Screen-printed Graphene Electrode Research Articles

Mechanism of SDBS functionalized PPy enhancing the electrochemical sensitivity of SPGE to dopamine and uric acid: Experimental and DFT investigations

A novel approach to enhance the electrochemical sensitivity of screen-printed graphene electrode (SPGE) to dopamine (DA) and uric acid (UA) utilizing sodium dodecylbenzene sulfonate (SDBS) functionalized polypyrrole (PPy) is presented. The functionalized PPy nanosheets (SDBS/PPy) were synthesized via low-temperature polymerization. The introduced dodecylbenzene sulfonate (DBS-) facilitated the dispersion of functionalized PPy nanosheets, resulting in a notably increased specific surface area. DA and UA adsorption behavior on PPy and SDBS/PPy surface was investigated using density functional theory (DFT). The adsorption energy of DA and UA on SDBS/PPy was 0.15 eV and 0.05 eV higher than that on PPy. The adsorption ability of DA and UA was greatly improved after doping DBS- in PPy. The electrochemical response of SDBS/PPy-modified SPGE (SDBS/PPy/SPGE) to different concentrations of DA and UA was evaluated. Compared with SPGE, the oxidation current sensitivity of SDBS/PPy/SPGE to DA increased from 0.08 μA·μM−1 to 0.13 μA·μM−1, the oxidation current sensitivity of SDBS/PPy/SPGE to UA increased from 0.01 μA·μM−1 to 0.04 μA·μM−1. Electrochemical measurement demonstrated that PPy doping with DBS- caused a unique improvement in DA and UA performance of SPGE.

Development of pectin-based gel electrolyte for wireless electrochemical determination of cadmium and lead using smartphone

A portable device offering effortlessness, mobility, and affordability for real-time and on-site monitoring of heavy metals is currently in great demand to maintain environmental sustainability. Herein, a platform utilizing a biopolymeric gel-based electrolyte for the on-field simultaneous determination of Cd(II) and Pb(II) is described. Pectin, a natural polymer, was exploited as a chemical delivery medium on account of its biodegradability, environmental friendliness, and rapid dissolving characteristics. The gel electrolyte was prepared by having pectin dissolved in KCl mixed with Sb(III)–Bi(III) bimetallic alloy solution, and casted onto a paper substrate. An in situ bimetallic alloy and pre-mixed bismuth nanoparticles modified screen-printed graphene electrode (Sb–Bi/BiNP/SPGE) were employed to enhance the electrochemical signals of Cd(II) and Pb(II) for the differential pulse anodic stripping voltammetry (DPASV). It was demonstrated that the platform was capable of generating sharp and well-defined current signals, achieving the low detection limits of 50.98 ng mL−1 for Cd(II) and 40.80 ng mL−1 for Pb(II). The reproducibility, as indicated by the relative standard deviation, was found to be less than 10.4 % (n = 10) for the developed gel-based device when coupled with a wireless near field communication (NFC) potentiostat. Lastly, the obtained sensor was applied for quantification of Cd and Pb in potentially contaminated groundwater samples. The recoveries obtained were satisfactorily within the acceptable range. The newly designed platform exhibited several advantages, including small sample volume (μL), low-cost, no sample preparation requirements, and being environmentally friendly. The convenience of a portable device utilizing the proposed biopolymeric gel-based electrolyte for on-field analysis makes it highly appealing for various applications.

Biolayer-Interferometry-Guided Functionalization of Screen-Printed Graphene for Label-Free Electrochemical Virus Detection.

