Graphite is a naturally occurring, soft, black, crystalline form of carbon. It has many desirable properties like high conductivity, thermal stability and chemical inertness, which make it a highly useful material for a variety of applications such as foundries, lithium-ion batteries etc. The raw material can be easily obtained and is relatively affordable for electrochemical purposes.
The conductive property in graphite was exploited to create biosensors for detecting biomarkers such as uric acid, blood and saliva. Biosensors work on the basis that graphite acts as an acceptor of electrons in electrochemical cells. The reaction between analyte and electrode generates a signal which can be used to measure the sample. Its low price, its ease of use, and its high sensitivity make this a very attractive approach.
It is recommended to use a polymer to improve the sensitivity of the graphite and the detection limits of the electrode. To achieve this, you can apply a water solution containing polyethylene over the GDE. This improves reproducibility, and decreases capacitive-currents. The result is a sensitive electrode.
A pyrolytic edge-plane graphite (EPPGE), was modified by adding functionalized nano-tubes of multi-walled carbon (f-MWCNTs/PGE). Cytarabine, an antiviral drug used for the treatment of CMV and SV40 virus infections, was determined on the EPPGE using differential pulse voltammetry. Linear ranges of 1-1500 uM and limit of detection values of 0.27 uM were obtained.
The ability of graphite to immobilize the enzymes bilirubin-oxidase and glucose-oxidase was also assessed through covalent coupling. Both enzymes can be addressed electrochemically either by direct electron transfer (DET) from the electrode surface to the catalytic center of the protein in the case of BOD, or via a redox mechanism with ferrocenemethanol in the case of GOD. The catalytic waves of both covalently-coupled and physically-adsorbed BOD/GOD had the same potential onset. This confirms that the GDE surface is appropriate for addressing proteins electrochemically.
Moreover, morphine, an opioid used as a painkiller and analgesic, was determined on the treated GDE by differential pulse voltammetry. The results were linear with a range from 1-1500uM, and a good apparent recovery. Using a UV/VIS spectrophotometer and chromatography, the quantification result of morphine was confirmed for both DPV method as well adsorptive-stripping DPV. The morphine concentration in spiked pharmaceutical, synthetic and urine samples was accurately determined. Using this method, morphine levels in human sera were also measured. These results showed that the GDE treated with morphine was highly applicable for determining morphine in clinical samples. The biofilms that grew on the surface of the treated GDE were stained with a BacLight viability kit and imaged by confocal laser scanning microscopy. The images that resulted clearly displayed the presence viable bacteria on surface of treated graphite.
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