Ultra-low level biodetection

The researchers were able to find biological particles down to 10 femtomolar, which is the equivalent dilution to 1 gram in 3.3 billion litres or 1 gram in 1300 Olympic-sized swimming pools. This ultra-low level biodetection capability has implications for biomedical research, clinical development and possibly even forensics as trace amounts of a biological substance in a sample can now be detected and quantified using standard commercially available equipment.

Resistive pulse sensing

The researchers from the University College Dublin and the MacDiarmid Institute used magnetic particle systems, which can be applied to any biological particle or protein that have specific antibodies or aptamers (oligonucleic acid or peptide molecules that bind to a specific target molecule). Resistive pulse sensing, the underlying technology of the qNano device, was used to monitor individual and aggregated rod-shaped nanoparticles as they move through tunable pores in elastomeric membranes – the holes or nanopores in the membrane are altered to match the particle size of the substance being hunted for as closely as possible to allow detection on a particle-by-particle basis.

The researchers wrote, “The strength of using the qNano is its simplicity and the ability to interrogate individual particles through a nanopore. This allowed us to establish a very sensitive measurement of concentration because we could detect the interactions occurring down to individual particle level.”

Signals different for rod-shaped and sphere-shaped particles

A molecule’s presence was detected by a process that results in end-on-end or side-by-side aggregation of rod-shaped nickel-gold particles. The rods were designed so that any specific aptamer (that correlates to the molecule being hunted for) could be attached to one end only.

“By comparing particles of similar dimensions, we demonstrated that the resistive pulse signal is fundamentally different for rod- and sphere-shaped particles and for rod-shaped particles of different lengths. We could exploit these differences in a new agglutination assay to achieve these low detection levels,” says lead researcher Dr Mark Platt, Loughborough University and formerly University College Dublin.

Developing standardised diagnostic kits

In a press release, Hans van der Voorn, Executive Chairman of Izon Science, said the research was a real milestone for Izon’s technology, “as being able to measure biomolecules down to these extremely low levels opens up new bioanalysis options for researchers.”

The release says that Izon Science will continue to work with Dr Platt, the University College Dublin and various customers to develop a series of diagnostic kits that can be used with the qNano to identify and measure biomolecules, viruses and microvesicles.

“We’re now developing standardised diagnostics kits for researchers, which will allow them to optimise protocols for their particular targets of interest. The interest is in accurate quantification as much as the core detection,” says Mr van der Voorn.

The findings by Dr Platt, Professor Gil Lee (University College Dublin) and Dr Geoff Willmott (MacDiarmid Institute, New Zealand) were published in Small, the peer-reviewed journal on microscale and nanoscale science, on 6 August 2012.

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