Publications by authors named "Michael R Hoffmann"

97 Publications

Membrane-Based In-Gel Loop-Mediated Isothermal Amplification (mgLAMP) System for SARS-CoV-2 Quantification in Environmental Waters.

Environ Sci Technol 2021 Dec 30. Epub 2021 Dec 30.

Linde Laboratories, California Institute of Technology, Pasadena, California 91125, United States.

Since the COVID-19 pandemic is expected to become endemic, quantification of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in ambient waters is critical for environmental surveillance and for early detection of outbreaks. Herein, we report the development of a membrane-based in-gel loop-mediated isothermal amplification (mgLAMP) system that is designed for the rapid point-of-use quantification of SARS-CoV-2 particles in environmental waters. The mgLAMP system integrates the viral concentration, in-assay viral lysis, and on-membrane hydrogel-based RT-LAMP quantification using enhanced fluorescence detection with a target-specific probe. With a sample-to-result time of less than 1 h, mgLAMP successfully detected SARS-CoV-2 below 0.96 copies/mL in Milli-Q water. In surface water, the lowest detected SARS-CoV-2 concentration was 93 copies/mL for mgLAMP, while the reverse transcription quantitative polymerase chain reaction (RT-qPCR) with optimal pretreatment was inhibited at 930 copies/mL. A 3D-printed portable device is designed to integrate heated incubation and fluorescence illumination for the simultaneous analysis of nine mgLAMP assays. Smartphone-based imaging and machine learning-based image processing are used for the interpretation of results. In this report, we demonstrate that mgLAMP is a promising method for large-scale environmental surveillance of SARS-CoV-2 without the need for specialized equipment, highly trained personnel, and labor-intensive procedures.
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http://dx.doi.org/10.1021/acs.est.1c04623DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8751019PMC
December 2021

Onsite Graywater Treatment in a Two-Stage Electro-Peroxone Reactor with a Partial Recycle of Treated Effluent.

ACS ES T Eng 2021 Dec 11;1(12):1659-1667. Epub 2021 Oct 11.

Department of Environmental Science and Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, California 91125, United States.

The efficacy of an uncoupled electro-peroxone (E-peroxone) prototype reactor system for the treatment of synthetic graywater is determined. The two-stage E-peroxone process integrates ozonation with the production of hydrogen peroxide (HO) in a first stage reactor before ozone (O) is converted via the peroxone reaction to a hydroxyl radical (OH). The two-stage prototype reactor system allows for the generation of HO via cathodic oxygen reduction in the first-stage reactor before mixing with O in the second-stage reactor. This approach prevents the degradation of polytetrafluoroethylene (PTFE) coated carbon cathodes by OH that takes place in a single well-mixed reactor that combines electrochemical peroxide generation with O. The dosage of HO into the second-stage reactor is optimized to enhance graywater treatment. Under these conditions, the uncoupled E-peroxone system is capable of treating synthetic graywater with an initial chemical oxygen demand (COD) of 358 mg O/L, a total organic carbon (TOC) of 96.9 mg/L, a biochemical oxygen demand (BOD) of 162 mg O/L, and a turbidity of 11.2 NTU. The two-stage electro-peroxone system can reduce the initial COD by 89%, the TOC by 91%, BOD by 86%, and the turbidity by 95% after 90 min of treatment. At this performance level, the reactor effluent is acceptable for discharge and for use in nonpotable applications such as toilet-water flushing. A portion of the effluent is recycled back into the first-stage reactor to minimize water consumption. Recycling can be repeated consecutively for four or more cycles, although the time required to achieve the desired HO concentration increased slightly from one cycle to another. The two-stage E-peroxone system is shown to be potentially useful for onsite or decentralized graywater treatment suitable for arid water-sensitive areas.
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http://dx.doi.org/10.1021/acsestengg.1c00240DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8669644PMC
December 2021

Role of Ferryl Ion Intermediates in Fast Fenton Chemistry on Aqueous Microdroplets.

Environ Sci Technol 2021 11 2;55(21):14370-14377. Epub 2021 Jul 2.

Linde Laboratories, California Institute of Technology, Pasadena, California 91125, United States.

In the aqueous environment, Fe ions enhance the oxidative potential of ozone and hydrogen peroxide by generating the reactive oxoiron species (ferryl ion, FeO) and hydroxyl radical (·OH) via Fenton chemistry. Herein, we investigate factors that control the pathways of these reactive intermediates in the oxidation of dimethyl sulfoxide (MeSO) in Fe solutions reacting with O in both bulk-phase water and on the surfaces of aqueous microdroplets. Electrospray ionization mass spectrometry is used to quantify the formation of dimethyl sulfone (MeSO, from FeO + MeSO) and methanesulfonate (MeSO, from ·OH + MeSO) over a wide range of Fe and O concentrations and pH. In addition, the role of environmentally relevant organic ligands on the reaction kinetics was also explored. The experimental results show that Fenton chemistry proceeds at a rate ∼10 times faster on microdroplets than that in bulk-phase water. Since the production of MeSO is initiated by ·OH radicals at diffusion-controlled rates, experimental ratios of MeSO/MeSO > 10 suggest that FeO is the dominant intermediate under all conditions. MeSO yields in the presence of ligands, L, vary as volcano-plot functions of E(LFeO+ O/LFe + O) reduction potentials calculated by DFT with a maximum achieved in the case of L≡oxalate. Our findings underscore the key role of ferryl FeO intermediates in Fenton chemistry taking place on aqueous microdroplets.
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http://dx.doi.org/10.1021/acs.est.1c01962DOI Listing
November 2021

Development of a Mechanically Flexible 2D-MXene Membrane Cathode for Selective Electrochemical Reduction of Nitrate to N: Mechanisms and Implications.

Environ Sci Technol 2021 08 16;55(15):10695-10703. Epub 2021 Jun 16.

