Sol-gel thin film as a matrix for cyanide sensing

A highly selective optical sensor for CN- ions was developed based on entrapment of a sensitive and selective reagent, ninhydrin, in a silica sol–gel thin film coated on a glass substrate. The influence of sol-gel parameters on sensing behavior of the fabricated sensor was also investigated. It is highly desirable to obtain sensors with no reagent leaching which have the capabilities to be used for a long period of time without changes in sensitivity and response time. The thin films fabricated based on tetraethoxysilane (TEOS) as precursor, water:alkoxide ratio of 4:1 and ninhydrin concentration of 0.112 mol L−1. It also showed reproducible results with relative standard deviation of 3.33 and 2.10% for 10and 100 ngmL−1 of CN-, respectively, along with a fast response time of ∼5 second. Interference studies showed a good selectivity for CN- with trapping ninhydrin into sol–gel matrix and appropriately adjusting the structure of doped sol-gel. The sensor was compared with other sensors and was applied to determine cyanide in different water samples with good results.