Noninvasive Label-Free Detection of Cortisol and Lactate Using Graphene Embedded Screen-Printed Electrode

A sensitive and specific immunosensor for the detection of the hormones cortisol and lactate in human or animal biological fluids, such as sweat and saliva, was devised using the label-free electrochemical chronoamperometric technique. By using these fluids instead of blood,the biosensor becomes noninvasive and is less stressful to the end user, who may be a small child or a farm animal.Electroreduced graphene oxide(e-RGO) was used as a synergistic platform for signal amplification and template for bioconjugation for the sensing mechanism on a screenprinted electrode. The cortisol and lactate antibodies were bioconjugated to the e-RGO using covalent carbodiimide chemistry. Label-free electrochemical chronoamperometric detection was used to analyze the response to the desired biomolecules over the wide detection range. A detection limit of 0.1 ng mL^(-1) for cortisol and 0.1 mM for lactate was established and a correlation between concentration and current was observed. A portable, handheld potentiostat assembled with Bluetooth communication and battery operation enables the developed system for point-of-care applications. A sandwich-like structure containing the sensing mechanisms as a prototype was designed to secure the biosensor to skin and use capillary action to draw sweat or other fluids toward the sensing mechanism. Overall, the immunosensor shows remarkable specificity, sensitivity as well as the noninvasive and point-of-care capabilities and allows the biosensor to be used as a versatile sensing platform in both developed and developing countries.

Enzyme Biosensor for Detection of Organophosphate Pesticide Residues Base on <i>Screen Printed Carbon Electrode</i>(SPCE)-Bovine Serum Albumin (BSA)

The maximum level of organophosphate pesticide residues in rice is 0.1 mg/kg and 0.5 mg/kg in vegetables. The control of pesticide residues in agricultural products required a method of analysis quickly and accurately. The research developed a biosensor for the detection of organophosphate pesticide residues in agricultural products. The research studied immobilized organophosphate hydrolase (OPH) mass and characterization of biosensor. The solution conductivity measurement in the conductivity cell consists of a 1 × 5 mm2 pair of electrodes screen printed carbon electrode (SPCE). The instrument is a converted local conductometer. From the results of study concluded that the optimum performance of the biosensor was obtained from the 105 μg OPH, at pH 8.5 with a response time of 45 seconds. In that condition the sensitivity of biosensor is 28.04 μS/ppm and 0.18 ppm detection limit and the maximum concentration of pesticide which can be measured is 1 ppm. Biosensors have been applied to measure pesticide residues in some vegetable samples.

Anodic voltammetric determination of gemifloxacin using screen-printed carbon electrode

The electrochemical oxidation behavior and voltammetric assay of gemifloxacin were investigated using differential-pulse and cyclic voltammetry on a screen-printed carbon electrode.The effects of pH,scan rates,and concentration of the drug on the anodic peak current were studied.Voltammograms of gemifloxacin in Tris-HCl buffer（pH 7.0） exhibited a well-defined single oxidation peak.A differential-pulse voltammetric procedure for the quantitation of gemifloxacin has been developed and suitably validated with respect to linearity,limits of detection and quantification,accuracy,precision,specificity,and robustness.The calibration was linear from 0.5 to 10.0 μM,and the limits of detection and quantification were 0.15 and 5.0 μM.Recoveries ranging from 96.26% to 103.64% were obtained.The method was successfully applied to the determination of gemifloxacin in pharmaceutical tablets without any pre-treatment.Excipients present in the tablets did not interfere in the assay.

Amperometric Hydrogen Peroxide Biosensor Based on Horseradish Peroxidase Entrapped in Titania Sol-Gel Film on Screen-Printed Electrode

We report the fabrication of disposable and flexible Screen-Printed Electrodes (SPEs). This new type of screen-printed electrochemical platform consists of Ag nanoparticles (AgNPs) and graphite composite. For this purpose, silver nanoparticles were first synthesized by a chemical reduction method. The morphology and structure of the AgNPs were analyzed using a Scanning Electron Microscope (SEM) and UV-Visible spectroscopy. Graphite was chosen as the working electrode material for the fabrication of a thick-film. The fabrication of a screen-printed hydrogen peroxide biosensor consisting of three electrodes on a polyethylene terephthalate (PET) substrate was performed with a spraying approach (working, counter and reference: enzyme electrode, graphite, pseudo reference: Ag/AgCl). This biosensor was fabricated by immobilizing the peroxidase enzyme (HRP) in a Titania sol-gel membrane which was obtained through a vapor deposition method. The biosensor had electrocatalytic activity in the reduction of H2O2 with linear dependence on H2O2 concentration in the range of 10-5 to 10-3 M;the detection limit was 4.5 × 10-6 M.

