Interfacial protein adsorption behavior can be connected across a wide range of timescales using the microfluidic EDGE (Edge-based droplet GEneration) tensiometer.

HYPOTHESIS: Our hypothesis is that dynamic interfacial tension values as measured by the partitioned-Edge-based Droplet GEneration (EDGE) tensiometry can be connected to those obtained with classical techniques, such as the automated drop tensiometer (ADT), expanding the range of timescales towards very short ones. EXPERIMENTS: Oil-water and air-water interfaces are studied, with whey protein isolate solutions (WPI, 2.5 - 10 wt%) as the continuous phase. The dispersed phase consists of pure hexadecane or air. The EDGE tensiometer and ADT are used to measure the interfacial (surface) tension at various timescales. A comparative assessment is carried out to identify differences between protein concentrations as well as between oil-water and air-water interfaces. FINDINGS: The EDGE tensiometer can measure at timescales down to a few milliseconds and up to around 10 s, while the ADT provides dynamic interfacial tension values after at least one second from droplet injection and typically is used to also cover hours. The interfacial tension values measured with both techniques exhibit overlap, implying that the techniques provide consistent and complementary information. Unlike the ADT, the EDGE tensiometer distinguishes differences in protein adsorption dynamics at protein concentrations as high as 10 wt% (which is the highest concentration tested) at both oil-water and air-water interfaces.

Addressing astringency of grape seed extract by covalent conjugation with lupin protein.

Astringency of phenolic-rich foods is a key tactile perception responsible for acceptability/rejection of plant extracts as ingredients in formulations. Covalent conjugation of phenolic extracts with plant proteins might be a promising strategy to control astringency, but suffers from a lack of mechanistic understanding from the lubrication point of view. To shed light on this, this ex vivo study evaluated the effect of conjugation of a phenolic grape seed extract (GSE) with legume protein (lupin, LP) on tribological and surface adsorption performance of GSE in the absence and presence of human saliva (ex vivo). Tribological results confirmed GSE had an inferior lubrication capacity as compared to LP. The lubrication performance of LP-GSE dispersions was comparable to their corresponding LP dispersion (p > 0.05) when covalently conjugated with LP (LP-GSE) with increasing LP:GSE ratio up to 1:0.04 w/w and at a specific degree of conjugation (DC: 2%). Tribological and surface adsorption measurements confirmed the tendency of GSE to interact with human saliva (ex vivo, n = 17 subjects), impairing the lubricity of salivary films. The covalent bonding of LP to GSE hindered GSE's interaction with human saliva, implying the potential influence of covalent conjugation on attenuating astringency. LP appeared to compete with human saliva for surface adsorption and governed the lubrication behaviour in LP-GSE dispersions. Findings from this study provide valuable knowledge to guide the rational design of sustainable, functional foods using conjugation of phenolics with plant proteins to incorporate larger proportions of health-promoting phenolics while controlling astringency, which needs validation by sensory trials.

Duplex Electrochemical Microfluidic Sensor for COVID-19 Antibody Detection: Natural versus Vaccine-Induced Humoral Response.

The rapid transmission and resilience of coronavirus disease 2019 (COVID-19) have led to urgent demands in monitoring humoral response for effective vaccine development, thus a multiplex co-detection platform to discriminate infection-induced from vaccine-induced antibodies is needed. Here a duplex electrochemical immunosensor for co-detection of anti-nucleocapsid IgG (N-IgG) and anti-spike IgG (S-IgG) is developed by using a two-working electrode system, via an indirect immunoassay, with antibody quantification obtained by differential pulse voltammetry. The screen-printed electrodes (SPEs) are modified by carbon black and electrodeposited gold nanoflowers for maximized surface areas, enabling the construction of an immunological chain for S-IgG and N-IgG electrochemical detection with enhanced performance. Using an optimized immunoassay protocol, a wide linear range between 30-750 and 20-1000 ng mL-1 , and a limit of detection of 28 and 15 ng mL-1 are achieved to detect N-IgG and S-IgG simultaneously in serum samples. This duplex immunosensor is then integrated in a microfluidic device to obtain significantly reduced detection time (≤ 7 min) while maintaining its analytical performance. The duplex microfluidic immunosensor can be easily expanded into multiplex format to achieve high throughput screening for the sero-surveillance of COVID-19  and other infectious diseases.

Microfluidics as a tool to assess and induce emulsion destabilization.

