Simultaneous local sensing of two chemical properties with dual soft probe scanning electrochemical microscopy

A new method for the rapid and economic fabrication of dual soft microelectrodes for Soft-Probe-Scanning electrochemical microscopy (Soft-Probe-SECM) and their use for the simultaneous local detection of locally generated species is presented. The process is based on encapsulating electrode wires, such as Pt, Au and carbon fiber, by UV-photo-polymerization of a dielectric material leading to two microdisc electrodes, which are individually addressable. Probe stability is realized by using a flexible plastic support. The thickness of the dielectric material that controls the distance between the microelectrodes and the substrate surface during lateral scans over a substrate in contact mode is highly controllable by the probe fabrication parameters. The thickness of the dielectric material of the soft probes fabricated here varies between 27 µm and 35 µm, while the two microelectrodes inter-distance varies between 180 µm and 250 µm. The dual soft probes combine Pt, Au and C microdiscs of different radii (12.5 µm for Pt and Au and 4 µm for C). The flexible selection of the electrode materials enables the fabrication of dual soft probes with electrode materials suitable to detect electro-active analytes of interest at solid/solution interfaces. The dual soft probes can be used in double amperometric, double potentiometric or mixed potentiometric-amperometric modes. As a proof-of concept of the latter mode, a dual platinum black/Pt (PtB/Pt)–iridium oxide/Au (IrOx/Au) soft probe is used to image in real time the chemically induced dissolution of inkjet printed silver patterns in 0.2 mM HNO3, generating locally reactive nitrogen species (RNS) and simultaneously changing the pH. RNS amounts are measured at 0.8 V (vs. Ag/AgCl, KCl, reference electrode) at the PtB/Pt microelectrode, while the corresponding pH changes are obtained from open circuit potential measurements with the IrOx/Au microelectrode.