State Key Laboratory of Pollution Control and Resource Reuse, Shanghai Institute of Pollution Control and Ecological Security, School of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China.

The contamination of water resources by nitrate is a major problem. Herein, we report a mechanically flexible 2D-MXene (TiCT) membrane with multilayered nanofluidic channels for a selective electrochemical reduction of nitrate to nitrogen gas (N). At a low applied potential of -0.8 V (vs Ag/AgCl), the MXene electrochemical membrane was found to exhibit high selectivity for NO reduction to N (82.8%) due to a relatively low desorption energy barrier for the release of adsorbed N (*N) compared to that for the adsorbed NH (*NH) based on density functional theory (DFT) calculations. Long-term use of the MXene membrane for treating 10 mg-NO-N L in water was found to have a high faradic efficiency of 72.6% for NO reduction to N at a very low electrical cost of 0.28 kWh m. Results of theoretical calculations and experimental results showed that defects on the MXene nanosheet surfaces played an important role in achieving high activity, primarily at the low-coordinated Ti sites. Water flowing through the MXene nanosheets facilitated the mass transfer of nitrate onto the low-coordinated Ti sites with this enhancement of particular importance under cathodic polarization of the MXene membrane. This study provides insight into the tailoring of nanoengineered materials for practical application in water treatment and environmental remediation.
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http://dx.doi.org/10.1021/acs.est.1c00264DOI Listing
August 2021

Porous carbon monoliths for electrochemical removal of aqueous herbicides by "one-stop" catalysis of oxygen reduction and HO activation.

J Hazard Mater 2021 07 5;414:125592. Epub 2021 Mar 5.

College of Environmental and Resource Science Zhejiang University, Hangzhou 310058, China. Electronic address:

The overuse of herbicides has posed a threat to human health and the aquatic environment via DNA mutations and antibiotic gene resistance. Carbon-based cathodic electrochemical advanced oxidation has evolved as a promising technology for herbicide degradation by generating hydroxyl radicals (•OH). However, conventional electro-Fenton process relies on interaction of multiple species that adds to the system complexity and cost and narrows the working pH range. Herein, a series of porous carbon monoliths (PCMs) were developed as a "one-stop" platform for catalysis of the 2-electron ORR coupled with further catalytic reductive cleavage of HO to produce •OH. A PCM prepared using 1,6-hexamethylene diamine (denoted as PCM-HDA) produced HO at a level that was 374% higher than that obtained using commercially available carbon black at circum-neutral pH. Meanwhile, the generated HO was catalytically decomposed to produce •OH. Based on these results, the PCM-HDA electrode achieved an 80 ± 2% degradation of napropamide in 60 min over the pH range of 4-10 at a mildly reducing potential, with a 69 ± 2% TOC reduction at circum-neutral condition in 2 h. This simplified system overcomes the system complexity and pH limitation of the conventional electron-Fenton processes.
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http://dx.doi.org/10.1016/j.jhazmat.2021.125592DOI Listing
July 2021

Single-Cell Phenotypic Analysis and Digital Molecular Detection Linkable by a Hydrogel Bead-Based Platform.

ACS Appl Bio Mater 2021 Mar 12;4(3):2664-2674. Epub 2021 Feb 12.

Linde+Robinson Laboratories, California Institute of Technology, Pasadena, California 91125, United States.

Cell heterogeneity, such as antibiotic heteroresistance and cancer cell heterogeneity, has been increasingly observed. To probe the underlying molecular mechanisms in the dynamically changing heterogeneous cells, a high throughput platform is urgently needed to establish single cell genotype-phenotype correlations. Herein, we report a platform combining single-cell viability phenotypic analysis with digital molecular detection for bacterial cells. The platform utilizes polyethylene glycol hydrogel that cross-links through a thiol-Michael addition, which is biocompatible, fast, and spontaneous. To generate uniform nanoliter-sized hydrogel beads (Gelbeads), we developed a convenient and disposable device made of needles and microcentrifuge tubes. Gelbead-based single cell viability and molecular detection assays were established. Enhanced thermal stability and uncompromised efficiency were achieved for digital polymerase chain reaction (PCR) and digital loop-mediated isothermal amplification (LAMP) within the Gelbeads. Reagent exchange for in situ PCR following viability phenotypic analyses was demonstrated. The combined analyses may address the genotypic differences between cellular subpopulations exhibiting distinct phenotypes. The platform promises unique perspectives in mechanism elucidation of environment-evolution interaction that may be extended to other cell types for medical research.
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http://dx.doi.org/10.1021/acsabm.0c01615DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7976597PMC
March 2021

Enhanced chlorine evolution from dimensionally stable anode by heterojunction with Ti and Bi based mixed metal oxide layers prepared from nanoparticle slurry.

J Catal 2020 Sep;389:1-8

Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Republic of Korea.

This study reports enhanced current (CE) and energy efficiency (EE) of reactive chlorine species (RCS) generation on IrTaO anode by Ti/Bi mixed metal oxide heterojunction layers despite reductions in pseudo-capacitance and film conductivity. In potentiostatic electrolysis of 50 mM NaCl solutions, dramatic improvement (0.61 mmol cm hr at 2.5 V NHE) was noted by simple coating of thin (~2 μm) TiO layer from ball-milled TiO nanoparticle (80-100 nm) suspension, even with moderate elevation in voltammetric wave. Decoration of BiO particles (1 - 2 μm) showed limited or adverse effects for RCS generation and stability. However, Bi-doped TiO layers prepared from polyol-mediated or co-precipitation methods marked the highest CE (~100%) and EE (8.16 mmol Wh at 2.5 V NHE) by increased mixing level and effective shift in surface charge. Surface ·OH exclusively mediated the RCS generation whose further transformation to higher oxide could be restrained by the heterojunction layer.
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http://dx.doi.org/10.1016/j.jcat.2020.04.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7539370PMC
September 2020

Proton-assisted electron transfer and hydrogen-atom diffusion in a model system for photocatalytic hydrogen production.

