Biodegradation characteristics and genomic analysis of a newly isolated indole-degrading strain Pseudomonas aeruginosa Jade-X / Características de biodegradación y análisis genómico de una cepa degradante de indol recientemente aislada Pseudomonas aeruginosa Jade-X

Indole is a typical heterocyclic compound derived from tryptophan widespread in nature. Pseudomonas aeruginosa is one of the most common opportunistic pathogens everywhere in the world. Indole and P. aeruginosa will encounter inevitably; however, the indole transformation process by P. aeruginosa remains unclear. Herein, an indole-degrading strain of P. aeruginosa Jade-X was isolated from activated sludge. Strain Jade-X could degrade 1 mmol/L indole within 48 h with the inoculum size of 1% (v/v). It showed high efficiency in indole degradation under the conditions of 30–42 °C, pH 5.0–9.0, and NaCl concentration less than 2.5%. The complete genome of strain Jade-X was sequenced which was 6508614 bp in length with one chromosome. Bioinformatic analyses showed that strain Jade-X did not contain the indole oxygenase gene. Three cytochrome P450 genes were identified and up-regulated in the indole degradation process by RT-qPCR analysis, while cytochrome P450 inhibitors did not affect the indole degradation process. It suggested that indole oxidation was catalyzed by an unraveled enzyme. An ant gene cluster was identified, among which the anthranilate 1,2-dioxygenase and catechol 1,2-dioxygenase genes were upregulated. An indole-anthranilate-catechol pathway was proposed in indole degradation by strain P. aeruginosa Jade-X. This study enriched our understanding of the indole biodegradation process in P. aeruginosa.(AU)

Deep insights into the biofilm formation mechanism and nitrogen-transformation network in a nitrate-dependent anaerobic methane oxidation biofilm.

Nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) process offers a promising solution for simultaneously achieving methane emissions reduction and efficient nitrogen removal in wastewater treatment. Although nitrogen removal at a practical rate has been achieved by n-DAMO biofilm process, the mechanisms of biofilm formation and nitrogen transformation remain to be elucidated. In this study, n-DAMO biofilms were successfully developed in the membrane aerated moving bed biofilm reactor (MAMBBR) and removed nitrate at a rate of 159 mg NO3--N L-1 d-1. The obvious increase in the content of extracellular polymeric substances (EPS) indicated that EPS production was important for biofilm development. n-DAMO microorganisms dominated the microbial community, and n-DAMO bacteria were the most abundant microorganisms. However, the expression of biosynthesis genes for proteins and polysaccharides encoded by n-DAMO archaea was significantly more active compared to other microorganisms, suggesting the central role of n-DAMO archaea in EPS production and biofilm formation. In addition to nitrate reduction, n-DAMO archaea were revealed to actively express dissimilatory nitrate reduction to ammonium and nitrogen fixation. The produced ammonium was putatively converted to dinitrogen gas through the joint function of n-DAMO archaea and n-DAMO bacteria. This study revealed the biofilm formation mechanism and nitrogen-transformation network in n-DAMO biofilm systems, shedding new light on promoting the application of n-DAMO process.

Differentiating Between V- and G-Series Nerve Agent and Simulant Vapours Using Fluorescent Film Responses.

In-field rapid and reliable identification of nerve agents is critical for the protection of Defence and National Security personnel as well as communities. Fluorescence-based detectors can be portable and provide rapid detection of chemical threats. However, most current approaches cannot differentiate between dilute vapors of nerve agent classes and are susceptible to false positives due to the presence of common acids. Here a fluorescence-based method is shown for rapid differentiation between the V-series and phosphonofluoridate G-series nerve agents and avoids false positives due to common acids. Differentiation is achieved through harnessing two different mechanisms. Detection of the V-series is achieved using photoinduced hole transfer whereby the fluorescence of the sensing material is quenched in the presence of the V-series agent. The G-series is detected using a turn-on mechanism in which a silylated excited state intramolecular proton transfer sensing molecule is selectively deprotected by hydrogen fluoride, which is typically found as a contaminant and/or breakdown product in G-series agents such as sarin. The strategy provided discrimination between classes, as the sensor for the G-series agent class is insensitive to the V-series agent, and vice versa, and neither responded to common acids.

Revisiting the Engineering Roadmap of Nitrate/Nitrite-Dependent Anaerobic Methane Oxidation.

