Chirality on nanoscopic surfaces can now be detected using polarised near-field scanning optical microscopy. 

The adsorption and assembly of chiral molecules on solid surfaces, and techniques to study these molecules, have become fruitful areas of research, as chiral surfaces are used in the pharmaceutical industry. 

So far, techniques to study chiral surfaces using polarised light have only been carried out on large areas. The characterisation of surfaces at the sub-micrometre scale is limited. Now, a technique to do just that, using polarised near-field scanning optical microscopy (NSOM), has been developed by Yitzhak Mastai and colleagues from Bar-Ilan University in Israel. 

Their NSOM technique was able to distinguish between enantiomerically pure L and D histidine crystals grown on gold surfaces with dimensions of 10 microns. 

In the future, polarised NSOM could be used in many other fields, such as the identification of chirality in nanostructures, asymmetric catalysis, chiral polymers and biological systems, and to measure interactions between drug small molecules and chiral surfaces for pharmacological research. 

Challenges in the area, said Mastai, include the improvement of NSOM for nanoscale resolution which may enable optical activity measurements at the nanometre scale, and the use of NSOM to explore the relationship between the optical activity of chiral surfaces and their surface properties, e.g. crystal structure and shape, crystal orientation, influence of defects and breaks in symmetry.  

Elinor L Richards