gvisbubblechart axes labels as variables

[Kanu]

how to give variable to axes labels of gvisbubblechart?

Here is my code:

gvisBubbleChart(iris.new,idvar="Species",xvar=input$xcol, yvar=input$ycol,colorvar="Species",options=list(hAxes="[{title:'input$xcol, titleTextStyle: {color: 'black'}}]", vAxes="[{title:'input$ycol', titleTextStyle: {color: 'red'}}]"))}

As in bolds,i want to give the axes labels as variable but unable to do so.Please tell how to do this.