using System;

public class Program {

    public static void Main() {

        var mainStr = "Joaquim Pedro Soares";

        Console.WriteLine(mainStr.Contains("JOA", StringComparison.OrdinalIgnoreCase));

        Console.WriteLine(mainStr.Contains("Quim", StringComparison.OrdinalIgnoreCase));

        Console.WriteLine(mainStr.Contains("PEDRO", StringComparison.OrdinalIgnoreCase));

        Console.WriteLine(mainStr.Contains("PeDro", StringComparison.OrdinalIgnoreCase));

    }

}

​

namespace System {

    public static class StringExt {

        public static bool Contains(this string source, string search, StringComparison comparison) {

            return source.IndexOf(search, comparison) >= 0;

        }

    }

}