Mixing in 384-well plates: issues, measurements, and solutions.
ABSTRACT Mixing in standard 384-well plates is different from mixing in 96-well formats. The aspect ratio of a typical well, the balance of surface tension and mass of the fluids, and the scale of diffusion all add to the increased difficulty in mixing fluids in higher-density plates. Here we examine two methods to measure mixing and some common techniques for mixing in 384-well plates. While conventional shaking can suffice, alternative methods can accelerate and improve the efficiency of mixing in 384-well plates.
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ABSTRACT: Serial dilution of compounds solubilized in dimethylsulfoxide (DMSO) for dose-response curves is a common method for efficacy analysis of potential drug candidates. In general, serial dilution methods are particularly prone to error propagation because each dilution is dependent on the previous concentration. Moreover, assumptions about quality control parameters (i.e., dye linearity) can lead to an erroneous process. Here, an inline performance measurement is sought to improve the precision and accuracy of dilution plates. Sulforhodamine 101 (S101) dye is introduced as the quantitative fluorometric method of choice for DMSO-based systems. Although S101 in DMSO behaves in a nonlinear fashion over its detectable range, we account for this with a direct calibration method that includes every point of the dilution template. This report contains dye selection rationale for the S101 dye and its use in quantifying the performance of 96- and 384-well dilution protocols as tested on five identical instruments.Journal of the Association for Laboratory Automation 06/2011; 16(3):235-40. · 1.50 Impact Factor
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ABSTRACT: Microscale bioreactors are an important tool in performing bioassays. The speed and efficiency of these devices is often limited by the rate of reagent mixing. In spite of the various micromixing approaches, the coupled mixing/reaction process has yet to be clearly understood. This article presents experimental and computational studies on the enhancement of bioreaction rates using a novel cilia reactor. In the experiments, a biotin-avidin assay and a DNA hybridization assay were conducted to show the benefit of a cilia bioreactor compared with a simple diffusion reactor. A cilia reactor showed a shorter reaction time for approaching equilibrium. A numerical computation examined the bioreaction rate of the cilia reactor compared with the diffusion for (1) a biotin-avidin assay, (2) an immunoassay, and (3) a DNA hybridization assay. The reaction rate was characterized for each assay using the Damkohler number (Da). When Da was greater than 10(2), the ratio of reaction time for the diffusion to cilia reactors linearly increased with Da, which could also save reagent usage by lowering the concentration of reagent probes. However, when the system had a Da smaller than 10(2), the reaction time of a cilia reactor could not be shortened because the assay was dominated by reaction rather than fluid mixing. The results offer a general approach for enhancing bioreaction rates by employing microfluidic mixers for a bioassay.Microfluidics and Nanofluidics 01/2012; 12(1-4-1-4):143-156. · 3.22 Impact Factor
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ABSTRACT: Microplating that (i) does not necessitate complex or precise machinery to dispense small liquid volumes, (ii) enables fluorescent optical diagnosis, and (iii) permits simple analyte mixing mechanically is desirable. We advance here a novel approach that employs the formation of a liquid bridge held in place by capillary forces between glass rod tubes located parallel to each other. Experimental investigations made on liquid filling characteristics show conformance to theoretical notions. Analytical development showed the presence of regions of minimal uncertainty in the cross-sectional area of the liquid body arising from variations in the contact angle which permit consistent fluorescence measurements. Cyclical translation of the rods relative to each other, which cause rupture and reattachment of the liquid bridge, was found to engender good mixing. Strong linear trends were found in fluorescence signals relative to EGFP fluorophore concentration using standard and optical fiber (which offer targeted) excitation illumination. The open nature of liquid handling in the approach reported here and the positive results obtained portend the ability for development as integrated lab-on-a-chip devices.Journal of Colloid and Interface Science 02/2013; · 3.55 Impact Factor