Structure and Properties Manipulations of Graphene: Towards Developing High Sensitivity Optical and Electrical Sensors

Document Type

Book

Publication Date

3-3-2023

Abstract

Sensors that can be employed in environmental or biological applications require high sensitivity, specificity, quick and reproducible response, as well as low cost, to allow them to be integrated in a point-of-care packages. Surface sensors are of much higher sensitivity and specificity than the bulk sensors, due to the limited vicinity to probe the target to be detected. Optical and electrical sensors that can be employed as surface sensors are mostly based on surface plasmon resonance and field effect transistors, respectively. Optical sensors are of very high sensitivity, however they come with high cost, which makes their use in a point-of-care format quite limited. Electrical sensors could be fabricated with lower cost, and moderate sensitivity.

In order to achieve all the required properties of a reliable sensor, new materials need to be developed, in this work, we show our efforts to manipulate the graphene properties, through its structure modification, in order to enhance both its optical and electrical properties to the extent that it can be used as a sensor.

Graphene, since isolated in 2004, has attracted great attention to be used in several applications despite its unusual properties, such as the zero band gap that limits its electronic applications, and the very high optical transparency, leading graphene to defy any attempt for absorption in a wide range of wavelengths. To overcome the problem of the zero bandgap and consequently the optical absorption, we manipulate the structure of the single graphene sheet by creating regular and irregular holes in the range of 15–25 nm, with an interplanar distances of 40–60 nm, this structure is referred to as nanomembrane graphene (NMG). We investigate the effect of these structures on the change in the optical properties through probing the localized surface plasmon resonance (LSPR) generated at the edges of these holes by imaging via scanning near field optical microscopy. Our results are confirmed by theoretical electromagnetic field mapping at the graphene membrane edges, which shows a noticeable absorption. The experimental results indicated that the wavelength is dependent on the holes’ diameters and the inter-hole distances; therefore, this nanomembrane graphene can support light harvesting and consequently, could be used as a mid-IR biosensor with a sensitivity of 850 nm/RIU.

We also show that UV absorption in single-layer graphene can be enhanced by creating this nanomesh or nanomembrane structure. Density functional theory (DFT) is used to confirm our experimental results, which has indicated that the absorption peaks are due to the changes in the band structures of the NMG as a result of the pore super lattice.

Another application which depends on this structure manipulation is using graphene-gold nanoparticles hybrid, where the gold nanoparticles are embedded in the graphene holes. This hybrid was used as an electrical pH sensor by using the hybrid as a substrate in a capacitive metal oxide semiconductor (C-MOS) format, leading to a pH sensitivity of 86 mV/pH.

The presented applications in this work show the benefits of manipulating the structure of the graphene and how much it can lead to enhancing its properties.

Comments

This book chapter introduces some information about optical biosensors.

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