Sanitise user input before parsing by Lucene

SanitiseUserQuery

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using System.Web;
using System.Web.UI.WebControls;

namespace ICO.Web.Analysis
{
    public static class LuceneHelper
    {
        public static string SanitiseUserQuery(string query)
        {
            if (query == null)
            {
                return null;
            }

            var specialChars = @"-+&|!(){}[]^~*?:\/";

            // add slash before each char. Regex.Escape() doesn't seem to escape ']' properly ?!?
            specialChars = string.Join("", specialChars.ToCharArray().Select(x => @"\" + x));

            // Escape special Chars
            query = Regex.Replace(query, "([" + specialChars + "])", @"\$1");

            // Escape AND OR NOT
            foreach (var word in new[] { "AND", "OR", "NOT" })
            {
                var escapedWord = string.Join("", word.ToCharArray().Select(x => @"\" + x));
                query = Regex.Replace(query, word, escapedWord, RegexOptions.IgnoreCase);
            }

            // Escape last " if there's an odd number
            var numQuotes = query.ToCharArray().Count(x => x == '"');
            if (numQuotes%2 == 1)
            {
                query = Regex.Replace(query, "(.*)\"(.*)", "$1\\\"$2");
            }

            return query;
        }
    }
}