Try the following codes:
do {
rowIndex = 2 + index;
row = dt.NewRow();
row[0] = Convert.ToString(((Microsoft.Office.Interop.Excel.Range)workSheet.Cells[rowIndex, 1]).Value2);
row[1] = Convert.ToString(((Microsoft.Office.Interop.Excel.Range)workSheet.Cells[rowIndex, 2]).Value2);
row[2] = Convert.ToString(((Microsoft.Office.Interop.Excel.Range)workSheet.Cells[rowIndex, 3]).Value2);
row[3] = Convert.ToString(((Microsoft.Office.Interop.Excel.Range)workSheet.Cells[rowIndex, 4]).Value2);
row[4] = Convert.ToString(((Microsoft.Office.Interop.Excel.Range)workSheet.Cells[rowIndex, 5]).Value2);
index++;
dt.Rows.Add(row);
}
while (((Microsoft.Office.Interop.Excel.Range)workSheet.Cells[rowIndex, 1]).Value2 != null)