Margarete Schulze

Turbo-Mixing in Microplates

How to effectively mix small volumes of liquids within microplate wells is a still underestimated and often neglected challenge. The method the authors introduce here relies on violent turbulent motion within a liquid caused by spotting an organic solvent drop onto its surface. The amount needed, less than 1 to 3 µL, is generally small enough not to alter bioactive molecules. Moreover, a solvent may be selected for its compatibility with assay components. The method was tested with layers of aqueous liquids that differ in pH and concentration of a pH-dependent dye, allowing mixing to be monitored optically. Rapid mixing was caused by spotting drops of alcohols, acetone, acetonitrile, and aqueous solutions of these, as long as the difference of surface tension between the drop and the uppermost layer of the bulk liquid surpassed 30 dynes/cm. Along with this difference, position and velocity of spotting, as well as viscosity and geometry of the bulk liquid volume, may influence the turbulence evoked. No significant difference was found for the activity of aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase when measured after mixing by shaking and after mixing by spotting 1 µL of methanol onto assays within 96-well microplates. (Journal of Biomolecular Screening 2007:361-369)

Maternal serum alpha-fetoprotein screening for neural tube defects and other disorders using an ultramicro-ELISA

SummaryIn Cuba and in the German Democratic Republic (GDR) a total of 24,412 pregnant women were tested for maternal serum alpha-fetoprotein (MSAFP) at the 16th to 20th week of gestation. An inexpensive and partly automated ultramicroliter enzyme immunoassay (ELISA) with final volumes of 10μl was used to analyze simultaneously 50 samples. The intraassay coefficient of variation (CV) of 5–8% and day/day CVs of 6–10.5% were obtained with a test frequency of 320 assays/day. A cut-off level of twice the median value (MoM) was chosen. An amniocentesis was done in a total of 0.5% (in the GDR) and 0.7% (in Cuba) of the screened women. The prevalence of open neural tube defects (ONTD) was calculated from the present study and was 1.43‰ in Cuba and 1.34‰ in the GDR. Through MSAFP screening 88.2% ONTD were detected. There was no therapeutic abortion of a normal fetus. The approximate cost for this program was about 2.36 marks-GDR per patient screened, or about 2,048 marks per ONTD detected.