Developing a screen-printed graphite–polyurethane composite electrode modified with gold nanoparticles for the voltammetric determination of dopamine

A screen-printed electrode (SPGPUE) was prepared with graphite–polyurethane composite ink containing gold nanoparticles (AuNPs), resulting in a screen-printed graphite–polyurethane composite electrode modified with gold nanoparticles (SPGPUE–AuNPs). Gold nanoparticles were prepared by the citrate method and extracted from the water medium since polyurethane is not compatible with humidity. After extraction to chloroform, they were characterized via transmission electron microscopy (TEM). The presence of gold on the SPGPUE–AuNP surface was confirmed via SEM and EDX analyses, while thermogravimetry revealed the presence of approximately 3.0% (m/m) gold in the composite. An electrochemical pretreatment in 0.10 mol L⁻¹ phosphate buffer (pH 7.0) with successive cycling between −1.0 V and 1.0 V (vs. pseudo-Ag/AgCl) under a scan rate of 200 mV s⁻¹ and 150 cycles was required in order to provide a suitable electrochemical response for the voltammetric determination of dopamine. After the optimization of the parameters of differential pulse voltammetry (DPV), an analytical curve was obtained within a linear dynamic range of 0.40–60.0 μmol L⁻¹ and detection limit (LOD) of 1.55 ×10⁻⁸ mol L⁻¹ for dopamine at the SPGPUE–AuNP. A non-modified SPGPUE was used for comparison and a linear range was obtained between 2.0 and 10 μmol L⁻¹ with an LOD of 2.94 × 10⁻⁷ mol L⁻¹. During the dopamine determination in cerebrospinal synthetic fluid (CSF), recoveries between 89.3 and 103% were achieved. There were no significant interferences from ascorbic acid and uric acid, but some from epinephrine due to the structural similarity.

A screen-printed modified composite electrode (SPGPUE) was prepared with graphite–polyurethane ink containing gold nanoparticles (AuNPs), resulting in a sensor with improved sensitivity regarding the unmodified device in dopamine determination.     

Construction of self-signal DNA electrochemical biosensor employing WS2 nanosheets combined with PIn6COOH

In this work, a novel self-signal DNA electrochemical biosensor was constructed based on tungsten disulfide (WS₂) nanosheets combined with poly(indole-6-carboxylic acid) (PIn6COOH) as the sensing interface. The WS₂ nanosheets were synthesized via a simple solvent exfoliation method from bulk WS₂, and then PIn6COOH was electropolymerized on the WS₂ nanosheet-modified carbon paste electrode to obtain a unique nanocomposite. The electropolymerization efficiency was remarkably improved, ascribed to the physical adsorption between WS₂ nanosheets and aromatic In6COOH monomers, resulting in an increase of the electrochemical response of PIn6COOH. Owing to the presence of π–π interactions between the conjugated PIn6COOH/WS₂ nanocomposite and DNA bases, the probe ssDNA was noncovalently assembled on the nanocomposite substrate. After the hybridization of the probe ssDNA with the target DNA, the formation of the double-helix structure induced the resulting dsDNA to be released from the surface of the conjugated nanocomposite, accompanied with the self-signal regeneration of the nanocomposite (“signal-on”). The constructed PIn6COOH/WS₂ nanocomposite was not only employed as an interface for DNA immobilization but also reflected the signal transduction stemming from DNA immobilization and hybridization without any external indicators or complex labeling processes. A detection limit of 2.3 × 10⁻¹⁸ mol L⁻¹ has been estimated and a dynamic range of 1.0 × 10⁻¹⁷ mol L⁻¹ to 1.0 × 10⁻¹¹ mol L⁻¹ has been shown for the detection of a PIK3CA gene related to lung cancer. Selectivity of the biosensor has been researched in the presence of noncomplementary and base mismatched DNA sequences.

A self-signal DNA electrochemical biosensor was constructed employing WS₂ nanosheets combined with PIn6COOH.     