Microfluidic technology enables judicious control of the process parameters on a small length scale, which in turn allows speeding up the destabilization of emulsion droplets interface in microfluidic devices. In this light, microfluidic channels can be used as an efficient tool to assess emulsion stability and to observe the behavior of the droplets immediately after their formation, enabling to determine whether or not they are prone to re-coalescence. Observation of the droplets after emulsifier adsorption also allows the investigation of emulsion stability over time. Both evaluations would contribute to determine emulsion stability aiming at specific applications in food and pharmaceutical industries. Furthermore, emulsion coalescence can also be performed under extremely controlled conditions within the microfluidic devices in order to explore emulsion droplets as micro-reactors (for regulated biological and chemical assays). Such microfluidic procedures can be performed either in confined environments or under dynamic flow conditions. Under confined environments, droplets are observed in fixed positions simulating different environmental conditions. On the other hand, with the scrutiny of emulsions under dynamic flow processes, it is possible to determine the behavior of the droplets when subjected to shear forces, comparable to those experienced in conventional emulsification techniques or even in pumping operations. Given the above, this paper reviews different microfluidic techniques (such as changing channel geometry or wettability) hitherto used to destabilize emulsions, mainly focusing on the specificities of each study, whether the droplets are destabilized in confined or dynamic flow processes. Thereby, by going deeper into this review, readers will be able to identify different strategies for emulsion destabilization (in order to understand stabilizing mechanisms or even to apply these droplets as micro-reactors), as this paper shows the particularities of the most recent studies and elucidates the current state-of-the-art of this microfluidic-related application.

Unraveling driving regimes for destabilizing concentrated emulsions within microchannels.

Coalescence is the most widely demonstrated mechanism for destabilizing emulsion droplets in microfluidic chambers. However, we find that depending on the channel wall surface functionalization, surface zeta potential, type of surfactant, characteristics of the oil as a dispersed phase, or even the presence of externally-induced stress, other different destabilization mechanisms can occur in subtle ways. In general, we observe four regimes leading to destabilization of concentrated emulsions: (i) coalescence, (ii) emulsion bursts, (iii) a combination of the two first mechanisms, attributed to the simultaneous occurrence of coalescence and emulsion bursts; and (iv) compaction of the droplet network that eventually destabilizes to fracture-like behavior. We correlate various physico-chemical properties (zeta potential, contact angle, interfacial tension) to understand their respective influence on the destabilization mechanisms. This work provides insights into possible ways to control or inflict emulsion droplet destabilization for different applications.

Modulating properties of polysaccharides nanocomplexes from enzymatic hydrolysis of chitosan.

Synthesis of nanocomplexes is a simple and low-cost technique for the production of encapsulation systems aiming industrial applications, based on the interaction of at least two oppositely charged molecules. Gellan gum (anionic) is a water-soluble biopolymer resistant to stomach pH conditions, therefore an interesting alternative as an encapsulating matrix. Chitosan (cationic) is also widely used due to its biocompatibility and mucoadhesive properties, although its low water solubility is an important step to be overcome for the production of the complexes. To improve this property, many techniques have been employed, but most of them use unsustainable techniques and chemical agents. The enzymatic hydrolysis of chitosan using proteases emerges as an alternative to these drawbacks and, therefore, this study aimed to evaluate the electrostatic nanocomplexation of native (C) or hydrolyzed (HC) chitosan (by porcine pepsin protease) with gellan gum (G). Polysaccharides and nanocomplexes formed with different G:C or G:HC ratio were evaluated by zeta potential measurements, particle size distribution, X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Transmission Electron Microscopy (STEM), intrinsic viscosity and turbidity analyses. Chitosan hydrolysis allowed the formation of a smaller (445.3 nm in pH 4.5) and more soluble structure (3 kDa), which positively influenced the formation of the complexes. The ratios G:HC of 7:3 and 8:2 formed complexes with lower values of zeta potential (13.9 mV and -5.0 mV, respectively), particle size (635.8 nm and 533.6 nm, respectively) and polydispersity (0.28 and 0.23) compared to complexes formed with native chitosan. Overall, our results show that enzymatic hydrolysis of chitosan favored the formation of electrostatic complexes with reduced size and low polydispersity, which can be used as efficient encapsulating matrices for improved targeted delivery and controlled release of bioactive compounds.

Colloidal particle deposition on microchannel walls, for attractive and repulsive surface potentials.

Surface interactions are an interplay of van der Waals adhesion forces with electrostatic charges. In colloidal deposition, at low ionic strengths, the Debye layer is sufficiently large to prevent particles from approaching the surface. It is only with the addition of higher salt concentrations, typically above 0.1 M, that surface charges are screened for interactions to take place via van der Waals-adhesion forces. This is true for repulsive charges, when both surfaces have similar charges and signs of the zeta potential are the same. However, with attractive charges, where zeta potential signs are opposite, the result is also opposite. By combining microfluidic experiments, theory, and numerical simulations, results show that when charges are attractive, particle deposition instead increases at low ionic strengths (at greater Debye lengths), at rates controlled by van der Waals forces but assisted by electrostatic forces. We propose a mechanism where particles approach the wall, mobilized by electrostatic attraction, up to a distance where van der Waals forces come into play, collecting the particles at the wall, which electrostatic forces alone are unable to achieve, owing to hindered diffusion. The present work thus allows us to understand the different mechanisms that govern deposition in the case where surface charges are opposite.