Nanometric chemical speciation of abnormal deposits in kidney biopsy: Infrared-nanospectroscopy reveals heterogeneities within vancomycin casts.

InfraRed (IR) spectromicroscopy allows chemical mapping of kidney biopsy. It is particularly interesting for chemical speciation of abnormal tubular deposits and calcification. In 2017 using IR spectromicroscopy, we described a new entity called vancomycin cast nephropathy. However, despite recent progresses IR microspectrometer spatial resolution is intrinsically limited by diffraction (few micrometers). Combining atomic force microscopy and IR lasers (AFMIR) allows acquisition of infrared absorption spectra with a resolution and sensitivity in between 10 and 100 nm. Here we show that AFMIR can be used on standard paraffin embedded kidney biopsies. Vancomycin cast could be identified in a damaged tubule. Interestingly unlike standard IR spectromicroscopy, AFMIR revealed heterogeneity of the deposits and established that vancomycin co-precipitated with phosphate containing molecules. These findings highlight the high potential of this approach with nanometric spatial resolution which opens new perspectives for studies on drug-induced nephritis, nanocrystals and local lipid or glucid alterations.