A homogeneous electrochemical DNA sensor on the basis of a self-assembled thiol layer on a gold support and by using tetraferrocene for signal amplification.

An unmodified electrochemical biosensor has been constructed, which can directly detect DNA in homogeneous solution. The synthesized new compound tetraferrocene was used for signal amplification. The dual-hairpin probe DNA was tagged with a tetraferrocene at the 3' terminal and a thiol at the 5' terminal. Without being hybridized with target DNA, the loop of probe prevented the thiol from contacting the exposed gold electrode surface with an applied potential. After hybridization with the target DNA, the loop-stem structure of the probe was opened, which led to the formation of the hairpin DNA structure. Afterwards, the thiol easily contacted the electrode and accomplished potential-assisted Au-S self-assembly. Its current signal depends on the concentration of target DNA in the 1.8 × 10-13 to 1.8 × 10-9 M concentration range, and the detection limit is 0.14 pM. The technique is a meaningful study because of its high selectivity and sensitivity. Graphical abstract Schematic diagram of the electrochemical DNA sensor operation. Target DNA and probe DNA hybridization, resulting in the disappearance of the steric hindrance of the probe stem ring. A higher signal was generated when tetraferrocene reached the electrode. The electrochemical signals were determined by differential voltammetric pulses (DPV).

Multi-signal amplification electrochemical DNA biosensor based on exonuclease III and tetraferrocene.

Homogeneous electrochemical DNA biosensors' unique qualities have been of great interest to researchers, mainly due to their high recognition efficiency in solutions. However, the processes of introducing additional markers and extra operations to obtain a signal are tedious and time consuming, which limits their overall potential applications. Herein, a novel tetraferrocene was synthesized and used as a homogeneous electrochemical DNA biosensor probe label. It contains four ferrocene units, which provide greater signaling potential compared to monoferrocene. Furthermore, the target DNA triggers the digestion of the double hairpin DNA probe with the aid of exonuclease III, promoting short single stranded DNA probe formation. With the combination of the incorporated tetraferrocene labeled short DNA probe strands and graphene's ability to adsorb single stranded DNA, the hybridization process can produce an electrode signal provided by tetraferrocene. A low detection limit of 8.2 fM toward target DNA with excellent selectivity was achieved. The proposed sensing system avoids tedious and time-consuming steps of DNA modification, making the experimental processes simpler and convenient. The advantages of high sensitivity, selectivity and simple operation make this strategy applicable to DNA detection.

Highly sensitive host-guest mode homogenous electrochemical thrombin signal amplification aptasensor based on tetraferrocene label.

The development of sensitive and convenient detection methods to monitor thrombin without the use of enzymes or complex nanomaterials is highly desirable for the diagnosis of cardiovascular diseases. In this article, tetraferrocene was first synthesized and then a sensitive and homogeneous electrochemical aptasensor was developed for thrombin detection based on host-guest recognition between tetraferrocene and ß-cyclodextrin (ß-CD). In the absence of thrombin, the double stem-loop of thrombin aptamer (TBA) prevented tetraferrocenes labeled at both ends from entering the cavity of ß-CD deposited on gold electrode surface. After binding with thrombin, the stem-loop structure of TBA opened and transformed into special G-quarter structure, forcing tetraferrocene into the cavity of ß-CD. As a result, thrombin allowed eight ferrocene molecules to reach the gold electrode surface, greatly amplifying the response signal. The obtained aptasensors showed dynamic detection range from 4 pM to 12.5 nM with detection limit around 1.2 pM. Overall, the results indicate that the proposed aptasensors are promising for future rapid clinical detection of thrombin and development of signal amplification strategies for detection of various proteins.