Direct Detection and Discrimination of Nucleotide Polymorphisms Using Anthraquinone Labeled DNA Probes

Biomarkers and biosensors for early cancer diagnosis, monitoring and prognosis

Cancers continue to be of major concern due to their serious global socioeconomic impact, apart from the continued increase in the incidence of various cancer types. A major challenge that this disease poses is due to the low "early detection" rates which limit the therapeutic outcomes for the affected individuals. Current research has highlighted the discovering biomarkers that help in early cancer detection and the development of technologies for the detection and quantification of such biomarkers. Biomarkers range from proteins to nucleic acids, and can be specific to a particular cancer type. Detection and quantification of such biomarkers at low levels from biological samples is being made possible by the advent of developing biosensors and by using biomedical engineering technologies such as tumor-on-a-chip models. Here, we present biomarkers that can be helpful for the early detection of breast, colorectal, esophageal, lung, liver, ovarian, and prostate cancer. In addition, we discuss the potential of circulating tumor cell DNA (ctDNA) as an early diagnostic marker. Finally, biosensors available for the detection of cancer biomarkers, which is a recent advancement in this area of research, are discussed.

A Review of Detection Methods for Vancomycin-Resistant Enterococci (VRE) Genes: From Conventional Approaches to Potentially Electrochemical DNA Biosensors

Vancomycin-resistant Enterococci (VRE) genes are bacteria strains generated from Gram-positive bacteria and resistant to one of the glycopeptides antibiotics, commonly, vancomycin. VRE genes have been identified worldwide and exhibit considerable phenotypic and genotypic variations. There are six identified phenotypes of vancomycin-resistant genes: VanA, VanB, VanC, VanD, VanE, and VanG. The VanA and VanB strains are often found in the clinical laboratory because they are very resistant to vancomycin. VanA bacteria can pose significant issues for hospitalized patients due to their ability to spread to other Gram-positive infections, which changes their genetic material to increase their resistance to the antibiotics used during treatment. This review summarizes the established methods for detecting VRE strains utilizing traditional, immunoassay, and molecular approaches and then focuses on potential electrochemical DNA biosensors to be developed. However, from the literature search, no information was reported on developing electrochemical biosensors for detecting VRE genes; only the electrochemical detection of vancomycin-susceptible bacteria was reported. Thus, strategies to create robust, selective, and miniaturized electrochemical DNA biosensor platforms to detect VRE genes are also discussed.

Recent progress of conductive 3D-printed electrodes based upon polymers/carbon nanomaterials using a fused deposition modelling (FDM) method as emerging electrochemical sensing devices

3D-printing or additive manufacturing is presently an emerging technology in the fourth industrial revolution that promises to reshape traditional manufacturing processes. The electrochemistry field can undoubtedly take advantage of this technology to fabricate electrodes to create a new generation of electrode sensor devices that could replace conventionally manufactured electrodes; glassy carbon, screen-printed carbon and carbon composite electrodes. In the electrochemistry research area, studies to date show that there is a demand for electrically 3D printable conductive polymer/carbon nanomaterial filaments where these materials can be printed out through an extrusion process based upon the fused deposition modelling (FDM) method. FDM could be used to manufacture novel electrochemical 3D printed electrode sensing devices for electrochemical sensor and biosensor applications. This is due to the FDM method being the most affordable 3D printing technique since conductive and non-conductive thermoplastic filaments are commercially available. Therefore, in this minireview, we focus on only the most outstanding studies that have been published since 2018. We believe this to be a highly-valuable research area to the scientific community, both in academia and industry, to enable novel ideas, materials, designs and methods relating to electroanalytical sensing devices to be generated. This approach has the potential to create a new generation of electrochemical sensing devices based upon additive manufacturing. This minireview also provides insight into how the research community could improve the electrochemical performance of 3D-printed electrodes to significantly increase the sensitivity of the 3D-printed electrodes as electrode sensing devices.

Use of Electrocatalysis for Differentiating DNA Polymorphisms and Enhancing the Sensitivity of Electrochemical Nucleic Acid-Based Sensors with Covalent Redox Tags-Part II

Single-nucleotide polymorphisms (SNPs), insertion/deletion (indel) polymorphisms, and DNA methylation are the most frequent types of genetic variations. As such, DNA polymorphisms play significant roles in genetic mapping and diagnostics. Thus, analytical methods enabling DNA polymorphism detection will provide an invaluable means for early disease diagnosis. However, no single electrochemical nucleic acid-based sensor has achieved the detection of the three major polymorphisms (SNPs, indel polymorphisms, and DNA methylation) with sufficient specificity and sensitivity. In response, we explore the utilization of a catalytic reaction between methylene blue (MB) covalently linked to surface-bound nucleic acid and freely diffusing ferricyanide (Fe(CN)₆^3-) to improve specificity and sensitivity of DNA polymorphism detection. We find that the dynamics of the nucleic acid tether is an additional rate-limiting factor for the electrocatalytic reaction, in addition to the more traditional kinetic and excess factors. Our proof-of-concept experiments demonstrate that the use of electrocatalysis enables differentiation of the three polymorphisms when target sequences are present at 10 nM. We hypothesize that this ability is a result of the distinct dynamics of the DNA probe with each respective polymorphism. In addition to the specificity the sensor displays, the sensor achieves a 20 pM limit of detection. We believe that the electrocatalysis between nucleic acid-tethered MB and Fe(CN)₆^3- is highly promising for electrochemical nucleic acid-based sensors to achieve better specificity and sensitivity.