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A novel sensing material for L-hydroxyproline (Hyp) detection was developed by synthesizing a bismuth film (BiF) and poly(L-hydroxyproline) (Poly(Hyp)) on a screen-printed graphene electrode (SPGE). Initially, the BiF electrodeposition was produced on the SPGE surface, followed by the Poly(Hyp) electropolymerization, resulting in the obtained Poly(Hyp)/BiF/SPGE. The morphology of a sponge-like thin film of Poly(Hyp)/BiF on SPGE had uniform nanometer-sized cavities on the graphene surface, offering a large electroactive area for interaction with the target substance. Cyclic and differential pulse voltammetry was used to examine the sensing performance of the proposed sensor, which revealed that the Poly(Hyp)/BiF/SPGE had the highest response toward Hyp detection. This was attributed to BiF and Poly(Hyp) can facilitate the transfer of electrons at an electrode/solution interface, resulting in an effective sensor for the detection of Hyp. Under the optimal conditions, the quantification of the proposed sensor was found to be linearly related to Hyp concentrations in the range of 0.01-5.0 mM with a limit of detection of 9.2 μM. Moreover, the interference of other substances detected in biological fluids showed no effect based on the ±5% error, indicating good selectivity for Hyp detection. In real applications, the proposed assay successfully analyzed Hyp in human urine samples, yielding satisfactory results with recoveries in the acceptable range of 98%-102%. Therefore, this facilely synthesized approach could be a suitable candidate to obtain a material to fabricate a new sensor for the measurement of Hyp, an important biomarker in the human body., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Discovering alternative analytical techniques is crucial for practical applications; thus, this work aims to develop an innovative and simple electrochemical sensor for melanoma and the clinical diagnosis of related disorders by the simultaneous determination of 3,4-dihydroxy-L-phenylalanine (L-DOPA) and L-tyrosine (L-Tyr). The fabrication is based on the layer-by-layer electrodeposition of poly L-proline (poly(L-pro)) and nanodiamond (ND) onto a screen-printed graphene electrode (SPGE). The poly(L-pro)/ND/SPGEs were morphologically characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, and Raman spectroscopy followed by electrochemical investigation using cyclic voltammetry, differential pulse voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. These modifier-based electrodes pave a feasible way to unlock the coexisting interfering substances from screen-printing ink composition and improve the sensitivity. Additionally, computational chemistry calculations were performed to fully comprehend the sensing behavior on both target analytes. Under optimal conditions, the developed sensor provided linear concentration ranges of 0.075-50 μM, with a detection limit of 0.021 μM for L-DOPA, and 2.5-120 μM with a detection limit of 0.74 μM for L-Tyr. To demonstrate the reliability of the poly(L-pro)/ND/SPGE in practical application, it was successfully applied to the determination of these analytes in human urine and blood serum samples, with satisfactory recovery ranges (81.73-110.62% for L-DOPA and 82.17-110.01% for L-Tyr) and relative standard deviations (0.69-9.90% for L-DOPA and 0.40-9.55% for L-Tyr). Due to its simplicity, long-term stability (> 87.8% of their initial currents after 35 days), and portability, the developed sensor is a promising alternative analytical method for on-site clinical monitoring., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Sepsis, an infectious disease affecting millions of people's health worldwide each year, calls for urgent attention to an improvement of analytical devices. Chemiluminescence immunoassay is a typical diagnostic method utilized to assess the risk development of sepsis. However, due to its high-cost, delayed, and complicated procedure, the practical utilization is therefore undoubtedly limited, especially for point-of-care test. Herein, we fabricated for the first time an immunosensor based on dendritic copper nanostructures (CuNSs) combined with 4-aminobenzoic acid (4-AB, the diazonium salt) as antibody linker modified on a screen-printed graphene electrode for the early detection of the sepsis biomarker interleukin-6 (IL-6). The electrode fabrication is made by electrodeposition, thus eliminating the multistep of nanomaterial synthesis and time wasting. The resulting dendritic CuNSs significantly increase the effective surface area (1.2 times) and the sensor's performance. The morphology of this combination was characterized using CV, EIS, SEM, EDX, and FTIR techniques. In the detection process, the appearance of IL-6 suppresses the current response of the redox probe indicator measured by differential pulse voltammetry due to the antibody-antigen complex. The subtraction of signal (ΔI) was interpreted as IL-6 concentration. This sensor exhibited a linear range from 0.05 to 500 pg mL -1 with low detection limit of 0.02 pg mL -1 , proving a possibility for early sepsis screening. In addition, the established immunosensor can successfully quantify IL-6 in human serum sample, in which the results agreed well with those achieved using the standard approach, further showing high practical applicability of this developed immunosensor., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Amino acid conductive polymers can easily form a thin film on a sensor surface by an electrochemical process. Therefore, we are pioneers in reporting the electropolymerization of L-methionine on the surface of a screen-printed graphene electrode to obtain a disposable electrochemical sensor for determining drug metabolites (5-aminosalicylic acid (5-ASA) and sulfapyridine (SPD)) of sulfasalazine (SSZ) simultaneously. In this work, the developed sensor was facilely created through a single step of electropolymerization under mild conditions (0.1 M phosphate buffer pH 7.0) using cyclic voltammetry. Important parameters in the synthesis process were systematically investigated followed by surface composition and morphology studies. Then, analytical performances, comprising sensitivity, selectivity, stability, reproducibility, and sample preparation, were carefully evaluated. Under optimal conditions, the proposed methodology demonstrated a highly sensitive and selective simultaneous detection of 5-ASA and SPD with wide linear dynamic ranges of 1-50 μM and 80-250 μM and low detection limits of 0.60 and 0.57 μM for 5-ASA and SPD, respectively. To evaluate the potential of the designed sensor, it was successfully applied by simultaneously determining 5-ASA and SPD in real human urine samples on the same day (intra-day study) and on three different days (inter-day study).

