Biosensing in USF

Glucose measurements involve a large variety of sensors and methodologies.[1-2] They have been around since 1967 when Updike and Hicks created the first glucose sensor.
The relevance of creating Glucose sensors is due to the problematic incidence of blood-sugar levels. One such problem is diabetes. Normal Glucose in blood ranges from 85 to 135 mg/dl, 
In the University of South Florida, working with enzyme biosensors is a good way to be introduced to the marvelous world of both nanotechnology and biology.
In order to create Silicon Oxide Nanowire glucose sensors, one needs:

1. Silicon oxide Nanowires.[4]
2. Electrodes.
3. Chemical reagents.
4. Glucose Oxidase.
5. Glucose.
6. Electronic circuitry.

Process on creating the electrodes. 1.- Starts with the creation of the Silicon Oxide Nanowires at the CVD.[4] 2.- Exemplifies the separation and posterior adhesion of nanowires to the electrodes. 3.- Chemical modification so the Glucose Oxidase can be integrated to the system.

In USF we use electrochemical experiments to detect glucose in various concentrations. Silicon oxide nanowires are first grown by Chemical Vapor Deposition (CVD).[4]

Silicon oxide in solution, Scanning Electron Microscope at USF

Then, they are deposited onto gold electrodes (glass substrate)

Gold electrodes with different amount of Silicon nanowires, the higher concentration at the left and the lower concentration (no silicon nanowires) to the right.

After Silicon oxide deposition, a chemically modified Glucose Oxidase (GOx) is attached to the nanowires creating the appropriate physicochemical structure that can detect Glucose.

Silicon Oxide Nanowires after deposition over the gold electrode, Focused Ion Beam at USF

Silicon Oxide Nanowires with Glucose Oxidase attached, note that its only attaching to the nanowires, Focused Ion Beam at USF

Electrochemical techniques such as Cyclic voltammetry(results not shown here), are used to detect glucose concentrations. [3] The main idea here is that the enzyme, acting as an electrocatalytical agent, [5] will modify glucose and for each modification we will have more electrons in the system. The larger the quantity of glucose in solution, the larger the increment in current that will be detected.

For more information on related topics, please read:

[1] Glucose monitoring: state of the art and future possibilities, Wilkins E, Atanasov P, Med. Eng. Phys, 18, 273-288(1996)
[2] Home blood glucose biosensors: a commercial perspective, Newman J. D, Turner, A. P. F, Biosensors and Bioelectronics, 20, 2435-2453(2005)
[3] Status of biomolecular recognition using electrochemical techniques, Sadik O. A, Aluoch A. O, Zhou A, Biosensors and Bioelectronics, 24, 2749-2765(2009) 
[4] Manufacturing aspects of oxide nanowires, Sekhar P. K, Bhansali S, Materials Letters, 64, 729-732(2010)
[5] Glucose oxidase from Aspergillus niger: the mechanism of action with molecular oxygen, quinones, and one-electron acceptors, Leskovac V, Trivić S, Wohlfahrt G, Kandrac J, Pericin D, IJBCB, 37, 731-750(2005)

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