In this work, fluorescent-based chemosensors for the detection of important analytes in aqueous solution are described. The sensors are based on different detection concepts, including analyte-induced aggregation/de-aggregation, pattern-based sensing and micelle-based sensing. In chapter 2, we present an analyte-induced aggregation-type chemosensor for the sensing of spermine. A charge-frustrated amphiphile composed of a highly fluorescent pyrene-1,3,6-trisulfonate head group and an eicosane side chain was used as a fluorescence chemosensor. Analyte-induced aggregation of the dye upon addition of spermine results in pronounced fluorescence quenching. The sensor enables the detection of spermine down to the nanomolar concentration range with good selectivity over closely related biogenic amines such as spermidine. In chapter 3, we describe a conceptually new ‘one-cuvette’ sensing system for the pattern-based analysis of seven aminoglycosides antibiotics. The antibiotics include amikacin, apramycin, gentamicin, kanamycin A and B, neomycin, and paromomycin. A mixture of two amphiphiles with fluorescent head groups was used as a sensing ensemble. In buffered aqueous solution, the amphiphiles form a dynamic mixture of micellar aggregates. In the presence of aminoglycosides, the relative amount and the composition of the micelles is modified. Accurate differentiation in the low micromolar concentration range is achieved by a principal component analysis of the spectral data. Also, the sensing system allows the differentiation of pure aminoglycosides from their mixtures. In chapter 4, a fluorescent chemosensor based on analyte-induced aggregation/de-aggregation is described for the sensing of Al3+ and citric acid. In buffered aqueous solution, the amphiphilic dye can form aggregates and the aggregation of the dye is associated with a strong quenching of its fluorescence. The Al3+-induced aggregation is used to sense Al3+ in the low micromolar concentration range with high selectivity. Furthermore, we demonstrate that the non-fluorescent dye-Al3+ complex can be used as a sensing ensemble for the detection of citric acid. The assay is able to quantify the citric acid content of commercial beverages such as energy drinks. A simple micelle-based assay for the fluorescence sensing of vitamin K1 is described. In the following chapter 5, the assay enables the detection of vitamin K1 in the low micromolar concentration range. As a sensing ensemble, a mixture of the surfactant triton X-100 and 1 aminopyrene in buffered aqueous solution is employed. Vitamin K1 co-localizes with the fluorescent pyrene dye in the micelle, resulting in fluorescence attenuation by dynamic quenching. The assay displays good selectivity and can be used to determine the concentration of vitamin K1 in a commercial preparation. In chapter 6, a fluorescent-based sensor array for the optical analysis of purine derivatives is described. The array is composed of four polysufonated fluorescent dyes. The complexation of the analytes results in partial quenching of the fluorescence. The Sensor array enables the identification of ten purine derivatives including caffeine, theophylline, theobromine, purine, hypoxanthine, paraxanthine, 8-chlorotheophylline, 6-mercaptopurine, cladribine and penciclovir at low millimolar concentration. Furthermore, it is possible to use the array for obtaining information about the quantity and the purity of samples.