Digital microfluidic biochip (DMFB) is one of the latest developments in bioelectronics. It can replace traditional bulky equipment to facilitate biochemical assays and save the labor cost. Latency optimization is a common optimization objective of synthesis on DMFBs for assay time reduction. It is helpful for latency minimization if an operation can freely select one from a set of functional modules with various area-latency tradeoffs. In this paper, we propose an efficient latency-optimization synthesis algorithm with module selection capability, LOSMOS, for DMFBs. Experimental results show that LOSMOS outperforms several existing state-of-the-art synthesis algorithms and an ILP-based method without module selection.