Help in Binding C #

I have this code:

private void DataGrid_DataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
{
    var i = 0;
    var d = DataContext as TicketExplorerViewModel;
    if (d == null) return;

    var entityTypes = d.EntityTypes.Select(entityType => new DataGridTextColumn
        {
            Header = entityType.EntityName,
            Binding = new Binding("[" + entityType.Id + "]"),
            MinWidth = 60,
        });

    foreach (var dgtc in entityTypes)
    {
        DataGrid.Columns.Insert(i + 1, dgtc);
        i++;
    }
}

Within Binding = new Binding("[" + entityType.Id + "]"),

I need to insert a string or variable to get a custom field.

I do not know how exactly to proceed to do this, I tried some forms that I know, but I had several errors, someone to help?

Thank you!