Contact Angle and Its Importance for Microarrays

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Contact Angle and Its Importance for Microarrays
Authored by: Corning Incorporated Life Sciences

Originally published as a Technical Bulletin from the Corning Applications Group. Reprinted with permission.

1 Contact Angle
2 Hydrophilic Surface
- 2.1 Pros:
- 2.2 Cons:
3 Hydrophobic Surface
- 3.1 Pros:
- 3.2 Cons:
4 Optimal Surface
- 4.1 Pros:

Contact Angle

Contact angle is a measure of the angle at which sample meets the slide surface — a critical factor for good spot morphology and consistent sample deposition. A carefully controlled manufacturing process, such as that developed and used in manufacturing of Corning CMT-GAPS™ Coated Slides, produces slides with an optimal contact angle. This bulletin describes hydrophilic, hydrophobic, and optimal surfaces as they relate to contact angle and microarray quality.

Hydrophilic Surface

With a hydrophilic slide, sample transfers from the pin onto the surface, almost completely emptying the pin of sample. Sample spreads rapidly across the surface in a thin layer.

Pros:

Large surface area for probe attachment
Maximal sample deposit Cons:
Spots are irregular
Spots can spread into neighboring spots

Cons:

Spots are irregular
Spots can spread into neighboring spots

Hydrophobic Surface

With hydrophobic surfaces, less sample transfers from the more hydrophilic pins. Sample volume deposited onto the slide is variable. Samples attach to the slide in a smaller area. In extreme cases, samples can bead on the surface and roll out of their original places. After drying, spots may be so thick that some printed DNA is unable to bind to the slide.

Pros:

Very round spot morphology

Cons:

Inconsistent sample volume deposited Spots may move from their original placement Less area for DNA binding Spot may oversaturate causing smearing or cometing

Optimal Surface

Up to a point, increasing contact angle changes transferred sample volume very little and spots become increasingly uniform, small and round. Further increasing contact angle would decrease spot size significantly and inconsistently decrease the DNA volume printed. Under optimal conditions, consistent sample volumes transfer to the slide surface and form uniformly round spots.