Additive manufacturing holds promise for rapid prototyping and low-cost production of biosensors for diverse pathogens. Among additive manufacturing methods, screen printing is particularly desirable for high-throughput production of sensing platforms. However, this technique needs to be combined with carefully formulated inks, rapid postprocessing, and selective functionalization to meet all requirements for high-performance biosensing applications. Here, we present screen-printed graphene electrodes that are processed with thermal annealing to achieve high surface area and electrical conductivity for sensitive biodetection via electrochemical impedance spectroscopy. As a proof-of-concept, this biosensing platform is utilized for electrochemical detection of SARS-CoV-2. To ensure reliable specificity in the presence of multiple variants, biolayer interferometry (BLI) is used as a label-free and dynamic screening method to identify optimal antibodies for concurrent affinity to the Spike S1 proteins of Delta, Omicron, and Wild Type SARS-CoV-2 variants while maintaining low affinity to competing pathogens such as Influenza H1N1. The BLI-identified antibodies are robustly bound to the graphene electrode surface via oxygen moieties that are introduced during the thermal annealing process. The resulting electrochemical immunosensors achieve superior metrics including rapid detection (55 s readout following 15 min of incubation), low limits of detection (approaching 500 ag/mL for the Omicron variant), and high selectivity toward multiple variants. Importantly, the sensors perform well on clinical saliva samples detecting as few as 103 copies/mL of SARS-CoV-2 Omicron, following CDC protocols. The combination of the screen-printed graphene sensing platform and effective antibody selection using BLI can be generalized to a wide range of point-of-care immunosensors.

Highly sensitive and disposable screen-printed graphene-based electrochemical sensor coupled with monolithic micro-solid-phase extraction for the determination of 3,4-methylenedioxymethamphetamine in forensic applications

The development of a productive assay to quantify 3,4-methylenedioxymethamphetamine (MDMA) levels in human urine samples is crucial in forensic applications. In this work, we examine the use of a disposable screen-printed graphene electrode coupled with in-tip monolithic micro-solid-phase extraction (µ-SPE) for the highly selective and sensitive determination of MDMA. To satisfy this requirement, we employ a sensor based on graphene nanomaterials integrated into a compact electrochemical device to enhance the sensitivity. In-tip monolithic µ-SPE is a facile and highly effective route for extraction and preconcentration (enrichment factor ∼ 10) to improve the sensitivity. The combination of our µ-SPE and an electrochemical sensor exhibits a remarkable performance in terms of sensitivity and selectivity for MDMA analysis. A wide linear range is observed within 0.10–10.00 µg mL−1, and the lowest limit of detection is calculated to be 0.03 µg mL−1. Moreover, no interference effect from other substances is observed for MDMA detection. The feasibility of the proposed assay is evaluated, and it is successfully used in MDMA determination in human urine samples with high accuracy, precision, reproducibility, stability, and reliability. Therefore, this novel proposed method is well suited as a compact disposable device for MDMA determination in forensic applications and can be employed by relevant government organizations to correctly identify MDMA levels in narcotic addicts.

Fabrication of Silver Nanoparticle Loaded into Nanocellulose Derived from Hemp and Poly(vinyl alcohol)-Based Composite as an Electrode for Electrochemical Sensors for Lactate Determination.

Nanocellulose derived from hemp (HNC) with the addition of silver nanoparticles (AgNPs) is utilized for improving the electrochemical sensing performances for lactate detection. Initially, HNC is chemically extracted and purified by using alkali treatment and acid hydrolysis. Then, AgNPs are nucleated in situ by the self-reduction process prior to forming a composite with poly(vinyl alcohol) (PVA). This nanocomposite significantly improves the electrochemical properties of the electrode, including electrochemical conductivity and electrocatalysis. The morphologies and chemical alterations of the HNC/AgNPs-PVA nanocomposite are investigated by field emission scanning electron microscopy. It demonstrates a three-dimensional network with random orientation of the nanocellulose fiber. The AgNPs are well-dispersed in the nanocomposite. Moreover, the nanocomposite provides high thermal stability up to 450 °C. Then, it is remarkably noted that 10 wt % HNC/AgNPs-PVA modified on the electrode provides the highest current responses, with a standard redox couple [(Fe(CN)6]3-/4-]. For lactate detection, this modified screen-printed graphene electrode with nonimmobilized lactate oxidase exhibits an increase in the current signal with the increment of lactate concentration and offered a linear range of 0-25 mM, covering a cutoff value (12.5 mM) for muscle fatigue indication. Eventually, this sensor is successfully applied for lactate detection with high potential for a wearable lactate sensor.

