Sixty years of electrochemical optical spectroscopy: a retrospective.

Sixty years ago, Reddy, Devanatan, and Bockris performed the first in situ electrochemical ellipsometry experiment, which ushered in a new era in the study of electrochemistry, using optical spectroscopy. After six decades of development, electrochemical optical spectroscopy, particularly electrochemical vibrational spectroscopy, has advanced from a phase of immaturity with few methods and limited applications to a phase of maturity with excellent substrate generality and significantly improved resolutions. Here, we divide the development of electrochemical optical spectroscopy into four phases, focusing on the proof-of-concept of different electrochemical optical spectroscopy studies, the emergence of plasmonic enhancement-based electrochemical optical spectroscopic (in particular vibrational spectroscopic) methods, the realization of electrochemical vibrational spectroscopy on well-defined surfaces, and the efforts to achieve operando spectroelectrochemical applications. Finally, we discuss the future development trend of electrochemical optical spectroscopy, as well as examples of new methodology and research paradigms for operando spectroelectrochemistry.

Adamgammadex in patients to reverse a moderate rocuronium-induced neuromuscular block.

AIMS: The aim of this study was to investigate the effectiveness, safety and pharmacokinetics of adamgammadex in surgical patients. METHODS: Forty-eight patients aged 18-64 years old were randomized to receive adamgammadex (2, 4, 6, and 8 mg.kg-1 ) or placebo at a ratio of 10:2 for reversal of 0.6 mg.kg-1 rocuronium-induced neuromuscular block. Neuromuscular function was monitored by TOF-Watch® SX. When the T2 of train-of-four (TOF) reappeared at the end of surgery, patients received an intravenous administration of adamgammadex or placebo. RESULTS: The recovery time of the TOF ratio to 0.9 decreased significantly from 39.3 [29.5, 50.2] minutes in the group that received placebo to 3.0 [2.3, 3.9] minutes, P < .0001; 2.1 [1.5, 3.0] minutes, P < .0001; 2.1 [1.8, 3.3] minutes, P < .0001; and 1.8 [1.5, 2.2] minutes, P < .0001 in the 2, 4, 6 and 8 mg.kg-1 adamgammadex groups, respectively. Then, adamgammadex also showed a shortened recovery time for the TOF ratio recovered to 0.8 and 0.7. Adamgammadex was well tolerated, and no cases of anaphylactic reactions, post-operative bleeding, recurarization, abnormal basic vital signs and prolonged QT intervals were observed. The pharmacokinetics of adamgammadex in plasma increased in dose-dependent manner. The 24-hour cumulative fraction of adamgammadex in urine was 65-83%, and that of rocuronium was increased after using adamgammadex from 15% to about 25-30%. CONCLUSION: Adamgammadex was found to be effective for reversal of rocuronium-induced neuromuscular block, and it was safe and well tolerated in patients.

Termite mound formation reduces the abundance and diversity of soil resistomes.

Termites are pivotal ecosystem engineers in tropical and subtropical habitats, where they construct massive nests ('mounds') that substantially modify soil properties and promote nutrient cycling. Yet, little is known about the roles of termite nesting activity in regulating the spread of antimicrobial resistance (AMR), one of the major Global Health challenges. Here, we conducted a large-scale (> 1500 km) investigation in northern Australia and found distinct resistome profiles in termite mounds and bulk soils. By profiling a wide spectrum of ARGs, we found that the abundance and diversity of antibiotic resistance genes (ARGs) were significantly lower in termite mounds than in bulk soils (P < 0.001). The proportion of efflux pump ARGs was significantly lower in termite mound resistome than in bulk soil resistome (P < 0.001). The differences in resistome profiles between termite mounds and bulk soils may result from the changes in microbial interactions owing to the substantial increase in pH and nutrient availability induced by termite nesting activities. These findings advance our understanding of the profile of ARGs in termite mounds, which is a crucial step to evaluate the roles of soil faunal activity in regulating soil resistome under global environmental change.

Precipitation increases the abundance of fungal plant pathogens in Eucalyptus phyllosphere.

