Silver or gold? A comparison of nanoparticle modified electrochemical genosensors based on cobalt porphyrin-DNA

We applied a cobalt-porphyrin modified DNA as electrochemical marker, which was attached to nanoparticles, to detect specific DNA sequences. We compare the performance of gold and silver NPs in oligonucleotide sensors to determine if a change in metal will lead to either higher sensitivity or different selectivity, based on the redox behaviour of silver vs. gold. Surprisingly, we find that using either gold or silver NPs yields very similar overall performance. The electrochemical measurements of both types of sensors show the same redox behaviour which is dominated by the cobalt porphyrin, indicating that the electron pathway does not include the NP, but there is direct electron transfer between the porphyrin and the electrode. Both sensors show a linear response in the range of 5 × 10^-17-1 × 10^-16 M; the limit of detection (LOD) is 3.8 × 10^-18 M for the AuNP sensor, and 5.0 × 10^-18 M for the AgNP sensor, respectively, which corresponds to the detection of about 20-50 DNA molecules in the analyte. Overall, the silver system results in a better DNA economy and using cheaper starting materials for the NPs, thus shows better cost-effectivness and could be more suitable for the mass-production of highly sensitive DNA sensors.

Approaching single DNA molecule detection with an ultrasensitive electrochemical genosensor based on gold nanoparticles and cobalt-porphyrin DNA conjugates

An ultrasensitive genosensor is obtained by using gold nanoparticles and cobalt-porphyrin labelled DNA reporter strands with an attomolar detection limit.

Ion Channels Made from a Single Membrane-Spanning DNA Duplex

Because of their hollow interior, transmembrane channels are capable of opening up pathways for ions across lipid membranes of living cells. Here, we demonstrate ion conduction induced by a single DNA duplex that lacks a hollow central channel. Decorated with six porpyrin-tags, our duplex is designed to span lipid membranes. Combining electrophysiology measurements with all-atom molecular dynamics simulations, we elucidate the microscopic conductance pathway. Ions flow at the DNA-lipid interface as the lipid head groups tilt toward the amphiphilic duplex forming a toroidal pore filled with water and ions. Ionic current traces produced by the DNA-lipid channel show well-defined insertion steps, closures, and gating similar to those observed for traditional protein channels or synthetic pores. Ionic conductances obtained through simulations and experiments are in excellent quantitative agreement. The conductance mechanism realized here with the smallest possible DNA-based ion channel offers a route to design a new class of synthetic ion channels with maximum simplicity.

Pseudorotaxane based on tetraazamacrocyclic copper complex and dibenzocrown ether

Host-guest interactions between two electron-rich dibenzocrown ethers and electron deficient macrocyclic copper(II) tetraimine complexes lead to the formation of pseudorotaxane in solution. The interactions are enhanced with the copper(III) complex compared to that of the copper(II) form as shown by the electrochemical studies. The larger--30-membered dibenzocrown donor interacted with the copper complex stronger than the smaller ones as revealed by NMR and electrochemical methods. The thiolated form of the copper(II) tetraimine complex was self-assembled at the gold electrode forming an electroactive monolayer able to interact with the crown ether in the solution. These donor-acceptor interactions lead to an increase of the barrier properties of the layer and decreased the electron transfer rate between the copper centre and the gold electrode surface as proved by the voltammetric data.

Interactions of dithiolated tetraazamacrocyclic copper(II) and nickel(II) complexes self-assembled on gold electrodes with pi-electron deficient molecules in solution

Self-assembled monolayers of dithiolated neutral monotetraazamacrocyclic complexes of copper(II) and nickel(II) can provide molecularly defined platforms for the formation of a pseudorotaxane-like nanostructures on the gold electrode surface. We propose these complexes as pi-donor building blocks for the construction of new molecular devices. We show that these perpendicularly oriented macrocyclic complexes anchored to the electrode surface act as pi-electron rich species interacting with pi-electron deficient compounds dissolved in solution, such as fluorine derivatives of tetracyanoquinodimethane (F(4)TCNQ) or a charged bismacrocyclic tetraaza complex of copper(II). The interactions of the surface immobilized macrocyclic complexes with F(4)TCNQ and with ring-shaped acceptor molecules are monitored and characterized by linear scan voltammetry. The interactions with the bismacrocyclic compound lead to a new pseudorotaxane array supported on the electrode surface and switched on and off by the application of appropriate potentials.