Commun Mater 2020 21;1(1):66. Epub 2020 Sep 21.

Division of Engineering and Applied Science, Linde-Robinson Laboratory, California Institute of Technology, Pasadena, CA 91125 USA.

Solar energy can be converted into chemical energy by photocatalytic water splitting to produce molecular hydrogen. Details of the photo-induced reaction mechanism occurring on the surface of a semiconductor are not fully understood, however. Herein, we employ a model photocatalytic system consisting of single atoms deposited on quantum dots that are anchored on to a primary photocatalyst to explore fundamental aspects of photolytic hydrogen generation. Single platinum atoms (Pt) are anchored onto carbon nitride quantum dots (CNQDs), which are loaded onto graphitic carbon nitride nanosheets (CNS), forming a [email protected]/CNS composite. [email protected]/CNS provides a well-defined photocatalytic system in which the electron and proton transfer processes that lead to the formation of hydrogen gas can be investigated. Results suggest that hydrogen bonding between hydrophilic surface groups of the CNQDs and interfacial water molecules facilitates both proton-assisted electron transfer and sorption/desorption pathways. Surface bound hydrogen atoms appear to diffuse from CNQDs surface sites to the deposited Pt catalytic sites leading to higher hydrogen-atom fugacity surrounding each isolated Pt site. We identify a pathway that allows for hydrogen-atom recombination into molecular hydrogen and eventually to hydrogen bubble evolution.
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http://dx.doi.org/10.1038/s43246-020-00068-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7505813PMC
September 2020

3D-Printed Flow Cells for Aptamer-Based Impedimetric Detection of Crooks Strain.

Sensors (Basel) 2020 Aug 7;20(16). Epub 2020 Aug 7.

Institute of Technical Chemistry, Leibniz University Hannover, Callinstraße 5, 30167 Hannover, Germany.

Electrochemical spectroscopy enables rapid, sensitive, and label-free analyte detection without the need of extensive and laborious labeling procedures and sample preparation. In addition, with the emergence of commercially available screen-printed electrodes (SPEs), a valuable, disposable alternative to costly bulk electrodes for electrochemical (bio-)sensor applications was established in recent years. However, applications with bare SPEs are limited and many applications demand additional/supporting structures or flow cells. Here, high-resolution 3D printing technology presents an ideal tool for the rapid and flexible fabrication of tailor-made, experiment-specific systems. In this work, flow cells for SPE-based electrochemical (bio-)sensor applications were designed and 3D printed. The successful implementation was demonstrated in an aptamer-based impedimetric biosensor approach for the detection of () Crooks strain as a proof of concept. Moreover, further developments towards a 3D-printed microfluidic flow cell with an integrated micromixer also illustrate the great potential of high-resolution 3D printing technology to enable homogeneous mixing of reagents or sample solutions in (bio-)sensor applications.
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http://dx.doi.org/10.3390/s20164421DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7472219PMC
August 2020

Rapid Detection Methods for Bacterial Pathogens in Ambient Waters at the Point of Sample Collection: A Brief Review.

Clin Infect Dis 2020 07;71(Suppl 2):S84-S90

Linde + Robinson Laboratories, California Institute of Technology, Pasadena, California, USA.

The world is currently facing a serious health burden of waterborne diseases, including diarrhea, gastrointestinal diseases, and systemic illnesses. The control of these infectious diseases ultimately depends on the access to safe drinking water, properly managed sanitation, and hygiene practices. Therefore, ultrasensitive, rapid, and specific monitoring platforms for bacterial pathogens in ambient waters at the point of sample collection are urgently needed. We conducted a literature review on state-of-the-art research of rapid in-field aquatic bacteria detection methods, including cell-based methods, nucleic acid amplification detection methods, and biosensors. The detection performance, the advantages, and the disadvantages of the technologies are critically discussed. We envision that promising monitoring approaches should be automated, real-time, and target-multiplexed, thus allowing comprehensive evaluation of exposure risks attributable to waterborne pathogens and even emerging microbial contaminants such as antibiotic resistance genes, which leads to better protection of public health.
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http://dx.doi.org/10.1093/cid/ciaa498DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7388722PMC
July 2020

In Situ-Generated Reactive Oxygen Species in Precharged Titania and Tungsten Trioxide Composite Catalyst Membrane Filters: Application to As(III) Oxidation in the Absence of Irradiation.

Environ Sci Technol 2020 08 29;54(15):9601-9608. Epub 2020 Jun 29.

School of Energy Engineering, Kyungpook National University, Daegu 41566, Korea.

This study demonstrates that in situ-generated reactive oxygen species (ROSs) in prephotocharged TiO and WO (TW) composite particle-embedded inorganic membrane filters oxidize arsenite (As(III)) into arsenate (As(V)) without any auxiliary chemical oxidants under ambient conditions in the dark. TW membrane filters have been charged with UV or simulated sunlight and subsequently transferred to a once-through flow-type system. The charged TW filters can transfer the stored electrons to dissolved O, producing ROSs that mediate As(III) oxidation in the dark. Dramatic inhibition of As(V) production with O removal or addition of ROS quenchers indicates an ROS-mediated As(III) oxidation mechanism. Electron paramagnetic spectroscopic analysis has confirmed the formation of the HO/O pair in the dark. The WO fraction in the TW filter significantly influences the performance of the As(III) oxidation, while As(V) production is enhanced with increasing charging time and solution pH. The As(III) oxidation is terminated when the singly charged TW filter is fully discharged; however, recharging of TW recovers the catalytic activity for As(III) oxidation. The proposed oxidation process using charged TW membrane filters is practical and environmentally benign for the continuous treatment of As(III)-contaminated water during periods of unavailability of sunlight.
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http://dx.doi.org/10.1021/acs.est.0c01550DOI Listing
August 2020

C-14 powered dye-sensitized betavoltaic cells.

