nA μM Research Articles

Modifying metal ion ratios in nickel-aluminum layered double hydroxide/reduced graphene oxide composites for selective electrochemical detection of antibiotics

Antimicrobial resistance (AMR) is a global threat that occurs as microorganisms evolve to resist antibiotic (ATB) overuse. To monitor this overuse, inexpensive, affordable, and adaptable sensors are required. While electrochemical sensors are promising, they cannot often distinguish between overlapping electrochemical interactions from multiple ATBs, resulting in poor analyte selectivity. To overcome this challenge, we design electrocatalysts consisting of nickel aluminum layered double hydroxides (NiAl-LDH) and their composites by altering the metal ion ratio to adjust the surface properties and selectivity of sensors. Synthesis of LDH and its graphene oxide (GO) composites is conducted using a low-temperature hydrothermal method. The prepared materials are characterized using various morphological and structural characterization techniques. Electrochemical characterization confirms that tuning the metal ion ratio allows sensors to differentiate between electrochemical reactions, improving the selective detection of amoxicillin and tetracycline from their mixtures. Addition of graphene oxide also enhances sensing capabilities. The optimized sensor has sensitivities of 137.6 nA µM−1 cm−2 and 161.4 nA µM−1 cm−2, and lower detection limits of 4.3 nM and 3.6 nM, respectively, for amoxicillin (Amx) and tetracycline (TC). Interferents have no significant effect on the detection of relatively low concentrations (10 µM) of the two ATBs. The electrodes can also detect the two analytes in tap water samples. This sensor methodology can potentially improve environmental antibiotic detection to mitigate the risk of antimicrobial resistance.

Highly Sensitive and Biocompatible Microsensor for Selective Dynamic Monitoring of Dopamine in Rat Brain.

Highly selective and sensitive in vivo neurotransmitter dynamic monitoring of the central nervous system has long been a challenging endeavor. Here, an implantable and biocompatible microsensor with excellent performances was reported by electrodepositing poly(3,4-ethylenedioxythiophene)-electrochemically reduced graphene oxide (PEDOT-ERGO) nanocomposites and poly(tannic acid) (pTA) sequentially on the carbon fiber electrode (CFE) surface, and its feasibility in in vivo electrochemical sensing applications were demonstrated. Due to the synergistic electrocatalytic effect of PEDOT-ERGO nanocomposites with the negative-charged pTA on dopamine (DA) redox reaction, the microsensor exhibits high detection sensitivities of 1.1 and 0.37 nA μM-1 in the detection ranges of 0.02-0.5 and 0.5-20 μM with a low limit of detection of 9.2 nM. Also, the microsensor shows excellent selectivity, good sensing stability, repeatability, and reproducibility. In addition, the highly hydrophilic and negative-charged pTA inhibits the nonspecific adsorption of hydrophobic proteins, which endows the microsensor with good antifouling ability. Moreover, DA dynamics in rat brain were successfully monitored in real time, and the selective sensing ability of the microsensor in vivo was also demonstrated. The present study provides a new method for selective dynamics monitoring of DA in the brain, which would help to better understand the pathological and physiological functions of DA.

Ionophore-Based SERS Sensing for Electrolyte Cations.

We present here a surface-enhanced Raman spectroscopy (SERS)-based platform for selectively detecting electrolyte cations. This platform facilitates the reorientation of the chromoionophore I (CHI) molecule positioned on the surface of silver nanoparticles, regulated by the targeted electrolyte cation within the ionophore-based ion-selective sensing framework. When exposed to the target ions, leading to deprotonation, the aromatic plane of the CHI molecule shifts from an endwise to an edgewise configuration on the SERS substrate surface. This reorientation improves the coupling of the induced dipole within the molecule and the induced electromagnetic field normal to the surface, leading to a heightened and more discernible SERS signal. Additionally, NMR data revealed a protonation-dependent conformational change in the CHI molecules. Upon protonation, the side chain of the CHI molecule extends away from its aromatic ring, whereas upon deprotonation, the carbon chain folds back and closely approaches the edge of the aromatic plane, further confirming this conclusion. Using Ca2+ and Na+ as examples, this method shows a detection limit of 0.1 μM for Ca2+ and 1 μM for Na+ with high selectivity. The successful application of the versatile and rapidly advancing SERS technique for electrolyte cation detection shows a promising pathway for enhancing current ion detection capabilities. As a preliminary demonstration, the total Ca2+ concentration in undiluted human serum was successfully determined, with common matrix interference effectively circumvented.

