Fabrication of optochemical and electrochemical sensors using thin films of porphyrin and phthalocyanine derivatives

This paper describes the fabrication of thin films of porphyrin and metallophthalocyanine derivatives on different substrates for the optochemical detection of HCl gas and electrochemical determination of L-cysteine (CySH). Solid state gas sensor for HCl gas was fabricated by coating meso-substituted porphyrin derivatives on glass slide and examined optochemical sensing of HCl gas. The concentration of gaseous HCl was monitored from the changes in the absorbance of Soret band. Among the different porphyrin derivatives, meso- tetramesitylporphyrin (MTMP) coated film showed excellent sensitivity towards HCl and achieved a detection limit of 0.03ppm HCl. Further, we have studied the self-assembly of 1,8,15,22-tetraaminometallophthalocyanine (4α-MTAPc; M = Co and Ni) from DMF on GC electrode. The CVs for the self-assembled monolayers (SAMs) of 4α-CoIITAPc and 4α-NiIITAPc show two pairs of well-defined redox couple corresponding to metal and ring. Using the 4α-CoIITAPc SAM modified electrode, sensitive and selective detection of L-cysteine was demonstrated. Further, the SAM modified electrode also successfully separates the oxidation potentials of AA and CySH with a peak separation of 320mV.

Selective electrochemical epinephrine sensor using self-assembled monomolecular film of 1,8,15,22-tetraaminophthalocyanatonickel(II) on gold electrode

This article describes the highly sensitive and selective determination of epinephrine (EP) using self-assembled monomolecular film (SAMF) of 1,8,15,22-tetraamino-phthalocyanatonickel(II) (4α-NiIITAPc) on Au electrode. The 4α-NiIITAPc SAMF modified electrode was prepared by spontaneous adsorption of 4α-NiIITAPc from dimethylformamide solution. The modified electrode oxidizes EP at less over potential with enhanced current response in contrast to the bare Au electrode. The standard heterogeneous rate constant (k°) for the oxidation of EP at 4α-NiIITAPc SAMF modified electrode was found to be 1.94×10−2 cm s−1 which was much higher than that at the bare Au electrode. Further, it was found that 4α-NiIITAPc SAMF modified electrode separates the voltammetric signals of ascorbic acid (AA) and EP with a peak separation of 250 mV. Using amperometric method the lowest detection limit of 50 nM of EP was achieved at SAMF modified electrode. Simultaneous amperometric determination of AA and EP was also achieved at the SAMF modified electrode. Common physiological interferents such as uric acid, glucose, urea and NaCl do not interfere within the potential window of EP oxidation. The present 4α-NiIITAPc SAMF modified electrode was also successfully applied to determine the concentration of EP in commercially available injection.

Amino group positions dependent morphology and coverage of electropolymerized metallophthalocyanine (M = Ni and Co) films on electrode surfaces

Electropolymerized films of teraaminometallophthalocyanines (MTAPc; M = Ni and Co) with amino groups at α- (4α-MTAPc) and β- (4β-MTAPc) positions were prepared on glassy carbon (GC) and indium tin oxide (ITO) electrodes. It was found that the electropolymerization growth rate of 4α-MTAPc was less than that of 4β-MTAPc prepared under identical conditions. Further, the surface coverage of the polymerized 4β-MTAPc film was greater than that of 4α-MTAPc polymerized film. Atomic force microscopy (AFM), X-ray diffraction (XRD) and UV–visible spectroscopic studies were carried out for the polymerized films of 4α-NiIITAPc (p-4α-NiIITAPc) and 4β-NiIITAPc (p-4β-NiIITAPc) alone because both Ni(II) and Co(II) polymerized films show similar trend in electropolymerization and surface coverage values. AFM images show that p-4α-NiIITAPc film contains islands and the thickness of this film was nearly three times less than that of p-4β-NiIITAPc. XRD patterns for the two polymerized films reveal that p-4β-NiIITAPc film was relatively more crystalline than p-4α-NiIITAPc film. Further, the compactness of these films was scrutinized from their barrier properties toward [Fe(CN)6]3−/4− redox couple. The differences in the polymerization growth rate of 4α-MTAPc and 4β-MTAPc, and the thicknesses of the resultant polymerized films suggest that unlike 4β-MTAPc one or two amino groups might have not involved in electropolymerization in the case of 4α-MTAPc. Further, the influence of surface coverage on the electrocatalytic properties of the polymerized films was studied by taking p-4β-CoIITAPc and p-4α-CoIITAPc films as examples. The electrocatalytic oxygen reduction current was almost same at both the electrodes suggesting that only the surface species were involved in the electrocatalytic reduction of oxygen.

