We propose chlorpromazine as a new mediator for the rapid, sensitive, and highly selective voltammetric determination of glutathione (GSH) using multiwall carbon nanotubes paste electrode. The experimental results showed that the carbon nanotubes paste electrode has a highly electrocatalytic activity for the oxidation of GSH in the presence of chlorpromazine as a mediator. A simple and sensitive electroanalytical method was developed for the determination of enrofloxacin (ENRO) by adsorptive cathodic stripping voltammetry (ADSV) using Cu(II) as a suitable probe. The complex of copper(II) with ENRO was accumulated at the surface of a hanging mercury drop electrode. Then, the preconcentrated complex was reduced and the peak current was measured using square wave voltammetry. The optimization of experimental variables was conducted by experimental design and least–squares support vector machine (LS-SVM) modeling. The model was used to find optimized values for the factors such as pH, Cu(II) concentration and accumulation potential. A highly selective electrochemical method was developed for the simultaneous determination of ascorbic acid (AA), dopamine (ephinephrine), and uric acid (UA) using Eriochrome Blue SE, Tiron, sulfonazo(III) and p -xylenol blue films-modified on glassy carbon electrode. The modified electrodes showed excellent electrocatalytic activity toward the oxidation of AA, DA(ephinephrine), and UA. The results confirm the high selectivity, good sensitivity, and stability of the modified electrodes. A simple, sensitive DNA impedance sensor was used for detection of chronic lymphocytic leukemia at pico molar. First, gold nanoparticles were electrodeposited on the surface of a gold electrode, and then probe ss–DNA was immobilized on the surface of the gold nanoparticles through a 5’–thiol–linker. The difference of electron transfer resistance was linear with the logarithm of complementary oligonucleotides sequence concentrations A simple and sensitive method is proposed for the electrochemical determination of ENRO and its primary metabolite ciprofloxacin (CIPRO) at a multi-wall carbon nanotubes/glassy carbon electrode (MWCNT/GCE) using a LS-SVM and linear sweep voltammetry. Simultaneous determination of ENRO and CIPRO at bare glassy carbon is associated with certain difficulties due to voltammogram overlapping and their low sensitivity. The resolution of the mixture was carried out using LS-SVM as a multivariate calibration method.