Zwitterionic hydrogel for preserving stability and activity of oxidase enzyme for electrochemical biosensor

Enzymatic electrochemical biosensor is the most common analytical platform for medical diagnosis. To mimic the biological environment of the enzyme for maintaining the function of biosensor, zwitterionic hydrogels have been recognized as effective matrices for enzymatic immobilization. Herein, a zwitterionic hydrogel derived from a copolymer, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-N-methacryloyloxyethyl tyrosine methylester (MAT)] (PMM) was firstly applied as versatile coating to preserve stability and activity of oxidase enzymes, glucose oxidase (GOx) and lactate oxidase (LOx) for enzymatic electrochemical sensor. A screen-printed carbon electrode (SPCE) was sequentially coated with nitrogen-doped graphene (NDG), oxidase enzyme, and PMM mixed with Ru(II)bpy32+ and (NH4)2S2O8 followed by visible light irradiation for 3 min to induce PMM gelation. Electrochemical detection of glucose and lactate using the modified SPCE was performed via amperometry in the presence of hydrogen peroxide. The activity of both GOx and LOx immobilized on the modified SPCE was well maintained for 49 days at 87 and 80 %, respectively. Additionally, two different electrodes, a screen-printed graphene electrode (SPGE), and a screen-printed silver electrode (SPAgE), similarly modified gave the same satisfactory detection of spiked glucose and lactate in human plasma and sweat with 93–118 % recovery. This indicates the potential of the PMM hydrogel as a universal platform for preservation of enzymes which can be easily fabricated without the need for specific chemical modification of the electrode.

Study on the mechanism of oxygen plasma-assisted polypyrrole to improve electrochemical performance of screen-printed graphene electrode based on density dunctional theory

In this work, polypyrrole (PPy) nanosheets was synthesized by low-temperature oxidative polymerization method. Subsequently, the as-synthesized PPy nanosheets were treated with oxygen plasma. The sensitive mechanism of oxygen plasma-assisted polypyrrole (PPy/O) to enhance the electrochemical performance of screen-printed graphene electrode (SPGE) was studied. The surface morphology and chemical composition of PPy/O were analyzed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), revealing that the oxygen plasma treatment etched the surface morphology and increased the number of oxygen-containing functional groups of PPy/O. The experimental results demonstrated that the oxidation current sensitivity of PPy and PPy/O modified SPGE to K3[Fe(CN)6](PF) increased by 5% and 19%, respectively. Furthermore, density functional theory (DFT) calculations were performed, revealing that the adsorption energy of PF molecules on oxygen plasma-assisted PPy was 1.79 times greater than that of untreated PPy nanosheets, and the electron transfer between PPy nanosheets and PF molecules also changed significantly. The remarkable improvement of SPGE in electrochemical performance can be attributed to the large specific surface area and increased number of oxygen-containing functional groups of PPy/O. Oxygen plasma assistance can effectively improve the modification effect of PPy on SPGE.

Ratiometric electrochemical lateral flow immunoassay for the detection of Streptococcus suis serotype 2

An electrochemical lateral flow immunoassay (eLFIA) strip with high reproducibility was developed to rapidly and accurately detect Streptococcus suis serotype 2. This proposed strip was fabricated by integrating ratiometric electrochemical detection and LFIA (R-eLFIA). The R-eLFIA exhibited excellent reproducibility, which was improved by 3.8 times compared to a single electrode. A dual-working screen-printed graphene electrode (SPGE) was designed by tuning the working electrode with electroactive species in the biosensing system. Ferrocene carboxylic acid (Fc) was used as a signal probe, and sunset yellow (SY) at one working electrode was used as an internal reference signal to provide a built-in correction for reducing the effects of inherent background current. S. suis serotype 2-specific antibodies were immobilized on a nitrocellulose membrane of LFIA, which is located on the position of Fc-SPGE. In the presence of the analyte, an immunocomplex formed on the region of Fc-SPGE, causing a decrease in Fc current while SY current remained constant. The current ratio's decrease was proportional to S. suis serotype 2's concentration. Under optimization, this biosensor showed good linearity in the range of 102–1010 CFU/mL with a limit of detection of 10 CFU/mL and achieved a rapid detection time (15 min). Moreover, the R-eLFIA biosensor exhibited excellent reproducibility and high selectivity and was applied in human serum samples. Thus, this study successfully matched the advantages of the ratiometric strategy and LFIA and has great potential to be used as an effective tool for rapidly detecting S. suis serotype 2 in clinical samples.

