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Application Notes
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Can purified lentivirus particles be used in this assay? As shown in the above case, both packaging supernatant and purified lentivirus particles can be used, as the sample pad contains detergent to efficiently lyse viral particles and release p24 protein during flow migration.
How is XpressCard compared with similar product on the market? When loaded with the same packaging supernatant, XpressCard showed the T line quickly in about 30 sec, much faster than Vendor A’s, which showed the T line around 2 min. When observed at 10 min, XpressCard showed the T line at somewhat stronger or at least equivalent intensity as Vendor A’s. Therefore, XpressCard is more sensitive than similar product on the market.
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Comment
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We tested XpressCards using serial dilution of purified concentrated lentivirus stock with known titres (Cellomics Technology, MD USA).
The results showed that the detection limit is at 1 x 10^5 TU/ml or 1 x 10^4 TU (in 100 μL).
According to the literature, one lentivirus particle carries about 2,000 p24 molecules, which is the analyte of the XpressCard :
1 x 10^5/ml × 2000 ÷ (6.23 × 10^23) × 24 × 10^3 g
＝ 2 × 10^8 ÷ (6.23 × 10^23) × 24 × 10^3 × 10^12 pg/ml
＝ 7.7 pg/ml
As a comparison, Vendor A's “Lenti-X? p24 Rapid Titer Kit” ELISA Kit has a sensitivity of 12.5 pg/ml, whereas Vendor B’s “QuickTiter Lentivirus Titer Kit” has a sensitivity of 1 ng/ml. These assays are all ELISA based, which need 3-4 hours. Therefore, XpressCard can reach ELISA sensitivity but with only 10-15 min on hand time.
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