Publications
Conducting polymer scaffolds: a new frontier in bioelectronics and bioengineering
Conducting polymer (CP) scaffolds have emerged as a transformative tool in bioelectronics and bioengineering, advancing the ability to interface with biological systems. Their unique combination of electrical conductivity, tailorability, and biocompatibility surpasses the capabilities of traditional nonconducting scaffolds while granting them access to the realm of bioelectronics. This review examines recent developments in CP scaffolds, focusing on material and device advancements, as well as their interplay with biological systems. We highlight applications for monitoring, tissue stimulation, and drug delivery and discuss perspectives and challenges currently faced for their ultimate translation and clinical implementation.
One-Pot Synthesis of a Robust Crosslinker-Free Thermo-Reversible Conducting Hydrogel Electrode for Epidermal Electronics
Traditional epidermal electrodes, typically made of silver/silver chloride (Ag/AgCl), have been widely used in various applications, including electrophysiological recordings and biosignal monitoring. However, they present limitations due to inherent material mismatches with the skin. This often results in high interface impedance, discomfort, and potential skin irritation, particularly during prolonged use or for individuals with sensitive skin. While various tissue-mimicking materials have been explored, their mechanical advantages often come at the expense of conductivity, resulting in low-quality recordings. We herein report the facile fabrication of conducting and stretchable hydrogels using a “one-pot” method. This approach involves the synthesis of a natural hydrogel, termed Golde, composed of abundant and eco-friendly components, including gelatin, chitosan, and glycerol. To enhance the conductivity of the hydrogel, various conducting materials, such as poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS), thermally reduced graphene (TRG), and MXene, are introduced. The resulting conducting hydrogels exhibit remarkable robustness, do not require crosslinkers, and possess a unique thermo-reversible property, simplifying the fabrication process and ensuring enhanced long-term stability. Moreover, their fabrication is sustainable, as it employs environmentally friendly materials and processes while retaining their skin-friendly characteristics. The resulting hydrogel electrodes were tested for electrocardiogram (ECG) signal acquisition and outperformed commercial electrodes even when implemented in an all-flexible electrode setup simply using copper tape, owing to their inherent adhesiveness.
Presently, on-skin wearable devices rely heavily on non-rechargeable batteries, which are not only harmful to the environment but also raise concerns about toxicity. As a result, there is a pressing need to develop self-powered energy sources that are environmentally friendly and compatible with human use. Triboelectric nanogenerators (TENGs) offer a promising solution as sustainable and biofriendly candidates for green energy generation. These TENG devices effectively convert mechanical energy from everyday activities, such as biomechanical motions, into electrical energy. They boast cost-effectiveness, easy fabrication, and high efficiency, making them ideal for self-powered electronics and independent power sources. However, a major drawback is that many TENGs still rely on non-eco-friendly fluorinated polymers, which can cause discomfort and skin infections when used in on-skin wearables. To overcome these challenges, our study introduces a novel approach, enhancing the performance of TENGs through a cellulose-based tribopositive layer integrated with nanomaterials. These nanomaterials include surface functional groups introduced via nano-coating or chemical/mechanical reduction to form nanocrystals or fibers. Moreover, we explore the potential of a new bio-polymer-based tribonegative layer, mimicking the chemical structure of conventional non-biodegradable materials, and incorporating nanomaterials for improved efficiency. In the pursuit for a completely biodegradable TENG, we replace the substrate with a biopolymer film and implement carbon-based electrodes, both integrated with nanomaterials. The resulting bio-TENGs exhibit remarkable flexibility, biocompatibility, and breathability, rendering them ideal for wearable devices capable of harvesting energy from biomechanical motions. Notably, these devices display outstanding performance, generating output voltage values surpassing 1 kV, attributed to the synergistic effects of nanomaterials in the triboelectric layers. This represents a twofold increase compared to conventional substrates and electrode materials that utilize polyimide as a negative triboelectric layer. Furthermore, our all-biopolymers-based TENGs surpass 500V in output voltage, outperforming other reported bio-TENG devices in voltage generation. The integration of nanomaterials components in these bio-TENGs opens up new possibilities for sustainable wearable electronics, ushering in a greener and more environmentally friendly era of energy generation and utilization.
