Preparation Of Graphene-Based Field-Effect Transistor Sensor And Its Applications In Detection Of Heavy Metal Ions In Water

Heavy metals are typtical pollutants in water, with high toxicity, persistence, and long-distance transport potential. Traditional methods for the detection of heavy metals include atomic absorption spectrometry, atomic emission spectrometry and inductively coupled plasma mass spectrometry. However, these methods have several shortcomings, such as the need for expensive equipment, complicated analytical procedures, long analysis time, and incapacity for on-site fast detection, etc. Hence, there is a great need to develop reliable analytical methods for the detection of heavy metals. In this thesis, a field-effect transistor based on electrochemical reduced graphene oxides ?rGO-FET? with DNA aptamers and functionalized gold nanoparticles were prepared and two method s were developed for the detection of Hg²⁺ and Cr⁶⁺ ions in water.The main contents are as follows:Au interdigitated electrodes ?IDE? were fabricated on SiO₂/Si substrates with standard photolithography, followed by the modification with 3-ammonia propyl triethoxy silane ?APTES?. Mono layer graphene oxides ?GO? were assembled on APTES modified Au IDE by electrostatic adsorption, followed by reduction with linear sweep voltammetry. The reduced GO ?rGO? channel was functionalized by 1-pyrenebutanoic acid succinimidyl ester ?PBASE? through ?-? interactions and then incubated with the DNA ?5'-?NH2?-TTCTTTCTTC CCCTTGTTTGT-3'? aptamer, which can specifically recognize the Hg²⁺ ion. The obtained rGO-FET sensor showed a selective response to Hg²⁺ ion in the presence of other metal ions and a linear relation between the sensor signal and Hg²⁺ concentration ranging from 0.5 to 990 nmol/L was observed. The lowest detection concentration was lower than the maximum concentration limit ?10 nmol/L? for Hg²⁺ in drinking water set by the US Environmental Protection Agency ?EPA?. The response time was less than 60 s. Relative standard deviations ?RSD? in repeated measurements were 5.5?28.7%. The proposed method was applied for the detection of Hg²⁺ in spiked real samples. The recoveries were 98.6?116.7% and RSDs were 3.4%?10.4%. Further, a comparison between FET sensors prepared with electrochemically and chemically derived rGO showed that the former had higher sensitivity ?2 times than the latter? and lower detection concentration ?one tenth of the latter? for detecting Hg²⁺ ion.An electrochemically derived rGO FET using DTT-Au NPs1 ?-7.5 nm? was designed and constructed for detecting Cr⁶⁺ in water. It was based on the specific interactions ofDTT-Au NPs2 ??38 nm? as free probe and Au NPsl attached on rGO channel as capture probe in presence of Cr⁶⁺, which resulted in aggregation of DTT-Au NPs2 on the rGO channel and then the decrease of resistance in the channel. Our findings showed that small Au NPs1 on the rGO channel could improve the detection sensitivity for Cr⁶⁺. The sensor showed a high selectivity of Cr⁶⁺towards other metal ions in water. There was a linear relationship between the sensor signals and the log values of Cr⁶⁺ concentrations ranging from 0.9 to 1320 nmol/L. The lowest detection concentration was 0.9 nmol/L, three orders of magnitude lower than the maximum concentration limit ?0.96 ?mol/L? for Cr⁶⁺ in drinking water set by Ministry of Environmental Protection of the People's Republic of China.In conclusion, this study provides a new method for the fast detection of Hg²⁺and Cr⁶⁺ ions in water and has a potential application in metal ions monitoring in water.