Amino group position dependent orientation of self-assembled monomolecular films of tetraaminophthalocyanatocobalt(II) on Au surfaces

Self-assembled monomolecular films of 1,8,15,22-tetraaminophthalocyanatocobalt(II) (4α-CoIITAPc) and 2,9,16,23-tetraaminophthalocyanatocobalt(II) (4β-CoIITAPc) on Au surfaces were prepared by spontaneous adsorption from solution. These films were characterized by cyclic voltammetry and Raman spectroscopy. Both the surface coverage (Γ) and intensity of the in-plane stretching bands obtained from Raman studies vary for these monomolecular films, indicating different orientations adopted by them on Au surfaces. The 4α-CoIITAPc-modified electrode exhibits an E1/2 of 0.35 V, while the 4β-CoIITAPc-modified electrode exhibits an E1/2 of 0.19 V, corresponding to the CoII/CoIII redox couple in 0.1 M H2SO4. The Γ estimated from the charge associated with the oxidation of Co(II) gives (2.62 ± 0.10) × 10-11 mol cm-2 for 4α-CoIITAPc and (3.43 ± 0.14) × 10-10 mol cm-2 for 4β-CoIITAPc. In Raman spectral studies, the intensity ratio between in-plane phthalocyanine (Pc) stretching and the Au−N stretching was found to be 6.6 for 4β-CoIITAPc, while it was 1.6 for 4α-CoIITAPc. The obtained lower Γ and intensity ratio values suggest that 4α-CoIITAPc adopts nearly a parallel orientation on the Au surface, while the higher Γ and intensity ratio values suggest that 4β-CoIITAPc adopts a perpendicular orientation. The electrochemical reduction of dioxygen was carried out using these differently oriented Pc's in phosphate buffer solution (pH 7.2). Both the Pc's catalyze the reduction of dioxygen; however, the 4α-CoIITAPc-modified electrode greatly reduces the dioxygen reduction overpotential compared to 4β-CoIITAPc-modified and bare Au electrodes.

Electrocatalytic oxidation of ascorbic acid using a single layer of gold nanoparticles immobilized on 1,6-hexanedithiol modified gold electrode

This paper describes the electrocatalytic oxidation of ascorbic acid (AA) in phosphate buffer solution by the immobilized citrate capped gold nanoparticles (AuNPs) on 1,6-hexanedithiol (HDT) modified Au electrode. X-ray photoelectron spectrum (XPS) of HDT suggests that it forms a monolayer on Au surface through one of the two single bondSH groups and the other single bondSH group is pointing away from the electrode surface. The free single bondSH groups of HDT were used to covalently attach colloidal AuNPs. The covalent attachment of AuNPs on HDT monolayer was confirmed from the observed characteristic carboxylate ion stretching modes of citrate attached with AuNPs in the infra-red reflection absorption spectrum (IRRAS) in addition to a higher reductive desorption charges obtained for AuNPs immobilized on HDT modified Au (Au/HDT/AuNPs) electrode in 0.1 M KOH when compared to HDT modified Au (Au/HDT) electrode. The electron transfer reaction of [Fe(CN)6]4−/3− was markedly hindered at the HDT modified Au (Au/HDT) electrode while it was restored with a peak separation of 74 mV after the immobilization of AuNPs on Au/HDT (Au/HDT/AuNPs) electrode indicating a good electronic communication between the immobilized AuNPs and the underlying bulk Au electrode through a HDT monolayer. The Cottrell slope obtained from the potential-step chronoamperometric measurements for the reduction of ferricyanide at Au/HDT/AuNPs was higher than that of bare Au electrode indicating the increased effective surface area of AuNPs modified electrode. The Au/HDT/AuNPs electrode exhibits excellent electrocatalytic activity towards the oxidation of ascorbic acid (AA) by enhancing the oxidation peak current to more than two times with a 210 mV negative shift in the oxidation potential when compared to a bare Au electrode. The standard heterogeneous electron transfer rate constant (ks) calculated for AA oxidation at Au/HDT/AuNPs electrode was 5.4 × 10−3 cm s−1. The oxidation peak of AA at Au/HDT/AuNPs electrode was highly stable upon repeated potential cycling. Linear calibration plot was obtained for AA over the concentration range of 1–110 μM with a correlation coefficient of 0.9950. The detection limit of AA was found to be 1 μM. The common physiological interferents such as glucose, oxalate ions and urea do not show any interference within the detection limit of AA. The selectivity of the AuNPs modified electrode was illustrated by the determination of AA in the presence of uric acid.