Electrified liquid – liquid interface strategy for sensing lactic acid in buttermilk extract

Lactic acid (LA) serves as a freshness marker in certain foods. In the present work, electrified interfaces of different nature (i.e., liquid-liquid and liquid-organogel) have been developed for the quantification of LA. Electrochemical sensing of LA at the liquid-organogel interface revealed that adsorptive stripping voltammetry, with a preconcentration time of 500 s offered better sensitivity. Electroanalytical ability of LA under optimized conditions displayed a detection limit of 0.97 μM and 0.71 μM with sensitivity of 2.84 nA μM−1 and 3.59 nA μM−1 for liquid-liquid and liquid-organogel interfaces respectively. Quantification of LA using the developed methodology has been demonstrated in buttermilk as the real matrix. Analysis demonstrate that electrified liquid-liquid and liquid-organogel interfaces are promising approach for sensing LA in buttermilk extract.

Pumpless microfluidic sweat sensing yarn

Textile sweat sensors possess immense potential for non-invasive health monitoring. Rapid in-situ sweat capture and prevention of its evaporation are crucial for accurate and stable real-time monitoring. Herein, we introduce a unidirectional, pump-free microfluidic sweat management system to tackle this challenge. A nanofiber sheath layer on micrometer-scale sensing filaments enables this pumpless microfluidic design. Utilizing the capillary effect of the nanofibers allows for the swift capture of sweat, while the differential configuration of the hydrophilic and hydrophobic properties of the sheath and core yarns prevents sweat evaporation. The Laplace pressure difference between the cross-scale fibers facilitates the management system to ultimately expulse sweat. This results in microfluidic control of sweat without the need for external forces, resulting in rapid (<5 s), sensitive (19.8 nA μM−1), and stable (with signal noise and drift suppression) sweat detection. This yarn sensor can be easily integrated into various fabrics, enabling the creation of health monitoring smart garments. The garments maintain good monitoring performance even after 20 washes. This work provides a solution for designing smart yarns for high-precision, stable, and non-invasive health monitoring.

Optimised graphite/carbon black loading of recycled PLA for the production of low-cost conductive filament and its application to the detection of β-estradiol in environmental samples

The production, optimisation, physicochemical, and electroanalytical characterisation of a low-cost electrically conductive additive manufacturing filament made with recycled poly(lactic acid) (rPLA), castor oil, carbon black, and graphite (CB-G/PLA) is reported. Through optimising the carbon black and graphite loading, the best ratio for conductivity, low material cost, and printability was found to be 60% carbon black to 40% graphite. The maximum composition within the rPLA with 10 wt% castor oil was found to be an overall nanocarbon loading of 35 wt% which produced a price of less than £0.01 per electrode whilst still offering excellent low-temperature flexibility and reproducible printing. The additive manufactured electrodes produced from this filament offered excellent electrochemical performance, with a heterogeneous electron (charge) transfer rate constant, k0 calculated to be (2.6 ± 0.1) × 10−3 cm s−1 compared to (0.46 ± 0.03) × 10−3 cm s−1 for the commercial PLA benchmark. The additive manufactured electrodes were applied to the determination of β-estradiol, achieving a sensitivity of 400 nA µM−1, a limit of quantification of 70 nM, and a limit of detection of 21 nM, which compared excellently to other reports in the literature. The system was then applied to the detection of ß-estradiol within four real water samples, including tap, bottled, river, and lake water, where recoveries between 95 and 109% were obtained. Due to the ability to create high-performance filament at a low material cost (£0.06 per gram) and through the use of more sustainable materials such as recycled polymers, bio-based plasticisers, and naturally occurring graphite, additive manufacturing will have a permanent place within the electroanalysis arsenal in the future.Graphical abstract

Multimodal integrated flexible neural probe for in situ monitoring of EEG and lactic acid.

