Electrospray: More than just an ionization source.

Electrospraying (ES) is a potential-driven process of liquid atomization, which is employed in the field of analytical chemistry, particularly as an ionization technique for mass spectrometric analyses of biomolecules. In this review, we demonstrate the extraordinary versatility of the electrospray by overviewing the specifics and advanced applications of ES-based processing of low molecular mass compounds, biomolecules, polymers, nanoparticles, and cells. Thus, under suitable experimental conditions, ES can be used as a powerful tool for highly controlled deposition of homogeneous films or various patterns, which may sometimes even be organized into 3D structures. We also emphasize its capacity to produce composite materials including encapsulation systems and polymeric fibers. Further, we present several other, less common ES-based applications. This review provides an insight into the remarkable potential of ES, which can be very useful in the designing of innovative and unique strategies.

GaTe-Sb2Te3 thin-films phase change characteristics.

A radio frequency magnetron co-sputtering technique exploiting GaTe and ${\rm Sb}_2 {\rm Te}_3$Sb2Te3 targets was used for the fabrication of Ga-Sb-Te thin films. Prepared layers cover broad region of chemical composition (${\sim}{10.0 {-} 26.3}\,\, {\rm at.}$∼10.0-26.3at. % of Ga, ${\sim}{19.9 {-} 34.4}\,\, {\rm at.}$∼19.9-34.4at. % of Sb) while keeping Te content fairly constant (53.8-55.6 at. % of Te). Upon crystallization induced by annealing, large variations in electrical contrast were found, reaching a sheet resistance ratio of ${{R}_{\rm annealed}}/{{R}_{\rm as - deposited}}\;\sim{2.2} \times {{10}^{ - 8}}$Rannealed/Ras-deposited∼2.2×10-8 for the ${{\rm Ga}_{26.3}}{{\rm Sb}_{19.9}}{{\rm Te}_{53.8}}$Ga26.3Sb19.9Te53.8 layer. Phase transition from the amorphous to crystalline state further leads to huge changes of optical functions demonstrated by optical contrast values up to $|\Delta n| + |\Delta k| = {4.20}$|Δn|+|Δk|=4.20 for ${{\rm Ga}_{26.3}}{{\rm Sb}_{19.9}}{{\rm Te}_{53.8}}$Ga26.3Sb19.9Te53.8 composition.

Chiral Templating of Polycarbonate Membranes by Pinene Using the Modified Atomic Layer Deposition Approach.

In this article, chiral templating of a polycarbonate (PC) membrane by (-)-α-pinene using the atomic layer deposition (ALD) approach is investigated. The templating with the enantiomer of (-)-α-pinene, used as a case compound, was performed either on the original commercial PC membrane or on the PC membrane with a beforehand deposited Al2O3 layer. The efficiency of the templating was assessed by a difference in the membrane ability to adsorb/absorb (-)-α-pinene, (+)-α-pinene, and their racemic mixture, using a very sensitive gas sorption analyzer. The results clearly show that the solution-diffusion mechanism rather than the sieving mechanism applied for adsorption/absorption of (-/+)-α-pinene enantiomers, which have the same size of the molecule. The PC membrane with the predeposited Al2O3 before the (-)-α-pinene templating shows significantly higher sorption of (-)-α-pinene compared to (+)-α-pinene and racemate, which clearly demonstrates the presence of a chiral recognition effect.

Photon-Upconversion Barcoding with Multiple Barcode Channels: Application for Droplet Microfluidics.

Barcoding facilitates high-throughput analytical methods in complex matrixes with a reduced volume of sample, reagents, time, and cost. Because of orthogonality to fluorescence, photon-upconversion barcodes attracted considerable attention in recent years. We constructed an epiluminescence detector, which, for the first time, demonstrated the reading of photon-upconversion spectra from microdroplets in a microfluidic chip with frequency up to 10 Hz. Non-negative least-squares deconvolution enabled the reading of an unprecedented number of photon-upconversion barcode channels (six) from emission spectra (excitation 980 nm, emission 430-875 nm). The standard deviation of barcode reading from microdroplets was ∼1%. Described barcoding can be, for example, used for multiparameter titrations, multiplexed biological and chemical assays, optimizations on a microfluidic platform, and preparation of barcoded concentration gradients and libraries.

