Browsing by Author "Pathirathna, P."

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Electrochemical detection of Cd2+ ions in aqueous samples at nanoelectrodes
(Faculty of Science, University of Kelaniya, Sri Lanka, 2021) Ahmed, M. M. N.; Bodowara, F.; Penteado, J.; Zhou, W.; Xavier, J.; Pathirathna, P.
Contamination from heavy metals has been a potent threat to the environment, and its detrimental effects are felt globally. They bio-accumulate through the food chain, thus leaving humans highly vulnerable to overwhelming health hazards. Most traditional metal-detecting analytical instruments necessitate extensive sample pre-treatment processes, consequently, change metal speciation, one of the most critical factors for evaluating metal toxicity. Furthermore, they are cumbersome, require expensive instruments that are less user-friendly, restricting real-time metal monitoring. As a result, the development of a low-cost, portable, and reliable sensor capable of delivering precise information on metal speciation will significantly assist in the efficient implementation of metal mitigation systems. In this study, we utilize ion transfer between two immiscible electrolyte solutions (ITIES) to design a Cd2+ sensor. The chemistry at ITIES is governed by Gibbs's free energy of transfer for an ion at the interface of two immiscible solvents. A potentiostat is used to supply the energy required to overcome the energy barrier in the form of potential energy, and the resulting current is measured. ITIES is less complicated as it does not involve electron transfer; hence more attractive over other redox-based electrochemical techniques. A suitable ionophore, which lowers the energy barrier and increases the selectivity, can be added to the organic phase, facilitating the transfer of ions at lower potentials. Our electrode is a borosilicate glass electrode with an inner radius of 300 nm. It follows a hemispherical diffusion regime, owing to its nanoscale interface that allows fast kinetic measurements. An ionophore- 1-10 phenanthroline was used to facilitate the Cd2+ transfer across the nano-interface. We performed ITIES based cyclic voltammetry and amperometry experiments with our nanosensor in various matrices, including simple electrolytes like KCl and complicated buffer solutions such as artificial seawater and artificial cerebellum fluid. We also tested the strength of our ionophore against other standard ligands such as Ethylenediamine tetraacetic acid, Nitrilotriacetic acid and Dimercaptosuccinic acid etc. We found out that our electrode shows excellent stability and can withstand the complex matrices without fouling, an attractive feature of an exemplary sensor. We tested our sensor with Cd2+ dissolved in a water sample collected from Indian River Lagoon, Melbourne, FL; thus, we showcase our sensor's power as an environmental monitoring tool. To the best of our knowledge, this is the first time reporting a glass electrode with a sub-nano-meter scale for Cd2+ detection in a natural environmental sample using ITIES. Our ultra-small electrode will enable us to study the kinetics of ion transfer across ITIES; thus, allowing us to modify the sensor to enhance the sensitivity and selectivity.
A novel, ultra-fast electrochemical tool to study speciation of trace metals in aqueous solution
(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Pathirathna, P.; Siriwardhane, T.; McElmurry, S.P.; Morgan, S.L.; Hashemi, P.
Trace metals play important roles in biological and ecological systems. In biology, trace metals act as catalytic or structural cofactors and regulate biochemical processes. In the environment, natural and anthropogenic sources of trace metals mobilized into natural waters where they can create harmful and persistent pollution. Trace metal chemistry in physiological and environmental systems can fluctuate rapidly which makes it difficult to clearly define trace metals’ roles in these systems with traditional analytical methods. Furthermore, these systems are often chemically harsh and physically delicate (e.g. the brain), factors that add to the challenge of analysis in real systems. Fast scan cyclic voltammetry (FSCV) is explored in the context of rapid, minimally invasive and robust analysis of Cu2+ in aqueous samples with carbon fiber microelectrodes (CFMs). Unique Cu2+-specific waveform was generated with an optimized potential window and scan rate to provide sub-second analysis of Cu2+. An array of electrochemical and spectroscopic techniques was employed to discover the underlying mechanisms of the ultra-fast FSCV response. Adsorption was explained as the fundamental mechanism for the rapid FSCV signal and the thermodynamic properties of adsorption of Cu2+ onto CFMs were evaluated with fast scan controlled adsorption voltammetry (FSCAV) in different matrices. In aquatic systems and soils, metals commonly exist in complexed forms with organic and inorganic ligands. It is generally the free, unbound metal that is the most toxic, thus metal speciation is a critical factor when considering metal pollution. Free Cu2+ concentrations and the solution formation constant (Kf), provide valuable speciation information. We show that FSCV and FSCAV can be utilized to study copper speciation. Mathematical relationships (Equation 1) were constructed from experimental data to predict free Cu2+ concentrations and the overall Kf of a solution with a range of model ligands, representing a range of Cu2+- ligand Kf expected to be encountered naturally. These findings showcase the power of FSCV as a real-time biocompatible, eco-friendly speciation sensor with excellent sensitivity and a temporal resolution of milliseconds. Equation 1: log10(Kf) = 12.21 – (5.49 x 107) x [Cu2+]free + (0.12) x Current + (1.74 x 105) x [Cu2+]free 2 x Current + (8.82 x 1011) x [Cu2+]free 2 – (4.21 x 10-4) x Current2
A novel, ultra-fast, robust microelectrodes for real-time detection of heavy metals using fast-scan cyclic voltammetry
(Faculty of Science, University of Kelaniya, Sri Lanka, 2021) Abbood, R.; Alkhalaf, A. S. K.; Xavier, J.; Pathirathna, P.