A sandwich-type bacteriophage-based amperometric biosensor for the detection of Shiga toxin-producing Escherichia coli serogroups in complex matrices

Immuno-based biosensors are a popular tool designed for pathogen screening and detection. The current antibody-based biosensors employ direct, indirect, or sandwich detection approaches; however, instability, cross-reactivity, and high-cost render them unreliable and impractical. To circumvent these drawbacks, here we report a portable sandwich-type bacteriophage-based amperometric biosensor, which is highly-specific to various Shiga toxin-producing Escherichia coli (STEC) serogroups. Environmentally isolated and biotinylated bacteriophages were directly immobilized onto a streptavidin-coated screen-printed carbon electrode (SPCE), which recognized and captured viable target cells. Samples (50 μL) were transferred to these bacteriophage-functionalized SPCEs (12 min, room temp) before sequentially adding a bacteriophage–gold nanoparticle solution (20 μL), H₂O₂ (40 mM), and 1,1′-ferrocenedicarboxylic acid for amperometric tests (100 mV s⁻¹) and analysis (ANOVA and LSD, P < 0.05). The optimum biotin concentration (10 mM) retained 94.47% bacteriophage viability. Non-target bacteria (Listeria monocytogenes and Salmonella Typhimurium) had delta currents below the threshold of a positive detection. With less than 1 h turn-around time, the amperometric biosensor had a detection limit of 10–10² CFU mL⁻¹ for STEC O157, O26, and O179 strains and R² values of 0.97, 0.99, and 0.87, respectively, and a similar detection limit was observed in complex matrices, 10–10² CFU g⁻¹ or mL⁻¹ with R² values of 0.98, 0.95, and 0.76, respectively. The newly developed portable amperometric biosensor was able to rapidly detect viable target cells at low inoculum levels, thus providing an inexpensive and improved alternative to the current immuno- and laboratory-based STEC screening methods.

Sandwich-type bacteriophage-based amperometric biosensor for the detection of Shiga toxin-producing Escherichia coli serogroups in complex matrices.     

An integrated microchannel biosensor platform to analyse low density lactate metabolism in HepG2 cells in vitro

In this study, we developed an electrochemical microchannel biosensor platform to analyse lactate metabolism in cells. This biosensor platform was fabricated by photolithography, thin-film deposition and microfluidic technology. A kind of functional biomaterial was prepared by mixing lactate oxidase, single-walled carbon nanotubes and chitosan, and platinum as working and blank electrodes of the biosensor was modified by a thin Prussian blue layer. The lactate biosensor was obtained by dropping functional biomaterials on the electrode. The results demonstrated that the sensitivity of the electrochemical biosensor was up to 567 nA mM⁻¹ mm⁻² and the limit of detection was 4.5 μM (vs. Ag/AgCl as the counter/reference electrode). The biosensor used to quantitatively detect metabolic lactate concentrations in HepG2 cells cultured with cancer drugs showed high sensitivity, selectivity and stability, and has potential applications in organ-on-a-chip and tissue engineering technologies, which typically involve low concentrations of metabolites.

In this study, we developed an electrochemical microchannel biosensor platform to analyse lactate metabolism in cells.     

Rapid electrochemical quantification of trace Hg2+ using a hairpin DNA probe and quantum dot modified screen-printed gold electrodes