Biocompatible, breathable and degradable microbial cellulose based triboelectric nanogenerator for wearable transient electronics
Advances in the processing of natural biomaterials have brought to the fore new approaches for the development of biofriendly and sustainable triboelectric nanogenerators (TENGs). In particular, bacterial cellulose (BC)-based TENGs have attracted considerable attention even though they still lack the key combination for transient wearable electronics. Herein, we report on a novel and facile method for in situ chemical modification of BC for the fabrication of degradable, breathable and biocompatible triboelectric nanogenerators (TENG). To achieve that, nanocoatings of polydopamine, polypyrrole or SiO2 have been used to decorate BC nanofibrils and thus tune the surface potential of the BC layer. Such a modification enables the repositioning of BC in the triboelectric series, allowing for the fabrication of various BC-based TENG devices. Polydopamine based BC TENG is found to exhibit superior performance (when coupled with a PVDF as negative triboelectric) with a maximum output voltage of ∼1010 V and a power density of ∼8.7 W/m2, a 7-fold enhancement in the power density as compared to pristine BC (VOC = 530 V and Pout = 1.1 W/m2). It is worthmentioning that all the nanocoated-BC films are found to be breathable, bio-/hemo-compatible and degradable, fulfilling the main criteria for transient electronics. As a proof of concept, we also demonstrate an on-body biomechanical energy harvester based on a single electrode All-BC TENG with the capability to generate an output voltage of 40 V upon physical motion. This TENG technology provides a unique combination of properties and has the potential to be implemented in wearables electronics and in vivo applications.
Plasma membrane mimetics can potentially play a vital role in drug discovery and immunotherapy owing to the versatility to assemble facilely cellular membranes on surfaces and/or nanoparticles, allowing for direct assessment of drug/membrane interactions. Recently, bacterial membranes (BMs) have found widespread applications in biomedical research as antibiotic resistance is on the rise, and bacteria-associated infections have become one of the major causes of death worldwide. Over the last decade, BM research has greatly benefited from parallel advancements in nanotechnology and bioelectronics, resulting in multifaceted systems for a variety of sensing and drug discovery applications. As such, BMs coated on electroactive surfaces are a particularly promising label-free platform to investigate interfacial phenomena, as well as interactions with drugs at the first point of contact: the bacterial membrane. Another common approach suggests the use of lipid-coated nanoparticles as a drug carrier system for therapies for infectious diseases and cancer. Herein, we discuss emerging platforms that make use of BMs for biosensing, bioimaging, drug delivery/discovery, and immunotherapy, focusing on bacterial infections and cancer. Further, we detail the synthesis and characteristics of BMs, followed by various models for utilizing them in biomedical applications. The key research areas required to augment the characteristics of bacterial membranes to facilitate wider applicability are also touched upon. Overall, this review provides an interdisciplinary approach to exploit the potential of BMs and current emerging technologies to generate novel solutions to unmet clinical needs.
3D organic bioelectronics for electrical monitoring of human adult stem cells
Three-dimensional in vitro stem cell models have enabled a fundamental understanding of cues that direct stem cell fate. While sophisticated 3D tissues can be generated, technology that can accurately monitor these complex models in a high-throughput and non-invasive manner is not well adapted. Here we show the development of 3D bioelectronic devices based on the electroactive polymer poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)–(PEDOT:PSS) and their use for non-invasive, electrical monitoring of stem cell growth. We show that the electrical, mechanical and wetting properties as well as the pore size/architecture of 3D PEDOT:PSS scaffolds can be fine-tuned simply by changing the processing crosslinker additive. We present a comprehensive characterization of both 2D PEDOT:PSS thin films of controlled thicknesses, and 3D porous PEDOT:PSS structures made by the freeze-drying technique. By slicing the bulky scaffolds we generate homogeneous, porous 250 μm thick PEDOT:PSS slices, constituting biocompatible 3D constructs able to support stem cell cultures. These multifunctional slices are attached on indium-tin oxide substrates (ITO) with the help of an electrically active adhesion layer, enabling 3D bioelectronic devices with a characteristic and reproducible, frequency dependent impedance response. This response changes drastically when human adipose derived stem cells (hADSCs) grow within the porous PEDOT:PSS network as revealed by fluorescence microscopy. The increase of cell population within the PEDOT:PSS porous network impedes the charge flow at the interface between PEDOT:PSS and ITO, enabling the interface resistance (R1) to be used as a figure of merit to monitor the proliferation of stem cells. The non-invasive monitoring of stem cell growth allows for the subsequent differentiation 3D stem cell cultures into neuron like cells, as verified by immunofluorescence and RT-qPCR measurements. The strategy of controlling important properties of 3D PEDOT:PSS structures simply by altering processing parameters can be applied for development of a number of stem cell in vitro models as well as stem cell differentiation pathways. We believe the results presented here will advance 3D bioelectronic technology for both fundamental understanding of in vitro stem cell cultures as well as the development of personalized therapies.
