Reducing Carryover and Improving Fluidic Circuits in Lab Instrumentation

Point-of-care testing, particularly in the at-home care and disease management sectors, is quickly growing. This expansion is due in part to an increasingly diverse offering of medical diagnostic technology that can be operated at or near the point of care. This ultimately results in easier testing and faster clinical decisions.
 
Point-of-care testing equipment is able to measure a wide range of health indicators like blood glucose, electrolyte concentrations, cardiovascular markers, cholesterol, drug levels, urine chemistry, infectious diseases, organ function, and immune response. Point-of-care testing is also growing because the instruments are becoming more functional, and also smaller and more compact. This makes the equipment much easier to use.
 
To make these devices faster and easier to operate, engineers design many steps into the instrument that are normally performed by separate instruments in a lab. Many different processes can be incorporated into a single cartridge, saving time, reducing sample handling, and minimizing potential for contamination or error.
 
Most point-of-care testing devices use a compact, reliable, and cost-effective cartridge to contain diagnostic reagents and reactions. Reliably moving liquids to perform the assay requires miniaturized, high-performance pumps and valves. These must be durable, precise, and chemically inert. Parker Precision Fluidics (a division of Parker Hannifin Corporation) recently unveiled such a valve—the Ultra Low Carryover Valve—to address the need for increased throughput, reduced carryover, and simplified fluidic circuits for clinical or analytical instrumentation.
 

In order to gain more insight on the technology, I spoke with Don McNeil, market development manager of Parker Precision Fluidics.
 
Brusco: Which types of medical or analytical instruments might this valve be useful for?
Don McNeil: Clinical diagnostic and analytical chemistry laboratory equipment handling liquids. In particular, those that handle multiple samples where increased throughput is desirable to increase lab output, reduce cost per sample, improve data quality, and reduce waste. A few examples include: in-vitro diagnostics, point of care testing, hematology, flow cytometry, liquid chromatography, genomics, and bioreactors.
 
Brusco: What benefits does the valve’s increased throughput offer to manufacturers of these instruments?
McNeil: The features of the valve allow the instrument manufacturer to design fluid circuits that reduce wash times and are more efficient. The valve’s design, minimal internal volume, and well swept fluid path allow it to clean out faster. This reduces wash times and allows the instrument to inject the next sample faster, increasing throughput. The shortened wash time has the additional advantage of reducing the amount of liquid waste generated, which is often expensive to dispose of. The valve enables more efficient fluid circuits due to its small internal volume and manifold mount capability. This shortens the fluid pathway, allowing liquids to move more rapidly through the instrument—again decreasing transfer times and increasing throughput. The valve’s unique design also allows it to shut off both channels, flow through channel A, flow through channel B, or flow through both channels simultaneously. A common feature of liquid circuits is to use a two-way valve as an on/off valve and a three-way valve to divert flow to channel A or B. This functionality can be performed by a single Ultra Low Carryover Valve, reducing fluid connections and lengths. This increases throughput by reducing fluid transit time.

 
Brusco: Why is decreased fluid circuit volume important for a fluidic system design?
McNeil: Reducing the amount of liquid if in a fluid circuit offers a number of advantages. Shorter fluid passageways translate into increased throughput, with less distance to travel—liquids get to their destination faster. Reduced fluid circuit volume reduces cross-contamination by decreasing the total volume in the circuit. This cuts down the amount of liquid that is subject to carryover. With a smaller amount of cross-contaminated liquid to clean out, wash cycles can be significantly reduced. Reducing the wash time presents the greatest opportunity to increase throughput as the machine can proceed to the next test sample faster. Many modern laboratory instruments spend 30-70 percent of their time washing to avoid carryover. Significantly reducing this wash time will greatly increase throughput. Reduced circuit volume also reduces the amount of potentially expensive reagents (or other chemicals) needed to complete a test, reducing the cost of operating an instrument. 
 
Brusco: How does the valve play a part in reducing waste?
McNeil: The time spent washing can be significantly reduced by reducing fluid circuit volume. Ensuring the fluid circuit is well swept is another key to improving wash times. The valve’s small internal volume and well swept design ensure it washes out much faster than conventional valves. Shorter wash times translate directly into reduced volume of waste. This can contribute greatly to reducing the cost of operation of the instrument because the disposal of waste fluids—especially those considered biohazards—can be very expensive. In some instruments the cost to dispose of this waste exceeds the cost of the reagents used to perform the test. This valve reduces the number of wash cycles required by washing out faster, through small internal volume and well swept cavities.

 
Brusco: How is the valve an improvement over typical two state operation or two-/three-way solenoid valves used for similar applications?
McNeil: Quite simply, this one valve can do the job of two because of the dual solenoid construction in a compact package. Applications that have traditionally used a diverter valve and a shutoff valve in series can now use this one valve to do both the jobs of selecting the fluid and metering the fluid. This not only reduces fluid circuit complexity and cuts down on the fluid volume in the circuit, but also enables designs that use fewer fluid connections, reducing potential leak points. Manufacturing costs are reduced as there are fewer valves to mount and the cost of manifolds can be reduced since the since the valve not only has a small footprint, but has a dramatically reduced footprint compared to the space taken by two valves.
Also, this valve was designed with material compatibility, cleanliness and inertness in mind, the well swept fluid path is only exposed to two materials, a PEEK (polyether ether ketone) body and the diaphragm made of FFKM (perfluoroelastomer) or EPDM (thylene propylene diene terpolymer) elastomer. In this totally isolated design, the fluid is not exposed to the coil or any other parts/materials of the mechanical workings of the valve.