Methods for analyzing biomolecules in a fast, sensitive and selective manner are important for the detection and treatment of diseases such as HIV and cancer. Recently, an assembly of single-walled carbon nanotubes (CNTs) and single-stranded DNA (ssDNA) was used as a fluorescent-based biosensor for the detection of DNA and proteins.

Now, Huang-Hao Yang at Fuzhou University in China and colleagues1 have constructed a superior version of the CNT-biosensor by replacing the CNTs with graphene oxide — an atomic layer of carbon. The inexpensive graphene-oxide sensor is simpler and more responsive than both CNTs and commercially available biosensors. “Compared to carbon nanotubes, the low cost and large production scale of graphene oxide makes it a more promising material for devising biosensors,” says Yang.

The biosensors were fabricated using an ssDNA sequence, in this case the complementary target for a strand of DNA from HIV. The ssDNA was tagged with a fluorescent dye before being adsorbed onto a graphene-oxide substrate. Using fluorescence spectroscopy, the team studied the light emitted by the ssDNA on its own and when adsorbed onto the graphene oxide. They found that adsorption reduced the fluorescence from the dye by up to 97%. “The graphene oxide binds with dye-labeled ssDNA and completely quenches the fluorescence of the dye,” says Yang.

Fig. 1: DNA sensing using a biosensor consisting of complementary DNA adsorbed onto graphene oxide.

A dramatic increase in fluorescence intensity was observed when the biosensor was exposed to the target DNA strand from HIV. According to the team, this occurred because the target DNA disturbed the interaction between the ssDNA and the graphene oxide in the sensor, causing the two components to separate and thereby restoring the fluorescence of the dye (Fig. 1).

The biosensor was also used to detect human thrombin — a coagulation protein that is a marker for many cardiovascular diseases. “This result clearly demonstrates that our sensing design could be used as a sensitive and selective platform for target protein detection,” says Yang.