In-Situ Spectro-Electrochemistry of Conductive Polymers Using Plasmonics to Reveal Doping Mechanisms
Conducting polymers are a key component for developing wearable organic electronics, but tracking their redox processes at the nanoscale to understand their doping mechanism remains challenging. Here we present an in-situ spectro-electrochemical technique to observe redox dynamics of conductive polymers in an extremely localized volume (<100 nm3). Plasmonic nanoparticles encapsulated by thin shells of different conductive polymers provide actively tuned scattering color through switching their refractive index. Surface-enhanced Raman scattering in combination with cyclic voltammetry enables detailed studies of the redox/doping process. Our data intriguingly show that the doping mechanism varies with polymer conductivity: a disproportionation mechanism dominates in more conductive polymers, while sequential electron transfer prevails in less conductive polymers.
Conducting polymer scaffold device as a tool to mimic and monitor 3D tissue microenvironment for use in organ-on-chip platforms (Conference Presentation)
In vitro cell models have experienced a tremendeous progress over the last decade, as materials, devices and cell culture protocols became the centre of intense research for tissue engineering, drug screening and toxicology assays. While the majority of recently developed microphysiological systems yield sufficient complexity, methods for in situ evaluation of 3D cell cultures in a label-free manner and high-throughput configuration are still limited. We herein demonstrate a novel well plate bioelectronic platform, namely e-transmembrane, capable to support and monitor complex 3D cell architectures. In particular, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) based scaffolds have been engineered to function both as separator membranes for compartmentalized cell cultures, as well as electronic elements for real time and in situ recording of tissue growth and function. Intrinsic limitations arising from the 3D dimensionality of the porous structures are addressed by tailoring the morphological characteristics of the scaffold transmembranes. Impedance spectroscopy measurements carried out throughout the cell culture period, allowed us to identify signatures from different cell types, assessing cell growth and extracting barrier function parameters. Being compatible with current biological standards, we believe that this platform has the potential to become a universal tool for biologists, laying foundation for the next generation of high-throughput drug screening assays.
Electronic plants: the future of agriculture and urban ecosystems?
Electroactive and functional materials can be integrated with plants to monitor and control their development or to harvest and store energy. Seminal work by Stavrinidou et al. demonstrated electrically conducting polymers that grow inside living plants and form circuitry, unleashing exciting applications in smart agriculture and modern urban ecosystems.
Organic electronic transmembrane device for hosting and monitoring 3D cell cultures
3D cell models have made strides in the past decades in response to failures of 2D cultures to translate targets during the drug discovery process. Here, we report on a novel multiwell plate bioelectronic platform, namely, the e-transmembrane, capable of supporting and monitoring complex 3D cell architectures. Scaffolds made of PEDOT:PSS [poly(3,4-ethylenedioxythiophene):polystyrene sulfonate] are microengineered to function as separating membranes for compartmentalized cell cultures, as well as electronic components for real-time in situ recordings of cell growth and function. Owing to the high surface area–to–volume ratio, the e-transmembrane allows generation of deep, stratified tissues within the porous bulk and cell polarization at the apico-basal domains. Impedance spectroscopy measurements carried out throughout the tissue growth identified signatures from different cellular systems and allowed extraction of critical functional parameters. This platform has the potential to become a universal tool for biologists for the next generation of high-throughput drug screening assays.
MXenes, is an attractive new class of two-dimensional (2D) materials, discovered in 2011. Since then, owing to their unique combination of properties, such as high specific area, high electrical conductivity, tunable hydrophilicity, tunable chemical composition, and potential cytocompatibility, MXenes have made a deep impact on various fields ranging from electronics to energy and more recently to biotechnology. A typical example for the latter, is their use as electroactive biointerfaces in a number of biosensor setups, exhibiting remarkable analytical performance. In particular, MXene-based nanocomposites can serve as bioreceptors, electrochemical transducers or amplification probes towards translating molecular recognition of biological targets into detectable signals, leading to ultrasensitive biosensors for probing biomarkers, or pathogens. This concise review highlights the recent advances of MXene-based electrochemical biosensors for highly selective and sensitive detection of nucleic acids, proteins and pathogens pertaining to biomarker identification and clinical diagnostics. In particular, the effects of synthetic routes, surface chemistry, nanocomposite design, and fabrication methods of MXenes on the resulting relationship between biointerfacial structure, electrochemical properties and device performance is discussed, providing unique perspectives and design criteria for the next wave of biosensors.
