Janus Emulsion Biosensors for Anti-SARS-CoV-2 Spike Antibody

Innovative Real-Time Flow Sensor Using Detergent-Free Complex Emulsions with Dual-Emissive Semi-Perfluoroalkyl Substituted Α-Cyanostilbene

In this study, the potential of complex emulsions is investigated as transducers in sensing applications. Complex emulsions are stabilized without external detergents by developing a novel α-cyanostilbene substituted with PEG and semi-perfluoroalkyl chain (CNFCPEG). CNFCPEG exhibits unique variable emission properties depending on its aggregation state, allowing dual blue and green emissions in complex emulsions with hydrocarbon-in-fluorocarbon-in-water (H/F/W) morphology. The green excimer emissions result from the self-assembly of CNFCPEG at the fluorocarbon/water interface, while the blue emission observed is due to aggregation in the organic phase. A novel flow-injection method is developed by incorporating complex emulsions with CNFCPEG into multiple-well flow chips (MWFC). Iodine is successfully detected in a mobile aqueous solution by monitoring morphology changes. The findings demonstrate that self-stabilized complex emulsions with MWFC hold great promise for real-time sensing without costly instruments.

Functionalized Amphiphilic Block Copolymers and Complex Emulsions for Selective Sensing of Dissolved Metals at Liquid-Liquid Interfaces

Increasing contamination in potable water supplies necessitates the development of sensing methods that provide the speed and selectivity necessary for safety. One promising method relies on recognition and detection at the liquid-liquid interface of dynamic complex emulsions. These all-liquid materials transduce changes in interfacial tensions into optical signals via the coupling of their chemical, physical, and optical properties. Thus, to introduce selectivity, it is necessary to modify the liquid-liquid interface with an interfacially stable and selective recognition unit. To this end, we report the synthesis and characterization of amphiphilic block copolymers modified with metal chelators to selectively measure the concentrations of dissolved metal ions. We find that significant reduction in interfacial tensions arises upon quantitative addition of metal ions with high affinity toward functionalized chelators. Furthermore, measurements from UV-vis spectroscopy reveal that complexation of the block copolymers with metal ions leads to an increase in surface excess and surfactant effectiveness. We also demonstrate selective detection of iron(III) cations (Fe3+) on the μM levels even through interference from other mono-, di-, or trivalent cations in complex matrices of synthetic groundwater. Our results provide a unique platform that couples selective recognition and modulation of interfacial behaviors and demonstrates a step forward in the development of the multiplexed sensing device needed to deconvolute the complicated array of contaminants that comprise real-world environmental samples.

Multicompartment colloid systems with lipid and polymer membranes for biomedical applications

Multicompartment structures have the potential for biomedical applications because they can act as multifunctional systems and provide simultaneous delivery of drugs and diagnostics agents of different types. Moreover, some of them mimic biological cells to some extent with organelles as separate sub-compartments. This article analyses multicompartment colloidal structures with smaller sub-units covered with lipid or polymer membranes that provide additional protection for the encapsulated substances. Vesosomes with small vesicles encapsulated in the inner pools of larger liposomes are the most studied systems to date. Dendrimer molecules are enclosed by a lipid bilayer shell in dendrosomes. Capsosomes, polymersomes-in-polymer capsules, and cubosomes-in-polymer capsules are composed of sub-compartments encapsulated within closed multilayer polymer membranes. Janus or Cerberus emulsions contain droplets composed of two or three phases: immiscible oils in O/W emulsions and aqueous polymer or salt solutions that are separated into two or three phases and form connected droplets in W/O emulsions. In more cases, the external surface of engulfed droplets in Janus or Cerberus emulsions is covered with a lipid or polymer monolayer. eLiposomes with emulsion droplets encapsulated into a bilayer shell have been given little attention so far, but they have very great prospects. In addition to nanoemulsion droplets, solid lipid nanoparticles, nanostructured lipid carriers and inorganic nanoparticles can be loaded into eLiposomes. Molecular engineering of the external membrane allows the creation of ligand-targeted and stimuli-responsive multifunctional systems. As a result, the efficacy of drug delivery can be significantly enhanced.

