Electrochemical detection of neurotransmitters at structurally small electrodes

Electroanalytical chemistry has been widely developed and applied to the study of neurochemical systems. This then leads to a better understanding of many aspects of neurotransmission, for example, neural circuitry and neural substrates of compulsive drug use. This feasibility partly stems from the ease of oxidative detection of many neurotransmitters including dopamine, acetylcholine, norepinephrine, serotonin, glutamic acid and γ–aminobutyric acid. At the same time, this has also stimulated the development of structurally small electrodes for applications to the detection of neurotransmitters in biological microenvironments. In this respect, the small dimension of such electrodes permits minimal tissue damage upon implantation and, of equal importance, permits very careful selection of the region of tissue where measurements can be performed. In addition, the inherent fast response time of structurally small electrodes makes it feasible to follow biochemical events frequently taking place on a millisecond time scale (e.g. neuronal firing). Various electrode materials used to construct structurally small electrodes of different geometries and sizes have hitherto been reported. Common electrode materials both modified and otherwise, include metals such as tungsten and aluminium, gold nanoparticledeposited aluminium, various forms of carbon e.g. doped diamond, nanocrystalline diamond, pyrolysed carbon, carbon fibres, and gold nanoparticles deposited onto glassy carbon. A common problem encountered while performing in vivo electrochemical analyses of neurotransmitters is the adsorption of lipids, peptides and high molecular weight proteins present in biological matrices on the electrode surface. Formation of these layers leads to electrode fouling which distorts the voltammetric signal and suppresses the sensitivity of the electrode. Considerable research effort has been devoted to addressing electrode fouling problems. Approaches ranging from fast scan voltammetry, immobilising a protective organic film on the electrode surface, completely altering the surface termination, fabrication of nanocrystalline diamond coated electrodes, or of doped diamond electrodes, to gold electrodes modified with gold nanorod and gold nanoparticles have been developed. Apart from overcoming fouling, the latter methods have also demonstrated other advantages such as wider potential windows, greater durability, increased robustness and enhanced sensitivity. In this paper, we aim to thoroughly review the techniques used in developing structurally small electrodes of different geometries, which were then applied to the detection of neurotransmitters. We will also pay special emphasis on the strategies used to minimize electrode fouling during electrochemical detection of neurotransmitters at these electrodes. A comparison of these methods and possible future directions in the development of structurally small electrodes for detection of neurotransmitters will conclude the review

First assessment of metals contamination in road dust and roadside soil of Suva City, Fiji

Studies have claimed that road dust and roadside soil are potential banks of pollutants generally in urban areas. Thus, quantifying the concentrations of metals in an urban area is a prerequisite for assessing pollution and their health effects. Hence, this study reports the concentration of the metals, such as Cd, Co, Cr, Ni, Cu, Pb, Zn, and Fe, in the road dust and the roadside soil of Suva City. A total number of 45 road dust and 36 roadside soil samples were collected at 18 different locations around Suva City with potential traffic influence and analysed. The respective metals concentration in the road dust and roadside soil samples of Suva City were Cd (3.7 and 3.1 mg/kg), Co (35.0 and 33.2 mg/kg), Cr (40.0 and 34.0 mg/kg), Ni (54.3 and 32.4 mg/kg), Cu (172.3 and 265.7 mg/kg), Pb (71.0 and 59.3 mg/kg), Zn (685.0 and 507.0 mg/kg), and Fe (41,010.4 and 39,525.5 mg/kg) and showed the decreasing order as Fe > Zn > Cu > Pb > Ni > Cr > Co > Cd and Fe > Zn > Cu > Pb > Cr > Co > Ni > Cd for road dust and roadside soil, respectively. Furthermore, the mean values of the metals surpassed their background levels, except for Fe, whereas the mean values of Cd, Ni, Cu, and Zn have exceeded their permissible limits in road dust. Similarly, Cd, Cu, and Zn have exceeded their permissible limit in roadside soil except for Ni. The geo-accumulation index (Igeo) assessment of Suva City road dust thus indicated nonpolluted to moderate pollution by Ni and Cu and moderate pollution by Zn. The Igeo assessment of the roadside soil showed moderately polluted by Cu and Zn but no pollution from the remaining studied metals. Overall, the study indicated that the sampling locations at an industrial site of Suva City is highly predominated with almost all of the studied metals and is a concern to the general public who live and work within the vicinity of Walu Bay industrial area

