Grabbing a string member from a WebClient stream

I'm trying to convert this code to VB.NET from java, it's the part with the "<<<<<<<<<<<<<<<<<<<<<" behind it.

			HttpURLConnection connection = (HttpURLConnection) new URL(String.format("https://www.google.com/recaptcha/api/challenge?k=%s", siteID)).openConnection(Proxy.NO_PROXY); //Opening a connection to the recaptcha site
			BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream())); //there's probably a better way of doing this, however, networking isn't my thing. If anyone knows anything better, feel free to share.
			Pattern challengePattern = Pattern.compile("challenge : '(.*?)',");
			for(String buffer; ((buffer = reader.readLine()) != null);)/>/>/>/> { //Loops until reader.readLine != null
				Matcher challengeMatcher = challengePattern.matcher(buffer);
				if(challengeMatcher.find()) { //There should only be one, no need for a loop
					captchaChallenge = challengeMatcher.group(1); //First group (.*?).          <<<<<<<<<<<<<<<<<<<<<
					break;
				}
			}

my code is :

            rx = New Regex("challenge : '(.*?)'", RegexOptions.Compiled & RegexOptions.IgnoreCase)
            Dim data As Stream = client.OpenRead("http://www.google.com/recaptcha/api/challenge?k=6LdIwrsSAAAAAKHnMqR20V32fL27MbkH_LR6vu8r")
            Dim reader As New StreamReader(data)
            Dim s As String = reader.ReadToEnd()
            If voteLink Is Nothing OrElse voteLink.Length = 0 Then
                Throw New ApplicationException("Specify the URI of the resource to retrieve.")
            End If
            siteHTML = s
            challengeMatches = rx.Matches(siteHTML)
            captchaChallenge = challengeMatches.ToString(1);          <<<<<<<<<<<<<<<<<<<<<
            ListBox1.Items.Add("captchaChallenge : " + captchaChallenge)

The part with the "<<<<<<<<<<<<<<<<<<<<<" behind it causes the problem. I know it's not correct. I'm trying to grab a group member from the Stream source, but I don't know how to convert it exactly from the Java code.

Any help will be appreciated, thanks.