Responsive Janus droplets as modular sensory layers for the optical detection of bacteria

The field of biosensor development is fueled by innovations in new functional transduction materials and technologies. Material innovations promise to extend current sensor hardware limitations, reduce analysis costs, and ensure broad application of sensor methods. Optical sensors are particularly attractive because they enable sensitive and noninvasive analyte detection in near real-time. Optical transducers convert physical, chemical, or biological events into detectable changes in fluorescence, refractive index, or spectroscopic shifts. Thus, in addition to sophisticated biochemical selector designs, smart transducers can improve signal transmission and amplification, thereby greatly facilitating the practical applicability of biosensors, which, to date, is often hampered by complications such as difficult replication of reproducible selector-analyte interactions within a uniform and consistent sensing area. In this context, stimuli-responsive and optically active Janus emulsions, which are dispersions of kinetically stabilized biphasic fluid droplets, have emerged as a novel triggerable material platform that provides as a versatile and cost-effective alternative for the generation of reproducible, highly sensitive, and modular optical sensing layers. The intrinsic and unprecedented chemical-morphological-optical coupling inside Janus droplets has facilitated optical signal transduction and amplification in various chemo- and biosensor paradigms, which include examples for the rapid and cost-effective detection of major foodborne pathogens. These initial demonstrations resulted in detection limits that rival the capabilities of current commercial platforms. This trend article aims to present a conceptual summary of these initial efforts and to provide a concise and comprehensive overview of the pivotal kinetic and thermodynamic principles that govern the ability of Janus droplets to sensitively and selectively respond to and interact with bacteria.

Electrokinetic Active Particles for Motion-Based Biomolecule Detection

Detection of biomolecules is essential for patient diagnosis, disease management, and numerous other applications. Recently, nano- and microparticle-based detection has been explored for improving traditional assays by reducing required sample volumes and assay times as well as enhancing tunability. Among these approaches, active particle-based assays that couple particle motion to biomolecule concentration expand assay accessibility through simplified signal outputs. However, most of these approaches require secondary labeling, which complicates workflows and introduces additional points of error. Here, we show a proof-of-concept for a label-free, motion-based biomolecule detection system using electrokinetic active particles. We prepare induced-charge electrophoretic microsensors (ICEMs) for the capture of two model biomolecules, streptavidin and ovalbumin, and show that the specific capture of the biomolecules leads to direct signal transduction through ICEM speed suppression at concentrations as low as 0.1 nM. This work lays the foundation for a new paradigm of rapid, simple, and label-free biomolecule detection using active particles.

ZnO-Based Electrochemical Immunosensor to Assess Vaccine-Induced Antibody-Mediated Immunity against Wild-Type and Gamma SARS-CoV-2 Strains

The evaluation of serological responses to COVID-19 is crucial for population-level surveillance, developing new vaccines, and evaluating the efficacy of different immunization programs. Research and development of point-of-care test technologies remain essential to improving immunity assessment, especially for SARS-CoV-2 variants that partially evade vaccine-induced immune responses. In this work, an impedimetric biosensor based on the immobilization of the recombinant trimeric wild-type spike protein (S protein) on zinc oxide nanorods (ZnONRs) was employed for serological evaluation. We successfully assessed its applicability using serum samples from spike-based COVID-19 vaccines: ChAdOx1-S (Oxford-AstraZeneca) and BNT162b2 (Pfizer-BioNTech). Overall, the ZnONRs/ spike-modified electrode displayed accurate results for both vaccines, showing excellent potential as a tool for assessing and monitoring seroprevalence in the population. A refined outcome of this technology was achieved when the ZnO immunosensor was functionalized with the S protein from the P.1 linage (Gamma variant). Serological responses against samples from vaccinated individuals were acquired with excellent performance. Following studies based on traditional serological tests, the ZnONRs/spike immunosensor data reveal that ChAdOx1-S vaccinated individuals present significantly less antibody-mediated immunity against the Gamma variant than the BNT162b2 vaccine, highlighting the great potential of this point-of-care technology for evaluating vaccine-induced humoral immunity against different SARS-CoV-2 strains.

