Recent advances in ionic liquid-based electrochemical biosensors

Coreactant-free strong Ru(bpy)32+ ECL at ionic liquid modified electrode and its application in sensitive detection of glucose based on resonance energy transfer

In this work, we have realized the strong anodic ECL emission of Ru(bpy)32+ at ionic liquid (N-butylpyridinium tetrafluoroborate) modified electrode without additional coreactant. Methylene blue (MB) could accept the energy of Ru(bpy)32+ ECL to construct resonance energy transfer (ECL-RET) system, leading to the decrease of ECL signal. In the presence of glucose oxidase, hydrogen peroxide generated from the oxidation process of glucose could oxidize MB and block the ECL-RET route, resulting in the recovery of ECL signal. As a consequence, the designed sensor showed outstanding performance for "signal-on" detection of glucose in the concentration range of 10 μM to 1 mM, and the detection limit was determined as 1.75 μM. Importantly, this study revealed new roles of ILs in the fabrication of coreactant-free ECL sensing, which might open up a promising route for the potential design and implement in clinical analysis.

Electroenzymatic cascade reaction on a biohybrid boosts the chiral epoxidation reaction

The chiral epoxidation of styrene and its derivatives is an important transformation that has attracted considerable scientific interest in the chemical industry. Herein, we integrate enzymatic catalysis and electrocatalysis to propose a new route for the chiral epoxidation of styrene and its derivatives. Chloroperoxidase (CPO) functionalized with 1-ethyl-3-methylimidazolium bromide (ILEMB) was loaded onto cobalt nitrogen-doped carbon nanotubes (CoN@CNT) to form a biohybrid (CPO-ILEMB/CoN@CNT). H2O2 species were generated in situ through a two-electron oxygen reduction reaction (2e-ORR) at CoN@CNT to initiate the following enzymatic epoxidation of styrene by CPO. CoN@CNT had high electroactivity for the ORR to produce H2O2 at a more positive potential, prohibiting the conversion of FeIII to FeII in the heme of CPO to maintain enzymatic activity. Meanwhile, CoN@CNT could serve as an ideal carrier for the immobilization of CPO-ILEMB. Hence, the coimmobilization of CPO-ILEMB and CoN@CNT could facilitate the diffusion of intermediate H2O2, which achieved 17 times higher efficiency than the equivalent amounts of free CPO-ILEMB in bulk solution for styrene epoxidation. Notably, an enhancement (∼45%) of chiral selectivity for the epoxidation of styrene was achieved.

Ionic Liquid/Water Binary Solvent Anti-Freezing Hydrogel for Strain and Temperature Sensors

Hydrogels are widely applied in the flexible wearable electronic devices field owing to their skin-like stretchability, superb biocompatibility, and high conductivity retention under mechanical deformations. Nevertheless, hydrogels are prone to freezing at low temperatures and losing water at high temperatures, which seriously limits their practical applications. Herein, a binary solvent system of ionic liquid (1-ethyl-3-methylimidazolium chloride) and water was prepared to endow the ionic hydrogel high ionic conductivity (0.28 S m-1 at 25 °C), high transparency (94.26%), and superior freezing tolerance (-50 °C). The multiple hydrogen bonds formed among polymer chains, water, and ionic liquids significantly improved the mechanical properties of the ionic hydrogel, enabling excellent tensile properties (strain >1800%) and durability (1000 times at 100% strain). Moreover, the ionic hydrogel was further assembled into a dual-response sensor, which exhibited satisfactory sensitivity to both tension (gauge factor = 2.15 at 200% strain) and temperature (temperature coefficient of resistance = -1.845%/°C) and can be applied for human motion and body temperature monitoring. This study provides a versatile method for preparing multifunctional hydrogels with a wide range of applications and lays the groundwork for human movement detection and smart health care.

Disposable biosensor based on ionic liquid, carbon nanofiber and poly(glutamic acid) for tyramine determination

In this study, an electrochemical biosensor based on carbon nanofibers (CNF), ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (IL), poly(glutamic acid) (PGA) and tyrosinase (Tyr) modified screen printed carbon electrode (SPE) was constructed for tyramine determination. Optimum experimental parameters such as CNF and IL amount, polymerization conditions of glutamic acid, enzyme loading, pH of test solution and operating potential were explored. The construction steps of the Tyr/PGA/CNF-IL/SPE were pursued by scanning electron microscopy and cyclic voltammetry. The Tyr/PGA/CNF-IL/SPE biosensor exhibited linear response to tyramine in the range of 2.0 × 10-7 - 4.8 × 10-5 M with a low detection limit of 9.1 × 10-8 M and sensitivity of 302.6 μA mM-1. The other advantages of Tyr/PGA/CNF-IL/SPE include its high reproducibility, good stability and anti-interference ability. The presented biosensor was also applied for tyramine determination in malt drink and pickle juice samples and mean analytical recoveries of spiked tyramine were calculated as 100.6% and 100.4% respectively.