Chem Commun (Camb) 2020 Jul 4;56(52):7080-7083. Epub 2020 Jun 4.

Department of Energy Science & Engineering, Daegu Gyeongbuk Institute of Science & Technology (DGIST), 333 Techno Jungang-daero, Hyeonpung-eup, Dalseong-Gun, Daegu, 42988, Republic of Korea.

A dye-sensitized betavoltaic cell is developed for the first time, which utilizes radioisotopic carbon, composed of nano-sized quantum dots, and ruthenium-based dye sensitized TiO as electrodes. In this cell, emitted beta radiations are absorbed by the dye rather than TiO, which resulted in enhanced performance compared to the pristine betavoltaic cell.
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http://dx.doi.org/10.1039/d0cc02046jDOI Listing
July 2020

Photochemical transformation of perfluoroalkyl acid precursors in water using engineered nanomaterials.

Water Res 2020 Aug 20;181:115964. Epub 2020 May 20.

Department of Environmental Science & Engineering, California Institute of Technology, Pasadena, CA, 91125, United States. Electronic address:

The production of perfluoroalkyl acids (PFAAs) has been phased out over recent decades; however, no significant decline in their environmental concentrations has been observed. This is partly due to the photochemical decomposition of PFAAs precursors (PrePFAAs) which remain in extensive use. The decomposition of PrePFAAs may be accelerated by the light-activated engineered nanomaterials (ENMs) in water. In light of this hypothesis, we investigated the photochemical transformation of three PrePFAAs, which are 8:2 fluorotelomer sulfonic acid (8:2 FTSA), 8:2 fluorotelomer alcohol (8:2 FTOH), and 2-(N-ethylperfluorooctane-1-sulfonamido ethyl] phosphate (SAmPAP), in the presence of six ENMs under simulated sunlight irradiation. The transformation rates of 8:2 FTSA and 8:2 FTOH were increased by 2-6 times when in the presence of six ENMs. However, most of ENMs appeared to inhibit the decomposition of SAmPAP. The transformation rates of PrePFAAs were found to depend on the yield of reactive oxygen species generated by ENMs, but the rates were also related to compound photo-stability, adsorption to surfaces, and photo-shielding effects. The PrePFAAs are transformed to perfluorooctanoic acid (PFOA) or/and perfluorooctane sulfonate (PFOS) with higher toxicity and longer half-life, PFOA or PFOS and a few PFAAs having shorter carbon chain lengths. Higher concentrations of the PFAAs photodegradation products were observed in the presence of most of the ENMs.
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http://dx.doi.org/10.1016/j.watres.2020.115964DOI Listing
August 2020

Synthesis and application of superabsorbent polymer microspheres for rapid concentration and quantification of microbial pathogens in ambient water.

Sep Purif Technol 2020 May;239:116540

Linde+ Robinson Laboratories, California Institute of Technology, Pasadena, CA 91125, United States.

Even though numerous methods have been developed for the detection and quantification of waterborne pathogens, the application of these methods is often hindered by the very low pathogen concentrations in natural waters. Therefore, rapid and efficient sample concentration methods are urgently needed. Here we present a novel method to pre-concentrate microbial pathogens in water using a portable 3D-printed system with super-absorbent polymer (SAP) microspheres, which can effectively reduce the actual volume of water in a collected sample. The SAP microspheres absorb water while excluding bacteria and viruses by size exclusion and charge repulsion. To improve the water absorption capacity of SAP in varying ionic strength waters (0-100 mM), we optimized the formulation of SAP to 180 g⋅L Acrylamide, 75 g⋅L Itaconic Acid and 4.0 g⋅L Bis-Acrylamide for the highest ionic strength water as a function of the extent of cross-linking and the concentration of counter ions. Fluorescence microscopy and double-layer agar plating respectively showed that the 3D-printed system with optimally-designed SAP microspheres could rapidly achieve a 10-fold increase in the concentration of () and bacteriophage MS2 within 20 min with concentration efficiencies of 87% and 96%, respectively. Fold changes between concentrated and original samples from qPCR and RT-qPCR results were found to be respectively 11.34-22.27 for with original concentrations from 10 to 10 cell·mL, and 8.20-13.81 for MS2 with original concentrations from 10 to 10 PFU·mL. Furthermore, SAP microspheres can be reused for 20 times without performance loss, significantly decreasing the cost of our concentration system.
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http://dx.doi.org/10.1016/j.seppur.2020.116540DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7045201PMC
May 2020

Electrochemical cell lysis of gram-positive and gram-negative bacteria: DNA extraction from environmental water samples.

Electrochim Acta 2020 Apr;338:135864

Linde+Robinson Laboratories, California Institute of Technology, Pasadena, CA 91125, USA.

Cell lysis is an essential step for the nucleic acid-based surveillance of bacteriological water quality. Recently, electrochemical cell lysis (ECL), which is based on the local generation of hydroxide at a cathode surface, has been reported to be a rapid and reagent-free method for cell lysis. Herein, we describe the development of a milliliter-output ECL device and its performance characterization with respect to the DNA extraction efficiency for gram-negative bacteria ( and Typhi) and gram-positive bacteria ( and ). Both gram-negative and gram-positive bacteria were successfully lysed within a short but optimal duration of 1 min at a low voltage of ∼5 V. The ECL method described herein, is demonstrated to be applicable to various environmental water sample types, including pond water, treated wastewater, and untreated wastewater with DNA extraction efficiencies similar to a commercial DNA extraction kit. The ECL system outperformed homogeneous chemical lysis in terms of reaction times and DNA extraction efficiencies, due in part to the high pH generated at the cathode surface, which was predicted by simulations of the hydroxide transport in the cathodic chamber. Our work indicates that the ECL method for DNA extraction is rapid, simplified and low-cost with no need for complex instrumentation. It has demonstrable potential as a prelude to PCR analyses of waterborne bacteria in the field, especially for the gram-negative ones.
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http://dx.doi.org/10.1016/j.electacta.2020.135864DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7063685PMC
April 2020

Finite-pulse waves for efficient suppression of evolving mesoscale dendrites in rechargeable batteries.