Understanding the current and future distributions of plant pathogens is critical to predict the plant performance and related economic benefits in the changing environment. Yet, little is known about the roles of environmental drivers in shaping the profiles of fungal plant pathogens in phyllosphere, an important habitat of microbiomes on Earth. Here, using a large-scale investigation of Eucalyptus phyllospheric microbiomes in Australia and the multiple linear regression model, we show that precipitation is the most important predictor of fungal taxonomic diversity and abundance. The abundance of fungal plant pathogens in phyllosphere exhibited a positive linear relationship with precipitation. With this empirical dataset, we constructed current and future atlases of phyllosphere plant pathogens to estimate their spatial distributions under different climate change scenarios. Our atlases indicate that the abundance of fungal plant pathogens would increase especially in the coastal regions with up to 100-fold increase compared with the current abundance. These findings advance our understanding of the distributions of fungal plant pathogens in phyllospheric microbiomes under the climate change, which can improve our ability to predict and mitigate their impacts on plant productivity and economic losses.

Termite mounds reduce soil microbial diversity by filtering rare microbial taxa.

Termites are ubiquitous insects in tropical and subtropical habitats, and some of them construct massive nests ('mounds'), which substantially promote substrate heterogeneity by altering soil properties. Yet, the role of termite nesting process in regulating the distribution and diversity of soil microbial communities remains poorly understood, which introduces uncertainty in predictions of ecosystem functions of termite mounds in a changing environment. Here, by using amplicon sequencing, we conducted a survey of 134 termite mounds across >1500 km in northern Australia and found that termite mounds significantly differed from bulk soils in the microbial diversity and community compositions. Compared with bulk soils, termite nesting process decreased the microbial diversity and the relative abundance of rare taxa. Rare taxa had a narrower habitat niche breadth than dominant taxa and might be easier to be filtered by the potential intensive microbial competition during the nesting processes. We further demonstrated that the shift in pH induced by termite nesting process was a major driver shaping the microbial community profiles in termite mounds. Together, our work provides novel evidence that termite nesting is an important process in regulating soil microbial diversity, which advances our understanding of the functioning of termite mounds.

In situ probing electrified interfacial water structures at atomically flat surfaces.

Solid/liquid interfaces are ubiquitous in nature and knowledge of their atomic-level structure is essential in elucidating many phenomena in chemistry, physics, materials science and Earth science1. In electrochemistry, in particular, the detailed structure of interfacial water, such as the orientation and hydrogen-bonding network in electric double layers under bias potentials, has a significant impact on the electrochemical performances of electrode materials2-4. To elucidate the structures of electric double layers at electrochemical interfaces, we combine in situ Raman spectroscopy and ab initio molecular dynamics and distinguish two structural transitions of interfacial water at electrified Au single-crystal electrode surfaces. Towards negative potentials, the interfacial water molecules evolve from structurally 'parallel' to 'one-H-down' and then to 'two-H-down'. Concurrently, the number of hydrogen bonds in the interfacial water also undergoes two transitions. Our findings shed light on the fundamental understanding of electric double layers and electrochemical processes at the interfaces.

Shell-Isolated Nanoparticle-Enhanced Phosphorescence.

The emerging field of plasmonics has promoted applications of optical technology, especially in plasmon-enhanced spectroscopy (PES). However, in plasmon-enhanced fluorescence (PEF), "metal loss" could significantly quench the fluorescence during the process, which dramatically limits its applications in analysis and high-resolution imaging. In this report, silver core silica shell-isolated nanoparticles (Ag@SiO2 NPs or SHINs) with a tunable thickness of shell are used to investigate the interactions between NPs and emitters by constructing coupling and noncoupling modes. The plasmonic coupling mode between Ag@SiO2 NPs and Ag film reveals an exceeding integrating spectral intensity enhancement of 330 and about 124 times that of the radiative emission rate acceleration for shell-isolated nanoparticle enhanced phosphorescence (SHINEP). The experimental findings are supported by theoretical calculations using the finite-element method (FEM). Hence, the SHINEP may provide a novel approach for understanding the interaction of plasmon and phosphorescence, and it holds great potential in surface detection analysis and singlet-oxygen-based clinical therapy.

Plasmon-Enhanced Ultrasensitive Surface Analysis Using Ag Nanoantenna.

