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A rapid and accurate medical diagnosis is essential in order to determine the health status of a patient. Nowadays, most of the clinical analyses are performed in specialized laboratory, which required specific instrumentation and trained personal, resulting in an increase of analysis costs and time. In this context, biosensors represent ideal tools capable to provide a specific and fast response together with low cost, easy use and portable size features. This work attempts to provide a review of the research progresses of electrochemical and photoelectrochemical biosensor platforms in clinical applications that have been published in recent years. Special emphasis will be devoted to discuss examples for breast cancer biomarker detection, because breast cancer, is considered the leading cause of cancer-related deaths worldwide in women, representing 15% of all cancer related amongst women, with a 6% mortality rate (based on overall cancer deaths). The manuscript is focused on aptamer-based biosensors, because, due to their stability and their relatively low cost, they have been successfully applied in many biosensor formats for breast cancer biomarker detection.

Aptamer-based sensors have been intensively investigated as potential analytical tools in clinical analysis providing the desired portability, fast response, sensitivity, and specificity, in addition to lower cost and simplicity versus conventional methods. The aim of this review, without pretending to be exhaustive, is to give the readers an overview of recent important achievements about electrochemical, electrochemiluminescence, and photoelectrochemical aptasensors for the protein biomarker determination, mainly cancer related biomarkers, by selected recent publications. Special emphasis is placed on nanostructured-based aptasensors, which show a substantial improvement of the analytical performances.

In this paper, a simple and sensitive approach for human epidermal growth factor receptor 2 (HER2) detection is presented, using antibody-functionalised magnetic beads coupled to screen-printed cells. The immunoassay is based on a sandwich format in which a primary monoclonal antibody anti-HER2 is coupled to protein A modified magnetic beads. The modified beads are then used to capture the protein from the sample solution and a sandwich assay is performed by adding a secondary monoclonal antibody anti-HER2 labelled with biotin. The enzyme alkaline phosphatase (AP) conjugated with streptavidin and its substrate (1-naphthyl-phosphate) are then used for the electrochemical detection by differential pulse voltammetry (DPV). The experimental conditions for the immunoassay were optimised. The performance of the assay in terms of sensitivity, reproducibility and selectivity has been studied in buffer and serum samples from hospital patients.

Recently, the development and optimization of a flow injection analysis (FIA) operated bacterial biosensor based on the aerobic catabolism of Pseudomonas putida ML2 was reported in the literature (Lanyon et al. 2004, 2005). By adapting information from these reports, we investigated whether operating parameters and procedures of the benzene biosensor could be directly applied to a new system based on a different bacterial strain for the detection of the whole benzene, toluene, ethylbenzene, and xylenes range. Cells of the investigated bacterial strain, Pseudomonas putida F1, were immobilized between two cellulose acetate membranes and fixed onto a Clark dissolved oxygen electrode. The P. putida F1 aerobically degrades benzene, toluene, and ethylbenzene (BTE) (Cho et al. 2000). The BTE biosensor in kinetic mode FIA displayed a linear range of 0.02-0.14 mM benzene (response time: 5 min, baseline recovery time: 15 min), 0.05-0.2 mM toluene (response time: 8 min, baseline recovery time: 20 min), and 0.1-0.2 mM ethylbenzene (response time: 12 min, baseline recovery time: 30 min), respectively. Due to the differences in sensitivity, response, and baseline recovery times for BTE, it was possible to differentiate each compound in mixtures of these volatile organic compounds (VOCs). No response for xylenes could be obtained since they cannot be completely metabolized by this bacterial strain. However, it was reported that the range of compounds degradable by P. putida F1 can possibly be expanded by cultivating the cells on different carbon sources (Choi et al. 2003). The sensor showed good intra- and interassay reproducibility, and all obtained results were comparable with those reported in the literature. The demonstrated reproducibility and the simplicity and ease of use as well as the portability for in situ measurements indicates that the biosensor could be suitable as a reliable initial warning device for elevated BTE levels in indoor and outdoor environments.

Genosensor technology relying on the use of carbon and gold electrodes is reviewed. The key steps of each analytical procedure, namely DNA-probe immobilisation, hybridisation, labelling and electrochemical investigation of the surface, are discussed in detail with separate sections devoted to label-free and newly emerging magnetic assays. Special emphasis has been given to protocols that have been used with real DNA samples. (C) 2003 Elsevier B.V. All fights reserved.