A novel signal amplification strategy for label-free electrochemical DNA sensor based on the interaction between α-cyclodextrin and ferrocenyl indicator

The synthesized ferrocene appended naphthalimide derivative (FND) exhibited great binding ability toward dsDNA, while its usage as the electrochemical hybridization indicator was restricted by the poor water solubility. Herein, a simple and effective signal amplification strategy for FND based label-free DNA biosensors was developed based on the interaction between FND and cyclodextrin. alpha-Cyclodextrin (alpha-CD), fl-cyclodextrin (fl-CD) and gamma-cyclodextrin (gamma-CD) were helpful to amplify the signal of the DNA biosensor, while the signal amplification effect of alpha-CD was better than that of fl-CD and gamma-CD. Under the optimum conditions, there was a 3-fold increase in the sensitivity of the DNA biosensor after the addition of alpha-CD. The interaction between FND and alpha-/fl-/gamma-CD was investigated by differential pulse voltammetry and fluorescence experiment. Experimental results showed that alpha-CD not only minimized the impact on the electrochemical activity of FND but also improved the dispersity of FND in aqueous solution. That was why the proposed biosensor showed higher sensitivity in the presence of alpha-CD. This strategy was universal for other ferrocenyl indicators with similar structures as used in this work.