Rapid, simple, sensitive and specific approaches for mercury(ii) (Hg²⁺) detection are essential for toxicology assessment, environmental protection, food analysis and human health. In this study, a ratiometric hairpin DNA probe based electrochemical biosensor, which relies on hairpin DNA probes conjugated with water-soluble and carboxyl functionalized quaternary Zn–Ag–In–S quantum dot (QD) on screen-printed gold electrodes (SPGE), referred to as the HP-QDs-SPGE electrochemical biosensor in this study, was developed for Hg²⁺ detection. Based on the “turn-off” reaction of a hairpin DNA probe binding with a mismatched target and Hg²⁺ through the formation of T–Hg²⁺–T coordination, the HP-QDs-SPGE electrochemical biosensor can rapidly quantify trace Hg²⁺ with high ultrasensitivity, specificity, repeatability and reproducibility. The conformational change of the hairpin DNA probe caused a significant decrease in electrochemical intensity, which could be used for the quantification of Hg²⁺. The linear dynamic range and high sensitivity of the HP-QDs-SPGE electrochemical biosensor for the detection of Hg²⁺ was studied in vitro, with a broad linear dynamic range of 10 pM to 1 μM and detection limits of 0.11 pM. In particular, this HP-QDs-SPGE electrochemical biosensor showed excellent selectivity toward Hg²⁺ ions in the presence of other metal ions. More importantly, this biosensor has been successfully used to detect Hg²⁺ in deionized water, tap water, groundwater and urine samples with good recovery rate and small relative standard deviations. In summary, the developed HP-QDs-SPGE electrochemical biosensor exhibited promising potential for further applications in on-site analysis.

A ratiometric hairpin DNA probe based electrochemical biosensor, which relies on hairpin DNA probes conjugated with water-soluble and carboxyl functionalized quantum dot on screen-printed gold electrodes, was developed for Hg²⁺ detection.     

Tungsten disulfide nanosheets supported poly(xanthurenic acid) as a signal transduction interface for electrochemical genosensing applications

Tungsten disulfide (WS₂) nanosheets supported poly(xanthurenic acid) (PXa) was used as the signal transduction interface for electrochemical genosensing. The WS₂ nanosheets were obtained from bulk WS₂ using a simple ultrasonic method. Due to the unique physical adsorption of Xa monomers to WS₂, the electropolymerization efficiency was greatly improved, accompanied with an increased electrochemical response of PXa. The obtained PXa/WS₂ nanocomposite not only served as a substrate for DNA immobilization but also reflected the electrochemical transduction originating from DNA immobilization and hybridization without any other indicators or complicated labelling steps. Owing to the presence of abundant carboxyl groups, the probe ssDNA was covalently attached on the carboxyl-terminated PXa/WS₂ nanocomposite through the free amines of DNA sequences based on the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydrosulfosuccinimide crosslinking reaction. The covalently immobilized probe ssDNA could selectively hybridize with its target DNA to form dsDNA on the surface of the PXa/WS₂ nanocomposite. This developed biosensor achieved a satisfactory detection limit down to 1.6 × 10⁻¹⁶ mol L⁻¹ and a dynamic range of 1.0 × 10⁻¹⁵ to 1.0 × 10⁻¹¹ mol L⁻¹ for detection of circulating tumor DNA related to gastric carcinoma. Selectivity of the biosensor has been investigated in presence of non-complementary, one-mismatched and two-mismatched DNA sequences.

An electrochemical signal transduction sensing interface for detecting PIK3CA gene was developed based on WS₂ nanosheets supported PXa.     

Chronoampermetric detection of enzymatic glucose sensor based on doped polyindole/MWCNT composites modified onto screen-printed carbon electrode as portable sensing device for diabetes

Doped-polyindole (dPIn) mixed with multi-walled carbon nanotubes (MWCNTs) were coated on a screen-printed electrode to improve the electroactive surface area and current response of the chronoamperometric enzymatic glucose sensor. Glucose oxidase mixed with chitosan (CHI-GOx) was immobilized on the electrode. (3-Aminopropyl) triethoxysilane (APTES) was used as a linker between the CHI-GOx and the dPIn. The current response of the glucose sensor increased with increasing glucose concentration according to a power law relation. The sensitivity of the CHI-GOx/APTES/dPIn was 55.7 μA mM⁻¹ cm⁻² with an LOD (limit of detection) of 0.01 mM, where the detectable glucose concentration range was 0.01–50 mM. The sensitivity of the CHI-GOx/APTES/1.5%MWCNT-dPIn was 182.9 μA mM⁻¹ cm⁻² with an LOD of 0.01 mM, where the detectable glucose concentration range was 0.01–100 mM. The detectable concentration ranges of glucose well cover the glucose concentrations in urine and blood. The fabricated enzymatic glucose sensors showed high stability during a storage period of four weeks and high selectivity relative to other interferences. Moreover, the sensor was successfully demonstrated as a continuous or step-wise glucose monitoring device. The preparation method employed here was facile and suitable for large quantity production. The glucose sensor fabricated here, consisting of the three-electrode cell of SPCE, were simple to use for glucose detection. Thus, it is promising to use as a prototype for real glucose monitoring for diabetic patients in the future.

