Curve fitting in C#

We collect a lot of data (numbers) from our nano sensors. We have developed C# based desktop app where the data is acquired in a computer and then stored in a file. The data is also plotted for about a second before the next data stream comes in. For each data stream, we need to fit a mathematical function on the data so that we can calculate different characteristics of the sensors. We mainly need to develop a library so that we can pass on all of the data to the library and then get result. The resultant fitted curve will also be overlayed on the raw data from the sensors.