Gold Nanoparticles/Thermochromic Composite Film on Screen-Printed Electrodes for Simultaneous Detection of Protein and Temperature

In this study, gold nanoparticles and thermochromic composite films modified screen-printed carbon electrodes (TM-AuNPsSPCEs) were developed as a platform for the simultaneous detection of protein and temperature. The TM-AuNPs composited film had better sensitivity resulting from the gold nanoparticles amplification effect. A phase transition model analysis of TM-AuNPs films found that the TM-AuNPs films had three-phase transition intervals (<45℃, 45℃ to 80℃ and >80℃) which accommodated the temperature requirements for protein denaturation. When used to detect different concentrations of haemoglobin (Hb) solution, the TM-AuNPs modified SPCEs had a better sensitivity in detecting the different concentrations in comparison to TM and AuNP modified SPCEs which showed no clear sensitivity towards the different Hb concentrations. The dual detection and excellent sensitivity show a good application prospect for the study of the TM-AuNPs composite film.

Highly Conductive Fractal-structured Silver Particles for Preparing Flexible Printed Circuits via Screen Printing

Fractal-structured silver particles(FSSPs)are conductive materials with a micron-scale trunk and nanoscale branches,and are characterized with high electrical conductivity and high connectivity.In this study,FSSPs were added to an aqueous additive solution for synthesizing a conductive ink,which was used to prepare two types of printing electrodes via screen printing.The first type included two flexible printed electrodes(FPEs):an FPE on a polyethylene terephthalate(PET)film and an FPE on paper.The second one was a polydimethylsiloxane(PDMS)-embedded FPE.The PETbased FPE exhibited high electrochemical stability when its sheet resistance was 0.38Ω/sq for a 50%(w/w)content of FSSPs in the prepared conductive ink.Moreover,the embedded FPE demonstrated excellent mechanical properties and high chemical stability.In addition,the embedded structure was endowed with stretchability,which is important for different devices,such as flexible biomedical sensors and flexible electronics.

基于rGO-AuNPS修饰丝网印刷电极的电化学生物传感器快速检测甲基对硫磷

目的:实现对甲基对硫磷的快速检测。方法:基于金纳米颗粒和还原氧化石墨烯制备了用于对甲基对硫磷进行定量检测的乙酰胆碱酯酶传感器。采用层层组装方法,将还原氧化石墨烯、金纳米颗粒、乙酰胆碱酯酶依次修饰在丝网印刷电极表面。对传感器的催化活性、阻抗特性、传感器的抑制率与甲基对硫磷浓度的关系、实际样品检测进行了评估。结果:制备的乙酰胆碱酯酶生物传感器对乙酰硫代胆碱氯化物表现出优异的亲和力,米氏常数为2.76 mmol/L。在最佳条件下,可以有效检测甲基对硫磷,线性范围为5~500 ng/mL,检出限为0.692 ng/mL。结论:该方法操作简单、成本低、稳定性好,适用于有机磷类农药的快速检测。

Microfibrillated Cellulose Based Ink for Eco-Sustainable Screen Printed Flexible Electrodes in Lithium Ion Batteries

Free organic solvent ink containing graphite, carboxymethyl cellulose and microfibrillated cellulose as active material, dispersing and binder, respectively, has been formulated to produce flexible and eco- sustainable electrodes for lithium ion batteries. Content ratio of components and dispersion protocol were tailored in order to have theological properties suitable for a large and cheap manufacturing process as well as screen printing. The bio-sourced printed electrodes exhibit a high porosity value of 70% that limits the electrochemical performances. However, the calendering process enhances electrode performances by increasing the reversible capacity from 85 until 315 mAh/g and reducing porosity to an optimal value of 34%. Moreover the introduction of 2% w/w of monofluoro-ethylene carbonate in the electrolyte reduced their reversible capacity loss of 11% in the printed electrode.

