Hanchang Shi

Aptamer-Based Optical Biosensor For Rapid and Sensitive Detection of 17β-Estradiol In Water Samples

Required routine monitoring of endocrine disrupting compounds (EDCs) in water samples, as posed by EPA Unregulated Contaminant Regulation (UCMR3), demands for cost-effective, reliable and sensitive EDC detection methods. This study reports a reusable evanescent wave aptamer-based biosensor for rapid, sensitive and highly selective detection of 17β-estradiol, an EDC that is frequently detected in environmental water samples. In this system, the capture molecular, β-estradiol 6-(O-carboxy-methyl)oxime-BSA, was covalently immobilized onto the optical fiber sensor surface. With an indirect competitive detection mode, samples containing different concentrations of 17β-estradiol were premixed with a given concentration of fluorescence-labeled DNA aptamer, which highly specifically binds to 17β-estradiol. Then, the sample mixture is pumped to the sensor surface, and a higher concentration of 17β-estradiol leads to less fluorescence-labeled DNA aptamer bound to the sensor surface and thus to lower fluorescence signal. The dose-response curve of 17β-estradiol was established and a detection limit was determined as 2.1 nM (0.6 ng mL(-1)). The high specificity and selectivity of the sensor were demonstrated by evaluating its response to a number of potentially interfering EDCs. Potential interference of real environmental sample matrix was assessed by spiked samples in several tertiary wastewater effluents. The sensor can be regenerated with a 0.5% SDS solution (pH 1.9) over tens of times without significant deterioration of the sensor performance. This portable sensor system can be potentially applied for on-site real-time inexpensive and easy-to-use monitoring of 17β-estradiol in environmental samples such as effluents or water bodies.

Recent Advances in Optical Biosensors for Environmental Monitoring and Early Warning

The growing number of pollutants requires the development of innovative analytical devices that are precise, sensitive, specific, rapid, and easy-to-use to meet the increasing demand for legislative actions on environmental pollution control and early warning. Optical biosensors, as a powerful alternative to conventional analytical techniques, enable the highly sensitive, real-time, and high-frequency monitoring of pollutants without extensive sample preparation. This article reviews important advances in functional biorecognition materials (e.g., enzymes, aptamers, DNAzymes, antibodies and whole cells) that facilitate the increasing application of optical biosensors. This work further examines the significant improvements in optical biosensor instrumentation and their environmental applications. Innovative developments of optical biosensors for environmental pollution control and early warning are also discussed.

Study of operational conditions of simultaneous nitrification and denitrification in a Carrousel oxidation ditch for domestic wastewater treatment.

The study on the operational conditions of simultaneous nitrification and denitrification (SND) in the channel of oxidation ditch (OD) without the need for a special anoxic tank was carried out based on lab-scale and pilot-scale experiments using real domestic wastewater. The influence of sludge loading and component proportion in influent, temperature, hydraulic retention time (HRT), dissolved oxygen (DO) and operational mode on SND was investigated. The result indicated that the optimal DO (ODO) of SND occurrence was confirmed majorly by the sludge loading of influent and temperature, the high TCOD/NH(3)-N and short HRT can enhance the occurrence of SND. A new operational mode was proposed that achieved a higher removal efficiency of 60-70% for total nitrogen by SND with HRT of 4-6h, and the concentrations of NH(3)-N and TN in effluent are less than 5 and 15 mg/L, respectively.

Portable optical immunosensor for highly sensitive detection of microcystin-LR in water samples

Fast and sensitive detection of microcystin-LR (MC-LR) was conducted with a portable trace organic pollutant analyzer (TOPA) based on the principle of immunoassay and total internal reflection fluorescence. The reusable fiber optic probe surface was produced by covalently immobilizing a MC-LR-ovalbumin (MC-LR-OVA) conjugate onto a self-assembled thiol-silane monolayer of fiber optic probe through a heterobifunctional reagent. It has been established that the MC-LR-OVA immobilized fiber optic probe is highly resistive to non-specific binding of proteins, while bound anti-MC-LR antibody can easily be eluted from the immunosurface with high recoveries (more than 150 assay cycles) in the way of pepsin solution, without any damage to the surface-immobilized MC-LR derivatives. One assay cycle including surface regeneration was less than 20 min. For the standard curve, the limit of detection (LOD) of 0.03 microg/L and the quantitative detection range of 0.1-10.1 microg/L was obtained when the concentration of antibody labeled by Cy5.5 was 0.28 microg/mL. Cross-reactivity against a few compounds structurally similar to MC-LR was little. The developed immunosensor method was applied to the monitoring of MC-LR in various types of water. The recovery of MC-LR added to water samples at different concentrations ranged from 80 to 110% with relative standard deviation (R.S.D.) values less than 5%. The immunoassay performance of the TOPA was validated with respect to conventional high-performance liquid chromatography, and the correlation between methods was in good agreement (r(2)=0.9978). The TOPA is a portable, easy-to-use, and robust immunoassay system and commercially obtained from the company JQ-environ Co. Ltd. (China).