Nitrate/nitrite-dependent anaerobic oxidation of methane (n-DAMO) is a recently discovered process, which provides a sustainable perspective for simultaneous nitrogen removal and greenhouse gas emission (GHG) mitigation by using methane as an electron donor for denitrification. However, the engineering roadmap of the n-DAMO process is still unclear. This work constitutes a state-of-the-art review on the classical and most recently discovered metabolic mechanisms of the n-DAMO process. The versatile combinations of the n-DAMO process with nitrification, nitritation, and partial nitritation for nitrogen removal are also clearly presented and discussed. Additionally, the recent advances in bioreactor development are systematically reviewed and evaluated comprehensively in terms of methane supply, biomass retention, membrane requirement, startup time, reactor performance, and limitations. The key issues including enrichment and operation strategy for the scaling up of n-DAMO-based processes are also critically addressed. Moreover, the challenges inherent to implementing the n-DAMO process in practical applications, including application scenario recognition, GHG emission mitigation, and operation under realistic conditions, are highlighted. Finally, prospects as well as opportunities for future research are proposed. Overall, this review provides a roadmap for potential applications and further development of the n-DAMO process in the field of wastewater treatment.

Evidence for Nitrous Oxide Emissions by Nitrite-Dependent Anaerobic Methane Oxidizing Bacteria.

Nitrite-dependent anaerobic methane oxidizing (n-DAMO) bacteria generally convert nitrite to dinitrogen and bypass the nitrous oxide (N2O) formation step. However, N2O is often detected in n-DAMO bacteria dominated cultures and it remains an open question as to the microbial origin of N2O in these enrichments. Using a stable nitrite consuming microbial community enriched for n-DAMO bacteria, we demonstrated that N2O production was coupled to methane oxidation and the higher initial nitrite concentrations led to increased quantities of N2O being formed. Moreover, continuous exposure of the enrichment culture to about 5 mg of N L-1 nitrite resulted in constant N2O being produced (12.5% of nitrite was reduced to N2O). Metatranscriptomic analyses revealed that nitrite reductase (nirS) and nitric oxide reductase (norZ) transcripts from n-DAMO bacteria increased in response to nitrite exposure. No other bacteria significantly expressed nor genes under these conditions, suggesting n-DAMO bacteria are responsible for N2O being produced. In a 35-day bioreactor experiment, N2O produced by the n-DAMO bacteria accumulated when nitrite was in excess; this was found to be up to 3.2% of the nitrogen that resulted from nitrite removal. Together, these results suggested that excess nitrite is an important driver of N2O production by n-DAMO bacteria. To this end, proper monitoring and control of nitrite levels in wastewater treatment plants would be effective strategies for mitigating N2O emissions to the atmosphere.

Model-based assessment of mainstream nitrate/nitrite-dependent anaerobic methane oxidation and Anammox process in granular sludge at low temperature.

The process of nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) coupled with anaerobic ammonium oxidation (Anammox) is one of groundbreaking discoveries for nitrogen removal and methane emission reduction from wastewater simultaneously. Yet its treatment of mainstream wastewater at low temperature is still a major challenge. In this work, a one-dimensional granular sludge model incorporating Arrhenius conversion for temperature effects was constructed to depict the relationships among n-DAMO microorganisms and Anammox. The model framework was successfully evaluated with 380 days measurement data from a membrane granular sludge reactor (MGSR) operated at temperature of 20-10 °C and fed with ammonium and nitrite. The model could satisfactorily predict the kinetics of nitrogen removal rates, effluent nitrogen concentrations and biomass fractions in MGSR at varying temperatures. Despite the decrease in microbial activity of functional microorganisms, the coupled n-DAMO and Anammox process based on granule system in mainstream wastewater treatment achieved a TN removal efficiency of about 98 % and a stable nitrogen removal rate of 0.55 g L-1 d-1. The model developed is expected to facilitate fundamentally understanding the underlying mechanisms of the coupled process and provide proposals for its practical engineering application in wastewater treatment plants.

Deep insights into the population shift of n-DAMO and Anammox in granular sludge: From sidestream to mainstream.