Rapid detection of organophosphorus pesticide residue on Prussian blue modified dual-channel screen-printed electrodes combing with portable potentiostat

A novel electrochemical method for the rapid detection of organophosphorus pesticide residues was realized on a dual-channel screen-printed electrode （DSPE） that was integrated with a portable smartphone-controlled potentiostat. The two carbon working channels of DSPE were first modified by electrodepositing of Prussian blue. The channels were then modified with acetylcholinesterase （ACHE） via Nation. The inhibition ratio of AChE was detected by comparing the electrical current of acetylthiocholine （ATCh） that was catalyzed by the enzyme electrodes with （channel 1） and without （channel 2） organophosphorus pesticide. Inhibition ratios were related with the negative logarithm of the organophosphorus pesticide （trichlorfon, oxamyl, and isocarbophos） concentrations at optimum experimental conditions （pH 6.9 of electrolyte, 0.2V working potential, 2.5μL AChE modification amount, and 15 min inhibition time）. The linear equations were 1%=32.301gC＋ 253.3 （R=0.9750） for isocarbophos, I% = 35.991gC＋ 270.1 （R = 0.9668） for chlorpyrifos, and 1% = 33.701gC＋ 250.5 （R = 0.9606） for trichlorfon. The detection limits were calculated as 10-7 g/mL. Given that the inhibition ratios were only related with pesticide concentration and not with pesticide species, the proposed electrodes and electrometer can rapidly detect universal organophosphorus pesticides and assess pesticide pollution.

Disposable amperometric biosensors based on xanthine oxidase immobilized in the Prussian blue modified screen-printed three-electrode system

The screen-printed three-electrode system was applied to fabricate a new type of disposable amperometric xanthine oxidase biosensor.Carbon-working,carbon-counter and Ag/AgCl reference electrodes were all manually printed on the polyethylene terephthalate substrate forming the screen-printed three-electrode system by the conventional screen-printing process.As a mediator,Prussian blue could not only catalyze the electrochemical reduction of hydrogen peroxide produced from the enzyme reaction,but also keep the favorable potential around 0 V.The optimum operational conditions,including pH,potential and temperature,were investigated.The sensitivities of xanthine and hypoxanthine detections were 13.83 mA/M and 25.56 mA/M,respectively.A linear relationship was obtained in the concentration range between 0.10μM and 4.98μM for xanthine and between 0.50μM and 3.98μM for hypoxanthine.The small Michaelis-menten constant value of the xanthine oxidase biosensor was calculated to be 3.90 μM.The results indicate that the fabricated xanthine oxidase biosensor is effective and sensitive for the detection of xanthine and hypoxanthine.

Immobilisation of electrochemically active bacteria on screen-printed electrodes for rapid in situ toxicity biosensing

are time-consuming and not sensitive enough.However,bacteria typically connect to electrodes through biofilm formation,leading to problems due to lack of uniformity or long device production times.A suitable immobilisation technique can overcome these challenges.Still,they may respond more slowly than biofilm-based electrodes because bacteria gradually adapt to electron transfer during biofilm formation.In this study,we propose a controlled and reproducible way to fabricate bacteria-modified electrodes.The method consists of an immobilisation step using a cellulose matrix,followed by an electrode polarization in the presence of ferricyanide and glucose.Our process is short,reproducible and led us to obtain ready-to-use electrodes featuring a high-current response.An excellent shelf-life of the immobilised electrochemically active bacteria was demonstrated for up to one year.After an initial 50% activity loss in the first month,no further declines have been observed over the following 11 months.We implemented our bacteria-modified electrodes to fabricate a lateral flow platform for toxicity monitoring using formaldehyde(3%).Its addition led to a 59% current decrease approximately 20 min after the toxic input.The methods presented here offer the ability to develop a high sensitivity,easy to produce,and long shelf life bacteria-based toxicity detectors.

Low Cost Fabrication of Parallel Grid Electrode Group for Carbon Nanotube Field Emission Display

Based on simple screen printing technique,the parallel grid electrode group was developed. One grid electrode included the left and the right branch electrodes,which were formed with the solidified silver slurry on grid substrate. Under one anode pixel,the left and the right branch electrodes would control respectively the electron emission of two independent carbon nanotube (CNT) field emitters on the same cathode electrode. With the parallel grid electrode group, the capacitance effect between grid-cathode electrodes would be reduced due to the decreased grid electrode fabrication area. And the service life of field emission display (FED) could be prolonged owing to the existence of spare branch electrode. Using CNT as field emitter,the FED with parallel grid electrode group was fabricated,which possessed better grid control performance, high luminescence image brightness, and low fabrication cost. The turn-on electric-field was 2. 13 V /mm and the maximum field emission current had reached 1 506. 2 mA.