Ionic Liquid-Induced Assembly of DNA at Air-Water Interface

DNA nanotechnology is the future of many products in the pharmaceutical and cosmetic industries. Self-assembly of this negatively charged biopolymer at surfaces and interfaces is an essential step to elaborate its field of applications. In this study, the ionic liquid (IL) monolayer-assisted self-assembly of DNA macromolecules at the air-water interface has been closely monitored by employing various quantitative techniques, namely, surface pressure-area (π-A) isotherms, surface potential, interfacial rheology, and X-ray reflectivity (XRR). The π-A isotherms reveal that the IL 1,3-didecyl 3-methyl imidazolium chloride induces DNA self-assembly at the interface, leading to a thick viscoelastic film. The interfacial rheology exhibits a notable rise in the viscoelastic modulus as the surface pressure increases. The values of storage and loss moduli measured as a function of strain frequency suggest a relaxation frequency that depends on the length of the macromolecule. The XRR measurements indicate a considerable increase in DNA layer thickness at the elevated surface pressures depending on the number of base pairs of the DNA. The results are considered in terms of the electrostatic and hydrophobic interactions, allowing a quantitative conclusion about the arrangement of DNA strands underneath the monolayer of the ILs at the air-water interface.

Facile immobilization of cholesterol oxidase on Pt,Ru-C nanocomposite and ionic liquid-modified carbon paste electrode for an efficient amperometric free cholesterol biosensing

In present work, the enzyme cholesterol oxidase (ChOx) was immobilized by Nafion® (Naf) on Pt,Ru-C nanocomposite and an ionic liquid (IL)-modified carbon paste electrode (CPE) in order to create cholesterol biosensor (Naf/ChOx/Pt,Ru-C/IL-CPE). The prepared working electrodes were characterized using scanning electron microscopy-energy-dispersive spectrometry, while their electrochemical performance was evaluated using electrochemical impedance spectroscopic, cyclic voltammetric, and amperometric techniques. Excellent synergism between IL 1-allyl-3-methylimidazolium dicyanamide ([AMIM][DCA]), Pt,Ru-C, and ChOx, as modifiers of CPE, offers the most pronounced analytical performance for improved cholesterol amperometric determination in phosphate buffer solution pH 7.50 at a working potential of 0.60 V. Under optimized experimental conditions, a linear relationship between oxidation current and cholesterol concentration was found for the range from 0.31 to 2.46 µM, with an estimated detection limit of 0.13 µM and relative standard deviation (RSD) below 5.5%. The optimized amperometric method in combination with the developed Naf/ChOx/Pt,Ru-C/IL-CPE biosensor showed good repeatability and high selectivity towards cholesterol biosensing. The proposed biosensor was successfully applied to determine free cholesterol in a human blood serum sample via its enzymatic reaction product hydrogen peroxide despite the presence of possible interferences. The percentage recovery ranged from 99.08 to 102.81%, while RSD was below 2.0% for the unspiked as well as the spiked human blood serum sample. The obtained results indicated excellent accuracy and precision of the method, concluding that the developed biosensor can be a promising alternative to existing commercial cholesterol tests used in medical practice.

Recent Developments in the Design and Fabrication of Electrochemical Biosensors Using Functional Materials and Molecules

Electrochemical biosensors are superior technologies that are used to detect or sense biologically and environmentally significant analytes in a laboratory environment, or even in the form of portable handheld or wearable electronics. Recently, imprinted and implantable biosensors are emerging as point-of-care devices, which monitor the target analytes in a continuous environment and alert the intended users to anomalies. The stability and performance of the developed biosensor depend on the nature and properties of the electrode material or the platform on which the biosensor is constructed. Therefore, the biosensor platform plays an integral role in the effectiveness of the developed biosensor. Enormous effort has been dedicated to the rational design of the electrode material and to fabrication strategies for improving the performance of developed biosensors. Every year, in the search for multifarious electrode materials, thousands of new biosensor platforms are reported. Moreover, in order to construct an effectual biosensor, the researcher should familiarize themself with the sensible strategies behind electrode fabrication. Thus, we intend to shed light on various strategies and methodologies utilized in the design and fabrication of electrochemical biosensors that facilitate sensitive and selective detection of significant analytes. Furthermore, this review highlights the advantages of various electrode materials and the correlation between immobilized biomolecules and modified surfaces.