Phys Rev E 2019 Oct;100(4-1):042801

California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA.

The ramified and stochastic evolution of dendritic microstructures has been a major issue on the safety and longevity of rechargeable batteries, particularly for the utilization of high-energy metallic electrodes. We analytically develop criteria for the pulse characteristics leading to the effective halting of the ramified electrodeposits grown during extensive timescales beyond inter-ionic collisions. Our framework is based on the competitive interplay between diffusion and electromigration and tracks the gradient of ionic concentration throughout the entire cycle of pulse-rest as a critical measure for heterogeneous evolution. In particular, the framework incorporates the Brownian motion of the ions and investigates the role of the geometry of the electrodeposition interface. Our experimental observations verify the analytical developments, where the dimension-free developments allows the application to the electrochemical systems of various scales.
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http://dx.doi.org/10.1103/PhysRevE.100.042801DOI Listing
October 2019

Substrate oxidation enhances the electrochemical production of hydrogen peroxide.

Chem Eng J 2019 Oct;374:958-964

Linde + Robinson Laboratories, California Institute of Technology, Pasadena, CA 91125, United States.

Hydrogen peroxide (HO) is electrochemically produced via oxygen (O) reduction on a carbon cathode surface. In order to enhance the production of HO, anodic loss pathways, which significantly reduce the overall HO production rate, should be inhibited. In this study, we investigate the effects of organic electron donors (, typical chemical contaminants) on the anodic loss pathways of HO in a single-cell electrochemical reactor that employs an anode composed of TiO over-coated on a mixed-metal oxide ohmic contact catalyst, IrTaO, deposited on a Ti-metal that is coupled with a graphite rod cathode in a sodium sulfate (NaSO) electrolyte that is saturated with oxygen (O). Organic electron donors are shown to enhance the electrochemical production of HO, while simultaneously undergoing oxidative degradation. The observed positive effect of organic electron donors on the electrochemical production of HO is due in part to a preferential adsorption of organic substrates on the TiO outer layer of the anode. The sorption of the organic electron donors inhibits the formation of surficial titanium hydroperoxo species ([bond, triple bond]Ti-OOH) on the anode surface. The organic sorbates also act as scavengers of surface-bound hydroxyl radical [bond, triple bond]Ti-OH. As a result, the decomposition of HO on the anode surface is significantly reduced. The cathodic production rate of HO at low pH is enhanced due to proton coupled electron transfer (PCET) to O, while the anodic decomposition of HO is inhibited due to electrostatic interactions between negatively-charged organic substrates and a positively-charged outer surface of the anode (TiO pH = 5.8) at low pH.
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http://dx.doi.org/10.1016/j.cej.2019.05.165DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6686209PMC
October 2019

Iodide Accelerates the Processing of Biogenic Monoterpene Emissions on Marine Aerosols.

ACS Omega 2019 Apr 25;4(4):7574-7580. Epub 2019 Apr 25.

Linde Center for Global Environmental Science, California Institute of Technology, Pasadena, California 91125, United States.

Marine photosynthetic organisms emit organic gases, including the polyolefins isoprene (CH) and monoterpenes (MTPs, CH), into the boundary layer. Their atmospheric processing produces particles that influence cloud formation and growth and, as a result, the Earth's radiation balance. Here, we report that the heterogeneous ozonolysis of dissolved α-pinene by O(g) on aqueous surfaces is dramatically accelerated by I, an anion enriched in the ocean upper microlayer and sea spray aerosols (SSAs). In our experiments, liquid microjets of α-pinene solutions, with and without added I, are dosed with O(g) for τ < 10 μs and analyzed online by pneumatic ionization mass spectrometry. In the absence of I, α-pinene does not detectably react with O(g) under present conditions. In the presence of ≥ 0.01 mM I, in contrast, new signals appear at / = 169 (CHO ), / = 183 (CHO ), / = 199 (CHO ), / = 311 (CHIO ), and / = 461 (CHIO ), plus / = 175 (IO ), and / = 381 (I ). Collisional fragmentation splits CO from CHO , CHO and CHO , and I plus IO from CHIO as expected from a trioxide IOOOCH structure. We infer that the oxidative processing of α-pinene on aqueous surfaces is significantly accelerated by I via the formation of IOOO intermediates that are more reactive than O. A mechanism in which IOOO reacts with α-pinene (and likely with other unsaturated species) in competition with its isomerization to IO accounts for present results and the fact that soluble iodine in SSA is mostly present as iodine-containing organic species rather than the thermodynamically more stable iodate. By this process, a significant fraction of biogenic MTPs and other unsaturated gases may be converted to water-soluble species rather than emitted to the atmosphere.
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http://dx.doi.org/10.1021/acsomega.9b00024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6648763PMC
April 2019

Activation of Peroxymonosulfate by Oxygen Vacancies-Enriched Cobalt-Doped Black TiO Nanotubes for the Removal of Organic Pollutants.

Environ Sci Technol 2019 06 29;53(12):6972-6980. Epub 2019 May 29.

Linde + Robinson Laboratories , California Institute of Technology , Pasadena , California 91125 , United States.