Multiplexed and continuous microfluidic sensors using dynamic complex droplets

Emissive complex droplets with reconfigurable morphology and dynamic optical properties offer exciting opportunities as chemical sensors due to their stimuli-responsive characteristics. In this work, we demonstrated a real-time optical sensing platform that combines poly(dimethylsiloxane) (PDMS) microfluidics and complex droplets as sensing materials. We utilized a mechanism, called directional emission, to transduce changes in interfacial tension into optical signals. We discuss the fabrication and integration of PDMS microfluidics with complex emulsions to facilitate continuous measurement of fluorescent emission and, ultimately, the interfacial tensions. Furthermore, by varying the interfacial functionalization and fluorescent dye with characteristic wavelength, we generate multiple formulations of droplets and obtain differential responses to stimuli that alter interfacial tensions (i.e., composition of surfactants, pH). Our results illustrate a proof-of-concept multiplexed and continuous sensing platform with potential applications in miniaturized, on-site environmental monitoring and biosensing.

Morphology-Dependent Aggregation-Induced Emission of Janus Emulsion Surfactants

We report a novel stimuli-responsive fluorescent material platform that relies on an evocation of aggregation-induced emission (AIE) from tetraphenylethylene (TPE)-based surfactants localized at one hemisphere of biphasic micro-scale Janus emulsion droplets. Dynamic alterations in the available interfacial area were evoked through surfactant-induced dynamic changes of the internal droplet morphology that can be modulated as a function of the balance of interfacial tensions of the droplet constituent phases. Thus, by analogy with a Langmuir-Blodgett trough that enables selective concentration of surfactants at a liquid-gas interface, we demonstrate here a method for controllable modulation of the available interfacial area of surfactant-functionalized liquid-liquid interfaces. We show that a morphology-dependent alteration of the interfacial area can be used to evoke an optical signal, by selectively assembling synthesized TPE-based surfactants on the respective droplet interfaces. A trigger-induced increase in the concentration of TPE-based surfactants at the liquid-liquid interfaces results in an evocation of aggregation-induced emission (AIE), inducing an up to 3.9-fold increase in the measured emission intensity of the droplets.

Recent advancements in Janus nanoparticle-based biosensing platforms

Nanoparticles have aided in the development of nano-based sensors for diagnostic applications. However, use of nanoparticles in the development of sensing devices for multiple analyte detection is constrained due to their inability to detect several analytes with a single type of nanoparticle. The term "Janus particle" refers to micro or nanoscale particles that have been divided into sections or compartments, each of which has a distinct set of chemical or physical properties, producing multifunctional particles endowed with distinctive qualities. Furthermore, Janus particles have the ability to perform multiple functions within a single particle at the same time, with no interference from adjacent sections. This review focuses on the use of Janus particles in the fabrication of biosensors as well as in the investigation of various properties endowed by these Janus particles for their use as biosensors. It also discusses the various types of Janus particle-based biosensors that are currently available. Finally, the limitations of Janus particles in sensor technologies and their future scope have been discussed.

Graphical abstract

Advances in Biosensing Technologies for Diagnosis of COVID-19

The COVID-19 pandemic has severely impacted normal human life worldwide. Due to its rapid community spread and high mortality statistics, the development of prompt diagnostic tests for a massive number of samples is essential. Currently used traditional methods are often expensive, time-consuming, laboratory-based, and unable to handle a large number of specimens in resource-limited settings. Because of its high contagiousness, efficient identification of SARS-CoV-2 carriers is crucial. As the advantages of adopting biosensors for efficient diagnosis of COVID-19 increase, this narrative review summarizes the recent advances and the respective reasons to consider applying biosensors. Biosensors are the most sensitive, specific, rapid, user-friendly tools having the potential to deliver point-of-care diagnostics beyond traditional standards. This review provides a brief introduction to conventional methods used for COVID-19 diagnosis and summarizes their advantages and disadvantages. It also discusses the pathogenesis of COVID-19, potential diagnostic biomarkers, and rapid diagnosis using biosensor technology. The current advancements in biosensing technologies, from academic research to commercial achievements, have been emphasized in recent publications. We covered a wide range of topics, including biomarker detection, viral genomes, viral proteins, immune responses to infection, and other potential proinflammatory biomolecules. Major challenges and prospects for future application in point-of-care settings are also highlighted.