The enzymatic glucose sensor based on a dPIn and dPIn/MWCNT modified screen-printed carbon electrode with a facile method possessed good glucose response. The detectable glucose concentration range covers well the glucose concentrations in urine and blood.     

Graphitic carbon nitride and APTES modified advanced electrochemical biosensor for detection of 17β-estradiol in spiked food samples

This work demonstrates a simple and inexpensive electrochemical biosensing pathway for selective and sensitive recognition of 17β-estradiol (E2) in environmental and food samples. The biosensing system is based on graphitic carbon nitride (g-C₃N₄) and a conductive polymer 3-aminopropyltriethoxysilane (APTES). The proposed biosensor shows the ability to detect E2 in attomolar levels within a wide linear logarithm concentration range of 1 × 10⁻⁶ to 1 × 10⁻¹⁸ mol L⁻¹ with a limit of detection (LOD) of 9.9 × 10⁻¹⁹ mol L⁻¹. The selectivity of the developed biosensor was confirmed by conducting the DPV of similarly structured hormones and naturally occurring substances. The proposed biosensor is highly stable and applicable to detect E2 in the presence of spiked food and environmental samples with satisfactory recoveries ranging from 95.1 to 104.8%. So, the designed electrochemical biosensor might be an effective alternative tool for the detection of E2 and other endogenous substances to attain food safety.

This work demonstrates a simple and inexpensive electrochemical biosensing pathway for selective and sensitive recognition of 17β-estradiol (E2) in environmental and food samples.     

Sensitive impedimetric detection of troponin I with metal–organic framework composite electrode

Metal–organic frameworks (MOFs) are promising materials for biosensing applications due to their large surface to volume ratio, easy assembly as thin films, and better biocompatibility than other nanomaterials. Their application in electrochemical biosensing devices can be realized by integrating them with other conducting materials, like polyaniline (PANI). In the present research, a composite of a copper-MOF (i.e., Cu₃(BTC)₂) with PANI has been explored to develop an impedimetric sensor for cardiac marker troponin I (cTnI). The solvothermally synthesized Cu₃(BTC)₂/PANI composite has been coated as a thin layer on the screen-printed carbon electrodes (SPE). This electroconductive thin film was conjugated with anti-cTnI antibodies. The above formed immunosensor has allowed the impedimetric detection of cTnI antigen over a clinically important concentration range of 1–400 ng mL⁻¹. The whole process of antigen analysis could be completed within 5 min. The detection method was specific to cTnI even in the co-presence of other possibly interfering proteins.

A Cu-MOF/PANI modified screen-printed electrode based immunosensing technique is described for the sensitive detection of cardiac troponin I. The sensor provides detection over a wide concentration range with a limit of detection of 0.8 ng mL⁻¹.     

Nitrogen-containing three-dimensional biomass porous carbon materials as an efficient enzymatic biosensing platform for glucose sensing

A novel glucose biosensor was developed by immobilizing glucose oxidase (GOD) on a three-dimensional (3D) porous cane vine (wisteria) stem-derived carbon (3D-CVS), which was firstly proposed as novel support material for electrochemical biosensors using loaded biomolecules. Here, an integrated 3D-CVS electrode was fabricated by loading GOD molecule onto a whole piece of 3D-CVS electrode for a glucose biosensor. The morphologies of integrated 3D-CVS and 3D-CVS/GOD electrode were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM results show the 3D macroporous structure of the integrated 3D-CVS electrode. TEM results show that there are some micro-holes and defects in the 3D-CVS electrode. Electrochemical behaviors and electrocatalytic performance of integrated 3D-CVS/GOD electrode were evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. The effects of pH and scanning rate on the electrochemical response of biosensors have been studied in detail. The glucose biosensor showed a wide linear range from 0.58 μM to 16 mM, with a high sensitivity of 86.17 μA mM⁻¹ and a low detection limit of 0.19 μM. Furthermore, the glucose biosensor exhibited high selectivity, good repeatability and nice stability.

