DNA On Silicon Devices: On-Chip Synthesis, Hybridization, and Charge Transfer

Abstract

Surface-immobilized DNA has an increasing number of roles in science and technology because of the ease with which it can be manipulated chemically and enzymatically in a highly controlled manner. Complex DNA architectures [1] and the use of DNA as a scaffold for making electronic connections [2] have been reported, and the use of DNA as a component in so-called molecular electronics has been frequently advocated. [3] Applications also include DNA microarrays [4] for sequencing through hybridization, the study of gene expression, and even for prototype computing devices which utilize the fidelity of the hybridization reaction. [5±7] In most cases, the DNA is immobilized on glass, oxidized silicon wafers, or other insulating supports. Methods for combining DNA with electronic materials are anticipated to be increasingly important in light of the considerable interest in DNAbased nanotechnology, [1] DNA-mediated charge transfer, [8] and DNA-based wires. [2] For substrates such as gold [9] or Si, [10] where there is the possibility of charge transfer through the DNA to the surface, immobilization has relied upon the attachment of presynthesized strands. However, to date there has been no demonstration of the use of automated solidphase DNA synthesis nor charge transfer through DNAbased assemblies at a semiconductor. For many proposed applications the ability to combine microelectronic processing techniques, [11] for example, photolithography and micromachining, with automated chemical synthesis has clear advantages. Herein we outline a method that enables the straightforward integration of DNA technology with microelectronics.Hydrogen-terminated surfaces represent the initial state from which silicon semiconductor devices are fabricated. [11] Chidsey and co-workers first demonstrated that such singlecrystal surfaces [12] react with alkenes to give chemically robust Si À C-bonded monolayers, and further advances have shown the applicability of this chemistry to porous silicon. [13±15] The reaction may be driven by thermal, catalytic, electrochemical, and photochemical methods, [13,16] and patterning of the monolayers, for example, by using photolithographic techniques, is possible. We have used a simple protecting group method to produce monolayers with terminal OH groups ( Figure 1); hydrogen-terminated silicon surfaces of oriented (111) single-crystal and porous silicon were alkylated with 4,4'-dimethoxytrityl-protected w-undecenol (trityl triphenylmethyl) by refluxing it in toluene; this is a previously

Ferrocenyl‐Modified DNA: Synthesis, Characterization and Integration with Semiconductor Electrodes

“…Recently, several groups, including our own, have demonstrated the attachment of DNA strands to bulk silicon substrates by using electrostatic interactions,1 post‐synthetic conjugation,2, 3 or automated solid‐phase synthesis 4. 5 These may provide opportunities for new types of gene sensing6–8 based on microelectronics; they may also be useful for the fabrication of nanoscale features using self‐assembly processes and be important in the development of DNA‐based molecular electronics 8–12…”

“…With these concepts in mind we have previously demonstrated the synthesis of regular oligonucleotides at modified silicon electrodes, by generating DNA strands tethered at the 3′ terminal 5. 11 Subsequent STM studies have established that, after hybridisation with complementary strands, the resulting duplex structures effectively lie on the surface 4.…”

“…14 Forms of DNA functionalised with redox‐active organometallic groups have been developed for some time as artificial nucleases 15–18. More recently they have been used for sensing applications,6, 19–27 and they are also important in studies on DNA‐mediated electron transfer 5. 6, 22, 28–44 There is also interest in tailoring the properties of DNA for direct use in electronics and photonics applications 5.…”

“…More recently they have been used for sensing applications,6, 19–27 and they are also important in studies on DNA‐mediated electron transfer 5. 6, 22, 28–44 There is also interest in tailoring the properties of DNA for direct use in electronics and photonics applications 5. 9–11, 45–48…”

“…The preparation of DNA oligonucleotides bearing metal‐containing groups has involved either post‐synthetic conjugation of a preformed complex at the terminal position of an oligonucleotide16, 38, 44, 49–51 or addition of metal ions to ligand‐modified oligonucleotides 15. 18, 40, 52, 53 More recently the synthesis of metal‐modified nucleosides as phosphoramidite monomers for use in automated solid‐phase synthesis, or triphosphates for polymerase substrates have also been explored 5. 20, 23, 50, 53–62 The advantages of this approach include the ease of synthesis and the ability to incorporate the modified base into the oligonucleotide sequence site‐specifically.…”