Application of Janus Particles in Point-of-Care Testing

Janus particles (JPs), named after the two-faced Roman god, are asymmetric particles with different chemical properties or polarities. JPs have been widely used in the biomedical field in recent years, including as drug carriers for targeted controlled drug release and as biosensors for biological imaging and biomarker detection, which is crucial in the early detection and treatment of diseases. In this review, we highlight the most recent advancements made with regard to Janus particles in point-of-care testing (POCT). Firstly, we introduce several commonly used methods for preparing Janus particles. Secondly, we present biomarker detection using JPs based on various detection methods to achieve the goal of POCT. Finally, we discuss the challenges and opportunities for developing Janus particles in POCT. This review will facilitate the development of POCT biosensing devices based on the unique properties of Janus particles.

Detection of PFAS and Fluorinated Surfactants Using Differential Behaviors at Interfaces of Complex Droplets

Contamination of per- and polyfluoroalkyl substances (PFAS) in water supplies will continue to have serious health and environmental consequences. Despite the importance of monitoring the concentrations of PFAS at potential sites of contamination and at treatment plants, there are few suitable and rapid on-site methods. Many nonconventional techniques do not possess the necessary selectivity and sensitivity to distinguish PFAS from other surface-active components and to quantify the low concentrations in real-world conditions. Herein, we report a novel and rapid method for the detection of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) by leveraging their differential behaviors at the interfaces of emissive complex droplets. Measurement of surface and interfacial tensions via a force tensiometer reveals that PFAS preferentially self-assemble at the water-fluorocarbon oil interface (F/W) rather than the water-hydrocarbon oil interface (H/W). We also observe an opposite behavior for hydrocarbon surfactants. This difference in interfacial behavior produces distinct effects on the morphological change and optical emission of biphasic oil-in-water droplets. The change in the intensity of fluorescence emission, measured with a simple spectroscopic setup, correlates with the concentrations of PFAS. We also demonstrate that the range of detection and sensitivity can be tuned by adjusting the initial composition of the complex droplets. Our results illustrate an alternative mode of sensors that may provide a rapid and on-site detection of PFAS.

Serological response after SARS-CoV2 vaccination in healthcare workers: a multicenter study

Introduction:

Characterizing immunological response following COVID-19 vaccination is an important public health issue. The objectives of the present analysis were to investigate the proportion, level and the determinants of humoral response from 21 days to three months after the first dose in vaccinated healthcare workers (HCWs).

Methods:

We abstracted data on level of anti-SARS-CoV-2 Spike antibodies (IgG) and sociodemographic characteristics of 17,257 HCWs from public hospitals and public health authorities from three centers in Northern Italy who underwent COVID-19 vaccination (average 70.6 days after first dose). We fitted center-specific multivariate regression models and combined them using random-effects meta-analyses.

Results:

A humoral response was elicited in 99.3% of vaccinated HCW. Female sex, young age, and previous COVID-19 infection were predictors of post-vaccination antibody level, and a positive association was also detected with pre-vaccination serology level and with time between pre- and post-vaccination testing, while a decline of antibody level was suggested with time since vaccination.

Conclusions:

These results stress the importance of analyzing retrospective data collected via occupational health surveillance of HCWs during the COVID-19 epidemic and following vaccination. They need to be confirmed in larger series based on prospectively collected data.

Multifunctional Photonic Janus Particles

Photonic Janus particles with a sphere fused to a cone are created from the phase separation of dendronized brush block copolymers (den-BBCP) and poly(4-vinylpyridine)-r-polystyrene (P4VP-r-PS) during the solvent evaporation of oil-in-water emulsions. Rapid self-assembly of den-BBCP generates well-ordered lamellar structures stacking along the long axis of the particles, producing structural colors that are dependent on the incident light angle. The colors are tunable over the visible spectrum by varying the molecular weight of den-BBCP. The P4VP-r-PS phase can undergo further surface modifications to produce multifunctional photonic Janus particles. Specifically, real-time magnetic control of the reflected color is achieved by coating the P4VP-r-PS phase with citric acid-capped Fe₃O₄ nanoparticles. Charged biomolecules (i.e., antibodies) are electrostatically immobilized to the Fe₃O₄ coating for potential applications in biosensing. As a demonstration, a new photonic sensor for the foodborne pathogen Salmonella is developed with antibody-modified photonic Janus particles, where the angle-dependent structural color plays a key role in the sensing mechanism.

