Accelerating high throughput screening and biochemical assay development
Liquid chromatography–mass spectrometry (LC-MS) is a fantastically capable analytical tool. With the high resolution of new accurate-mass systems, the qualitative and quantitative performance is unrivaled. The technique’s label-free nature simplifies assay development, reducing both time and cost. LC-MS delivers high content data which not only identifies compounds from complex matrices, but can also provide molecular fragmentation data fundamental for structural elucidation.
Unfortunately, LC-MS suffers when it comes to speed. HPLC/UPLC-MS’s ability to deliver results at a rate of between 1–10 minutes per sample may be perfectly acceptable in some cases. However, if you need to screen a library of a million or more compounds, the pace of LC-MS makes it unusable. At 0.5 mL/min, and
5 minutes/sample, screening a million-compound library would consume 2,500 liters of mobile phase.
At about 10 seconds per sample, Automated Solid Phase Extraction-MS, a slimmed down version of LC-MS, is much faster. However, it is still too slow for prosecuting large library screens. High throughput MALDI-MS is very fast, but comes with the overhead of complex sample preparation and the risk of cross-contamination.
Over the past 15 years, Labcyte has demonstrated a consistent history of innovation in the use of acoustic energy to transfer liquid samples without making actual contact with the sample. A gentle burst of ultrasonic energy creates a mound on the liquid surface in a source well and then ejects a 2.5 nL droplet of sample. Thanks to surface tension, this droplet can be captured by an inverted well located over the source well. This occurs very quickly, at a rate of up to 500 Hz. This fast, contamination- and carryover-free liquid handling technology has become a standard tool in many areas of life science research, including cancer, genomics and pharmaceutical drug discovery.
Research into droplet formation led to the ability to generate a mist of nano-droplets similar to those created in a mass spectrometer’s electrospray ionization source. Working in collaboration with the AstraZeneca and Waters Inc., a prototype of a new ionization source has been designed to demonstrate this technology’s potential.
We refer to this technology as Acoustic Mist Ionization, or AMI. Combined with a Waters Xevo G2-XS, the Acoustic-MS system can analyze a 384-well microplate at better than 3 wells per second. Unlike LC-MS, there is no consumption of mobile phase, saving huge amounts of solvent.
For large sample sets, data is collected, compiled, and the results viewed as a heat-map, displaying the presence/absence of a target compound. The mass spectrum for each well can be subsequently inspected.
In tests using real samples, Acoustic-MS has shown itself to be a reliable technology with unparalleled speed. In an early trial, the system enabled AstraZeneca to save 95% of the cost to develop the assay. It also reduced the development time from an estimated 6 months to 2 weeks, and screened 230,000 compounds (600 plates) in 10 working days. A subsequent screen of a 2.5 million compound library against a different target was completed in 40 days, with a demonstrated capability to process over 100,000 samples per workday. Because of the high-quality MS data, there were fewer false positives needing further investigation.
Image courtesy of AstraZeneca
The emerging technology of Acoustic-MS offers the promise of ultra-high throughput (100,000 samples per day), high quality MS data, and label-free assay development with low sample consumption. We anticipate it will soon become a commercially available system with tremendous power to overcome the challenges of high throughput biochemical analysis.