Bare Screen-printed Electrode Research Articles

Electrochemical Biosensor Enabling Sensitive Detection of miRNA Biomarkers

Biomarkers are becoming increasingly important for early diagnosis, exploration of responses to medication, and assessment of therapeutic efficacy of various diseases [1]. Increasing evidence shows that miRNAs can be employed as biomarkers for cancer and cardiovascular diseases. In this context, the development of powerful electrochemical diagnostic tools has grown in interest due to their sensitivity, speed, and low cost [1]. Additionally, electrochemical technologies offer a facile means to fabricate well-defined nanostructured surfaces in a controlled environment. The gold (Au)-based surface stands out for its ability to improve charge transfer characteristics, enhancing conductivity. It also serves as a stable substrate for further modification, enabling the detection of target analytes [2]. Here, we utilized an electrochemical platform by using a 3-electrode carbon-based screen-printed electrode (SPE) electrochemically modified with gold and subsequently attached a specific DNA-based redox probe to detect low levels of miRNAs as a biomarker. Our design was applied to detect miRNA-1 (5′-TGG AAT GTA AAG AAG TAT GTA T-3′), demonstrating exceptional sensitivity and a low detection limit (LOD) of 120 fM. We also discuss how the developed platform broadly benefits numerous other miRNA sequences. Device preparation method: A screen-printed electrode (SPE) consisting of a 3 mm diameter carbon working electrode, an Ag reference electrode, and a carbon counter electrode was used as a base for device development. The bare SPE was activated during 10 cycles of cyclic voltammetry (CV) with potentials ranging from -0.5 to +1 V at a scan rate of 20 mVs-1 using PBS as the electrolyte. Before gold electrodeposition, the activated SPE was rinsed with PBS and deionized water. The electrode was submerged in a solution of 115 mM HAuCl4 (in 0.5 M H2SO4) during 10 CV cycles with the same parameters described above. Next, the DNA-probe sequence was attached to the working surface of the Au-decorated screen-printed electrode (Au-SPE). The DNA-probe sequence was modified in advance with C6-S-S-R at the 5′ end (enabling covalent binding onto Au) and methylene blue (MB) at the 3′ end (allowing electron transport at the electrode). Before modification of SPE, the disulfide bond was reduced using tris(2-carboxyethyl)-phosphine hydrochloride) (TCEP) to enable covalently attachment of the HS-DNA-MB probe to the Au-SPE [2]. The attachment of the DNA-probe sequence was achieved by placing 10 µL of the diluted probe onto the working electrode area and allowing for 1 hour of modification at room temperature to take place, as shown in Fig. 1(A). Results & Discussion: The device was evaluated for analytical performance in the presence of increasing target concentrations, as shown in Fig. 1 (A). In the absence of a miRNA-1 target, the stem-loop structure of the DNA probe remains closed, forcing the redox MB-reporter into proximity to the electrode, allowing for efficient electron transport. In the presence of miRNA-1, the target molecule binds to a complementary sequence of the DNA probe, opening the loop. The structure assumes a relatively rigid conformation where MB is farther from the gold surface, reducing the observed signal, Fig. 1 (B). The observed current gradually decreases upon the successive addition of miRNA target molecules for both cathodic, Ipc, and anodic, Iac, peaks. Using the dependence of anodic peak, Iac, the sensor was calibrated as a function of added miRNA-1 concentration in the range between 0 and 4 nM. Using the calibration curve shown in Fig. 1 (C), the detection limit was estimated to be 120 femtoM. The device was further tested for stability and exhibited robust performance over an extended period displaying minimal fluctuations in the recorded current. While we demonstrate the sensitive detection of miRNA-1, the design can be easily adapted for other miRNA sequences [3]. Additionally, it introduces exciting prospects for multiplexing, where multiple miRNA sequences can be easily detected with only minor adjustments to the established design. Fig. 1 (A) Schematics of the device fabrication process and mechanism for the development of Smart Electrochemical Sensors setup; (B) Cyclic Voltammetry (CV) responses during Au electrodeposition (black) in the absence of miRNA-1 target (red) and presence of miRNA-1 target (blue); (C) The device response curve concerning successive addition of miRNA-1 target molecule into the device chamber (different concentrations of target from 0 to ~ 4000 pM), the inset shows CV response used to plot the calibration curve. Acknowledgment: NSF DMR 2204027, US DOE EPSCoR DE-SC0024284

