ssDNA/十八酸修饰碳糊电极的制备及伏安法表征

将石墨粉与十八酸在80 ℃下混合制成表面富含—COOH的基底碳糊电极(SA/CPE), 然后在活化剂N-羟基琥珀酰亚胺(NHS)和1-乙基-3-(3-二甲基氨丙基)碳二亚胺盐酸盐(EDC)存在下将ssDNA固定到电极表面制备ssDNA修饰电极(ssDNA/SA/CPE). 以亚甲基蓝(MB)为指示剂, 用循环伏安法对SA/CPE和ssDNA/SA/CPE进行电化学表征, 发现其在ssDNA/SA/CPE上较在SA/CPE上的氧化峰电流(i_pa)和还原峰电流(i_pc)分别增大1.9倍和1.7倍, 式电势(E_f)负移8 mV. 把ssDNA/SA/CPE放在互补ssDNA溶液中杂交后, MB的i_pa 和i_pc较在SA/CPE上分别增大1.0倍和0.8倍, E_f负移18 mV. 用0.5 mol/L 的NaOH溶液冲洗使电极表面杂交而成的dsDNA变性洗脱, MB的伏安信号几乎与在ssDNA/SA/CPE上一样. i_pc与SA/CPE上固定的ssDNA质量在1.0×10^－7～5.0×10^－6 g范围内成线性关系, 检测限为2.0×10^－9 g (S/N＝3). 这种既廉价又灵敏的电化学生物传感器有望在转基因植物产品检测研究中得到应用.

Fabrication and Voltammetric Characteristics of Carbon Paste Electrode Modified by ssDNA/Stearic Acid

The fabrication and voltammetric characteristics of carbon paste electrode modified by ssDNA/ stearic acid are described here, where ssDNA denotes single stranded DNA. A modified carbon paste electrode (SA/CPE) was prepared by mixing carbon powder with stearic acid at 80 ℃, the surface of which has an abundance of —COOH. Stearic acid was used as a binder and a chemical modification agent as well. After the activation of the SA/CPE with water-soluble carbodiimide (EDC) and N-hydroxysuccinimide (NHS), ssDNA was covalently bound to the surface of the electrode to fabricate an ssDNA modified electrode (ssDNA/SA/CPE). The hybridization of ssDNA on ssDNA/SA/CPE with the complementary stranded ssDNA (cDNA) was conducted in phosphate buffer solution and a dsDNA modified electrode was obtained. Cyclic voltammograms of methylene blue [3,7-bis(dimethylamino)phenothiazin-5-ium chloride, MB] at SA/CPE, ssDNA/SA/CPE and dsDNA/SA/CPE in B-R buffer solution were recorded, respectively. The i_pa and the i_pc of MB at ssDNA/SA/CPE were 2.9 and 2.7 times of those at SA/CPE, respectively. The E_f of MB at ssDNA/SA/CPE was shifted negatively by 8 mV from that at SA/CPE. The i_pa and the i_pc of MB at dsDNA/SA/CPE were 2.0 and 1.8 times of those at SA/CPE, respectively. The E_f of MB at dsDNA/SA/CPE was shifted negatively by 18 mV from that at SA/CPE. After the denaturation of dsDNA on dsDNA/SA/CPE by washing with 0.5 mol/L NaOH, the voltammetric parameters for MB at the denaturized DNA modified CPE became almost the same as those at ssDNA/SA/CPE. The i_pc of MB at ssDNA/SA/CPE was directly proportional to the quantity of ssDNA immobilized on SA/CPE in the range from 1.0×10^－7 to 5.0×10^－6 g with a detection limit of 2.0×10^－9 g (S/N＝3). Such an inexpensive and sensitive DNA modified CPE may be used to fabricate electrochemical biosensor for determining the products of the genetically modified plants.