The Role of Long-Alkyl-Group Spacers in Glycolated Copolymers for High-Performance Organic Electrochemical Transistors
Semiconducting polymers with oligoethylene glycol (OEG) sidechains have attracted strong research interest for organic electrochemical transistor (OECT) applications. However, key molecular design rules for high-performance OECTs via efficient mixed electronic/ionic charge transport are still unclear. In this work, new glycolated copolymers (gDPP-TTT and gDPP-TTVTT) with diketopyrrolopyrrole (DPP) acceptor and thiophene (T) and vinylene (V) thiophene-based donor units are synthesized and characterized for accumulation mode OECTs, where a long-alkyl-group (C12) attached to the DPP unit acts as a spacer distancing the OEG groups from the polymer backbone. gDPP-TTVTT shows the highest OECT transconductance (61.9 S cm–1) and high operational stability, compared to gDPP-TTT and their alkylated counterparts. Surprisingly, gDPP-TTVTT also shows high electronic charge mobility in a field-effect transistor, suggesting efficient ion injection/diffusion without hindering its efficient electronic charge transport. The elongated donor unit (TTVTT) facilitates hole polaron formation to be more localized to the donor unit, leading to faster and easier polaron formation with less impact on polymer structure during OECT operation, as opposed to the TTT unit. This is supported by molecular dynamics simulation. These simultaneously high electronic and ionic charge-transport properties are achieved due to the long-alkyl-group spacer in amphipathic sidechains, providing an important molecular design rule for glycolated copolymers.
3D Bioelectronic Model of the Human Intestine
Organ on chip (OoC) technologies have the potential to improve the translation of promising therapies currently failing in clinical trials at great expense and time due to dissimilarities between animal and human biology. Successful OoC models integrate human cells within 3D tissues with surrounding biomolecular components, and have benefited from the use of inert 3D gels and scaffolds used as templates, prompting tissue formation. However, monitoring technologies used to assess tissue integrity and drug effects are ill adapted to 3D biology. Here, a tubular electroactive scaffold serves as a template for a 3D human intestine, and enables dynamic electrical monitoring of tissue formation over 1 month. Cell- and extracellular matrix component-invoked changes in the properties of the scaffold alleviate the need for posthoc placement of invasive metallic electrodes or downstream analyses. Formation of in vivo-like stratified and polarized intestinal tissue compete with lumen contrasts with other quasi-3D models of the intestine using rigid porous membrane to separate cell types. These results provide unprecedented real-time information on tissue formation with highly sensitive multimodal operation, thanks to dual electrode and transistor operation. This device and the methodology for tissue growth within it represents a paradigm shift for disease modeling and drug discovery.
The convergence of traditional and digital biomarkers through AI-assisted biosensing: A new era in translational diagnostics?
Advances in consumer electronics, alongside the fields of microfluidics and nanotechnology have brought to the fore low-cost wearable/portable smart devices. Although numerous smart devices that track digital biomarkers have been successfully translated from bench-to-bedside, only a few follow the same fate when it comes to track traditional biomarkers. Current practices still involve laboratory-based tests, followed by blood collection, conducted in a clinical setting as they require trained personnel and specialized equipment. In fact, real-time, passive/active and robust sensing of physiological and behavioural data from patients that can feed artificial intelligence (AI)-based models can significantly improve decision-making, diagnosis and treatment at the point-of-procedure, by circumventing conventional methods of sampling, and in person investigation by expert pathologists, who are scarce in developing countries. This review brings together conventional and digital biomarker sensing through portable and autonomous miniaturized devices. We first summarise the technological advances in each field vs the current clinical practices and we conclude by merging the two worlds of traditional and digital biomarkers through AI/ML technologies to improve patient diagnosis and treatment. The fundamental role, limitations and prospects of AI in realizing this potential and enhancing the existing technologies to facilitate the development and clinical translation of “point-of-care” (POC) diagnostics is finally showcased.
Organic Bioelectronics for In Vitro Systems
Bioelectronics have made strides in improving clinical diagnostics and precision medicine. The potential of bioelectronics for bidirectional interfacing with biology through continuous, label-free monitoring on one side and precise control of biological activity on the other has extended their application scope to in vitro systems. The advent of microfluidics and the considerable advances in reliability and complexity of in vitro models promise to eventually significantly reduce or replace animal studies, currently the gold standard in drug discovery and toxicology testing. Bioelectronics are anticipated to play a major role in this transition offering a much needed technology to push forward the drug discovery paradigm. Organic electronic materials, notably conjugated polymers, having demonstrated technological maturity in fields such as solar cells and light emitting diodes given their outstanding characteristics and versatility in processing, are the obvious route forward for bioelectronics due to their biomimetic nature, among other merits. This review highlights the advances in conjugated polymers for interfacing with biological tissue in vitro, aiming ultimately to develop next generation in vitro systems. We showcase in vitro interfacing across multiple length scales, involving biological models of varying complexity, from cell components to complex 3D cell cultures. The state of the art, the possibilities, and the challenges of conjugated polymers toward clinical translation of in vitro systems are also discussed throughout.