Site-Specific Functionalization of Recombinant Spider Silk Janus Fibers

Biotechnological production is a powerful tool to design materials with customized properties. The aim of this work was to apply designed spider silk proteins to produce Janus fibers with two different functional sides. First, functionalization was established through a cysteine‐modified silk protein, ntag^CyseADF4(κ16). After fiber spinning, gold nanoparticles (AuNPs) were coupled via thiol‐ene click chemistry. Significantly reduced electrical resistivity indicated sufficient loading density of AuNPs on such fiber surfaces. Then, Janus fibers were electrospun in a side‐by‐side arrangement, with “non‐functional” eADF4(C16) on the one and “functional” ntag^CyseADF4(κ16) on the other side. Post‐treatment was established to render silk fibers insoluble in water. Subsequent AuNP binding was highly selective on the ntag^CyseADF4(κ16) side demonstrating the potential of such silk‐based systems to realize complex bifunctional structures with spatial resolutions in the nano scale.

Amphiphilic Janus Microspheres Prepared by Caged Photoactivatable Alkoxysilane

A simple photolysis route was proposed to prepare Amphiphilic Janus Particles (AJP) based on SiO2 microspheres. The surface of SiO2 microspheres were modified by photoactive alkoxysilane, which was synthesized by dealcoholization condensation of 6-nitroveratroyloxycarbonyl and isocyanatopropyl-triethoxysilane. UV irradiation caused eater-breaking allowed for the precise control of hydrophilic modification of the hemispherical exposed particles surfaces. The component and morphology of the obtained particles were characterized by fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy, and the Janus feature was evaluated by scanning electron microscopy, transmission electron microscopy, and dispersity in the oil–water dual-phases. The following results were obtained. The AJP with 450 nm size processes the hydrophilic amino groups on one side and the hydrophobic 6-nitroveratryloxycarbonyl moieties on the other. Additionally, the AJP were located at the phase boundary between water and n-hexane, and the negative charged gold nanoparticles with 25 nm size were adsorbed only onto the side with the positive charged amino groups. The AJP have interfacial adsorption energies that can be as much as three times larger than that of homogeneous particles and thus exhibit excellent surface activities.

Column Agglutination Assay Using Polystyrene Microbeads for Rapid Detection of Antibodies against SARS-CoV-2

Rapid serology platforms are essential in disease pandemics for a variety of applications, including epidemiological surveillance, contact tracing, vaccination monitoring, and primary diagnosis in resource-limited areas. Laboratory-based enzyme-linked immunosorbent assay (ELISA) platforms are inherently multistep processes that require trained personnel and are of relatively limited throughput. As an alternative, agglutination-based systems have been developed; however, they rely on donor red blood cells and are not yet available for high-throughput screening. Column agglutination tests are a mainstay of pretransfusion blood typing and can be performed at a range of scales, ranging from manual through to fully automated testing. Here, we describe a column agglutination test using colored microbeads coated with recombinant SARS-CoV-2 spike protein that agglutinates when incubated with serum samples collected from patients recently infected with SARS-CoV-2. After confirming specific agglutination, we optimized centrifugal force and time to distinguish samples from uninfected vs SARS-CoV-2-infected individuals and then showed concordant results against ELISA for 22 clinical samples, and also a set of serial bleeds from one donor at days 6-10 postinfection. Our study demonstrates the use of a simple, scalable, and rapid diagnostic platform that can be tailored to detect antibodies raised against SARS-CoV-2 and can be easily integrated with established laboratory frameworks worldwide.

Janus particles and motors: unrivaled devices for mastering (bio)sensing

Janus particles are a unique type of materials combining two different functionalities in a single unit. This allows the combination of different analytical properties leading to new analytical capabilities, i.e., enhanced fluid mixing to increase sensitivity with targeting capturing abilities and unique advantages in terms of multi-functionality and versatility of modification, use, and operation both in static and dynamic modes. The aim of this conceptual review is to cover recent (over the last 5 years) advances in the use of Janus microparticles and micromotors in (bio)-sensing. First, the role of different materials and synthetic routes in the performance of Janus particles are described. In a second main section, electrochemical and optical biosensing based on Janus particles and motors are covered, including in vivo and in vitro methodologies as the next biosensing generation. Current challenges and future perspectives are provided in the conclusions section.