Design complexity of DPN patterning with Cr3+ and Co2+ metallic ions on Au (111) thin film

Highlights: • Fabrication of miniaturized electrochemical sensor platform for detection of metallic ions. • Fabrication of high quality Au(111) electrodes using MBE deposition technique. • Nanolithography of Cr³⁺ and Co²⁺ species on the Au electrode was performed by DPN. • Molecular recognition analysis was performed through impedance spectroscopy measurements. We present in this work a fabrication chain of an electrochemical sensor platform based on detection of Cr³⁺ and Co²⁺ metallic ions species. Through molecular beam epitaxy (MBE) technique, a high quality Au (111) thin film was firstly fabricated in ultra-high vacuum (UHV) conditions, and used as support for chemical SAMs functionalization with 1,4-dithiothreitol (DTT) spacers. On the formed hybrid surface/linker structures, we employed Dip Pen Nanolithography (DPN) for patterning various templates of Cr³⁺ and Co²⁺ metallic ion species. Coated AFM tips with metallic molecular inks were used to fabricate different paths on the Au substrate, offering a unique functional design complexity. By varying the tip speed and/or dwell time, micro-nano-scale templates of both species were patterned in the form of square, double-square, triangle and lines. A full control of molecular ink transport mechanisms during the drawing process was assured, succeeding the writing of Cr³⁺ and Co²⁺ metallic ions on Au film substrate. Surface topology analyzed by Lateral Force Microscopy demonstrated the chemical contrast of patterned species, being a clear indicative of DPN tracing paths. Molecular recognition of both Cr³⁺ and Co²⁺ metallic ions has been made by potentio-electrochemical impedance spectroscopy (PEIS) measurements. The Nyquist plots were compared and the equivalent circuits obtained in both conformations (Cr^3+/DTT/Au, Co^2+/DTT/Au) were discussed in the light of experimental parameters.