Schematic illustration of the fabrication and structure of the 3D-CVS/GOD electrode.     

Disposable gold nanoparticle functionalized and bare screen-printed electrodes for potentiometric determination of trazodone hydrochloride in pure form and pharmaceutical preparations

In the present study, screen-printed electrodes unmodified and chemically modified with gold nanoparticles were used as sensitive electrochemical sensors for the determination of trazodone hydrochloride. The sensors were based on the use of a tetraphenylborate ion association complex as an electroactive material in screen-printed electrodes with dioctyl phthalate (DOP) as a solvent mediator modified with gold nanoparticles which improve the electrode conductivity and enhance the surface area. The sensors displayed a stable response for 5, 6 and 7 months with a reproducible potential and linear response over the concentration range 1 × 10⁻⁵–1 × 10⁻² mol L⁻¹ at 25 ± 1 °C with Nernstian slopes of 57.50 ± 0.66, 58.30 ± 0.45 and 59.05 ± 0.58 mV per decade and detection limits of 7.9 × 10⁻⁶, 7.6 × 10⁻⁶ and 6.8 × 10⁻⁶ mol L⁻¹ for sensor 1, 2 and 3 respectively. The analytical performance of the screen printed electrodes in terms of selectivity coefficients for trazodone hydrochloride relative to the number of potentially interfering substances was investigated. The proposed method has been applied successfully for the analysis of the drug in its pure and dosage forms and there is no interference from any common pharmaceutical additives.

In the present study, screen-printed electrodes unmodified and chemically modified with gold nanoparticles were used as sensitive electrochemical sensors for the determination of trazodone hydrochloride.     

Graphene nanosheet-sandwiched platinum nanoparticles deposited on a graphite pencil electrode as an ultrasensitive sensor for dopamine

An ultra-sensitive sensor of dopamine is introduced. The sensor is constructed by encapsulating platinum nanoparticles (PtNPs) between reduced graphene oxide (GR) nanosheets. The sandwiched PtNPs between GR layers acted as a spacer to prevent aggregation and provided a fine connection between the GR nanosheets to provide fast charge transfer. This specific orientation of the GR nanosheets and PtNPs on the graphite pencil electrode (GPE) substantially improved the electrocatalytic activity of the sensor. The synthesized graphene oxide and the fabricated sensor were comprehensively characterized by Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, field emission-scanning electron microscopy (FE-SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and square wave voltammetry (SWV). The value of the charge transfer coefficient (α), apparent heterogeneous electron transfer rate constant (k_s), and electroactive surface area for dopamine were found to be about 0.57, 8.99 s⁻¹, and 0.81 cm², respectively. The developed sensor is highly sensitive towards dopamine, and the detection limit is 9.0 nM. The sensor response is linear for dopamine concentration from 0.06 to 20 μM (R² = 0.9991). The behavior of the sensor for dopamine in the presence of a high concentration of l(+) Ascorbic acid and other potential interferents was satisfactory. High recovery percentage between 90% and 105% in the human urine sample, good reproducibility, and facile fabrication of the electrode make it a good candidate for dopamine sensing.

An efficient, highly sensitive, and selective electrochemical sensor using PtNPs sandwiched graphene layered modified graphite pencil electrode.     