Granular sludge combined n-DAMO and Anammox (n-D/A) is an energy-efficient biotechnique for the simultaneous removal of nitrogen and dissolved methane from wastewater. However, the lack of knowledge so far about the metabolic interactions between n-DAMO and Anammox in response to operation condition in granular sludge restrains the development of this biotechnology. To address this gap, three independent membrane granular sludge reactors (MGSRs) were designed to carry out the granule-based n-D/A process under different conditions. We provided the first deep insights into the metabolic interactions between n-DAMO and Anammox in granular sludge via combined metagenomic and metatranscriptomic analyses. Our study unveiled a clear population shift of n-DAMO community from Candidatus Methanoperedens to Candidatus Methylomirabilis from sidestream to mainstream. Candidatus Methanoperedens with relative abundance of 25.2% played the major role in nitrate reduction and methane oxidation under sidestream condition, indicated by the high expression activities of mcrA and narG. Candidatus Methylomirabilis dominated the microbial community under mainstream condition with relative abundance of 32.1%, supported by the high expression activities of pmoA and hao. Furthermore, a transition of Anammox population from Candidatus Kuenenia to Candidatus Brocadia was also observed from sidestream to mainstream. Candidatus Kuenenia and Candidatus Brocadia jointly contributed to the primary anaerobic ammonium oxidation suggested by the high expression value of hdh and hzs. Candidatus Methylomirabilis was speculated to perform ammonium oxidation mediated by pMMO under mainstream condition. These findings might help to reveal the microbial interactions and ecological niches of n-DAMO and Anammox microorganisms, shedding light on the optimization and management of the granule-based n-D/A system.

Biodegradation characteristics and genomic analysis of a newly isolated indole-degrading strain Pseudomonas aeruginosa Jade-X.

Indole is a typical heterocyclic compound derived from tryptophan widespread in nature. Pseudomonas aeruginosa is one of the most common opportunistic pathogens everywhere in the world. Indole and P. aeruginosa will encounter inevitably; however, the indole transformation process by P. aeruginosa remains unclear. Herein, an indole-degrading strain of P. aeruginosa Jade-X was isolated from activated sludge. Strain Jade-X could degrade 1 mmol/L indole within 48 h with the inoculum size of 1% (v/v). It showed high efficiency in indole degradation under the conditions of 30-42 °C, pH 5.0-9.0, and NaCl concentration less than 2.5%. The complete genome of strain Jade-X was sequenced which was 6508614 bp in length with one chromosome. Bioinformatic analyses showed that strain Jade-X did not contain the indole oxygenase gene. Three cytochrome P450 genes were identified and up-regulated in the indole degradation process by RT-qPCR analysis, while cytochrome P450 inhibitors did not affect the indole degradation process. It suggested that indole oxidation was catalyzed by an unraveled enzyme. An ant gene cluster was identified, among which the anthranilate 1,2-dioxygenase and catechol 1,2-dioxygenase genes were upregulated. An indole-anthranilate-catechol pathway was proposed in indole degradation by strain P. aeruginosa Jade-X. This study enriched our understanding of the indole biodegradation process in P. aeruginosa.

Reactivated biofilm coupling n-DAMO with anammox achieved high-rate nitrogen removal in membrane aerated moving bed biofilm reactor.

As a promising technology, the combination of nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) with Anammox offers a solution to achieve effective and sustainable wastewater treatment. However, this sustainable process faces challenges to accumulate sufficient biomass for reaching practical nitrogen removal performance. This study developed an innovative membrane aerated moving bed biofilm reactor (MAMBBR), which supported sufficient methane supply and excellent biofilm attachment, for cultivating biofilms coupling n-DAMO with Anammox. Biofilms were developed rapidly on the polyurethane foam with the supply of ammonium and nitrate, achieving the bioreactor performance of 275 g N m-3 d-1 within 102 days. After the preservation at -20 °C for 8 months, the biofilm was successfully reactivated and achieved 315 g N m-3 d-1 after 188 days. After reactivation, MAMBBR was applied to treat synthetic sidestream wastewater. Up to 99.9% of total nitrogen was removed with the bioreactor performance of 4.0 kg N m-3 d-1. Microbial community analysis and mass balance calculation demonstrated that n-DAMO microorganisms and Anammox bacteria collectively contributed to nitrogen removal in MAMBBR. The MAMBBR developed in this study provides an ideal system of integrating n-DAMO with Anammox for sustainable wastewater treatment.

Mainstream Nitrogen and Dissolved Methane Removal through Coupling n-DAMO with Anammox in Granular Sludge at Low Temperature.