Diagnostic kit based on halloysite nanoclay-ionic liquid nanocomposite modified electrode for electrochemical determination of cancer biomarker

Nucleic acid hybridization is occurred between the selective single-stranded nucleic acid sequence and its target sequence, which is one of the essential procedure for electrochemical detection of nucleic acid. microRNA-21 (miRNA-21) is known as a biomarker in various cancers. The determination of miRNA-21 was attained through by hybridization of inosine substituted miRNA-21 specific DNA probe (P_inosine) with its target miRNA-21. In this study, the surface of pencil graphite electrode (PGE) was firstly modified with halloysite nanoclay-ionic liquid (HNT/IL) nanocomposite. The characterization of surface was performed by Scanning Electron Microscope (SEM) images and Energy Dispersive X-Ray Analysis (EDX) analysis, and the differences at surface modifications were also shown by electrochemical methods with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). For sensitive and selective determination of miRNA-21, P_inosine and target miRNA concentration, immobilization and hybridization time were optimized by using HNT/IL modified PGE in combination with differential pulse voltammetry (DPV). The detection limit was achieved as 0.17 μg/mL (equals to 23.69 nM) in the linear range of 0.25-2 μg/mL miRNA-21. The selectivity of voltammetric method based on HNT/IL-PGE developed for miRNA-21 was examined in the presence of mismatch (MM) and non-complementary (NC) sequences. Because miRNA-21 is over-expressed in cancer cells, it has been tested in total RNA samples isolated from cancer cell line (breast cancer cell line, MCF-7). In the total RNA samples obtained from MCF-7, the detection limit was calculated as 0.28 μg/mL in the linear range of 1-4 μg/mL. Besides, the healthy cell line (human embryonic kidney cell line, HEK-293) was used as a control group and the results obtained by MCF-7 total RNA samples were compared to the results using HEK-293 total RNA samples in terms of miRNA-21 level.

A New Trend and Future Perspectives of the Miniaturization of Conventional Extraction Methods for Elemental Analysis in Different Real Samples: A Review

Sample preparation is one of the viable procedures to be used before analysis to enhance sensitivity and reduce the matrix effect. The current review is mainly emphasized the latest outcome and applications of microextraction techniques based on the miniaturization of the classical conventional methods based on liquid-phase and solid-phase extraction for the quantitative elemental analysis in different real samples. The limitation of the conventional sample preparation methods (liquid and solid phase extraction) has been overcome by developing a new way of reducing size as compared with the conventional system through the miniaturization approach. Miniaturization of the sample preparation techniques has received extensive attention due to its extraction at microlevels, speedy, economical, eco-friendly, and high extraction capability. The growing demand for speedy, economically feasible, and environmentally sound analytical approaches is the main intention to upgrade the conventional procedures apply for sample preparation in environmental investigation. A growing trend of research has been perceived to quantify the trace for elemental analysis in different natures of real samples. This review also recapitulates the current futuristic scenarios for the green and economically viable procedure with special overemphasis and concentrates on eco-friendly miniaturized sample-preparation techniques such as liquid-phase microextraction (LPME) and solid-phase microextraction (SPME). This review also emphasizes the latest progress and applications of the LPME and SPME approach and their future perspective.

Properties and Recent Advantages of N,N’-dialkylimidazolium-ion Liquids Application in Electrochemistry

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N,Nʹ-dialkylimidazolium-ion liquids is one of the important ionic liquids with a wide range of application as conductive electrolyte and in electrochemistry. The modified electrodes create a new view in fabrication of electroanalytical sensors. Many modifiers have beeen suggested for modification of electroanalytical sensor since many years ago. Over these years, ionic liquids and especially room temperature ionic liquids have attracted more attention due to their wide range of electrochemical windows and high electrical conductivity. N,Nʹ-dialkylimidazolium-ion liquids are one of the main important ionic liquids suggested for modification of bare electrodes and especially carbon paste electrodes. Although many review articles have reported onthe use of ionic liquids in electrochemical sensors, no review article has been specifically introduced so far on the review of the advantages of N,Nʹ-dialkylimidazolium ionic liquid. Therefore, in this review paper we focused on the introduction of recent advantages of N,Nʹ-dialkyl imidazolium ionic liquid in electrochemistry.

