Optical biosensors utilizing graphene and functional DNA molecules
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Single-stranded DNA molecules capable of molecular recognition and catalysis can now be routinely generated via the technique of in vitro selection. When coupled with adequate signal transduction modes, these synthetic functional DNA species represent a potential paradigm shift in the research and development of biosensors to meet the challenges of our rapidly changing world. Coupling functional DNA molecules with graphene materials for the design of optical biosensors has become an exciting research area in recent years, mostly because graphene materials are not only excellent quenchers of fluorescence, but they also display considerably different affinities for free and ligand-bound functional DNA molecules. We will discuss notable progress in this area in this mini-review by highlighting representative studies.
I. INTRODUCTION
The development of cost-effective, simple, sensitive, and selective biosensing platforms is essential for designing biological assays and point-of-care (POC) diagnostic tests. Generally speaking, biosensors include two elements, a recognition element that is responsible for recognizing a target of interest and a transducer that converts the recognition activity into a measurable signal. Functional nucleic acids, simplified here as FNAs, particularly DNA aptamers and DNAzymes, have been regarded as excellent recognition elements because they can be made to have excellent recognition specificity and affinity, in addition to high chemical stability and convenient availability via chemical synthesis.1,2 Graphene-based materials, on the other hand, have emerged as an excellent platform to set up various effective signal transduction mechanisms, owing to their remarkable physicochemical and structural properties.3–7 Two outstanding properties make graphene oxide, simplified as GO in this review, a favorite choice of material for the design of optical biosensors with FNAs: its varying affinity for structured and unstructured nucleic acids, and its ability to function as an effective quencher for fluorescence. In this mini-review, we will use selective examples to illustrate the usefulness of GO in the design of optical biosensors employing DNA aptamers and DNAzymes. A. Functional DNA molecules: DNA aptamers and DNAzymes
DNA is renowned for its role as the genetic information carrier of life. However, certain single-stranded DNA Contributing Editor: Venkatesan Renugopalakrishnan a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.103
molecules can fold into well-defined tertiary structures to carry out intricate functions including molecular recognition and enzymatic catalysis.8–10 DNA molecules capable of recognizing a target of interest are called aptamers and those with ability to speed up a chemical transformation are termed DNAzymes. DNA aptamers and DNAzymes have not been found in biological systems but they can be isolated from a large pool of DNA sequences through a process called in vitro selection.11–13 A general scheme for selecting functional DNA s
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