Deciphering the Role of p-Type ZnCo2O4 Semiconductor Nanoflakes for Selective Enhancement of Voltammetric Responses Toward Redox Species System: Interfacial Electron-Transfer Kinetics and Adsorption Capacity

In this study, we describe experimental efforts to decipher the role of ZnCo2O4 nanoflakes (ZCO-NFs) for selective enhancement of voltammetric responses of screen-printed electrode (SPE) toward redox species system. The ZCO-NFs sample was characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and UV–vis spectroscopy. The electrochemical characterization of bare SPE and modified SPE electrodes was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Mott−Schottky analysis. A series of redox systems including paracetamol (PA), dopamine (DA), chloramphenicol (CAP), furazolidone (FZD), p-nitrophenol (p-NP), carbaryl (CBR), ofloxacin (OXF), and erythromycin (ERY) were selected to investigate for (i) reversible redox process, (ii) irreversible electrochemical oxidation process, and (iii) irreversible electrochemical reduction process on both bare-SPE and ZCO-NFs/SPE electrodes. The obtained results showed that ZCO-NFs possess the selective enhancement of electrochemical response for redox systems with an increase of 24%–90% for PAR, DA, FZD, CAP, and CBR and a decrease of 13%–49% for p-NP, ERY, and OFX. The different electrochemical response of redox species at nanostructured semiconductor electrodes is attributed to the contribution of both the adsorption capacity of redox species and the interfacial electron transfer process between electrode and redox species. An insight into the interfacial electron transfer kinetics and its contribution to the enhancement of electrochemical response on p-type semiconductor electrode is helpful in designing high-performance sensing platforms based on spinel oxide nanostructures.

Application of two-dimensional zeolitic imidazolate framework-L (Co)/multi-walled carbon nanotube nanocomposite modified electrode as a sensitive voltammetric sensor for determination of cannabidiol

In this study, a two-dimensional (2D) leaf-like zeolitic imidazolate framework-L (Co)/multi-walled carbon nanotubes (2D ZIF-L (Co)/MWCNTs) nanocomposite was synthesized using a simple method and utilized as an effective material for voltammetric determination of cannabidiol (CBD). The morphology, structure, and composition of the synthesized ZIF-L (Co)/MWCNTs were characterized through techniques including field-emission scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRD), and Energy Dispersive X-ray spectroscopy (EDS). The screen-printed electrode (SPE) modified with ZIF-L (Co)/MWCNTs was fabricated by the drop-casting of ZIF-L (Co)/MWCNTs suspension on the SPE surface. To study the electrochemical behavior of CBD, cyclic voltammetry (CV), chronoamperometry, and differential pulse voltammetric (DPV) analysis was performed, and compare the oxidation behavior on ZIF-L (Co)/MWCNTs/SPE and bare SPE. The peak current of the DPV of CBD showed a linear increase with its concentration in the range of 0.5 μM – 280.0 μM, and a low detection limit (LOD) of 0.02 μM was achieved. Moreover, the proposed sensor was successfully used to determine CBD in real specimens.

