Carbon nanotube-based electrochemical biosensing platforms: fundamentals, applications, and future possibilities

Biosensors can be considered as a most plausible and exciting application area for nanobiotechnology. The recent bloom of nanofabrication technology and biofunctionalization methods of carbon nanotubes (CNTs) has stimulated significant research interest to develop CNT-based biosensors for monitoring biorecognition events and biocatalytic processes. The unique properties of CNTs, rolled-up sheets of carbon atoms with a diameter less than 1 nm, offer excellent prospects for interfacing biological recognition events with electronic signal transduction. CNT-based biosensors could be developed to sense only a few or even a single molecule of a chemical or biological agent. Both hydrogen peroxide and NADH, two by-products of over 300 oxidoreductases, are efficiently oxidized by CNT-modified electrodes at significantly lower potentials with minimal surface fouling. This appealing feature enables the development of useful biosensors for diversified applications. Aligned CNT "forests" can act as molecular wires to allow efficient electron transfer between the detecting electrode and the redox centers of enzymes to fabricate reagentless biosensors. Electrochemical sensing for DNA can greatly benefit from the use of CNT based platforms since guanine, one of the four bases, can be detected with significantly enhanced sensitivity. CNTs fluoresce, or emit light after absorbing light, in the near infrared region and retain their ability to fluoresce over time. This feature will allow CNT-based sensors to transmit information from inside the body. The combination of micro/nanofabrication and chemical functionalization, particularly nanoelectrode assembly interfaced with biomolecules, is expected to pave the way to fabricate improved biosensors for proteins, chemicals, and pathogens. However, several technical challenges need to be overcome to tightly integrate CNT-based platforms with sampling, fluidic handling, separation, and other detection principles. The biosensing platform must function well in a real-world sample environment where selectivity, sensitivity, detection limits, and ruggedness are the four prerequisites. Carbon nanotube patents look more controversial in electronics but are less problematical in energy, health care, and cosmetics. The use of CNTs in biosensing looks very promising as reflected by some significant patents in this area and other research and development endeavors.