Ionic Liquid-Based Extraction System for In-Depth Analysis of Membrane Protein Complexes

Limited by the rare efficient extraction system in extracting hydrophobic membrane protein complexes (MPCs) without compromising the stability of protein-protein interactions (PPIs), the in-depth functional study of MPCs has lagged far behind. In this study, the first systematic screening of ionic liquids (ILs) was performed and showed that triethylammonium acetate (TEAA) IL exhibited excellent performance in stabilizing PPIs, which was further confirmed by molecular docking simulations. By combining TEAA with the conventional detergent Nonidet P-40 (NP-40), a novel IL-based extraction system, i-TAN (TEAA IL with 1% NP-40), was proposed, which demonstrated superior performance in extracting and stabilizing MPCs, attributed to its larger size, more uniform distribution, and closer-to-neutral microenvironment of micelles. Extraction of MPCs with i-TAN allowed the confident identification of more hydrophobic EGFR-interacting proteins that are easily dissociated during the extraction process. Quantitative analysis of the difference in EGFR complexes between trastuzumab-sensitive and trastuzumab-resistant breast cancer cells provided comprehensive insights to understand the drug resistance mechanism, suggesting that i-TAN has great potential in interactomics and functional analysis of MPCs. This study provides a novel strategy for MPC extraction and downstream processing.

Laccase bioconjugate and multi-walled carbon nanotubes-based biosensor for bisphenol A analysis

Bisphenol A (BPA) is an endocrine disruptor compound that has been detected in aquatic ecosystems. In this work, the development of an electrochemical biosensor for BPA determination based on laccase from Trametes versicolor is reported. A bioconjugate was optimized to maximize the biosensor electrocatalytic activity and stability, which for the first time involved the synergistic effect of this specific enzyme (6.8 UmL^-1), chitosan (5 mgmL^-1) and the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate in an optimum 5:5:2 (v/v/v) proportion. This bioconjugate was deposited onto a screen-printed carbon electrode previously modified with multi-walled carbon nanotubes (MWCNTs). Nanostructuration with MWCNTs enlarged the electrocatalytic activity and surface area, thus improving the biosensor performance. The BPA electrochemical reaction follows an EC mechanism at the optimum pH value of 5.0. Linearity up to 12 µM, a sensitivity of (6.59 ± 0.04) × 10^-2 μAμM^-1 and a detection limit of 8.4 ± 0.3 nM were obtained coupled with high reproducibility (relative standard deviations lower than 6%) and stability (87% of the initial response after one month). The developed biosensor was employed to the analysis of BPA in river water displaying appropriate accuracy (94.6-97.9%) and repeatability (3.1 to 6% relative standard deviations) proving its high potential applicability for in situ environmental analysis.

Functional Ionic Liquids Decorated Carbon Hybrid Nanomaterials for the Electrochemical Biosensors

Ionic liquids are gaining high attention due to their extremely unique physiochemical properties and are being utilized in numerous applications in the field of electrochemistry and bio-nanotechnology. The excellent ionic conductivity and the wide electrochemical window open a new avenue in the construction of electrochemical devices. On the other hand, carbon nanomaterials, such as graphene (GR), graphene oxide (GO), carbon dots (CDs), and carbon nanotubes (CNTs), are highly utilized in electrochemical applications. Since they have a large surface area, high conductivity, stability, and functionality, they are promising in biosensor applications. Nevertheless, the combination of ionic liquids (ILs) and carbon nanomaterials (CNMs) results in the functional ILs-CNMs hybrid nanocomposites with considerably improved surface chemistry and electrochemical properties. Moreover, the high functionality and biocompatibility of ILs favor the high loading of biomolecules on the electrode surface. They extremely enhance the sensitivity of the biosensor that reaches the ability of ultra-low detection limit. This review aims to provide the studies of the synthesis, properties, and bonding of functional ILs-CNMs. Further, their electrochemical sensors and biosensor applications for the detection of numerous analytes are also discussed.