Nanomolar detection of organic pollutant -tartrazine in food samples using zinc-metal organic framework/carbon nano fiber - composite modified screen-printed electrode

In this study, we achieved a significant breakthrough by applying a binder-free Zn-MOF@CNF composite as a modifier on a screen-printed electrode (SPE) to achieve highly sensitive and selective detection of tartrazine (TRZ). This composite, with its unique rod-like structure for Zn-MOF and a curl thread-like morphology for carbon nanofibers (CNF), demonstrated a remarkable threefold increase in the sensing current of TRZ at a lower anodic oxidation potential (0.92 V) compared to the bare SPE. The Zn-MOF@CNF/SPE also exhibited a reduced charge transfer resistance of 61.9 Ω, elevated electrochemical active surface area of 0.416 cm2, and high heterogeneous electron transfer rate constant (k0) of 9.77×10−5 cm s−1. Furthermore, it displayed a broad linear range from 0.2 μM to 1000 μM with a remarkable sensitivity of 0.136 µAµM−1cm−2 and an impressive detection limit of 54 nM. Ultimately, the developed Zn-MOF@CNF/SPE sensor demonstrated excellent selectivity amidst various structurally similar overlapping species, outstanding repeatability, reproducibility, and stability in TRZ detection. The practical applicability of Zn-MOF@CNF/SPE was validated through 97 – 100.9 % recovery results in food samples such as jelly, ice cream, soft drinks, and candies.

Synergistic Effect of 3D/2D Vanadium Diselenide/Tungsten Diselenide Hybrid Materials: Electrochemical Detection of 5-Nitroquinoline a Hazard to the Aquatic Environment.

The development of multidimensional structured electrode materials with simple synthetic methods and their electrochemical sensing ability against environmental pollution is still a challenge. In this article, we propose a hybrid formed using multidimensional (3D/2D) vanadium diselenide microspheres and tungsten diselenide nanosheets (VSe2/WSe2) for the electrochemical detection of 5-nitroquinoline (5-NQ), a highly toxic and hazardous substance that is polluting aquatic life due to increasing industrial activities. The 3D/2D VSe2/WSe2 hybrids were prepared by a simple solvothermal method and their morphological and structural analysis was confirmed by various spectroscopy and analytical techniques such as powder X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy-energy dispersive X-ray spectroscopy, transmission electron microscopy, cyclic voltammetry, and differential pulse voltammetry. The proposed 3D/2D architecture showed a strong synergistic effect between the two components as well as high electrical conductivity. As a result, an increased peak current for the reduction and detection of 5-NQ was achieved compared to other modified and unmodified disposable screen-printed electrodes (SPE), such as bare SPE, VSe2/SPE, and WSe2/SPE. Under the optimized electrochemical conditions, VSe2/WSe2/SPE showed large linear response ranges (0.012-1053, 1183-3474 μM), a low detection limit (0.002 μM), good sensitivity along with good selectivity, and repeatability for the detection of 5-NQ. With this prominent electrochemical behavior, the VSe2/WSe2 electrode has clear potential to produce high-performance sensor devices.

Eco-friendly fabrication of silver nanoparticle-decorated electrodes for aqueous bisphenol A sensing

This work fabricated an electrochemical sensor for detecting bisphenol A (BPA) by employing silver nanoparticles (AgNPs) synthesized through an eco-friendly approach. The AgNPs were produced using parsley leaf extract, which acted as a reducing and stabilizing agent in the synthesis process. The AgNPs synthesized using the green approach exhibited an average size of 15.2 ± 2.1 nm. The AgNP-modified screen-printed electrode (SPE) exhibited excellent electrocatalytic activity towards BPA oxidation, with an enhanced peak current of 28.6 μA compared to 5.2 μA for the bare SPE. The optimized sensor exhibited impressive analytical performance, boasting a broad linear range spanning 0.05–5 μM for BPA detection. Remarkably, it achieved a low limit of detection of 0.02 μM, coupled with high sensitivity. Furthermore, the sensor demonstrated commendable reproducibility, with a RSD of 3.6%, and exceptional repeatability, evidenced by an RSD of 2.4%. Upon evaluating the sensor's performance in analyzing real water specimens, the recoveries oscillated between 95.8% and 103.5%, accompanied by RSDs not exceeding 4.2%, thereby demonstrating its successful application for BPA detection. The eco-friendly synthesis approach and superior analytical performance make the AgNP-modified SPE a promising tool for on-site environmental monitoring and drinking water analysis.

