Fabrication of paper-based analytical device by silanisation of filter cellulose using alkyltrimethoxysilane coupled with UV radiation

A method was developed for the fabrication of microfluidic paper-based analytical devices (μPAD). This method was based on the silanisation of cellulose in filter paper using alkyltrimethoxysilane coupled with UV radiation. The filter paper sheet was hydrophobised by immersion in an octadecyltrimethoxysilane/heptane (OTMS/heptane) solution (0.25 vol. %) containing 5 vol. % of ethyl acetate (EtOAc). The hydrophobic-hydrophilic contrast was generated on the filter paper after the hydrophobised paper sheet was exposed to UV light with a metal mask creating the desired pattern on the sheet. The exposed area was oxidised to create a hydrophilic area, while the hydrophobic area was protected by the metal mask. The optimal conditions for the fabrication of μPAD were studied; these included ethyl acetate concentration ( C EtOAc ), immersion time, octadecyltrimethoxysilane concentration ( C OTMS ) and exposure time. This method is cost-effective and simple. In addition, different functional groups could be further grafted for various assay purposes. To demonstrate the feasibility of the μPAD in analytical applications, a flower-shaped μPAD with eight channels and eight detection units was fabricated and used to determine the nitrite content in pickled vegetables. The nitrite content (124 µg g −1 ) in the sample determined by this method compared favourably with that measured using a standard method (137 µg g −1 ).