Lasers are the pillars of modern optics and sensing. Microlasers based on whispering-gallery modes (WGMs) are miniature in size and have excellent lasing characteristics suitable for biosensing. WGM lasers have been used for label-free detection of single virus particles, detection of molecular electrostatic changes at biointerfaces, and barcode-type live-cell tagging and tracking. The most recent advances in biosensing with WGM microlasers are described in this review. We cover the basic concepts of WGM resonators, the integration of gain media into various active WGM sensors and devices, and the cutting-edge advances in photonic devices for micro- and nanoprobing of biological samples that can be integrated with WGM lasers.

respect, the theoretical work of Barzukov and co-workers [ 7 ] suggests that the catalysis of the ORR on CPs can be ascribed to the weakening of molecular O O bonds during the chemisorption of oxygen on the polymer surface. For example, in the case of carbon black/PPy composites, the onset potential for ORR (−0.34 V) is more anodic than that observed in carbon blackcoated electrodes (−0.60 V). However, the ORR current densities are highly dependent on the loading of the PPy catalyst because of the low oxygen diffusion in the electrode surface. [ 13 ] In this regard, one of the major challenges for the optimization of electrochemical energy-conversion devices (e.g., metal-air batteries), is to increase the O 2 reduction and evolution effi ciencies, thus requiring the development of new effective electrocatalytic interfacial architectures compatible with the operation in aqueous electrolytes using air as the oxygen source.This point is where MOFs come into the picture as a valuable tool to engineer the oxygen uptake properties of the electrochemical interface in order to increase its concentration on the electrode surface. MOFs represent an emergent and versatile class of microporous materials constituted by an infi nite arrangement of metal (or metal cluster) centers coordinated via noncovalent interactions with organic linkers. [ 14,15 ] A great deal of effort has been devoted also to test strategies directed to control MOFs' growth and to synthesize mixed composites and supported fi lms, [ 16 ] whose distinctive properties have given rise to an increasing number of interesting applications (e.g., mixed matrix membranes for pervaporation, [ 17 ] or thin fi lms for sensor and separation technologies [ 18 ] ).Very recently, Díaz et al. [ 19 ] reported a comprehensive work describing the selective gas adsorption of fi lms constituted by ZIF-8 MOF (a member of a subclass of MOFs known as Zeolitic Imidazole Frameworks, constituted of Co 2+ or Zn 2+ metal ions tetrahedrally coordinated by imidazole-based linkers). It was shown that selectivity of O 2 adsorption over N 2 is close to 6, thus confi rming that ZIF-8 would undergo preferential uptake of O 2 even in the case of atmospheric O 2 :N 2 composition.Taking into account these concepts and being aware of the outstanding features of gas storage exhibited by metal-organic frameworks, we took this new paradigm one step further by integrating MOFs onto CPs and using them as oxygen reservoirs sitting atop the electrocatalytic active material. However, it is important to consider that such interfacial architectures require the tailored production and organization of complex matter displaying spatially addressed chemistry using different wet chemical processes. Therefore, to achieve this goal it is important to test strategies for the controlled preparation of multicomponent nanostructures on surfaces. Research efforts The oxygen reduction reaction (ORR), where molecular oxygen is electrocatalytically reduced on the electrode surface, plays a decisive role in energy conver...

In the present work, we have synthesized and fully characterized the photophysical and photochemical properties of a selected group of N-methyl-b-carboline derivatives (9-methylb-carbolines and iodine salts of 2-methyl-and 2,9-dimethyl-bcarbolinium) in aqueous solutions, in the pH range 4.0-14.5. Moreover, despite the quite extensive studies reported in the literature regarding the overall photophysical behavior of Nunsubstituted bCs, this work constitutes the first full and unambiguous characterization of anionic species of N-unsubstituted bCs (norharmane, harmane and harmine), present in aqueous solution under highly alkaline conditions (pH > 13.0). Acid dissociation constants (K a ), thermal stabilities, room temperature UV-visible absorption and fluorescence emission and excitation spectra, fluorescence quantum yields (Ф F ) and fluorescence lifetimes (s F ), as well as quantum yields of singlet oxygen production (Ф D ) have been measured for all the studied compounds. Furthermore, for the first time to our knowledge, chemometric techniques (MCR-ALS and PARAFAC) were applied on these systems, providing relevant information about the equilibria and species involved. The impact of all the foregoing observations on the biological role, as well as the potential biotechnological applications of these compounds, is discussed.

