A novel method for glucose determination based on electrochemical impedance spectroscopy using glucose oxidase self-assembled biosensor

Impedance-based polymer microneedle patch sensor for continuous interstitial fluid glucose monitoring

Early detection and effective blood glucose control are critical for preventing and managing diabetes-related complications. Conventional glucometers provide point-in-time measurements but are painful and cannot facilitate continuous monitoring. Continuous glucose monitoring systems are comfortable but face challenges in terms of accuracy, cost, and sensor lifespan. This study aimed to develop a microneedle-based sensor patch for minimally invasive, painless, and continuous glucose monitoring in the interstitial fluid to address these limitations. Experimental results confirm painless and minimally invasive penetration of the skin tissue with cylindrical microneedles (3 × 3 array) to a depth of approximately 520 μm with minimal loading. The microneedle sensors fabricated with precision using the complementary metal-oxide semiconductor process were immobilized with glucose oxidase, as confirmed through phase angle analysis. Long-term tests confirmed the effective operation of the sensor for up to seven days. Glucose concentrations determined from the fitted concentration-impedance curves correlated well with those measured using commercial glucometers, indicating the reliability and precision of the microneedle sensor. The flexible and minimally invasive sensor developed in this study facilitates painless and continuous glucose monitoring.

Functional characterization and analysis of transcriptional regulation of sugar transporter SWEET13c in sugarcane Saccharum spontaneum

BACKGROUND

Sugarcane is an important crop for sugar production worldwide. The Sugars Will Eventually be Exported Transporters (SWEETs) are a group of sugar transporters recently identified in sugarcane. In Saccharum spontaneum, SsSWEET13c played a role in the sucrose transportation from the source to the sink tissues, which was found to be mainly active in the mature leaf. However, the function and regulation of SWEETs in sugarcane remain elusive despite extensive studies performed on sugar metabolism.

RESULTS

In this study, we showed that SsSWEET13c is a member of SWEET gene family in S. spontaneum, constituting highest circadian rhythm-dependent expression. It is a functional gene that facilitates plant root elongation and increase fresh weight of Arabidopsis thaliana, when overexpressed. Furthermore, yeast one-hybrid assays indicate that 20 potential transcription factors (TFs) could bind to the SsSWEET13c promoter in S. spontaneum. We combined transcriptome data from developmental gradient leaf with distinct times during circadian cycles and stems/leaves at different growth stages. We have uncovered that 14 out of 20 TFs exhibited positive/negative gene expression patterns relative to SsSWEET13c. In the source tissues, SsSWEET13c was mainly positively regulated by SsbHLH34, SsTFIIIA-a, SsMYR2, SsRAP2.4 and SsbHLH035, while negatively regulated by SsABS5, SsTFIIIA-b and SsERF4. During the circadian rhythm, it was noticed that SsSWEET13c was more active in the morning than in the afternoon. It was likely due to the high level of sugar accumulation at night, which was negatively regulated by SsbZIP44, and positively regulated by SsbHLH34. Furthermore, in the sink tissues, SsSWEET13c was also active for sugar accumulation, which was positively regulated by SsbZIP44, SsTFIIIA-b, SsbHLH34 and SsTFIIIA-a, and negatively regulated by SsERF4, SsHB36, SsDEL1 and SsABS5. Our results were further supported by one-to-one yeast hybridization assay which verified that 12 potential TFs could bind to the promoter of SsSWEET13c.

CONCLUSIONS

A module of the regulatory network was proposed for the SsSWEET13c in the developmental gradient of leaf and circadian rhythm in S. spontaneum. These results provide a novel understanding of the function and regulation of SWEET13c during the sugar transport and biomass production in S. spontaneum.

Impedance Analysis of Electrochemical Systems

Interpretation of impedance spectroscopy data requires both a description of the chemistry and physics that govern the system and an assessment of the error structure of the measurement. The approach presented here includes use of graphical methods to guide model development, use of a measurement model analysis to assess the presence of stochastic and bias errors, and a systematic development of interpretation models in terms of the proposed reaction mechanism and physical description. Application to corrosion, batteries, and biological systems is discussed, and emerging trends in interpretation and implementation of impedance spectroscopy are presented.