Humans are highly vulnerable to being exposed to multiple sources of arsenic and cadmium, such as drinking water, foods, inhalation, and occupational means. The detrimental effects of arsenic and cadmium poisoning are well documented. Electrochemical sensors are more attractive over other analytical tools available for metal detection mainly due to the excellent selectivity, sensitivity, cost, and ease of use by a non-expert in the field. Interestingly, the reported electrochemical sensors for As3+ and Cd2+ in aqueous samples have been primarily performed with gold-based electrodes or other surface-modified electrode materials such as glassy carbon due to their enhanced sensitivity. However, the fabrication process of these electrodes is complex and expensive. Furthermore, most of these experiments were conducted in extreme pH conditions. Although the data obtained with environmental samples are promising, these tools are not suitable for in vivo detection of low concentrations of metals, particularly in the brain, and cannot perform fast measurements. Therefore, in this study, we developed a novel, ultra-fast, and robust electrochemical sensor that can perform real-time detection of As3+ and Cd2+ with a temporal resolution of 100 ms. Our electrode is fabricated with carbon-fibers, thus making an excellent biocompatible sensor for future in vivo studies. We performed our electrochemical measurements with cutting-edge electrochemical technology, fast-scan cyclic voltammetry. We optimized electrochemical parameters (potential window, resting potential, and scan rate) to generate unique cyclic voltammograms to identify As3+ and Cd2+ at a sub-second temporal resolution. Interestingly, we show that we can measure As3+ in the ambient air. We also performed calibration studies, selectivity, and stability studies to evaluate our novel metal sensors. Our preliminary data showcases the power of our tool as an excellent environmental sensor that can detect these two metal ions in aqueous samples. More importantly, these data indicate a great potential for developing this device to perform real-time in vivo measurements of metals in the brain.
Ultrafast, simultaneous detection of neurotransmitters and heavy metals at four- bore carbon-fiber microelectrodes using fast-scan cyclic voltammetry
(Faculty of Science, University of Kelaniya, Sri Lanka, 2021) Laud, M,; Ahmed, M. M. N; Penteado, J; Sibert, L; Page, R.; Pathirathna, P.
Progressive deterioration of brain cells leads to devastating neurological disorders such as Parkinson's and Alzheimer's. Despite the efforts taken by scientists, the pharmaceutical industry, and medical professionals to develop medicines that slow down the progression of the disease, these have become a major global concern. It is known that the etiology of these diseases is multifactorial; however, it is not fully understood yet. In addition to the currently available knowledge of some risk factors such as aging, the fundamentals of some other vital factors remain hidden due to the incompetence of existing methods. In particular, the contribution of heavy metals and the role of co-transmission on these illnesses haven't been explored experimentally in real time yet. Therefore, in this study, we fabricated the fastest four-bore carbon-fiber microelectrode (CFM) that can perform real time, simultaneous measurements of heavy metals and neurotransmitters with a temporal resolution of 100 ms. We used fast-scan cyclic voltammetry (FSCV) as our electrochemical measuring tool to perform fast measurements. Each bore in our novel electrode contains a single carbon-fiber (diameter of 5-7 µm) that acts as a single electrode. We characterized our sensor with dopamine (DA), serotonin (5-HT), ascorbic acid (AA), and Cu2+ ions in tris buffer using FSCV. To the best of our knowledge, this is the first time reporting simultaneous measurements of four analytes using FSCV. Interestingly, we find that the sensitivity of CFMs towards Cu2+ ions increases in the presence of DA and AA; this may be presumably due to the increased surface-active sites on the secondary film formed by DA, AA, and their products catalyzing the surface adsorption of Cu2+ ions. Additionally, we find that 5-HT detection with a bare electrode is not feasible in the presence of Cu2+ ions. Most likely, it is because the active sites are already occupied by Cu2+ ions, thus, leaving no room for the adsorption of 5-HT molecules. This finding is fundamentally novel and will provide an excellent platform for surface modification strategies for multi-bore CFMs to perform in vivo experiments.