Optimization of background electrolyte composition for simultaneous contactless conductivity and fluorescence detection in capillary electrophoresis of biological samples.

In this article, optimization of BGE for simultaneous separation of inorganic ions, organic acids, and glutathione using dual C4 D-LIF detection in capillary electrophoresis is presented. The optimized BGE consisted of 30 mM 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid, 15 mM 2-amino-2-hydroxymethyl-propane-1,3-diol, and 2 mM 18-crown-6 at pH 7.2 and allowed simultaneous separation of ten inorganic anions and cations, three organic acids and glutathione in 20 min. The samples were injected hydrodynamically from both capillary ends using the double-opposite end injection principle. Sensitive detection of anions, cations, and organic acids with micromolar LODs using C4 D and simultaneously glutathione with nanomolar LODs using LIF was achieved in a single run. The developed BGE may be useful in analyses of biological samples containing analytes with differing concentrations of several orders of magnitude that is not possible with single detection mode.

Resistive pulse sensing as particle counting and sizing method in microfluidic systems: Designs and applications review.

Resistive pulse sensing is a well-known and established method for counting and sizing particles in ionic solutions. Throughout its development the technique has been expanded from detection of biological cells to counting nanoparticles and viruses, and even registering individual molecules, e.g., nucleotides in nucleic acids. This technique combined with microfluidic or nanofluidic systems shows great potential for various bioanalytical applications, which were hardly possible before microfabrication gained the present broad adoption. In this review, we provide a comprehensive overview of microfluidic designs along with electrode arrangements with emphasis on applications focusing on bioanalysis and analysis of single cells that were reported within the past five years.

Recent strategies toward microfluidic-based surface-enhanced Raman spectroscopy.

Surface-enhanced Raman spectroscopy (SERS) is an extremely powerful analytical tool, which not only yields information about the molecular structure of the analyte in the form of characteristic vibrational spectrum but also gives sensitivities approaching those in fluorescence spectroscopy. The SERS measurement on the microfluidic platform provides possibility to manufacture the device with design perfectly fulfilling the needs of the application with minimal sample consumption. This review aims at describing basic strategies for SERS measurement in microfluidic devices published in the last decade and covers current trends in microfluidics with SERS detection in the field of bioanalysis and approaches toward on-line coupling of liquid-based separation techniques with SERS detection.

Atomic Layer Deposition Al2O3 Coatings Significantly Improve Thermal, Chemical, and Mechanical Stability of Anodic TiO2 Nanotube Layers.

We report on a very significant enhancement of the thermal, chemical, and mechanical stability of self-organized TiO2 nanotubes layers, provided by thin Al2O3 coatings of different thicknesses prepared by atomic layer deposition (ALD). TiO2 nanotube layers coated with Al2O3 coatings exhibit significantly improved thermal stability as illustrated by the preservation of the nanotubular structure upon annealing treatment at high temperatures (870 °C). In addition, a high anatase content is preserved in the nanotube layers against expectation of the total rutile conversion at such a high temperature. Hardness of the resulting nanotube layers is investigated by nanoindentation measurements and shows strongly improved values compared to uncoated counterparts. Finally, it is demonstrated that Al2O3 coatings guarantee unprecedented chemical stability of TiO2 nanotube layers in harsh environments of concentrated H3PO4 solutions.

Reproducible preparation of nanospray tips for capillary electrophoresis coupled to mass spectrometry using 3D printed grinding device.

The use of high quality fused silica capillary nanospray tips is critical for obtaining reliable and reproducible electrospray/MS data; however, reproducible laboratory preparation of such tips is a challenging task. In this work, we report on the design and construction of low-cost grinding device assembled from 3D printed and commercially easily available components. Detailed description and characterization of the grinding device is complemented by freely accessible files in stl and skp format allowing easy laboratory replication of the device. The process of sharpening is aimed at achieving maximal symmetricity, surface smoothness and repeatability of the conus shape. Moreover, the presented grinding device brings possibility to fabricate the nanospray tips of desired dimensions regardless of the commercial availability. On several samples of biological nature (reserpine, rabbit plasma, and the mixture of three aminoacids), performance of fabricated tips is shown on CE coupled to MS analysis. The special interest is paid to the effect of tip sharpness.

