Carbon paste electrode incorporated with cobalt(II) octaethoxyphthalocyanine for the amperometric detection of hydrogen peroxide

Development of a cobalt(II) phthalocyanine- MWCNT modified carbon paste electrode for the detection of polyunsaturated fatty acids

In this work the development of an electrochemical sensor for the determination of polyunsaturated fatty acids (PUFAs), in particular linoleic acid, in commercially available safflower oil as complex matrix is described. The sensor consists of a carbon paste electrode with cobalt(II) phthalocyanine, Co(II)Pc, as mediator and multiwalled carbon-nanotubes (MWCNT) as nanomaterial. As carrier medium a sodium borate buffer (0.1 M, pH 9) was used. PUFAs were detected at a working voltage of 0.35-0.45 V (vs. Ag/AgCl). The sensor development was carried out in a batch system with differential pulse voltammetry (DPV) and cyclic voltammetry (CV). Sensor specification was tested by using various fatty acids (stearic acid, oleic acid, linoleic acid, linolenic acid and arachidonic acid) as well as esterified fatty acids, resulting in a specific applicability towards PUFAs, especially linoleic acid (LAH). The optimized sensor was applied in a flow injection analysis system (FIA) for the analysis of PUFAs in complex matrix. Linoleic acid was used as standard substrate to determine the analytical parameters. The linearity ranges between 7.5 and 200 μg mL^-1 LAH, while the limit of detection was determined to be 2.5 μg mL^-1 and the limit of quantification is approximately 7.5 μg mL^-1 LAH. The LAH content was successfully detected in commercially available safflower oil via standard addition method and the results could be confirmed by a reference method. The PUFA content was calculated as LAH-equivalent.

Advances in management of type 1 diabetes mellitus

Treatment of type 1 diabetes mellitus has always posed a challenge to balance hyperglycemia control with hypoglycemia episodes. The quest for newer therapies is continuing and this review attempts to outline the recent developments. The insulin molecule itself has got moulded into different analogues by minor changes in its structure to ensure well controlled delivery, stable half-lives and lesser side effects. Insulin delivery systems have also consistently undergone advances from subcutaneous injections to continuous infusion to trials of inhalational delivery. Continuous glucose monitoring systems are also becoming more accurate and user friendly. Smartphones have also made their entry into therapy of diabetes by integrating blood glucose levels and food intake with calculated adequate insulin required. Artificial pancreas has enabled to a certain extent to close the loop between blood glucose level and insulin delivery with devices armed with meal and exercise announcements, dual hormone delivery and pramlintide infusion. Islet, pancreas-kidney and stem cells transplants are also being attempted though complete success is still a far way off. Incorporating insulin gene and secretary apparatus is another ambitious leap to achieve insulin independence though the search for the ideal vector and target cell is still continuing. Finally to stand up to the statement, prevention is better than cure, immunological methods are being investigated to be used as vaccine to prevent the onset of diabetes mellitus.

A promising solution to enhance the sensocompatibility of biosensors in continuous glucose monitoring systems

BACKGROUND

Continuous glucose monitors (CGMs) measure glucose in real time, making it possible to improve glycemic control. A promising technique involves glucose sensors implanted in subcutaneous tissue measuring glucose concentration in interstitial fluid. A major drawback of this technique is sensor bioinstability, which can lead to unpredictable drift and reproducibility. The bioinstability is partly due to sensor design but is also affected by naturally occurring subcutaneous inflammations. Applying a nonbiofouling coating to the sensor membrane could be a means to enhancing sensocompatibility.

METHODS

This study evaluates the suitability of a polyethylene-glycol-based coating on sensors in CGMs. Methods used include cross hatch, wet paper rub, paper double rub, bending, hydrophilicity, protein adsorption, bio-compatibility, hemocompatibility, and glucose/oxygen permeability testing.

RESULTS

Results demonstrate that coating homogeneity, adhesion, integrity, and scratch resistance are good. The coating repels lysozyme and bovine serum albumin, and only a low level of fibrin and blood platelet adsorption to the coating was recorded when testing in whole human blood. Cytotoxicity, irritation, sensitization, and hemolysis were assessed, and levels suggested good biocompatibility of the coating in subcutaneous tissue. Finally, it was shown that the coating can be applied to cellulose acetate membranes of different porosity without changing their permeability for glucose and oxygen.

CONCLUSIONS

These results suggest that the mechanical properties of the coating are sufficient for the given application, that the coating is effective in preventing protein adsorption and blood clot formation on the sensor surface, and that the coating can be applied to membranes without hindering their glucose and oxygen transport.

Silver nanoparticle assemblies supported on glassy-carbon electrodes for the electro-analytical detection of hydrogen peroxide

Electrochemical detection of hydrogen peroxide using an edge-plane pyrolytic-graphite electrode (EPPG), a glassy carbon (GC) electrode, and a silver nanoparticle-modified GC electrode is reported. It is shown, in phosphate buffer (0.05 mol L(-1), pH 7.4), that hydrogen peroxide cannot be detected directly on either the EPPG or GC electrodes. However, reduction can be facilitated by modification of the glassy-carbon surface with nanosized silver assemblies. The optimum conditions for modification of the GC electrode with silver nanoparticles were found to be deposition for 1 min at -0.5 V vs. Ag from 5 mmol L(-1) AgNO3/0.1 mol L(-1) TBAP/MeCN, followed by stripping for 2 min at +0.5 V vs. Ag in the same solution. A wave, due to the reduction of hydrogen peroxide on the silver nanoparticles is observed at -0.68 V vs. SCE. The limit of detection for this modified nanosilver electrode was 2.0 x 10(-6) mol L(-1) for hydrogen peroxide in phosphate buffer (0.05 mol L(-1), pH 7.4) with a sensitivity which is five times higher than that observed at a silver macro-electrode. Also observed is a shoulder on the voltammetric wave corresponding to the reduction of oxygen, which is produced by silver-catalysed chemical decomposition of hydrogen peroxide to water and oxygen then oxygen reduction at the surface of the glassy-carbon electrode.

Elongation of the pi-system of phthalocyanines by introduction of thienyl substituents at the peripheral beta positions. Synthesis and characterization

1,4,8,11,15,18,22,25-octabutoxyphthalocyanines ((OBu)8Pcs) having eight 2-thienyl (1) and [2,2'-bithiophene]-5-yl (2) groups at beta positions and their zinc(II) and cobalt(II) derivatives were prepared from 2-thienyl- (3) or [2,2'-bithiophene]-5-yl (4)-substituted phthalonitriles in moderate to good yields. The electronic absorption spectra of the Pcs showed red-shifted Q-bands relative to beta-unsubstituted (OBu)8Pcs. The longer substituent, the [2,2'-bithiophene]-5-yl group, is more effective than the 2-thienyl group in enlarging the pi-conjugated system of the Pcs. The ring oxidation potential obtained by cyclic voltammetry shifted cathodically with increasing chain length, indicating destabilization of the HOMOs. Due to the shift of the Q-band, 2-thienyl- and [2,2'-bithiophene]-5-yl-substituted Pcs exhibit a remarkable color change from the original green color.