Ytterbium 10-carboxyperylene-3,4,9-tricarboxylates for targeted NIR luminescent bioimaging.

Two new ytterbium coordination compounds Yb(HPTC)(H2O)2 (Yb1) and Yb(HPTC)(Phen) (Yb2) were obtained using 10-carboxyperylene-3,4,9-tricarboxylate ion (HPTC3-) as a sensitizer. Both coordination compounds exhibited intense NIR-II luminescence upon excitation in the visible range and formed stable suspensions with nanoparticles of 50-70 nm in size in an aqueous solution of sodium alginate. Both complexes demonstrated non-toxicity up to at least 25 mg L-1 in two cell cultures: cancer cells MCF7 and embryonic cells HEK293T - making them suitable for bioimaging. For both complexes, the accumulation in cells was directly measured and it was shown that the accumulation of Yb2 was the same for both cell types (0.51-0.52 πg per cell), while Yb1 demonstrated selective accumulation in cancer cells (0.04 πg per cell for HEK293T and 7.00 πg per cell for MCF7). Thus, Yb1 can also be proposed as a selective vis-excited NIR emitting bioprobe.

Tunable Sieving of Ions Using Graphene Oxide: Swelling Peculiarities in Free-Standing and Confined States.

The paper describes a comparative study of swelling processes in free-standing graphene oxide (GO) membranes and GO laminates encapsulated with epoxy glue. For free-standing graphene oxide membranes, a huge variation in d-spacing in the range of 8-12 Å depending on the ambient humidity and from 12 to >30 Å depending on the electrolyte type and its concentration was revealed using direct in situ and in operando XRD studies. Limited swelling at various humidity levels as well as in electrolyte solution with low constriction/expansion of epoxy-encapsulated GO is counterposed to that of free-standing graphene oxides. The swelling suppression was explained by both physical constriction and the intercalation of amines into GO laminates, which was proved by local EDX studies. This results in ion diffusivity variation for over 2 orders of magnitude in free-standing and constrained graphene oxide membranes and provides factual evidence for tunable sieving of ions with confined graphene oxides.

Pulse Power Generation Chronoamperometry as an Advanced Readout for (Bio)sensors: Application for Noninvasive Diabetes Monitoring.

We propose pulse power generation (PPG) amperometry as an advanced readout realized for Prussian blue (PB)-based (bio)sensors. In contrast to the conventional power generation mode, when the current response is generated upon continuous short-circuiting, the suggested pulse regime is fulfilled by periodic opening and shorting of the circuit. Despite PB being electroactive, the pulse readout is advantageous over conventional steady-state power generation, providing up to a 15-fold increased signal-to-background ratio as well as dramatically improved sensitivity exceeding 10 A·M-1·cm-2 for H2O2 sensors and 3.9 A·M-1·cm-2 for glucose biosensors. Such analytical performance characteristics are, most probably, achieved due to the enrichment of the diffusion layer by analyte mass transfer from the bulk upon opening of the circuit. Due to an improved sensitivity-to-background ratio, reduced flow-rate dependence, and enhanced operational stability, the regime allows reliable monitoring of blood glucose variations through sweat analysis with the on-skin device.

Dimeric and 1D polymeric low-chlorinated C60 fullerenes, (C60Cl5)2 and (C60Cl4)∞.

Low-chlorinated fullerenes, dimeric (C60Cl5)2 and one-dimensional, polymeric (C60Cl4)∞, were obtained by high-temperature (270 °C) chlorination of C60 with a SbCl5/SbCl3 mixture, as revealed by X-ray crystallography. The compounds were characterized by IR and Raman spectroscopy and theoretical calculations. This is the first observation of a fullerene polymer with single C-C bonding and neutral building blocks.

Mass transport limitations for electrochemical sensing in low-flux excretory fluids.