In physiological activities, the brain's electroencephalogram (EEG) signal and chemical concentration change are crucial for diagnosing and treating neurological disorders. Despite the advantages of flexible neural probes, such as their flexibility and biocompatibility, it remains a challenge to achieve in situ monitoring of electrophysiological and chemical signals on a small scale simultaneously. This study developed a new method to construct an efficient dual-sided multimodal integrated flexible neural probe, which combines a density electrode array for EEG recordings and an electrochemical sensor for detecting lactic acid. The EEG electrode array includes a 6-channel recording electrode array with each electrode 30 × 50 μm in size, and the lactic acid sensor with overall contact is approximately 100 μm wide. The EEG electrodes have an average impedance of 2.57 kΩ at 1 kHz and remained stable after immersing in NS (normal saline) for 3 months. The lactic acid sensor showed a sensitivity of 52.8 nA mM-1. The in vivo experiments demonstrated that the probe can reliably monitor electrophysiological signals. The probe is able to be implanted into the desired site with the help of a guide port. This flexible neural probe can provide more comprehensive insights into brain activity in the field of neuroscience and clinical practices.

Biomimetic laser-induced graphene fern leaf and enzymatic biosensor for pesticide spray collection and monitoring.

Monitoring of pesticide concentration distribution across farm fields is crucial to ensure precise and efficient application while preventing overuse or untreated areas. Inspired by nature's wettability patterns, we developed a biomimetic fern leaf pesticide collection patch using laser-induced graphene (LIG) alongside an external electrochemical LIG biosensor. This "collect-and-sense" system allows for rapid pesticide spray monitoring in the farm field. The LIG is synthesized and patterned on polyimide through a high-throughput gantry-based CO2 laser process, making it amenable to scalable manufacturing. The resulting LIG-based leaf exhibits a remarkable water collection capacity, harvesting spray mist/fog at a rate approximately 11 times greater than a natural ostrich fern leaf when the collection is normalized to surface area. The developed three-electrode LIG pesticide biosensor, featuring a working electrode functionalized with electrodeposited platinum nanoparticles (PtNPs) and the enzyme glycine oxidase, displayed a linear range of 10-260 μM, a detection limit of 1.15 μM, and a sensitivity of 5.64 nA μM-1 for the widely used herbicide glyphosate. Also, a portable potentiostat with a user-friendly interface was developed for remote operation, achieving an accuracy of up to 97%, when compared to a standard commercial benchtop potentiostat. The LIG "collect-and-sense" system can consistently collect and monitor glyphosate spray after 24-48 hours of spraying, a time that corresponds to the restricted-entry interval required to enter most farm fields after pesticide spraying. Hence, this innovative "collect-and-sense" system not only advances precision agriculture by enabling monitoring and mapping of pesticide distribution but also holds the potential to significantly reduce environmental impact, enhance crop management practices, and contribute to the sustainable and efficient use of agrochemicals in modern agriculture.

High‐Speed Waveguide‐Integrated InSe Photodetector on SiN Photonics for Near‐Infrared Applications

On‐chip integration of two‐dimensional (2D) materials holds immense potential for novel optoelectronic devices across diverse photonic platforms. In particular, indium selenide (InSe) is a very promising 2D material due to its ultra‐high carrier mobility and outstanding photoresponsivity. Herein, a high‐speed photodetector based on a multilayer 90 nm thick InSe integrated on a silicon nitride (SiN) waveguide is reported. The device exhibits a remarkable low dark current density of ≈40 nA μm−2, a photoresponsivity of 0.38 A W−1, and an external quantum efficiency of ≈48.4%. Tested under ambient conditions at near‐infrared 976 nm wavelength, it exhibits an absorption coefficient of 0.11 dB μm−1. Additionally, the photodetector demonstrates a 3‐dB radiofrequency bandwidth of 85 MHz and an open‐eye diagram at data transmission of 1 Gbit s−1. Based on these exceptional optoelectronic advantages, integrated multilayer InSe enables the realization of active photonic devices for a range of applications, such as short‐reach optical interconnects, LiDAR imaging, and biosensing.