Mainstream anaerobic wastewater treatment has received increasing attention for the recovery of methane-rich biogas from biodegradable organics, but subsequent mainstream nitrogen and dissolved methane removal at low temperatures remains a critical challenge in practical applications. In this study, granular sludge coupling n-DAMO with Anammox was employed for mainstream nitrogen removal, and the dissolved methane removal potential of granular sludge at low temperatures was investigated. A stable nitrogen removal rate (0.94 kg N m-3 d-1 at 20 °C) was achieved with a high-level effluent quality (<3.0 mg TN L-1) in a lab-scale membrane granular sludge reactor (MGSR). With decreasing temperature, the nitrogen removal rate dropped to 0.55 kg N m-3 d-1 at 10 °C, while the effluent concentration remained <1.0 mg TN L-1. The granular sludge with an average diameter of 1.8 mm proved to retain sufficient biomass (27 g VSS L-1), which enabled n-DAMO and Anammox activity at a hydraulic retention time as low as 2.16 h even at 10 °C. 16S rRNA gene sequencing and scanning electron microscopy revealed a stable community composition and compact structure of granular sludge during long-term operation. Energy recovery could be maximized by recovering most of the dissolved methane in mainstream anaerobic effluent, as only a small amount of dissolved methane was capable of supporting denitrifying methanotrophs in granular sludge, which enabled high-level nitrogen removal.

Nitrate/nitrite dependent anaerobic methane oxidation coupling with anammox in membrane biotrickling filter for nitrogen removal.

Combining nitrate/nitrite dependent anaerobic methane oxidation (n-DAMO) and anaerobic ammonium oxidation (Anammox) is a promising sustainable wastewater treatment technology, which simultaneously achieve nitrogen removal and methane emission mitigation. However, the practical application of n-DAMO has been greatly limited by its extremely slow growth-rate and low reaction rate. This work proposes an innovative Membrane BioTrickling Filter (MBTF), which consist of hollow fiber membrane for effective methane supplementation and polyurethane sponge as support media for the attachment and growth of biofilm coupling n-DAMO with Anammox. When steady state with a hydraulic retention time (HRT) of 6.00 h was reached, above 99.9% of nitrogen was removed from synthetic sidestream wastewater at a rate of 3.99 g N L-1 d-1. This system presented robust capacity to withstand unstable partial nitritation effluent, achieving complete nitrogen removal at a varied nitrite to ammonium ratio in the range of 1.10-1.40. It is confirmed that n-DAMO and Anammox microorganisms jointly dominated the microbial community by pyrosequencing technology. The complete nitrogen removal potential at high-rate and efficient biomass retention (12.4 g VSS L-1) of MBTF offers promising alternative for sustainable wastewater treatment by the combination of n-DAMO and Anammox.

Acid is a potential interferent in fluorescent sensing of chemical warfare agent vapors.

A common feature of fluorescent sensing materials for detecting chemical warfare agents (CWAs) and simulants is the presence of nitrogen-based groups designed to nucleophilically displace a phosphorus atom substituent, with the reaction causing a measurable fluorescence change. However, such groups are also basic and so sensitive to acid. In this study we show it is critical to disentangle the response of a candidate sensing material to acid and CWA simulant. We report that pyridyl-containing sensing materials designed to react with a CWA gave a strong and rapid increase in fluorescence when exposed to Sarin, which is known to contain hydrofluoric acid. However, when tested against acid-free diethylchlorophosphate and di-iso-propylfluorophosphate, simulants typically used for evaluating novel G-series CWA sensors, there was no change in the fluorescence. In contrast, simulants that had been stored or tested under a standard laboratory conditions all led to strong changes in fluorescence, due to acid impurities. Thus the results provide strong evidence that care needs to be taken when interpreting the results of fluorescence-based solid-state sensing studies of G-series CWAs and their simulants. There are also implications for the application of these pyridyl-based fluorescence and other nucleophilic/basic sensing systems to real-world CWA detection.

Development of granular sludge coupling n-DAMO and Anammox in membrane granular sludge reactor for high rate nitrogen removal.

The integration of nitrate/nitrite dependent anaerobic methane oxidation (n-DAMO) and anaerobic ammonium oxidation (Anammox) provides sustainable solution to simultaneously remove nitrate, nitrite and ammonium. This study demonstrated the sludge granulation process coupling n-DAMO and Anammox from mixed inoculum including river sediment, return activated sludge and crushed anaerobic granule sludge in a novel membrane granular sludge reactor (MGSR). Flocculent biomass gradually turned into compact aggregates and retained as granular sludge with an average diameter of 2.2 mm in MGSR after 684 days' operation. When steady state with a hydraulic retention time of 1.19 days was reached, the MGSR achieved a nitrogen removal rate of 1.77 g N L-1 d-1. Granules with density of 1.043 g mL-1, settling velocity of 72 m h-1 and sludge volume index of 22 mL g-1 leaded to excellent biomass retention (42 g VSS L-1). Pyrosequencing analysis revealed that two dominant microbial groups, n-DAMO archaea and Anammox bacteria, in the microbial community of the granule were enriched to 31.09% and 12.45%. Fluorescence in situ hybridization revealed a homogenous distribution of n-DAMO archaea and Anammox bacteria throughout the granule. The granular sludge coupling n-DAMO and Anammox microorganisms provides significant potential for high rate nitrogen removal from wastewater.

