Bridge SECM and SECCM with a Coaxial Microelectrode@Micropipette Probe

A novel type of coaxial Pt-disk-microelectrode@micropipette probe was designed and fabricated, which comprises an internal Pt ultramicroelectrode (UME) wrapped with an Ag/AgCl wire on its glass shield and an external micropipette. This new probe can integrate the advantages of scanning electrochemical microscopy (SECM) and scanning electrochemical cell microscopy (SECCM) and overcome the disadvantages of both methods. Optical microscopy and SECM-SECCM measurements confirmed that the device with a stable, renewable nanoliter-scale electrochemical droplet cell exhibited excellent electrochemical performances. Crucially, the probe achieved long-term and large-area imaging of the conductivity and morphology on diverse dry surfaces. Moreover, confining the reaction within the droplet significantly enhances tip-collection efficiency, thereby substantially improving spatial resolution and sensitivity in the substrate-generation/tip-collection mode. Significantly, leveraging the renewable droplet cell to minimize multisample heterogeneity errors, the probe was applied to high-throughput detection of alkaline phosphatase activity in an authentic blood fingerprint at different storage periods and established a high-precision time since deposition estimation with unprecedented accuracy of ∼97%. In all, this flexible design construction of the probe can combine SECM and SECCM advantages in various applications with high sensitivity, high-resolution, high-throughput, and high-accuracy detection.