Plasma neurofilament light chain (NfL) has been identified as a promising early-stage Alzheimer's disease (AD) biomarker, reflecting neuroaxonal degeneration at preclinical stages. However, its extremely low concentration in blood presents a major analytical challenge. Although single-molecule array (Simoa) assays provide exceptional sensitivity, they remain costly, instrumentation-intensive, and difficult to implement in decentralized settings. Here, we report the identification and engineering of high-affinity DNA aptamers against NfL using capillary electrophoresis-SELEX. Solution-phase fluorescence polarization was used to evaluate the binding capability of the aptamer candidates and the effect of aptamer truncation. Molecular modelling provided structural insights into aptamer-protein interactions, thereby supporting the rational optimization of aptamer design. The optimized truncated aptamers were integrated onto microfabricated gold electrodes to construct electrochemical aptasensors, exhibiting a Kd value of 1.67 ± 0.47 nM. To further enhance analytical performance, the aptamers were implemented in ion-gated organic electrochemical transistors (iOECTs), yielding an ultrasensitive and highly selective platform capable of detecting NfL in 0.1 × human serum with an ultralow limit of detection of 9 aM. This work establishes a scalable, minimally invasive, cost-effective alternative to antibody-based assays and provides a versatile biosensing strategy for early neurodegenerative disease diagnostics.

Microelectrode arrays (MEAs) hold inherent potential for the parallel analysis of foodborne pathogens; however, their miniaturized scale introduces critical challenges for multitarget detection, including cross-talk between adjacent units during functionalization and a severely limited sensing area that restricts probe immobilization and ultimate sensitivity. To overcome these limitations, a MEA-based aptasensor is constructed by integrating site-selective electrodeposition with a directed molecular allocation strategy for highly sensitive and specific simultaneous detection of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). A graphene oxide-polypyrrole nanocomposite and an AuNPs/chitosan-gold composite were precisely deposited on different microelectrode units, enabling the spatially resolved immobilization of aptamers against S. aureus and E. coli, respectively. Fluorescence and Raman spectroscopy confirmed the selective allocation of the respective aptamers to their targeted electrode units, effectively preventing cross-talk. Using methylene blue as an electroactive probe, the binding of target pathogens to their respective aptamers was quantified by square wave voltammetry. With optimized conditions, the limit of detection for S. aureus and E. coli was as low as 25.4 CFU mL-1 and 8.8 CFU mL-1. Real-sample assays confirmed that the MEA-based aptasensor is a precise and viable tool for high-speed quantification of S. aureus and E. coli, exhibiting considerable potential for applications in environmental and food safety monitoring practices.

Cable bacteria are multicellular microorganisms capable of charge transport over centimeter-scale distances through a network of conductive fibers embedded in the cell envelope. Understanding the charge injection mechanism into these fibers is essential to obtain a complete picture of their long-distance charge transport and a crucial step for their application in biobased electronics. To this aim, we fabricated "crosses" of two filaments, either native bacteria or extracted fiber skeletons, placed one on top of each other. By probing charge transport both through individual filaments and in cross-cable configurations, i.e., with current flowing from one filament to the other, it is possible to isolate the charge injection contribution. The results indicate that charge transfer between two contacting fibers is possible, albeit with increased resistance. We characterized the crosses at different temperatures, from 300 down to 50 K, observing thermally activated Arrhenius behavior both for single filaments and cross-conduction. The corresponding activation energy for filament-to-filament transport ranged from 15 to 40 meV, slightly smaller than that of individual cable bacterium filaments. We conclude that charge injection into the fibers must rely on the same mechanism as charge transport along the fibers. A structural model of the fibers is proposed in which internally winding conductive channels are embedded in a protein matrix. These channels can locally reach the surface of the fibers, where they can establish electrical contact with the external environment.

Organic electrochemical transistors (OECTs) can be optimized by tuning the gate-channel capacitance ratio via geometry or materials. However, electrolyte properties also critically influence performance, which is a phenomenon unexplained by capacitive models alone. This study demonstrates that varying electrolyte concentration modulates the on-state current (Ion), the off-state current (Ioff), the on-off ratio (Ion/Ioff), and the threshold voltage (VT). We propose a new impedance-based model incorporating both capacitive coupling and resistive voltage division across the electrolyte to explain these effects. This model successfully predicts and verifies a frequency-dependent VT shift under high-frequency signals. Leveraging this insight, we demonstrate that appropriately increasing the gate DC bias compensates for this shift, thereby enhancing transconductance in high-frequency applications.