A Microfluidic PET-Based Electrochemical Glucose Sensor

Paper-based microfluidic sensors have gained increased attention in the field of analytical assays in recent years due to their self-driven nature, ease of preparation, high integration, low reagent consumption, and low cost. However, paper-based microfluidic sensors still have many deficiencies when it comes to the detection of some specific detectors such as blood glucose. For example, the processing procedure for microfluidic channels is tedious, the sensor electrodes are easily damaged by bending, and they can only be used as disposable products. To solve the above problems, a PET-based microfluidic sensor was proposed in this paper, the performance of which was tested with glucose as the target detector. The experimental results showed that the analytical performance of this sensor is comparable to that of existing commercial glucose meters. This work provides implications for the substrate selection of microfluidic chips for some biochemical analyses.

A glucose biosensor based on glucose oxidase fused to a carbohydrate binding module family 2 tag that specifically binds to the cellulose-modified electrode

The method of immobilization of glucose oxidase (GOD) on electrodes is especially important for the fabrication and performance of glucose biosensors. In this study, a carbohydrate binding module family 2 (CBM2) was successfully fused to the C terminal of GOD with a natural linker (NL) in endo-β-xylanase by genetic recombination, and a fusion GOD (GOD-NL-CBM2) was obtained. The CBM2 was used as an affinity adsorption tag for immobilization of the GOD-NL-CBM2 on a cellulose modified electrode. The specific activity of GOD-NL-CBM2 was comparable to that of the wild type GOD. In addition, the CBM2 tag of fusion GOD almost maintained its highest binding capacity under optimal catalytic conditions (pH 5.0, 50 °C). The morphology and composition analysis of the cellulose film reacted with and without GOD or GOD-NL-CBM2 confirmed the immobilization of GOD-NL-CBM2. The electrochemical properties of the GOD-NL-CBM2/cellulose film bioelectrode, with a characteristic peak of H₂O₂ at +0.6 V in the presence of glucose, revealed the capability of the immobilized GOD-NL-CBM2 to efficiently catalyze glucose and produce H₂O₂. Additionally, the current signal response of the biosensor to glucose was linear in the concentration range from 1.25 to 40 mM (r² ≥ 0.99). The sensitivity and detection limit of the GOD-NL-CBM2/cellulose film bioelectrode were 466.7 μA mol^-1 L cm^-2 and 0.475 mM (S/N = 3), respectively. Moreover, the glucose biosensor exhibited a rapid current change (< 5 s), high reproducibility (Relative standard deviation, RSD < 5%), substrate selectivity and stability, and retained about 80 % of the original current response after 2 months. The affinity adsorption-based immobilization strategy for GOD provides a promising approach to develop a high performance glucose biosensor.

Development of a functional impedimetric immunosensor for accurate detection of thyroid-stimulating hormone

Thyroid-stimulating hormone (TSH), which regulates the synthesis of thyroid gland hormones affecting the whole metabolism, is a pituitary hormone. Determination of TSH is crucial for monitoring thyroid gland-related disorders and some metabolic diseases.In this study, a nonlabeled immunosensor based on covalent immobilization of anti-TSH antibody by using the formation of self-assembled monolayers (SAM) of 4-mercaptophenylacetic acid (4-MPA) and functionalization of carboxyl ends with 1-ethyl-3-(3-dimetilaminopropil) carbodiimide (EDC)/N-Hydroxysuccinimide (NHS) was fabricated for detection of TSH. Immobilization steps including the concentration of 4-MPA, the concentration of anti-TSH antibody, and duration of anti-TSH antibody incubation were optimized by utilizing electrochemical impedance spectroscopy. Under optimal conditions, a sensitive, rapid, and accurate determination of TSH at a concentration range between 0.7 and 3.5 mIU/L was accomplished with a notable linearity and LOD value of 0.034 mIU/L, as well as reproducibility and repeatability. Moreover, for comparison, linear range experiments were also carried out by using other electrochemical methods, including linear sweep voltammetry, cyclic voltammetry, and capacitance spectroscopy. Finally, the constructed immunosensor was used for analyzing TSH levels spiked in the artificial serum samples.

