Hoow to print the variable bolder text in local notification

I have a code

                this.localNotifications.schedule({
                title: 'RAK taxi App',
                text: "This is a bolder text",
                led: 'FF0000',
                icon: 'file://assets/img/Rak_icon.png',
                smallIcon: 'file://assets/icon/arabialogo.png'

              });

i want to print the text in bolder format. how to do ?