3D Organic Bioelectronics for Monitoring In Vitro Stem Cell Cultures
Three-dimensional in vitro stem cell models has enabled a fundamental understanding of cues that direct stem cell fate and be used to develop novel stem cell treatments. While sophisticated 3D tissues can be generated, technology that can accurately monitor these complex models in a high-throughput and non-invasive manner is not well adapted. Here we show the development of 3D bioelectronic devices based on the electroactive polymer poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) - PEDOT:PSS and their use for non-invasive, electrical monitoring of stem cell growth. We show that the electrical, mechanical and wetting properties as well as the pore size/architecture of 3D PEDOT:PSS scaffolds can be fine-tuned simply by changing the processing crosslinker additive. We present a comprehensive characterization of both 2D PEDOT:PSS thin films of controlled thicknesses, and 3D porous PEDOT:PSS structures made by the freeze-drying technique. By slicing the bulky scaffolds we show that homogeneous, porous 250 um thick PEDOT:PSS slices are produced, generating biocompatible 3D constructs able to support stem cell cultures. These multifunctional membranes are attached on Indium-Tin oxide substrates (ITO) with the help of an adhesion layer that is used to minimize the interface charge resistance. The optimum electrical contact result in 3D devices with a characteristic and reproducible, frequency dependent impedance response. This response changes drastically when human adipose derived stem cells grow within the porous PEDOT:PSS network as revealed by fluorescence microscopy. The increase of these stem cell population within the PEDOT:PSS porous network impedes the charge flow at the interface between PEDOT:PSS and ITO, enabling the interface resistance to be extracted by equivalent circuit modelling, used here as a figure of merit to monitor the proliferation of stem cells. The strategy of controlling important properties of 3D PEDOT:PSS structures simply by altering processing parameters can be applied for development of a number of stem cell in vitro models. We believe the results presented here will advance 3D bioelectronic technology for both fundamental understanding of in vitro stem cell cultures as well as the development of personalized therapies.
Microelectrode Arrays Measure Blocking of Voltage-Gated Calcium Ion Channels on Supported Lipid Bilayers Derived from Primary Neurons
Drug studies targeting neuronal ion channels are crucial to understand neuronal function and develop therapies for neurological diseases. The traditional method to study neuronal ion-channel activities heavily relies on the whole-cell patch clamp as the industry standard. However, this technique is both technically challenging and labour-intensive, while involving the complexity of keeping cells alive with low throughput. Therefore, the shortcomings are limiting the efficiency of ion-channel-related neuroscience research and drug testing. Here, this work reports a new system of integrating neuron membranes with organic microelectrode arrays (OMEAs) for ion-channel-related drug studies. This work demonstrates that the supported lipid bilayers (SLBs) derived from both neuron-like (neuroblastoma) cells and primary neurons are integrated with OMEAs for the first time. The increased expression of voltage-gated calcium (CaV) ion channels on differentiated SH-SY5Y SLBs compared to non-differentiated ones is sensed electrically. Also, dose-response of the CaV ion-channel blocking effect on primary cortical neuronal SLBs from rats is monitored. The dose range causing ion channel blocking is comparable to literature. This system overcomes the major challenges from traditional methods (e.g., patch clamp) and showcases an easy-to-test, rapid, ultra-sensitive, cell-free, and high-throughput platform to monitor dose-dependent ion-channel blocking effects on native neuronal membranes.
Organic Electronic Platform for Real-Time Phenotypic Screening of Extracellular-Vesicle-Driven Breast Cancer Metastasis
Tumor-derived extracellular vesicles (TEVs) induce the epithelial-to-mesenchymal transition (EMT) in nonmalignant cells to promote invasion and cancer metastasis, representing a novel therapeutic target in a field severely lacking in efficacious antimetastasis treatments. However, scalable technologies that allow continuous, multiparametric monitoring for identifying metastasis inhibitors are absent. Here, the development of a functional phenotypic screening platform based on organic electrochemical transistors (OECTs) for real-time, noninvasive monitoring of TEV-induced EMT and screening of antimetastatic drugs is reported. TEVs derived from the triple-negative breast cancer cell line MDA-MB-231 induce EMT in nonmalignant breast epithelial cells (MCF10A) over a nine-day period, recapitulating a model of invasive ductal carcinoma metastasis. Immunoblot analysis and immunofluorescence imaging confirm the EMT status of TEV-treated cells, while dual optical and electrical readouts of cell phenotype are obtained using OECTs. Further, heparin, a competitive inhibitor of cell surface receptors, is identified as an effective blocker of TEV-induced EMT. Together, these results demonstrate the utility of the platform for TEV-targeted drug discovery, allowing for facile modeling of the transient drug response using electrical measurements, and provide proof of concept that inhibitors of TEV function have potential as antimetastatic drug candidates.