Enzyme Immobilization on Gold Nanoparticles for Electrochemical Glucose Biosensors

More than 50 years have passed since Clark and Lyon developed the concept of glucose biosensors. Extensive research about biosensors has been carried out up to this day, and an exponential trend in this topic can be observed. The scope of this review is to present various enzyme immobilization methods on gold nanoparticles used for glucose sensing over the past five years. This work covers covalent bonding, adsorption, cross-linking, entrapment, and self-assembled monolayer methods. The experimental approach of each modification as well as further results are described. Designated values of sensitivity, the limit of detection, and linear range are used for the comparison of immobilization techniques.

Comparing glucose and urea enzymatic electrochemical and optical biosensors based on polyaniline thin films

Analytical sensors that can detect chemical (including biological) analytes are becoming increasingly widespread within the field of analytical chemistry. More than this, in a world tending towards the 'internet-of-things', the miniaturization of such devices is becoming increasingly urgent. Accordingly, electrochemical methods that are simultaneously multiplexable and effective at a miniature scale are receiving much attention. In the present work, we compare the label-free electrochemical response of enzymatic biosensors with the response of their optical counterpart. As a proof-of-concept we compare the electrochemical impedimetric response and the first time described capacitive response of enzymatic biosensors to their optical reflectance response (measured in the visible region using a portable handset spectrophotometer). The target was the detection of glucose and urea. The chemical platform of the sensors was composed of enzymatically functionalized polyaniline thin films. Sensitivity, linearity, and the limit of detection were analyzed for both electrochemical and optical instrumental settings. We found that the impedimetric/capacitive electrochemical setup produced a response that was of a similar quality to the optical response (sensitivities of 10.7 ± 0.7, 7.4 ± 0.7 and 4.3 ± 0.2% per decade for impedimetric, capacitive and optical glucose biosensors, respectively) with a broader linear range (10^-4 to 10^-1 mol L^-1 for both glucose and urea biosensors) and similar limit-of-detection in the range of 1 μmol L^-1 within a relevant and practical diagnosis range for biomedical applications.

Equivalent circuit models for a biomembrane impedance sensor and analysis of electrochemical impedance spectra based on support vector regression

In this study, an electrochemical impedance biosensor was developed as a simple and fast method for real-time monitoring of biofilm binding properties via continuous impedance spectroscopy. To prepare the sensing membrane, cells were immobilized onto gold electrodes with nitrocellulose membranes. Different cell growth features were measured with the impedance instrument and analyzed using an equivalent model for data fitting and support vector regression (SVR) for data processing. The collected impedance spectra revealed that the binding attachment areas of cells differ depending on the cell density. Our results demonstrate the usefulness and feasibility of training our impedance-based sensor with a small amount of data to predict the effective area of different biofilms (GE, NGE, and CNGE), with a prediction error of 9.8%.

Third generation impedimetric sensor employing direct electron transfer type glucose dehydrogenase

Faradaic electrochemical impedance spectroscopy (faradaic EIS) is an attractive measurement principle for biosensors. However, there have been no reports on sensors employing direct electron transfer (DET)-type redox enzymes based on faradaic EIS principle. In this study, we have attempted to construct the 3rd-generation faradaic enzyme EIS sensor, which used DET-type flavin adenine dinucleotide (FAD) dependent glucose dehydrogenase (GDH) complex, to elucidate its characteristic properties as well as to investigate its potential application as the future immunosensor platform. The gold disk electrodes (GDEs) with DET-type FADGDH prepared using self-assembled monolayer (SAM) showed the glucose concentration dependent impedance change, which was confirmed by the change in the charge transfer resistance (R_ct). The Δ(1/R_ct) values were also affected by DC bias potential and the length of SAM. Based on the Nyquist plot and Bode plot simulations, glucose sensing by imaginary impedance monitoring under fixed frequency (5 mHz) was carried out, revealing the higher sensitivity at low glucose concentration with wider linear range (0.02-0.2 mM). Considering this high sensitivity toward glucose, the 3rd-generation faradaic enzyme EIS sensor would provide alternative platform for future impedimetric immunosensing system, which does not use redox probe.