(Digital Presentation) PLA Additive Manufactured Electrode for Non-Enzymatic Electrochemical Detection of Urea in Human Urine

The fourth industrial revolution is currently seeing the emergence of additive manufacturing, also known as 3D printing, which has the potential to transform current manufacturing procedures. In this work we present an electrochemical sensor for detection of urea in human urine by using the 3D-printed electrode. A commercial 3D conductive filament of carbon black and polylactic acid (PLA) is used by the fused deposition modeling (FDM) printer for the manufacturing of the electrode. The mechanical strength of the electrode was analyzed by performing the tensile, flexural, and impact tests using a Universal testing Machine. The fracture failures were studied using the Scanning Electron Microscope. The stability and reproducibility of the electrode is analyzed by performing fifteen repeated cyclic voltammetric responses to 0.1M of uric acid. The 3D printed electrode offered the detection limit of uric acid with 1.18 μM and a sensitivity of 97.9 nA μM-1. Keywords: 3D-Printing, Additive Manufacturing, Polylactic acid, Uric Acid and Electrochemical Sensor

Intermittent pulse amperometry as an effective electrochemical assay of 4-nitrophenol

4-nitrophenol (4-NP) is a precursor of many industrial products and drugs, an environmental pollutant, and is used as a reporter molecule in many enzyme assays and disease biomarker screens. Accordingly, 4-NP analysis is a cross-disciplinary requirement, and we propose intermittent pulse amperometry (IPA) as an alternative to spectrophotometric methods. The sensor signal is acquired by applying 0.5 s pulses of 0.95 V once every 99.5 s during continuous amperometric recordings at 0 V resting potential to drive intermittent 4-NP detection at a diffusion-limited rate. With IPA, sensor surface fouling by polymerization of radical intermediates formed in the anodic oxidation process, which is a severe problem in constant-potential amperometry and voltammetry of phenols, is kept at acceptable minimum by restriction of the time at the potential that produces contamination. Complex potential profiles with electrochemical activation steps and/or electrolyte supplementation with anti-fouling agents are not required. Calibration plots are linear up to 500 μM with a sensitivity of 35 nA μM−1 and a practical detection limit of 10 μM. Model samples of 100 μM 4-NP were assessed with suitable recovery rates, and in a proof-of-principle test as electrochemical readout of an enzyme assay, IPA accurately reported the time course of enzymic release of 4-NP from GlcNAc-4NP, a synthetic substrate of glucosaminidases. Simplicity and high performance are the major features of the proposed electrochemical 4-NP testing, and unless the analytical target is present only at trace levels, the technique is a promising alternative for the evaluation of 4-NP, either as a solution component or as a reporter molecule in enzyme assays.

Fully Integrated Wearable Device for Continuous Sweat Lactate Monitoring in Sports.

The chemical digitalization of sweat using wearable sensing interfaces is an attractive alternative to traditional blood-based protocols in sports. Although sweat lactate has been claimed to be a relevant biomarker in sports, an analytically validated wearable system to prove that has not yet been developed. We present a fully integrated sweat lactate sensing system applicable to in situ perspiration analysis. The device can be conveniently worn in the skin to monitor real-time sweat lactate during sports, such as cycling and kayaking. The novelty of the system is threefold: advanced microfluidics design for sweat collection and analysis, an analytically validated lactate biosensor based on a rational design of an outer diffusion-limiting membrane, and an integrated circuit for signal processing with a custom smartphone application. The sensor covering the range expected for lactate in sweat (1-20 mM), with appropriate sensitivity (-12.5 ± 0.53 nA mM-1), shows an acceptable response time (<90 s), and the influence of changes in pH, temperature, and flow rate are neglectable. Also, the sensor is analytically suitable with regard to reversibility, resilience, and reproducibility. The sensing device is validated through a relatively high number of on-body tests performed with elite athletes cycling and kayaking in controlled environments. Correlation outcomes between sweat lactate and other physiological indicators typically accessible in sports laboratories (blood lactate, perceived exhaustion, heart rate, blood glucose, respiratory quotient) are also presented and discussed in relation to the sport performance monitoring capability of continuous sweat lactate.