This study aimed to create a miniaturized electrochemical platform for detecting As(III) contamination in herbal medicines. To reduce the operational steps of modification and determination, only a single drop of mixed standard Au(III) and sample solution is proposed to perform the electrochemical measurements using a screen-printed graphene electrode (SPGE). Square wave anodic stripping voltammetry was employed to integrate the simultaneous modification and determination processes. To perform the measurement, As(III) and Au(III) migrate to the SPGE surface while the reduction potential is held at -0.5 V, forming an Au-As intermetallic alloy. Then, As is stripped off for the electrochemical determination of As(III). The total assay time is less than 3 min. Under suitable conditions, the electrochemical sensing system can detect As(III) at concentrations ranging from 0.1 to 3.0 ppm, with a limit of quantification and limit of detection of 0.1 and 0.03 ppm, respectively. The applicability and accuracy of the proposed sensor were verified by determining As(III) in herbal medicinal samples, and they were found to be in line with the standard method (ICP-OES). The benefits of simple operation, rapid detection, portability, and low cost (<1 USD) make this a more powerful tool for routine monitoring and on-site analysis applications.

The electrochemical determination of five heavy metals is demonstrated using a wireless and card-sized potentiostat coupled with a smartphone through near-field communication (NFC) technology. A smartphone application was customized to command the NFC potentiostat, collect real-time signals, process the data, and ultimately display the quantities of the selected elements. The screen-printed graphene electrode (SPGE) was simply fabricated and modified using different nanomaterials for each heavy metal. Using differential pulse voltammetry (DPV) mode on the smartphone, the signal peaks were presented at + 10 mV for As(III), + 350 mV for Cr(VI), 0 mV for Hg(II), - 900 mV for Cd(II), and - 680 mV vs. Ag/AgCl for Pb(II). The linear ranges were 25-500, 250-25,000, 100-1,500, 25-750, 25-750 ng mL -1 with detection limits of 3.0, 40, 16, 2.0, and 0.95 ng mL -1 for As(III), Cr(VI), Hg(II), Cd(II), and Pb(II), respectively. The reproducibility in terms of relative standard deviation was less than 8.8% (n = 5 devices) of the developed SPGE coupled with the NFC potentiostat. Various samples for different applications (e.g., food safety and environmental monitoring) were analyzed and quantified using the proposed sensors. The results from this sensor indicate that there is no significant difference (95% confidence level) compared with those obtained from the traditional ICP-OES method, while the recoveries were found in the acceptable range of 80-111%. Hence, it can be deduced that this recent advanced technology of the NFC potentiostat developed for heavy metal analysis offers a highly sensitive and selective detection, yet the sensor remains compact, low-cost, and readily accessible to end-users., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

The high requirement for food quality control has inspired the creation of high-performance sensing, cost-effectiveness, and ease to use. Therefore, the aim of this work is to develop nonenzymatic electrochemical platforms for direct detection of histamine using unmodified screen-printed graphene electrodes (SPGEs) for their applications such as evaluation of fish freshness. In alkaline media (0.2 M NaOH), unmodified SPGEs showed a very low oxidation potential of histamine at +0.58 V (vs. Ag/AgCl) avoiding perturbations from other biogenic amines. The developed method offers an excellent selectivity, sensitivity (a limit of detection (at 3SD/slope) of 0.62 mg L -1 ) and wide working linear range (5-100 mg L -1 ) for histamine detection. In addition, the proposed method was successfully applied to detect histamine in canned fish samples with recovery values ranging from 90.72% to 101.21%. Therefore, this newly proposed method is promising as an alternative choice for the determination of histamine in fish samples and related food products.

