Graphene Oxide Modified Electrode for DNA Amperometric Detection Using Microfluidic Electrophoresis Chip

Abstract

The amperometric technique of capillary electrophoresis (CE) is an electrochemical detection method with various advantages that is suitable for biosensors. The amperometric detection system can be easily integrated with the CE system without the need for complicated additional equipment for optical detection. For this reason, the size of the sensor can be reduced to micro-scale, also reducing the cost of the fabrication process, enabling this system to be used in point-of-care applications [1]. The optical method depends on the detection of the fluorescence intensity of the target sample. However, amperometric detection omits the pretreatment process of the sample, such as purification extraction of samples and fluorescent staining for detection [2]. These features allow the device system to be miniaturized and having a rapid response for applications like lab-on-a-chip [3]. Modified Au electrodes integrated with PDMS based microfluidic channels were proposed as an on-chip amperometric detection of CE for DNA sensors. The graphene oxide (GO)-modified Au electrodes were fabricated via photolithography process and drop-casting deposition. First, the deposited Au electrodes were patterned with positive photoresist (PR) using the photolithography method. Next, the graphene oxide was deposited 5 layers on the bare Au using drop-casting technique. Finally, the PR was dissolved by acetone and the unwanted GO was lifted-off. The surface characterization of this the GO-modified Au electrodes is shown in Fig. 1(a) by microscopy image. It was observed that the GO was deposited on Au electrodes following the desired pattern. This treatment amplifies the current signal of amperometric detection of the CE microchip. The performance of the CE amperometric detection device has been demonstrated by sensing an amplicon lambda phage DNA. Then, 1 µL of amplified lambda phage DNA (1 ng/µL) using the conventional polymerase chain reaction (PCR) with a 30-cycle reaction was used as target sample. Figure 1(b) shows the current peak of amperometric detection before (1.9 µA) and after (6.6 µA) GO-modified on the Au electrodes which amplified the sensitivity more than 3.5 times before electrode modification. The emphasized detection of lambda phage DNA using modified electrodes gives a further possibility of biomedical applications through our developed microchip. References 1. D. E. Scott, S. D. Willis, S. Gabbert, D. Johnson, E. Naylor, E. M. Janle, J. E. Krichevsky, C. E. Lunte and S. M. Lunte, Analyst, 2015, 140, 3820–3829. 2. N.-C. Chen, C.-H. Chen, M.-K. Chen, L.-S. Jang, M.-H. Wang, Sens. Actuators B Chem. 2014, 190, 570–577. 3. K. Ha, G. S. Joo, S. K. Jha, Y.-S. Kim, Microelectr. Eng. 2009, 86, 1407–1410. Figure 1