The greening of electronics remains a grand societal challenge, with no radical improvement within sight. Sustainable solutions for electronics, such as biobased and transient materials, are hence receiving growing attention. Presently, there are no biobased alternatives to conventional conductors such as metals and organic polymers, as their conductivity is too low. The discovery of cable bacteria, which are filamentous microorganisms capable of conducting electricity over centimeter-scale distances, has the potential to change this. In cable bacteria, conductivity occurs through thin wires embedded in the cell envelope, displaying conductivities comparable to those of the best highly doped organic polymers. However, exposure to ambient air leads to a gradual loss of their conductivity. To enhance stability, a bioderived protective coating could be useful, thus retaining a fully biobased system. To this end, we investigated pullulan, a polysaccharide polymer primarily used in food packaging that is known for its excellent oxygen-barrier properties. Cable bacterium filaments protected with a film derived from a 10 wt % pullulan solution exhibited a 10-fold increase in conduction stability under ambient conditions compared to uncoated controls. Reducing ambient moisture also preserved the long-term conductivity of the cable bacteria, even in the absence of a protective coating, indicating that humidity plays a critical role in conductance deterioration. Our findings provide an important step toward further technological implementation of the highly conductive wires of cable bacteria and offer practical guidelines for developing biobased coatings for O2-sensitive materials in electronics, thus contributing to the advancement of next-generation green technologies.

Nanostraw arrays represent a novel and promising approach for the controlled delivery of substances into cells characterized by very little cellular activation or damage. Herein, we describe a sensitive strategy to establish intracellular contact with human macrophage-like differentiated THP-1 cells. Macrophages must function under stressful in-vivo conditions in oxygen-deprived tissues with inflammation. THP-1 cells stayed healthy and did not show signs of activation when cultured on nanostraw arrays. Importantly, we found convincing evidence for the successful delivery of gold nanoparticles and fluorescence-labeled antibodies into THP-1 cells. Future applications of nanostraw arrays are the functionalization with silane coating to immobilize proteins and/or the analysis of membrane located ion channels in THP-1 cells by electrophysiology. Our findings demonstrate that nanostraw arrays can enable intracellular contact for substance delivery and they might also allow measurements of the cellular membrane potential under stressful culture conditions like hypoxia in the future, in particular for immune cells.

With the goal of fast and accurate diagnosis of infectious diseases, this study presents a novel electrochemical biosensor that employs a refined aptamer (C9t) for the detection of spike (S) protein SARS-CoV-2 variants in a flexible multielectrode aptasensor array with PoC capabilities. Two aptamer modifications were employed: removing the primer binding sites and including two dithiol phosphoramidite anchor molecules. Thus, reducing fabrication time from 24 to 3 h and increasing the stability and sparseness for multi-thiol aptasensors compared to a standard aptasensor using single thiols, without a reduction in aptamer density. The biosensor fabrication, optimization, and detection were verified in detail by electrochemistry, QCM-D, SPR, and XPS. The analyte-receptor binding was further confirmed spectroscopically at the level of individual molecules by AFM-IR. The aptasensor possesses a low limit of detection (8.0 fg/mL), the highest sensitivity reported for S protein (209.5 signal per concentration decade), and a wide dynamic detection range (8.0 fg/mL-38 ng/mL) in nasopharyngeal samples, covering the clinically relevant range. Furthermore, the C9t aptasensor showed high selectivity for SARS-CoV-2 S proteins over biomarkers for MERS-CoV, RSV, and Influenza. Even more, it showed a three times higher sensitivity for the Omicron in comparison to the Wuhan strain (wild type), alpha, and beta variants of the SARS-CoV-2 virus. Those results demonstrate the creation of an affordable and variant-selective refined C9t aptasensor that outperformed current rapid diagnosis tests.