Tailoring the Surface Chemistry of PEDOT:PSS to Promote Supported Lipid Bilayer Formation
This communication reports on a versatile and substrate-agnostic method to tune the surface chemistry of conducting polymers with the aim of bridging the chemical mismatch between bioelectronic devices and biological systems. As a proof of concept, the surface of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is grafted with a short-chain oligoethylene glycol monolayer to favor the formation of cell-derived supported lipid bilayers (SLBs). This method is tuned to optimize the affinity between the supported lipid bilayer and the conducting polymer, leading to significant improvements in bilayer quality and therefore electronic readouts. To validate the impact of surface functionalization on the system's ability to transduce biological phenomena into quantifiable electronic signals, the activity of a virus commonly used as a surrogate for SARS-CoV-2 (mouse hepatitis virus) is monitored with and without surface treatment. The functionalized devices exhibit significant improvements in electronic output, stemming from the improved SLB quality, therefore strengthening the case for the use of such an approach in membrane-on-a-chip systems.
The 2022 applied physics by pioneering women: a roadmap
Women have made significant contributions to applied physics research and development, and their participation is vital to continued progress. Recognizing these contributions is important for encouraging increased involvement and creating an equitable environment in which women can thrive. This Roadmap on Women in Applied Physics, written by women scientists and engineers, is intended to celebrate women's accomplishments, highlight established and early career researchers enlarging the boundaries in their respective fields, and promote increased visibility for the impact women have on applied physics research. Perspectives cover the topics of plasma materials processing and propulsion, super-resolution microscopy, bioelectronics, spintronics, superconducting quantum interference device technology, quantum materials, 2D materials, catalysis and surface science, fuel cells, batteries, photovoltaics, neuromorphic computing and devices, nanophotonics and nanophononics, and nanomagnetism. Our intent is to inspire more women to enter these fields and encourage an atmosphere of inclusion within the scientific community.
Nanoscale Features of Tunable Bacterial Outer Membrane Models Revealed by Correlative Microscopy
The rise of antibiotic resistance is a growing worldwide human health issue, with major socioeconomic implications. An understanding of the interactions occurring at the bacterial membrane is crucial for the generation of new antibiotics. Supported lipid bilayers (SLBs) made from reconstituted lipid vesicles have been used to mimic these membranes, but their utility has been restricted by the simplistic nature of these systems. A breakthrough in the field has come with the use of outer membrane vesicles derived from Gram-negative bacteria to form SLBs, thus providing a more physiologically relevant system. These complex bilayer systems hold promise but have not yet been fully characterized in terms of their composition, ratio of natural to synthetic components, and membrane protein content. Here, we use correlative atomic force microscopy (AFM) with structured illumination microscopy (SIM) for the accurate mapping of complex lipid bilayers that consist of a synthetic fraction and a fraction of lipids derived from Escherichia coli outer membrane vesicles (OMVs). We exploit the high resolution and molecular specificity that SIM can offer to identify areas of interest in these bilayers and the enhanced resolution that AFM provides to create detailed topography maps of the bilayers. We are thus able to understand the way in which the two different lipid fractions (natural and synthetic) mix within the bilayers, and we can quantify the amount of bacterial membrane incorporated into the bilayer. We prove the system’s tunability by generating bilayers made using OMVs engineered to contain a green fluorescent protein (GFP) binding nanobody fused with the porin OmpA. We are able to directly visualize protein–protein interactions between GFP and the nanobody complex. Our work sets the foundation for accurately understanding the composition and properties of OMV-derived SLBs to generate a high-resolution platform for investigating bacterial membrane interactions for the development of next-generation antibiotics.