Despite non-invasive instant monitoring of sweat metabolites is becoming a general trend in early diagnostics and screening, the reliability and accuracy of the on-skin electrochemical biosensors in real-life scenarios still remain questionable. As a rule, mass transport effects in scantily excreted liquids are ignored, when considering the design of such wearable setups. Here we provide a comprehensive investigation of the disruption factors for commonly used Prussian Blue based (bio)sensors under different hydrodynamic conditions (2 × 10-5 - 5 × 100 mm s-1 electrolyte velocity). A huge effect of flow on the (bio)sensors response has been revealed and explained with transport limitations for both analyte influx and reaction product outflux. It suggests no need for improving the sensor sensitivity, while minimizing analyte consumption and enhancing product withdrawal. Some strategies concerning measurement schemes and sensor design ensuring reliable sweat analysis have been discussed and illustrated for lactate and glucose on-skin monitoring.

Influence of heat transfer and wetting angle on condensable fluid flow through nanoporous anodic alumina membranes.

The flow of isobutane and of freon 142b (1-chloro-1,1-difluoro-ethane) through anodic alumina membranes with pore diameters between 18 and 60 nm in a capillary condensation regime is experimentally and theoretically explored. The capillary condensation effect increases the membrane permeance for condensable gases from 25 to 150 m3(STP) m-2 bar-1 h-1 at certain conditions. To describe the experimental results, a model is suggested accounting for heat transfer from the condensing to the evaporating meniscus, different boundary conditions for the heat transfer between the environment and the membrane, and wettability of the pore wall. The proposed model indicates a large influence of heat supply from the environment to the membrane on the permeance in the capillary condensation regime and a moderate influence of condensate contact angle in the range of 0-60°. Measuring the temperature of the permeate side of the membrane allows to find a suitable boundary condition to describe heat transfer. The obtained boundary condition yields an excellent fit of experimental results of condensate flow through membranes with different pore diameters for the two utilized fluids. Also, confocal Raman spectroscopy gave evidence on the fraction of pores filled with condensate.

Oxidized Carbon-Based Spacers for Pressure-Resistant Graphene Oxide Membranes.

In this study, we report the influence of carbon-based spacer-oxidized derivatives of fullerenes (fullerenols) C60(OH)26−32 and graphene oxide nanoribbons on the performance and pressure stability of graphene-oxide-based composite membranes. The impact of the intercalant shape and composition on the permeance of the selective layers for water vapors has been studied under pressure gradients. It is shown that the insertion of ball-shaped fullerenols between graphene oxide nanoflakes allows a suppression in irreversible permeance loss to 2−4.5% and reversible permeance loss to <25% (at 0.1 MPa), while retaining large H2O/N2 selectivities of up to ~30,000. The demonstrated approach opens avenues for the highly effective stabilization of GO membranes at elevated pressures for industrial-scale dehumidification.

Simultaneous monitoring of sweat lactate content and sweat secretion rate by wearable remote biosensors.

We report on the simultaneous monitoring of sweat lactate concentration and sweat secretion rate. For this aim lactate oxidase-Prussian Blue enzyme-nanozyme type lactate biosensors were elaborated. The use of siloxane-perfluorosulfonated ionomer composite membrane for enzyme-nanozyme immobilization results in the biosensor displaying flux independence in the whole range of physiological sweat secretion rates (0.025-2 µl cm-2 min-1). On the contrary, current response of the biosensor based on solely siloxane membranes becomes saturated at physiological sweat lactate concentration, depending mostly on the flow rate. Accordingly, for simultaneous monitoring of sweat lactate concentration and its secretion rate both flow-through biosensors were integrated with high-accuracy wearable electronic devices allowing real-time remote monitoring. As found, during exhaustive physical exercise sweat secretion rate and lactate content are independent of each other, thus, confirming that this excretory liquid is suitable for non-invasive diagnostics.

Surface-Enhanced Raman Scattering-Active Gold-Decorated Silicon Nanowire Substrates for Label-Free Detection of Bilirubin.

