Redox Buffering Effects in Potentiometric Detection of DNA Using Thiol-Modified Gold Electrodes.

Xingxing Xu,Si Chen,Qitao Hu,Yingtao Yu,Leif Nyholm,Zhen Zhang

doi:10.1021/acssensors.0c02700

Abstract

Label-free potentiometric detection of DNA molecules using a field-effect transistor (FET) with a gold gate offers an electrical sensing platform for rapid, straightforward, and inexpensive analyses of nucleic acid samples. To induce DNA hybridization on the FET sensor surface to enable potentiometric detection, probe DNA that is complementary to the target DNA has to be immobilized on the FET gate surface. A common method for probe DNA functionalization is based on thiol–gold chemistry, immobilizing thiol-modified probe DNA on a gold gate with thiol–gold bonds. A self-assembled monolayer (SAM), based on the same thiol–gold chemistry, is also needed to passivate the rest of the gold gate surface to prevent non-specific adsorption and to enable favorable steric configuration of the probe DNA. Herein, the applicability of such FET-based potentiometric DNA sensing was carefully investigated, using a silicon nanoribbon FET with a gold-sensing gate modified with thiol–gold chemistry. We discover that the potential of the gold-sensing electrode is determined by the mixed potential of the gold–thiol and gold–oxygen redox interactions. This mixed potential gives rise to a redox buffer effect which buffers the change in the surface charge induced by the DNA hybridization, thus suppressing the potentiometric signal. Analogous redox buffer effects may also be present for other types of potentiometric detections of biomarkers based on thiol–gold chemistry.

Highlights

Has to be immobilized on the field-effect transistor (FET) gate surface
The probe DNA was heated at 95 °C for 5 min and cooled on ice for gold-gated siliconnanoribbon FET (SiNRFET) are shown in Figure 1a,b, respectively
As much as possible, eliminate the common signal drift the SiNRFETs on the chip were incubated in solutions caused by, for example, the reference electrode or non-specific containing probe DNA for 16 h at room temperature using a interactions, during the measurements

Summary

■ METHODS

Found that similar pH buffering effects can completely suppress the ISFET signal associated with protein detection.[17]. Potentiometric determinations of DNA were made using SiNRFETs interactions with gold oxide have been found to decrease with a gold-coated gate surface [see Figure 1a,b for the scanning the ISFET signal for potentiometric detection of Ca2+.18. The 200 nm lightly p-type doped silicon layer was first thinned down to 120 nm by potentiometric DNA detection employing a gold-gated siliconnanoribbon FET (SiNRFET) sensor, using an optimized thiolbased surface DNA hybridization protocol.[15]. The resulting 24 nanoribbons were either 100 nm wide and 1 μm long or interactions Their associated redox buffer capacities make it difficult to detect the potentiometric signal generated by the DNA hybridization. A 40 nm-thick gold layer with 10 nm Ti as an adhesion layer was patterned on the silicon channel region, that is, the gate surface, using a lift-off process (see Figure 1a for the top-view SEM image). The flow rate was initially set to 100 μL/min for 10 s to quickly replace the electrolyte in the microfluidic channel and set to 5 μL/min for 15 min

■ RESULTS AND DISCUSSION

■ ACKNOWLEDGMENTS

■ CONCLUSIONS