A simple one-step assay platform based on fluorescence quenching of macroporous silicon

Aptamer-modified nanomaterials: principles and applications

Aptamers are promising alternative binders that can substitute antibodies in various applications. Due to the advantages of aptamers, namely their high affinity, specificity and stability, along with the benefits originating from the chemical synthesis of aptamers, they have attracted attention in various applications including their use on nanostructured material. This necessitates the immobilization of aptamers on a solid support. Since aptamer immobilization may interfere with its binding properties, the immobilization of aptamers has to be investigated and optimized. Within this review, we give general insights into the principles and factors controlling the binding affinity of immobilized aptamers. Specific features of aptamer immobilization on nanostructured surfaces and nanoparticles are highlighted and a brief overview of applications of aptamer-modified nanostructured materials is given.

Rapid and label-free detection of protein a by aptamer-tethered porous silicon nanostructures

Protein A, which is secreted by and displayed on the cell membrane of Staphylococcus aureus is an important biomarker for S. aureus. Thus, its rapid and specific detection may facilitate the pathogen identification and initiation of proper treatment. Herein, we present a simple, label-free and rapid optical biosensor enabling specific detection of protein A. Protein A-binding aptamer serves as the capture probe and is immobilized onto a nanostructured porous silicon thin film, which serves as the optical transducer element. We demonstrate high sensitivity of the biosensor with a linear detection range between 8 and 23μM. The apparent dissociation constant was determined as 13.98μM and the LoD is 3.17μM. Harnessing the affinity between protein A and antibodies, a sandwich assay format was developed to amplify the optical signal associated with protein A capture by the aptamer. Using this approach, we increase the sensitivity of the biosensor, resulting in a three times lower LoD.

Metal-organic framework MIL-101 as a low background signal platform for label-free DNA detection

A label-free and sensitive fluorescence method for recognition of sequence-specific DNA using DNA-intercalating dye and metal-organic frameworks (MOFs) is developed. Here, MIL-101 (Cr3F(H2O)2O[(O2C)-C6H4-(CO2)]3·nH2O) is introduced as a quenching platform to decrease the high background fluorescence of SYBR Green I (SG)/probe DNA complex. Mechanism investigations show that MIL-101 can strongly adsorb the SG/probe DNA complex through π-π stacking and electrostatic interactions, and as a consequence, the fluorescence of the SG dye is greatly quenched. While in the presence of target DNA, the as-formed rigid double-stranded (ds) structure of DNA will be far away from the surface of MIL-101; meanwhile, the SG dye can be bound with the dsDNA in the mode of intercalation and minor groove binding, resulting in enhancement of the SG dye fluorescence. The increased signal-to-background ratio has a linear relationship with the concentration of target DNA in the range of 0.1-14 nM. It is confirmed that the detection limit is 73 pM (3σ), which is much lower than that based on the carbon nanotubes and graphene oxide platform. Moreover, one-base-mismatched target DNA can be discriminated effectively. With the introduction of MIL-101, the signal-to-background ratio has been improved ∼8-fold, demonstrating that MIL-101 is an efficient low-background signal platform.