Atomic Layer Deposition for Coating of High Aspect Ratio TiO2 Nanotube Layers.

We present an optimized approach for the deposition of Al2O3 (as a model secondary material) coating into high aspect ratio (≈180) anodic TiO2 nanotube layers using the atomic layer deposition (ALD) process. In order to study the influence of the diffusion of the Al2O3 precursors on the resulting coating thickness, ALD processes with different exposure times (i.e., 0.5, 2, 5, and 10 s) of the trimethylaluminum (TMA) precursor were performed. Uniform coating of the nanotube interiors was achieved with longer exposure times (5 and 10 s), as verified by detailed scanning electron microscopy analysis. Quartz crystal microbalance measurements were used to monitor the deposition process and its particular features due to the tube diameter gradient. Finally, theoretical calculations were performed to calculate the minimum precursor exposure time to attain uniform coating. Theoretical values on the diffusion regime matched with the experimental results and helped to obtain valuable information for further optimization of ALD coating processes. The presented approach provides a straightforward solution toward the development of many novel devices, based on a high surface area interface between TiO2 nanotubes and a secondary material (such as Al2O3).

Fluorescence detector for capillary separations fabricated by 3D printing.

A simple inexpensive light-emitting diode (LED)-based fluorescence detector for detection in capillary separations is described. The modular design includes a separate high power LED source, detector head, designed in the epifluorescence arrangement, and capillary detection cells. The detector head and detection cells were printed using a 3D printer and assembled with commercially available optical components. Optical fibers were used for connecting the detector head to the LED excitation source and the photodetector module. Microscope objective or high numerical aperture optical fiber were used for collection of the fluorescence emission from the fused silica separation capillary. As an example, mixture of oligosaccharides labeled by 8-aminopyrene-1,3,6-trisulfonate (APTS) was separated by capillary zone electrophoresis and detected by the described detector. The performance of the detector was compared with both a semiconductor photodiode and photomultiplier as light sensing elements. The main advantages of the 3D printed parts, compared to the more expensive alternatives from the optic component suppliers, include not only cost reduction, but also easy customization of the spatial arrangement, modularity, miniaturization, and sharing of information between laboratories for easy replication or further modifications of the detector. All information and files necessary for printing the presented detector are enclosed in the Supporting Information.

Laser desorption time-of-flight mass spectrometry of atomic switch memory Ge2Sb2Te5 bulk materials and its thin films.

RATIONALE: Although the structure of atomic switch Ge2Sb2Te5 (GST) thin films is well established, the composition of the clusters formed in the plasma plume during pulsed-laser deposition (PLD) is not known. Laser Desorption Ionization Time-of-Flight Mass Spectrometry (LDI-TOF MS) is an effective method for the generation and study of clusters formed by laser ablation of various solids and thus for determining their structural fragments. METHODS: LDI of bulk or PLD-deposited GST thin layers and of various precursors (Ge, Sb, Te, and Ge-Te or Sb-Te mixtures) using a nitrogen laser (337 nm) was applied while the mass spectra were recorded in positive and negative ion modes using a TOF mass spectrometer equipped with a reflectron while the stoichiometry of the clusters formed was determined via isotopic envelope analysis. RESULTS: The singly negatively or positively charged clusters identified from the LDI of GST were Ge, Ge2, GeTe, Ge2Te, Ten (n = 1-3), GeTe2, Ge2Te2, GeTe3, SbTe2, Sb2Te, GeSbTe2, Sb3Te and the low abundance ternary GeSbTe3, while the LDI of germanium telluride yielded Gem Ten (+) clusters (m = 1-3, n = 1-3). Several minor Ge-H clusters were also observed for pure germanium and for germanium telluride. Sbn clusters (n = 1-3) and the formation of binary TeSb, TeSb2 and TeSb3 clusters were detected when Sb2Te3 was examined. CONCLUSIONS: This is the first report that elucidates the stoichiometry of Gem Sbn Tep clusters formed in plasma when bulk or nano-layers of GST material are ablated. The clusters were found to be fragments of the original structure. The results might facilitate the development of PLD technology for this memory phase-change material.

