Electrochemical Sensors for Detection of Toxins in Aqueous Phase

先進電化學傳感器的開發及其在水相毒素檢測中的應用

Student thesis: Doctoral Thesis

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Supervisors/Advisors
Award date12 Oct 2018

Abstract

Drinking water has become critical resource, especially with the population boom and the ever increasing scarcity of fresh water supply. To cope with the increasing demand, new technologies are springing up with the objective of water treatment and purification. Additionally, new materials such as plastics are being used to store and transport water. All these changes lead into new forms of water contamination. Over the past few decades, there have been several high-profile instances of severe water contamination affecting entire communities and lowering the quality of life such as the Flint, Michigan lead contamination, 2015 Hong Kong public estates lead contamination and 2011 Taiwan food scandal. Therefore, it is of paramount importance to rigorously monitor the quality of water in order to maintain good general public health. Presently, the technologies to monitor water quality mostly use expensive laboratory based equipment, requiring specially trained users to operate. Generally speaking, these tests take up a significant amount of time and sometimes fail to mitigate contamination events in the early stages when it is easier to locate the source of the problem. To supplement these establish lab based techniques, cheap on-site techniques to test water quality reliably are in demand as pre-screening tools. In this work, we describe three new innovative on-site techniques to detect 3 different toxins in drinking water.

On-site monitoring of heavy metals in drinking water has become crucial due to several high profile instances of contamination. Presently, reliable techniques for trace level heavy metal detection are mostly laboratory based while the detection limits of contemporary field methods based are barely meeting the exposure limits set by regulatory bodies such as. World Health Organization (W.H.O). Here we show an on-site deployable, Pb2+ sensor on a dual-gated transistor platform whose lower detection limit is two orders of magnitude better than the traditional sensor and one order of magnitude lower than the exposure limit set by W.H.O. The enhanced sensitivity of our design is verified by numerically solving PNP (Planck-Nernst-Poisson) model. We demonstrate that the enhanced sensitivity is due to the suppression of ionic flux. The simplicity and the robustness of the design make it applicable for on-site screening, thereby facilitating rapid response to contamination events.

Phthalates, which are proven to have adverse health effects, are globally restricted for use in all kinds of plastics through various regulations. Although there are laboratory based techniques for phthalate detection, there is a pressing need for a field based technique so samples can be pre-screened. Here, we report a molecularly imprinted polymer (MIP) functionalized extended gate field effect transistor (EGFET) as a field sensor to identify di-2-ethlyhexyl phthalate (DEHP), which is the one of the most commonly used phthalate. In DI water, DEHP is detected at the extremely low concentration of 25μg/L while exhibiting excellent selectivity. We are able to tune the linear dynamic range of the sensor by synthesizing the MIP with a different monomer-to-template ratio and by choice of the functional monomer. Finally, the sensor is calibrated for DEHP in artificial saliva at sub 50μg/L, showing applicability in phthalate migration tests, which are used in assessing the safety of plastic toys. Furthermore, our sensor platform can be further extended to identify other phthalates as fast pre-screening tool.

Using electrochemical impedance spectroscopy, we developed a flexible sensor for histamine using molecularly imprinted polymer as the sensing layer. The sensor can be produced easily on a large scale using roll-roll technologies. In DI water, the sensor can achieve a detection limit of 100 mg/L and a range between 100 – 500 mg/L. This is a biologically relevant limit as the exposure limit of histamine in water is set at 200 mg/L. Selectivity tests show the sensor is able to distinguish histamine (100 mg/L) even with a high background concentration of histidine (1000 mg/L).

    Research areas

  • Electrochemical sensor, extended gate field effect transistor, EIS electrochemical impedance spectroscopy sensor, ion selective membrane, molecular imprinted polymer, heavy metal sensor, phthalate sensor, histamine sensor