By making use of the aggregation-induced emission feature of silole, compound 1 with an ammonium group is designed and synthesized with a view to developing a new optical probe for fluorescence turn-on detection of DNA and label-free fluorescence nuclease assay. The fluorescence of 1 increases largely upon mixing with DNA, in particular for long DNA, indicating that 1 can be used for fluorescence turn-on detection of DNA. More interestingly, 1 can be employed to follow the DNA cleavage process by nuclease. Therefore, a label-free fluorescence nuclease assay method is successfully established with 1. Furthermore, this label-free fluorescence assay can also be used for inhibitor screening of nucleases. Given its simplicity, easy operation, sensitivity and cost-effectiveness, this method can be extended to other nuclease assays and high-throughput screening of nuclease inhibitors.