This new microscopy technique achieves unprecedented contrast for the study of nanomaterials and their chemical modification.

The Backside Absorbing Layer Microscopy (BALM) is a recently introduced surface imaging technique in reflected light with an unprecedented combination of sensitivity and lateral resolution, hence very promising for the development of imaging sensors. This requires to turn BALM images into quantitative measurements. The usual way to analyze reflectivity measurements is to compare the optical signal and a numerical model with many adjustable parameters. Here we demonstrate a universal relationship between the sample reflectivity and the physical thickness of the sample, ruled by three measurable quantities. Mapping the true sample thickness becomes possible whatever the instrument configuration and the sample refractive index. Application to kinetic measurements is discussed.

Using a recent optical contrast method, real-time and quantitative imaging of submolecular layers was performed with the help of a simple optical microscope. The measuring technique is exposed and documented by three examples. In particular, it allowed label-free detection of peptide-antibody binding interactions with 50 pg/mm2 sensitivity while keeping full optical lateral resolution.

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