High-performance sample prep on-cartridge
Any developer of a sample-to-answer device knows that getting sample prep working on-cartridge is a major source of risk. It makes matters worse that issues with sample prep usually arise late in the development process. Sample prep is often responsible when product development runs over time and over budget.
Sample prep surprises often occur when developers transition a working benchtop protocol to a microfluidic cartridge. Off-the-shelf sample prep tools such as centrifuges, rotators, and pipettes have no direct counterpart on-cartridge. Others, like magnetic beads, can be used on-cartridge but won’t perform as well as they did at the bench. As such, early benchtop experiments might lead to overestimate the performance of the final product.
But, how does one achieve the needed assay performance on cartridge?
The go-to method
The term “sample prep” covers a lot of territory, but broadly speaking, it encompasses some combination of analyte extraction, purification, and concentration. Of the myriad sample prep techniques, affinity sorting stands out among the rest. It is ubiquitous in the life sciences, and mostly takes the form of magnetic bead pull-downs.
Affinity sorting has its drawbacks. The target must be known and a suitable probe is needed to catch it. If the target is mutable, like many pathogens or cancers, finding a stable probe-target combination may be challenging.
The industry has room enough for all kinds of sample prep methods, but no method can match affinity sorting in flexibility and scalability. The affinity probe set, from antibodies to aptamers, is vast and constantly expanding. There are probes that can isolate targets over a wide size range, from a few nanometers to tens of microns. As a result, affinity sorting can be used before or after extraction, in both positive selection (binding to the analyte) or negative selection (binding to a source of background signal). Also, magnetic beads come in a wide range of sizes and shapes. But, most importantly, beads are production-ready: once an assay is working at the bench, it can be rapidly transferred to a liquid handling system, instantly raising throughput to tens of millions of tests per year.
Affinity sorting in cartridges
Traditionally, affinity sorting happens on magnetic microbeads, but beads are problematic in cartridges. They’re hard to install, hard to resuspend, hard to keep from settling out, and hard to keep where you want them when fluids are exchanged.
This is why magnetic beads fail on cartridges, underperforming tube-based assays by as much as 1000x (as demonstrated in a recent application note entitled Using STR to port sample prep to a cartridge).
In microfluidics, the obvious place to put the probes is on the surface of the microfluidic channels or chambers. To create extra binding capacity, one can design chambers with micro-texture that increases the surface area-to-volume ratio and reduces the distance from each analyte to the nearest binding surface. But these methods are custom-designed, and many are subject to blocking patents or other barriers to access. For system engineers seeking to advance their firm’s next generation differentiated solutions, the practicality of such customized solutions presents a real obstacle in product development.
However, what if lab-quality magnetic bead performance was truly accessible to any cartridge developer who needs it? What if the solution was practical and readily available for purchase?
Lab-quality bead-based assays on-cartridge
Here’s the good news: there is a microfluidic component that fits the bill. It is called STR™BeadPak.
STR™BeadPak is a method for using magnetic beads in microfluidic chambers that performs as well as—and sometimes, better than—the benchtop equivalent. STR™BeadPak can capture targets of widely varying size, from cells to exosomes to nucleic acids. It can concentrate sample from widely varying volume range, from microliters to milliliters of sample.
Most importantly, STR™BeadPak works with the magnetic beads developers are already using in assays at the bench. There’s nothing new to design or develop. Just put magnetic beads in the STR™BeadPak chip, and the assay is cartridge-ready.
Redbud’s goal with STR™BeadPak is to offer a sample prep tool of first resort: whatever needs to get extracted out of the sample, there’s a good chance STR can help deliver a compact, high-performing solution.
To learn more about STR™BeadPak and how it works, visit the STR product page on the Redbud Labs website to download the STR brochure or to connect with Redbud for a no-obligation assay consult anytime.
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