With grid ui you have to use the selection.on.rowSelectionChanged to update a scope variable that store the selectedItem.
In this way you can use the value in a binding expression.
var SelectController = function($scope) {
    ...
    $scope.selectedItem = null;
    $scope.gridOptions = {
            data : 'articles',
            enableRowSelection : true,
            multiSelect : false,
            enableRowHeaderSelection : false,
            ...
        };
        $scope.gridOptions.onRegisterApi = function(gridApi) {
            // set gridApi on scope
            this.$scope.gridApi = gridApi;
        }.bind(this);
        $scope.gridOptions.onRegisterApi = function(gridApi) {
            // set gridApi on scope
            this.$scope.gridApi = gridApi;
            this.$scope.gridApi.selection.on.rowSelectionChanged($scope,
                    function(row) {
                        this.$scope.selectedItem = row.entity;
                    }.bind(this));
        }.bind(this);
Use a an array instead of a plain object if you need multiple selection.