Precise and selective sensing of DNA-DNA hybridization by graphene/Si-nanowires diode-type biosensors

Abstract

Single-Si-nanowire (NW)-based DNA sensors have been recently developed, but their sensitivity is very limited because of high noise signals, originating from small source-drain current of the single Si NW. Here, we demonstrate that chemical-vapor-deposition-grown large-scale graphene/surface-modified vertical-Si-NW-arrays junctions can be utilized as diode-type biosensors for highly-sensitive and -selective detection of specific oligonucleotides. For this, a twenty-seven-base-long synthetic oligonucleotide, which is a fragment of human DENND2D promoter sequence, is first decorated as a probe on the surface of vertical Si-NW arrays, and then the complementary oligonucleotide is hybridized to the probe. This hybridization gives rise to a doping effect on the surface of Si NWs, resulting in the increase of the current in the biosensor. The current of the biosensor increases from 19 to 120% as the concentration of the target DNA varies from 0.1 to 500 nM. In contrast, such biosensing does not come into play by the use of the oligonucleotide with incompatible or mismatched sequences. Similar results are observed from photoluminescence microscopic images and spectra. The biosensors show very-uniform current changes with standard deviations ranging ~1 to ~10% by ten-times endurance tests. These results are very promising for their applications in accurate, selective, and stable biosensing.

Figure 1. Schematic illustrations describing structure and detecting mechanism of graphene/Si-NW-arrays biosensors.

(a) Schematic diagram showing the mechanism of graphene/Si-NW-array biosensors for selectively detecting p- and t-, and d-ss oligonucleotides. The Si NWs are decorated with p-ss oligonucleotide in advance for the sensing tests of t- or d- oligonucleotide. (b) Schematic diagram of complementary ss oligonucleotide pairs of p- and t-ss oligonucleotides, and incompatible ss oligonucleotide pairs of p- and d-ss oligonucleotides.

Figure 2. Schematic diagrams describing fabrication processes of graphene/Si-NWs biosensors.

Schematic diagram of fabrication processes at each step: 1) preparing vertically-aligned Si-NW arrays by MaCE, 2) modifying the surface of Si NWs for sensing DNAs, 3) forming the vertical junction of graphene/surface-modified Si NWs, and 4) finally completing graphene/Si-NWs vertical-diode-type biosensors by depositing top/bottom metal contacts. These fabrication steps are detailed in the text.

Figure 3. SEM images at each step for fabricating of graphene/Si-NWs biosensors.

Planar SEM images of (a) Au mesh with hole arrays on the Si substrate, (b) Si-NW arrays prepared by MaCE, and (c) uniformly-transferred graphene on the top of Si NWs. (d) Tilted SEM image of graphene/Si-NWs biosensors, clearly showing the uniform contact between graphene and Si NWs.

Figure 4. Responsivity of graphene/Si-NWs biosensors.

(a) Current of a graphene/Si-NWs biosensor as a function of mole fraction of p-ss oligonucleotide. (b) Current of a graphene/Si-NWs biosensor as a function of mole fraction of t- or d-ss oligonucleotide loaded on the surface of NWs decorated with 1000 nM p-ss oligonucleotide in advance. The error bars in (a,b) indicate 6%. (c) Endurance histogram for ten-times consecutive sensing of 0.1 nM t-ss oligonucleotide loaded on the surface of NWs decorated with 1000 nM p-ss oligonucleotide in advance. The hybridized p- and t-ss oligonucleotides were well dehybridized and t-ss oligonucleotide was removed without any damage on the device by treatment with sodium chloride.

Figure 5. PL microscopic mapping images and spectra of DNA-decorated Si NWs.

(a) Planar PL microscopic images and (b) spectra of Si NWs decorated with p-ss oligonucleotide, p- and t-ss oligonucleotides, and p- and d-ss oligonucleotides. The PL spectra of separate t- and d-ss oligonucleotides are also plotted for the comparisons with those of the hybridized oligonucleotides. The marked area in the PL microscopic image indicates green PL scattered from several spots of Si NWs after d-ss oligonucleotide is added and the inset in the PL spectra clarifies the peak shift. The scale bars indicate 15 μm.