"Springy Capillary Pins": A New Concept in
DNA and Protein Microarray Printing

A fundamentally new type of microcontact printing tool, which is based on a spring loaded, hollow bore silicon nozzle that has been anodically bonded to a Pyrex^® capillary tube (Figure 1), can hold up to 35µL and can print up to 200,000 spots before revisiting the source plate

Fig. 1 The print tip region of a “Springy Capillary Pin” showing the micromachined silicon nozzle and springs bonded to the end of a glass capillary tube.		Fig. 2 The Springy Capillary Pins (SCP) fit directly onto all of the popular arrayer models. Users of Parallel’s silicon pins need only two adapters to use the SCP. A printhead with 48 of the SCP could print up to 10 million spots without refilling the pins.

At the heart of this revolutionary printing tool is a micromachined silicon part (Fig. 3 ) consisting of a cylindrical print nozzle with a printing tip that is attached to a silicon frame by a set of four flexible silicon tethers. The silicon springs will flex and return with essentially the same force indefinitely because, due to the lack of any grain boundaries in the single crystal silicon from which the parts are micromachined, they will not fatigue or work harden.

Fig. 3 The micromachined silicon part found at the end of each “Springy Capillary Pin”. Each silicon part contains (a)  a cylindrical nozzle, (b) four spiral springs and (c) a frame by which it is bonded to a Pyrex® capillary tube with a 1mm ID and a 2mm OD.

The judicious design of the dimensions, thickness and force constant of the silicon springs allows a wide variety of critical performance attributes to be simultaneously fulfilled and optimized. As shown in Fig. 4 , the spring loaded tip on the capillary tube (Fig. 4A) may assume one of three basic deflection modes as shown. When there is no load on the tip the silicon springs assume their unloaded position as shown in Fig. 4B. During normal printing conditions the printhead containing the SCP travels further in the z direction beyond the point where the tips begin to touch the printing substrate. This causes the SCP to “lift” out of the printhead at which point the Springy Capillary Pin stands on its print tip (Fig. 4C) which can support the entire weight of the pin (~350mg). Therefore, since the printhead has no lid to restrain the heads of the pins the print tip deflection in Fig. 4C will obtain for all values of overtravel in z. However, if a force larger than that required to partially deflect the silicon springs (i.e. Fig. 4C) the silicon springs are designed to be able to pushed into the ID of the glass capillary without breaking (Fig. 4D).

Fig. 4 The silicon spring and print tip can deflect various amounts in the z diretion depending on the force applied to the tip. In the resting position the springs are flat while they undergo a partial deflection when the weight of the pin is placed on the springs. If the pin is pushed into the substrate with enough force the springs and tip will deflect into the ID of the glass capillary without breaking.

Plug-and-Play: Use Your Current Arrayer The printhead of the new glass-silicon printing tools (Fig. 2 ) will attach directly to any of the common arrayers (Genetix, Gene Machines, etc.) and can be used with your current source plates, washer and dryer. Users of Parallel’s silicon pins can use these pins directly with the current printhead by employing a simple adapter. Other users need only purchase a printhead to hold the Springy Pins. A printhead filled with 48 of these pins could deliver around 10⁷spots/printhead/source plate visit making the pins very suitable for either high volume manufacturing or everyday use.

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Features, Advantages and Benefits

The advantages of the Springy Capillary Pins are numerous, substantial and direct.

1. Extremely robust design: the fine nozzle (50-125µ OD) is suspended on single crystal silicon springs which will never work-harden because of the complete absence of grain boundaries. The combination of the tip hardness, the strength of single crystal silicon and the lack of fatigue or work hardening provides a design that can last for millions of print cycles.
2. A very large number of spots per source plate aspiration: up to 200,000 spots per nozzle per loading
3. Pins and printheads can be used directly on existing arrayers with no custom adapters needed.
4. Visits to wash/dry station reduced by 25-50 times due to larger loading volume
5. Close to 100% successful printing rate; few missed spots due to pin failing to return to
   printing position
6. Far more uniform spots: spot size %CV (coefficient of variance = standard
   deviation/mean x 100) for one tip <2% and %CV for 100 tips ~5%; no more sorting
   many pins for similar pins (see Fig. 5) as all pins are operationally identical.
7. Printhead prints to dryness utilizing ~100% of the printing fluid aspirated.
8. Each pin can be individually filled and used as a storage container if needed; pin shafts and nozzles can also act as a filter beads or particles of size >30 µ.
9. Can print small beads (<5 µ) out the nozzle tip.

Fig. 5 Scanned image of arrays printed with two different oligoes and hybridized with their Cy3 and Cy5 labeled compliments. The spots are ~ 75 µ in diameter and printed on 125 µ centers.

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Summary A totally new micromachined printing tool, based on micromachined silicon nozzles mounted on flexible, spiral silicon tethers, provides a new method for the fabrication of microarrays. Remember that since Parallel designs, provides mechanical and silicon process engineering and manufactures all of its own hardware, we welcome custom design and engineering projects. Please call for a confidential discussion.

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The development of the Silicon "Springy Capillary Pins " is supported by the
National Human Genome Research Institute, National Institutes of Health (NIH).