A MXene/MoS2 heterostructure based biosensor for accurate sweat ascorbic acid detection

Biosensors with high sensitivity to sweat composition analysis are essential for non-invasive, real-time physiological monitoring of individual health status. However, it is challenging to construct a well-conductive and stable interface for electrochemical sensors. Here, we construct a sensitive sweat biosensor for ascorbic acid (AA) quantification built on a heterostructure with three-dimensional (3D) linked network microstructures made from two-dimensional (2D) MoS2 nanosheets and 2D Ti3C2 MXene. The as obtained 2D/2D heterostructures presented numerous active sites and avoid the issue of reduced surface areas, which was generally brought on by the accumulation of 2D nanomaterials. The electrode modified with 2D/2D heterostructure could realize efficient electron transport by abundant accesses to absorb AA molecules. Based on the inherent conductivity, extremely porous structure, and active catalytic properties of 2D/2D heterostructures, the biosensor for detecting the AA in artificial sweat had a sensitivity of 54.6nA μM−1 and a detection limit of 4.2 μM. This study provided a new promising approach for the design of high-performance sensing interfaces and facilitated the widespread use of personalized diagnostic devices.

PtNPs/rGO-GluOx/mPD Directionally Electroplated Dual-Mode Microelectrode Arrays for Detecting the Synergistic Relationship between the Cortex and Hippocampus of Epileptic Rats.

Precise and directional couplings of functional nanomaterials with implantable microelectrode arrays (IMEAs) are critical for the manufacture of sensitive enzyme-based electrochemical neural sensors. However, there is a gap between the microscale of IMEA and conventional bioconjugation techniques for enzyme immobilization, which leads to a series of challenges such as limited sensitivity, signal crosstalk, and high detection voltage. Here, we developed a novel method using carboxylated graphene oxide (cGO) to directionally couple the glutamate oxidase (GluOx) biomolecules onto the neural microelectrode to monitor glutamate concentration and electrophysiology in the cortex and hippocampus of epileptic rats under RuBi-GABA modulation. The resulting glutamate IMEA exhibited good performance involving less signal crosstalk between microelectrodes, lower reaction potential (0.1 V), and higher linear sensitivity (141.00 ± 5.66 nA μM-1 mm-2). The excellent linearity ranged from 0.3 to 68 μM (R = 0.992), and the limit of detection was 0.3 μM. For epileptic rats, the proposed IMEA sensitively obtained synergetic variations in the action potential (Spike), local field potentials (LFPs), and glutamate of the cortex and hippocampus during seizure and RuBi-GABA inhibition. We found that the increase in glutamate preceded the burst of electrophysiological signals. At the same time, both changes in the hippocampus preceded the cortex. This reminded us that glutamate changes in the hippocampus could serve as important indicators for early warning of epilepsy. Our findings provided a new technical strategy for directionally stabilizing enzymes onto the IMEA with versatile implications for various biomolecules' modification and facilitated the development of detecting tools for understanding the neural mechanism.

Direct Electrochemistry of Glucose Dehydrogenase-Functionalized Polymers on a Modified Glassy Carbon Electrode and Its Molecular Recognition of Glucose.