Bioelectronic Screening Platform for Real-Time Monitoring of Tumour-derived Extracellular Vesicle-Induced Epithelial-to-Mesenchymal Transition
Tumour-derived extracellular vesicles (TEVs) induce the epithelial-to-mesenchymal (EMT) in non-malignant cells to promote invasion and cancer metastasis. As such, TEVs represent a novel therapeutic target in a field severely lacking in efficacious anti-metastasis treatments. However, scalable technologies that allow continuous, multiparametric monitoring of therapeutic response for identifying metastasis inhibitors are missing. Here, we report the development of a platform based on organic electrochemical transistors (OECTs) for the real-time monitoring of TEV-induced EMT and screening of anti-metastatic drugs. We used TEVs derived from the triple-negative breast cancer (TNBC) cell line MDA-MB-231, to induce EMT in non-malignant breast epithelial cells (MCF10A) over a 9-day period, recapitulating a model of invasive ductal carcinoma metastasis. We performed extensive biological validation using immunofluorescence (IF) imaging and protein expression analysis, providing mechanistic insight using an epigenetics approach, and demonstrate our ability to obtain multiparametric functional readouts of cells using OECTs. Further, by employing OECT-based phenotypic drug screening, we identify heparin as an effective blocker of TEV-induced EMT in vitro, showcasing a promising anti-metastatic drug.
Biomembrane-based bioelectronic research has shown exponential growth since the inception of the field in the 1960s. The field is driven by parallel development of more representative membrane systems coupled with compatible substrates.Conducting polymers emerge as a promising class of materials that can significantly accelerate the development of bioelectronic sensors for biomedical applications. Cell membranes are integral to the functioning of the cell and are therefore key to drive fundamental understanding of biological processes for downstream applications. Here, we review the current state-of-the-art with respect to biomembrane systems and electronic substrates, with a view of how the field has evolved towards creating biomimetic conditions and improving detection sensitivity. Of particular interest are conducting polymers, a class of electroactive polymers, which have the potential to create the next step-change for bioelectronics devices. Lastly, we discuss the impact these types of devices could have for biomedical applications.
Understanding electrochemical properties of supported lipid bilayers interfaced with organic electronic devices
Supported lipid bilayers (SLBs) are cell–membrane-mimicking platforms of varying biological complexity, that can be formed on solid surfaces and used to characterise the properties of the plasma membrane or to study membrane interactions at the molecular level. The incorporation of microfabricated electrodes and transistors has allowed for their electrochemical characterisation using techniques such as Electrochemical Impedance Spectroscopy (EIS) and transistor-based impedance spectroscopy. In this work, we combine experimental data with numerical simulation to explore the relationship between changes in SLB quality and impedance output, delving into a deeper understanding of the impedance profiles of devices with and without SLB, as well as extracted parameters such as membrane resistance (Rm). We extrapolate this approach to investigate the relationship between microelectrode area and sensor sensitivity to changes in SLB state, towards rational device design. We highlight the trend of electrode size (polymer volume) required for sensing bilayer presence as well as the dependence of the electrode sensitivity to the SLB capacitance and resistance. Finally, we illustrate how our flexible approach of including electrode and transistor measurements to amalgamate characteristic impedance spectra of transistors, overcomes the problem of low frequency noise and errors seen with traditional EIS.
Dual Mode Sensing of Binding and Blocking of Cancer Exosomes to Biomimetic Human Primary Stem Cell Surfaces
Cancer-derived exosomes (cEXOs) facilitate transfer of information between tumor and human primary stromal cells, favoring cancer progression. Although the mechanisms used during this information exchange are still not completely understood, it is known that binding is the initial contact established between cEXOs and cells. Hence, studying binding and finding strategies to block it are of great therapeutic value. However, such studies are challenging for a variety of reasons, including the need for human primary cell culture, the difficulty in decoupling and isolating binding from internalization and cargo delivery, and the lack of techniques to detect these specific interactions. In this work, we created a supported biomimetic stem cell membrane incorporating membrane components from human primary adipose-derived stem cells (ADSCs). We formed the supported membrane on glass and on multielectrode arrays to offer the dual option of optical or electrical detection of cEXO binding to the membrane surface. Using our platform, we show that cEXOs bind to the stem cell membrane and that binding is blocked when an antibody to integrin β1, a component of ADSC surface, is exposed to the membrane surface prior to cEXOs. To test the biological outcome of blocking this interaction, we first confirm that adding cEXOs to cultured ADSCs leads to the upregulation of vascular endothelial growth factor, a measure of proangiogenic activity. Next, when ADSCs are first blocked with anti-integrin β1 and then exposed to cEXOs, the upregulation of proangiogenic activity and cell proliferation are significantly reduced. This biomimetic membrane platform is the first cell-free label-free in vitro platform for the recapitulation and study of cEXO binding to human primary stem cells with potential for therapeutic molecule screening as it is compatible with scale-up and multiplexing.
