Nano-pore Ion: Improving Mass Spectroscopy with Direct Ion Delivery

A nano-pore ion source invented at Brown University offers a novel means of producing ions directly in mass spectrometry, which theoretically yields an order of magnitude greater sensitivity and substantial reductions in sample loss relative to most common methods.

At the heart of proteomics lies mass spectrometry that opens to scientists unprecedented dimensions for the identification of amino acids and peptides. The most commonly used method-an electrospray ionization (ESI) -is very ineffective at times in the process of ionization itself and also leads to great losses in samples. 

Researchers at Brown University have now come up with a pioneering solution: the nanopore ion source. This novel process of transferring ions directly from aqueous solutions to high vacuum addresses problems in current techniques and significantly improves the sensitivity.

Direct Ion Transfer Without Sample Loss

Although ESI has been a proven technique for generating ions in mass spectrometry, the main drawback of this technique is that it causes heavy loss of sample material. As droplets are charged to a high charge and are dispersed in a background gas during flight, only some of those become detectable by the mass spectrometer, which reduces their sensitivity. Nicholas Drachman of Brown University and colleagues emphasize that, in the classical designs, only a trace of the analyte is detected. 

The researchers have been able to circumvent many of these difficulties with the nanopore ion source. Directed directly from solution into vacuum through a sub-100 nm opening in a quartz pipette, it avoids the charged droplet plume characteristic of ESI and hence there is no background gas requirement, and sample loss is very small,over 90% of the emitted current is recovered compared with ESI methods. The nanopore technique successfully produces desolvated ions from different amino acids and peptides, including post-translationally modified versions of glutathione and the peptide angiotensin II.

A higher sensitivity and more clear mass spectra

A key advantage of the nanopore ion source is that highly resolved mass spectra are generated with minimal interference. Since, with ESI, ions often collide with parts of the instrument prior to reaching the detector, in the nanopore approach, ions can travel straight to the detector along collision-free paths. In experiments conducted by Brown University, the group demonstrated that this method already possesses transmission efficiency two orders of magnitude greater than ESI. Mass spectra obtained from arginine solutions were quite sharp and defined with prominent peaks and no noise, which indicates that this technology can be used to achieve very high sensitivity.

Potential Applications in Proteomics and Beyond

The nano-pore ion source is of particular interest for proteomics studies in which the investigation of very small biological samples is crucial. Due to its very high sensitivity, it seems especially well suited for single-cell proteomics as well as for studies of post-translational modifications, which are important in pharmaceutical research. The ability of the technology to support the direct injection of ions into the vacuum could indicate a revolution in workflows across a range of scientific disciplines.

Nano-pore ion source from Brown University is a much welcome leap forward in mass spectrometry in terms of filling in the inefficiencies of more orthodox ionisation methods. Much of the simplicity comes in the hardware through direct delivery of the ions into the mass spectrometer, greatly enhancing sensitivity-especially useful in small sample analyses.

Know more about the Nanopore ion source here.