Enhanced dechlorination of an enzyme-catalyzed electrolysis system by ionic liquids: Electron transfer, enzyme activity and dichloromethane diffusion

Enzyme-catalyzed electrolysis system (EES) is a promising technique for the efficient dechlorination of pollutants. In this study, ionic liquids (ILs) was first introduced to enhance the dichloromethane dechlorination performance of an EES. An imidazole-based IL, 1-ethyl-3-methylimidazole tetrafluoroborate ([EMIM][BF₄]), was chosen due to its excellent performance on dechlorination enhancement than other three ILs. The cyclic voltammograms with different scan rates shows that the presence of IL increased the apparent electron transfer rate constant (k_s) from 0.008 to 0.013 s^-1. The calculated surface electroactive species concentration (τ_c) also increased from 7.8 × 10^-9 to 9.5 × 10^-9 mol cm^-2. Electrochemical impedance spectroscopy analysis illustrates that the IL mainly weakened the interfacial resistance between electrolyte and cathode to accelerate the electron communication in the EES. The introduction of IL facilitated the regeneration of reduced glutathione from oxidized glutathione, whereas inhibited the catalytic activity of dehalogenase via the disruption of secondary structure shown in circular dichroism spectra. The presence of IL was also facilitated the dichloromethane diffusion from electrolyte to cathode. The mass transfer rate constants of dichloromethane (k_m,d) increased by 6.9 times after the addition of IL. The optimum volume concentration, pH value, reaction temperature and applied voltage were 20%, 7, 35 °C and -0.8 V vs Ag/AgCl, respectively. The study is helpful to understand the promotion mechanism of IL on the dechlorination performance of EES when it is adopted as a treatment technique.

Room Temperature Ionic Liquids-Based Electrochemical Sensors: An Overview on Paracetamol Detection

Paracetamol (PAR) is an effective antipyretic and analgesic drug utilized worldwide, safer at therapeutic levels but over-dosing and the chronic usage of PAR results in accumulation of toxic metabolites, which leads to kidney and liver damages. Hence, a simple, rapid, cost-effective, and sensitive analytical technique is needed for the accurate determination of PAR in pharmaceutical and biological samples. Though numerous techniques have been reported for PAR detection, electrochemical methods are being receiving more interest due to their advantages. Moreover, in the past few decades, room temperature ionic liquids (RTILs) have been utilized in electrochemical sensors due to their attractive properties. In this present review, authors gathered research findings available for the determination of PAR using RTIL-based electrochemical sensors and discussed. The advantages and limitations in these systems as well as the future research directions are summarized.

A boron nitride electrode modified with a nanocomposite prepared from an ionic liquid and tungsten disulfide for voltammetric sensing of 4-aminophenol

Boron nitride (BN) was used as a support and covered with an ionic liquid (IL) and tungsten disulfide (WS₂) nanoparticles to obtain an electrode for the determination of 4-aminophenol (4-AP). BN was prepared using a "solvent cutting" method, and the BN-IL-WS₂ nanocomposite was obtained by an ultrasonic method. BN and its hybrids were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. When the BN-IL-WS₂ composites were coated on the surface of the electrode, the response to 4-AP was strongly amplified due to the strong synergetic effect between the three materials. The voltammetric response of the modified sensor (with a maximum at 0.29 V vs. Ag/AgCl) in solutions with a pH of 6 is linear in the 0.01-50 μΜ 4-AP concentration range, and the limit of detection is 3 nM. A modified glassy carbon electrode was applied for the determination of 4-AP in seawater and dispersions containing paracetamol tablets. The results were consistent with those obtained by HPLC. Graphical abstract Schematic representation of the voltammetric determination process of 4-aminophenol (4-AP). The electrochemical sensor based on the glassy carbon electrode modified with boron nitride (BN), ionic liquid (IL) and tungsten disulfide (WS₂) nanomaterials. They, exhibit an excellent performance compared with other electrodes.

Recent Advances on Electrochemical Sensors for the Detection of Organic Disinfection Byproducts in Water

Irreversible organ damage or even death frequently occurs when humans or animals unknowingly drink contaminated water. Therefore, in many countries drinking water is disinfected to ensure removal of harmful pathogens from drinking water. If upstream water treatment prior to disinfection is not adequate, disinfection byproducts (DBPs) can be formed. DBPs can exist as wide variety of compounds, but up until now, only several typical compounds have drinking water standards attributed to them. However, it is apparent that the range of DBPs present in water can comprise hundreds of compounds, some of which are at high enough concentrations to be toxic or potentially carcinogenic. Hence, it becomes increasingly significant and urgent to develop an accessible, affordable, and durable sensing platform for a broader range and more sensitive detection of DBPs. Compared with well-established laboratory detection techniques, electrochemical sensing has been identified as a promising alternative that will provide rapid, affordable, and sensitive DBP monitoring in remote water sources. Therefore, this Review covers current state-of-the-art development (within the past decade) in electrochemical sensing to detect organic DBPs in water, which covered three major aspects: (1) recognition mechanism, (2) electrodes with signal amplification, and (3) signal read-out techniques. Moreover, comprehensive quality assessments on electrochemical biosensors, including linear detection range, limit of detection (LoD) and recovery, have also been summarized.