Cobalt-mediated activation of peroxymonosulfate (PMS) has been widely investigated for the oxidation of organic pollutants. Herein, we employ cobalt-doped Black TiO nanotubes (Co-Black TNT) for the efficient, stable, and reusable activator of PMS for the degradation of organic pollutants. Co-Black TNTs induce the activation of PMS by itself and stabilized oxygen vacancies that enhance the bonding with PMS and provide catalytic active sites for PMS activation. A relatively high electronic conductivity associated with the coexistence of Ti and Ti in Co-Black TNT enables an efficient electron transfer between PMS and the catalyst. As a result, Co-Black TNT is an effective catalyst for PMS activation, leading to the degradation of selected organic pollutants when compared to other TNTs (TNT, Co-TNT, and Black TNT) and other Co-based materials (CoO, Co-TiO, CoFeO, and CoO/rGO). The observed organic compound degradation kinetics are retarded in the presence of methanol and natural organic matter as sulfate radical scavengers. These results demonstrate that sulfate radical is the primary oxidant generated via PMS activation on Co-Black TNT. The strong interaction between Co and TiO through Co-O-Ti bonds and rapid redox cycle of Co/Co in Co-Black TNT prevents cobalt leaching and enhances catalyst stability over a wide pH range and repetitive uses of the catalyst. Electrode-supported Co-Black TNT facilitates the recovery of the catalyst from the treated water.
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http://dx.doi.org/10.1021/acs.est.9b01449DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6587153PMC
June 2019

Multiphase Porous Electrochemical Catalysts Derived from Iron-Based Metal-Organic Framework Compounds.

Environ Sci Technol 2019 06 15;53(11):6474-6482. Epub 2019 May 15.

Department of Environmental Science and Engineering , California Institute of Technology , Pasadena , California 91126 , United States.

Herbicide use has attracted attention recently due to potential damage to human health and lethality to the honey bees and other pollinators. Fenton reagent treatment processes can be applied for the degradation of herbicidal contaminants from water. However, the need to carry out the normal Fenton reactions under acidic conditions often hinders their practical application for pollution control. Herein, we report on the synthesis and application of multiphasic porous electro-Fenton catalysts prepared from calcinated metal-organic framework compounds, [email protected], and their application for the mineralization of herbicides in aqueous solution at circum-neutral pH. CMOF nanoparticles (NPs) are anchored on porous carbon monolithic (PCM) substrates, which allow for binder-free application. HO is electrochemically generated on the PCM substrate which serves as a cathode, while ·OH is generated by the CMOF NPs at low applied potentials (-0.14 V). Results show that the structure and reactivity of the [email protected] electro-Fenton catalysts are dependent on the specific MOF precursor used during synthesis. For example, CMIL-88-NH, which is prepared from MIL-88(Fe)-NH, is a porous core-shell structured NP comprised of a cementite (FeC) intermediate layer that is sandwiched between a graphitic shell and a magnetite (FeO) core. The electro-Fenton production of hydroxyl radical on the [email protected] composite material is shown to effectively degrade an array of herbicides.
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http://dx.doi.org/10.1021/acs.est.9b01143DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6551571PMC
June 2019

Urine microbial fuel cells in a semi-controlled environment for onsite urine pre-treatment and electricity production.

J Power Sources 2018 Oct;400:441-448

Linde+Robinson Laboratories, California Institute of Technology, Pasadena, CA, USA.

Microbial fuel cell (MFC) systems have the ability to oxidize organic matter and transfer electrons to an external circuit as electricity at voltage levels of <1 V. Urine has been shown to be an excellent feedstock for various MFC systems, particularly MFCs inoculated with activated sludge and with a terracotta ceramic membrane separating carbon-based electrodes. In this article, we studied a MFC system composed of two stacks of 32 individual cells each sharing the same anolyte. By combining the current produced by the 32 cells connected in parallel and by adding the potential of both stacks connected in series, an average power density of 23 mW m was produced at an effective current density of 65 mA m for more than 120 days. [NH], TIC, COD, and TOC levels were monitored frequently to understand the chemical energy conversion to electricity as well as to determine the best electrical configuration of the stacks. Archaeal and bacterial populations on selected anode felts and in the anolyte of both stacks were investigated as well. Indicator microorganisms for bacterial waterborne diseases were measured in anolyte and catholyte compartments to evaluate the risk of reusing the catholyte in a non-regulated environment.
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http://dx.doi.org/10.1016/j.jpowsour.2018.08.051DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6472131PMC
October 2018

Digital Loop-Mediated Isothermal Amplification on a Commercial Membrane.

ACS Sens 2019 01 15;4(1):242-249. Epub 2019 Jan 15.

Linde + Robinson Laboratories , California Institute of Technology , Pasadena , California 91125 , United States.

In this work, we report digital loop-mediated isothermal amplification (LAMP) or reverse-transcription LAMP (RT-LAMP) on a commercial membrane, without the need for complex chip fabrication or use of specialized equipment. Due to the pore size distribution, the theoretical error for digital LAMP on these membranes was analyzed, using a combination of Random Distribution Model and Multivolume Theory. A facile peel-off process was developed for effective droplet formation on the commercial track-etched polycarbonate (PCTE) membrane. Each pore functions as an individual nanoreactor for single DNA amplification. Absolute quantification of bacteria genomic DNA was realized with a dynamic range from 11 to 1.1 × 10 copies/μL. One-step digital RT-LAMP was also successfully performed on the membrane for the quantification of MS2 virus in wastewater. With the introduction of new probes, the positive pores can be easily distinguished from negative ones with 100 times difference in fluorescence intensities. Finally, the cost of a disposable membrane is less than $0.10/piece, which, to the best of our knowledge, is the most inexpensive way to perform digital LAMP. The membrane system offers opportunities for point-of-care users or common laboratories to perform digital quantification, single cell analysis, or other bioassays in an inexpensive, flexible, and simplified way.
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http://dx.doi.org/10.1021/acssensors.8b01419DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6350201PMC
January 2019

Enhancing the activity of oxygen-evolution and chlorine-evolution electrocatalysts by atomic layer deposition of TiO.

Energy Environ Sci 2019 14;12:358-365. Epub 2018 Dec 14.

