FUNCTIONALIZED MONOLAYER FOR NUCLEIC-ACID IMMOBILIZATION ON GOLD SURFACES AND METAL-COMPLEX BINDING-STUDIES

Adsorption of 4-thiopyridine on gold electrode surfaces followed by me thylation of the pyridine moiety produces a cationic monolayer on whic h DNA adsorbs from neutral, buffered aqueous solution. The metal compl ex binding properties of the immobilised DNA can be studied using both cyclic voltammetry (CV) and quartz crystal microgravimetry (QCM), Ele ctroactive metal complexes bound to the immobilised DNA can be quantif ied by CV after transfer to blank electrolyte. The binding of hexaammi neruthenium(ur) to immobilised DNA could be fitted by a Langmuir isoth erm. The maximum surface coverage of hexaammineruthenium(III) was 0.32 nmol cm(-2) and a binding constant of 2.0 x 10(4) l mol(-1) was obtai ned. Metal complex binding could also be detected using DNA immobilise d on a gold-coated quartz crystal oscillator, Crystal admittance measu rements were consistent with rigid layer behaviour for the adsorbed DN A; however, the apparent mass of adsorbed hexaammineruthenium(III) det ermined by QCM was considerably larger (1.6 nmol cm(-2)) than that det ected by CV, The difference between the two analytical techniques is a ttributed to desorption of the metal complex following the transfer st ep in CV and the effect of liquid density and incorporation of water i n the adsorbed films on the QCM measurement.