An Electrochemical Sensor of Theophylline on a Boron-Doped Diamond Electrode Modified with Nickel Nanoparticles.

Theophylline is a drug with a narrow therapeutic range. Electrochemical sensors are a potentially effective method for detecting theophylline concentration to prevent toxicity. In this work, a simple modification of a boron-doped diamond electrode using nickel nanoparticles was successfully performed for a theophylline electrochemical sensor. The modified electrode was characterized using a scanning electron microscope and X-ray photoelectron spectroscopy. Square wave voltammetry and cyclic voltammetry methods were used to study the electrochemical behavior of theophylline. The modified nickel nanoparticles on the boron-doped diamond electrode exhibited an electrochemically active surface area of 0.0081 cm2, which is larger than the unmodified boron-doped diamond's area of 0.0011 cm2. This modified electrode demonstrated a low limit of detection of 2.79 µM within the linear concentration range from 30 to 100 µM. Moreover, the modified boron-doped diamond electrode also showed selective properties against D-glucose, ammonium sulfate, and urea. In the real sample analysis using artificial urine, the boron-doped diamond electrode with nickel nanoparticle modifications achieved a %recovery of 105.10%, with a good precision of less than 5%. The results of this work indicate that the developed method using nickel nanoparticles on a boron-doped diamond electrode is promising for the determination of theophylline.

Photoelectrochemical performance of BiOI/TiO2 nanotube arrays (TNAs) p-n heterojunction synthesized by SILAR-ultrasonication-assisted methods.

In order to extend the visible region activity of titania nanotube array (TNAs) films, the successive ionic layer adsorption and reaction (SILAR)-ultrasonication-assisted method has been used to prepare BiOI-modified TiO2 nanotube arrays (BiOI/TNAs). The band gap of BiOI/TNAs for all the variations reveals absorption in the visible absorption. The surface morphology of BiOI/TNAs is shown in the nanoplate, nanoflake and nanosheet forms with a vertical orientation perpendicular to TiO2. The crystalline structure of BiOI did not change the structure of the anatase TNAs, with the band gap energy of the BiOI/TNAs semiconductor in the visible region. The photocurrent density of the BiOI/TNAs extends to the visible-light range. BiOI/TNAs prepared with 1 mM Bi and 1 mM KI on TNAs 40 V 1 h, 50 V 30 min show the optimum photocurrent density. A tandem dye-sensitized solar cell (DSSC)-photoelectrochemical (PEC) was used for hydrogen production in salty water. BiOI/TNAs optimum was used as the photoanode of the PEC cell. The solar to hydrogen conversion efficiency (STH) of tandem DSSC-PEC reaches 1.34% in salty water.

An acetylcholinesterase-based biosensor for isoprocarb using a gold nanoparticles-polyaniline modified graphite pencil electrode.

An analysis tool for isoprocarb has been successfully developed as a biosensor system based on enzymatic inhibition of acetylcholinesterase (AChE) by isoprocarb. A gold nanoparticles-polyaniline modified graphite pencil electrode (AuNPs-PANI-GPE) was utilized to detect the change of thiocholine in the presence of isoprocarb. This electrode was prepared by two cyclic voltammetry steps, including the electro-polymerization of aniline on a graphite pencil and the electro-deposition of gold nanoparticles on the polyaniline surface. Characterization performed by SEM-EDX indicates that 8-80 nm size of gold nanoparticles could be deposited on the surface of polyaniline-modified graphite pencil (PANI-GPE). Electrochemical characterization using cyclic voltammetry suggested that the active surface area of the prepared electrode was 0.17019 cm2, which was about 4 times higher than (PANI-GPE) and 13 times higher than the unmodified GPE. Furthermore, an oxidation peak of thiocholine could be observed at the modified GPE at a potential of + 0.675 V (vs. Ag/AgCl), formed by an enzymatic reaction of AChE in the presence of acetylthiocholine. This peak current was found to linearly increase with acetylthiocholine concentrations, while in the presence of isoprocarb in a constant concentration of AChE and acetylthiocholine the peak linearly decreases. At the optimum condition of 0.1 M phosphate buffer solution pH 7.4 containing 0.1 M KCl; 100 mU/ml AChE; and 1 mM acetylthiocholine chloride in an inhibition and contact time of 25 and 15 min, respectively, a linear calibration curve of isoprocarb in the concentration range of 0.05-1.0 µM could be provided. Estimated limits of detection and quantifications of 0.1615 nM and 0.5382 nM, respectively, with a sensitivity of 1.7771 µA/µM.mm2 could be achieved. Furthermore, an excellent stability for 8 times measurements was observed with an RSD of 4.87%, suggesting that the developed tool is promising for the real detection of isoprocarb.

Modification of carbon foam with 4-mercaptobenzoic acid functionalised gold nanoparticles for an application in a yeast-based microbial fuel cell.

Modification of carbon foam with gold nanoparticles (AuNPs) was successfully performed through a hydrothermal method. The modified AuNPs were functionalised with 4-mercaptobenzoic acid (MBA) to improve their affinity toward microorganisms. TEM and SEM characterization indicated that although polydisperse spherical nanoparticles of AuNPs with particle sizes around 17 nm were obtained, the attached nanoparticles were agglomerated to be around 0.4 to 1.5 µm in size on the carbon foam surface. The electrochemical studies using cyclic voltammetry technique affirmed that the modified carbon foam electrodes have electroactive properties against glucose. Evaluation of the electrode was performed for a microbial fuel cell using Candida fukuyamaensis yeast as the microorganisms. The polarization curves showed that functionalisation of AuNPs-modified carbon foam with MBA provides around three times higher current density (1226.93 mA m-2) and power density (330.61 mW m-2) compared to the unmodified one. This result indicated that the modification is suitable to improve yeast attachment on the electrode surface.

Core-shell copper-gold nanoparticles modified at the boron-doped diamond electrode for oxygen sensors.

Bimetallic copper-gold (Cu@Au) nanoparticles were synthesized and utilised to modify boron-doped diamond (BDD) electrodes. Nanorod particles with a diameter size of around 10 nm and a length of around 20 nm were successfully synthesized. These nanoparticles were then attached to the BDD surface by using allylamine as the bridge. Comparison among the BDD modified with Cu@Au and individual gold nanoparticles showed that Cu@Au nanoparticles created around 3 times higher gold coverage on the BDD surface than normal gold nanoparticles. It was also found that the use of allylamine as the bridge can attach more gold than copper nanoparticles. Moreover, around two times higher current responses of oxygen reduction reaction were observed at Cu@Au-modified BDD. Good linearity in a concentration range from 2 to 9 ppm could be achieved with a sensitivity of 0.0138 mA ppm-1 and limit detection of 1.98 ppm. An application of the modified BDD for a biochemical oxygen demand (BOD) sensor using Rhodotorula mucilaginosa UICC Y-181 as the biosensing agent was also demonstrated with glucose solutions as the solution model. Sensitivity equivalent to 17.4 µA mM-1 BOD could be achieved. The system showed good stability with an RSD of 3.45% in 10 measurements.