Electroless Ionization Mass Spectrometry Using a Compact Electrokinetic Ionization Source.

We introduce a new ionization technique for compact, portable mass spectrometers. It consists of a syringe with sample liquid capped by a self-ionizing spray nozzle containing a microfabricated nozzle chip. Interaction of the sample liquid with the nozzle wall results in electrical charging without the need for electronics. Elaborate cleaning procedures are redundant when disposable syringes and mass-fabricated spray nozzles are used. This self-named electroless spray ionization (ELI) technique shows comparable performance to conventional ionization techniques. In contrast to commonly used electrospray ionization, ELI exhibits excellent ionization efficiency for low-conductive solutions such as water or acetonitrile. Due to its compact size and the absence of high-voltage electronics, it can also be readily integrated in other ionization sources. Besides reviewing the main properties of ELI, we showcase the technique's potential for two on-site, ambient mass spectroscopy applications: perfume fingerprinting and fast screening of fungicides on citrus fruits.

Realizing Symmetry-Breaking Architectures in Soap Films.

We show here that soap films-typically expected to host symmetric molecular arrangements-can be constructed with differing opposite surfaces, breaking their symmetry, and making them reminiscent of functional biological motifs found in nature. Using fluorescent molecular probes as dopants on different sides of the film, resonance energy transfer could be employed to confirm the lack of symmetry, which was found to persist on timescales of several minutes. Further, a theoretical analysis of the main transport phenomena involved yielded good agreement with the experimental observations.

Low energy nebulization preserves integrity of SARS-CoV-2 mRNA vaccines for respiratory delivery.

Nebulization of mRNA therapeutics can be used to directly target the respiratory tract. A promising prospect is that mucosal administration of lipid nanoparticle (LNP)-based mRNA vaccines may lead to a more efficient protection against respiratory viruses. However, the nebulization process can rupture the LNP vehicles and degrade the mRNA molecules inside. Here we present a novel nebulization method able to preserve substantially the integrity of vaccines, as tested with two SARS-CoV-2 mRNA vaccines. We compare the new method with well-known nebulization methods used for medical respiratory applications. We find that a lower energy level in generating LNP droplets using the new nebulization method helps safeguard the integrity of the LNP and vaccine. By comparing nebulization techniques with different energy dissipation levels we find that LNPs and mRNAs can be kept largely intact if the energy dissipation remains below a threshold value, for LNP integrity 5-10 J/g and for mRNA integrity 10-20 J/g for both vaccines.

Fluorescence-enabled evaluation of nasal tract deposition and coverage of pharmaceutical formulations in a silicone nasal cast using an innovative spray device.

INTRODUCTION: The characterisation of nasal formulations is a critical point. However, there are still no recommendations or guidelines in terms of standard approaches for evaluating the formulation's nasal deposition and/or coverage profile. This study optimises a method for quantifying silicone nasal cast deposition and coverage of liquid formulations using different nasal devices. OBJECTIVES: The present work investigates the nasal deposition and coverage patterns of innovative nasal spray nozzles producing slow velocity soft mists, using a nasal cavity replica and a fluorescent dye. METHODS: The study of the deposition pattern of a fluorescent liquid formulation in a transparent nasal cast was carried out in both the presence and absence of a simulated inhalation flow. The extent of the deposition pattern was investigated using ImageJ and fluorescence in the nasal cast, quantified by fluorometric analysis. The particle size distribution and initial droplet velocity were determined using a laser diffractometer and a high-speed camera with a frame rate of 1000 fps. RESULTS: A uniform intranasal coverage was obtained with droplets of a volume median particle size (Dv50) between 15 and 25 µm in airflow between 10 and 30 L/min. In these conditions, aerosol formulations can be uniformly deposited in the vestibule and turbinate cavity nasal regions, with less than 10 % passing beyond the nasopharyngeal region. CONCLUSION: The method applied allowed for the determination of the coverage of the nasal cast in different regions using images analysis and fluorometric analysis. Droplet velocity is a critical parameter in the deposition in the nasal cavity. With standard swirl nozzles, many droplets are found on the surface of the nasal vestibule. Soft mist nozzles produce smaller droplets at a much lower initial velocity (<1 m/s), resulting in a more uniform coverage.

Improved Olfactory Deposition of Theophylline Using a Nanotech Soft Mist Nozzle Chip.

