This electrode showed the linear responses between 0.5 15 M, 2.0 50 M, and 1.0 75 M for estradiol, estrone, and estriol, respectively, in the square wave voltammetry. Wei and co workers used composite of nano silver coated MWCNTs to determine a trace of thiocyanate in urine and saliva samples from smokers and nonsmokers and observed the decrease of anodic CHIR-99021 CT99021 current upon addition of trace amount of thiocyanate in nM level. Liu et al. designed a sensor by electropolymerization of thionine at the GCE modified with GNPs/MWCNTs composites for simultaneous determination of adenine and guanine in DNA. The detection limits of 10 nM and 8.0 nM , respectively. Carbon paste electrodes have been widely used as a suitable matrix for preparation of modified electrodes due to their simple preparation, renewability, and compatibility with various types of modifiers.
CNT modified CPEs showed considerable improvements in electrochemical behavior of materials. Zhuang et al. reported the fabrication of CPE modified with MWCNTs for the determination of bergenin using CV and differential pulse voltammetry. MK-2206 They found that the oxidation peak current of bergenin increased significantly upon increase of the contents of MWCNT and the linear dynamic range of 0.6 10 M was observed at an optimum experimental condition with a detection limit of 70 nM. Shahrokhian and Fotouhi added cobalt salophen for the determination of tryptophan. The MWCNTs/CoSal CPE exhibited an electrocatalytic activity on the oxidation of tryptophan. Furthermore, this electrode could be used to detect tryptophan separately from the interferences of AA and cysteine.
They also showed Nafion incorporated MWCNTs/CoSal modified CPE can be used for the simultaneous detection of UA and AA. The detection limits were determined to be 60 and 100 nM, respectively. When thionine Nafion was incorporated into MWCNTs/CPE, it could be used to detect DA and AA simultaneously. Recently, an electrode coated with SWCNTs paste was developed for sensitive voltammetric detection of methylparathion. Fan et al. fabricated such electrode using ionic liquid as a binder and they found a good electro catalytic behavior to the electrochemical reduction of methylparathion. It was also found that the same electrode can be used to detect methylparathion and its hydrolysate simultaneously. The similar approach was applied for the voltammetric determination of xanthine and UA.
A highly sensitive and fast responding electrochemical sensor was also prepared for piroxicam with MWCNTs paste electrodes by Abbaspour and Mirzajani. It exhibited a high catalytic activity towards electrooxidation of piroxicam in a mild pH medium, showing the linear response range of 0.15 5 g/mL, with the detection limit of 0.1 g/mL. The same electrode was applied for the determinations of urapidil and quercetin. Composite film of CNTs with other materials such as conducting polymers, ceramics etc are very attractive combination of materials for the development of electrochemical sensors. Yang et al. fabricated a novel electrode using a poly/ MWCNTs composite film modified GCE for simultaneous detection of dihydroxybenzene isomers in real water samples by applying the first order linear sweep derivative voltammetry. The detection limits for hydroquinone, catechol, and resorcinol were 100, 100, and 90 nM, respectively with this electrode.