A glucose biosensor was layer-by-layer assembled on a modified glassy carbon electrode (GCE) from a nanocomposite of NAD(P)+-dependent glucose dehydrogenase, aminated polyethylene glycol (mPEG), carboxylic acid-functionalized multi-wall carbon nanotubes (fMWCNTs), and ionic liquid (IL) composite functional polymers. The electrochemical electrode was denoted as NF/IL/GDH/mPEG-fMWCNTs/GCE. The composite polymer membranes were characterized by cyclic voltammetry, ultraviolet-visible spectrophotometry, electrochemical impedance spectroscopy, scanning electron microscopy, and transmission electron microscopy. The cyclic voltammogram of the modified electrode had a pair of well-defined quasi-reversible redox peaks with a formal potential of -61 mV (vs. Ag/AgCl) at a scan rate of 0.05 V s-1. The heterogeneous electron transfer constant (ks) of GDH on the composite functional polymer-modified GCE was 6.5 s-1. The biosensor could sensitively recognize and detect glucose linearly from 0.8 to 100 µM with a detection limit down to 0.46 μM (S/N = 3) and a sensitivity of 29.1 nA μM-1. The apparent Michaelis-Menten constant (Kmapp) of the modified electrode was 0.21 mM. The constructed electrochemical sensor was compared with the high-performance liquid chromatography method for the determination of glucose in commercially available glucose injections. The results demonstrated that the sensor was highly accurate and could be used for the rapid and quantitative determination of glucose concentration.

Selective Purity Modulation of Semiconducting Single-Walled Carbon Nanotube Networks for High-Performance Thin-Film Transistors

Single-walled carbon nanotube (SWCNT) random networks have become strong candidates for next-generation electronics due to their exceptional mechanical, electrical, and optical properties. However, metallic nanotubes in networks generally incur a trade-off between the charge carrier mobility and on/off ratio, limiting the performance of SWCNT-based devices. Therefore, various methods to increase the purity of semiconducting nanotubes in entire random networks have been reported, but this direction has faced other issues, such as nanotube shortening, higher cost, and higher energy. Here, we introduce SWCNT random network-based thin-film transistors (SWCNT TFTs) with a varying purity profile of semiconducting SWCNTs across the channel, exploiting the superior mobility of metallic SWCNTs by partially tuning the semiconducting SWCNT purity and developing a novel perspective on metallic nanotubes in semiconductor channels. Based on the high-precision drop-on-demand capability of inkjet printing and various concentrations of semiconducting SWCNT ink, we form selectively patterned channel regions with different semiconducting SWCNT purities. The metallic nanotube-dominant region drastically increases the carrier density with a minimized Schottky barrier, while high-purity semiconducting regions at the channel boundaries effectively block off-state leakage through carrier depletion. As a result, the SWCNT TFTs with selectively patterned metallic nanotube regions show superior carrier mobility (75.50 cm2 V–1 s–1) and channel width normalized on-current (34.33 nA μm–1) without compromising the on/off ratio (1.62 × 107). To show the feasibility of our device in high-performance electronics, we demonstrate all-inkjet-printed flexible display driving circuits with two transistors that enable low-power, high-performance operation in display applications.

Systematic Design of a Graphene Ink Formulation for Aerosol Jet Printing.

Aerosol jet printing is a noncontact, digital, additive manufacturing technique compatible with a wide variety of functional materials. Although promising, development of new materials and devices using this technique remains hindered by limited rational ink formulation, with most recent studies focused on device demonstration rather than foundational process science. In the present work, a systematic approach to formulating a polymer-stabilized graphene ink is reported, which considers the effect of solvent composition on dispersion, rheology, wetting, drying, and phase separation characteristics that drive process outcomes. It was found that a four-component solvent mixture composed of isobutyl acetate, diglyme, dihydrolevoglucosenone, and glycerol supported efficient ink atomization and controlled in-line drying to reduce overspray and wetting instabilities while maintaining high resolution and electrical conductivity, thus overcoming a trade-off in deposition rate and resolution common to aerosol jet printing. Biochemical sensors were printed for amperometric detection of the pesticide parathion, exhibiting a detection limit of 732 nM and a sensitivity of 34 nA μM-1, demonstrating the viability of this graphene ink for fabricating functional electronic devices.

Microcontact printing of choline oxidase using a polycation-functionalized zwitterionic polymer as enzyme immobilization matrix.