The Linde Center for Global Environmental Science, Caltech, Caltech, Pasadena, CA 91125, USA.

We report that TiO coatings formed atomic layer deposition (ALD) may tune the activity of IrO, RuO, and FTO for the oxygen-evolution and chlorine-evolution reactions (OER and CER). Electrocatalysts exposed to ~3-30 ALD cycles of TiO exhibited overpotentials at 10 mA cm of geometric current density that were several hundred millivolts lower than uncoated catalysts, with correspondingly higher specific activities. For example, the deposition of TiO onto IrO yielded a 9-fold increase in the OER-specific activity in 1.0 M HSO (0.1 to 0.9 mA cm at 350 mV overpotential). The oxidation state of titanium and the potential of zero charge were also a function of the number of ALD cycles, indicating a correlation between oxidation state, potential of zero charge, and activity of the tuned electrocatalysts.
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http://dx.doi.org/10.1039/c8ee02351dDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7680952PMC
December 2018

3D Printed Microfluidic Mixers-A Comparative Study on Mixing Unit Performances.

Small 2019 01 10;15(2):e1804326. Epub 2018 Dec 10.

Institute of Technical Chemistry, Leibniz University Hannover, Callinstraße 5, 30167, Hannover, Germany.

One of the basic operations in microfluidic systems for biological and chemical applications is the rapid mixing of different fluids. However, flow profiles in microfluidic systems are laminar, which means molecular diffusion is the only mixing effect. Therefore, mixing structures are crucial to enable more efficient mixing in shorter times. Since traditional microfabrication methods remain laborious and expensive, 3D printing has emerged as a potential alternative for the fabrication of microfluidic devices. In this work, five different passive micromixers known from literature are redesigned in comparable dimensions and manufactured using high-definition MultiJet 3D printing. Their mixing performance is evaluated experimentally, using sodium hydroxide and phenolphthalein solutions, and numerically via computational fluid dynamics. Both experimental and numerical analysis results show that HC and Tesla-like mixers achieve complete mixing after 0.99 s and 0.78 s, respectively, at the highest flow rate (Reynolds number (Re) = 37.04). In comparison, Caterpillar mixers exhibit a lower mixing rate with complete mixing after 1.46 s and 1.9 s. Furthermore, the HC mixer achieves very good mixing performances over all flow rates (Re = 3.7 to 37.04), while other mixers show improved mixing only at higher flow rates.
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http://dx.doi.org/10.1002/smll.201804326DOI Listing
January 2019

Degradation and Mineralization of Carbamazepine Using an Electro-Fenton Reaction Catalyzed by Magnetite Nanoparticles Fixed on an Electrocatalytic Carbon Fiber Textile Cathode.

Environ Sci Technol 2018 11 22;52(21):12667-12674. Epub 2018 Oct 22.

Department of Environmental Science and Engineering , California Institute of Technology , Pasadena , California 91126 , United States.

Pharmaceutical wastes are considered to be important pollutants even at low concentrations. In this regard, carbamazepine has received significant attention due to its negative effect on both ecosystem and human health. However, the need for acidic conditions severely hinders the use of conventional Fenton reagent reactions for the control and elimination of carbamazepine in wastewater effluents and drinking water influents. Herein, we report of the synthesis and use of flexible bifunctional nanoelectrocatalytic textile materials, [email protected], for the effective degradation and complete mineralization of carbamazepine in water. The nonwoven porous structure of the composite binder-free [email protected] textile is used to generate HO on the carbon nanofiber (CNF) substrate by O reduction. In addition, ·OH radical is generated on the surface of the bonded FeO nanoparticles (NPs) at low applied potentials (-0.345 V). The FeO-NPs are covalently bonded to the CNF textile support with a high degree of dispersion throughout the fiber matrix. The dispersion of the nanosized catalysts results in a higher catalytic reactivity than existing electro-Fenton systems. For example, the newly synthesized FeO-NPs system uses an Fe loading that is 2 orders of magnitude less than existing electro-Fenton systems, coupled with a current efficiency that is higher than electrolysis using a boron-doped diamond electrode. Our test results show that this process can remove carbamazepine with high pseudo-first-order rate constants (e.g., 6.85 h) and minimal energy consumption (0.239 kW·h/g carbamazepine). This combination leads to an efficient and sustainable electro-Fenton process.
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http://dx.doi.org/10.1021/acs.est.8b03916DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6222555PMC
November 2018

Asymmetric Membrane for Digital Detection of Single Bacteria in Milliliters of Complex Water Samples.

ACS Nano 2018 10 19;12(10):10281-10290. Epub 2018 Sep 19.

Linde + Robinson Laboratories , California Institute of Technology , Pasadena , California 91125 , United States.

In this work, we introduce an asymmetric membrane as a simple and robust nanofluidic platform for digital detection of single pathogenic bacteria directly in 10 mL of unprocessed environmental water samples. The asymmetric membrane, consisting of uniform micropores on one side and a high density of vertically aligned nanochannels on the other side, was prepared within 1 min by a facile method. The single membrane covers all the processing steps from sample concentration, purification, and partition to final digital loop-mediated isothermal amplification (LAMP). By simple filtration, bacteria were enriched and partitioned inside the micropores, while inhibitors typically found in the environmental samples ( i.e., proteins, heavy metals, and organics) were washed away through the nanochannels. Meanwhile, large particles, indigenous plankton, and positively charged pollutants in the samples were excluded by using a sacrificial membrane stacked on top. After initial filtration, modified LAMP reagents, including NaF and lysozyme, were loaded onto the membrane. Each pore in the asymmetric membrane functioned as an individual nanoreactor for selective, rapid, and efficient isothermal amplification of single bacteria, generating a bright fluorescence for direct counting. Even though high levels of inhibitors were present, absolute quantification of Escherichia coli and Salmonella directly in an unprocessed environmental sample (seawater and pond water) was achieved within 1 h, with sensitivity down to single cell and a dynamic range of 0.3-10000 cells/mL. The simple and low-cost analysis platform described herein has an enormous potential for the detection of pathogens, exosomes, stem cells, and viruses as well as single-cell heterogeneity analysis in environmental, food, and clinical research.
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http://dx.doi.org/10.1021/acsnano.8b05384DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6202633PMC
October 2018

Quantification of SO Oxidation on Interfacial Surfaces of Acidic Micro-Droplets: Implication for Ambient Sulfate Formation.