In this work, we combined plasmon-enhanced fluorescence and electrochemical (PEF-EC) trans- duction mechanisms to realize a highly sensitive dual-transducer aptasensor. To implement two traducers in one biosensor, a novel large-scale nanoimprint lithography process was introduced to fabricate gold nanopit arrays (AuNpA) with unique fringe structures. Light transmitting through the AuNpA samples exhibited a surface plasmon polariton peak overlapping with the excitation peak of the C7 aptamer associated fluorophore methylene blue (MB). We observed a five and seven times higher average fluorescence intensity over the AuNpA and fringe structure, respectively, in comparison to a plane Au film. Furthermore, the MB fluorophore was simultaneously utilized as a redox probe for electrochemical investigations and is described here as a dual transduction label for the first time. The novel dual transducer system was deployed for the detection of SARS-CoV-2 Spike protein via a C7 aptamer in combination with a strand displacement protocol. The PEF transducer exhibited a detection range from 1 fg/mL to 10 ng/mL with a detection limit of 0.07 fg/mL, while the EC traducer showed an extended dynamic range from 1 fg/mL to 100 ng/mL with a detection limit of 0.15 fg/mL. This work provides insights into an easy-to-perform, large-scale fabrication process for nanostructures enabling plasmon- enhanced fluorescence, and the development of an advanced but universal aptasensor platform.

Rapid development of artificial intelligence requires the implementation of hardware systems with bioinspired parallel information processing and presentation and energy efficiency. Electrolyte-gated organic transistors (EGOTs) offer significant advantages as neuromorphic devices due to their ultra-low operation voltages, minimal hardwired connectivity, and similar operation environment as electrophysiology. Meanwhile, ionic–electronic coupling and the relatively low elastic moduli of organic channel materials make EGOTs suitable for interfacing with biology. This review presents an overview of the device architectures based on organic electrochemical transistors and organic field-effect transistors. Furthermore, we review the requirements of low energy consumption and tunable synaptic plasticity of EGOTs in emulating biological synapses and how they are affected by the organic materials, electrolyte, architecture, and operation mechanism. In addition, we summarize the basic operation principle of biological sensory systems and the recent progress of EGOTs as a building block in artificial systems. Finally, the current challenges and future development of the organic neuromorphic devices are discussed.

Accurate and simultaneous determination of multiple neurotransmitters (NTs) is crucial for a thorough understanding of brain functions and for diagnosing neurological disorders. We have developed an electrochemical biosensor utilizing aptamer recognition for the highly sensitive and simultaneous detection of multiple neurotransmitters, including glutamate quantification for the first time in multiplex detection. Microelectrode arrays (MEAs) served as biosensing platforms to facilitate the recording of signals from multiple channels, rapid mass transfer rates, and high spatial resolution, fundamental for studying NTs release in nervous tissue. To enhance aptamer receptor loading, gold nanostructures were electrodeposited onto the microelectrodes, enhancing the active surface area and electrode morphology. A potential-pulse-assisted method was employed to achieve site-selective immobilization of three different aptamers on a single MEA chip within 30 min, enabling fast and reproducible sensor fabrication. This unique strategy ensured aptamer-specific immobilization, minimized cross-talk, and allowed for multiplex detection of serotonin, glutamate, and dopamine with high sensitivity and specificity. Additionally, using polyethylene glycol (PEG) as a blocking molecule, the aptamer-functionalized MEAs showed enhanced antifouling properties and maintained detection capabilities in complex environments. This multiplexed detection strategy enables a high-performance and robust biosensor platform with strong clinical relevance, offering substantial potential for in vivo monitoring of neurotransmitter release and the diagnosis of neurological disorders.

