It seems everybody is focused on using nanostructures for designing new and hopefully better biosensors of the future. However, integrating nanostructures into real world size biosensors is not trivial and that’s where the importance of three recent reports on manipulating nanostructures comes into play. These reports show possible routes for improving biosensor performance by precise control of the nanostructure shape, size and position.
First report in Nature Nanotechnology from Shana O. Kelly of University of Toronto used nanostructured gold microelectrodes to achieve attomolar sensitivity for detecting oligonucleotides. For detecting oligonucleotide she used a label free sensing method developed in her group that uses catalytic reaction between two transition-metal ions, Ru(NH3)63+ and Fe(CN)6 3-. Further enhancement in sensitivity was achieved by using peptide nucleic acids (PNA) that have higher affinity to complementary sequence than DNA/RNA. The key feature of the work is that increasing the surface nanotexture of the microelectrode increased the accessibility of oligonucleotide to bind to their complementary PNA sequence that in turn increased the sensitivity of the biosensor. Moreover, by modulating the nanotexture of their microelectrode the sensor can be tailored for their sensitivity and their linear dynamic range. The next challenge for the sensor will be to detect oligonucleotide in complex biological samples like serum or cell lysates.
Second report though not directly aimed at improving biosensor sensitivity can nonetheless be used for biosensor applications. The report in Nature Nanotechnology from Tel Aviv University describes a method for fabricating highly oriented and aligned aromatic dipeptide nanotubes (ADNTs) using vapor deposition method. The length, thickness and surface density of the ADNTs can be controlled by simply adjusting the deposition parameters. Moreover, the fabrication method can be scaled up to coat large substrates or can be scaled down to design microfluidics channel or micro/nano patterns. ADNTs have already been used for creating metal nanowires and for biosensing and hence an scalable and easy to implement fabrication method will further improve their applications. Since ADNTs dramatically increases the surface area of the substrate hence the “better accessibility” hypothesis implemented in previous report should provide additional handle for improving sensitivity of ADNTs based biosensors.
Third and final report again is not directly aimed at designing biosensors but their applications to biosensing are easy to see. The report in Science from University of Colorado aligns lithographically created polygonal microparticles in liquid crystals. Though a proof-of-principle at this stage, the technology provides a facile method for creating (meta)materials with unique properties by simply aligning nano/micro meter sized particles with exact control over their position, orientation and assembly. Metamaterials and aligned metallic particles are already been used extensively for biosensing and better methods are constantly needed for further improvement in biosensor fabrication and sensitivity.