Ferritin, a blood cell protein containing iron, is a crucial biomarker that is used to estimate the risk assessment of iron deficiency anemia. For point-of-care analysis, a reliable, cost-effective, selective, sensitive, and portable tool is extremely necessary. In this study, a label-free electrochemical immunosensor for detecting ferritin using a paper-based analytical device (ePAD) was created. The device pattern was custom designed onto filter paper to successfully fabricate a deliverable immunosensor. Graphene oxide was first modified onto the working electrode using an inkjet printing technique. An activation step of the electrode surface was then performed using standard 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/N-hydroxysulfosuccinimide (sulfo-NHS) chemistry. Anti-ferritin antibodies were covalently immobilized onto the amine-reactive ester surface. The amount of ferritin was monitored by observing the electrochemical signal of the selected redox couple by differential pulse voltammetry (DPV). In the presence of ferritin, the sensor showed a considerable decrease in electrochemical response in a concentration-dependent manner. In contrast, there was no observable change in current response detected in the absence of ferritin. The current response provided a good correlation with ferritin concentrations in the range of 1 to 1000 ng mL-1, and the limit of detection (3SD/slope) was found to be 0.19 ng mL-1. This fabricated immunosensor offered good selectivity, reproducibility, and long-term storage stability. In addition, this proposed immunosensor was successfully applied to detect ferritin in human serum with satisfactory results. The promising results suggested that this handmade paper-based immunosensor may be an alternative device for the diagnosis of iron deficiency anemia.

In this present work, a novel electrochemical immunosensor employing a screen-printed graphene electrode (SPGE) for a simple and highly sensitive determination of C-reactive protein (CRP) in a sandwich-type format was proposed. The sensor comprised of two CRP-specific antibodies: an unlabeled capture primary antibody (Anti-1°Ab) and an electrochemically detectable anthraquinone-labeled signaling secondary (AQ-2°Ab) antibody. The Anti-1°Ab was first covalently anchored onto an L-cysteine/gold-modified disposable SPGE (L-Cys/Au/SPGE) to create the anti-CRP surface. After binding of the CRP and the AQ-2°Ab, the electrochemical signal response was measured using differential pulse voltammetry (DPV). In the presence of CRP, the sensor exhibited a significant increase in the AQ current at AQ-2°Ab compared to the negative control. The CRP concentration was detected in the range of 0.01-150 µg/mL, and the limit of detection (LOD) (S/N = 3) and limit of quantitation (LOQ) (10 SD/Slope) were 1.5 ng/mL and 10 ng/mL, respectively. This sensor exhibited very high sensitivity in determining CRP and was successfully applied to detect CRP in certified human serum with satisfactory results. The developed sensor is suitable as an alternative method for determination of CRP and the same principle may be further applied to determine other clinically important target molecules., (Copyright © 2018 Elsevier B.V. All rights reserved.)

We introduce for the first time a paper-based analytical device (PAD) for the non-enzymatic detection of glucose by modifying a screen-printed carbon electrode with cobalt phthalocyanine, graphene and an ionic liquid (CoPc/G/IL/SPCE). The modifying composite was characterized by UV-visible spectroscopy, energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The disposable devices show excellent conductivity and fast electron transfer kinetics. The results demonstrated that the modified electrode on PADs had excellent electrocatalytic activity towards the oxidation of glucose with NaOH as supporting electrolyte (0.1M). The oxidation potential of glucose was negatively shifted to 0.64V vs. the screen-printed carbon pseudo-reference electrode. The paper-based sensor comprised a wide linear concentration range for glucose, from 0.01 to 1.3mM and 1.3-5.0mM for low and high concentration of glucose assay, respectively, with a detection limit of 0.67µM (S/N = 3). Additionally, the PADs were applied to quantify glucose in honey, white wine and human serum. The disposable, efficient, sensitive and low-cost non-enzymatic PAD has great potential for the development of point-of-care testing (POCT) devices that can be applied in healthcare monitoring., (Copyright © 2017 Elsevier B.V. All rights reserved.)

