14-02-2013, 01:13 PM
DNA electronics
[attachment=50871]
Abstract
Large area molecular junctions [1] have proven to be a robust and reliable system for studying electronic transport through molecules, shedding plenty of light on the parameters that affect it. We propose the use of this system for a systematic study of the charge transport properties of DNA molecules and how this depends on the molecules’ structure or environment. This knowledge can not only be used to design and synthesize DNA molecules that carry desired properties, such as rectification, for use in DNA molecular electronics devices, but provide valuable information for DNA’s complex role in biology as well.
Introduction
Molecular Electronics
Moore’s law, stating that the number of transistors in an integrated circuit doubles every two years [2], requires a miniaturization of the electronic components that will soon not be attainable with current silicon‐based technologies. Molecular electronics, the field that bloomed after the theoretical prediction of Aviram and Ratner in 1974 that a specially designed molecule can act as a diode [3], presents itself as a promising successor of silicon‐based technology at the end of its roadmap. Apart from the apparent advantage of being small, molecules can be synthesized and tailored so as to possess the necessary functionalities to act as electronic components.
DNA
Deoxyribonucleic acid (DNA) is a long polymer made from repeating units called nucleotides. The DNA chain is 22 to 26 Ångströms wide, and one nucleotide unit is 3.3 Å long. In living organisms, DNA does not usually exist as a single molecule, but as a tightly‐associated pair of molecules that form a double helix (Figure 1). The helix is stabilized by hydrogen bonds between the bases attached to the two strands, made of alternating phosphate and sugar residues (Figure 2). The four bases found in DNA are adenine (abbreviated A), cytosine ©, guanine (G) and thymine (T).
Each type of base on one strand forms a bond with just one type of base on the other strand. This is called complementary base pairing. A is bonding only to T, and C bonding only to G. The double helix is also stabilized by the hydrophobic effect and pi stacking, which are not influenced by the sequence of the DNA. Pi stacking is considered important for the molecules’ charge transfer characteristics[4] (Figure 2). As hydrogen bonds are not covalent, they can be broken and rejoined relatively easily. The two strands of DNA in a double helix can therefore be pulled apart, either by a
mechanical force or high temperature. As a result of this complementarity, all the information in the double‐stranded sequence of a DNA helix is duplicated on each strand, which is vital in DNA replication.
Large Area Molecular Junctions
Measuring the charge transport through molecules, even for those that have much simpler structure than DNA, has proven to be a difficult task. Different experimental testbeds have been employed, that yielded differences in the resistance value of a simple alkanedithiol of 8 orders of magnitude [14]. The basic problems of most of the methods used are reproducibility issues and the ability to be implemented in real devices.
At the Zernike Institute for Advanced Materials of the University of Groningen two‐terminal devices with a self assembled monolayer (SAM) of molecules as active component have been materialized. All steps in the flow chart are conventional and industrially used processes such as spin coating and photolithography (Figure 4). The key step in this flow chart is spin coating the conducting polymer PEDOT
SS on top of the SAM. The large, hydrophilic molecules of PEDOTSS (a water‐based suspension) will not penetrate the hydrophobic interior of the SAM during spin coating, forming a layer on top of the SAM. This extra layer acts as a protective cushion, which prevents filamentary growth through the SAM during the evaporation of the top gold contact, that is a cause of short circuits [15].
Figur
DNA Molecular Rectifiers
A diode is a two‐terminal device that allows an electric current to pass in one direction (called the forward biased condition) and to block it in the opposite direction (the reverse biased condition). The directionality of current flow most diodes exhibit is generically called the rectifying property. The most common type of diode in silicon technology is the p‐n junction, which is formed by combining p‐type and n‐type semiconductors together in very close contact. Another interesting device, in which the negative differential resistance (NDR) phenomenon can also be observed, is the resonant tunneling diode. This structure is formed when a quantum well is surrounded by two thin barriers and is transparent to carriers of certain energies associated with the discrete energy levels within the well. An increase in carrier energy leads to a decrease in transmission, that is macroscopically manifested as the NDR effect.