A Non-Disposable Electrochemical Sensor Based on Laser-Synthesized Pd/LIG Nanocomposite-Modified Screen-Printed Electrodes for the Detection of H2O2.

There have been many studies on the significant correlation between the hydrogen peroxide content of different tissues or cells in the human body and the risk of disease, so the preparation of biosensors for detecting hydrogen peroxide concentration has been a hot topic for researchers. In this paper, palladium nanoparticles (PdNPs) and laser-induced graphene (LIG) were prepared by liquid-phase pulsed laser ablation and laser-induced technology, respectively. The complexes were prepared by stirring and used for the modification of screen-printed electrodes to develop a non-enzymatic hydrogen peroxide biosensor that is low cost and mass preparable. The PdNPs prepared with anhydrous ethanol as a solvent have a uniform particle size distribution. The LIG prepared by laser direct writing has good electrical conductivity, and its loose porous structure provides more adsorption sites. The electrochemical properties of the modified electrode were characterized by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. Compared with bare screen-printed electrodes, the modified electrodes are more sensitive for the detection of hydrogen peroxide. The sensor has a linear response range of 5 µM-0.9 mM and 0.9 mM-5 mM. The limit of detection is 0.37 µM. The above conclusions indicate that the hydrogen peroxide electrochemical biosensor prepared in this paper has great advantages and potential in electrochemical catalysis.

Simple Fabrication of Mesoporous Praseodymium Cerate via an Eco-Friendly Route for Development of Carbendazim Electrochemical Sensor

This study introduces an easy and efficient ultrasonic-assisted approach for the preparation of mesoporous praseodymium cerate (MS-Pr2Ce2O7) by employing maltose as a novel and eco-friendly capping agent. Some techniques such as field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used for the characterization of nanoparticles. For the detection of carbendazim (CBZ), a new electrochemical sensor based on the modified screen-printed electrode (SPE) has been presented. The modification of the electrode surface was made using praseodymium cerate. Cyclic voltammetry (CV) has been utilized to study the electrochemical behavior of the MS-Pr2Ce2O7/SPE and better electrochemical performance was observed compared to bare SPE for the oxidation of CBZ. The optimization of pH and accumulation time was done. Under optimized conditions (pH = 7 and accumulation time:160 s), the oxidation peak currents that responded to CBZ concentration between 0.01 and 175.0 μM exhibited a linear relationship (R2 = 0.9977), and the detection limit was calculated 4.6 nM. In addition, MS-Pr2Ce2O7/SPE showed high stability and repeatability. At last, real sample tests of the MS-Pr2Ce2O7/SPE were validated by applying them to the detection of CBZ in vegetable samples, which were promising in our preliminary experiments.

Optimization of Gold Nanoparticles Electrodeposition Duration on Screen Printed Electrode to Enhance Electrochemiluminescence of Nitrogen-doped Carbon Dots

In this work, the electrodeposition method was utilized to form gold nanoparticles on a carbon screen-printed electrode (SPE) using chronoamperometry at -0.4 V with various durations from 50 to 200 seconds. Scanning Electron Microscopy (SEM) images have proven that the electrodeposition method is capable of uniformly forming AuNPs on SPE (AuNPs- SPE). Apart from that, electrodeposition durations have increased the size of AuNPs by up to 66% based on average size measurements using ImageJ software. It can be observed that long electrodeposition durations permit the agglomeration of AuNPs on the electrode surface. The effect of electrodeposition duration on electrocatalytic performance in potassium ferricyanide and electrochemiluminescence (ECL) intensity of nitrogen-doped carbon dots (NCDs) was evaluated. Cyclic voltammetry (CV) of ferricyanide demonstrates that as the electrodeposition duration increases, AuNPs-SPE shows better electrochemical performance than bare SPE. ECL of NCDs displays that 100 s electrodeposition durations give the highest ECL intensity of 184% compared to bare SPE and have been chosen as the optimum parameter. The ECL mechanisms of bare SPE and AuNPs-SPE reveal that AuNPs- SPE has greater electrochemical and ECL performance than bare SPE, as evidenced by the CV of AuNPs-SPE having a faster reduction current, which rises to 87.2% ECL intensity and 510 mV faster ECL occurrence. These phenomena confirmed that the electrodeposition of AuNPs has improved the conductivity of SPE.

