Scanning Droplet Cell (SDC) is a localized electroanalytical technique consisting of a miniaturized mobile electrochemical cell, in which the entire three-electrode cell assembly is contained within a small reservoir of electrolyte solution that is formed locally on the sample surface, rather than immersing the entire sample. While the sample acts as the working electrode, the electrolyte, reference, and counter electrodes are integrated into the SDC head.

The Sensolytics SDC creates the electrochemical cell by bringing a PTFE tip into controlled mechanical contact with the sample surface. A force sensor applies a defined contact force (typically between 400 and 500 mN), creating a reproducible seal between the tip and the sample that confines the electrolyte to a well-defined measurement area. This design provides reliable measurements even on surfaces where wettability or porosity would otherwise influence droplet formation.

During a measurement, the confined electrolyte forms a localized three-electrode electrochemical cell whose diameter corresponds to the tip aperture (typically ranging from micrometers to millimeters), allowing for a wide range of electrochemical techniques, such as cyclic voltammetry, electrochemical impedance spectroscopy (EIS), polarization curves, chronoamperometry, and many others, including user-defined routines, at specific, predefined locations on the grid.

After each measurement, the electrolyte is pumped back into the SDC body, the SDC head is lifted off the surface, and moved to the next predefined position. Before the next measurement, the probe is automatically rinsed with fresh electrolyte, ensuring that every measurement is performed under identical conditions and preventing cross-contamination between different measurement points.

By repeating this sequence across a user-defined grid, the SDC allows users to generate electrochemical maps with spatial resolution or perform point-specific stationary measurements, enabling a direct comparison of localized electrochemical behavior in heterogeneous materials without affecting the rest of the sample.

Conventional electrochemical testing typically consists of immersing all or a large part of the sample in an electrolyte, providing a single measurement that represents the average electrochemical behavior of the exposed area. While this approach is well suited for evaluating overall material performance, it cannot resolve local variations across heterogeneous surfaces.

In contrast, a Scanning Droplet Cell (SDC) confines the electrochemical measurement to a small, well-defined area of the sample, typically ranging from micrometer- to millimeter-scale, depending on the SDC tip aperture. The SDC head is automatically moved across user-defined measurement positions, enabling reproducible localized electrochemical measurements over large, flat sample surfaces. This allows high-throughput materials screening and spatially resolved mapping of electrochemical properties for direct comparison of microstructural features, coatings, welds, phase boundaries, or surface treatments without immersing the entire sample.

Since only a small area is exposed during each measurement, the SDC technique minimizes electrolyte consumption and preserves the integrity of the rest of the sample surface. This makes it ideal for the systematic screening of materials and characterization using multiple techniques on a single sample.

While all three techniques are considered electrochemical localized methods, they are designed for different measurement principles, spatial resolutions, and applications:

• SECM usually involves an ultramicroelectrode (UME) immersed in an electrolyte solution to probe the local electrochemical activity near a sample surface without the probe making contact with that surface. The measured current reflects the local electrochemical behavior of the sample below the probe, enabling high-resolution imaging of electrochemical activity with spatial resolutions ranging from the micrometer to nanometer scale.
• SECCM employs a glass (sub)micro- or nanopipette filled with electrolyte to form a microscopic liquid meniscus between the pipette and the sample surface. This creates a confined electrochemical cell, making SECCM particularly suitable for nanoscale electrochemical measurements, single-particle studies, and investigations of individual grains or crystal facets.
• SDC uses a mechanically sealed PTFE tip that contains the electrolyte, reference electrode, and counter electrode within the probe head. During each measurement, the tip is brought into controlled contact with the sample, forming a localized electrochemical cell over an area typically ranging from hundreds of micrometers to several millimeters, depending on the tip aperture. After the measurement, the electrolyte is withdrawn, the probe is lifted, and the system automatically moves to the next predefined location using fresh electrolyte. This makes SDC particularly well suited for automated, high-throughput electrochemical screening and mapping of large, flat samples, coatings, welds, material libraries, and heterogeneous surfaces without immersing the entire specimen.

The SDC system is highly versatile and enables the analysis of samples that are difficult or impractical to study using conventional electrochemical cells. Examples of such samples include large metal plates, complex welded joints, and coated substrates. Since the electrochemical cell is formed locally by bringing the PTFE tip into controlled contact with the sample surface. Combined with the high-resolution XYZ positioning system and force-controlled approach, irregular surfaces can be investigated while maintaining reproducible electrochemical cell formation.

SDC requires minimal sample preparation. This is because the sample area under analysis is determined solely by the footprint of the electrolyte droplet; therefore, there is no need to section a large sample to meet a standard cell size, embed a sample in a resin, or use masking tapes or lacquers to isolate the area of interest. Samples may be analyzed in their native or as-received condition, which maintains sample integrity and speeds the experimental process.

No. The SDC system is specifically designed to perform localized electrochemical measurements without immersing the entire sample in an electrolyte. Instead, the electrochemical cell is formed locally by bringing the PTFE tip of the SDC head into controlled contact with the sample surface. The SDC head contains the electrolyte, reference electrode, and counter electrode, while the measurement area is defined by the tip aperture, typically ranging from the micrometer to millimeter scale. Since only a small region of the sample is exposed during each measurement, the rest of the surface remains unaffected, making the technique well suited for targeted electrochemical characterization of large, valuable, or complex components.