cell Systematic Evolution of Ligands by Exponential Enrichment (CELL-SELEX) procedure, the last selection pool against ETEC K88, which is named “DNA aptamer library” here, was selected and subsequently identified by flow cytometric analysis and confocal imaging. A K88 monoclonal antibody (mAb) with high affinity (Kaff: 1.616 ± 0.033 × 108 M−1) against K88 fimbrial protein was prepared, biotinylated and conjugated to streptavidin-coated magnetic beads (MBs). After the bacteria were effectively captured and enriched from the complex sample by immuno-magnetic beads (IMBs), 5′-FITC modified aptamer library was directly bound to target cells as a specific reporter for its detection. The detection system showed clearly high specificity and sensitivity with the detection limit of 1.1 × 103 CFU/ml in pure culture and 2.2 × 103 CFU/g in artificially contaminated fecal sample. The results also indicated that fluorophore-lablled DNA aptamer library as specific reporter could generate more reliable signals than individual aptamer with best affinity against target cells and implied it would have great applied potential in directly reporting bacteria from complex samples combined with IMS technology.

In this paper, a novel and cost-effective homogeneous detection method was constructed for the detection of genomic DNA and Staphylococcus aureus (S. aureus), based on the noncovalent assembly of DNAzyme-labeled detection probe and single-walled carbon nanotubes (SWNTs). When the target genomic DNA and hemin was existed in the detection solution, the detection probe wrapped on the SWNTs by π-stacking interactions would keep away from SWNTs and form a DNAzyme-self-assembly construction. This DNAzyme construction could catalyze 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS2−) and generate a colored product which could lead to the absorbance changes. Hence, according to its catalyzed capacity, the DNAzyme construction could amplify the detection signal. The concentration of target DNA could be quantified by exploiting their optical absorption changes at 414 nm and the concentration limit of detection of the method was 30 nM. And this detection method detected S. aureus quantitatively. In addition, this work proved that the method obtain higher detection sensitivity compared with the method without SWNTs because of the protection profile of SWNTs towards the detection probe.

Fluorescence resonance energy transfer (FRET) between a quantum dot as donor and an organic fluorophore as acceptor has been widely used for detection of nucleic acids and proteins. In this paper, we developed a new method, characterized by 605-nm quantum dot (605QD) fluorescence intensity increase and corresponding Cy5 fluorescence intensity decrease, to detect adenosine triphosphate (ATP). The new method involved the use of three different oligonucleotides: 3′-biotin-modified DNA that binds to streptavidin-conjugated 605QD; 3′-Cy5-labelled DNA; and a capture DNA consisting of an ATP aptamer and a sequence which could hybridize with both 3′-biotin-modified DNA and 3′-Cy5-labelled DNA. In the absence of the target ATP, the capture DNA binds to 3′-biotin-modified DNA and 3′-Cy5-labelled DNA, bringing quantum dot and Cy5 into close proximity for greater FRET efficiency. When ATP is introduced, the release of the 3′-Cy5-labelled DNA from the hybridization complex took place, triggering 605QD fluorescence intensity increase and corresponding Cy5 fluorescence intensity decrease. Taken together, the virtue of FRET pair 605QD/Cy5 and the property of aptamer-specific conformation change caused by aptamer–ATP interaction, combined with the fluorescence intensity change of both 605QD and Cy5, provide prerequisites for simple and convenient ATP detection.

This study reported the hexavalent chromium removal by untreated Mucor racemosus biomass and the possible mechanism of Cr (VI) removal to the biomass. The optimum pH, biomass dose, initial Cr (VI) concentration and contact time were investigated thoroughly to optimize the removal condition. The metal removal by the biomass was strongly affected by pH and the optimum pH ranged from 0.5 to 1.0. The residual total Cr was determined. It was found that dichromate reduction occurred at a low very low pH value. At biomass dose 6 g/l, almost all the Cr (VI) ions were removed in the optimum condition. Higher removal percentage was observed at lower initial concentrations of Cr (VI) ions, while the removal capacity of the biomass linearly depended on the initial Cr (VI) concentration. More than half of Cr (VI) ions were diminished within 1 h of contact and removal process reached a relative equilibrium in approximately 8 h. Almost all of the Cr (VI) ions were removed in 24 h when initial concentrations were below 100 mg/l. The equilibrium data were fitted in to the Langmuir and the Freundlich isotherm models and the correlated coefficients were gained from the models. A Fourier transform infrared spectra was employed to elucidate clearly the possible biosorption mechanism as well.

Outbreaks of Salmonella paratyphi A (S. paratyphi A) infection continue to occur worldwide and have drawn close attention. A useful practical detection platform is essential to the early rapid diagnosis of the infection. In this study, a simple and cost-effective DNA aptasensor was constructed, which was composed of a designed aptamer (DA) and two short carboxyfluorescein (FAM)-modified sequences (probe 1 and probe 2) for fluorimetric determination of S. paratyphi A. In the absence of a target, the two-FAM aptasensor (the aptasensor) was bound to graphene oxide (GO) and the fluorescence of FAM was quenched. In the presence of a target, however, the aptasensor was released from the surface of GO due to specific binding of the aptasensor to the target and a strong fluorescence signal could subsequently be detected. More importantly, the fluorescence signal could be substantially amplified by a DNase I-mediated target recycling process. Under the optimized conditions, the fluorescence intensity increased linearly with the target concentrations ranging from 1 × 102 to 1 × 1011 cells per mL with a detection limit of 1 × 102 cells per mL. These results demonstrated that this detection platform exhibited high sensitivity and specificity for the detection of S. paratyphi A, and it might even be a potential alternative approach for the detection of other bacteria.