My recommendation here would be to look at using Linq2Couchbase. It will probably make your job a lot easier by writing the query for you.
Another option might be to use query parameters rather than string concatenation. This is more secure as it projects against injection attacks and can allow you to prepare the query for improved performance on repeat queries. You can add named parameters such as $Item in your query text and then use .AddNamedParameter("Item", items) to add the parameter to your QueryOptions.