We have developed a two-dimensional graphene biomolecular interface to detect biologically important proteins such as cancer markers. Until this work, water-dispersive graphene oxide (GO) in aqueous media has been preferred as a biosensor platform. By contrast, we have designed and demonstrated a protein detection system on a solid surface where we can use either water-dispersive GO or hydrophobic graphene as the sensor platform [Fig. 1(left)]. This allows us to combine the protein detection system with microfluidic techniques to realize an on-chip type sensor. We have successfully demonstrated the quantitative detection of multiple targets by using a sensor array built in a multichannel configuration .
We compared the protein detection performance quantitatively by using graphene and GO biosensors prepared on the same chip. We fixed graphene and GO on the SiO2 surface of a solid substrate and modified both surfaces with a dye-labeled aptamer (single-stranded DNA that recognizes and forms a complex with a specific target molecule such as a protein) under the same conditions. Here we used prostate specific antigen (PSA, a cancer marker) as the target molecule. We observed increases in the fluorescence intensity on both the graphene and GO surfaces when we added PSA (33 μg/mL @ t = 100 s) [Fig. 1(right)]. After performing several observations under constant PSA concentration conditions, we added deionized water to dilute the PSA solution. The fluorescence intensities became weaker as the concentration of the PSA solution decreased (20, 14, 11, 9 μg/mL @ t = 300 s, 400 s, 500 s, and 600 s). We thus demonstrated the successful operation of the sensor on both graphene and GO surfaces. We compared the performance of the graphene sensor with that of the GO sensor by subtracting the average fluorescence intensities before PSA addition from the maximum fluorescence intensities after PSA detection. The graphene sensor yielded a larger intensity than GO, and the ratio exceeded 3 . We conclude that the graphene is superior to GO in terms of building a biomolecular interface for fluorescence-based sensors.
This work was supported by JSPS KAKENHI JP26286018.
|Fig. 1. (Left) Schematic of graphene biosensor. (Right) Quantitative comparison of PSA detection performance of graphene and GO sensors.|