Comparative electrochemical properties of polyaniline/carbon quantum dots nanocomposites modified screen-printed carbon and gold electrodes

In this study, carbon quantum dots (Cdots) synthesized from a pencil graphite precursor using a bottom-up method were incorporated into polyaniline (PANI) to form Cdots-PANI nanocomposite. Cdots, PANI and Cdots-PANI nanocomposites were characterized using the Fourier-Transform infrared spectroscopy (FT-IR), UV–visible spectroscopy (UV–vis), X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The FT-IR spectra of graphene and Cdots show the emergence of a peak at 3500 cm−1, which was initially absent in graphene, after the formation of Cdots, among other peaks. The peak at 3500 cm−1 and the stretching vibration at 1647 cm−1 suggest the presence of –OH and C=C in the Cdots. The FT-IR spectra of PANI/Cdots and PANI show that the peaks in PANI shifted to higher wavenumbers after composite formation. Similarly, the UV–visible spectra of the PANI/Cdots composite revealed a hypsochromic shift of the characteristic PANI peaks at 320 and 600 nm to 300 and 560 nm, respectively. Electrochemical characterization of Cdots, PANI and Cdots-PANI nanocomposites was done with screen-printed carbon electrodes (SPCE) and screen-printed gold electrodes (SPAuE) modified with the nanomaterials and the nanocomposites. The electrochemical properties of the as-synthesized nanomaterials and the nanocomposite were investigated with Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) in 10 mM K3[Fe(CN)6] solution using the bare screen-printed electrodes and the modified electrodes. The modified electrodes gave higher anodic peak current (Ipa) responses and lower charge transfer resistance (Rct) values in the redox probe than the bare electrodes. The SPCE-Cdots-PANI nanocomposite-modified electrode exhibited better redox potentials, faster electron transfer kinetics, larger surface area, and greater stability than the bare electrodes and the other modified electrodes. The outstanding electrochemical properties of SPCE-Cdots/PANI underscores its potentials as a sensitive electrochemical sensor for a wide range of analytes.

Adsorption and Electropolymerization of p-Aminophenol Reduces Reproducibility of Electrochemical Immunoassays

Electrochemical immunoassays are a class of biosensors that achieve high specificity, low detection limits, and low cost attributed to strong antibody-antigen interactions and inexpensive electrochemical instrumentation. Electrochemical assays typically use an enzyme/substrate pair to enable electrochemical signal production. p-Aminophenyl phosphate is a commonly used enzymatic substrate which is hydrolyzed into p-aminophenol (PAP)by alkaline phosphatase. PAP exhibits low oxidation potential and electrochemical reversibility, making it an appealing candidate for assay design. The electrochemical oxidative signal from PAP is increased by its adsorption to the electrode. This is further confirmed by the prevention of PAP adsorption via self-assembled monolayers on gold electrodes reducing PAP’s oxidative current. On bare screen-printed electrodes (SPE), PAP adsorption results in oxidative current variability depending on the electroactive surface area of the working electrode. This variability could not be remedied by cleaning and reusing the same gold SPE. However, adsorption of PAP displays concentration dependence, as the decrease ofthe PAP concentration to 3.8 μM greatly improved the consistency of the measurements. PAP use is also limited in continuous monitoring applications as multiple PAP oxidations on the same electrode caused polymerization. The results from this study suggest that the use of PAP production in immunoassays with SPEs must be fine-tuned and electrodes must be cleaned or disposed of between measurements.