Bilirubin (BR) is a product of hemoglobin breakdown, and its increasing levels in the blood may indicate liver disorders and lead to jaundice. Kernicterus is most dangerous in newborns when the unconjugated BR concentration can quickly rise to toxic levels, causing neurological damage and even death. The development of an accurate, fast, and sensitive sensor for BR detection will help reduce diagnostic time and ensure successful treatment. In this study, we propose a new method for creating a surface-enhanced Raman scattering (SERS)-active substrate based on gold-decorated silicon nanowires (Au@SiNWs) for sensitive label-free BR detection. Gold-assisted chemical etching of crystalline silicon wafers was used to synthesize SiNWs, the tops of which were then additionally decorated with gold nanoparticles. The low detection limit of model analyte 4-mercaptopyridine down to the concentration of 10-8 M demonstrated the excellent sensitivity of the obtained substrates for SERS application. The theoretical full-wave electromagnetic simulations of Raman scattering in the Au@SiNW substrates showed that the major contribution to the total SERS signal comes from the analyte molecules located on the SiNW surface near the gold nanoparticles. Therefore, for efficient BR adsorption and SERS detection, the surface of the SiNWs was modified with amino groups. Label-free detection of BR using amino modified Au@SiNWs with high point-to-point, scan-to-scan, and batch-to-batch reproducibility with a detection limit of 10-6 M has been demonstrated. Artificial urine, mimicking human urine samples, was used as the matrix to get insights into the influence of different parameters such as matrix complexity on the overall BR SERS signal. The signal stability was demonstrated for 7 days after adsorption of BR with a concentration of 5 × 10-5 M, which is the required sensitivity for clinical applications.

Mass flow and momentum flux in nanoporous membranes in the transitional flow region.

An experimental study of momentum transfer in nanoporous polymeric track-etched membranes with pore diameters ranging from 100 to 1300 nm and nanochannel lengths of 12-20 µm was performed using He, N2, CO2, and SF6 propellants in a wide range of plenum and background pressures. Mass flux through the membranes was elaborated as a combination of Knudsen diffusion and viscous flow at Knudsen numbers above 0.1 and become choked at lower Knudsen numbers. The discharge coefficient for the membranes attained was 0.6, making the permeation rate similar to that of thin orifices. The effect is attributed to the mirror reflection of the molecules from the pore walls at low angles of incidence. The exhaust gas velocity is found to be dependent on the plenum to background pressure ratio and channel length-to-diameter ratio, reaching 0.9 of the velocity of the gas expanded to vacuum (up to 2 M). Close to an isothermal expansion occurs in nanochannels of all sizes. A general quantitative description for gas expansion in nanochannels is provided. The highest thrust is generated in the choked flow regime with the SF6 propellant and a value of 4.5 N cm-2 is attained at a propellant consumption of 0.165 kg (cm2 s)-1 for the membranes with 1300 nm nanochannels. The specific impulse of 138 s is reached for helium. The results show the prospects of the utilization of nanoporous membranes in cold gas propulsion systems.

Core-Shell Nanozymes "Artificial Peroxidase": Stability with Superior Catalytic Properties.

We report on the nanoparticles composed of the catalytically synthesized Prussian Blue (PB) core stabilized with the nickel hexacyanoferrate (NiHCF) shell. Catalyzing hydrogen peroxide reduction, the resulting nanozymes (ø = 66 nm) display catalytic rate constants, which for pyrogallol or ferrocyanide are, respectively, 25 and 35 times higher than those for peroxidase enzyme. After more than half a year of storage at a room temperature, the core-shell PB-NiHCF nanozymes retain both their size and physicochemical properties; such stability is unreachable for the enzymes. Being immobilized, core-shell PB-NiHCF nanozymes (ø = 45 nm) result in a hydrogen peroxide sensor with a sensitivity similar to that of the sensor based on sole PB nanoparticles. However, whereas the latter response in hard inactivating conditions (25 min in 1 mM H2O2) drops down to 7.5%, the PB-NiHCF nanozymes-based sensor retains >75% of initial sensitivity. Application of the core-shell PB-NiHCF nanozymes "artificial peroxidase" would obviously open new horizons in elaboration of anti-inflammatory drugs and (bio)sensors.

Anodic alumina membrane capacitive sensors for detection of vapors.