Neuromorphic interfaces represent a transformative frontier in neural engineering, enabling seamless communication between the nervous system and external devices through biologically inspired computing architectures. These systems offer promising avenues for diagnosing and treating neurological disorders by emulating the brain's computational strategies. Neural devices, including sensors and stimulators, monitor or modulate neural activity, playing a pivotal role in deciphering brain function and neuropathologies. Yet, clinical translation remains limited due to persistent challenges such as foreign body responses, low signal-to-noise ratios, and constraints in real-time data processing. Recent breakthroughs in neuromorphic hardware, neural recording, and stimulation technologies are addressing these challenges, paving the way for more adaptive and efficient brain-machine interfaces and neuroprosthetics. This review highlights the emerging class of neurohybrid interfaces, where neuromorphic systems might be integrated to enhance bidirectional neural communication. It emphasizes novel material strategies engineered for seamless neural interfacing and their incorporation into advanced neuromorphic chip architectures capable of real-time signal processing and closed-loop feedback. Furthermore, this review explores cutting-edge neuromorphic biointerfaces and evaluates the technological, biological, and ethical challenges involved in their clinical deployment. By bridging materials science, neuroscience, and neuromorphic engineering, these systems hold the potential to redefine the landscape of neurotechnology.

Direct electrostatic self-assembly of cationic AuNPs on glass delivers ultra-uniform, high-density metasurfaces via solvent exchange and fast drying. When particle size is optimal, far-field coupling emerges, boosting plasmonic Q -factors up to ∼15.

Biosensors based on DNA aptamer receptors are increasingly used in diagnostic applications. To improve the sensitivity and specificity of aptasensors, parameters affecting the stability and binding efficiency of the receptor layer need to be identified and studied. For example, the blocking step, i.e., the addition of inert molecules to the receptor layer, can improve sensor performance, but can also cause phase separation into nanodomains of unknown composition and structure. Here, nano-IR spectroscopy is used together with complementary macroscopic spectroscopic methods to study the nano-structural variations during the fabrication of a recently developed SARS-CoV-2 aptasensor. The blocking step by polyethylene glycol (PEG) causes a significant thickening of the receptor layer and a phase separation into nanodomains consisting of an aptamer-rich and a slightly thicker PEG-rich phase. The unambiguous chemical identification of the nanodomains is achieved by analysis of nano-IR images. Furthermore, bound analyte (spike protein of SARS-CoV-2) is detected at the single molecule level. Detailed analysis of the local nano-IR spectra revealed structural properties such as the amorphous state of the PEG molecules within the nanodomains and a strong change in the secondary structure of the analyte. This study significantly advances the understanding of nanoscale chemical processes in the receptor layer of aptasensors.

The rapid and reliable detection and quantification of nucleic acids is crucial for various applications, including infectious disease and cancer diagnostics. While conventional methods, such as the quantitative polymerase chain reaction are widely used, they are limited to the laboratory environment due to their complexity and the requirement for sophisticated equipment. In this study, we present a novel amplification-free digital sensing strategy by combining the collateral cleavage activity of the Cas12a enzyme with single-impact electrochemistry. In doing so, we modified silver nanoparticles using a straightforward temperature-assisted cofunctionalization process to subsequently detect the collision events of particles released by the activated Cas12a as distinct current spikes on a microelectrode array. The functionalization resulted in stable DNA-AgNP conjugates, making them suitable for numerous biosensor applications. Thus, our study demonstrates the potential of clustered regularly interspaced short palindromic repeats-based diagnostics combined with impact-based digital sensing for a rapid and amplification-free quantification of nucleic acids.

Biosensors based on DNA aptamers are increasingly used in diagnostic applications. To improve the sensitivity and specificity of aptasensors, parameters affecting the stability and binding efficiency of the receptor layer need to be identified and studied. For example, the influence of blocking, i.e. the addition of inert molecules to the receptor layer, on sensor performance is well accepted, but its effects on the nano-structure have not been studied in detail. Phenomena such as phase separation into nanodomains have been reported, but their effect on analyte binding remains uncertain. Here, nano-IR spectroscopy is used together with complementary macroscopic spectroscopic methods to study the nano-structural variations during the fabrication of an aptasensor consisting of a mixed self-assembled monolayer (SAM) of sensing aptamers and inert polyethylene glycol. The investigated sensor was recently developed and optimized for the detection of the spike protein of the omega variant of SARS-CoV-2. The initially formed aptamer layer is homogeneous and flat compared to the length of the DNA. In contrast, the film after blocking is much thicker and phase separated into nanodomains consisting of an aptamer-rich and a slightly thicker PEG-rich phase. The unambiguous chemical identification of the nanodomains is achieved by analysis of nano-IR spectra and nano-IR imaging. Furthermore, the analyte bound to the receptor layer was detected at the single molecule level. The detailed analysis of the local nano-IR spectra further revealed chemical properties such as the amorphous state of the PEG molecules within the nanodomains and a strong change in the secondary structure of the analyte. This study significantly advances our understanding of the chemical processes in the receptor layer of biosensors at the nanoscale.