Oxygen reduction reaction (ORR), essential in many energy conversion devices, takes particular relevance in facing the increasing global demand for clean energy sources and vectors. In this context, desirable features for ORR-based electrochemical cells are operability under environmentally friendly conditions, such as pH 7 biocompatible electrolytes, and the usage of relatively low electrocatalyst loadings. On the other hand, the improvement of the cathode performance in neutral solutions is commonly focused on the development of electrocatalyzers for reducing the ORR overpotential. In this work, we took advantage of the possibilities brought by a novel strategy toward construction of complex interfacial architectures, the so-called "nanoarchitectonics" approach. In order to achieve enhanced ORR currents and reduced overpotentials, we combined three different building blocks with defined functionalities: a conducting polymer (CP) nanofilm (the connecting electroactive matrix), well dispersed Pt-nanoparticles (the electrocatalyzer), and a layer of a Zn-based metal−organic framework (MOF) nanocrystals (the in situ oxygen reservoir). The sequential synthetic procedure includes the electrosynthesis of a polyaniline-like electroactive film, the synthesis of Pt nanoparticles within this film, and the deposition of a layer of MOF nanocrystals, which adds micro/mesoporosity to the assembly. The incorporation of the MOF nanocrystals layer incorporates two fundamental aspects: it allows for the ionic transport through its interparticle interstices, and also selectively promotes the O 2 preconcentration, which is then available for the ORR on the embedded catalytically active metallic nanoparticles. The rational integration of these blocks yields a functional interfacial architecture for enhanced ORR currents in eco-friendly neutral pH KCl solutions.

Metal–organic framework (MOF) thin films are promising materials for multiple technological applications, such as chemical sensing. However, one potential limitation for their widespread use in different settings is their stability in aqueous environments. In the case of ZIF-8 (zeolitic imidazolate framework) thin films, their stability in aqueous media is currently a matter of debate. Here, we show that optical waveguide spectroscopy (OWS), in combination with surface plasmon resonance (SPR) spectroscopy, offers a convenient way for answering intriguing questions related to the stability of MOF thin films in aqueous solutions and, eventually provide a tool for assessing changes in MOF layers under different environmental conditions. Our experiments relied on the use of ZIF-8 thin films grown on surface-modified gold substrates, as optical waveguides. We have found a linear thickness increase after each growing cycle and observed that the growing characteristics are strongly influenced by the nature of the primer layer. One of our findings is that substrate surface modification with a 3-mercapto-1-propanesulfonate (MPSA) primer layer is critical to achieve ZIF-8 layers that can effectively act as optical waveguides. We observed that ZIF-8 films are structurally stable upon exposure to pure water and 50 mM NaCl solutions but they exhibit a slight swelling and an increase in porosity probably due to the permeation of the solvent in the intergrain mesoporous cavities. However, OWS revealed that exposure of ZIF-8 thin films to phosphate-buffered saline solutions (pH 8) promotes significant film degradation. This poses an important question as to the prospective use of ZIF-8 materials in biologically relevant applications. In addition, it was demonstrated that postsynthetic polyelectrolyte modification of ZIF-8 films has no detrimental effects on the structural stability of the films

Platinum nanoparticles of 3 nm diameter were included in mesoporous silica thin films by controlling the mesopore surface charge with a short polymer brush. This metal-polymer-mesopore nanocomposite presents high catalytic activity toward ammonia oxidation at low temperatures with 4.5% weight platinum loading. An anomalous partial selectivity toward nitrous oxide is observed for the first time, which can be traced back to the synergy of the particles and modified surface. This effect opens a path toward the design of nanocomposite catalysts with highly controlled environments, in which the size- and function-controlled cavities can be tuned in order to lower the reaction barriers.

We present the results of Monte Carlo simulations of the adsorption of single-component ethane and ethylene and of equimolar mixtures of these two gases on bundles of closed, single-walled carbon nanotubes. Two types of nanotube bundles were used in the simulations: homogeneous (i.e., those in which all the nanotubes have identical diameters) and heterogeneous (those in which nanotubes of different diameters are allowed). We found that at the same pressure and temperature more ethane than ethylene adsorbs on the bundles over the entire range of pressures and temperatures explored. The simulation results for the equimolar mixtures show that the pressure at which maximum separation is attained is a very sensitive function of the diameter of the nanotubes present in the bundles. Simulations using heterogeneous bundles yield better agreement with single-component experimental data for isotherms and isosteric heats than those obtained from simulations using homogeneous bundles. Possible applications of nanotubes in gas separation are discussed. We explored the effect of the diameter of the nanotubes on the separation ability of these sorbents, both for the internal and for the external sites. We found that substrate selectivity is a decreasing function of temperature.

Nanoarchitectonics can lead to electrode materials with enhanced electrocatalytic properties.