Dip-Pen Nanolithography-Based Fabrication of Meta-Chemical Surface for Heavy Metal Detection: Role of Poly-Methyl Methacrylate in Sensor Sensitivity.

A meta-chemical surface is being patterned via dip-pen nanolithography (DPN) for novel electrochemical heavy metal sensors. The unique feature of DPN allows a precise transfer of desired ink onto various surfaces. Two kinds of sensors are being developed, which differ by the ligand in the poly-methyl methacrylate (PMMA)-based ink: 1,8-diaminonaphthalene (DAN) and D-penicillamine (D-PA). The nanosize, the surface-to-volume ratio (18.6 and 23.1 μm^-1 for DAN- and D-PA-based ink, respectively), and the binding strength between the ligand and the cation (2.21 and -21.37 kcal mol^-1 for DAN- and D-PA-based ink, respectively) are found to be the source of their high sensitivity, with limit of detection values of 0.40 and 0.30 ppb for DAN and D-PA, respectively. According to the DFT calculations, the binding reactions in the presence of PMMA are more exergonic; this indicates that PMMA added to the ink for the patterning process improves the binding between the metals and the ligands. This enhanced binding between the metals and the ligands is a crucial and innovative function of the PMMA that can enhance sensor performance.