Design challenge: Detect finger-to-finger touch with nothing in between
You could do this with three electrodes on the fingers. Two would establish an excitation and the third would be an input to determine if current is flowing down a finger. Conceptually, something like this: 







simulate this circuit &ndash; Schematic created using CircuitLab

In this case, V1 is a low voltage AC source, preferably of a frequency much higher than mains frequency so that mains hum can be filtered out and sufficiently low voltage as to not cause problems with the skin or safety in general. R1, R2 and R3 represent the electrode-to-skin impedances (I think that's roughly right for EKG type electrodes). The 10K resistances represent the impedance of fingers and hand. 

So, before the top (blue) finger touches the bottom (cyan) finger, there is a bit of AC current flowing through the hand (R5) but very little current flowing through the blue finger. When the fingers touch, an AC voltage appears at A and can be detected by the AC voltmeter VM1. Ideally VM1 is sensitive to the frequency from V1 and insensitive to other frequencies. 

There are potential dangers associated with anything connected in this sort of way to a human body, and this answer does not attempt to address those issues. Probably if power is supplied solely from something like a 3V CR2032 battery (no mains connections or adapters or power supplies or computer connections other than wireless) some of the issues will go away, but this aspect requires careful evaluation by someone familiar with the proposed setup and biomedical safety issues.