They certainly keep pushing the envelope.
A group led by Markus Arndt has now shown quantum interferences of the largest molecule to date: a derivative of phthalocyanine molecules, with 1298 AMU. Nature Nanotechnology is also right now listing the paper as available for "free" (not sure for how long).
Abstract: The observation of interference patterns in double-slit experiments with
massive particles is generally regarded as the ultimate demonstration
of the quantum nature of these objects. Such matter–wave interference
has been observed for electron, neutrons, atoms and molecules
and, in contrast to classical physics, quantum interference can be
observed when single particles arrive at the detector one by one. The
build-up of such patterns in experiments with electrons has been
described as the “most beautiful experiment in physics”.
Here, we show how a combination of nanofabrication and nano-imaging
allows us to record the full two-dimensional build-up of quantum
interference patterns in real time for phthalocyanine molecules and for
derivatives of phthalocyanine molecules, which have masses of 514 AMU and 1,298 AMU
respectively. A laser-controlled micro-evaporation source was used to
produce a beam of molecules with the required intensity and coherence,
and the gratings were machined in 10-nm-thick silicon nitride membranes
to reduce the effect of van der Waals forces. Wide-field fluorescence
microscopy detected the position of each molecule with an accuracy of
10 nm and revealed the build-up of a deterministic ensemble interference
pattern from single molecules that arrived stochastically at the
detector. In addition to providing this particularly clear demonstration
of wave–particle duality, our approach could also be used to study
larger molecules and explore the boundary between quantum and classical
Edit: click on this YouTube link to see the video of this. The authors, for some reason, are disabling any imbedded video.
 T. Juffmann et al., Nature Nanotechnology doi:10.1038/nnano.2012.34, published online March 25, 2012.