Immobilized Enzymes in Biosensor Applications

Enzyme-based biosensing devices have been extensively developed over the last few decades, and have proven to be innovative techniques in the qualitative and quantitative analysis of a variety of target substrates over a wide range of applications. Distinct advantages that enzyme-based biosensors provide, such as high sensitivity and specificity, portability, cost-effectiveness, and the possibilities for miniaturization and point-of-care diagnostic testing make them more and more attractive for research focused on clinical analysis, food safety control, or disease monitoring purposes. Therefore, this review article investigates the operating principle of enzymatic biosensors utilizing electrochemical, optical, thermistor, and piezoelectric measurement techniques and their applications in the literature, as well as approaches in improving the use of enzymes for biosensors.

An impedimetric micro-immunosensing assay to detect Alzheimer's disease biomarker: Aβ40

A miniaturized biosensing platform, based on monoclonal amyloid-beta antibodies (mAβ_ab) that were immobilized on a disc-shaped platinum/iridium (Pt/Ir) microelectrode surface coupled with an impedimetric signal transducer, was developed for the label-free and sensitive detection of amyloid-beta peptide fragment 1-40 (Aβ40); a reliable biomarker for early diagnosis of Alzheimer's disease (AD). A Pt/Ir microelectrode was electropolymerized with poly (ortho-phenylenediamine), a conducting free amine-containing aromatic polymer; followed by crosslinking with glutaraldehyde for subsequent coupling of mAβ_ab on the microelectrode surface. This modification strategy efficiently improved the impedimetric detection performance of Aβ40 in terms of charge transfer resistance (∼400-fold difference) and normalized impedance magnitude percentage change (∼40% increase) compared with a passive adsorption-based immobilization method. The sensitivity of the micro-immunosensing assay was found to be 1056 kΩ/(pg/mL)/cm² and the limit of detection was found to be 4.81 pg/mL with a dynamic range of 1-10⁴ pg/mL (R² = 0.9932). The overall precision of the assay, as measured by relative standard deviation, ranged from 0.84 to 5.15%, demonstrating its reliability and accuracy; while in respect to assay durability and stability, the immobilized mAβ_ab were able to maintain 80% of their binding activity to Aβ40 after incubation for 48 h at ambient temperature (25 °C). To validate the practical applicability, the assay was tested using brain tissue lysates prepared from AD-induced rats. Results indicate that the proposed impedimetric micro-immunosensing platform is highly versatile and adaptable for the quantitative detection of other disease-related biomarkers.

Functional, RF-Trilayer Sensors for Tooth-Mounted, Wireless Monitoring of the Oral Cavity and Food Consumption

Wearable devices have emerged as powerful tools for personalized healthcare in spite of some challenges that limit their widespread applicability as continuous monitors of physiological information. Here, a materials-based strategy to add utility to traditional dielectric sensors by developing a conformal radiofrequency (RF) construct composed of an active layer encapsulated between two reverse-facing split ring resonators is applied. These small (down to 2 mm × 2 mm) passive dielectric sensors possess enhanced sensitivity and can be further augmented by functionalization of this interlayer material. Demonstrator devices are shown where the interlayer is: (i) a porous silk film, and (ii) a modified PNIPAM hydrogel that swells with pH or temperature. In vivo use is demonstrated by adhesion of the device on tooth enamel to detect foods during human ingestion. Such sensors can be easily multiplexed and yield data-rich temporal information during the diffusion of analytes within the trilayer structure. This format could be extended to a suite of interlayer materials for sensing devices of added use and specificity.

Synthesis, design and sensing applications of nanostructured ceria-based materials

Cerium-based materials possess redox properties due to the presence of dual valence states of Ce³⁺ and Ce⁴⁺.

Skin-like biosensor system via electrochemical channels for noninvasive blood glucose monitoring

Currently, noninvasive glucose monitoring is not widely appreciated because of its uncertain measurement accuracy, weak blood glucose correlation, and inability to detect hyperglycemia/hypoglycemia during sleep. We present a strategy to design and fabricate a skin-like biosensor system for noninvasive, in situ, and highly accurate intravascular blood glucose monitoring. The system integrates an ultrathin skin-like biosensor with paper battery-powered electrochemical twin channels (ETCs). The designed subcutaneous ETCs drive intravascular blood glucose out of the vessel and transport it to the skin surface. The ultrathin (~3 μm) nanostructured biosensor, with high sensitivity (130.4 μA/mM), fully absorbs and measures the glucose, owing to its extreme conformability. We conducted in vivo human clinical trials. The noninvasive measurement results for intravascular blood glucose showed a high correlation (>0.9) with clinically measured blood glucose levels. The system opens up new prospects for clinical-grade noninvasive continuous glucose monitoring.