In this work, for the first time, manganese (IV) oxide-modified screen-printed graphene electrodes (MnO 2 /SPGEs) were developed for the simultaneous electrochemical detection of coenzyme Q10 (CoQ10) and α-lipoic acid (ALA). This sensor exhibits attractive benefits such as simplicity, low production costs, and disposability. Cyclic voltammetry (CV) was used to characterize the electrochemical behavior of the analyte and investigate the capacitance and electroactive surface area of the unmodified and modified electrode surfaces. The electrochemical behavior of CoQ10 and ALA on MnO 2 /SPGEs was also discussed. Additionally, square wave anodic stripping voltammetry (SWASV) was used for the quantitative determination of CoQ10 and ALA. Under optimal conditions, the obtained signals are linear in the concentration range from 2.0 to 75.0 μg mL -1 for CoQ10 and 0.3-25.0 μg mL -1 for ALA. The low limits of detection (LODs) were found to be 0.56 μg mL -1 and 0.088 μg mL -1 for CoQ10 and ALA, respectively. Moreover, we demonstrated the utility and applicability of the MnO 2 /SPGE sensor through simultaneous measurements of CoQ10 and ALA in dietary supplements. The sensor provides high accuracy measurements, exhibiting its high potential for practical applications., (Copyright © 2017 Elsevier B.V. All rights reserved.)

A simple paper-based sensor with electrochemical detection was first developed for rapid, selective, and sensitive determination of acetylcholinesterase (AChE). The screen-printed graphene electrode was used as working electrode providing sensitivity for the sensor. The amperometric detection of AChE is based on the determination of thiocholine (TCh) produced from hydrolysis of acetylthiocholine chloride (ATCh) by AChE. To detect TCh, the ATCh immobilized sheet was stacked onto the detection sheet using double adhesive tape, then samples of AChE were dropped on the back side of an ATCh immobilized sheet with only 1min of incubation time. To avoid interference, glutathione (GSH), the potential of 0.5V vs. Ag/AgCl was applied onto a graphene electrode and the current, which depends on AChE concentration, was measured. Under optimized conditions, the limit of detection (LOD) from the experiment of AChE determination was 0.1U/mL with AChE concentration in range of 0.1-15U/mL. The data correlated well with the data obtained using spectrophotometric method. The developed sensor had been successfully applied to detect AChE in blood samples., (Copyright © 2017 Elsevier B.V. All rights reserved.)

A simple and highly sensitive electrochemical sensor based on an electrochemically reduced graphene oxide-modified screen-printed carbon electrode (ERGO-SPCE) for the simultaneous determination of sunset yellow (SY) and tartrazine (TZ) was proposed. An ERGO film was coated onto the electrode surface using a cyclic voltammetric method and then characterized by scanning electron microscopy (SEM). In 0.1M phosphate buffer at a pH of 6, the two oxidation peaks of SY and TZ appeared separately at 0.41 and 0.70V, respectively. Surprisingly, the electrochemical response remarkably increased approximately 90- and 20-fold for SY and TZ, respectively, using the modified electrode in comparison to the unmodified electrode. The calibration curves exhibited linear ranges from 0.01 to 20.0µM for SY and from 0.02 to 20.0µM for TZ. The limits of detection were found to be 0.50 and 4.50nM (at S/N=3) for SY and TZ, respectively. Furthermore, this detection platform provided very high selectivity for the measurement of both colorants. This electrochemical sensor was successfully applied to determine the amount of SY and TZ in commercial beverages. Comparison of the results obtained from this proposed method to those obtained by an in-house standard technique proved that this developed method has good agreement in terms of accuracy for practical applications. This sensor offers an inexpensive, rapid and sensitive determination. The proposed system is therefore suitable for routine analysis and should be an alternative method for the analysis of food colorants., (Copyright © 2016 Elsevier B.V. All rights reserved.)

