Novel Carbon Nanomaterials For Electrochemical Sensing

The development of nanoscience and nanotechnology has inspired scientists to continuously explore new nanomaterials for constructing the superior performance of sensor devices. Carbon nanomaterials have been proved to possess unique electronic, chemical and structural features that make them very attractive for electrochemical studies and electrochemical applications. By functionalization methods, novel carbon nanocomposites can be prepared readily. Through these approaches, the intrinsic properties of carbon materials would be preserved, some functional groups with special properties can be also introduced, thus possessing great application potential in constructing functional sensor devices. With emphasis on the preparation of the functionalized carbon nanocomposites, as well as their applications in electrochemical sensors and biosensors, following works have been carried out:1. Noncovalent assembly of picket-fence prophyrin on carbon nanotubes as effective peroxidase-like catalysts for detection of hydrogen peroxide in beveragesA water-insoluble picket-fence porphyrin, bromo [iron (Ⅲ)5,10,15,20-tetrakis (aaaa-2-pivalamidopheny) porphyrin](FeTpivPP), was first assembled on multi-walled carbon nanotubes (MWNTs) through π-π interactions for highly efficient catalysis and sensing. Scanning electron micrographs, Raman spectra, UV/Vis absorption spectra, and electrochemical impedance spectra were employed to characterize this novel nanocomposite. Functionalized MWNTs greatly accelerated the electron transfer of FeTpivPP to produce a well-defined redox couple of FeⅢ/FeⅡ at-0.426and-0.371V. Due to the synergic effect between MWNTs and FeTpivPP, the nanocomposite showed excellent electrocatalytic activity toward the reduction of hydrogen peroxide (H2O2), thus leading to highly sensitive amperometric sensing at low applied potential. The sensor for H2O2showed a linear range from0.2to143μM with a detection limit of0.05μM at signal-to-noise ratio of3. Furthermore, the developed method could be applied for the determination of H2O2in different commercial beverages and held great promise for routine sensing applications.2. Potassium-doped carbon nanotubes toward the direct electrochemistry of cholesterol oxidase and its application in highly sensitive cholesterol biosensorChemical doping with foreign atoms is an effective method to intrinsically modify the properties of host materials. Among them, potassium (K) doping plays a critical role in regulating the electronic properties of carbon materials. K-doped MWNTs (KMWNTs) have been synthesized according to the chemical K-doping at room temperature. We demonstrate herein a newly developed serum total cholesterol biosensor by using the direct electron transfer of cholesterol oxidase (ChOx) which is based on the immobilization of cholesterol oxidase and cholesterol esterase (ChEt) on the KMWNTs modified electrodes. The KMWNTs accelerate the electron transfer from electrode surface to the immobilized ChOx than that of undoped MWNTs, achieving the direct electrochemistry of ChOx and maintaining its bioactivity. As a new platform in cholesterol analysis, the resulting electrode (ChOx/KMWNTs/GCE) exhibits a sensitive response to free cholesterol, with a linear range of0.050-16.0μM and a detection limit of5.0nM at signal-to-noise ratio of3. Coimmobilization of ChEt and ChOx (ChEt/ChOx/KMWNTs/GCE) allows the determination of both free cholesterol and esterified cholesterol. The resulting biosensor shows the same linear range of0.050-16.0μM for free cholesterol and cholesteryl oleate, with the detection limit of 10.0and12.0nM at signal-to-noise ratio of3, respectively. The concentrations of total (free and esterified) cholesterol in human serum samples, determined by using the techniques developed in the present study, are in good agreement with those determined by the well-established techniques using the spectrophotometry.3. Potassium-doped carbon nanotubes-ionic liquid composite gels modified electrode for the determination of superoxide anions released from cancer cellsA newly developed electrochemical biosensor for the determination of superoxide anion ((O2·-) released from cancer cells using KMWNTs-l-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) ionic liquid composite gels is demonstrated. The KMWNTs-[BMIM]PF6can electrocatalyze oxygen reduction to generate strong current signal in neutral solution. Compared with KMWNTs without [BMIM]PF6or MWNTs-[BMIM]PF6composite, the KMWNTs-[BMIM]PF6can enhance the oxygen reduction peak current by6.2-fold and2.8-fold, which greatly increases the detection sensitivity of oxygen. Then, O2·-biosensors are fabricated by mixing superoxide dismutase (SOD) in the KMWNTs-[BMIM]PF6gels via monitoring oxygen produced by an enzymic reaction between SOD/O2·-without the help of electron mediators. The resulting biosensors show a linear range from0.04to38μM with a high sensitivity of98.2μA mM-1, and a lower detection limit of0.024μM. The common interferents such as hydrogen peroxide (H2O2), ascorbic acid (AA), uric acid (UA), and metabolites of neurotransmittersetters, do not interfere with the detection of O2·-The proposed biosensor is tested to determine O2·-in vitro and from liver cancer and leukemia cells and show good application potential in biological electrochemistry.4. Synthesis of potassium-doped graphene and its application in nitrite selective sensingRecently, graphene, as a true two-dimensional carbon material, has attracted much attention on electrochemical sensing. In this work, a facile and mild strategy to doping K in graphene at room-temperature was reported for the first time. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman spectra and cyclic voltammetry were employed to characterize this K-doped graphene. The K-doped graphene has higher conductivity and more efficiently promote charge transfer than that of undoped graphene. A highly sensitive and stable amperometric sensor based on its excellent electrocatalytic activity toward the oxidation of NO2-was proposed. The sensor showed a linear range from0.5μmol L-1to7.8mM with a detection limit of0.2μM at a signal-to-noise ratio of3. The modified electrode had excellent analytical performance and could be successfully applied in the determination of NO2-released from liver cancer and leukemia cells.