Flexible carbon nanotube-enriched silver electrode films with high electrical conductivity and reliability prepared by facile screen printing

Flexible electrode films play critical and fundamental roles in the successful development of flexible electronic devices. In this study, carbon nanotubes（CNTs） were implanted into silver（Ag） ink to enhance the electrical conductivity and the reliability of the printed Ag electrode films. The fabricated carbon nanotubes-enriched silver（Ag-CNTs） electrode films were printed on the polyimide substrates by a facile screen printing method and sintered at a relatively low temperature. The resistivity of Ag-CNTs films was decreased by 62.27% compared with the pure Ag film. Additionally, the Ag-CNTs films exhibited excellent flexibility under a bending radius of 4 mm（strain ε = 2.09%） over 1000 cycles. Furthermore, the Ag-CNTs film displayed unchangeable electrical conductivity together with a strong adhesion after an accelerated aging test with 500 thermal shock cycles. These improvements were attributed to the AgCNTs interconnected network structure, which can provide electronic transmission channels and prevent cracks from initiating and propagating.

Voltammetric determination of venlafaxine as an antidepressant drug employing Gd_2O_3 nanoparticles graphite screen printed electrode

Graphite screen printed electrode modified with Gd_2 O_3 nanoparticles(Gd_2 O_3/SPE) was developed for the determination of venlafaxine(VF). The Gd_2 O_3 nanoparticles were thoroughly characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM) and X-ray diffraction(XRD) analyses. To study the electrochemical behaviour of venlafaxine cyclic voltammetry(CV), chronoamperometry(CHA)and differential pulse voltammetry(DPV) were employed. These studies reveal that the oxidation of venlafaxine is facilitated at Gd_2 O_3/SPE. After optimization of analytical conditions, analysis of venlafaxine using the modified electrode in 0.1 mol/L PBS(pH 7.0) demonstrates that the peak currents corresponding to venlafaxine vary linearly with its concentration in the range of 5.0 ×10^(-6)-9.0 × 10^(-4) mol/L. The detection limit(S/N = 3) of 2.1 × 10^(-7) mol/L is obtained for venlafaxine using DPV. The prepared modified electrode benefits from advantages such as simple preparation method, high sensitivity and low detection limit.Moreover, the evaluation of practical applicability of this proposed method is successful in the identification of venlafaxine in pharmaceutical formulations, urine and water samples.

Application of graphite screen printed electrode modified with dysprosium tungstate nanoparticles in voltammetric determination of epinephrine in the presence of acetylcholine

The current work focuses on the development of a sensitive and selective electrochemical device based on a graphite screen printed electrode modified with Dy2（WO4）3 nanoparticles（DWO/SPE） for the analysis of epinephrine in samples also containing acetylcholine. The study proves that the sensor has excellent electron-mediating behavior in the oxidation of epinephrine in a 0.1 mol/L phosphate buffer solution（PBS）（pH 7.0）. The application of the DWO/SPE in differential pulse voltammetry（DPV） is found to lead to distinct response for the oxidation of epinephrine and acetylcholine, with the potentials of the epinephrine and acetylcholine peaks（△Ep） to be 550 mV apart. The detection limits of the method for epinephrine and acetylcholine are 0.5 and 0.7 μmol/L（S/N = 3） and the responses are found to be linear in the concentration ranges of 1.0-900.0 μmol/L and 1.0-1200.0 μmol/L in a PBS buffer（pH = 7.0）respectively. The modified electrode was used for the detection of epinephrine and acetylcholine in real samples and found to produce satisfactory results. These results can be a proof that Dy2（WO4）3 nanoparticles can find promising applications in electrochemical sensors to be used for the analysis of（bio）chemical species.

