How To Use LIKE In Stored Procedure With Single Quotes

I'm trying to build a dynamic sql statement in a stored procedurre and can't get the like statement to work. My problem is with the single quote.  for example LIKE '%@searchvalue%'.  This works fine: select * from view_searchprinters where serialnumber like '%012%' But I can't figure out how to create this in a stored procedure.  What syntax should I use for the line in bold?

SET NOCOUNT ON;
DECLARE @sn varchar(50)
SET @sn = N'012'

DECLARE @sql nvarchar(4000)
SELECT @sql = 'select top 10 * from view_searchprinters'
    + ' WHERE 1 = 1 '
SELECT @sql = @sql + ' '
IF @sn IS NOT NULL
   SELECT @sql = @sql + 'and serialnumber LIKE ''' + '%' + '@sn' + '%' + ''' '

EXEC sp_executesql @sql, N'@sn varchar(50)', @sn