Environ Sci Technol 2018 08 6;52(16):9079-9086. Epub 2018 Aug 6.

Linde Center for Global Environmental Science , California Institute of Technology Linde-Robinson Laboratory Pasadena , California 91125 , United States.

Sulfate formation on the surface of aqueous microdroplets was investigated using a spray-chamber reactor coupled to an electrospray ionization mass spectrometer that was calibrated using NaSO(aq) as a function of pH. The observed formation of SO, SO, and HSO at pH < 3.5 without the addition of other oxidants indicates that an efficient oxidation pathway takes place involving direct interfacial electron transfer from SO to O on the surface of aqueous microdroplets. Compared to the well-studied sulfate formation kinetics via oxidation by HO(aq), the interfacial SO formation rate on the surface of microdroplets was estimated to be proportional to the collision frequency of SO with a pH-dependent efficiency factor of 5.6 × 10[H]/([H]+10). The rate via the acidic surface reactions is approximately 1-2 orders of magnitude higher than that by HO(aq) for a 1.0 ppbv concentration of HO( g) interacting with 50 μg/m of aerosols. This finding highlights the relative importance of the interfacial SO oxidation in the atmosphere. Chemical reactions on the aquated aerosol surfaces are overlooked in most atmospheric chemistry models. This interfacial reaction pathway may help to explain the observed rapid conversion of SO to sulfate in mega-cities and nearby regions with high PM2.5 haze aerosol loadings.
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http://dx.doi.org/10.1021/acs.est.8b01391DOI Listing
August 2018

Cobalt-Doped Black TiO Nanotube Array as a Stable Anode for Oxygen Evolution and Electrochemical Wastewater Treatment.

ACS Catal 2018 May 10;8(5):4278-4287. Epub 2018 Apr 10.

Division of Engineering and Applied Science, Linde-Robinson Laboratory, California Institute of Technology, Pasadena, California 91125, United States.

TiO has long been recognized as a stable and reusable photocatalyst for water splitting and pollution control. However, it is an inefficient anode material in the absence of photoactivation due to its low electron conductivity. To overcome this limitation, a series of conductive TiO nanotube array electrodes have been developed. Even though nanotube arrays are effective for electrochemical oxidation initially, deactivation is often observed within a few hours. To overcome the problem of deactivation, we have synthesized cobalt-doped Black-TiO nanotube array (Co-Black NTA) electrodes that are stable for more than 200 h of continuous operation in a NaClO electrolyte at 10 mA cm. Using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, electron paramagnetic resonance spectroscopy, and DFT simulations, we are able to show that bulk oxygen vacancies (O) are the primary source of the enhanced conductivity of Co-Black. Cobalt doping both creates and stabilizes surficial oxygen vacancies, O, and thus prevents surface passivation. The Co-Black electrodes outperform dimensionally stable IrO anodes (DSA) in the electrolytic oxidation of organic-rich wastewater. Increasing the loading of Co leads to the formation of a CoO film on top of Co-Black electrode. The CoO /Co-Black composite electrode was found to have a lower OER overpotential (352 mV) in comparison to a DSA IrO (434 mV) electrode and a stability that is greater than 200 h in a 1.0 M KOH electrolyte at a current density of 10 mA cm.
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http://dx.doi.org/10.1021/acscatal.7b04340DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5939910PMC
May 2018

Smartphone-Based in-Gel Loop-Mediated Isothermal Amplification (gLAMP) System Enables Rapid Coliphage MS2 Quantification in Environmental Waters.

Environ Sci Technol 2018 06 16;52(11):6399-6407. Epub 2018 May 16.

Linde + Robinson Laboratories , California Institute of Technology , Pasadena , California 91125 , United States.

Model coliphages (e.g., ΦX174, MS2, and PRD1) have been widely used as surrogates to study the fate and transport of pathogenic viruses in the environment and during wastewater treatment. Two groups of coliphages (F-specific and somatic) are being explored as indicators of viral fecal pollution in ambient water. However, the detection and quantification of coliphages still largely rely on time-consuming culture-based plaque assays. In this study, we developed an in-gel loop-mediated isothermal amplification (gLAMP) system enabling coliphage MS2 quantification within 30 min using standard laboratory devices. Viral particles (MS2) were immobilized with LAMP reagents in polyethylene glycol hydrogel, and then viral RNAs were amplified through a LAMP reaction. Due to the restriction effect of the hydrogel matrix, one viral particle would only produce one amplicon dot. Therefore, the sample virus concentrations can be determined based on the number of fluorescent amplicon dots using a smartphone for imaging. The method was validated by using artificially spiked and naturally contaminated water samples. gLAMP results were shown to correlate well with plaque assay counts ( R = 0.984, p < 0.05) and achieved similar sensitivity to quantitative reverse-transcription polymerase chain reaction (RT-qPCR; 1 plaque-forming unit per reaction). Moreover, gLAMP demonstrated a high level of tolerance against inhibitors naturally present in wastewater, in which RT-qPCR was completely inhibited. Besides MS2, gLAMP can also be used for the quantification of other microbial targets (e.g., Escherichia coli and Salmonella). Considering its simplicity, sensitivity, rapidity, and versatility, gLAMP holds great potential for microbial water-quality analysis, especially in resource-limited settings.
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http://dx.doi.org/10.1021/acs.est.8b00241DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5990930PMC
June 2018
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