Functionalisation of glass substrates with silanes. Glass slides were activated by plasma treatment using a plasma etcher (HPT-200, Henniker Plasma) before being immersed into silane solutions at room temperature overnight. The degree of thiol moieties on glass substrates were controlled by varying the molar ratios between mercaptopropyl trimethoxy silane and propyl trimethoxy silane in anhydrous toluene. The total concentration of silanes was fixed at 40 mM. The treated slides were rinsed thoroughly with toluene and isopropanol, and kept away from dusts in a nitrogen box.