Novel ruthenium-doped vanadium carbide/polymeric nanohybrid sensor for acetaminophen drug detection in human blood

The use of advanced electroactive catalysts enhances the performance of electrochemical biosensors in real-time biomonitoring and has received much attention owing to its excellent physicochemical and electrochemical possessions. In this work, a novel biosensor was developed based on the electrocatalytic activity of functionalized vanadium carbide (VC) material, including VC@ruthenium (Ru), VC@Ru-polyaniline nanoparticles (VC@Ru-PANI-NPs) as non-enzymatic nanocarriers for the fabrication of modified screen-printed electrode (SPE) to detect acetaminophen in human blood. As-prepared materials were characterized using SEM, TEM, XRD, and XPS techniques. Biosensing was carried out using cyclic voltammetry and differential pulse voltammetry techniques and has revealed imperative electrocatalytic activity. A quasi-reversible redox method of the over-potential of acetaminophen increased considerably compared with that at the modified electrode and the bare SPE. The excellent electrocatalytic behaviour of VC@Ru-PANI-NPs/SPE is attributed to its distinctive chemical and physical properties, including rapid electron transfer, striking ᴫ-ᴫ interface, and strong adsorptive capability. This electrochemical biosensor exhibits a detection limit of 0.024 μM, in a linear range of 0.1–382.72 μM with a reproducibility of 2.45 % relative standard deviation, and a good recovery from 96.69 % to 105.59 %, the acquired results ensure a better performance compared with previous reports. The enriched electrocatalytic activity of this developed biosensor is mainly credited to its high surface area, better electrical conductivity, synergistic effect, and abundant electroactive sites. The real-world utility of the VC@Ru-PANI-NPs/SPE-based sensor was ensured via the investigation of biomonitoring of acetaminophen in human blood samples with satisfactory recoveries.

A screen-printed electrode modified with gold nanoparticles/cellulose nanocrystals for electrochemical detection of 4,4′-methylene diphenyl diamine

Developing simple, cost-effective, easy-to-use, and reliable analytical devices if of utmost importance for the food industry for rapid in-line checks of their products that must comply with the provisions set by the current legislation. The purpose of this study was to develop a new electrochemical sensor for the food packaging sector. More specifically, we propose a screen-printed electrode (SPE) modified with cellulose nanocrystals (CNCs) and gold nanoparticles (AuNPs) for the quantification of 4,4′-methylene diphenyl diamine (MDA), which is one of the most important PAAs that can transfer from food packaging materials into food stuffs. The electrochemical performance of the proposed sensor (AuNPs/CNCs/SPE) in the presence of 4,4′-MDA was evaluated using cyclic voltammetry (CV). The modified AuNPs/CNCs/SPE showed the highest sensitivity for 4,4′-MDA detection, with a peak current of 9.81 μA compared with 7.08 μA for the bare SPE. The highest sensitivity for 4,4′-MDA oxidation was observed at pH = 7, whereas the detection limit was found at 57 nM and the current response of 4,4′-MDA rose linearly as its concentration increased from 0.12 μM to 100 μM. Experiments using real packaging materials revealed that employing nanoparticles dramatically improved both the sensitivity and the selectivity of the sensor, which can be thus considered as a new analytical tool for quick, simple, and accurate measurement of 4,4′-MDA during converting operations.

Electrochemical Sensor Based on Ni-Co Layered Double Hydroxide Hollow Nanostructures for Ultrasensitive Detection of Sumatriptan and Naproxen.

In this work, Ni-Co layered double hydroxide (Ni–Co LDH) hollow nanostructures were synthesized and characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), and Fourier-transform infrared spectroscopy (FT-IR) techniques. A screen-printed electrode (SPE) surface was modified with as-fabricated Ni–Co LDHs to achieve a new sensing platform for determination of sumatriptan. The electrochemical behavior of the Ni–Co LDH-modified SPE (Ni-CO LDH/SPE) for sumatriptan determination was investigated using voltammetric methods. Compared with bare SPE, the presence of Ni-Co LDH was effective in the enhancement of electron transport rate between the electrode and analyte, as well as in the significant reduction of the overpotential of sumatriptan oxidation. Differential pulse voltammetry (DPV) was applied to perform a quantitative analysis of sumatriptan. The linearity range was found to be between 0.01 and 435.0 μM. The limits of detection (LOD) and sensitivity were 0.002 ± 0.0001 μM and 0.1017 ± 0.0001 μA/μM, respectively. In addition, the performance of the Ni-CO LDH/SPE for the determination of sumatriptan in the presence of naproxen was studied. Simultaneous analysis of sumatriptan with naproxen showed well-separated peaks leading to a quick and selective analysis of sumatriptan. Furthermore, the practical applicability of the prepared Ni-CO LDH/SPE sensor was examined in pharmaceutical and biological samples with satisfactory recovery results.