Modification of bismuth film and poly(L-hydroxyproline) onto a screen-printed graphene electrode: A step towards a non-enzymatic platform for determining L-hydroxyproline in human urine samples

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.

Innovative electrochemical platform for the simultaneous determination of L-DOPA and L-tyrosine using layer-by-layer assembled L-proline-linked nanodiamonds on printed graphene.

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 0.075-50μM, with a detection limit of 0.021μM for L-DOPA, and 2.5-120μM with a detection limit of 0.74μM for L-Tyr. To demonstrate the reliability of the poly(L-pro)/ND/SPGE in practical application, it was successfully applied tothe 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 35days), and portability, the developed sensor is a promising alternative analytical method for on-site clinical monitoring.

Toward the rapid diagnosis of sepsis: dendritic copper nanostructure functionalized diazonium salt modified screen-printed graphene electrode for IL-6 detection.

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 madeby electrodeposition, thus eliminating the multistep of nanomaterial synthesis and time wasting. The resulting dendritic CuNSs significantly increase theeffective 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 500pgmL-1 with low detection limit of 0.02pgmL-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 wellwith those achieved using the standard approach, further showing highpractical applicability of this developed immunosensor.

Sequential Flow Controllable Microfluidic Device for G-Quadruplex DNAzyme-Based Electrochemical Detection of SARS-CoV-2 Using a Pyrrolidinyl Peptide Nucleic Acid.

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been a significant health issue globally. Point-of-care (POC) testing that can offer a rapid and accurate diagnosis of SARS-CoV-2 at the early stage of infection is highly desirable to constrain this outbreak, especially in resource-limited settings. Herein, we present a G-quadruplex DNAzyme-based electrochemical assay that is integrated with a sequential flow controllable microfluidic device for the detection of SARS-CoV-2 cDNA. According to the detection principle, a pyrrolidinyl peptide nucleic acid probe is immobilized on a screen-printed graphene electrode for capturing SARS-CoV-2 DNA. The captured DNA subsequently hybridizes with another DNA probe that carries a G-quadruplex DNAzyme as the signaling unit. The G-quadruplex DNAzyme catalyzes the H2O2-mediated oxidation of hydroquinone to benzoquinone that can be detected using square-wave voltammetry to give a signal that corresponds to the target DNA concentration. The assay exhibited high selectivity for SARS-CoV-2 DNA and showed a good experimental detection limit at 30 pM. To enable automation, the DNAzyme-based assay was combined with a capillary-driven microfluidic device featuring a burst valve technology to allow sequential sample and reagent delivery as well as the DNA target hybridization and enzymatic reaction to be operated in a precisely controlled fashion. The developed microfluidic device was successfully applied for the detection of SARS-CoV-2 from nasopharyngeal swab samples. The results were in good agreement with the standard RT-PCR method and could be performed within 20 min. Thus, this platform offers desirable characteristics that make it an alternative POC tool for COVID-19 diagnosis.

