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 Application of Diamond for Biosensing



Semiconductor and Biotechnology

The application of semiconductor technology for the bio technology is relatively new region of technology but the development of many techniques to detect the biomolecules has been demonstrated from a lot of research organizations. The fabrication of micro structure on many kinds of materials can be obtained by applying the semiconductor fabrication technique and the surface treatments such as plasma enhanced treatment confirm the change in the surface properties on materials. These techniques are supporting the IT society. In these days, many researcher are seeking the application of semiconductor technology to biotechnology.

Here, the one example of applying the semiconductor technology to biotechnology is explained. Figure1. shows the micropatterned diamond surface observed by the optical microscope. The patterns are fabricated from Au and the diameter of dot pattern is 5~20um. These micro patterns cannot be fabricated without semiconductor technology called by photolithography. The DNA is immobilized on this surface after treatment by ultraviolet irradiation or plasma treatment on this surface. The DNA is functionalized with the fluorescence dye and observed by the florescence microscope. The result of this observation is shown in figure2. The fluorescence dot can be observed and the DNA immobilization on diamond surface can be confirmed. [1]

The other cases, the micro electrode fabricated by this micropattern are applied to biosensor and the fabrication of MEMS for extracting the bimoleculs from our bodies, and the fabrication of field-effect transistor (FET) which is researched on our group. From these examples, the semiconductor technique is begun to apply the many parts relating the biotechnology.


Figure 1. Micropatterns on diamond surface


Figure 2. Observation of immobilized DNA by the fluorescence microscope(Optical method)

DNA sensor with diamond surface

My research topic is the development of DNA sensor to detect the single-nucleotide-polymorphisms (SNPs). The DNA is fabricated by the sequence of four kinds of bases (A, T, G, C) and which codes the synthesis of protein. Generally, the two strands of complementary DNA makes the A-T or G-C pairs in these bases and form the double-helix structure (which is also called Watson-Click structure). The SNP is the site where the two bases in each DNA strands cannot fabricate the pair such as A and G or C and T etc. The existence of SNP is controlling the controlactability for such diseases and the affectability of some medicine. (See figure3. )

The merits of fabricating the sensor with diamond substrate are the high biocompatibility, simply modification on surface and the high stability both in air and in aqueous solution. And the semiconductor devices can be fabricated on the diamond substrate because the hydrogen terminated surface natively has the p-type surface conductive layer.

We fabricate the FET-type DNA sensor which operates stably in electrolyte solution to apply these attractive merits of semiconductive diamond surface. (Figure4) The gate surface of diamond FET is directly exposed to the electrolyte solution and the DNA is immobilized on this surface. This FET is operated as the sensor to measure the surface potential on gate surface, while FET generally operates as the "switch" controlling the drain-source current by the applied gate voltage. The surface potential on gate becomes more negative when the single strand DNA (target DNA) is hybridized with immobilized single strand DNA (probe DNA), because DNA is natively negatively charged by the ionization of phosphate groups in it. This surface potential change induces the more holes in the surface conductive layer and the conductivity of gate channel (the conductance between drain and source electrode). This shift caused by the surface potential change can be shown in figure5.


Figure3. complementary DNA and single-mismatched DNA


Figure4. Diamond electrolyte solution-gate field effect transistor.


Figure5. Detection of DNA by the diamond electrolyte solution gate FET


The detection of target DNA by the electrolyte solution gate FET is applied to detect the mismatched DNA. The hybridization efficiency of double strand DNA is degreased by the existence of mismatched site in target DNA which means the rate of immobilized double strand DNA is degreased when target DNA is mismatched. It indicates that the change in gate potential by the hybridization of mismatched DNA is smaller than that by the hybridization of complementary DNA and the mismatched DNA detection is determined by this difference of change in gate potential. Figure7. shows the result of mismatch detection on electrolyte solution gate FET. The difference of change in gate potential between complementary DNA and single-mismatched DNA is 3mV. [3] By advancement of this detection, the process of partially oxidation on gate surface is induced which cause the diamond surface more negative than the perfectly hydrogenated diamond surface. This negative charge originates the oxygen terminated surface can apply the repulsion force to DNA. The effect between the surface and DNA is degreased by this force and it makes the sensitivity of mismatched DNA increased. The difference of change in gate potential between complementary DNA and single mismatched DNA is increased to be 19mV by inducing this oxidation process. This difference is sufficiently large and it means the diamond electrolyte solution gate FET has sufficient sensitivity to discriminate mismatched DNA.[4] From now on, we investigate the interactions between diamond surface and DNA to develop the more sensitive detection method. And the interaction between RNA and binding protein will be inquired.


[1] G. J. Zhang, K. S. Song, Y. Nakamura, T. Ueno, T. Funatsu, I. Ohdomari, H.Kawarada,; Langmuir 2006, 22, 3728.
[2] J. H. Yang, K. S. Song, S. Kuga, H.Kawarda, ; Jpn. J. Appl. Phys. 2006, 45, 42, L1114.
[3] K. S. Song, G. J. Zhang,Y. Nakamura,K. Furukawa, T. Hiraki, J. H. Yang, T. Funatsu, I. Ohdomari,
H. Kawarada, ; Phys. Rev. E 2006, 74, 041919.
[4] S. Kuga, J. H. Yang, H. Takahashi, K. Hirama, T. Iwasaki, H. Kawarada "Detection of mismatched DNA on partially negatively charged diamond surface by optical and potentiometric methods", J. Am. Chem. Soc., 130, 13251-13263 (2008)
[5] S. Kuga, S. Tajima, J.H. Yang, K. Hirama, H. Kawarada, "Precise Detection Of Single Mismatched DNA With Functionalized Diamond Electrolyte Solution Gate FET", Tech. Dig. IEEE IEDM, p483 (2008)