Carbon Nanomaterials and their application to Electrochemical Sensors: A review

Carbon has long been applied as an electrochemical sensing interface owing to its unique electrochemical properties. Moreover, recent advances in material design and synthesis, particularly nanomaterials, has produced robust electrochemical sensing systems that display superior analytical performance. Carbon nanotubes (CNTs) are one of the most extensively studied nanostructures because of their unique properties. In terms of electroanalysis, the ability of CNTs to augment the electrochemical reactivity of important biomolecules and promote electron transfer reactions of proteins is of particular interest. The remarkable sensitivity of CNTs to changes in surface conductivity due to the presence of adsorbates permits their application as highly sensitive nanoscale sensors. CNT-modified electrodes have also demonstrated their utility as anchors for biomolecules such as nucleic acids, and their ability to diminish surface fouling effects. Consequently, CNTs are highly attractive to researchers as a basis for many electrochemical sensors. Similarly, synthetic diamonds electrochemical properties, such as superior chemical inertness and biocompatibility, make it desirable both for (bio) chemical sensing and as the electrochemical interface for biological systems. This is highlighted by the recent development of multiple electrochemical diamond-based biosensors and bio interfaces

Minimizing fouling at hydrogenated conical - tip carbon electrodes during Dopamine detection in vivo

In this paper, physically small conical-tip carbon electrodes (∼2−5 μm diameter and ∼4 μm axial length) were hydrogenated to develop a probe capable of withstanding fouling during dopamine detection in vivo. Upon hydrogenation, the resultant hydrophobic sp3 carbon surface deters adsorption of amphiphilic lipids, proteins, and peptides present in extracellular fluid and hence minimizes electrode fouling. These hydrogenated carbon electrodes showed a 35% decrease in sensitivity but little change in the limit of detection for dopamine over a 7-day incubation in a synthetic laboratory solution containing 1.0% (v/v) caproic acid (a lipid), 0.1% (w/v) bovine serum albumin and 0.01% (w/v) cytochrome C (both are proteins), and 0.002% (w/ v) human fibrinopeptide B (a peptide). Subsequently, during dopamine detection in vivo, over 70% of the dopamine oxidation current remained after the first 30 min of a 60-min experiment, and at least 50% remained over the next half-period at the hydrogenated carbon electrodes. On the basis of these results, an initial average electrode surface fouling rate of 1.2% min−1 was estimated, which gradually declined to 0.7% min−1. These results support minimal fouling at hydrogenated carbon electrodes applied to dopamine detection in vivo

Study of Heavy Metal Fractionation in the Lami Municipal Disposal Facility, Fiji

This work reports the first screening study of the bioavailability of heavy metals such as copper, zinc, lead and nickel in the Lami municipal disposal facility, Suva, Fiji where virtually uncontrolled dumping had been carried out for over fifty years. The soil samples from three parts of the facility were collected and the potential for mobility into the surrounding marine environment was assessed according to international guidelines. The results showed high levels of Pb in Site A (109.0 mg kg-1) and that Zn was the predominant metal across Sites B and C with 550.7 mg kg-1 and 206.8 mg kg-1, respectively. Ni was present in the least amount with the highest value 8.7 mg kg-1. In addition, Cu, Pb and Zn concentrations exceeded commonly used eco-toxicity threshold values. Moreover, there were indications that considerable leaching of the studied heavy metals may have been occurring for long periods of time at the sites. Overall, this study showed that even in areas with little industrialization, lack of adequate waste management controls could result in unusually high levels of heavy metals contamination of the soil. The results raise concerns about the wellbeing of the communities living adjacent to the Lami municipal disposal facility that depend on the adjacent marine environment for their subsistence

An Undergraduate-Level Electrochemical Investigation of Gold Nanoparticles-Modified Physically Small Carbon Electrodes

This paper reports an undergraduate experiment based on analytical chemistry, electrochemistry and materials science of carbon microelectrodes. The modification of the electroactive surface of the carbon microelectrode was done using gold nanoparticles electrodeposited from gold solution. To determine the changes on the surface, the electrode was subjected to simple optical microscopy. Next, the electrode was characterized using fast-scan cyclic voltammetry of two known electrochemical redox markers: hexaamineruthenium(III) chloride and potassium hexacyanoferrate (III), i.e. potassium ferricyanide. The redox behavior of both markers demonstrated the change in electrode surface. After modification, the ferricyanide reduction peaks were observed to increase significantly, as a consequence of accelerated electron transfer. Furthermore, changes in wave slope and half-wave potentials (E1⁄2) of the redox waves also confirmed an altered electrode surface that students can logically trace back to the modification. The electrode tip dimension was also determined using a modified form of the Cottrell equation, confirming the tip size to be 2.0 μm. The discussion of these results enables an understanding of electrochemistry, analytical chemistry and materials chemistry, and presents an excellent opportunity to apply these in an undergraduate setting