An ultrasensitive electrochemical anti-lysozyme aptasensor with biorecognition surface based on aptamer/amino-rGO/ionic liquid/amino-mesosilica nanoparticles

In this work, a novel method based on aptamers is proposed for electrochemical measurement of lysozyme. To this end, screen-printed carbon electrode (SPCE) was modified with a nanocomposite made from amino-reduced graphene oxide (Amino-rGO) synthesized from natural graphite powder, an ionic liquid (IL), and amino-mesosilica nanoparticles (Amino-MSNs). The composition of the nanocomposite (Amino-rGO/IL/Amino-MSNs) results in high thermal and chemical stability, conductivity, surface-to-volume ratio, cost efficiency, biocompatibility, and great bioelectrocatalysis characteristics. Presence of numerous amino groups, as well as remaining oxygen defects in rGO, provides a suitable site for immobilization of aptamers. Furthermore, use of this nanocomposite leads to considerable enhancement of the electrochemical signal and improved method sensitivity. Covalent coupling of aptamer's amino groups with that of the nanocomposite using glutaraldehyde (GLA) as a linker helps immobilize amino-linked lysozyme aptamers (Anti-Lys aptamers) on nanocomposite. The modified electrode was characterized using electrochemical methods such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The immobilized aptamer selectively adsorbs lysozyme (Lys) on the electrode interface, leading to increased Charge Transfer Resistance (R_CT) in EIS and decrease in the DPV peak currents which are used as analytical signals. Two separate calibration curves were drawn using the data acquired from EIS and DPV. The prepared anti-Lys aptasensor has two very low LODs equal to 2.1 and 4.2 fmol L^-1 with wide detection ranges of 10 fmol L^-1 to 200 nmol L^-1, and 20 fmol L^-1 to 50 nmol L^-1 for EIS and DPV calibration curves, respectively. The SPCE/Amino-rGO/IL/Amino-MSNs/APT also showed high reproducibility, specificity, sensitivity, and rapid response to Lys which has various applications in fields of bioengineering and biomedicine.

Electrochemical and Spectroscopic Analysis of the Ionogel-Electrode Interface

Ionogels, pseudo-solid-state electrolytes consisting of an ionic liquid electrolyte confined in a mesoporous inorganic matrix, have attracted interest recently due to their high ionic conductivity and physicochemical stability. These traits, coupled with their inherent solution processability, make them a viable solid electrolyte for solid-state battery systems. Despite the promising properties of ionogels, there have been very few investigations of the electrode-ionogel interface. In the present study, X-ray photoelectron spectroscopy, Raman spectroscopy, and electrochemical measurements were utilized to probe the surface reactions occurring at the electrode-ionogel interface for several electrode materials. Our results indicate that the sol acidity initiates breakdown of the organic constituents of the sol and reduction of the transition metals present in the electrode materials. This chemical attack forms an organic surface layer and affects the electrode composition, both of which can impede Li⁺ access. By modifying the silica sol-gel reaction via a two-step acid-base catalysis, these interfacial reactions can be avoided. Results are shown for a LiCoO₂ electrode in which a high Li-ion capacity and stable cycling were achieved.

Highly sensitive wearable sensor based on a flexible multi-layer graphene film antenna

The use of advanced carbon nanomaterials for flexible antenna sensors has attracted great attention due to their outstanding electromechanical properties. However, carbon nanomaterial based composites have yet to overcome drawbacks, such as low conductivity and toughness. In this work, a flexible multi-layer graphene film (FGF) with a high conductivity of 10⁶ S/m for antenna based wearable sensors is investigated. A 1.63 GHz FGF antenna sensor exhibits significantly high strain sensitivity of 9.8 for compressive bending and 9.36 for tensile bending, which is super than the copper antenna sensor (5.39 for compressive bending and 4.05 for tensile bending). Moreover, the FGF antenna sensor shows very good mechanical flexibility, reversible deformability and structure stability, and thus is well suited for applications like wearable devices and wireless strain sensing.