Raman scattering and fluorescence spectroscopy permeate analytic science and are featured in the plasmon-enhanced spectroscopy (PES) family. However, the modest enhancement of plasmon-enhanced fluorescence (PEF) significantly limits the sensitivity in surface analysis and material characterization. Herein, we report a Ag nanoantenna platform, which simultaneously fulfills very strong emission (an optimum average enhancement of 105-fold) and an ultrafast emission rate (∼280-fold) in PES. For applications in surface science, this platform has been examined with a diverse array of fluorophores. Meanwhile, we utilized a finite-element method (FEM) and time-dependent density functional theory (TD-DFT) to comprehensively investigate the mechanism of largely enhanced radiative decay. PES with a shell-isolated Ag nanoantenna will open a wealth of advanced scenarios for ultrasensitive surface analysis.

Plasmon-enhanced fluorescence spectroscopy.

Fluorescence spectroscopy with strong emitters is a remarkable tool with ultra-high sensitivity for detection and imaging down to the single-molecule level. Plasmon-enhanced fluorescence (PEF) not only offers enhanced emissions and decreased lifetimes, but also allows an expansion of the field of fluorescence by incorporating weak quantum emitters, avoiding photobleaching and providing the opportunity of imaging with resolutions significantly better than the diffraction limit. It also opens the window to a new class of photostable probes by combining metal nanostructures and quantum emitters. In particular, the shell-isolated nanostructure-enhanced fluorescence, an innovative new mode for plasmon-enhanced surface analysis, is included. These new developments are based on the coupling of the fluorophores in their excited states with localized surface plasmons in nanoparticles, where local field enhancement leads to improved brightness of molecular emission and higher detection sensitivity. Here, we review the recent progress in PEF with an emphasis on the mechanism of plasmon enhancement, substrate preparation, and some advanced applications, including an outlook on PEF with high time- and spatially resolved properties.

Shell-Isolated Tip-Enhanced Raman and Fluorescence Spectroscopy.

Tip-enhanced Raman spectroscopy can provide molecular fingerprint information with ultrahigh spatial resolution, but the tip will be easily contaminated, thus leading to artifacts. It also remains a great challenge to establish tip-enhanced fluorescence because of the quenching resulting from the proximity of the metal tip. Herein, we report shell-isolated tip-enhanced Raman and fluorescence spectroscopies by employing ultrathin shell-isolated tips fabricated by atomic layer deposition. Such shell-isolated tips not only show outstanding electromagnetic field enhancement in TERS but also exclude interference by contaminants, thus greatly promoting applications in solution. Tip-enhanced fluorescence has also been achieved using these shell-isolated tips, with enhancement factors of up to 1.7×103 , consistent with theoretical simulations. Furthermore, tip-enhanced Raman and fluorescence signals are acquired simultaneously, and their relative intensities can be manipulated by changing the shell thickness. This work opens a new avenue for ultrahigh resolution surface analysis using plasmon-enhanced spectroscopies.

Correction: Shell-isolated nanoparticle-enhanced Raman spectroscopy study of the adsorption behaviour of DNA bases on Au(111) electrode surfaces.

Correction for 'Shell-isolated nanoparticle-enhanced Raman spectroscopy study of the adsorption behaviour of DNA bases on Au(111) electrode surfaces' by Bao-Ying Wen et al., Analyst, 2016, DOI: 10.1039/c6an00180g.

Shell-isolated nanoparticle-enhanced Raman spectroscopy study of the adsorption behaviour of DNA bases on Au(111) electrode surfaces.

For the first time, we used the electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) technique to in situ characterize the adsorption behaviour of four DNA bases (adenine, guanine, thymine, and cytosine) on atomically flat Au(111) electrode surfaces. The spectroscopic results of the various molecules reveal similar features, such as the adsorption-induced reconstruction of the Au(111) surface and the drastic Raman intensity reduction of the ring breathing modes after the lifting reconstruction. As a preliminary study of the photo-induced charge transfer (PICT) mechanism, the in situ spectroscopic results obtained on single crystal surfaces are excellently illustrated with electrochemical data.

In Situ Monitoring of Electrooxidation Processes at Gold Single Crystal Surfaces Using Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy.

Identifying the intermediate species in an electrocatalytic reaction can provide a great opportunity to understand the reaction mechanism and fabricate a better catalyst. However, the direct observation of intermediate species at a single crystal surface is a daunting challenge for spectroscopic techniques. In this work, electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) is utilized to in situ monitor the electrooxidation processes at atomically flat Au(hkl) single crystal electrode surfaces. We systematically explored the effects of crystallographic orientation, pH value, and anion on electrochemical behavior of intermediate (AuOH/AuO) species. The experimental results are well correlated with our periodic density functional theory calculations and corroborate the long-standing speculation based on theoretical calculations in previous electrochemical studies. The presented in situ electrochemical SHINERS technique offers a unique way for a real-time investigation of an electrocatalytic reaction pathway at various well-defined noble metal surfaces.

