Figure 1.

Detailed illustration of the liquid transfer by a spotting pin. Close-up view of one pin spotting a PCR product onto a glass slide. In the outer-left picture, the 250-μm pin tip end is loaded with a 2-nL droplet. The left picture shows the actual spotting process onto the epoxysilanated glass surface. In the right picture the pin goes up again, showing that the liquid's surface tension is present and does not allow the immediate delivery of the whole droplet, which might be one reason for the well-known doughnut effect. The outer-right picture finally shows pin and glass surface after liquid delivery. It is obvious that a tiny amount of DNA solution is still sticking to the pin, which requires careful cleaning procedures prior to the next spotting run.