A facile and automated microfluidic electrochemical platform for the in-field speciation analysis of inorganic arsenic

An automated microfluidic electrochemical platform was developed for the rapid in-field analysis of arsenic speciation. Herein, we integrated an electrochemical sensing and microfluidic channel for the simultaneous determination of As(III) and total inorganic As (total iAs) within a single device. The platform was fabricated by assembling a gold nanoparticle-modified screen-printed graphene electrode (AuNP/SPGE) on a hydrophilic polyethylene terephthalate (PET) sheet that was specially designed to enclose a microfluidic channel with dual flow channels for separate determination of the two species. While As(III) can be promptly detected with the AuNP/SPGE on one end, thioglycolic acid stored in glass fiber is employed on the other end to reduce As(V) before being electrochemically analyzed on the AuNP/SPGE as total iAs; the difference represents the amount of As(V). With a wireless potentiostat and a smartphone equipped with Bluetooth technology, the overall procedure can be fully automated and accomplished merely within 9 min. The linear ranges for the determination of As(III) and total iAs were found to be 50–1000 and 100–1500 ng/mL with detection limits of 3.7 and 17 ng/mL, respectively. The proposed method was validated and applied for the inorganic As speciation of various food samples with satisfactory results compared to those obtained with the standard HPLC-ICP‒MS protocol. This novel microfluidic electrochemical platform offers numerous advantages, notably for its simplicity, speed, low cost, and portability for on-site analysis, which conclusively makes it a highly promising analytical device for the speciation of inorganic arsenic.

Identification of early stage and metastatic prostate cancer using electrochemical detection of beta-2-microglobulin in urine samples from patients

To improve prostate cancer (PCa) diagnosis, it is imperative to identify novel biomarkers and establish effective screening techniques. Here, we introduce electrochemical biosensing of β-2-Microglobulin (β2M) in urine as a potential diagnostic tool for PCa. The immunosensor is composed of a screen-printed graphene electrode coated with anti β2M antibodies. The sensor is capable of detecting the protein directly in urine without any sample pretreatment within 45 min including sample incubation and a lower limit of detection of 204 µg/L. The sensor demonstrated a significant difference in the β2M-creatinine ratio in urine between control and both local- and metastatic PCa (mPCa) (P = 0.0302 and P = 0.0078 respectively), and between local- and mPCa (P = 0.0302). This first example of electrochemical sensing of β2M for the diagnosis of PCa may set the stage for an affordable, on-site screening technique for PCa.

Pathogen sensing device based on 2D MoS2/graphene heterostructure.

In this work we propose a new methodology for selective and sensitive pathogen detection based on a 2D layered heterostructured biosensing platform. As a proof of concept, we have chosen SARS-CoV-2 virus because the availability of new methods to detect this virus is still a great deal of interest. The prepared platform is based on the covalent immobilization of molybdenum disulphide functionalized with a diazonium salt (f-MoS2) onto graphene screen-printed electrodes (GPH SPE) by electrografting of the diazonium salt. This chemistry-based method generates an improved heterostructured biosensing platform for aptamer immobilization and aptasensor development. Electrochemical impedance spectroscopy (EIS) is used to obtain the signal response of the device, proving the ability of the sensor platform to detect the virus. SARS-CoV-2 spike RBD recombinant protein (SARS-CoV-2 S1 protein) has been detected and quantified with a low detection limit of 2.10 fg/mL. The selectivity of the developed biosensor has been confirmed after detecting the S1 protein even in presence of other interfering proteins. Moreover, the ability of the device to detect SARS-CoV-2 S1 protein has been also tested in nasopharyngeal swab samples.

