Search

A compact model of an ion-sensitive floating gate FET (ISFGFET) is presented. Unlike in the conventional ISFET, the ISFGFET has a dual gate structure, a sensing gate and a control gate. With the interplay between the control gate and the reference electrode the charging of the fluidic part of the sensor can be controlled and the sensing surface can be programmed. We present an intuitive macromodel with SPICE implementation and discuss the fluidic gating, sensitivity, chemical and electrical tuning of the ionic screening layer as well as the methods to combat the limitations such as the dielectric breakdown of the sensing oxide as well as the design trade-offs of the sensor. Additionally the model allows the integration of this new type of chemical sensor to the CMOS design flow. The proposed model relies on experimentally verified site-binding theory and double layer capacitance formulation explaining the interfacial potential. Unlike previous models we created a unified model where the sensing interface and the FET are coupled and the system is solved as such without unnecessary simplifications used earlier. The model validity is verified by comparing the results with well-established ISFET models and with experimental results. [ABSTRACT FROM AUTHOR]

Abstract: A facile electrochemical method to prepare thiophene oligomers has been developed. The synthesis was conducted by terminating a growing macromolecular chain with bromine radicals. This method is based on the proximity of the polymerization potential of 2,2′-bithiophene (BT) and the oxidation potential of bromide. Layers of short thiophene oligomers can be deposited by increasing concentration of bromide in the electrolyte solution. The characteristic UV–vis absorbance maximum shifted consistently to the bromide concentration, which suggests the possibility of accurately turning the optical band gap of electrodeposited material. This method is versatile and has also been successfully applied to synthesize 3,4-ethylenedioxythiophene (EDOT) oligomers. The layer of electrodeposited EDOT oligomers was incorporated as a hole transporting layer in a polymer solar cell to test its performance in a functional device. [Copyright &y& Elsevier]

The latest Zika virus (ZIKV) pandemic caused great international concern from explosively proliferating throughout the Americas. Currently, there is no vaccine to prevent Zika virus infection and available tests rely on antibodies or RNA. Unfortunately, antibody-based detection systems can result in false positive results and RNA-based detection systems are costly, time-consuming, and impractical for testing in remote regions. In this study, a potential point-of-care (POC) diagnostic system was developed using a chip-based potentiometric sensor to detect Zika virus using a 3D molecular imprinting technique. This chip-based potentiometric sensor system was able to detect 10−1 PFU mL−1 ZIKV in a buffered solution under 20 minutes without any sample manipulation. This sensor was tested against Dengue virus at clinical viral loads and showed no sign of cross-reactivity. When tested against human saliva samples containing clinical viral loads, this sensor was able to detect 10 PFU mL−1 ZIKV among the pool of bio-macromolecules. The high sensitivity and high selectivity demonstrated here proved that this lab-on-a-chip diagnostic has the potential to become a POC detection system for rapid and accurate screening of flaviviruses. [ABSTRACT FROM AUTHOR]

Thiolation of polyaniline (PANI) films with 2-mercaptoethanol was studied by cyclic voltammetry (CV) and chronoamperometry (CA). The sulfur content in the PANI films thiolated in acidic and neutral conditions at different applied potentials was used as the measure of the degree of thiolation. FTIR spectroscopy was used to study the changes in the PANI structure after thiolation. The thiolation experiments were performed in 1.0 M HCl and 0.1 M KCl with three different thiol concentrations. Thiolation provides an easy and straight-forward method to bind covalently molecules, even biomolecules to the PANI backbone. Optimization of the thiolation conditions is the key issue when designing PANI-based biosensors. The results show that with the CA technique it is possible to bind thiolated molecules on PANI both in HCl and in KCl. Furthermore, the results indicate that the potential applied, the thiolation medium and the concentration of the added thiol affect the thiolation process. CA offers an opportunity to enhance the thiolation allowing to some extent also to control the entire process opening up new possibilities to prepare PANI based biosensor substrates. [ABSTRACT FROM AUTHOR]

The drive towards all solid state lithium ion batteries requires discovery of new methods for synthesis of true hybrid solid electrolytes in which organic and inorganic components are chemically associated to simultaneously maximize lithium ion conductivity and processability. Herein, the first mechanochemical milling synthesis of an ambient processable hybrid lithium aluminum germanium phosphate (Li 1.5 Al 0.5 Ge 1.5 (PO 4) 3)/polyethylene glycol (PEG) solid electrolyte is presented. Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA) provide evidence that the mechanochemical milling procedure impels a condensation reaction between the ceramic and organic phases which produces a surface product, water. Solid state nuclear magnetic resonance (NMR) spectroscopy confirms that protons from the polymer or associated surface water product are in bonding proximity to the Q2 metaphosphate sites of the glassy phase of the ceramic. This work thus establishes the viability of mechanochemical milling as a synthetic pathway for a class of promising ambient processable hybrid electrolytes. • Mechanochemical synthesis shown for hybrid solid electrolyte for Li-ion batteries. • They hybrid polymer/ceramic electrolyte is composed of moisture stable materials. • Polymer and ceramic are established to be in bonding proximity. [ABSTRACT FROM AUTHOR]

