| As the development of urbanization and industrialization in China, heavy metal contamination in aquatic environment has received great concerns due to the undegradability, bio-accumulation and high toxicity of heavy metals. However, how to detect heavy metals rapidly and accurately is the key challenge to investigate for researchers. Besides, it is also significant for the ecosystem and human health to monitor heavy metals on site in extensive areas such as lakes and seas.In this dissertation, micro-nano electrode arrays were mainly utilized for heavy metal analysis in water with anodic stripping voltammetry. The trends of sensors for heavy metal analysis are microminiturization, integration, nanomaterial modification and screen printing. Thus, a micro-fabricated microelectrode array (MEA) was designed and used for detecting cadmium and lead with different data processing algorithms. Further, light addressable potentiometric sensor (LAPS) and counter electrode were integrated with MEA on the same silicon substrate to form multisensor array. Characterizations of different sensor areas were studied in detail and multivariate linear regression (MLR) was introduced for quantitative analysis. Besides, a screen printed gold electrode (SPGE) was used for heavy metal analysis with gold nanoparticle modification. Based on the SPGE, a portable heavy metal analyser was developed for rapid and convenient detection of heavy metals in situ. A wireless buoy sensor network was developed for heavy metal monitoring in Lake Taihu based on the multisensor array. Stability and reliability of the sensor network were verified in the field experimentation. The research work in this dissertation was supported by the National High Technology Research Program (863 Program), the National Key Basic Research Program (973 Program) and National Research Foundation.The major contributions and innovations of this study are listed below:1. Partial least square regression (PLSR) and local optimum method (LOM) were proposed for quantitative determination of cadmium and lead in different samples based on gold microelectrode arrays (MEA).Gold MEAs with different sizes were fabricated with a series of microfabrication technologies. The working potential window of the MEA was assured from-0.6V to 0.9V. The inter-electrode spacing of MEAs was studied in which linear diffusion was observed when ratio of the inter-spacing of MEA to the diameter was 5. When the inter-electrode spacing increased to 5 times of the diameter of MEA, the MEA presented distinct radial diffusion. Gold MEA was used for cadmium and lead detection and PLSR was introduced to construct models for samples with uniform background, in which quantification could be achieved with single detection. However, for complicated samples with background drift, LOM was proposed with the standard addition due to the inaccurate prediction of PLSR. On the contrary, more precedures are involved in LOM for heavy metal quantification with relatively strong anti-interference capability. With the two algorithms, rapid and accurate detection of cadmium and lead can be achieved with gold MEAs in different samples.2. The integrated sensor array with LAPS and micro-nano electrode array was originally proposed and studied, which can effectively solve the interference by pH variation in heavy metal detection.MEA and nanoband electrode array (NEA) were integrated with LAPS for heavy metal and pH analysis due to the significant influence of pH to electrochemical analysis. MEA-LAPS multisensor array was packaged with working cells made by PDMS or organic glass, which can be easily combined with microfludics. NEA-LAPS was designed as a pen-type structure for easy replacement and renewal of sensors. Characterizations of MEA-LAPS and NEA-LAPS about sensitivity, linearity and reproducibility were respectively studied in detail. MLR was applied for calibration of MEA data on the basis of pH value provided by LAPS. The calibration can enhance the accuracy and anti-interference capability for heavy metal analysis under various pH conditions.3. Gold nanoparticles-modified screen-printed gold electrode (GNPs-SPGE) and the portable heavy metal analyser were developed and utilized for rapid heavy metal detection in situ.A screen printed gold electrode (SPGE), integrated with counter electrode, pseudo-reference and working electrode, was utilized for simultaneous detection of lead and copper. Comparison of electrochemical behaviour was systemically studied befor and after the activation and GNPs modification of SPGE, which contributed a remarkable enhancement of response current. Deposition potential and deposition time were optimized with square wave anodic stripping voltammetry (SWASV). The sensitivity, linearity, reproducibility and consistency of GNPs-SPGE were investigated to verify the electrochemical behaviour, also including the integrated counter electrode and pseudo-reference electrode. Based on the GNPs-SPGE, a portable heavy metal analyser was developed with ZigBee wireless communication. The preliminary tests have demonstrated that the analyser presented good reliability for in-situ heavy metal analysis with merits of simplicity, minuturization and portability.4. A wireless buoy sensor network was designed and developed for in-situ heavy metal monitoring on Lake Taihu, which implemented real-time monitoring in extensive water areas.Based on wireless sensoer network (WSN) technology, a wireless buoy sensor network was designed based on Wi-Fi for heavy metal monitoring in Lake Taihu. The sensor network, connected through Wi-Fi, was comprised of sensor node, wireless router and the control centre. The sensor node, fixed on a buoy, was capable of on-line and real-time monitoring of pH and heavy metals based on MEA-LAPS multisensor array. Self-developed control software was installed on the control centre for management of sensor nodes in the WSN. Field experiments were accomplished to verify the performance of the sensor network, suggesting good reliability and accuracy for detection of heavy metals and pH. |
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