Graphene-Based Electrodes for Monitoring of Estradiol

This study explores the potential use of graphene-based electrodes in the electrochemical determination of estradiol using amperometric techniques as a simple, enzyme-free approach. Graphene, a carbon-based nanomaterial, has been extensively investigated in materials science as a sensing material. Its remarkable properties, such as its high electron mobility and conductivity, robust mechanical characteristics, and good surface-to-volume ratio, have led to its adoption in numerous applications, including electrochemical sensing. Estradiol is a crucial sex hormone that affects metabolism and reproduction. However, excessive amounts may disrupt endocrine functions. Electrochemical sensors suffer from electrode fouling, leading to passivation that ultimately affects performance. We exploit the inherent properties of various types of graphene-based electrodes, including graphene screen-printed electrodes (GHSPE), electrochemically exfoliated graphene-modified electrodes (EEFGHSPE), and 3D graphene foam screen-printed electrodes (3D-GFSPE), for the amperometric studies. The electrochemical properties and structural characteristics of these sensors are evaluated using cyclic voltammetry and scanning electron microscopy. The analytical performance of these sensors is at an applied potential of +0.65 V (vs. Ag/AgCl) over the concentration range 0.83 to 4.98 μM estradiol. Sensitivities of 0.151 µAµM−1 cm−2, 0.429 µAµM−1 cm−2, and 0.273 µA µM−1 cm−2, with detection limits of 0.0041 µM, 0.097 µM, and 0.018 µM (S/N = 3), are found for GHPSPE, 3D-GFSPE and EEFGHSPE, respectively. The possibility of amperometrically determining the estradiol levels in a potable tap water sample are then investigated over the concentration range 0.83–4.98 µM.

Effect of Magnesium Chloride in Supporting Electrolyte for Enhancing Sensitive and Selective Electrochemical Sensor: An Approach for Anti-Rheumatic Sulfasalazine Detection

In this work, an electroanalytical evaluation for voltammetric sensing of the anti-rheumatic sulfasalazine (SSZ) at an unmodified screen-printed graphene electrode (SPGE) is demonstrated. By using the differential pulse (DPV) technique, the SSZ produced a well-defined peak of around −0.3 V (vs Ag AgCl−1) in Britton-Robinson (BR) buffer pH 4. Supporting electrolytes, pH, and salts all significantly impact SSZ reduction. Therefore, their impact on the working solutions was assessed. We discovered that using a mixture of Britton–Robinson (BR) buffer with pH 4 and MgCl2 as a supporting electrolyte can enhance SSZ sensitivity by approximately 1.7 times while simultaneously increasing detection selectivity. Under optimal conditions, the proposed assay demonstrated the ultrasensitive determination of SSZ with a broad linear detection range from 0.01 to 100 μM and a low detection limit of 4.7 nM (S/N = 3). To demonstrate the impact of the proposed method, the sensor has been successfully applied for the quantitative determination of SSZ in pharmaceutical, urine, and artificial serum sample. Therefore, this approach could offer simplicity, and rapidity, and serve as an alternative to the SSZ detection in practical applications.

Microfluidic paper-based analytical devices for simultaneous detection of oxidative potential and copper in aerosol samples.

The potential reach of point-of-care (POC) diagnostics into daily routines for exposure to reactive oxygen species (ROS) and Cu in aerosolized particulate matter (PM) demands that microfluidic paper-based analytical devices (μPADs) take into consideration the simple detection of these toxic PM components. Here, we propose μPADs with a dual-detection system for simultaneous ROS and Cu(II) detection. For colorimetric ROS detection, the glutathione (GSH) assay with a folding design to delay the reaction yielded complete ROS and GSH oxidation, and improved homogeneity of color development relative to using the lateral flow pattern. For electrochemical Cu(II) determination, 1,10-phenanthroline/Nafion modified graphene screen-printed electrodes showed ability to detect Cu(II) down to pg level being low enough to be applied to PM analysis. No intra- and inter-interference affecting both systems were found. The proposed μPADs obtained LODs for 1,4-naphthoquinone (1,4-NQ), used as the ROS representative, and Cu(II) of 8.3 ng and 3.6 pg, respectively and linear working ranges of 20 to 500 ng for ROS and 1 × 10-2 to 2 × 102 ng for Cu(II). Recovery of the method was between 81.4 and 108.3% for ROS and 80.5-105.3% for Cu(II). Finally, the sensors were utilized for simultaneous ROS and Cu(II) determination in PM samples and the results statistically agreed with those using the conventional methods at 95% confidence.

