Over the past decade there has been an amazing set of experiments performed which involve seeing quantum interference associated with the wave nature of very large molecules. The figure below is taken from a nice review article by Markus Arndt and Klaus Hornberger. It shows some of molecules, including as many as one hundred atoms and of the order of one thousands of elementary particles (protons, neutrons, and electrons).
The figure below shows some of the interference fringes seen.
Occasionally I hear these incredible experiments used as a "proof of principle" to justify the possible role of significant quantum effects in biology. However, I think this a fanciful view because of the following significant constraints in the experiments:
- They involve single molecules
- They are performed in vacuum.
- The quantum interference is associated with the centre of mass degree of freedom. By, definition this does not couple to all the internal degrees of freedom.
This is a very long way from a biological cell where the molecules are packed close to one another and interact strongly with their surrounding environment of water.