Currently, nasal administration of active pharmaceutical ingredients is most commonly performed using swirl-nozzle-based pump devices or pressurized syringes. However, they lead to limited deposition in the more active regions of the nasal cavity, especially the olfactory region, which is crucial for nose-to-brain drug delivery. This research proposes to improve deposition in the olfactory region by replacing the swirl nozzle with a nanoengineered nozzle chip containing micrometer-sized holes, which generates smaller droplets of 10-50 µm travelling at a lower plume velocity. Two nanotech nozzle chips with different hole sizes were tested at different inhalation flow rates to examine the deposition patterns of theophylline, a hyposmia treatment formulation, using a nasal cavity model. A user study was also conducted and showed that the patient instructions influenced the inhalation flow rate characteristics. Targeted flow rates of between 0 and 25 L/min were used for the in vitro deposition study, yielding 21.5-31.5% olfactory coverage. In contrast, the traditional swirl nozzle provided only 10.8% coverage at a similar flow rate. This work highlights the potential of the nanotech soft mist nozzle for improved intranasal drug delivery, particularly to the olfactory region.

Self-charging of sprays.

The charging of poorly conducting liquids due to flows is a well-known phenomenon, yet the precise charging mechanism is not fully understood. This is especially relevant for sprays, where the spray plume dynamics and maximum distance travelled of a spray dramatically changes for different levels of charging: charging of the droplets makes them repel, thereby preventing drop coalescence and altering the shape of the spray plume. As the charging depends on many factors including the flow and the interactions between the liquid and the nozzle, many models and scaling laws exist in the literature. In this work we focus on perhaps the simplest flow regime, laminar jets created by ultra short channels, and quantify the charging as a function of the different parameters. We present a simple model that collapses all the data for over 4 orders of magnitude difference in streaming currents for various nozzle sizes, flow velocities and surface treatments. We further show that the charging polarity can even be reversed by applying an oppositely charged coating to the nozzle, an important step for any application.

Measurement of small droplet aerosol concentrations in public spaces using handheld particle counters.

We measure aerosol persistence to assess the risk of transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in public spaces. Direct measurement of aerosol concentrations, however, has proven to be technically difficult; we propose the use of handheld particle counters as a novel and easily applicable method to measure aerosol concentrations. This allows us to perform measurements in typical public spaces, each differing in volume, the number of people, and the ventilation rate. These data are used to estimate the relation between the aerosol persistence time and the risk of infection with SARS-CoV-2.

Aerosol persistence in relation to possible transmission of SARS-CoV-2.

Transmission of SARS-CoV-2 leading to COVID-19 occurs through exhaled respiratory droplets from infected humans. Currently, however, there is much controversy over whether respiratory aerosol microdroplets play an important role as a route of transmission. By measuring and modeling the dynamics of exhaled respiratory droplets, we can assess the relative contribution of aerosols to the spreading of SARS-CoV-2. We measure size distribution, total numbers, and volumes of respiratory droplets, including aerosols, by speaking and coughing from healthy subjects. Dynamic modeling of exhaled respiratory droplets allows us to account for aerosol persistence times in confined public spaces. The probability of infection by inhalation of aerosols when breathing in the same space can then be estimated using current estimates of viral load and infectivity of SARS-CoV-2. The current known reproduction numbers show a lower infectivity of SARS-CoV-2 compared to, for instance, measles, which is known to be efficiently transmitted through the air. In line with this, our study of transmission of SARS-CoV-2 suggests that aerosol transmission is a possible but perhaps not a very efficient route, in particular from non-symptomatic or mildly symptomatic individuals that exhibit low viral loads.

Co-current crossflow microfiltration in a microchannel.

Steady state crossflow microfiltration (CMF) is an important and often necessary means of particle separation and concentration for both industrial and biomedical processes. The factors controlling the performance of CMF have been extensively reviewed. A major factor is transmembrane pressure (TMP). Because microchannels have small height, they tend to have high pressure gradients in the feed-flow direction. In the extreme, these gradients may even reverse the pressure across the membrane (inciting backflow). It is therefore desirable to compensate for the effect of feed-flow on the TMP, aiming at constant transmembrane pressure (cTMP) at a value which maximizes filtrate flux. This is especially critical during filtration of deformable particles (e.g. erythrocytes) through low intrinsic resistance membranes. Filtration flux is generally taken to be directly proportional to TMP, with pressure drop along the channel decreasing in the flow direction. A co-current flow of filtrate in a suitably designed filtrate collecting channel is shown to allow the TMP to remain constant and permit the sieving surface to perform optimally, permitting up to twice as much filtration over that of a naïve configuration. Manipulation of the filtrate channel may be even more beneficial if it prevents backflow that might otherwise occur at the end of a sufficiently long channel. Experiments with erythrocyte suspensions, reported here, validate these concepts.

Emanating Jets As Shaped by Surface Tension Forces.