基于差分脉冲伏安法快速检测花椒油树脂中的麻味物质

麻味物质含量是花椒油树脂的重要品质指标,文章基于电化学原理中的差分脉冲伏安法首次建立了一种采用未修饰的丝网印刷电极测定花椒油树脂中麻味物质的快速检测方法,通过优化电化学工作站中的富集时间、电压以及待测液中的甲醇占比、pH值,并以紫外分光光度计检测法为对照构建出了该方法。结果表明,以未修饰的丝网印刷电极检测花椒油树脂中麻味物质的适宜条件:富集时间为120 s,富集电压为0.2 V,甲醇在待测液中占比小于5%,pH值为1,2,3,山椒素的电流值与其浓度在2~50 mg/L范围内呈良好的线性关系(R^(2)=0.999),加标回收率在97.60%~108.40%之间,检出限为0.22 mg/L。经验证,该方法与行业标准GH/T 1290—2020方法具有良好的检测一致性(RSD=4.75%),建立的快速检测方法既具有操作简单、方便快速的优点,又兼具传统方法的准确性与重复性,因此可以作为花椒及其制品中麻味物质的快速检测方法进行科学研究与企业生产实践,且有望基于该方法开发出便携式麻味物质快速检测仪器。

检测2,4-D的一次性安培型免疫传感器

2,4-D是广泛使用的除草剂,以2,4-D为检测目标,研究了安培型免疫传感器.首先采用1-乙基-3-(3-二甲基氨丙基)碳二亚胺盐酸盐(EDC)作为交联剂制备2,4-D与BSA以及PLL的偶联物.用结合比1:16的2,4-D与偶联物制备兔抗血清.免疫传感器的制备包括2个步骤,使用丝网印刷工艺制备一次性碳电极,然后通过戊二醛交联在电极表面固定2,4-D与多聚赖氨酸(PLL)的偶联物.待测水样与2,4-D抗血清和HRP酶标二抗进行间接免疫竞争反应.在HRP酶在邻苯二胺和H2O的共同作用下发生酶促反应,检测还原电流以反映2,4-D的浓度.试验了不同浓度抗血清和酶标二抗对检测信号的影响,结果表明,2,4-D的检测下限达到1.69ng/mL,线性区间1.69～30 000ng/mL,适合饮用水中2,4-D的检测要求.

溶胶-凝胶型陶瓷碳硫离子选择性电极的研制

将溶胶 凝胶技术与印制电极技术相结合制作了复合陶瓷碳硫离子选择性电极。对溶胶 凝胶形成条件和印刷浆液的组成进行了试验 ,电极制作过程包括电极膜基质制备、溶胶 凝胶型陶瓷碳硫离子敏感膜制备、敏感膜在基质上的固定化三步。对电极的参数进行了测试。该电极稳定性、重现性好 ,响应快。应用于实际和模拟样品分析 ,取得满意效果。采用该法制备离子选择性电极具有简易、价廉、易集成化等特点 。

基于丝网印刷碳电极的微囊藻毒素-(亮氨酸-精氨酸)的电流型免疫传感器

将微囊藻毒素-（亮氨酸-精氨酸）-鸡卵白蛋白（Microcystin-（leucine-arginine）-ovalbumin,MCLR-OVA）固定在锇联吡啶聚（4-乙烯基吡啶）聚合物修饰的丝网印刷碳电极表面,制备了一种检测MCLR的电流型免疫传感器。该传感器基于间接竞争免疫分析模式,以辣根过氧化物酶偶联的羊抗鼠免疫球蛋白抗体为标记物。其电流信号响应与MCLR的浓度在0.43~10.72 mg/L范围内呈负线性相关,检出限为0.17 mg/L。3种实际水样的平均添加回收率为83%~121%,相对标准偏差为3.6%~7.6%。本方法为MCLR的环境监测提供了科学依据。

基于溶胶-凝胶及印制技术制备复合陶瓷碳pH电极

将溶胶 凝胶技术与丝网印制技术相结合研制了一种新型复合陶瓷碳pH电极和参比电极 ,并组合制备了pH复合电极。pH电极利用天然沸石作质子接受体 ,用溶胶 凝胶法进行固定。对溶胶 凝胶法与印制技术相结合制作包埋沸石的复合陶瓷碳敏感膜的条件进行了实验 ,并对电极参数进行了测试。该电极测定范围为pH 1～ 1 2 ,响应斜率为 0 .0 6V dec。电极稳定性、重现性好、响应快 ,利用此电极对多种水样进行了分析 ,取得了满意效果。采用该法制备离子选择性电极具有简易、价廉、易批量化生产和推广应用等特点。