Infectious diseases caused by pathogens have become a life-threatening problem for millions of people around the world in recent years. Therefore, the need of efficient, fast, low-cost and user-friendly biosensing systems to monitor pathogen has increased enormously in the last few years. This paper presents an overview of different fluorescent labels and the utilization of fluorescence-based biosensor techniques for rapid, direct, sensitive and real-time identification of bacteria. In these biosensors, organic dyes, nanomaterials and rare-earth elements are playing an increasing role in the design of biosensing systems with an interest for applications in bacterial analysis.

The high sensitivity of optical detection techniques and the highly specific reactions between antibodies and antigens mean that optical immunoassays have attracted much interest in the fields of protein, hormone, drug, and microorganism detection, without the need for complex separation and extraction steps. The immobilization of an antibody on a solid support is a crucial step for optical immunoassays. This review surveys the latest advances in current antibody immobilization techniques in detail, including physical adsorption, covalent attachment, bioaffinity immobilization, and some recently developed methods. Furthermore, specific consideration is given to oriented immobilization, which may improve the homogeneous surface covering the accessibility of the active site and surface coverage, and the analytical performance of immunoassays. Finally, new perspectives for antibody immobilization techniques in optical immunoassays are outlined.

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In this communication, we present a nano-graphite-DNA hybrid sensor for fluorescent detection of mercury(II) ions in aqueous solution for the first time. Furthermore, an amplification strategy based on nano-graphite for Hg(2+) detection by using DNase I was demonstrated. The proposed amplified assay was simple and cost-effective with a limit of detection (LOD) for Hg(2+) of 0.5 nM, which was about 20-fold lower than that of traditional unamplified homogeneous assays. We further demonstrated its practical application to detect Hg(2+) in a real sample.