Surface-immobilized hairpin DNA sensors for direct and specific detection of target DNA

Abstract

Gene-sensors show great promise as tools for various applications, such as clinical diagnosis, reliable forensic analysis, environmental monitoring, and biological research. There is a great demand for DNA sensors that are able to detect single-base mismatches, which are the most common genetic defects that need to be discriminated for medical diagnostic purposes. The development of label free, direct, and fast sensors can be essential in meeting that requirement. Current gene-sensing technology relies heavily on fluorescent labeling of samples but this approach suffers from the disadvantage of time-consuming, expensive and multi-stepped procedures, especially during the sample preparation stage. Although the use of fluorescent labels has overcome the hazards involved with radioactive markers, development of alternative approaches to the traditional assays is still vital to advance the area of DNA sensors. The aim of this research was to develop a one-step sensor, offering direct and specific detection of a target DNA. Nanostructured materials, such as quantum dots (QDs) and self-assembled monolayers, together with hairpin structured DNA probes were applied and investigated for optical as well as electrochemical sensors. The properties of inorganic quantum dots (or nanoparticles), such as narrow and intensive emission spectra, resistance to photobleaching and a wide range of possible surface functionalities, give QDs a great potential as labels in biological sensing applications. Self-assembled monolayers provide well established and versatile platforms for biosensors and hairpin probes, which are able to discriminate single-base mismatches in the target sequences, are ideal components for DNA sensors. Generally, the electrochemical sensors demonstrated a superior response compared to the optical sensors. The best prepared sensor showed sensitivity down to 4.7 fM of target and was capable of detecting single-base mismatches, fulfilling the requirements for a high-quality DNA sensor.