Breast Cancer Susceptibility Gene mRNAs Quantified by Microarrays with Electrochemical Detection

Abnormalities in the expression of specific genes have been linked to a large and increasing number of diseases. Quantification of gene expression is a promising basis for early diagnosis, but analysis at the mRNA level has shown to be difficult because of the limited sensitivity of existing nucleic-acid-detection techniques. The most commonly used methods for quantification of gene expression include Northern blotting (1), ribonuclease protection assays (RPAs) (2), and reverse transcription-polymerase chain reaction (RT-PCR) (3)(4). The main limitation of the first two techniques is their relatively low sensitivity. RT-PCR can theoretically amplify a single nucleic acid molecule millions of times, but optimization of primer sets prolongs the assay time, and different genes in a starting mRNA mixture may not be present in the same amounts in the final RT-PCR products because of selective and nonlinear target amplification (5). These limitations affect the precision and quality of the resulting data and often provide distorted information on gene expression. Sensitive, reliable gene detection is one of the challenges in molecular diagnostics. Electrochemical detection provides a simple, accurate, and inexpensive platform for molecular diagnostics. Despite the enormous progress made in electrochemical nucleic acid biosensor research in the past 5 years, to be one step closer to commercialization, this research must overcome several important hurdles. The first is validation of the biosensor results on a statistically large population of real samples rather than the commonly reported relatively short synthetic oligonucleotides (6). Another challenge is to multiplex the electrochemical biosensors into useful sensor arrays. Typically, arrays of 30–100 sensors are needed for diagnostic purposes. For example, breast cancer screening requires the testing of 20–30 cancer susceptibility genes plus positive and negative controls (7). Of …