Implantable blood glucose sensor fabricated from carbon nanotubes

Sensor Review

ISSN: 0260-2288

Article publication date: 1 December 2005

150

Keywords

Citation

Bogue, R. (2005), "Implantable blood glucose sensor fabricated from carbon nanotubes", Sensor Review, Vol. 25 No. 4. https://doi.org/10.1108/sr.2005.08725daf.004

Publisher

:

Emerald Group Publishing Limited

Copyright © 2005, Emerald Group Publishing Limited


Implantable blood glucose sensor fabricated from carbon nanotubes

Implantable blood glucose sensor fabricated from carbon nanotubes

Keywords: Sensors, Nanotechnology, Carbon

As noted elsewhere in this issue, many diabetics are obliged to take regular blood samples and test them for glucose levels with disposable biosensors. Whilst ensuring steady consumption for the sensor manufacturers, this approach is less than ideal for the patient and efforts are underway to develop non-intrusive techniques and other more convenient testing strategies. Research in the US could resolve this issue, as recent work involving biosensors which combine established glucose sensing chemistry with IR optics and nanotechnology suggests that implantable devices that could be interrogated through the skin are now technically feasible. This research is being conducted by a group from the University of Illinois at Urbana-Champaign led by Michael Strano, Professor of chemical and biomolecular engineering, and is funded by the American National Science Foundation. The critical factor that could allow these sensors to be implanted and interrogated externally is that they are based on modified, single-walled carbon nanotubes (CNTs) which fluoresce in the near-IR region of the spectrum where human tissues and fluids are transparent.

Figure 1 The capillary tube on a fingertip (photograph) and a schematic of the sensor within a capillary dialysis tube

Single-walled CNTs were produced by the HiPco (high-pressure CO decomposition) process and the surfaces coated with a monolayer of the enzyme glucose oxidase. This acts as a selective binding site for the glucose and also prevents the CNTs from cohering to one another. The surfaces were then functionalised with ferricyanide ions which attach to the CNTs through the porous enzyme layer. In the presence of glucose, the enzyme reacts to produce hydrogen peroxide which forms a complex with the ferricyanide ions and changes the electron density of the nanotube and consequently its optical properties. When interrogated with an IR photodiode laser at 785 nm, the CNTs fluoresce and the intensity of this fluorescence, measured at 1,017 nm with a thermoelectrically cooled CCD camera, varies as a function of the glucose concentration.

Figure 2 Change in sensor fluorescence with glucose concentration

To test the feasibility of the technique for in vivo monitoring, the group sealed the CNT sensors in a 200 μm per diameter dialysis capillary tube with a 13 kDa (kilodalton) molecular weight cut-off, which confined the nanotubes but allowed any glucose present to enter (Figure 1). This was then inserted into a human epidermal tissue sample and it was found that the intensity of the fluorescence from the implanted sensor corresponded to the local glucose concentration. The sensor has been tested over the concentration range 1.4-8.0 mM (Figure 2) and the calculated limit of detection is 34.4 μM. As well as offering the potential for implantation into thick tissues or whole blood media, where the signal may penetrate up to several cm, CNTs do not degrade as do many fluorescent organic molecules, making them suitable for long-term glucose monitoring applications. Further, many other medical analytes could be detected in this manner by simply changing the functionalising compounds on the CNTs. The group has applied for patents covering this work which was first reported in Nature Materials.

Robert BogueAssociate Editor, Sensor Review

Related articles