Electrochemical biosensors
>>> Biosensors—Recent Advances and Future Challenges in Electrode Materials
In comparison with other methods of detection such as optical, spectroscopic, and chromatographic, electrochemical sensors possess advantages such as simplicity, rapid response times, and high sensitivity. Electrochemical sensors can be easily adapted for the detection of a wide range of analytes and can be incorporated into robust, portable, low cost, miniaturized devices that can be tailored for particular applications. Taking advantage of these attributes and the incorporation of highly specific biological recognition elements (enzymes, nucleic acids, cells, tissues, and so on), electrochemical biosensors are capable of selectively detecting a broad range of target analytes. As defined by IUPAC, electrochemical biosensors are “self-contained integrated devices, which are capable of providing specific quantitative or semi-quantitative analytical information using a biological recognition element (biochemical receptor), which is retained in direct spatial contact with an electrochemical transduction element”. Bioelectrochemical sensors are used in environmental monitoring, healthcare, and biological analysis, among others. Depending on the recognition process, biosensors can be subdivided into two main categories: affinity and biocatalytic sensors. Affinity sensors operate via selective binding between the analyte and the biological component (i.e., antibody and nucleic acid). In contrast, biocatalytic devices incorporate enzymes, whole cells, or tissue slices that recognize the target analyte, and subsequently produce an electroactive species
a DNA electrochemical biosensor for the detection of a sequence of the p53 tumour suppressor gene has been described. A structural rearrangement of the hairpin probe into a linear DNA double strand was induced by binding with cDNA of different lengths that enabled the electrochemical detection at nanomolar scale. Different surface probe densities were used to maximise the analytical performance of the biosensor. Using 21 nt tDNA sequences, the biosensor displayed high discrimination factor between cDNA and TBM sequences. However, the biosensor did not discriminate between the cDNA and the SBM sequences. Using a 15 nt tDNA sequence, the biosensor displayed enhanced discrimination for SNP, that was more pronounced at short hybridization times. The biosensor also displayed good storage and operational stability as measured using cyclic voltammetry. Hairpin DNA sequences can also be designed for the detection of genetic polymorphism. However, the length of the duplex is an important factor in the detection of mismatches and can only be considered for the diagnosis of relatively short tDNA sequences (less than 21 nt). Displacement-based approaches have the potential to play a role in clinical analysis due to their relative simplicity, good selectivity and response times. However, the sensitivities of these methods still remains low and needs improvement to meet clinical requirements.
