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Phenothiazines are a group of basic drugs that include a phenothiazine ring with different substituents attached at the 2-and 10-position, which are used as anti-psychotics, neuroleptics and antihistamines. 1 Several methods have been applied to detect phenothiazine derivatives, such as spectrophotometry, 2 colorimetry, 3 liquid chromatography (LC) 4 and titrimetry. 5 Promethazine hydrochloride, a prominent compound in the large group of phenothiazine derivatives, is widely used as a therapeutic agent for treating various mental and personality disorder. Daniela et al. 6 have reported the determination of promethazine hydrochloride in a pharmaceutical preparation using a flow-injection spectroelectroanalytical method. Lara et al. 7 utilized a capillary zone electrophoresis (CZE) technique for the quantitative analysis of three kinds of phenothiazines. The detection limit for promethazine hydrochloride was obtained to be 3.3 μg/mL; DPV and DC techniques were also applied to detect some phenothiazine drugs. 8 The quantification of drugs or drug monitoring based on DNA-drug interactions has been reported. [9][10][11][12] DNA is usually chosen as a surface-modification element because of its high sensitivity, and compatibility with modern micro-fabrication technologies; it is especially promising for rapid detection. 13,14 Measurements of some trace phenothiazine drugs were performed with a DNA-modified carbon paste electrode (CPE) by using a potentiometric stripping analysis (PSA) method. DNA-modified CPE permits measurements at low concentration levels of some phenothiazines with an accumulation step. 15 These previous studies suggested that a DNA-modified electrode might provide a very promising basis for determining trace promethazine.In the present work, DNA-modified electrode was assembled by immobilizing dsDNA onto the surface of a pretreated glassy carbon electrode (GCE(ox)). A pair of well-defined reversible redox peaks of promethazine was observed at low potential on the DNA/GCE(ox). The redox peak current was evaluated by using CV and DPV techniques. The signal was about 100-fold higher on DNA/GCE(ox) than that obtained on the DNA/GCE. By means of the redox peak currents of promethazine sensitively responding to the promethazine concentration, DNA/GCE(ox) could be applied to determine trace promethazine. The influence of a glassy carbon electrode pretreatment on the sensitivity of determining promethazine was considered. DNA/GCE(ox) was used to determine promethazine in healthy human serum with satisfactory results. Experimental Apparatus and reagentsElectrochemical measurements were performed with a CHI660A electrochemical analyzer (Shanghai Chenhua Apparatus Corporation, China). Glassy carbon electrodes (diameter 3 mm) and DNA modified glassy carbon electrodes were used as the working electrode, respectively. A platinum auxiliary electrode and an Ag/AgCl reference electrode were used for the measurements.Calf thymus (CT) DNA (Cat. No. D1501) and promethazine hydrochloride (Cat. No. P4651) were purchase...

The electrochemical behavior and the interaction of alizarin red S (ARS) with calf thymus DNA was investigated on a bare glassy carbon electrode (GCE) and DNA modified GCE (DNA/GCE), respectively. ARS showed a pair of redox peaks at À 0.445 V and À 0.414 V on a bare GCE. On addition of DNA into the ARS solution, the peak current of ARS decreased and the peak potential positively shifted, but without new redox peaks appeared. The ARS reduction peak current increased with immersion time on a DNA/GCE. The results showed that ARS could interact with DNA molecules by intercalative binding mode. The equilibrium constant, binding number and the ratio of binding constant for oxidized and reduced ARS forms were obtained. The DNA damage was directly detected by appearance of guanosine and adenosine bases oxidation signal. The influence of experimental conditions on DNA damage extent was discussed in detail.

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