Challenges in Fluorescence Detection of Chemical Warfare Agent Vapors Using Solid-State Films.

Organophosphorus (OP)-based nerve agents are extremely toxic and potent acetylcholinesterase inhibitors and recent attacks involving nerve agents highlight the need for fast detection and intervention. Fluorescence-based detection, where the sensing material undergoes a chemical reaction with the agent causing a measurable change in the luminescence, is one method for sensing and identifying nerve agents. Most studies use the simulants diethylchlorophosphate and di-iso-propylfluorophosphate to evaluate the performance of sensors due to their reduced toxicity relative to OP nerve agents. While detection of nerve agent simulants in solution is relatively widely reported, there are fewer reports on vapor detection using solid-state sensors. Herein, progress in organic semiconductor sensing materials developed for solid-state detection of OP-based nerve agent vapors is reviewed. The effect of acid impurities arising from the hydrolysis of simulants and nerve agents on the efficacy and selectivity of the reported sensing materials is also discussed. Indeed, in some cases it is unclear whether it is the simulant that is detected or the acid hydrolysis products. Finally, it is highlighted that while analyte diffusion into the sensing film is critical in the design of fast, responsive sensing systems, it is an area that is currently not well studied.

Granular Sludge Coupling Nitrate/Nitrite Dependent Anaerobic Methane Oxidation with Anammox: from Proof-of-Concept to High Rate Nitrogen Removal.

This work developed a novel Membrane Granular Sludge Reactor (MGSR) equipped with a gas permeable membrane module for efficient methane delivery to cultivate nitrate/nitrite dependent anaerobic methane oxidation (n-DAMO) microorganisms in granular sludge. As proof of concept, the MGSR was fed with synthetic wastewater containing nitrate and ammonium to facilitate the growth of n-DAMO microorganisms. The granular sludge of n-DAMO and Anammox was gradually developed and achieved a nitrogen removal rate of 1.08 g NO3--N L-1 d-1 and 0.81 g NH4+-N L-1 d-1. Finally, enriched granular sludge was successfully applied for nitrogen removal from the synthetic partial nitritation effluent. The combined dominance of n-DAMO archaea, Anammox bacteria, and n-DAMO bacteria in the microbial community was confirmed by 16S rRNA amplicon sequencing. Fluorescence in situ hybridization revealed that a layered structure was formed in the granular sludge with Anammox bacteria in the outer layer and n-DAMO microorganisms in the inner layer when granules were fed with nitrite and ammonium. The high performance of nitrogen removal (16.53 kg N m-3 d-1) with satisfactory effluent quality (∼8 mg N L-1) and excellent biomass retention capacity (43 g VSS L-1) make the MGSR promising for the practical application of n-DAMO and Anammox in wastewater treatment.

Solid-State Fluorescence-based Sensing of TATP via Hydrogen Peroxide Detection.

Fluorenylboronate ester chromophore-based thin films were investigated for the detection of triacetone triperoxide (TATP) vapors via the decomposition product, hydrogen peroxide. Sensing with a high level of sensitivity was achieved using a fluorescence "turn-on" mechanism based on the significant shifts in the absorption and photoluminescence spectra that occurs when the boronate esters were converted to phenoxides by hydrogen peroxide under basic conditions. The addition of an organic base was found to be critical for achieving fast conversion reactions and the formation of the phenoxide anions. Addition of a nitrile group to the fluorenyl boronate ester moiety improved the stability of the material to photooxidation, increased the photoluminescence quantum yields, and enhanced the absorption and emission shifts to longer wavelengths. In real-time sensing measurements, films comprising the cyanofluorenyl boronate ester moiety and tetra- n-butylammonium hydroxide had a response time to acid-decomposed TATP vapor of seconds and a limit of detection of 40 ppb in 60 s.

Sensitive and fast fluorescence-based indirect sensing of TATP.

