PCLCrypto Import public key generated with OpenSSL

Question

I create a keypair in serverside with openssl.

        string serverPublicKey;
        string serverPrivateKey;
        using (var serverRsa = new OpenSSL.Crypto.RSA())
        {
            serverRsa.GenerateKeys(512, 65537, null, null);
            serverPublicKey = serverRsa.PublicKeyAsPEM;
            serverPrivateKey = serverRsa.PrivateKeyAsPEM;
        }

On client side (Xamarin) I would like to import the public key with PCLCrypto, but I get always the error "Unexpected format or unsupported key", see code below.

        var publicServerKey = _serverKeys.RsaKey;

        var keyBuffer = Encoding.UTF8.GetBytes(publicServerKey);

        var asym = WinRTCrypto.AsymmetricKeyAlgorithmProvider.OpenAlgorithm(AsymmetricAlgorithm.RsaPkcs1);
        var key = asym.ImportPublicKey(keyBuffer, CryptographicPublicKeyBlobType.Pkcs1RsaPublicKey);

How can I Import teh public key, to encrypt data?