Patulin-imprinted origami 3D-ePAD based on graphene screen-printed electrode modified with Mn–ZnS quantum dot coated with a molecularly imprinted polymer

We developed a novel, compact, three-dimensional electrochemical paper-based analytical device (3D-ePAD) for patulin (PT) determination. The selective and sensitive PT-imprinted Origami 3D-ePAD was constructed based on a graphene screen-printed electrode modified with manganese-zinc sulfide quantum dots coated with patulin imprinted polymer (Mn–ZnS QDs@PT-MIP/GSPE). The Mn–ZnS QDs@PT-MIP was synthesized using 2-oxindole as the template, methacrylic acid (MAA) as a monomer, N,N′-(1,2-dihydroxyethylene) bis (acrylamide) (DHEBA) as cross-linker and 2,2′-azobis (2-methylpropionitrile) (AIBN) as initiator, respectively. The Origami 3D-ePAD was designed with hydrophobic barrier layers formed on filter paper to provide three-dimensional circular reservoirs and assembled electrodes. The synthesized Mn–ZnS QDs@PT-MIP was quickly loaded on the electrode surface by mixing with graphene ink and then screen-printing on the paper. The PT-imprinted sensor provides the greatest enhancement in redox response and electrocatalytic activity, which we attributed to synergetic effects. This arose from an excellent electrocatalytic activity and good electrical conductivity of Mn–ZnS QDs@PT-MIP, which improved electron transfer between PT and the electrode surface. Under the optimized DPV conditions, a well-defined PT oxidation peak appears at +0.15 V (vs Ag/AgCl) using 0.1 M of phosphate buffer (pH 6.5) containing 5 mM K3Fe(CN)6 as the supporting electrolyte. Our developed PT imprinted Origami 3D-ePAD revealed excellent linear dynamic ranges of 0.001–25 μM, with a detection limit of 0.2 nM. Detection performance indicated that our Origami 3D-ePAD possesses outstanding detection performance from fruits and CRM in terms of high accuracy (%Error for inter-day is 1.11%) and precision (%RSD less than 4.1%). Therefore, the proposed method is well-suited as an alternative platform for ready-to-use sensors in food safety. The imprinted Origami 3D-ePAD is an excellent disposable device with a simple, cost-effective, and fast analysis, and it is ready to use for determining patulin in actual samples.

Mechanism research of SDBS-functionalized polypyrrole to improve electrochemical performance of screen-printed graphene electrode

A novel method to enhance the response sensitivity of screen-printed graphene electrode (SPGE) by modifying functionalized polypyrrole (PPy) is proposed. Functionalized PPy was synthesized at low temperature by doping sodium dodecyl benzene sulfonate (SDBS) using a non-covalent modification technique, and then modified on the surface of SPGE. Due to the introduction of hydrophilic heads dodecyl benzene sulfonate (DBS−), SDBS-functionalized polypyrrole exhibited a larger specific surface area and high dispersion. The structure and morphology of SDBS-functionalized polypyrrole were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical behavior of SDBS-functionalized polypyrrole-modified SPGE (SDBS/PPy-SPGE) was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of potassium ferricyanide (K3[Fe(CN)6]). Compared with bare SPGE, the anodic currents sensitivity of SDBS/PPy-SPGE was improved from 11.38 μA·mM−1 to 15.17 μA·mM−1, and the oxidation current was increased by 78.06% in measuring 1 mM K3[Fe(CN)6] (PF). The adsorption energy and electron transfer of pure PPy and SDBS/PPy to PF molecules were calculated based on density functional theory (DFT). The adsorption energy (from -0.41 eV to -1.11 eV) and electron transfer (from 0.4 e to 0.56 e) of SDBS/PPy to PF molecules were significantly enhanced. These can be attribute to the large specific surface area, high dispersibility and chemical stability of PPy upon being non-covalently functionalized by SDBS. The electrochemical sensitivity and stability of SPGE was greatly enhanced by the synergistic effect of graphene and SDBS/PPy. Thus, SDBS-functionalized polypyrrole is a promising material for improving the electrochemical properties of electrode.