Biodegradation of 2,4-dichlorophenol in sequencing batch reactors augmented with immobilized mixed culture

2,4-Dichlorophenol (2,4-DCP) degrading mixed culture was immobilized in polyvinyl alcohol jel beads and supplemented to sequencing batch reactors (SBR) to treat 2,4-DCP containing wastewater. Impacts of bioaugmentation level on the performance of bioaugmented systems were studied. Results show that inoculum size affected the start-up time of the SBR systems. For the non-augmented SBR system, nine days was needed for the system to start-up, whereas it only took six, four, three and two days for the SBRs with 1.9%, 3.7%, 5.6% and 9.3% immobilized culture, respectively. In addition, bioaugmented SBR systems demonstrated stronger capacity to cope with high 2,4-DCP shock loading than the control system. The control SBR failed to treat 2,4-DCP at 166 mg/l in influent, while the SBR with 1.9% inoculation could successfully cope with 2,4-DCP at 166 mg/l, but failed at 250 mg/l, and the SBR with 3.7%, 5.6% and 9.3% immobilized culture could successfully degrade 250 mg/l 2,4-DCP in feed. Furthermore, the contributions to the removal of 2,4-DCP by the introduced and indigenous culture in an augmented SBR system at various operation stages were investigated. It was found that augmented culture played the primary role in degrading 2,4-DCP at the beginning of system start-up, but after one-month operation, both the indigenous and the introduced culture posed strong ability to degrade 2,4-DCP.

Biodegradation of 2,4-dichlorophenol and phenol in an airlift inner-loop bioreactor immobilized with Achromobacter sp

An airlift inner-loop bioreactor packed with honeycomb-like ceramic as the carrier was developed and its capacity to immobilize microorganism was studied through adding bacteria, Achromobactersp., capable of degrading 2,4-dichlorophenol (2,4-DCP), directly to the reactor under continuous operation. Effects of phenol in the feed with 2,4-DCP on 2,4-DCP removal were investigated under fed-batch and continuous operations. The results showed that the pure strain could be easily immobilized on the carrier and proliferated using 2,4-DCP as the sole carbon source. In the process of fed-batch operation, removal rate of 2,4-DCP decreased with the increase in run number, while that of phenol was just to the contrary. In the continuous operation, 2,4-DCP loading rate was kept at 29.72‐32.23 mg/(l day), but phenol loading rate was increased stepwise from 325.56 to 602.79 mg/(l day). The results showed that with the increase of phenol loading rates, the removal efficiency of 2,4-DCP declined from 100 to 87.9%, while that of phenol remained at about 99.6%. Presence of phenol in feed inhibited the biodegradation of 2,4-DCP and caused the major carbon source shift from 2,4-DCP to phenol.

A reusable aptamer-based evanescent wave all-fiber biosensor for highly sensitive detection of Ochratoxin A.

Although aptamer-based biosensors have attracted ever-increasing attentions and found potential applications in a wide range of areas, they usually adopted the assay protocol of immobilizing DNA probe (e.g., aptamer, aptamer-complementary oligonucleotides) on a solid sensing surface, making it critical and challengeable to keep the integration of nucleic acid surface during the regeneration and the restoration to its original DNA probe form after repeated uses. In order to address the issue, we report a novel aptamer-based biosensing strategy based on an evanescent wave all-fiber (EWA) platform. In a simple target capturing step using aptamer-functionalized magnetic microbeads, signal probes conjugated with streptavidin are released and further detected by a EWA biosensor via a facial dethiobiotin-streptavidin recognition. Apart from the inherent advantages of aptamer-based evanescent wave biosensors (e.g. target versatility, sensitivity, selectivity and portability), the proposed strategy exhibits a high stability and remarkable reusability over other aptasensors. Under the optimized conditions, the typical calibration curve obtained for Ochratoxin A has a detection limit of 3nM with a linear response ranging from 6nM to 500nM. The dethiobiotin-streptavidin sensing surface instead of the traditional nucleic acid one can be reused for over 300 times without losing sensitivity.

