How to enable button if item selected in a GridView

How to enable button if item selected in a GridView

I want to enable button when a grid view item is selected so that i will
update my GUI in metro apps. The button is also include as a list view
item. Below is the code snippet of what i want to do. Please help.
<GridView Name="searchPanelGrid" SelectionMode="Single"
HorizontalAlignment="Left"
ScrollViewer.IsHorizontalScrollChainingEnabled="True"
ScrollViewer.IsVerticalScrollChainingEnabled
="True"
ScrollViewer.HorizontalScrollBarVisibility="Auto"
ScrollViewer.VerticalScrollBarVisibility="Auto"
ScrollViewer.HorizontalScrollMode="Enabled"
ScrollViewer.VerticalScrollMode="Enabled"
ItemsSource="{Binding
Source={StaticResource CollectionItems}}"
Grid.Row="2">
<GridView.ItemsPanel>
<ItemsPanelTemplate>
<WrapGrid Orientation="Horizontal" />
</ItemsPanelTemplate>
</GridView.ItemsPanel>
<GridView.ItemTemplate>
<DataTemplate>
<Grid Margin="6" Height="175" Width="150"
Background="#FFFAFAFA">
<Grid.RowDefinitions>
<RowDefinition Height="85"/>
<RowDefinition Height="50"/>
<RowDefinition Height="30"/>
</Grid.RowDefinitions>
<StackPanel Background="#FF0A56BF" Width="150"
Height="85" Grid.Row="0">
<Image Source="{Binding Path=ThumnailUrl}"
Stretch="UniformToFill" HorizontalAlignment="Left"
VerticalAlignment="Top"/>
</StackPanel>
<TextBlock Text="{Binding Path=VideoName}"
TextWrapping="Wrap" Foreground="#FF017DD5"
Grid.Row="1" HorizontalAlignment="Left"
VerticalAlignment="Top" Height="Auto" FontSize="12"/>
<Button x:Name="downloadButton" Grid.Row="3"
Content="Download Video" HorizontalAlignment="Left"
VerticalAlignment="Bottom" Style="{StaticResource
DownloadButtonStyle}" Click="downloadButton_Click"
IsEnabled="{Binding}" />
</Grid>
</DataTemplate>
</GridView.ItemTemplate>
</GridView>
Unable to bind button property IsEnabled. Any suggestion how i do this ??