1Whereas electric circuits and surface-based (bio)chemical sensors are mostly constructed in-plane due to ease of manufacturing, 3D microscale and nanoscale structures allow denser integration of electronic components and improved mass transport of the analyte to (bio)chemical sensor surfaces. This work reports the first out-of-plane metallic nanowire formation based on stretching of DNA through a porous membrane. We use rolling circle amplification (RCA) to generate long single-stranded DNA concatemers with one end anchored to the surface. The DNA strands are stretched through the pores in the membrane during liquid removal by forced convection. Because the liquid-air interface movement across the membrane occurs in every pore, DNA stretching across the membrane is highly efficient. The stretched DNA molecules are transformed into trans-membrane gold nanowires through gold nanoparticle hybridization and gold enhancement chemistry. A 50 fM oligonucleotide concentration, a value two orders of magnitude lower than previously reported for flat surface-based nanowire formation, was sufficient for nanowire formation. We observed nanowires in up to 2.7% of the membrane pores, leading to an across-membrane electrical conductivity reduction from open circuit to o 20 Ω. The simple electrical read-out offers a high signal-to-noise ratio and can also be extended for use as a biosensor due to the high specificity and scope for multiplexing offered by RCA.

No abstract

No abstract

No abstract

Sensors for detecting ultra-low concentrations are limited by the efficient transport of target molecules from large sample volumes to small detection regions. We here report a small-format digital DNA sensor in the shape of a microporous membrane that electrically detects DNA substrates with a concentration as low as 790 zM. This ultra-high sensitivity follows from optimising the mass transport of target DNA to specific receptors on the membrane across multiple spatial scales. mm-sized membranes support the rapid convection of a large sample volume to the detection zone; µm-sized pores ensure that DNA diffusion to the surface-based receptors dominates over convective loss through the pores (low Péclet number), and; at the nm-scale, target-receptor binding dominates over diffusive transport (high Damköhler number). After their efficient capture, the DNA molecules are converted with high specificity into trans-membrane gold nanowires that are detected using a simple, high signal-to-noise, electrical resistance measurement. This sensor design is of interest for detecting low-abundant target molecules without the need for sample amplification or up-concentration, and the mass-transport strategy could be adapted to other surfacebased sensing schemes.