We show that emanating jets can be regarded as growing liquid towers, which are shaped by the twofold action of surface tension: first the emanated fluid is being accelerated back by surface tension force, herewith creating the boundary conditions to solve the shape of the liquid tower as a solution of an equation mathematically related to the hydrostatic Young-Laplace equation, known to give solutions for the shape of pending and sessile droplets, and wherein the only relevant forces are gravity g and surface tension γ. We explain that for an emanating jet under specific constraints all mass parts with density ρ will experience a uniform time dependent acceleration a( t). An asymptotic solution is subsequently numerically derived by making the corresponding Young-Laplace type equation dimensionless and by dividing all lengths by a generalized time dependent capillary length λc( t) = [Formula: see text]. The time dependent surface tension γ( t) can be derived by measuring both time dependent acceleration a( t) and time dependent capillary length λc( t). Jetting experiments with water and coffee show that the dynamic surface tension behavior according to the emanating jet method and with the well-known maximum bubble pressure method are the same, herewith verifying the proposed model.

Erythrocyte fouling on micro-engineered membranes.

Crossflow microfiltration of plasma from blood through microsieves in a microchannel is potentially useful in many biomedical applications, including clinically as a wearable water removal device under development by the authors. We report experiments that correlate filtration rates, transmembrane pressures (TMP) and shear rates during filtration through a microscopically high channel bounded by a low intrinsic resistance photolithographically-produced porous semiconductor membrane. These experiments allowed observation of erythrocyte behavior at the filtering surface and showed how their unique deformability properties dominated filtration resistance. At low filtration rates (corresponding to low TMP), they rolled along the filter surface, but at higher filtration rates (corresponding to higher TMP), they anchored themselves to the filter membrane, forming a self-assembled, incomplete monolayer. The incompleteness of the layer was an essential feature of the monolayer's ability to support sustainable filtration. Maximum steady-state filtration flux was a function of wall shear rate, as predicted by conventional crossflow filtration theory, but, contrary to theories based on convective diffusion, showed weak dependence of filtration on erythrocyte concentration. Post-filtration scanning electron micrographs revealed significant capture and deformation of erythrocytes in all filter pores in the range 0.25 to 2 µm diameter. We report filtration rates through these filters and describe a largely unrecognized mechanism that allows stable filtration in the presence of substantial cell layers.

Droplet Formation by Confined Liquid Threads inside Microchannels.

A confined liquid thread can form monodisperse droplets near the exit of a microchannel, provided the continuous phase is able to enter the microchannel. A general model that accurately predicts the droplet size including the breakup position inside the microchannel is presented and is verified with experimental observations; breakup occurs as long as the capillary number (Ca) of the liquid thread is below a critical capillary number (Cacr); for cylindrical microchannels, it is derived that Cacr = 1/16. Below Cacr, the formed droplets at the exit of the microchannel have a diameter approximately two times the diameter of the liquid thread; around and above Cacr, the liquid thread remains stable and the formed droplets grow infinitely large. The presented controlled droplet generation method is a useful tool for producing monodisperse emulsions and has great potential for the food and pharmaceutical industry.

Feasibility of a simple microsieve-based immunoassay platform.

The intrinsic properties of silicon microsieves, such as an optically flat surface, high overall porosity, and low flow resistance have led to an increasing number of biotechnology applications. In this report, the feasibility of creating a microsieve-based immunoassay platform was explored. Microsieves containing 5µm pores were coupled with poly-acrylic acid chains, and then mounted into a plastic holder to enable rapid reagent exchanges via a wicking mechanism. The mounted microsieves were coated with infectious disease-related antigens at [2.5 and 25µg/mL], [20 and 50µg/mL], and [20 and 100µg/mL] to facilitate detection of serum-derived human antibodies against Rubella (3-day measles), B. burgdorferi (Lyme disease), or T. pallidum (syphilis), respectively. The prototype microsieve-based immunoassay platform was able to distinguish positive control sera containing antibodies against Rubella, T. pallidum, and B. burgdorferi from negative control sera with similar qualitative results as FDA-approved ELISA tests. Testing of a WHO IgG syphilitic standard at 0.3, 0.15, 0.075, 0.0375, and 0.01875IU/mL demonstrated that the T. pallidum microsieve assay is able to distinguish disease-specific IgG signal from background signal at similar, and possibly lower, levels than the corresponding ELISA. The T. pallidum microsieve assay prototype also differentiated positive clinical serum samples from negative donor samples, and the results were in good agreement with ELISA (R(2)=0.9046). These feasibility studies demonstrate the potential for utilizing microsieves, along with a reagent wicking device, as a simple diagnostic immunoassay platform.

Capture of Tumor Cells on Anti-EpCAM-Functionalized Poly(acrylic acid)-Coated Surfaces.