An SECM study on the influence of cationic, membrane-active peptides on a gold-supported self-assembled monolayer

The influence of the membrane active peptides, Tat44–57 (activator in HIV-1) and melittin (active content of bee venom), on self-assembled monolayers of 6-mercaptohexanoic acid (MHA) on gold electrodes has been studied with scanning electrochemical microscopy (SECM). It was found that MHA, when deprotonated at physiological pH, significantly affected the relative rates of electron transfer between the [Fe(CN)6]4− solution based mediator and the underlying gold electrode, predominantly by the electrostatic interaction between the mediator and MHA. Upon the introduction of Tat44–57 ormelittin to the electrolyte, the relative rate of electron transfer through the MHA layer could be increased or decreased depending on the mediator used. However, in all cases it was found that these peptides have the ability to be incorporated into synthetic SAMs, which has implications for future electrochemical studies carried out using cell mimicking membranes immobilised on such layers.

Nanoscale texture on glass and titanium substrates by physical vapor deposition process

The aim of the paper is to give a feasibility study on the material deposition of Nanoscale textured morphology of titanium and titanium oxide layers on titanium and glass substrates. As a recent development in nanoscale deposition, Physical Vapor Deposition (PVD) based DC magnetron sputtering has been the choice for the deposition process. The nanoscale morphology and surface roughness of the samples have been characterized using Atomic Force Microscope (AFM). The surface roughnesses obtained from AFM have been compared using surface profiler. From the results we can say that the roughness values are dependent on the surface roughness of the substrate. The glass substrate was relatively smoother than the titanium plate and hence lower layer roughness was obtained. From AFM a unique nano-pattern of a boomerang shaped titanium oxide layer on glass substrate have been obtained. The boomerang shaped nano-scale pattern was found to be smaller when the layer was deposited at higher sputtering power. This indicated that the morphology of the deposited titanium oxide layer has been influenced by the sputtering power.

Response of laminated glass panels to near field blast events

This thesis develops and applies an analytical method to treat the blast response of glass façades and studies the influence of controlling parameters such as all component materials and geometric properties, support conditions and energy absorption, and hence establishes a framework for their design for a credible blast event.

pH testing for detecting the position of nasogastric tubes in adults and children (Intervention Protocol)

This is the protocol for a review and there is no abstract. The objectives are as follows: Our objective is to determine if there is sufficient evidence to recommend the use of pH testing (the intervention under scrutiny) for verification of correct placement of nasogastric tubes in adults and children. To this end, we will attempt to answer the following questions: 1. In adults and children, is pH testing an effective and safe method for determining whether nasogastric tubes are correctly positioned in the stomach before feeding (or delivery of any fluid) begins? 2. What evidence is there about the risk of adverse events in the case of incorrect placement? For this review, pH testing is defined as: litmus paper, pH indicator test strips, pH meters. These will be tested against other methods used for detecting placement of nasogastric tubes, including visual examination of aspirate, auscultation with insufflation of air, detection of air bubbles in a bowl of water, X-ray, ultrasonography, endoscopy, enzyme analysis of aspirate, capnography, and other methods that do not rely on measurement of pH.

Organic photovoltaics using thin gold film as an alternative anode to indium tin oxide

Indium Tin Oxide (ITO) is the most commonly used anode as a transparent electrode and more recently as an anode for organic photovoltaics (OPVs). However, there are significant drawbacks in using ITO which include high material costs, mechanical instability including brittleness and poor electrical properties which limit its use in low-cost flexible devices. We present initial results of poly(3-hexylthiophene): phenyl-C61-butyric acid methyl ester OPVs showing that an efficiency of 1.9% (short-circuit current 7.01 mA/cm2, open-circuit voltage 0.55 V, fill factor 0.49) can be attained using an ultra thin film of gold coated glass as the device anode. The initial I-V characteristics demonstrate that using high work function metals when the thin film is kept ultra thin can be used as a replacement to ITO due to their greater stability and better morphological control.

Influence of interlayer properties on the blast performance of laminated glass panels

This paper investigates the influence of interlayer properties on the blast performance of laminated glass (LG) panels. A parametric study is carried out by varying the thickness and Young’s modulus (E) of the interlayer under two different blast loads. Results indicate the existence of a critical interlayer thickness (or E) that causes the onset of interlayer failure. This should be achieved in the design to enhance energy absorption, reduce support reactions and initiate a safer failure mode. Present findings provide information to achieve such design targets and enable safe and efficient performance of LGs under credible blast loads.