error when using serial port hardware under linux system

I am developing a software system running on linux with unity3D, and need use the serial port. The source code is as follows:

 **sp = new SerialPort("/dev/ttyUSB0", 9600, Parity.None, 8, StopBits.One);
 ports = SerialPort.GetPortNames();
   
 try {
     if(!sp.IsOpen) {
         sp.Open();
         Debug.Log("successful");
         }
     }
 catch(Exception e) {
     Debug.Log(e);
 }**

when running,error occurs, it seems like that the dynamic link library: libMonoPosixHelper.dylib.so can not be found, could you help me, thank you!