Sensing of TATP vapours via the decomposition product, hydrogen peroxide, was achieved using a fluorescence "turn-on" mechanism through conversion of boronate esters to phenoxides under basic conditions in solid-state films. High sensitivity was achieved with two new fluorenylboronate esters comprising either 2,4-difluorophenyl or 4-(trifluoromethyl)phenyl substituents. The key to the sensitivity was the fact that the phenoxide anion products from the hydrogen peroxide oxidation absorbed at longer wavelengths than the starting boronate esters. Selective excitation of the phenoxide anions avoided the background fluorescence from the corresponding boronate esters. The use of the electron withdrawing substituents also led to greater photostability. The derivative containing the 4-(trifluoromethyl)phenyl moiety was found to give the most stable phenoxide, and demonstrated fast fluorescence "turn-on" kinetics with a lower limit of detection of ≈2.5 ppb in 60 s.

Evaluation of Microvascular Decompression as Rescue Therapy for Trigeminal Neuralgia in Patients with Failed Gamma Knife Surgery.

OBJECTIVE: Owing to increasing use of Gamma Knife surgery (GKS) for trigeminal neuralgia (TN), physicians are challenged over the problem of choosing an appropriate treatment if GKS fails. The aim of this study was to determine whether microvascular decompression (MVD) is a safe and effective alternative therapy for trigeminal neuralgia in patients with failed GKS. METHODS: Between January 1, 2010, and January 1, 2012, data of 32 patients with trigeminal neuralgia who presented with persistent or recurrent pain after GKS and elected to undergo MVD were collected. Clinical characteristics, operative findings, outcomes of MVD, and complications were reviewed. RESULTS: Mean interval time between GKS and MVD was 16 ± 5.64 months (range, 6-27 months). During MVD, the most common offending vessel was the superior cerebellar artery, followed by the anterior inferior cerebellar artery and vertebral artery. Immediately after MVD, 29 patients (90.63%) experienced complete pain relief without medication. At the end of the follow-up period, 25 patients were pain-free without medication. CONCLUSIONS: Our data confirm that MVD is an effective and safe alternative therapy after GKS, although the risk of facial numbness seems higher in patients with a history of GKS than in patients without a history of GKS.

Photophysics of detection of explosive vapours via luminescence quenching of thin films: impact of inter-molecular interactions.

Fluorescence-based detection of explosive analytes requires an understanding of the nature of the excited state responsible for the luminescence response of a sensing material. Many measurements are carried out to elucidate the fundamental photophysical properties of an emissive material in solution. However, simple transfer of the understanding gained from the solution measurements to the solid-state can lead to errors. This is in part due to the absence of inter-molecular interactions of the chromophores in solution, which are present in the solid-state. To understand the role of inter-molecular interactions on the detection of explosive analytes we have chosen dendrimers from two different families, D1 and D2, which allow facile control of the inter-molecular interactions through the choice of dendrons and emissive chromophores. Using ultrafast transient absorption spectroscopy we find that the solution photoinduced absorption (PA) for both materials can be explained in terms of the generation of singlet excitons, which decay to the ground state, or intersystem cross (ISC) to form a triplet exciton. In neat films however, we observe different photophysical behaviours; first, ISC to the triplet state does not occur, and second, depending on the chromophore, charge transfer and charge separated states are formed. Furthermore, we find that when either dendrimer is interfaced with analyte vapour, the singlet state is strongly quenched, generating a charge transfer state that undergoes geminate recombination.

Detection of Explosive Vapors: The Roles of Exciton and Molecular Diffusion in Real-Time Sensing.

Time-resolved quartz crystal microbalance with in situ fluorescence measurements are used to monitor the sorption of the nitroaromatic (explosive) vapor, 2,4-dinitrotoluene (DNT) into a porous pentiptycene-containing poly(phenyleneethynylene) sensing film. Correlation of the nitroaromatic mass uptake with fluorescence quenching shows that the analyte diffusion follows the Case-II transport model, a film-swelling-limited process, in which a sharp diffusional front propagates at a constant velocity through the film. At a low vapor pressure of DNT of ≈16 ppb, the analyte concentration in the front is sufficiently high to give an average fluorophore-analyte separation of ≈1.5 nm. Hence, a long exciton diffusion length is not required for real-time sensing in the solid state. Rather the diffusion behavior of the analyte and the strength of the binding interaction between the analyte and the polymer play first-order roles in the fluorescence quenching process.