"Smart" Ag Nanostructures for Plasmon-Enhanced Spectroscopies.

Silver is an ideal candidate for surface plasmon resonance (SPR)-based applications because of its great optical cross-section in the visible region. However, the uses of Ag in plasmon-enhanced spectroscopies have been limited due to their interference via direct contact with analytes, the poor chemical stability, and the Ag(+) release phenomenon. Herein, we report a facile chemical method to prepare shell-isolated Ag nanoparticle/tip. The as-prepared nanostructures exhibit an excellent chemical stability and plasmonic property in plasmon-enhanced spectroscopies for more than one year. It also features an alternative plasmon-mediated photocatalysis pathway by smartly blocking "hot" electrons. Astonishingly, the shell-isolated Ag nanoparticles (Ag SHINs), as "smart plasmonic dusts", reveal a ∼1000-fold ensemble enhancement of rhodamine isothiocyanate (RITC) on a quartz substrate in surface-enhanced fluorescence. The presented "smart" Ag nanostructures offer a unique way for the promotion of ultrahigh sensitivity and reliability in plasmon-enhanced spectroscopies.

Unconventional interfacial water structure of highly concentrated aqueous electrolytes at negative electrode polarizations.

Water-in-salt electrolytes are an appealing option for future electrochemical energy storage devices due to their safety and low toxicity. However, the physicochemical interactions occurring at the interface between the electrode and the water-in-salt electrolyte are not yet fully understood. Here, via in situ Raman spectroscopy and molecular dynamics simulations, we investigate the electrical double-layer structure occurring at the interface between a water-in-salt electrolyte and an Au(111) electrode. We demonstrate that most interfacial water molecules are bound with lithium ions and have zero, one, or two hydrogen bonds to feature three hydroxyl stretching bands. Moreover, the accumulation of lithium ions on the electrode surface at large negative polarizations reduces the interfacial field to induce an unusual "hydrogen-up" structure of interfacial water and blue shift of the hydroxyl stretching frequencies. These physicochemical behaviours are quantitatively different from aqueous electrolyte solutions with lower concentrations. This atomistic understanding of the double-layer structure provides key insights for designing future aqueous electrolytes for electrochemical energy storage devices.

[Seasonal Removal Efficiency and Degradation Products of Two Typical PPCPs in Subsurface Flow Constructed Wetlands].

The pollution of surface waters by pharmaceuticals and personal care products (PPCPs) has aroused widespread concern. Constructed wetlands (CWs) have outstanding advantages in the removal of PPCPs; however, few studies have focused on the interaction of different types of PPCPs in CWs. In this study, two typical PPCPs[broad-spectrum antimicrobial agents triclosan (TCS) and non-steroidal anti-inflammatory drug diclofenac (DCF)] were selected as target pollutants and their removal behavior in subsurface flow CWs was analyzed. The effects of different seasons and influent conditions (i.e., single and combined addition of TCS and DCF) on removal efficiency was also examined. The main parameters of the CW system were as follows:the up-flow subsurface CW had a hydraulic load of 0.20 m·d-1 and a hydraulic residence time of 3 d with a continuous flow inlet. The initial influent concentration of PPCPs was 80 g·L-1 for TCS and 25 g·L-1 for DCF. The results showed that the average removal efficiencies for TCS and DCF in summer (91.72% and 85.86%, respectively) were significantly higher than in winter (52.88% and 32.47%, respectively). Independent sample t-tests confirmed that there was no significant difference in the removal efficiency of TCS and DCF under the different influent conditions (single and combined addition). The degradation products of TCS and DCF were also no different between the influent systems, and the representative degradation products of TCS were not detected in all systems. The main degradation products of DCF in the different systems were 3,5-dichlorobenzoic acid and m-dichlorobenzene. The two studied PPCPs showed no significant antagonism and competition effects at trace levels.

Biotic and abiotic factors distinctly drive contrasting biogeographic patterns between phyllosphere and soil resistomes in natural ecosystems.