Bioluminescence determination of active caspase-3 in single apoptotic cells.

Caspase-3 is an executive caspase, in the central position within apoptotic machinery. Apoptosis as a way of programmed cell death is a physiological process that plays an essential role in the development and homeostasis maintenance; moreover, its deregulations are linked to tumor progression or various autoimmune disorders. Therefore, an investigation of apoptosis pathways on the level of individual cells is not only of biological but also medical importance. In this work we report on the development of a high-sensitivity instrumentation and protocol for detection of active caspase-3 in individual mammalian apoptotic cells. The technology is based on the specific cleavage of modified luciferin by caspase-3, an immediate bioluminescence reaction of free luciferin with luciferase followed by emissions of photons and their detection by photomultiplier tube working in the photon counting regime. Three different instrumental arrangements are compared for the determination of caspase-3 in free cells or tissue samples. Thus, in our best miniaturized system the mean amount as low as about 6.5 fg corresponding to 122 000 molecules of caspase-3 can be detected in individual apoptotic mouse leg cells.

Mixed organotin(IV) chalcogenides: from molecules to Sn-S-Se semiconducting thin films deposited by spin-coating.

Put the right spin on it: Mixed monomeric organotin(IV) chalcogenides of the general formula L(2)Sn(2)EX(2) containing two terminal Sn-X (X = Se, Te) bonds were prepared and were tested as potential single-source precursors for the deposition of semiconducting thin films. Spin-coating deposition of [{2,6-(Me(2)NCH(2))(2)C(6)H(3)}SnSe](2)(µ-S), as the useful single-source precursor, provided amorphous Sn-S-Se semiconducting thin films.

Giant change of MoS2 optical properties along amorphous-crystalline transition: broadband spectroscopic study including the NIR therapeutic window.

This work deals with an ellipsometric study of magnetron sputtered thin MoS2 films. The evolution of the UV-VIS-NIR optical properties of as-deposited and subsequently annealed films is thoughtfully investigated, covering amorphous, amorphous relaxed, partially crystallized, and polycrystallized MoS2 films. The transition from the mixed 1T'@2H local order in the amorphous phase toward the long-range 2H order in the polycrystalline phase is systematically correlated with film optical properties. The early stage of a few-layer 2H ordering toward the 2H bulk-like polycrystalline structure during annealing is evidenced through the energy shift of MoS2 prominent excitonic peaks. A considerable change in optical response between metallic (amorphous) and semiconducting (polycrystalline) MoS2 phases is reported and presented in terms of dielectric permittivity and normal reflectance NIR-VIS-UV spectra. Results of light-heat conversion in the NIR therapeutic window show so far uncovered potential of amorphous MoS2 as an agent for photothermal therapy. Spectroscopic ellipsometry provided sensitive characterization disclosing essential results complementary to other characterization tools. The benefit of these results is expected to be employed in fundamental and application-motivated research, for example, in the field of phase change materials, photothermal cancer therapy, and magneto-optical study of magnetic ordering in metal transition dichalcogenides, among others.

Nanospray-assisted deposition of silver nanoparticles for mapping of a peptide in nanofibrous layers via surface-enhanced Raman spectrometry.

Surface-enhanced Raman spectrometry (SERS) is a universal detection tool identifying molecules via vibrations of their chemical bonds. Its function requires the close localization of metal nanostructures and the analyte. In this work, we present a lab-made instrumentation for the deposition of silver nanoparticles on a strongly hydrophilic nanofibrous composite via a nanospray for SERS mapping of an incorporated peptide. The nanospray-sample distance was revealed as the most crucial parameter since it directly influences the moisture of the deposited colloid. Residual water was recognized as a sensitivity enhancer. Additionally, we continuously introduced a solution of sodium chloride to the colloid increasing its ionic strength, which formed a more homogeneous profile of the deposit. After the deposition process, the treated sample was scanned via a SERS laser and the collected Raman spectra were transformed into a distribution map of the peptide at a concentration of 5 µg/g.

High-quality and easy-to-regenerate personal filter.