Electrooxidation of Phenol on Polyelectrolyte Modified Carbon Electrodes for Use in Insulin Pump Infusion Sets.

Many type 1 diabetes patients using continuous subcutaneous insulin infusion (CSII) suffer from the phenomenon of unexplained hypoglycemia or "site loss." Site loss is hypothesized to be caused by toxic excipients, for example, phenolic compounds within insulin formulations that are used as preservatives and stabilizers. Here, we develop a bioinspired polyelectrolyte-modified carbon electrode for effective electrooxidative removal of phenol from insulin and eventual incorporations into an infusion set of a CSII device. We modified a carbon screen printed electrode (SPE) with poly-L-lysine (PLL) to avoid passivation due to polyphenol deposition while still removing phenolic compounds from insulin injections. We characterized these electrodes using scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) and compared their data with data from bare SPEs. Furthermore, we performed electrochemical measurements to determine the extent of passivation, and high-performance liquid chromatography (HPLC) measurements to confirm both the removal of phenol and the integrity of insulin after phenol removal. Voltammetry measurements show that electrode passivation due to polyphenol deposition is reduced by a factor of 2X. HPLC measurements confirm a 10x greater removal of phenol by our modified electrodes relative to bare electrodes. Using bioinspired polyelectrolytes to modify a carbon electrode surface aids in the electrooxidation of phenolic compounds from insulin and is a step toward integration within an infusion set for mitigating site loss.

Modification of polyacrylonitrile-derived carbon nanofibers and bacteriophages on screen-printed electrodes: A portable electrochemical biosensor for rapid detection of Escherichia coli

A facile method was developed for fabricating a disposable phage-based electrochemical biosensor for the detection of Escherichia coli. Bare screen-printed electrodes (SPEs) were modified using a two-step drop-casting method, in which polyacrylonitrile-derived electrospun carbon nanofibers (CNFs) were deposited, followed by E. coli bacteriophage immobilization. The deposition of CNFs increased the surface area for bacteriophage immobilization while maintaining a conductive link for ferro/ferricyanide redox transitions. Cyclic voltammetry and electrochemical impedance spectroscopy confirmed that the CNF modification increased the electron-transfer rate, whereas bacteriophages and E. coli blocked electron transfer at the electrode. The biosensor achieved a response within 10 min and a linear response in the E. coli concentration range of 102–106 CFU/mL. A limit of detection (LOD) of 36 CFU/mL in phosphate-buffered saline was achieved, which is the lowest LOD reported thus far for phage-based disposable SPE sensors. The biosensor exhibited recovery rates between 106 % and 119 % for E. coli detection in apple juice. The proposed fabrication method allowed electrodes to be obtained from different production batches with remarkable consistency and reproducibility, and they remained stable at room temperature for one month. Thus, a phage-based disposable SPE that can be used for bacterial detection was developed for the first time.