An ultrasensitive immunosensor based on potentiometric ELISA for the detection of a cardiac biomarker, troponin I–T–C (Tn I–T–C) complex, was developed. The sensor fabrication involves typical sandwich ELISA procedures, while the final signal readout was achieved using open circuit potentiometry (OCP). Glassy carbon (GC) working electrodes were first coated with emulsion-polymerized polyaniline/dinonylnaphthalenesulfonic acid (PANI/DNNSA) and the coated surface was utilized as a transducer layer on which sandwich ELISA incubation steps were performed. An enzymatic reaction between o-phenylenediamine (OPD) and hydrogen peroxide (H 2 O 2 ) was catalyzed by horseradish peroxidase (HRP) labeled on the secondary antibodies. The polymer transducer charged state was mediated through electron (e − ) and charge transfers between the transducer and charged species generated by the same enzymatic reaction. Such a change in the polymer transducer led to potential variations against an Ag/AgCl reference electrode as a function of Tn I–T–C complex concentration during incubations. The sequence of OPD and H 2 O 2 additions, electrochemical properties of the PANI/DNNSA layer and non-specific binding prevention were all crucial factors for the assay performance. Under optimized conditions, the assay has a low limit of detection (LOD) (<5 pg/mL or 56 fM), a wide dynamic range (>6 orders of magnitude), high repeatability (coefficient of variance <8% for all concentrations higher than 5 pg/mL) and a short detection time (<10 min). [ABSTRACT FROM AUTHOR]

Abstract: Polyaniline (PANI) is a conducting polymer, easily synthesized and lucrative for many electrochemical applications like ion-selective sensors and biosensors. Thiolated molecules, including biological ones, can be bound by nucleophilic attachment to the polyaniline backbone. These covalently bound thiols add functionality to PANI, but also cause changes in the electrochemical properties of PANI. Polyaniline studied in this work was electropolymerized on glassy carbon electrodes. 2-Mercaptoethanol (MCE) and 6-(ferrocenyl)hexanethiol (FCHT) were used as the thiols to form functionalized films. The films were characterized by cyclic voltammetry (CV), ex situ FTIR and Raman spectroscopies, electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The goal of this work was to confirm the thiolation by spectroscopic methods and to study the impact of thiolation on the electrochemical properties of PANI. Our study showed that thiolated PANI has different electrochemical properties than PANI. Although the thiolation partially reduced the PANI backbone it still remained conductive after the thiolation. Detailed understanding of the thiolation process can be very useful for future applications of PANI. [Copyright &y& Elsevier]

Abstract: PEDOT layers were electrodeposited from aqueous solutions in the presence of various solubilizing agents. A systematic study involving a large number of solubilizers was conducted. The six surfactants used were sodium dodecyl sulfate (SDS) and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) (both anionic), Tween 80 and Triton X-100 (both non-ionic), hexadecyltrimethylammonium p-toluenesulfonate (HDTMA) and hexadecyl(2-hydroxyethyl)dimethylammonium dihydrogen phosphate (HDHEDMA) (both cationic). Two polyelectrolytes, sodium polystyrene sulfonate (PSS) and κ-carrageenan were also used. It was found that the nature of the solubilizing agent has a drastic effect on the polymerization conditions. The anionic solubilizing agents decreased the polymerization potential and eliminated the induction period of the polymerization. As a result, PEDOT layers with longer conjugation length as well as higher conductivity and transparency were deposited. These layers were incorporated into polymer solar cell as hole transporting layers and efficiencies close to the traditional spin-coated PEDOT:PSS layers have been reported. By contrast, cationic surfactants increased the polymerization potential by 0.21V and a significant induction period was observed during the polymerization. In this case, PEDOT layers of poor quality were deposited and the efficiencies of the solar cells dropped by an order of magnitude. PEDOT layers deposited in the presence of non-ionic surfactants or without any solubilizing agent showed an intermediate performance. In addition to the strong effect of charge, the bulkiness of the solubilizing agent was also found to significantly affect the polymerization and properties of PEDOT. [Copyright &y& Elsevier]

