Electrodeposition of reduced graphene oxide onto gold electrodes: creating thin electrochemically active and optically transparent overlayers

An electrochemical sensor integrated lab-on-a-CD system for phenylketonuria diagnostics

Phenylketonuria (PKU) is characterized by an autosomal recessive mutation in the phenylalanine hydroxylase (PAH) gene. Impaired PAH enzyme activity leads to the accumulation of phenylalanine (Phe) and its metabolites in the bloodstream, which disrupts the central nervous system and causes psychomotor retardation. Early diagnosis of PKU is essential for timely intervention. Moreover, continuous monitoring of blood Phe levels is indispensable for prognosis, requiring a robust and reliable monitoring system. This study presents an automated lab-on-a-CD-based system for early diagnosis and monitoring of PKU treatment. This miniaturised system contains CD-shaped disposable cartridges, a mini centrifuge, and an electrochemical sensing unit. Modified screen-printed gold electrodes were used for the electrochemical measurements in cartridges. Electrode modification was conducted by electrochemical graphene oxide reduction and deposition on the electrode surface, which increased the sensitivity of the measurement 1.5 fold. The system used amperometric detection to measure Phe in the blood through oxidation of NAD+ to NADH by the enzyme phenylalanine dehydrogenase. The limit of detection (LOD), limit of quantification (LOQ), and sensitivity of the system were 0.0524, 0.1587 mg dL-1 and 0.3338 μA mg-1 dL, respectively, within the 0-20 mg dL-1 measurement range (R2 = 0.9955). The performance of the lab-on-a-CD system was compared to the gold standard HPLC method. The accuracy was 83.1% for HPLC and 84.1% for the lab-on-a-CD system. In conclusion, this study successfully developed a portable diagnostic device for rapid (under 20 min), accurate and highly sensitive detection of Phe in whole blood.

Direct electrochemical reduction of graphene oxide thin film for aptamer-based selective and highly sensitive detection of matrix metalloproteinase 2

Simple and low-cost biosensing solutions are suitable for point-of-care applications aiming to overcome the gap between scientific concepts and technological production. To compete with sensitivity and selectivity of golden standards, such as liquid chromatography, the functionalization of biosensors is continuously optimized to enhance the signal and improve their performance, often leading to complex chemical assay development. In this research, the efforts are made on optimizing the methodology for electrochemical reduction of graphene oxide to produce thin film-modified gold electrodes. Under the employed specific conditions, 20 cycles of cyclic voltammetry (CV) are shown to be optimal for superior electrical activation of graphene oxide into electrochemically reduced graphene oxide (ERGO). This platform is further used to develop a matrix metalloproteinase 2 (MMP-2) biosensor, where specific anti-MMP2 aptamers are utilized as a biorecognition element. MMP-2 is a protein which is typically overexpressed in tumor tissues, with important roles in tumor invasion, metastasis as well as in tumor angiogenesis. Based on impedimetric measurements, we were able to detect as low as 3.32 pg mL-1 of MMP-2 in PBS with a dynamic range of 10 pg mL-1 - 10 ng mL-1. Further experiments with real blood samples revealed a promising potential of the developed sensor for direct measurement of MMP-2 in complex media. High specificity of detection is demonstrated - even to the closely related enzyme MMP-9. Finally, the potential of reuse was demonstrated by signal restoration after experimental detection of MMP-2.

Development of a Graphene-Oxide-Deposited Carbon Electrode for the Rapid and Low-Level Detection of Fentanyl and Derivatives

The opioid overdose crisis in North America worsened during the COVID-19 pandemic, with multiple jurisdictions reporting more deaths per day due to the fentanyl-contaminated drug supply than COVID-19. The rapid quantitative detection of fentanyl in the illicit opioid drug supply or in bodily fluids at biologically relevant concentrations (i.e., <80 nM) remains a significant challenge. Electroanalytical techniques are inexpensive and can be used to rapidly detect fentanyl, but detection limits need to be improved. Herein, we detail the development of an electrochemical-based fentanyl analytical detection strategy that used a glassy carbon electrode modified with electrochemically reduced graphene oxide (ERGO) via electrophoretic deposition. The resulting surface was further electrochemically reduced in the presence of fentanyl to enhance the sensitivity. Multiple ERGO thicknesses were prepared in order to prove the versatility and ability to fine-tune the layer to the desired response. Fentanyl was detected at <10 ppb (<30 nM) with a limit of detection of 2 ppb and a calibration curve that covered 4 orders of concentration (from 1 ppb to 10 ppm). This method was sensitive to fentanyl analogues such as carfentanil. Interference from the presence of 100-fold excess of other opioids (heroin, cocaine) or substances typically found in illicit drug samples (e.g. caffeine and sucrose) was not significant.

Nanocomposite Materials Based on Electrochemically Synthesized Graphene Polymers: Molecular Architecture Strategies for Sensor Applications

The use of graphene and its derivatives in the development of electrochemical sensors has been growing in recent decades. Part of this success is due to the excellent characteristics of such materials, such as good electrical and mechanical properties and a large specific surface area. The formation of composites and nanocomposites with these two materials leads to better sensing performance compared to pure graphene and conductive polymers. The increased large specific surface area of the nanocomposites and the synergistic effect between graphene and conducting polymers is responsible for this interesting result. The most widely used methodologies for the synthesis of these materials are still based on chemical routes. However, electrochemical routes have emerged and are gaining space, affording advantages such as low cost and the promising possibility of modulation of the structural characteristics of composites. As a result, application in sensor devices can lead to increased sensitivity and decreased analysis cost. Thus, this review presents the main aspects for the construction of nanomaterials based on graphene oxide and conducting polymers, as well as the recent efforts made to apply this methodology in the development of sensors and biosensors.