Problem: Liquid retention in pipette tips and interaction between the materials with which the tip is made and the sample it contains are a great concern. Sample loss percentage and the subsequent cost for purchasing additional sample becomes significantly more important when expensive reagents such as antibodies and siRNA inhibitors are being pipetted. Furthermore, interaction of the tip plastic with DNA samples during the pipetting process can be detrimental to sample integrity. In addition, barriers that are utilized to reduce sample aerosols are sometimes composed of materials that can contribute to sample contamination. Consideration of overall value must also reflect concerns about experimental accuracy and time needed to repeat and verify results. While users have often sought to mitigate dispensing loss by pre-wetting the tip, various manufacturers worked on these problems in their own unique ways with varying degrees of success.
Solution: One such manufacturer, St. Louis-based MIDSCI, addressed these issues by working with their supplier to produce a tip that promised precision when aspirating and dispensing and that delivered a lack of binding or interaction with the sample components. AvantGμard Low Binding Barrier Tips (Figure 1) and Avant Low Binding Tips avoided the need for silicone treatment or pre-wetting by utilizing a proprietary resin that is added in the tip molding process. Functioning as a low-binding polymer, the resin lines the inner surface of the tip and prevents interaction between the sample and the polypropylene tip. The resin used has proven to functionally avoid the binding of DNA and proteins in samples.
It was also necessary to address the filter or barrier that is used in some tips. Because cellulose degrades over time, components of filters or barriers made with this material can end up in samples. To address this issue, a polyethylene barrier was developed that is 100 percent chemically inert and nonporous; filter integrity is preserved during the shelf life of the tip and prevents the liquid or aerosol parts of a sample from passing into the pipettor during accidental over-aspiration. A sophisticated test ensures the impermeability of the barrier, using 32P probes to measure post-pipetting radioactivity counts at the bottom, middle and top parts of the dissected barrier.
This process ensures tip performance not only in the pipetting of hazardous liquid samples but also during sensitive assays like qPCR, Western blots and cell culture treatments. Aerosols generated during pipetting can be a culprit in the contamination of qPCR reactions due to carry over into postsample transfer and the consequent development of false positive signals. This is completely eliminated by the filtered low binding tip as demonstrated by negative amplification of anthrax DNA present in the sample (Figure 2).
For more information please visit www.midsci.com; references available from MIDSCI.