Covalent attachment of thiolated probes to conducting polymers such as polyaniline (PANI) is a promising approach towards the development of electrochemical sensors and biosensors. However, thiolation alters the conjugated polymer backbone and influences the electrochemical behavior of the conducting polymer. PANI studied in this work was electropolymerized on glassy carbon (GC) electrodes from a solution of 0.1 M aniline in 0.5 or 1.0 M HSO. The GC/PANI electrodes were then functionalized by covalent attachment of 2-mercaptoethanol to the PANI backbone. The progress of thiolation was studied by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Thiolation of PANI was found to cause an initial decrease in electroactivity at 0-0.25 V and an increase in electroactivity at 0.25-0.6 V. However, prolonged thiolation caused a loss of electroactivity of PANI, which could be seen from EIS measurements as a dramatic decrease in the bulk redox capacitance of PANI. [ABSTRACT FROM AUTHOR]

Abstract: A new electrochemical approach to fabricate polymer solar cell has been developed. Electropolymerization of 2,2′-bithiophene was done on top of the electrodeposited p-doped PEDOT layer. Fullerene was deposited as a third layer after initiating n-doping of the polymers. Composition and oxidation states of the polymers were monitored by UV-Vis-NIR spectroscopy. Morphological changes were followed with Atomic Force Microscopy (ATM) revealing rough nanostructures of the layers. The composition and performance of the solar cells were compared to the cells fabricated by using conventional spin-coating technique. Photoresponse with the maximum V oc of 0.47 V and the highest J sc of 0.55 mA/cm2 was measured. [Copyright &y& Elsevier]

Abstract: The continuing discovery of cancer biomarkers necessitates improved methods for their detection. Molecular imprinting using artificial materials provides an alternative to the detection of a wide range of substances. We applied surface molecular imprinting using self-assembled monolayers to design sensing elements for the detection of cancer biomarkers and other proteins. These elements consist of a gold-coated silicon chip onto which hydroxyl-terminated alkanethiol molecules and template biomolecule are co-adsorbed, where the thiol molecules are chemically bound to the metal substrate and self-assembled into highly ordered monolayers, the biomolecules can be removed, creating the foot-print cavities in the monolayer matrix for this kind of template molecules. Re-adsorption of the biomolecules to the sensing chip changes its potential, which can be measured potentiometrically. We applied this method to the detection of carcinoembryonic antigen (CEA) in both solutions of purified CEA and in the culture medium of a CEA-producing human colon cancer cell line. The CEA assay, validated also against a standard immunoassay, was both sensitive (detection range 2.5–250ng/mL) and specific (no cross-reactivity with hemoglobin; no response by a non-imprinted sensor). Similar results were obtained for human amylase. In addition, we detected virions of poliovirus in a specific manner (no cross-reactivity to adenovirus, no response by a non-imprinted sensor). Our findings demonstrate the application of the principles of molecular imprinting to the development of a new method for the detection of protein cancer biomarkers and to protein-based macromolecular structures such as the capsid of a virion. This approach has the potential of generating a general assay methodology that could be highly sensitive, specific, simple and likely inexpensive. [Copyright &y& Elsevier]

The occurrence of scanning electron microscopy (SEM) and atomic force microscopy (AFM) side-by-side is becoming increasingly common in analytical research. This article shows microscopy techniques to image Bacillus spores, to measure spore dimensions, and to demonstrate how these methods provide supplementary information to study plasma torch effects. This paper demonstrates that observed morphologies of spores before and after exposure to a plasma torch are remarkably different. The use of SEM and AFM as a tool complex enables examination of spore morphology and dimensions as well as their alterations during decontamination using plasma torch. [ABSTRACT FROM AUTHOR]

The air plasma effluent of an arc-seed microwave torch is used to kill bacterial spores contained inside an envelope. The torch is operated at a 60-Hz periodic mode (with about 40% duty cycle) and runs stably at a low airflow rate (e.g., 0.3931/s). The images of plasma torch plumes show that the arc loop of the discharge prolongs from the electrodes by nearly 3 cm and microwave energizes the charge particles along the arc loop considerably. The emission spectroscopy of the torch indicates that the plasma effluent contains an abundance of reactive atomic oxygen. Bacillus cereus is chosen for the biological agent in the decontamination experiment. The experiment and the decontamination efficacy of this torch are presented. The averaged temperature inside the envelope is measured to be less than 40 °C, thus ruling out the thermal decontamination mechanism. [ABSTRACT FROM AUTHOR]