[attachment=50871]
Abstract
Large area molecular junctions [1] have proven to be a robust and reliable system for studying electronic transport through molecules, shedding plenty of light on the parameters that affect it. We propose the use of this system for a systematic study of the charge transport properties of DNA molecules and how this depends on the molecules’ structure or environment. This knowledge can not only be used to design and synthesize DNA molecules that carry desired properties, such as rectification, for use in DNA molecular electronics devices, but provide valuable information for DNA’s complex role in biology as well.
Introduction
Molecular Electronics
Moore’s law, stating that the number of transistors in an integrated circuit doubles every two years [2], requires a miniaturization of the electronic components that will soon not be attainable with current silicon‐based technologies. Molecular electronics, the field that bloomed after the theoretical prediction of Aviram and Ratner in 1974 that a specially designed molecule can act as a diode [3], presents itself as a promising successor of silicon‐based technology at the end of its roadmap. Apart from the apparent advantage of being small, molecules can be synthesized and tailored so as to possess the necessary functionalities to act as electronic components.
DNA
Deoxyribonucleic acid (DNA) is a long polymer made from repeating units called nucleotides. The DNA chain is 22 to 26 Ångströms wide, and one nucleotide unit is 3.3 Å long. In living organisms, DNA does not usually exist as a single molecule, but as a tightly‐associated pair of molecules that form a double helix (Figure 1). The helix is stabilized by hydrogen bonds between the bases attached to the two strands, made of alternating phosphate and sugar residues (Figure 2). The four bases found in DNA are adenine (abbreviated A), cytosine ©, guanine (G) and thymine (T).
Each type of base on one strand forms a bond with just one type of base on the other strand. This is called complementary base pairing. A is bonding only to T, and C bonding only to G. The double helix is also stabilized by the hydrophobic effect and pi stacking, which are not influenced by the sequence of the DNA. Pi stacking is considered important for the molecules’ charge transfer characteristics[4] (Figure 2). As hydrogen bonds are not covalent, they can be broken and rejoined relatively easily. The two strands of DNA in a double helix can therefore be pulled apart, either by a
mechanical force or high temperature. As a result of this complementarity, all the information in the double‐stranded sequence of a DNA helix is duplicated on each strand, which is vital in DNA replication.
Large Area Molecular Junctions
Measuring the charge transport through molecules, even for those that have much simpler structure than DNA, has proven to be a difficult task. Different experimental testbeds have been employed, that yielded differences in the resistance value of a simple alkanedithiol of 8 orders of magnitude [14]. The basic problems of most of the methods used are reproducibility issues and the ability to be implemented in real devices.
At the Zernike Institute for Advanced Materials of the University of Groningen two‐terminal devices with a self assembled monolayer (SAM) of molecules as active component have been materialized. All steps in the flow chart are conventional and industrially used processes such as spin coating and photolithography (Figure 4). The key step in this flow chart is spin coating the conducting polymer PEDOT
SS on top of the SAM. The large, hydrophilic molecules of PEDOTSS (a water‐based suspension) will not penetrate the hydrophobic interior of the SAM during spin coating, forming a layer on top of the SAM. This extra layer acts as a protective cushion, which prevents filamentary growth through the SAM during the evaporation of the top gold contact, that is a cause of short circuits [15].Figur
DNA Molecular Rectifiers
A diode is a two‐terminal device that allows an electric current to pass in one direction (called the forward biased condition) and to block it in the opposite direction (the reverse biased condition). The directionality of current flow most diodes exhibit is generically called the rectifying property. The most common type of diode in silicon technology is the p‐n junction, which is formed by combining p‐type and n‐type semiconductors together in very close contact. Another interesting device, in which the negative differential resistance (NDR) phenomenon can also be observed, is the resonant tunneling diode. This structure is formed when a quantum well is surrounded by two thin barriers and is transparent to carriers of certain energies associated with the discrete energy levels within the well. An increase in carrier energy leads to a decrease in transmission, that is macroscopically manifested as the NDR effect.