An electrochemical aptasensor based on AuNRs/AuNWs for sensitive detection of apolipoprotein A-1 (ApoA1) from human serum

For early detection and diagnosis of cancer, it is essential to develop an electrochemical biosensor that is quick, accurate, and sensitive. Here, we use gold nanorod (AuNR) and gold nanowire (AuNW) nanocomposites (AuNR/AuNW/CS) as electrode modifiers on a glassy carbon electrode (GCE) to construct a sensitive label-free electrochemical aptasensor to detect ApoA1. The thiolated ApoA1-specific aptamers were immobilized onto the modified electrode surface through self-assembled monolayers. Electrochemical techniques, such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV), were used to analyze the fabrication steps. The concentration of ApoA1 was measured with DPV on the aptasensor, with a linear range of 0.1 to 1000 pg mL⁻¹ and a detection limit of 0.04 pg mL⁻¹. When compared to results from ELISA tests (which have a detection limit of 80 pg mL⁻¹), the results achieved here were over 2000 times better. The aptasensor''s performance was successfully evaluated using human serum spiked with ApoA1, suggesting that it has great potential for practical application. The electrochemical apatsensor additionally demonstrated outstanding selectivity responses and strong stability toward the target analyte.

For early detection and diagnosis of cancer, it is essential to develop an electrochemical biosensor that is quick, accurate, and sensitive.     

Electrochemical sensor based on screen printed carbon electrode–zinc oxide nano particles/molecularly imprinted-polymer (SPCE–ZnONPs/MIP) for detection of sodium dodecyl sulfate (SDS)

The foremost objective of this work is to prepare a novel electrochemical sensor-based screen-printed carbon electrode made of zinc oxide nanoparticles/molecularly imprinted polymer (SPCE–ZnONPs/MIP) and investigate its characteristics to detect sodium dodecyl sulfate (SDS). The MIP that is polyglutamic acid (PGA) film was synthesized via in situ electro-polymerization. The SDS''s recognition site was left on the surface of the PGA film after extraction using the cyclic voltammetry (CV) technique, facilitating the specific detection of SDS. Moreover, the ZnONPs (∼71 nm, polydispersity index of 0.138) were synthesized and effectively combined with the MIP by a drop-casting method, enhancing the current response. The surface of the prepared SPCE–ZnONPs/MIP was characterized by scanning electron microscopy and energy dispersive X-ray. Besides, the electrochemical performance of the SPCE–ZnONPs/MIP was also studied through CV and differential pulse voltammetry (DPV) techniques. As an outstanding result, it is observed that the current response of SPCE–ZnONPs/MIP for detection of SDS remarkably increased almost four times higher from 0.009 mA to 0.041 mA in comparison with bare SPCE. More importantly, the proposed SPCE–ZnONPs/MIP exhibited an excellent selectivity (in the presence of interfering molecules of Ca²⁺, Pb²⁺, as well as sodium dodecylbenzene sulfonate (SDBS)), sensitivity, reproducibility, and repeatability. Since the modified sensor offers portability, it is suitable for in situ environment and cosmetic monitoring.

The foremost objective of this work is to prepare a novel electrochemical sensor-based screen-printed carbon electrode made of zinc oxide nanoparticles/molecularly imprinted polymer (SPCE–ZnONPs/MIP) and investigate its characteristics to detect sodium dodecyl sulfate (SDS).     

Highly sensitive and convenient aptasensor based on Au NPs@Ce-TpBpy COF for quantitative determination of zearalenone

In this work, an aptasensor based on a portable U-disk electrochemical workstation in combination with a screen-printed electrode (SPE) is demonstrated for the quantitative determination of zearalenone (ZEN). The aptamer is immobilized on Au NPs@Ce-TpBpy COF (Covalent organic frameworks), which is modified on the surface of glassy carbon electrode. ZEN specifically binds to ZEN aptamer, which hinders the electron transfer and decreases the catalytic current of Au NPs@Ce-TpBpy COF for the reduction of hydrogen peroxide, measured by chronoamperometry (i–t). The quantitative detection of ZEN toxin is realized by a decrease of the catalytic current (ΔI). Under the optimal experimental conditions, the aptamer sensor exhibited excellent sensitivity, selectivity, reproducibility. A wide linear range of 1 pg mL⁻¹–10.0 ng mL⁻¹ with a detection limit of 0.389 pg mL⁻¹ (at 3σ) was obtained. The linear equation is ΔI = 0.401 lg c + 1.948 with a correlation coefficient of 0.9906. The recovery is in the range of 93.0–104.7% for the cornflour samples. The proposed method offers a new strategy for the rapid, inexpensive, and real-time detection of ZEN.