Correlative microscopy reveals the nanoscale morphology of E. coli-derived supported lipid bilayers
Supported lipid bilayers (SLBs) made from reconstituted lipid vesicles are an important tool in molecular biology. A breakthrough in the field has come with the use of vesicles derived from cell membranes to form SLBs. These new supported bilayers, consisting both of natural and synthetic components, provide a physiologically relevant system on which to study protein-protein interactions as well as protein-ligand interactions and other lipid membrane properties. These complex bilayer systems hold promise but have not yet been fully characterised in terms of their composition, ratio of natural to synthetic component and membrane protein content. Here, we describe a method of correlative atomic force (AFM) with structured illumination microscopy (SIM) for the accurate mapping of complex lipid bilayers that consist of a synthetic fraction and a fraction of lipids derived from Escherichia coli outer membrane vesicles (OMVs). We exploit the enhanced resolution and molecular specificity that SIM can offer to identify areas of interest in these bilayers and the atomic scale resolution that the AFM provides to create detailed topography maps of the bilayers. We are thus able to understand the way in which the two different lipid fractions (natural and synthetic) mix within the bilayers, quantify the amount of bacterial membrane incorporated in the bilayer and directly visualise the interaction of these bilayers with bacteria-specific, membrane-binding proteins. Our work sets the foundation for accurately understanding the composition and properties of OMV-derived SLBs and establishes correlative AFM/ SIM as a method for characterising complex systems at the nanoscale.
Functional Infectious Nanoparticle Detector: Finding Viruses by Detecting Their Host Entry Functions Using Organic Bioelectronic Devices
Emerging viruses will continue to be a threat to human health and wellbeing into the foreseeable future. The COVID-19 pandemic revealed the necessity for rapid viral sensing and inhibitor screening in mitigating viral spread and impact. Here, we present a platform that uses a label-free electronic readout as well as a dual capability of optical (fluorescence) readout to sense the ability of a virus to bind and fuse with a host cell membrane, thereby sensing viral entry. This approach introduces a hitherto unseen level of specificity by distinguishing fusion-competent viruses from fusion-incompetent viruses. The ability to discern between competent and incompetent viruses means that this device could also be used for applications beyond detection, such as screening antiviral compounds for their ability to block virus entry mechanisms. Using optical means, we first demonstrate the ability to recapitulate the entry processes of influenza virus using a biomembrane containing the viral receptor that has been functionalized on a transparent organic bioelectronic device. Next, we detect virus membrane fusion, using the same, label-free devices. Using both reconstituted and native cell membranes as materials to functionalize organic bioelectronic devices, configured as electrodes and transistors, we measure changes in membrane properties when virus fusion is triggered by a pH drop, inducing hemagglutinin to undergo a conformational change that leads to membrane fusion.
Detection of Ganglioside-Specific Toxin Binding with Biomembrane-Based Bioelectronic Sensors
Gangliosides, glycolipids that are abundant in the plasma membrane outer leaflet, play an integral role in cellular recognition, adhesion, and infection by interacting with different endogenous molecules, viruses, and toxins. Model membrane systems, such as ganglioside-enriched supported lipid bilayers (SLBs), present a useful tool for sensing, characterizing, and quantifying such interactions. In this work, we report the formation of ganglioside GM1-rich SLBs on conducting polymer electrodes using a solvent-assisted lipid bilayer assembly method to investigate changes in membrane electrical properties upon binding of the B subunit of cholera toxin. The sensing capabilities of our platform were investigated by varying both the receptor and the toxin concentrations in the system as well as using a complex sample (milk contaminated with the toxin) and monitoring the changes in the electrical properties of the membrane. Our work highlights the potential of such conducting polymer-supported biomembrane-based platforms for detecting the toxins within a complex environment, studying ganglioside-specific biomolecular interactions with toxins and screening inhibitory molecules to prevent these interactions.
N-type polymer based electrochemical device for direct enzymatic metabolite sensing and methods of making and using
N-type polymer based electrochemical devices include one or more source electrodes, one or more drain electrodes, one or more channels, a gate electrode, and an electrolyte solution are disclosed. The channels include one or more n-type polymers and one or more enzymes. The gate electrode includes one or more n-type polymers and one or more enzymes. The source and the drain electrodes are electrically connected by the corresponding channel. The electrolyte solution contains one or more metabolites capable of reacting with the one or more enzymes in the channel and the gate electrode and is in electrical contact with the channel and the gate electrode. Saturation current that flows through the channel increases when the metabolites react with the enzymes to produce electrons, which are directly transferred to the n-type polymers at the gate electrode and the channel. Methods of making and using the n-type electrochemical device are also disclosed.