Characterization of carbon electrode surfaces development of biosensors for forensic DNA applications
Churinsky, Candace Renee
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Quantitative polymerase chain reaction (qPCR) techniques are currently used to quantify samples containing deoxyribonucleic acid (DNA) in forensic analyses. This technology can provide valuable information to an analyst regarding the amount of DNA present but lacks the ability to determine the quality of the sample. Electrochemistry-based biosensors that utilize screen-printed electrodes may provide a method to determine the number of DNA molecules and the length of those molecules in a single assay. This work aimed to create a biosensor by electrostatically loading TPOX oligonucleotides onto a carbon screen-printed electrode for the purpose of quantifying genomic DNA. Electrochemical signal was obtained via the indicating molecule bis-benzimide H33258, which preferentially interacts with double-stranded DNA and would indicate a hybridization event. Cyclic voltammetry was chosen to measure the current signal; peaks obtained using this technique can be analyzed with the Randles-Sevčik equation, which relates current signal with concentration of the target species. A large amount of signal variation and background charging current was observed when H33258 was used as the redox probe. This led to a study of the surface characteristics of the carbon electrodes themselves (i.e. effective surface area) by utilizing the reversible and well-characterized redox couple hexaammine ruthenium. The effect of electrode activation at high anodic potentials was also studied. Though highly recommended in the literature, activation of the carbon surface caused effective surface area and charging current to increase. While a larger electro-active surface is often desirable, the high background current generated when activation is used within the protocol can mask the signal of interest. Due to the low signal-to-noise ratio and inability to reuse the carbon electrode, it was concluded that carbon screen printed electrodes are not optimal forensic DNA biosensors.
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