Microplates based on liquid bridges between glass rods.

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.

Microplate well coverage mixing using superhydrophobic contact.

Two important challenges in microplate instrumentation are to achieve full well sample coverage and complete mixing. An effective approach of using superhydrophobic rods to accomplish these challenges is reported here. Experiments conducted showed that analytes above 50µl could be made to completely cover the bottom of 96-well standard and transparency microplates. Complete mixing was accomplished by moving the rod parallel to the well bottom while contacting the liquid. The approach is simple and controlled, and it minimizes the problems of spillage and cross-contamination. It works with analytes with varied volumes and of different viscosities present in each well of the microplate.

Surface tension drawing of liquid from microplate capillary wells.

Pressure differentials are routinely used to actuate flow in capillaries. We advance here an alternative means of flow generation that capitalizes on the extension of a liquid bridge achieved by the drawing of a rod through the action of surface tension. This meets the exigencies of creating controllable flow using simpler and more compact means. We found the ability to generate controllable flow to be strongly affected by the liquid bridge sustaining features, and that the use of rod diameters larger than the capillary was more conducive. The extensional flow resulting from the rupture of the liquid bridge was also found to have a strong circulation component which facilitated mixing. The approach here is highly amenable for use in capillary well microplates which have significant advantages over standard microplates. The features of this approach offer usage possibilities in biochemical applications in the field, such as in the leukocyte cell adhesion and hemagglutination tests of blood samples.

Evaporative preconcentration of fluorescent protein samples in capillary based microplates.

The preconcentration of analytes is important in biochemical analysis as it offers the ability to detect for trace species, and increase signal-to-noise ratios when using optical sensing on fluorophores. A strong advantage of the evaporation technique lies in its ability to operate without the need of any energy source; albeit major challenges exist on how to increase the surface area exposure to air for heightened evaporation, ensure no further increases once specified analyte concentrations have been achieved, and not needing any intervening membranes. We demonstrate here that the droplet creation and retraction approach in capillary based microplates offers such abilities whilst at the same time facilitating mixing.

Strong upstream flow characteristics in the formation of rivulets.

In a fully formed rivulet, the flow profile across the total cross section is downward, as would be intuitively expected. However, prior to this stage being reached, a strong backflow capable of carrying particles up to 125 mm up the incline back to the source is shown to occur. Two phases are described prior to a fully formed rivulet being established. First, a forming rivulet, in which a bulbous drop head slides down a slope with a flow occurring in the wetted trail behind it. In this stage, a linear increase in backflow height is observed over time. Subsequently, a transient rivulet occurs, with the transition happening once the end of the inclined solid surface is reached. The backflow decreases through this phase in a stepwise manner, coinciding with fluid dripping off the surface. The findings here strongly challenge common assumptions made regarding cleaning, whereby fluid will transport particulate matter downhill, and has significant implications on irrigation applied to remove bacterial biofilms in clinical medicine.

A capacity for mixing in capillary wells for microplates.

Sample/reagent mixing is important in microplate instrumentation and the approach of mixing prior to dispensation into the wells can be problematic when assays involve a mixture of different proportions of reagents. We demonstrate here with capillaries, a simple and highly effective method that uses air actuation and liquid surface tension to create pendant drops in which the inherent inner circulatory flow within accomplishes mixing. The approach portends the capability to be incorporated into microplates in order to provide a useful feature for assay investigations.