Cable bacteria are filamentous, multicellular microorganisms that display an exceptional form of biological electron transport across centimeter-scale distances. Currents are guided through a network of nickel-containing protein fibers within the cell envelope. Still, the mechanism of long-range conduction remains unresolved. Here, we characterize the conductance of the fiber network under dry and wet, physiologically relevant, conditions. Our data reveal that the fiber conductivity is high (median value: 27 S cm-1; range: 2 to 564 S cm-1), does not show any redox signature, has a low thermal activation energy (Ea = 69 +/- 23 meV), and is not affected by humidity or the presence of ions. These features set the nickel-based conduction mechanism in cable bacteria apart from other known forms of biological electron transport. As such, conduction resembles that of an organic semi-metal with a high charge carrier density. Our observation that biochemistry can synthesize an organometal-like structure opens the way for novel bio-based electronic technologies.

BackgroundDiabetes patients suffer either from insulin deficiency or resistance with a high risk of severe long-term complications, thus the quantitative assessment of insulin level is highly desired for diabetes surveillance and management. Utilizing insulin-capturing aptamers may facilitate the development of affordable biosensors however, their rigid G-quadruplex structures impair conformational changes of the aptamers and diminish the sensor signals.ResultsHere we report on a ratiometric, electrochemical insulin aptasensor which is achieved by hybridization of an insulin-capturing aptamer and a partially complementary ssDNA to break the rigid G-quadruplex structures. To improve the durability of the aptasensor, the capturing aptamer was immobilized on gold electrodes via two dithiol-phosphoramidite functional groups while methoxy-polyethylene glycol thiol was used as a blocking molecule. The exposure of the sensor to insulin-containing solutions induced the dissociation of the hybridized DNA accompanied by a conformational rearrangement of the capturing aptamer back into a G-quadruplex structure. The reliability of sensor readout was improved by the adoption of an AND logic gate utilizing anthraquinone and methylene blue redox probes associated to the aptamer and complementary strand, respectively. Our aptasensor possessed an improved detection limit of 0.15 nM in comparison to aptasensors without strand displacement.SignificanceThe sensor was adapted for detection in real blood and is ready for future PoC diagnostics. The capability of monitoring the insulin level in an affordably manner can improve the treatment for an increasing number of patients in developed and developing nations. The utilization of low-cost and versatile aptamer receptors together with the engineering of ratiometric electrochemical signal recording has the potential to considerably advance the current insulin detection technology toward multi-analyte diabetes sensors.

The scalable fabrication of plasmonic metasurfaces that generate reflective plasmonic colors is achieved by using industrially manufactured antireflective moth-eye films. The periodically arranged dielectric nanopillar arrays on the moth-eye film serve as templates for fabricating ordered metal nanostructure arrays. The plasmonic colors exhibit angular independence and can be tuned by varying the species and thickness of the metal layer. Cross-sectional SEM observation and numerical simulations revealed that the changes in the reflection spectra related to the color generation are caused by the deformation of the metal layer, depending on its thickness. Furthermore, analysis of the electric field intensity distribution showed changes in the mode and wavelength of the plasmon resonance depending on the thickness of the metal layer. As a potential application, colorimetric plasmonic sensing was performed based on bulk refractive index measurements. The bulk refractive index sensitivity of the Ag-coated moth-eye film reached 347 nm/RIU (refractive index unit) and -730 degrees/RIU using hue as an indicator of colors. The refractive index resolution of 2 x 10(-5) RIU and the sensitivity obtained through colorimetric detection are superior to those of other colorimetric plasmonic sensors. The distinctive plasmonic colors produced by the metal-coated moth-eye films can be utilized to expand the application areas of plasmonic metasurfaces, such as colorimetric plasmonic biosensors and flexible displays, with their remarkable simplicity and affordability.