Multifunctional porous NiCo2O4 nanorods: sensitive enzymeless glucose detection and supercapacitor properties with impedance spectroscopic investigations

Multifunctional NiCo₂O₄ nanorods fabricated by a simple two-step method exhibit excellent performance in glucose sensors as well as supercapacitors.

Multiparameter Microwave Characterization and Probing of Ultralow Glucose Concentration Using a Microfabricated Biochip

This paper presents a planar biochip consisting of electromagnetically coupled, symmetric, square open loops for the multiparameter microwave characterization of deionized water, a phosphate-buffered saline solution, and a fructose-deionized water solution. The characterization additionally includes the probing of an ultralow glucose concentration in a very small volume of human sera and in solutions of d-glucose powder and deionized water. The interaction between the coupled electromagnetic field and the aqueous solution sample translates into a predictable relationship between the electrical characteristics of the biochip (magnitude and phase of S-parameters, attenuation, phase constant, group delay, characteristic impedance, and effective complex permittivity) and the physical properties of the solution. Owing to the microfabrication technology used for fabricating the proposed microbiochip, it is possible to develop robust, compact square open loops with a microsized coupling gap that characterizes a very small volume (1 μL) of the sample. Additionally, the biochip's impedance peaks at its resonances were modeled using glucose-level-dependent coupling capacitance between folded square open loops and mutual inductance between center-loaded T-shaped stubs. These peaks linearly shifted in frequencies and markedly varied in impedance. Consequently, a physiologically relevant amount of glucose (50⁻400 mg/dL) with a high sensitivity (up to 2.036 Ω/(mg·dL^-1)) and an ultralow detection limit (up to 4.8 nmol/L) was linearly detected.

A polysulfobetaine hydrogel for immobilization of a glucose-binding protein

A hydrogel based on sulfobetaine methacrylate monomer and crosslinker was investigated as a potential material for fluorescent glucose biosensor applications.

Development of glucose biosensors based on nanostructured graphene-conducting polyaniline composite

A biosensor was fabricated by immobilizing glucose oxidase (GOD) into nanostructured graphene (GRA)-conducting polyaniline (PANI) nanocomposite, which was based on electrochemical polymerization of aniline in GRA synthesized by using electrochemical expansion of graphite in propylene carbonate electrolyte. Scanning electron spectroscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the morphology and performance of the as-prepared biosensor, respectively. Amperometric measurements were carried out to optimize test conditions (pH and applied potential) of the biosensor. Under the optimal conditions, the biosensor showed a linear range from 10.0 μM to 1.48 mM (R(2)=0.9988) with a sensitivity of 22.1 μA mM(-1) cm(-2), and a detection limit of 2.769 μM (S/N=3). The apparent Michaelis-Menten constant (KM(a)) was estimated to be 3.26 mM. The interference from glycine (Gly), D-galactose (D-Gal), urea (Urea), L-phenylalanine (L-Phe), ascorbic acid (AA), and L-tyrosine (L-Tyr) was also investigated. The results indicated that the biosensor exhibit high sensitivity and superior selectivity, providing a hopeful candidate for glucose biosensing.

An electrochemical sensor based on rhodamine B hydrazide-immobilized graphene oxide for highly sensitive and selective detection of Cu(ii)

A novel Cu²⁺ sensor based on rhodamine B hydrazide (RBH)-immobilized graphene oxide (GO) was fabricated and estimated to be a detection limit of 0.061 nM for Cu²⁺ detection.

A novel electrochemical hydrogen peroxide biosensor based on hemoglobin capped gold nanoclusters–chitosan composite

In this work, the first direct electrochemistry of Hb-AuNCs and its electrocatalysis towards H₂O₂ in a biosensing system has been reported.