Here we report membrane capacitive sensors based on anodic aluminum oxide (AAO) Au/AAO/Au structures fabricated by aluminum anodization, followed by gold electrodes sputtering on the countersides of porous ceramic membrane. Electrochemical impedance spectroscopy with AC amplitude 5-100 mV in the frequency range of 1-1000 Hz was utilized for sensor characterization in the presence of water and organic vapors in a full range of P/P0. The sensors illustrate ultimate sensitivity to ambient environment with exponential-scale capacitance relation to vapors content resulting in typical 4-6 orders of magnitude response signal change for 15-85% P/P0 range at a single AC frequency, and up to 7 orders of magnitude response range for 0-100% P/P0 pressure range with using two different AC frequencies. In case of water vapors, the sensitivity increases from ~0.5 nF/RH% at ~20 RH% to over ~1.0 µF/RH% at ~80 RH%. The sensors are capable for highly accurate sensing of gas humidity as well as any dissociative vapors with pKa <30. They are also sensible to polar components with high enough dipole moment or polarizability. The capacitance is affected by any adsorbed molecules, including those having zero dipole moment. The data for sensor response to CH3OH, C2H5OH, CH2ClCHF2, i-C4H10 depending on partial pressures is provided. Due to high porosity (10-30%) and gaseous permeance (up to 200 m3(STP) m-2 bar-1 h-1) the sensors offer fast response rate and a possibility for flow-through measurements, providing also a mass-flow response option, which was tested with SF6, CO2, N2 and He. The basic principles of dielectric loss sensor and the equivalent scheme were proposed for sensor operation in different environment, allowing estimating sensor response.

Bismuth nanowires: electrochemical fabrication, structural features, and transport properties.

Electrochemical aspects of Bi electrocrystallization from a bath containing bismuth nitrate in a mixture of ethylene glycol and water are addressed. Bismuth nanowires with diameters of 50-120 nm and a length of up to a few dozen microns were prepared by electrodeposition into the pores of anodic aluminium oxide templates. Crystal structure and morphology of electrodeposited materials were characterized using electron microscopy, selected area electron diffraction, and X-ray diffraction analysis. Factors affecting the formation of single or polycrystalline nanowires and their crystallographic orientation are discussed. The prospects of electrodeposited Bi nanostructures for microelectronics are illustrated by the quantitative resistivity measurements of highly texturized Bi nanowires with a diameter of ca. 100 nm and a length varying from 160 to 990 nm in a temperature range from 300 to 1.2 K.

Spontaneous MXene monolayer assembly at the liquid-air interface.

Here we report on the spontaneous assembly of Ti3C2Tx MXene flakes into monolayer films at the liquid-air interface. According to X-ray reflectivity and grazing incidence X-ray fluorescence both the structure of the layers and assembly kinetics depends on the pH value of the solution. At pH > 4 MXene flakes form a single ∼1.5 nm thick layer carrying a negative charge, while in the acidic medium the layer contains coordinated anions with the formation of the Braq-/Ti3C2Tx/subphase interface. The surface layer compression allows the assembling of MXene flakes into a dense monolayer films with the surface coverage of up to 96% and surface pressure exceeding 40 mN m-1 in the case of the acidic subphase. The films can readily be transferred onto solid substrates by the conventional Langmuir-Blodgett approach or modified by surfactants to form MXene/surfactant composite films.

Silver Eco-Solvent Ink for Reactive Printing of Polychromatic SERS and SPR Substrates.

A new reactive ink based on a silver citrate complex is proposed for a photochemical route to surface-enhanced Raman spectroscopy active substrates with controllable extinction spectra. The drop-cast test of the ink reveals homogeneous nucleation of silver and colloid particle growth originating directly from photochemical in situ reduction in droplets, while the following evaporation of the deposited ink produces small nano- and micron-size particles. The prepared nanostructures and substrates were accurately characterized by electron microscopy methods and optical extinction spectroscopy. Varying the duration of UV irradiation allows tuning the morphology of individual silver nanoparticles forming hierarchical ring structures with numerous "hot spots" for most efficient Raman enhancement. Raman measurements of probe molecules of rhodamine 6G and methylene blue reached the largest signal enhancement of 106 by the resonance effects.

Structural and Optical Properties of Silicon Nanowire Arrays Fabricated by Metal Assisted Chemical Etching With Ammonium Fluoride.

