Wednesday, June 3, 2015

Nanopipettes for DNA detection fine tuned by ALD

Joshua Edel and his group at Imperial College London has been developing Nano pipettes [On-Demand Delivery of Single DNA Molecules Using Nanopipets]. Now they have gone a step further to fine tune the pipette for DNA dellivery and detection among other interesting things by using ALD.

Background on the group of Joshua Edel 

Analytical Sensors plays a crucial role in today’s highly demanding exploration and development of new detection strategies. Whether it be medicine, biochemistry, bioengineering, or analytical chemistry the goals are essentially the same: 

1) improve sensitivity
2) maximize throughput
3) and reduce the instrumental footprint. 

In order to address these key challenges, the analytical community has borrowed technologies and design philosophies which has been used by the semiconductor industry over the past 20 years. By doing so, key technological advances have been made which include the miniaturization of sensors and signal processing components which allows for the efficient detection of nanoscale object. One can imagine that by decreasing the dimensions of a sensor to a scale similar to that of a nanoscale object, the ultimate in sensitivity can potentially be achieved - the detection of single molecules.

Research activities within the Edel group runs at the interface between chemistry, chemical biology, physics, and medicine in order to improve and develop new classes of sensors based on these principles. As such expertise within our group includes an array of techniques and methods which includes micro and nanofabrication, material processing, surface modification chemistries, semiconductor processing and characterization techniques, confocal microscopy, plasmonics, surface enhanced Raman spectroscopy, and single molecule techniques using both optical and electrical methods.

Fine Tuning of Nanopipettes Using Atomic Layer Deposition for Single Molecule Sensing 

Jasmine Sze, Shailabh Kumar, Aleksandar P Ivanov, SAng-Hyun Oh and Joshua Edel 
Analyst, 2015,
Published online 03 Jun 2015 

 Nanopipettes are an attractive single-molecule tool for identification and characterisation of nucleic acids and proteins in solutions. They enable label-free analysis and reveal individual molecular properties, which are generally masked by ensemble averaging. Having control over the pore dimensions is vital to ensure that the dimensions of the molecules being probed match that of the pore for optimization of the signal to noise. Although nanopipettes are simple and easy to fabricate, challenges exist, especially when compared to more conventional solid-state analogues. For example, a sub-20 nm pore diameter can be difficult to fabricate and the batch-to-batch reproducibility is often poor. To improve on this limitation, atomic layer deposition (ALD) is used to deposit ultrathin layers of alumina (Al2O3) on the surface of the quartz nanopipettes enabling sub-nm tuning of the pore dimensions. Here, Al2O3 with a thickness of 8, 14 and 17 nm was deposited onto pipettes with a starting pore diameter of 75 ± 5 nm whilst a second batch had 5 and 8 nm Al2O3 deposited with a starting pore diameter of 25 ± 3 nm respectively. This highly conformal process coats both the inner and outer surfaces of pipettes and resulted in the fabrication of pore diameters as low as 7.5 nm. We show that Al2O3 modified pores do not interfere with the sensing ability of the nanopipettes and can be used for high signal-to-noise DNA detection. ALD provides a quick and efficient (batch processing) for fine-tuning nanopipettes for a broad range of applications including the detection of small biomolecules or DNA-protein interactions at the single molecule level.