Proper respiratory tract protection is the key factor to limiting the rate of COVID-19 spread and providing a safe environment for health care workers. Traditional N95 (FFP2) respirators are not easy to regenerate and thus create certain financial and ecological burdens; moreover, their quality may vary significantly. A solution that would overcome these disadvantages is desirable. In this study a commercially available knit polyester fleece fabric was selected as the filter material, and a total of 25 filters of different areas and thicknesses were prepared. Then, the size-resolved filtration efficiency (40-400 nm) and pressure drop were evaluated at a volumetric flow rate of 95 L/min. We showed the excellent synergistic effect of expanding the filtration area and increasing the number of filtering layers on the filtration efficiency; a filter cartridge with 8 layers of knit polyester fabric with a surface area of 900 cm2 and sized 25 × 14 × 8 cm achieved filtration efficiencies of 98% at 95 L/min and 99.5% at 30 L/min. The assembled filter kit consists of a filter cartridge (14 Pa) carried in a small backpack connected to a half mask with a total pressure drop of 84 Pa at 95 L/min. In addition, it is reusable, and the filter material can be regenerated at least ten times by simple methods, such as boiling. We have demonstrated a novel approach for creating high-quality and easy-to-breathe-through respiratory protective equipment that reduces operating costs and is a green solution because it is easy to regenerate.

Capillary electrophoresis immunoassays with conjugated quantum dots.

Water-soluble CdTe quantum dots (QDs) and their conjugates with antibodies and antigenes were prepared by optimized procedures for applications in CE immunoassays. The QD size of 3.5 nm, excitation spectrum in the range of 300-500 nm, the maximum wavelength of the emission spectrum at 610 nm, quantum yield of 0.25 and luminescence lifetimes in the range of 3.6-43 ns were determined. The 0.1 M solution of TRIS/TAPS (pH 8.3) was found to be the optimum buffer for the separation of the antiovalbumin-ovalbumin immunocomplex from the free conjugates of QDs.

3D printed device for epitachophoresis.

Polyacrylamide or agarose gels are the most frequently used sieving and stabilizing media in slab gel electrophoresis. Recently, we have introduced a new electrophoretic technique for concentration/separation of milliliter sample volumes. In this technique, the gel is used primarily as an anticonvection media eliminating liquid flow during the electromigration. While serving well for the liquid stabilization, the gels can undergo deformation when exposed to a discontinuous electrolyte buffer system used in epitachophoresis. In this work, we have explored 3D printing to form rigid stabilizing manifolds to minimize liquid flow during the epitachophoresis run. The whole device was printed using the stereolithography technique from a low water-absorbing resin. The stabilizing manifold, serving as the gel substitute, was printed as a replaceable composite structure preventing electrolyte mixing during the separation. Different geometries of the 3D printed stabilizing manifolds were tested for use in concentrating ionic sample components without spatial separation. The presented device can focus analytes from 3 or 4 mL of the sample to 150 µL or less, depending on the collection cup size. With the 150 µL collection cup, this represents the enrichment factor from 20 to 27. The time of concentration was from 15 to 25 min, depending on stabilization media and power used.

Thin TiO2 Coatings by ALD Enhance the Cell Growth on TiO2 Nanotubular and Flat Substrates.

The present work exploits Ti sheets and TiO2 nanotube (TNT) layers and their surface modifications for the proliferation of different cells. Ti sheets with a native oxide layer, Ti sheets with a crystalline thermal oxide layer, and two kinds of TNT layers (prepared via electrochemical anodization) with a defined inner diameter of 12 and 15 nm were used as substrates. A part of the Ti sheets and the TNT layers was additionally coated by thin TiO2 coatings using atomic layer deposition (ALD). An increase in cell growth of WI-38 fibroblasts (>50%), MG-63 osteoblasts (>30%), and SH-SY5Y neuroblasts (>30%) was observed for all materials coated by five cycles ALD compared to their uncoated counterparts. The additional ALD TiO2 coatings changed the surface composition of all materials but preserved their original structure and protected them from unwanted crystallization and shape changes. The presented approach of mild surface modification by ALD has a significant effect on the materials' biocompatibility and is promising toward application in implant materials.