An aptasensor based on a portable U-disk electrochemical workstation is demonstrated for the quantitative determination of zearalenone. The aptamer sensor exhibited excellent sensitivity, selectivity, reproducibility.     

Flexible and high energy density solid-state asymmetric supercapacitor based on polythiophene nanocomposites and charcoal

An asymmetric supercapacitor (ASC) was constructed using a polythiophene/aluminium oxide (PTHA) nanocomposite as an anode electrode and charcoal as a cathode electrode. The highest specific capacitance (C_sp) of the PTHA electrode was found to be 554.03 F g⁻¹ at a current density (CD) of 1 A g⁻¹ and that of the charcoal electrode was 374.71 F g⁻¹ at 1.4 A g⁻¹, measured using a three electrode system. The maximum C_sp obtained for the assembled PTHA//charcoal asymmetric supercapacitor (ASC) was 265.14 F g⁻¹ at 2 A g⁻¹. It also showed a high energy density of 42.0 W h kg⁻¹ at a power density of 735.86 W kg⁻¹ and capacitance retention of 94.61% even after 2000 cycles. Moreover, it is worth mentioning that the asymmetric device was used to illuminate a light emitting diode (LED) for more than 15 minutes. This PTHA//charcoal ASC also possesses stable electrochemical properties in different bending positions and hence finds a promising application in flexible, wearable and portable energy storage electronic devices.

A high energy density flexible solid-state asymmetric supercapacitor is fabricated using polythiophene nanocomposites and charcoal which exhibits stable electrochemical properties in different bending position.     

Electrochemical behaviour of cellulose/reduced graphene oxide/carbon fiber paper electrodes towards the highly sensitive detection of amitrole

Amitrole is a non-selective triazole herbicide that is widespread used to control a variety of weeds in agriculture, but it may pollute the environment and do harm to organisms. Thus, it is of critical significance to enlist a low-cost, sensitive, stable and renewable method to detect amitrole. In this paper, electrochemical experiments were carried out using carbon fibers/reduced graphene oxide/cellulose paper electrodes, which demonstrated good electrocatalytic performance for amitrole detection. The electrochemical process of amitrole on the surface of the reduced paper electrode was a quasi-reversible reaction controlled by diffusion. Cyclic voltammetry and the amperometric i–t curve method were used for amitrole determination at a micro molar level and higher-concentration range with the following characteristics: linear range 5 × 10⁻⁶ mol L⁻¹ to 3 × 10⁻⁵ mol L⁻¹, detection limit 2.44 × 10⁻⁷ mol L⁻¹. In addition, the relative standard deviation of repeatability is 3.74% and of stability is 4.68%. The reduced paper electrode with high sensitivity, low detection limit, good stability and repeatability provides novel ideas for on-site amitrole detection in food and agriculture.

A cellulose/reduced graphene oxide/carbon fibers paper electrode exhibits high electrocatalytic performance for the oxidation of amitrole, showing high sensitivity, wide linear range and low detection limit.     

Effective screen-printed potentiometric devices modified with carbon nanotubes for the detection of chlorogenic acid: application to food quality monitoring

