Analysis of bacterial polyhydroxybutyrate production by multimodal nanoimaging.

In this paper, we will employ two microscopy techniques, transmission electron microscopy and infrared nanospectromicroscopy, to study the production of polyhydroxybutyrate in Rhodobacter capsulatus and to evaluate the influence of glucose and acetone on the production yield. The results overlap which leads us to a consistent conclusion, highlighting that each technique brings specific and complementary information. By using electron microscopy and infrared nanospectromicroscopy we have proved that both glucose and acetone had a positive effect on the biopolymer production, although the first study done by Fourier transform infrared spectroscopy only identified the effect of acetone. In conclusion, we have now established a method to be able to perform fast diagnostic for PHB production.

In situ identification and imaging of bacterial polymer nanogranules by infrared nanospectroscopy.

We have employed atomic force microscope-based infrared spectroscopy (AFM-IR) to spatially map energy storage polymers inside individual bacteria Rhodobacter capsulatus. AFM-IR allows chemical mapping of sub-cellular features with a spatial resolution of <100 nm. We have used key absorption bands of the energy storage polymer polyhydroxybutyrate (PHB) known from FTIR to spatially map the molecular distribution of PHB inside bacteria. We have also compared FTIR measurements on bulk PHB with AFM-IR measurements of PHB inside bacteria. We observe a shift in the location of the carbonyl absorption peak between bulk PHB and PHB inside bacteria. We have also used finite element analysis to model AFM-IR measurements of PHB granules, allowing for estimation of the real size of the granules. We have also performed transmission electron microscopy (TEM) of R. capsulatus to determine the size distribution of the PHB granules. Sizes measured by AFM-IR correspond well to TEM measurements.

Midinfrared absorption measured at a lambda/400 resolution with an atomic force microscope.

Midinfrared absorption can be locally measured using a detection combining an atomic force microscope and a pulsed excitation. This is illustrated for the midinfrared bulk GaAs phonon absorption and for the midinfrared absorption of thin SiO(2) microdisks. We show that the signal given by the cantilever oscillation amplitude of the atomic force microscope follows the spectral dependence of the bulk material absorption. The absorption spatial resolution achieved with microdisks is around 50 nanometer for an optical excitation around 22 micrometer wavelength.

Ultraweak-absorption microscopy of a single semiconductor quantum dot in the midinfrared range.

We show that we can measure the room temperature ultraweak absorption of a single buried semiconductor quantum dot. This is achieved by monitoring the deformation field induced by the absorption of midinfrared laser pulses and locally detected with an atomic force microscope tip. The absorption is spectrally and spatially resolved around lambda approximately 10 microm wavelength with 60 nm lateral resolution (lambda/150). The electronic S-D intersublevel absorption of a single quantum dot is identified around 120 meV and exhibits a homogeneous linewidth of approximately 10 meV at room temperature.