The field of nanotechnology has advanced following the discovery of a two-dimensional material of sp 2 hybridized carbon atoms, graphene in 2004 by Geim and Novoselov. Graphene has received so much attention due to its exceptional electronic, thermal, mechanical, and optical properties in addition to its large surface area and single-atom thickness. This has led to the discovery of several techniques to obtain graphene such as chemical exfoliation, chemical vapor deposition (CVD), chemical synthesis etc. However, these techniques are majorly challenged with developing graphene with fewer defects and in large scale; thus, there is an increasing need to produce graphene in large quantities with high quality. Several studies have been carried out to find routes to producing high-quality graphene. This paper focuses majorly on the synthesis and fabrication methods of producing graphene and its derivative, graphene oxide. Characterization techniques to identify graphene such as optical microscopy, scanning electron microscopy (SEM), Raman spectroscopy, scanning probe microscopy (SPM) used to determine number of layers, quality, atomic structures, and defects in graphene is also briefly discussed. This article also covers a short description of graphene applications in transparent electrodes, composites and energy storage devices.

Conducting polymers are of interest due to their unique behavior on exposure to electric fields, which has led to their use in flexible electronics, sensors, and biomaterials. The unique electroactive properties of conducting polymers allow them to be used to prepare biosensors that enable real time, point of care (POC) testing. Potential advantages of these devices include their low cost and low detection limit, ultimately resulting in increased access to treatment. This article presents a review of the characteristics of conducting polymer-based biosensors and the recent advances in their application in the recognition of disease biomarkers.

Emerging research in the area of conducting polymer-based electrochemical biosensors has revealed the need for the development of techniques that can enable easy functionalization with biorecognition molecules and enhance biosensor stability. In this work, an electrochemical biosensor for the detection of the small molecule adenosine was developed utilizing a conducting copolymer as a transducing agent. First, a method was developed to modify the surface of indium tin oxide-coated glass slides to enable robust copolymer deposition. A 3,4-ethylenedioxythiophene (EDOT) and 2H-thieno[3,4-b][1,4]dioxepin-3,3(4H)-diacetic acid (ProDOT−(COOH) 2 ) copolymer was then electrochemically grown on the surface of the modified slides. This copolymer was used to covalently attach an aptamer specific to adenosine to the biosensing platform to provide the system with target selectivity. The electroactivity of the conducting polymer before and after aptamer attachment in aqueous electrolyte solutions was studied. The attachment of the aptamers to the conducting polymer was confirmed using fluorescence microscopy and cyclic voltammetry. The fabricated aptamer-based sensors were then used for the electrochemical detection of adenosine, and the performance of the sensor was investigated. The adenosine aptasensor had a limit of detection of 2.33 nM and a linear range from 9.6 nM to 600 μM. The adenosine aptasensor showed good selectivity against competing interfering agents and specificity relative to scrambled oligonucleotide stands. In addition, the sensor showed good stability for up to 6 days when stored in 0.1 M phosphate-buffered saline or argon.

Electrochemically deposited electroactive polymer (EAP) films were investigated for their potential to enhance the performance of ambient ionization mass spectrometry (MS). Several EAPs of varying hydrophobicity were evaluated, including the superhydrophobic polymer poly­[3,4-(2-dodecyl­ethylene­dioxy)­thiophene] (PEDOT-C12). The EAPs were electropolymerized onto indium tin oxide-coated glass, placed in front of the inlet of a mass spectrometer, and charged to 3.5–4.5 kV. Analyte solutions were then applied to the surface, initiating ionization events. Analytes including peptides and small molecule pharmaceuticals were studied in 0.1% formic acid in methanol/water (“spray solvent”) as well as in synthetic biological fluid matrices, using both EAP spray ionization (EAPSI) and paper spray ionization (PSI). Each EAPSI analysis required as little as 0.1 μL of solution, and the resulting sprays were stable and reproducible. The sensitivity, limit of detection (LOD), and limit of quantification (LOQ) were evaluated using bradykinin, cannabinol, and cannabidiol, which were prepared in pure solvents, artificial urine, and artificial saliva. The limits of detection and quantitation for EAPSI were improved relative to PSI by 1–2 orders of magnitude for analytes prepared in methanol/water and on the same order of magnitude as PSI for analytes prepared in artificial saliva and urine. This EAP-based spray ionization technique offers possibilities for rapid MS analysis with small sample sizes, high accuracy, and miniaturization of MS instruments.

Mucin-1 (MUC1) is a glycoprotein found in epithelial tissues; its function is to protect the body by blocking pathogens from reaching the cells. Overexpression and elevated serum levels of this protein are observed in breast cancer, lung cancer, stomach cancer, ovarian cancer, and many other types of malignancies. Current methods used to detect cancer are expensive and therefore not readily accessible; some methods are also invasive. The ability to detect MUC1 could allow for early detection of cancer, leading to more successful outcomes. This research focuses on the development of a robust biosensor platform based on aptamer-functionalized electroactive polymers (EAPs) that can be used for the detection of cancer. To achieve this, indium tin oxide slide surfaces were modified to enable the electrochemical growth of an electroactive copolymer of 3,4-ethylenedioxythiophene (EDOT) and 2,2-(3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine-3,3-diyl)diacetic acid (ProDOT(COOH)2), with the carboxylic acid functionalities added to introduce bonding sites for a MUC1-specific aptamer. Three copolymer ratios were investigated to maximize the performance. The aptamer was then attached to the EAPs to create aptasensors that could be used for the electrochemical detection of a MUC1 polypeptide. The limits of detection of the biosensors and their stabilities were evaluated. The MUC1 aptasensor showed stability for at least 6 days, depending on the ratio of the copolymer, when stored in 0.1 M phosphate-buffered saline. The 1:2 EDOT/ProDOT(COOH)2 copolymer was found to be the most stable over time and to offer one of the smallest limits of detection, making it the most favorable ratio for aptasensor optimization. Specifically, the 1:2 EDOT/ProDOT(COOH)2 biosensor provided a limit of detection of 369 fg/mL (418 fM) and a linear range of 625 fg/mL to 6.25 ng/mL (709 fM to 7.09 nM) with the MUC1 peptide APDTRPAPG. The sensor also showed selectivity when tested with competing agents including IgG and cell media. The performance of the aptasensor demonstrated its potential as a highly sensitive and selective biosensor for MUC1 detection.