Anal. Chem. 2007, 79, 5429-5434
Tailored Quartz Pins for High-Density Microsensor Array Fabrication Elizabeth C. Tehan, Daniel J. Higbee, Troy D. Wood, and Frank V. Bright*
Department of Chemistry, Natural Sciences Complex, University at Buffalo, The State University of New York, Buffalo, New York 14260-3000
We report on a quartz pin that can be interfaced easily to existing pin printers. The new pin surface can be reversibly derivatized using silanization chemistry, allowing one to reliably print a wide variety of liquid solutions. Feature sizes as small as 9 µm can be produced with the new pin, allowing one to readily create microarrays with a feature density approaching 106 spots/cm2. Microarray technologies have created a plethora of opportunities in fields like drug discovery, genomics, and proteomics.1 Microarrays consist of an ordered ensemble of microscale elements (spots) that each contain an immobilized recognition element, probe, or target on a largely planar surface that allows one to simultaneously perform a large number of parallel measurements. Numerous factors govern the potential and utility of microarraybased techniques2 including the number of distinct spots that can be formed per unit area (i.e., the spot density, D). D (in spots/ cm2) depends on the center-to-center (CTC) spacing between adjacent spots within the array:
D ) 100(1000/CTC)2
(1)
CTC is normally given by the actual spot feature size (e.g., spot diameter) multiplied by a factor of 1.2-1.4.1 Thus, microarrays with 100-µm feature sizes exhibit D values ranging from 5100 to 6900/cm2. If possible to produce, microarrays that possessed 10µm feature sizes would exhibit D values ranging from 510 000 to 690 000 spots/cm2. Clearly, the production of spots that exhibit smaller feature sizes has substantial appeal and benefit. Pins represent the most widely used tools for fabricating modern microarrays. Today’s commercial pins are either quill, solid, or capillary designs made from stainless steel, tungsten, ceramics, silicon, or other nonmetallic materials (cf., Stealth and Chipmaker from TeleChem; Accelerator from Point Technologies; aQu from Genetix; MicroSpot C from Apogent Discoveries; * Corresponding author. Phone: (716) 645-6800 ext 2162. Fax: (716) 6456963. E-mail:
[email protected]. (1) Schena, M. Microarray Analysis; Wiley-Liss: Hoboken, NJ, 2003; Chapter 7. (2) (a) Bier, F. F.; Kleinjung, F. Fresenius J. Anal. Chem. 2001, 371, 151-6. (b) Smith, J. T.; Viglianti, B. J.; Reichert, W. M. Langmuir 2002, 18, 628993. (c) Smith, J. T.; Reichert, W. M. Langmuir 2003, 19, 3078-80. (d) McQuain, M. M.; Seale, K.; Peek, J.; Levy, S.; Haselton, F. R. Anal. Biochem. 2003, 320, 281-91. (e) Reese, M. O.; vanDam, A.; Quake, S. R. Genome Res. 2003, 13, 2348-52. 10.1021/ac070533r CCC: $37.00 Published on Web 05/27/2007
© 2007 American Chemical Society
AccuPins from Bioneer; Silicon Microarray Technology from PSTI; and Xtend from LabNEXT). Within this commercial pin portfolio, the smallest reported feature size that can be produced is 50 µm (i.e., D ) 20 000-28 000 spots/cm2). Photolithography3 and lightdirected photomasking,4 among other approaches, have allowed researchers to shrink the feature size down to 16-18 µm (i.e., D ) 157 000-270 000 spots/cm2). (Note: Although elegant, we do not include nanoscale methods like dip pen nanolithography5 in the current discussion because theses approaches are not readily incorporated within existing microarray printing systems.) In this note, we report a new quartz pin that can be readily adapted to existing microarray systems. The quartz pins are inexpensive, simple to produce, and allow one to print features as small as 9 µm in diameter, tune the feature size by at least 4-fold for the same printing solution (adjust D by ∼16×), and print a wider variety of solutions in comparison to the aforementioned pin types. Xerogel-based microsensor arrays6 with high density are particularly straightforward to form with the quartz pins; the new pins are also useful for genomic and proteomic applications. EXPERIMENTAL SECTION Reagents. An amine-terminated capture oligonucleotide (cDNA, H2N-5′-CCACGGACTACTTCAAAACTA-3′) and its fluorescently labeled complementary target (tDNA, Cy3-5′-TAGTTTTGAAGTAGTCCGTGG-3′) were purchased from MWG Biotech. Antifluorescein (AF) antibodies and fluorescein (F) were obtained from Invitrogen. The ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]) (stated 99+% pure;