Amplified electrochemical sensor employing screen-printed electrode modified with Ni-ZIF-67 nanocomposite for high sensitive analysis of Sudan I in present bisphenol A

This study utilized a facile one-pot protocol to synthesize Ni-cobalt zeolitic imidazolate framework (Ni-ZIF-67) nanocomposite, which was then characterized by Fourier transform infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectroscopy and scanning electron microscopy. The Ni-ZIF-67 nanocomposite was subsequently applied to modify a screen-printed electrode (SPE) as a durable sensor for detection of Sudan I concomitantly with bisphenol A (BPA), with remarkably increased electrochemical response when comparing with a bare SPE. The results showed the calibration plot to be linear in the concentration range between 0.03 μM and 535.0 μM, with a narrow limit of detection of 9.0 nM (S/N = 3). Our proposed protocol was successful in detecting target analytes in real tap water and food specimens.

Bismuth-Nanocomposites Modified SPCEs for Non-Enzymatic Electrochemical Sensors

We present newly developed electrochemical sensors based on screen-printed carbon electrodes functionalized with HO-BiONO3, polyethylene glycol coated HO-BiONO3, and Bi5O7 NO3. The performance of these sensors has been studied by cyclic voltammetry experiments and compared in terms of the kinetic rate constant, the sensitivity, and the limit of detection. The polyethylene glycol coated HO-BiONO3 sensor was found with higher oxidation peak current, lower oxidation peak potential, and assured a faster paracetamol reaction due to a higher kinetic rate constant of 42.0 ± 9.8 ms−1. This sensor also possessed lesser peak-to-peak separation ( $\Delta \text{E}_{p}$ ) of 243 ± 10 mV with a higher chance of reversible reaction compared to other developed sensors. The polyethylene glycol coated HO-BiONO3 sensor also registered a sensitivity of 43.50 ± $0.54~\mu \text{A}$ /mM with a relative standard deviation of 1.24 %, which is more than double compared to the bare screen-printed electrode with a limit of detection of 2.24 ± $0.03~\mu \text{M}$ ( $\text{R}^{2} =0.998$ , n = 3). HO-BiONO3 and Bi5O7 NO3 sensors also performed much better with slightly higher kinetic rate constant and higher sensitivity than the bare screen-printed electrode sensor.

3D-Printed Flow Cells for Aptamer-Based Impedimetric Detection of E. coli Crooks Strain.

Electrochemical spectroscopy enables rapid, sensitive, and label-free analyte detection without the need of extensive and laborious labeling procedures and sample preparation. In addition, with the emergence of commercially available screen-printed electrodes (SPEs), a valuable, disposable alternative to costly bulk electrodes for electrochemical (bio-)sensor applications was established in recent years. However, applications with bare SPEs are limited and many applications demand additional/supporting structures or flow cells. Here, high-resolution 3D printing technology presents an ideal tool for the rapid and flexible fabrication of tailor-made, experiment-specific systems. In this work, flow cells for SPE-based electrochemical (bio-)sensor applications were designed and 3D printed. The successful implementation was demonstrated in an aptamer-based impedimetric biosensor approach for the detection of Escherichia coli (E. coli) Crooks strain as a proof of concept. Moreover, further developments towards a 3D-printed microfluidic flow cell with an integrated micromixer also illustrate the great potential of high-resolution 3D printing technology to enable homogeneous mixing of reagents or sample solutions in (bio-)sensor applications.

Flow injection analysis of kojic acid in cosmetics by a carbon-nanotube modified screen-printed electrode

A novel carbon-nanotube modified screen-printed electrode (CNT/SPE) was successfully prepared and validated to be a useful detector in the flow injection system. Compared to a bare screen-printed electrode (SPE), CNT/ SPE improved the detection limit for kojic acid (KA). The detection limit on S/N = 3 was as low as 0.01 ppm. Furthermore, several factors, including the pH, applied potential, flow rate and coating quantity of CNT, were assessed. The attractive response of CNT/SPE has allowed it to be used for constant-potential FIA (Flow-Injection Analysis) of KA and indicates great potential for monitoring chromatographic effluents. The linear relationship between KA concentration (0.1-120 ppm) and the current response was established. Meanwhile five different CNT/SPEs for the detection KA of 20 ppm yielded a RSD value of 4.43%, indicating acceptable reproducibility of the present analysis. Finally, two real samples on the market were analyzed using the proposed system with appreciable results.