All-solid state screen-printed electrodes were fabricated for chlorogenic acid (CGA) detection. The screen-printed platforms were modified with multi-walled carbon nanotubes (MWCNTs) to work as a lipophilic solid-contact transducer. The sensing-membrane was plasticized with a suitable solvent mediator and incorporating [Ni^II(bathophenanthroline)₃][CGA]₂ complex as a sensory material. In a 30 mM phosphate solution (buffer, pH 6), the sensor revealed a Nernstian-response towards CGA ions with a slope of −55.1 ± 1.1 (r² = 0.9997) over the linear range 1.0 × 10⁻⁷ to 1.0 × 10⁻³ (0.035–354.31 μg mL⁻¹) with a detection limit 7.0 × 10⁻⁸ M (24.8 ng mL⁻¹). It revealed a stable potentiometric response with excellent reproducibility and enhanced selectivity over several common ions. Short-term potential stability and the interfacial sensor capacitance was estimated using both electrochemical-impedance spectroscopy (EIS) and chronopotentiometry techniques. The presented electrochemical platform revealed the merits of design simplicity, ease of miniaturization, good potential-stability, and cost-effectiveness. It is successfully applied to CGA determination in different coffee beans extracts and juice samples. The data obtained were compared with those obtained by liquid chromatography reference method (HPLC).

All-solid state screen-printed electrodes were fabricated for chlorogenic acid (CGA) detection.     

Nanocellulose/polypyrrole aerogel electrodes with higher conductivity via adding vapor grown nano-carbon fibers as conducting networks for supercapacitor application

Nanocellulose-based conductive materials have been widely used as supercapacitor electrodes. Herein, electrode materials with higher conductivity were prepared by in situ polymerization of polypyrrole (PPy) on cellulose nanofibrils (CNF) and vapor grown carbon fiber (VGCF) hybrid aerogels. With increase in VGCF content, the conductivities of CNF/VGCF aerogel films and CNF/VGCF/PPy aerogel films increased. The CNF/VGCF₂/PPy aerogel films exhibited a maximum value of 11.25 S cm⁻¹, which is beneficial for electron transfer and to reduce interior resistance. In addition, the capacitance of the electrode materials was improved because of synergistic effects between the double-layer capacitance of VGCF and pseudocapacitance of PPy in the CNF/VGCF/PPy aerogels. Therefore, the CNF/VGCF/PPy aerogel electrode showed capacitances of 8.61 F cm⁻² at 1 mV s⁻¹ (specific area capacitance) and 678.66 F g⁻¹ at 1.875 mA cm⁻² (specific gravimetric capacitance) and retained 91.38% of its initial capacitance after 2000 cycles. Furthermore, an all-solid-state supercapacitor fabricated by the above electrode materials exhibited maximum energy and power densities of 15.08 W h Kg⁻¹, respectively. These electrochemical properties provide great potential for supercapacitors or other electronic devices with good electrochemical properties.

The electrochemical performances of nanocellulose-based electrode materials were improved via building nano-carbon conducting networks.     

Voltammetric determination of Salmonella typhimurium in minced beef meat using a chip-based imprinted sensor

Early detection of pathogens is necessary for food quality monitoring, and increasing the survival rate of individuals. Conventional microbiological methods used to identify microorganisms, starting from bacterial culture and ending with advanced PCR gene identification, are time-consuming, laborious and expensive. Thus, in this study, a bacterial imprinted polymer (BIP)-based biosensor was designed and fabricated for rapid and selective detection of Salmonella typhimurium. Bio-recognition sites were made by creating template-shaped cavities in the electro-polymerized polydopamine matrices on a gold screen-printed electrode. The overall changes of the sensor, during the imprinting process, have been investigated with cyclic voltammetry, atomic force microscopy and scanning electron microscopy. The assay optimization and validation were accomplished, hence the highest sensitivity and selectivity towards S. typhimurium were achieved. As a result, a very low limit of detection of 47 CFU ml⁻¹, and a limit of quantification of 142 CFU ml⁻¹ were achieved using the newly-developed biosensor. No interference signals were detected when the S. typhimurium was tested in a mixed culture with other non-targeted pathogens such as Staphylococcus aureus, Listeria monocytogenes and Campylobacter jejuni. Eventually, the biosensor was applied to minced beef meat samples offering not only fast detection but also direct determination with no bacterial enrichment steps.

A bacterial imprinted polymer (BIP)-based biosensor was designed and fabricated for rapid and selective detection of Salmonella typhimurium in minced beef meat.