We report herein the first development of graphene-polyaniline modified carbon paste electrode (G-PANI/CPE) coupled with droplet-based microfluidic sensor for high-throughput detection of 4-aminophenol (4-AP) in pharmaceutical paracetamol (PA) formulations. A simple T-junction microfluidic platform using an oil flow rate of 1.8 μL/min and an aqueous flow rate of 0.8 μL/min was used to produce aqueous testing microdroplets continuously. The microchannel was designed to extend the aqueous droplet to cover all 3 electrodes, allowing for electrochemical measurements in a single droplet. Parameters including flow rate, water fraction, and applied detection potential (Edet) were investigated to obtain optimal conditions. Using G-PANI/CPE significantly increased the current response for both cyclic voltammetric detections of ferri/ferrocyanide [Fe(CN)6](3-/4-) (10 times) and 4-AP (2 times), compared to an unmodified electrode. Using the optimized conditions in the droplet system, 4-AP in the presence of PA was selectively determined. The linear range of 4-AP was 50-500 μM (R(2) = 0.99), limit of detection (LOD, S/N = 3) was 15.68 μM, and limit of quantification (LOQ, S/N = 10) was 52.28 μM. Finally, the system was used to determine 4-AP spiked in commercial PA liquid samples and the amounts of 4-AP were found in good agreement with those obtained from the conventional capillary zone electrophoresis/UV-Visible spectrophotometry (CZE/UV-Vis). The proposed microfluidic device could be employed for a high-throughput screening (at least 60 samples h(-1)) of pharmaceutical purity requiring low sample and reagent consumption., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A nanocomposite of graphene (G), polyvinylpyrrolidone (PVP) and polyaniline (PANI) modified onto screen-printed carbon electrode (SPCE) using an electrospraying technique was developed for simultaneous determination of five parabens in beverages and cosmetic products by high performance liquid chromatography. PVP and PANI were used as the dispersing agents of graphene, and also for the enhancement of electrochemical conductivity of the electrode. The electrochemical behavior of each paraben was investigated using the G/PVP/PANI nanocomposite-modified SPCE, compared to the unmodified SPCE. Using HPLC along with amperometric detection at a controlled potential of +1.2V vs Ag/AgCl, the chromatogram of five parabens obtained from the modified SPCE exhibits well defined peaks and higher current response than those of its unmodified counterpart. Under the optimal conditions, the calibration curves of five parabens similarly provide a linear range between 0.1 and 30 µg mL(-1) with the detection limits of 0.01 µg mL(-1) for methyl paraben (MP), ethyl paraben (EP) and propyl paraben (PP), 0.02 and 0.03 µg mL(-1) for isobutyl paraben (IBP) and butyl paraben (BP), respectively. Furthermore, this proposed method was applied for the simultaneous determination of five parabens in real samples including a soft drink and a cosmetic product with satisfactory results, yielding the recovery in the range of 90.4-105.0%., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A development of ultra-high performance liquid chromatographic coupled with a novel inkjet-printed conductive ink-modified electrode for a fast and simultaneous determination of polyphenolic antioxidants was achieved. Two printing techniques were selected for fabrication and modification including (i) an in-house screen-printing method and (ii) an inkjet-printing method, respectively. A conductive ink containing graphene and polyaniline nanocomposite (G-PANI) was precisely casted onto the surface of screen-printed carbon electrode (SPCE) using a dimatix inkjet material printer. Compared to a bare SPCE, the G-PANI-modified screen-printed carbon electrode (G-PANI/SPCE) exhibited higher electrochemical sensitivity with increase (2-4 times) of peak current of each antioxidant. Moreover, four antioxidants were successfully separated and determined within 3 min using a reverse phase ultra-high performance liquid chromatography (UHPLC) with a mobile phase containing phosphate buffer and acetonitrile (90:10 v/v). Under an optimal detection potential at +1.2V vs. Ag/AgCl, linear calibrations and limits of detection (S/N=3) for antioxidants were found to be 0.01-10 µg mL(-1) and 1.38-1.94 ng mL(-1), respectively. Finally, this proposed method has been successfully used for the determination of antioxidants in tea samples, the results obtained from our presented method were within a highly good agreement those obtained from a standard UHPLC-UV method., (Copyright © 2015 Elsevier B.V. All rights reserved.)

An ultra-performance liquid chromatography (UPLC) coupled with graphene/polyaniline (G/PANI)-modified screen-printed carbon electrode was developed for separation and sensitive determination of eight sulfonamides (SAs) in shrimp. Electrospraying was selected for electrode modification because it can generate the well dispersion of G/PANI nanocomposites on the electrode surface. Prior to electrochemical detection, eight SAs were completely separated within 7 min by using reversed phase UPLC (C4) with mobile phase containing 70:25:5 (v/v/v) of potassium hydrogen phosphate (pH 3):acetonitrile:ethanol. For amperometric detection, the detection potential acquired from hydrodynamic voltammetry was found to be +1.4V. Under optimal conditions, a wide linearity and low limit of detection were obtained for eight SAs in the range of 0.01-10 µg mL(-1) and 1.162-6.127 ng mL(-1), respectively. Compared to boron-doped diamond (BDD) electrode, a G/PANI-modified screen-printed carbon electrode offered higher sensitivity with lower operating cost. To determine SAs in shrimp samples, solid-phase extraction was used to clean up and preconcentrate the samples prior to UPLC separation. To validate this developed method, a highly quantitative agreement was accomplished with UPLC-UV system. Thus, this proposed system might be an alternative approach for rapid, inexpensive, and sensitive determination of SAs in shrimps., (Copyright © 2014 Elsevier B.V. All rights reserved.)