The phyllosphere and soil are two of the most important reservoirs of antibiotic resistance genes (ARGs) in terrestrial ecosystems. However, comparative studies on the biogeographic patterns of ARGs in these two habitats are lacking. Based on the construction of ARG abundance atlas across a > 4,000 km transect in eastern and northern Australia, we found contrasting biogeographic patterns of the phyllosphere and soil resistomes, which showed their distinct responses to the biotic and abiotic stresses. The similarity of ARG compositions in soil, but not in the phyllosphere, exhibited significant distance-decay patterns. ARG abundance in the phyllosphere was mainly correlated with the compositions of co-occurring bacterial, fungal and protistan communities, indicating that biotic stresses were the main drivers shaping the phyllosphere resistome. Soil ARG abundance was mainly associated with abiotic factors including mean annual temperature and precipitation as well as soil total carbon and nitrogen. Our findings demonstrated the distinct roles of biotic and abiotic factors in shaping resistomes in different environmental habitats. These findings constitute a major advance in our understanding of the current environmental resistomes and contribute to better predictions of the evolution of environmental ARGs by highlighting the importance of habitat difference in shaping environmental resistomes.

Microbial functional attributes, rather than taxonomic attributes, drive top soil respiration, nitrification and denitrification processes.

We lack empirical evidence for the relative importance of microbial functional attributes vs taxonomic attributes in regulating specified soil processes related to carbon (C) and nitrogen (N) cycling, which has hindered our ability to predict the responses of ecosystem multifunctionality to environmental changes. Here, we collected soil samples from a long-term experimental field with eight inorganic and organic fertilization treatments and evaluated the linkage between microbial functional attributes (abundance of functional genes), taxonomic attributes (microbial taxonomic composition), and soil processes including soil respiration, denitrification and nitrification. Long-term fertilization had no significant effect on the bacterial or fungal alpha-diversity. The treatments of chicken manure and sewage sludge addition significantly altered the rates of soil respiration, denitrification and nitrification, which were significantly correlated with the abundances of relevant functional genes. Random forest model indicated that the abundance of functional genes was the main diver for the rate of soil processes. The predominant effect of microbial functional attributes in driving soil processes was maintained when simultaneously accounting for multiple abiotic (total C, total N and soil pH) and biotic drivers (bacterial and fungal community structure), indicating that microbial functional attributes were the predominant driver predicting the rate of soil respiration, denitrification and nitrification. Our results suggested the importance of developing a functional gene-centric framework to incorporate microbial communities into biogeochemical models, which may provide new insights into the biodiversity-functions relationship and have implications for future management of the consequences of biodiversity loss for ecosystem multifunctionality.

Real-time detection of single-molecule reaction by plasmon-enhanced spectroscopy.

Determining structural transformations of single molecules (SMs) is an important fundamental scientific endeavor. Optical spectroscopies are the dominant tools used to unravel the physical and chemical features of individual molecules and have substantially contributed to surface science and biotechnology. In particular, Raman spectroscopy can identify reaction intermediates and reveal underlying reaction mechanisms; however, SM Raman experiments are subject to intrinsically weak signal intensities and considerable signal attenuation within the spectral dispersion systems of the spectrometer. Here, to monitor the structural transformation of an SM on the millisecond time scale, a plasmonic nanocavity substrate has been used to enable Raman vibrational and fluorescence spectral signals to be simultaneously collected and correlated, which thus allows a detection of photo-induced bond cleavage between the xanthene and phenyl group of a single rhodamine B isothiocyanate molecule in real time. This technique provides a novel method for investigating light-matter interactions and chemical reactions at the SM level.

Observation of inhomogeneous plasmonic field distribution in a nanocavity.

The progress of plasmon-based technologies relies on an understanding of the properties of the enhanced electromagnetic fields generated by the coupling nanostrucutres1-6. Plasmon-enhanced applications include advanced spectroscopies7-10, optomechanics11, optomagnetics12 and biosensing13-17. However, precise determination of plasmon field intensity distribution within a nanogap remains challenging. Here, we demonstrate a molecular ruler made from a set of viologen-based, self-assembly monolayers with which we precisely measures field distribution within a plasmon nanocavity with ~2-Å spatial resolution. We observed an unusually large plasmon field intensity inhomogeneity that we attribute to the formation of a plasmonic comb in the nanocavity. As a consequence, we posit that the generally adopted continuous media approximation for molecular monolayers should be used carefully.