Abstract: A method for detecting free metal ions in a sample includes, providing a liquid sample potentially comprising free metal ions. A fluorescent probe comprising an organic fluorescent core and one or more metal binding functional group is added to the sample. The one or more metal binding functional group is selected from a group comprising a phosphonic acid group and an arsonic acid group and is covalently linked to a sp or sp2-carbon atom or a nitrogen atom of the fluorescent core via a P or As atom. A fluorescence of the sample is measured. A presence of the metal ions leads to a concentration-dependent decrease, increase or shift of fluorescence compared to a reference sample. The method preferably involves determining a concentration of the metal ions in the sample. The liquid sample may be a biological sample, such as a bodily fluid, a tissue sample or a sample comprising cells.

Abstract: A fluorescent probe includes one or more metal binding functional group, such as phosphonic acid group and an arsonic acid group, in which the functional group is covalently linked to a fluorescent core via a sp2-carbon atom of the fluorescent core. In embodiments, the fluorescent core is an organic fluorescent compound/moiety, that can be a tetrapyrrole derivative, such as porphyrin or phthalocyanine, acridine, BODIPY, cyanine or cyanine derivatives, carbazole, coumarine or coumarine derivatives, xanthene or xanthene derivatives such as fluorescein or rhodamine. The fluorescent probe can bind to calcium and/or a calcification, such as hydroxyapatite (HAP). In a further aspect, a fluorescent probe is used in a method of detecting calcium, such as a calcification or HAP, in a bodily tissue. The use of the fluorescent probe is also provided for detecting calcium, a calcification and/or HAP, such as calcium depositions in a bodily tissue.