Highly sensitive and selective choline microbiosensors were constructed by microcontact printing (μCP) of choline oxidase (ChOx) in a crosslinked, polyamine-functionalized zwitterionic polymer matrix on microelectrode arrays (MEAs). μCP has emerged as a potential means to create implantable, multiplexed sensor microprobes, which requires the targeted deposition of different sensor materials to specific microelectrode sites on a MEA. However, the less than sufficient enzyme loading and inadequate spatial resolution achieved with current μCP approaches has limited adoption of the method for electroenzymatic microsensors. A novel polymer, poly(2-methacryloyloxyethyl phosphorylcholine)-g-poly(allylamine hydrochloride) (PMPC-g-PAH), has been developed to address this challenge. PMPC-g-PAH contributes to a higher viscosity "ink" that enables thicker immobilized ChOx deposits of high spatial resolution while also providing a hydrophilic, biocompatible microenvironment for the enzyme. Electroenzymatic choline microbiosensors with sensitivity of 639 ± 96 nA μM-1 cm-2 (pH 7.4; n = 4) were constructed that also are selective against both ascorbic acid and dopamine, which are potential electroactive interfering compounds in the mammalian brain. The high sensitivities achieved can lead to smaller MEA microprobes that minimize tissue damage and make possible the monitoring of multiple neurochemicals simultaneously in vivo with high spatial resolution.

Wireless, Battery-Free Implants for Electrochemical Catecholamine Sensing and Optogenetic Stimulation.

Neurotransmitters and neuromodulators mediate communication between neurons and other cell types; knowledge of release dynamics is critical to understanding their physiological role in normal and pathological brain function. Investigation into transient neurotransmitter dynamics has largely been hindered due to electrical and material requirements for electrochemical stimulation and recording. Current systems require complex electronics for biasing and amplification and rely on materials that offer limited sensor selectivity and sensitivity. These restrictions result in bulky, tethered, or battery-powered systems impacting behavior and that require constant care of subjects. To overcome these challenges, we demonstrate a fully implantable, wireless, and battery-free platform that enables optogenetic stimulation and electrochemical recording of catecholamine dynamics in real time. The device is nearly 1/10th the size of previously reported examples and includes a probe that relies on a multilayer electrode architecture featuring a microscale light emitting diode (μ-LED) and a carbon nanotube (CNT)-based sensor with sensitivities among the highest recorded in the literature (1264.1 nA μM-1 cm-2). High sensitivity of the probe combined with a center tapped antenna design enables the realization of miniaturized, low power circuits suitable for subdermal implantation even in small animal models such as mice. A series of in vitro and in vivo experiments highlight the sensitivity and selectivity of the platform and demonstrate its capabilities in freely moving, untethered subjects. Specifically, a demonstration of changes in dopamine concentration after optogenetic stimulation of the nucleus accumbens and real-time readout of dopamine levels after opioid and naloxone exposure in freely behaving subjects highlight the experimental paradigms enabled by the platform.

Tissue-like Conductive Ti3C2/Sodium Alginate Hybrid Hydrogel for Electrochemical Sensing.

Endowed with a soft and conductive feature, hydrogels have been widely used as interface materials in bioelectronics to fulfill mechanical matching and bidirectional exchange between electronic platforms and living samples. Despite their ionic conductivity, the lack of electron mobility has limited their further applications in biosensing, especially in the field of electrochemical sensing. Here, we propose a Ti3C2/sodium alginate (SA) hybrid hydrogel with not only a tissue-like mechanical strength (down to 80 kPa) but also a combined exchange interface for ions and electrons, realizing both mechanical and electrical coupling toward biological tissues. Due to the shared gelation tendency with cations, the Ti3C2 sheets and SA chains can be easily in situ coassembled through a one-step electrogelation method, making the hybrid hydrogel a well-suited interface layer for device functionalization. In addition, the typical two-dimensional (2D) structure and the abundant active terminals of Ti3C2 have endowed the Ti3C2/SA with a massive loading capacity toward catalytic nanoparticles. For example, the Prussian Blue (PB)-loaded Ti3C2/SA hybrid hydrogel exhibited an excellent electrochemical performance (sensitivity: 600 nA μM-1 cm-2; LOD: 12 nM) toward hydrogen peroxide sensing in tissue fluids, illustrating a promising application potentiality of the hybrid hydrogel in biochemical detection at tissue interfaces.