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DNA has well-defined ability to recognize a wide variety of targets, such as small biological molecules, proteins, inorganic ions and small organic molecules. As molecular recognition elements, DNA can be used to build simple, rapid and sensitive biosensors for detection of these targets. DNA-based SPR sensors are considered to be a real-time and label-free tool. We present a systematical and critical review on DNA-based SPR biosensors and their signal amplification via various strategies, focusing on recent advances in nanomaterials, novel DNA amplifications, redox reactions on surface, enzyme amplifications, as well as promising multiplex amplification strategies. [ABSTRACT FROM AUTHOR]

Circulating cell-free DNA (cfDNA) is a promising biomarker of liquid biopsy, but it still faces some difficulties in achieving sensitive and convenient detection. Herein, an Ω-shaped fiber optic localized surface plasmon resonance (FO-LSPR) biosensor based on hybridization chain reaction (HCR) coupled with gold nanoparticles (AuNPs) was developed, and applied in simple and sensitive detection of cfDNA. Specifically, one-base mismatch was designed in HCR hairpins (H1 and H2) to obtain high reaction efficiency, and AuNPs was introduced onto H1 through poly-adenine to construct HCR coupled with AuNPs strategy. Meanwhile, target cfDNA was designed into two domains: one could trigger HCR to generate dsDNA concatemer carrying numerous AuNPs, and the other could hybridize with capture DNA on the surface of Ω-shaped fiber optic (FO) probes. Thus, the presence of target cfDNA would initiate HCR, and bring the formed dsDNA concatemer and AuNPs to approach the probe surface, resulting in dramatically amplified LSPR signal. Besides, HCR required simple isothermal and enzyme-free condition, and Ω-shaped FO probe with high refractive index sensitivity just needed to be immersed into HCR solution directly for signal monitoring. Benefiting from the synergetic amplification of mismatched HCR and AuNPs, the proposed biosensor exhibited high sensitivity with a limit of detection of 14.0 pM, and therefore could provide a potential strategy for biomedical analysis and disease diagnosis. [ABSTRACT FROM AUTHOR]