The presence of tumor cells in blood is predictive of short survival in several cancers and their isolation and characterization can guide toward the use of more effective treatments. These circulating tumor cells (CTC) are, however, extremely rare and require a technology that is sufficiently sensitive and specific to identify CTC against a background of billions of blood cells. Immuno-capture of cells expressing the epithelial cell adhesion molecule (EpCAM) are frequently used to enrich CTC from blood. The choice of bio conjugation strategy and antibody clone is crucial for adequate cell capture but is poorly understood. In this study, we determined the binding affinity constants and epitope binding of the EpCAM antibodies VU1D-9, HO-3, EpAb3-5, and MJ-37 by surface plasmon resonance imaging (SPRi). Glass surfaces were coated using a poly(acrylic acid) based coating and functionalized with anti-EpCAM antibodies. Binding of cells from the breast carcinoma cell line (SKBR-3) to the functionalized surfaces were compared. Although EpAb3-5 displayed the highest binding affinity HO-3 captured the highest amount of cells. Hence we report differences in the performance of the different antibodies and more importantly that the choice of antibody to capture CTC should be based on multiple assays.

The detection of EpCAM(+) and EpCAM(-) circulating tumor cells.

EpCAM expressing circulating tumor cells, detected by CellSearch, are predictive of short survival in several cancers and may serve as a liquid biopsy to guide therapy. Here we investigate the presence of EpCAM(+) CTC detected by CellSearch and EpCAM(-) CTC discarded by CellSearch, after EpCAM based enrichment. EpCAM(-) CTC were identified by filtration and fluorescent labelling. This approach was validated using different cell lines spiked into blood and evaluated on blood samples of 27 metastatic lung cancer patients. The majority of spiked EpCAM(+) cells could be detected with CellSearch, whereas most spiked cells with EpCAM(low) or EpCAM(-) expression were detected using filtration. Five or more CTC were detected in 15% of the patient samples, this increased to 41% when adding the CTC detected in the discarded blood. The number of patients with CTC and the number of CTC detected were doubled by the presence of EpCAM(-) CTC. In this pilot study, the presence of EpCAM(+) CTC was associated with poor outcome, whereas the EpCAM(-) CTC were not. This observation will need to be confirmed in larger studies and molecular characterization needs to be conducted to elucidate differences between EpCAM(-) and EpCAM(+) CTC.

Self-seeding microwell chip for the isolation and characterization of single cells.

A self-seeding microwell chip is introduced for the isolation and interrogation of single cells. A cell suspension is transferred to a microwell chip containing 6400 microwells, each microwell with a single 5 µm pore in the bottom. The fluid enters the microwell and drags a cell onto the pore. After a cell has landed onto the pore, it will stop the fluid flow through this microwell. The remaining fluid and cells will be diverted to the next available microwell. This results in a fast and efficient distribution of single cells in individual microwells. After identification by fluorescence microscopy, the cells of interest are isolated from the microwell by punching the bottom together with the cell. The overall single cell recovery of seeding followed by isolation of the single cell, is >70% with a specificity of 100% as confirmed by the genetic make-up of the isolated cells.

Adhesion and friction properties of fluoropolymer brushes: on the tribological inertness of fluorine.

The effects of fluorination on the adhesion and friction properties of covalently bound poly(fluoroalkyl methacrylate) polymer brushes (thickness ∼80 nm) were systematically investigated. Si(111) surfaces were functionalized with a covalently bound initiator via a thiol-yne click reaction to have a high surface coverage for initiator immobilization. Surface-initiated atom-transfer radical polymerization (SI-ATRP) was employed for the synthesis of four different fluoropolymer brushes (SPFx, where x = 0, 3, 7, or 17 F atoms per monomer), based on fluoroalkyl methacrylates. All polymer brushes were characterized with static contact angle measurements, X-ray photoelectron spectroscopy (XPS), and infrared absorption reflection spectroscopy (IRRAS). The polymer brushes exhibited an excellent hydrophobicity, with static water contact angles of up to 121° depending on the number of fluorine atoms per side chain in fluoroalkyl methacrylate. The degree of swelling was precisely studied by using ellipsometry in different solvents such as acetone, hexadecane, hexafluoroisopropanol, nonafluorobutyl methyl ether, and Fluorinert FC-40. The polymer brushes have shown nanoscale swelling behavior in all solvents except hexadecane. The grafting density decreased upon increasing fluorine content in polymer brushes from 0.65 chains/nm(2) (SPF0) to 0.10 chains/nm(2) (SPF17) as observed in Fluorinert FC-40 as a good solvent. Adhesion and friction force measurements were conducted with silica colloidal probe atomic force microscopy (CP-AFM) under ambient, dry (argon), and lubricating fluid conditions. SPF17 showed the lowest coefficient of friction 0.005 under ambient condition (RH = 44 ± 2%) and a further decrease with 50% under fluidic conditions. These polymer brushes also showed adhesion forces as low as 6.9 nN under ambient conditions, which further went down to 0.003 nN under fluidic conditions (Fluorinert FC-40 and hexadecane) at 10 nN force.