Rapid on-site/in-situ detection of heavy metal ions in environmental water using a structure-switching DNA optical biosensor.

A structure-switching DNA optical biosensor for rapid on-site/in situ detection of heavy metal ions is reported. Mercury ions (Hg2+), highly toxic and ubiquitous pollutants, were selected as model target. In this system, fluorescence-labeled DNA containing T-T mismatch structure was introduced to bind with DNA probes immobilized onto the sensor surface. In the presence of Hg2+, some of the fluorescence-labeled DNAs bind with Hg2+ to form T-Hg2+-T complexes through the folding of themselves into a hairpin structure and dehybridization from the sensor surface, which leads to decrease in fluorescence signal. The total analysis time for a single sample was less than 10 min with detection limit of 1.2 nM. The rapid on-site/in situ determination of Hg2+ was readily performed in natural water. This sensing strategy can be extended in principle to other metal ions by substituting the T-Hg2+-T complexes with other specificity structures that selectively bind to other analytes.

Aggregation behavior of engineered nanoparticles and their impact on activated sludge in wastewater treatment

The ever-increasing daily use of engineered nanoparticles will lead to heightened levels of these materials in the environment. These nanomaterials will eventually go into the wastewater treatment plant (WWTP), therefore, resulting into a pressing need for information on their aggregation behavior and kinetics in the wastewater aqueous matrix. In this work, we dispersed two different metal oxide nanoparticles (ZnO and TiO2) into the influent of two different WWTPs. Through the time-resolved dynamic light scattering analysis and transmission electron microscopy, the metal oxide nanoparticles (NPs) were quite stably existed in the wastewater matrix with aggregates of diameter 300-400 nm after 4.5h or more suspension. We confirmed that the dissolved organic matters (DOMs) attributed to the stability of nanoparticles. No propensity of NPs to aggregate were observed in the presence of both monovalent and divalent electrolytes even at high concentrations up to 0.15 M in NaCl or 0.025 M in CaCl2, indicating that the destabilization of nanoparticles in the complicated wastewater matrix was not achieved by the compression of electrical double layer, therefore, their aggregation kinetics cannot be simply predicted by the classic Derjaguin-Landau-Verwey-Overbeek theory of colloidal stability. However, obvious aggregation of nanoparticles in the Al2(SO4)3 solution system was observed with the likely mechanism of bridging of the metal oxide nanoparticles and aggregates due to the formation of hydrous alumina (Al(OH)3·H2O) in the Al2(SO4)3 solution. In the wastewater matrix, we used the noninvasive measurement technology to detect the O2 flux of activated sludge before and after treatment with 1, 10 and 100 mg L(-1) NPs. The results confirmed that both ZnO and TiO2 NPs showed an adverse impact on the O2 uptake of activated sludge when the exposure time extended to 4.5 h.

Removal of 2,4-dichlorophenol in a conventional activated sludge system through bioaugmentation

For the removal of toxic and recalcitrant organic substances intermittently appearing in wastewater, bioaugmentation with bacteria having specific degradation ability could be a powerful tool to improve the treatment process. 2,4-Dichlorophenol (2,4-DCP) was chosen as the target recalcitrant substance and a 2,4-DCP degrading special mixed culture was used as bioaugmentation microorganisms. The feasibility and strategies to combine bioaugmentation into a conventional activated sludge (CAS) system in terms of enhancing its efficiency and reliability was investigated. Results showed that for domestic wastewater with multiple chlorophenols, bioaugmentation with a 2,4-DCP degrading culture in a CAS system not only enhanced the removal of 2,4-DCP effectively, but also improved the removal of other chlorophenols such as 4-monochlorophenol (4-MCP) and 2,4,5-trichlorophenol (2,4,5-TCP). A separate bioaugmented bioreactor was combined into the original CAS system at different locations and the effects of the bioaugmentation location on the performance of the combined biotreatment process were studied. Results indicated that the CAS-Bioaug system, in which the bioaugmented bioreactor was set at a location after the original CAS reactor, performed better than the Bioaug-CAS system, in which the bioaugmented bioreactor was placed before the original CAS reactor. Bioaugmentation could be used as an effective and efficient method to improve a CAS process facing sudden toxic pollutant shock loading.