Study And Development Of An Electrochemical Sensor Based On Aryldiazonium Salt Monolayers Modified Electrodes For The Detection Of Cadmium Ions

Metal cadmium is known as the most easily accumulated toxic substance in the body, is a highly toxic environmental pollutants, and in nature it often presents as its compounds. Study on the method for the determination of low content of cadmium ion and study on the determination of cadmium ion in water treatment are urgently needed. The classical method for the determination of metal cadmium in the environment is rapid with high accuracy, but the determination process is very complicated, the instrument costs are high, and specially trained personnel are needed. But those methods lack selectivity, and they are not suitable for field monitoring and continuous on-line analysis. The electrochemical sensor as a method with high degree of automation, miniaturization and integration to reduce user environment and technical requirements, is suitable for field analysis, and it provides a convenient, fast, cheap analysis of toxic heavy metal ions in environment detection with very high sensitivity and selectivity. The sensor is a solid state device, and the general public can operate. It can be placed in the interest sample to be detected without any sample preparation process. At present, there are many kinds of electrochemical sensors for a range of environmental heavy metal ions monitoring. A variety of sensors for the determination of cadmium are based on the redox reaction of cadmium ions on the electrode surface. Therefore, the electrode surface design is the most important.Based on this, we have developed an electrochemical sensor for the determination of cadmium ion in water, and we pay attention to the sensor interface design, performance test and its applied research. The alkyl thiol modification sensor electrode surface was a great success. But the alkyl thiol chemical modification method has many disadvantages, such as the molecular layer is not stable, the potential range is very narrow, and gold sulfur bond is easily oxidized. Thus another more stable monolayer system is needed for surface modification of a sensing interface. The aryldiazonium salt chemistry is a considerable candidate. Aryldiazonium salt modified electrode surface has all advantages with alkyl thiol modified electrode, but can overcome the shortcomings of alkyl thiol modified electrodes. The aryldiazonium salt modified sensor interface has a great application potential to the electrochemical sensors. This paper adopts the aryldiazonium salt modified electrode interface method to establish the electrochemical sensor for determination of cadmium ions in water.First of all, we adopt the relatively low price of glassy carbon electrode modified with aryldiazonium salts. And then EDC/NHS was used for the activation the carboxlylic acid on the electrode surface. Finally glutathione cysteamine (Glutathine, GSH) was attached to aryldiazonium modified electrode to form the sensing interface. The experimental results show that, there is a linear relationship between the current and the cadmium concentration range of 50 nM-100 nM. The detection limit is 50 nM. In order to reduce the limit of detection, we use 4-aminophenyl modified glassy carbon electrode for the determination of cadmium ions with the hope of improving the sensitivity. The experimental results show that there is good linear relationship between the current and the cadmium ion concentration range of 10 nM-50 nM The detection limit for the cadmium ions is 10 nM. Comparing to the 4-carboxyphenyl modified glassy carbon electrode, the determination of the detection limit is reduced. Comparing to the thiol gold chemistry modified sensing interface, the aryldiazonium salt modified glassy carbon interface has higher stability, however the sensitivity is not so desirable, which might be related to the low electron transfer rate with glassy carbon itself. Thus alternatively we use the aryldiazonium salts modified gold electrodes as the sensing interface for the detection of cadmium ions. Similarly, the gold surface was modified with 4-carboxylphenyl, followed by the EDC/NHS activation, then GSH was attached to the electrodes to fabricate the electrochemical sensors based on aryldiazonium salt modified gold electrodes for determination of cadmium ions in the environment. Measurement results are satisfactory, and the detection limit for the electrochemical sensors based on aryldiazonium salt modified gold electrodes for metal cadmium determination is 1 nM, which is significantly lower than that for the aryldiazonium salt modified glassy carbon electrode for the determination of cadmium ions. The fabricated electrochemical sensors based on aryldiazonium salt modified gold electrodes show high sensitivity, strong stability for the determination of cadmium ions, and has potential applications for the low concentration of cadmium determination in the environment monitoring.