Advantage of the transistor miniaturization

As a big advantage of the transistor type biosensor, if we miniaturize biosensor, the sensitivity would not decrease. For scaling rule of transistor miniaturization, if the length of the gate and the width of the transistor reduce to 1/k, a necessary amount of the sample becomes 1/k2 or less (Fig.1) .So it can be said that to miniaturize the transistor is indispensable for high density, high sensitivity, and a high-speed sensors.

Fig.１ Scaling rule of transistor miniaturization

The highly sensitive DNA-sensors

Applying the fabrication process of MISFETs, we fabricate the miniaturized diamond electrolyte solution- gate FET. And the highly sensitive DNA-sensors are made by immobilizing the probe DNA oligonucleotide with 24-mer on the channel surface. The complementary oligonucleotide hybridizes with probe and the gate potential is positively shift by enhanced negative charge on the channel surface (Fig.2). In the case of non-complementary DNA, the unspecific binding has been occurred on the channel surface and the gate potential is positively shift by that. However, this shift of gate potential is much smaller than that of complementary hybridization.

Fig.2 DNA-sensing mechanism

The device characteristics of the miniaturized diamond SGFET DNA-sensor before and after hybridization are shown in Fig.3. It experimented with complementary DNA 10pM and the change in 15mV was seen as a gate voltage by hybridization of DNA. Figure 4 shows the change of the voltage of the gate by the denature processing, non-complementary DNA, complementary DNA are similarly repeated. The highly sensitive miniaturized diamond DNA-sensor could detect complementary DNA and non-complementary DNA (DNAconc=10pM). In addition, even if the denature processing is given, the performance is almost maintained.

It doesn't limit to DNA, the range of the research is expanded to RNA and LNA, etc. , and it will aim at the achievement of the more stable and practicing biosensing application in the future.

References

[1] K. S. Song, T. Hiraki, H. Umezawa, H. Kawarada "Miniaturized diamond field-effect transistors for application in biosensors in electrolyte solution", Appl. Phys. Lett. 90, 6, 063901 (2007)
[2] 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)