Here we report on the metal assisted chemical etching method of silicon nanowires (SiNWs) manufacturing, where the commonly used hydrofluoric acid (HF) has been successfully replaced with ammonium fluoride (NH4F). The mechanism of the etching process and the effect of the pH values of H2O2: NH4F solutions on the structural and optical properties of nanowires were studied in detail. By an impedance and Mott-Schottky measurements it was shown that silver-assisted chemical etching of silicon can be attributed to a facilitated charge carriers transport through Si/SiOx/Ag interface. It was shown that the shape of nanowires changes from pyramidal to vertical with pH decreasing. Also it was established that the length of SiNW arrays non-linearly depends on the pH for the etching time of 10 min. A strong decrease of the total reflectance to 5-10% was shown for all the studied samples at the wavelength <800 nm, in comparison with crystalline silicon substrate (c-Si). At the same time, the intensities of the interband photoluminescence and the Raman scattering of SiNWs are increased strongly in compare to c-Si value, and also they were depended on both the length and the shape of SiNW: the biggest values were for the long pyramidal nanowires. That can be explained by a strong light scattering and partial light localization in SiNWs. Hereby, arrays of SiNWs, obtained by using weakly toxic ammonium fluoride, have great potential for usage in photovoltaics, photonics, and sensorics.

Diffusion doping route to plasmonic Si/SiO x nanoparticles.

Semiconductor nanoparticles (SNPs) are a valuable building block for functional materials. Capabilities for engineering of electronic structure of SNPs can be further improved with development of techniques of doping by diffusion, as post-synthetic introduction of impurities does not affect the nucleation and growth of SNPs. Diffusion of dopants from an external source also potentially allows for temporal control of radial distribution of impurities. In this paper we report on the doping of Si/SiO x SNPs by annealing particles in gaseous phosphorus. The technique can provide efficient incorporation of impurities, controllable with precursor vapor pressure. HRTEM and X-ray diffraction studies confirmed that obtained particles retain their nanocrystallinity. Elemental analysis revealed doping levels up to 10%. Electrical activity of the impurity was confirmed through thermopower measurements and observation of localized surface plasmon resonance in IR spectra. The plasmonic behavior of etched particles and EDX elemental mapping suggest uniform distribution of phosphorus in the crystalline silicon cores. Impurity activation efficiencies up to 34% were achieved, which indicate high electrical activity of thermodynamically soluble phosphorus in oxide-terminated nanosilicon.

Liquid permeation and chemical stability of anodic alumina membranes.

A study on the chemical stability of anodic alumina membranes and their performance in long-term water and organic solvent permeation experiments is reported. Anodic alumina possesses high stability for both protonic and aprotonic organic solvents. However, serious degradation of the membrane occurs in pure water, leading to a drastic decrease of permeance (over 20% of the initial value after the passing of 0.250 m3/m2 of pure water). The drying of the membrane induces further permeance drop-off. The rate of membrane degradation strongly depends on the pH of the penetrant solution and increases in basic media. According to 27Al NMR and thermogravimetry results, the degradation of the membranes is associated with the dissolution of water-soluble [Al13O4(OH)24(H2O)12]7+ polyhydroxocomplexes and their further redeposition in the form of [Al(OH)4]-, resulting in channels blocking. This process intensifies in basic pH due to the high positive charge of the anodic alumina surface. An approach for improving anodic aluminum oxide stability towards dissolution in water by carbon CVD coating of the membrane walls is suggested.

Size-Dependent Structure Relations between Nanotubes and Encapsulated Nanocrystals.

The structural organization of compounds in a confined space of nanometer-scale cavities is of fundamental importance for understanding the basic principles for atomic structure design at the nanolevel. Here, we explore size-dependent structure relations between one-dimensional PbTe nanocrystals and carbon nanotube containers in the diameter range of 2.0-1.25 nm using high-resolution transmission electron microscopy and ab initio calculations. Upon decrease of the confining volume, one-dimensional crystals reveal gradual thinning, with the structure being cut from the bulk in either a <110> or a <100> growth direction until a certain limit of ∼1.3 nm. This corresponds to the situation when a stoichiometric (uncharged) crystal does not fit into the cavity dimensions. As a result of the in-tube charge compensation, one-dimensional superstructures with nanometer-scale atomic density modulations are formed by a periodic addition of peripheral extra atoms to the main motif. Structural changes in the crystallographic configuration of the composites entail the redistribution of charge density on single-walled carbon nanotube walls and the possible appearance of the electron density wave. The variation of the potential attains 0.4 eV, corresponding to charge density fluctuations of 0.14 e/atom.