**2.4. Pintool transfer devices**

Pintool is a contact-based dispensing method widely used for handling volumes at the nanoliter scale (Cleveland and Koutz 2005). It consists of a set of stainless steel pins (Fig. 1B) carefully crafted for consistent dimensions. The bottom end of the pins can be solid, grooved or slotted, with the option of having a hydrophobic coating to prevent non-specific binding (Dunn and Feygin 2000; Rudnicki and Johnston 2009). Solutions are transferred through a combination of capillary action and surface tension, with the volume being highly depend‐ ent on the contact surfaces and solution properties (Dunn and Feygin 2000). The pin array is normally assembled in a floating pin cassette to ensure soaking of all the pins amid uneven surfaces, which also minimizes pin damage. After liquid transfer, the pins have to cycle through washing steps to prevent cross-contamination.

#### **2.5. Piezoelectric devices**

The piezoelectric dispenser is a non-contact technology, where solutions are delivered as multiple tiny drops of defined size (Niles and Coassin 2005). This technology has been uti‐ lized in contemporary inject printers and refined to be implemented in the biological scien‐ ces. Various biochemical solutions (DNA, RNA, proteins) and bacterial suspensions have been tested with no negative effects (Schober et al. 1993). The system is composed of a capil‐ lary tube made of quartz or steel, with one end connected to the reagent reservoir and the other end ending in an orifice from which droplets are ejected (Niles and Coassin 2005). A piezoelectric crystal collar is bound to the capillary, which is filled with solution. Upon volt‐ age application, the piezoelectric element contracts causing pressure on the capillary to gen‐ erate fine drops. The ejection is at high acceleration with minimal wetting of the nozzle (Schober et al. 1993). Several thousand drops can be dispensed per second, with attainable drop sizes spanning the picoliter and nanoliter range (Schober et al. 1993). Droplet volume depends on several factors, including bore diameter, solution viscosity and the voltage pulse amplitude and frequency (James and Papen 1998; Kong et al. 2012).
