Construction Of High Performance Photoelectrochemical Aptasensors For Antibiotics Detection Based On Novel Carbon Materials

Photoelectrochemical (PEC) sensing is a new type of analytical method based on photo-electric conversion. Due to the advantages of simple device structure, low cost and high sensitivity, PEC sensing has been widely employed for the detection of all kinds of analytes. Photoelectrochemical aptasensor is a high selective PEC sensor constructed with aptamer which has specific recognition ability to analyte. Photoactive materials are the core component of PEC sensor. Their photo-electric conversion efficiency decides the responsive performance of PEC sensor. Therefore, exploiting high conversion efficiency of photoactive materials is an effective appraoch to the development of high-performance PEC sensor. On the other hand, the abuse of antibiotics is becoming a more and more severe problem in the whole world. Absuse of antibiotics not only causes serious harm to water and soil (e.g. destroying ecological system, producing "superbugs", etc.), but also do harm to human body (e.g. making human body resistance, damaging the body organs, producing a variety of allergic reactions or allergy, etc.). Therefore, it is of important significance to develop rapid and accurate methods for detection of antibiotic residues. This thesis prepared several highly photoactive carbon materials, which were combined with aptamers to build high-performance PEC aptasensors for highly sensitive and selective detection of antibiotics. The main contents of this thesis were summarized as follows:(1) The composite of water-dispersible graphite-like carbon nitride (w-g-C3N4) and graphene oxide (GO) was prepared as visible light-active material. Based on such a composite, a novel PEC aptasensor for the specific detection of kanamycin was developed using aptamer as bio-recognition element. The results showed that while suitable amount of GO was doped in w-g-C3N4, the visible light photocurrent response was enhanced, which was beneficial to the construction of PEC sensor. Additionally, the large specific surface area and ?-conjugated structure of GO/w-g-C3N4 provided an excellent platform for immobilizing the kanamycin-binding DNA aptamer on the surface of the sensor via ?-? stacking interaction. On such a sensor, the capture of kanamycin molecules by aptamer resulted in increased photocurrent, which was used for the detection of kanamycin. The experimental results demonstrated that the PEC response current of the sensor was found to be linearly proportional to the concentration of kanamycin in the range from 1 nM to 230 nM with a detection limit (3S/N) of 0.2 nM. Moreover, the proposed sensor displayed high selectivity, good reproducibility, and high stability, demonstrating the successful combination of GO/w-g-C3N4 with aptamer in fabricating high performance PEC aptasensors(2) A PEC aptamer sensing platform for chloramphenicol detection was constructed using nitrogen-doped graphene quantum dots (N-GQDs) as transducer species and label-free aptamer as biological recognition element. N-GQDs, synthesized via a facile one-step hydrothermal method, were explored to achieve highly efficient photon-to-electricity conversion under visible light irradiation. The obtained N-GQDs were characterized by transmission electron microscopy, which displayed a narrow size distribution with a mean diameter of 2.14 nm. The X-ray photoelectron spectroscopic and Fourier transform infrared spectroscopic analysis confirmed that nitrogen was successfully doped in GQDs. The UV-visible absorption spectra indicated that nitrogen doping obviously enhanced the absorption of GQDs in visible light region. As a result, the PEC activity of GQDs was promoted by nitrogen doping. Additionally, the ^-conjugated structure of N-GQDs provided an excellent platform for aptamer immobilization via ?-? stacking interaction. The experimental results demonstrated that such an aptamer/N-GQDs based sensor showed a linear PEC response to chloramphenicol concentration in the range of 10 to 250 nM with a detection limit (3S/N) of 3.1 nM. The developed PEC aptasensor exhibited high sensitivity and selectivity, good reproducibility and high stability, and successful applied in the detection of real samples.(3) g-C3N4 coupled with CdS Quantum dots (QDs) was synthesized and served as highly efficient photoactive species in a PEC sensor. The surface morphological analysis showed that CdS QDs with a size of ca.4 nm were grafted on the surface of g-C3N4 with closely contacted interfaces. The UV-visible diffuse reflection spectra indicated that the absorption of g-CsN4 in the visible region was enhanced by CdS QDs. As a result, g-C3N4-CdS nanocomposites demonstrated higher PEC activity as compared with either pristine g-C3N4 or CdS QDs. When g-C3N4-CdS nanocomposites were utilized as transducer and tetracycline-binding aptamer was immobilized as biorecognition element, a visible light-driven PEC aptasensing platform for tetracycline determination was readily fabricated. The sensor showed a linear PEC response to tetracycline in the concentration range from 10 to 250 nM with a detection limit (3S/N) of 5.3 nM. Thus, g-C3N4 sensitized with CdS QDs was successfully demonstrated as useful photoactive nanomaterials for developing a highly sensitive and selective PEC aptasensor.