Parkinson's Disease and the Environment

Parkinson's disease (PD) is a heterogeneous neurodegenerative disorder that affects an estimated 10 million sufferers worldwide. The two forms of PD include familial and sporadic, and while the etiology of PD is still largely unknown, the condition is likely to be multifactorial with genetic and environmental factors contributing to disease genesis. Diagnosis of the condition is attained through the observation of cardinal clinical manifestations including resting tremor, muscle rigidity, slowness or loss of movement, and postural instability. Unfortunately, by the time these features become apparent extensive neurological damage has already occurred. A cure for PD has not been identified and the current therapy options are pharmaceutical- and/or surgical-based interventions to treat condition symptoms. There is no specific test for PD and most diagnoses are confirmed by a combination of clinical symptoms and positive responses to dopaminergic drug therapies. The prevalence and incidence of PD vary worldwide influenced by several factors such as age, gender, ethnicity, genetic susceptibilities, and environmental exposures. Here, we will present environmental factors implicated in sporadic PD onset. By understanding the mechanisms in which environmental factors interact with, and affect the brain we can stride toward finding the underlying cause(s) of PD

Attitude to the study of chemistry and its relationship with achievement in an introductory undergraduate course

A positive attitude to a subject may be congruent with higher achievement; however, limited evidence supports this for students in undergraduate chemistry – this may result from difficulties in quantifying attitude. Therefore, in this study, the Attitude to the Study of Chemistry Inventory (ASCI) – a validated instrument to quantify attitude, was used to measure attitude to chemistry in 125 undergraduates s udying an introductory course in chemistry, as part of a BSc Chemistry major. The 13 week course contained 4 summative assessments: practical (PRAC), tutorial (TUT), on-line web-based learning (OWL), and a final exam (FE). Sub-scales within ASCI which quantify the ‘affective’ and ‘cognitive’ components of attitude were determined. Firstly, for all 125 students, weak correlations (r) between the affective scale score and FE (r=0.275, P<0.01) and TOTAL (r=0.228, P<0.05), were recorded. Secondly, a low achieving (LA, n=48) and a high achieving (HA, n=77) group were identified using a cluster analysis procedure. The HA group scored higher than the LA group in PRAC, OWL, FE and TOTAL (all P<0.001), but the clusters were not different in their scores for either the affective or the cognitive components of attitude. There was no correlation between attitude and achievement in the HA group, and only one weak positive correlation (0.409), between the affective score and achievement in the LA group. We suggest that although a positive attitude may be an important part of the undergraduate experience, it is at best only weakly associated with achievement in undergraduate chemistry

Conquering the oceanic divide: 12 centers one link – ICT

The University of the South Pacific, one of only two regionally-owned institutions in the world encompasses twelve nations in the South Pacific Ocean. The institution provides education delivery through a total of seventeen campuses, with at least one in each country. To be able to overcome the physical divide and distance, while ensuring the quality of learning and teaching, the University utilizes internet bandwidth with student/staff interfacing applications such as Moodle, together with satellite and mobile phone technology to provide virtual classroom experience to students irrespective of location. The university has been a successful in these endeavors since the 1990s. This paper outlines the approaches adopted in offering a first year chemistry course (CH 101) in dual mode; through face-to-face teaching as well as distance and flexible learning. The course enrolls 393 students, of which 25% are registered in distance learning mode hundreds of kilometers away from the lecturer, who they will certainly never see during the delivery of the course. Yet, the course ensures delivery of course content, while students are able to share and access materials irrespective of location and mode, and have participative interactions with the teaching team and each other. The virtual classroom setup is aided by an educational support tool developed in Australia – Moodle. Moodle not only delivers their content, but allows assessment, real-time grade information, communication, performance analysis and intervention and upload of content for sharing with the class. In addition, the use of mobile phones in learning has been instrumental in ensuring students receive grading information on their mobile phones as and when they need, including while on a night out! Furthermore, these attributes of bridging the physical divide will be presented, and the paper will conclude with a discussion of new innovations that will further bring the classroom to the student irrespective of where the student is on the planet