In this paper, we prepared fluorescence-tunable water-soluble CdS quantum dots (QDs) with hexametaphosphate
as stabilizers by a simple route. The prepared CdS QDs were utilized to detect
calcium ion (Ca2+) based on an obvious fluorescence enhancement of CdS QDs induced by Ca2+. The
results demonstrated there was an excellent linear relationship between the fluorescence intensity
ofhexametaphosphate-capped CdS QDs and Ca2+ concentration in the range from 10 mol/L to 400 mol/L
and the detection limit for Ca2+ was 4 mol/L. Furthermore, fluoride ions (F−) can react with Ca2+ to generate
the insoluble calcium fluoride that would inhibit the Ca2+-induced fluorescence enhancement of CdS
QDs. Therefore, the designed Ca2+-induced fluorescence enhancement system was also able to effectively
detect fluoride.