Image courtesy of Vladimir Korolkov Photography
Confocal Raman Microscope
Raman spectroscopy is a non-invasive optical technique used to determine the chemical identity and state of a sample by its unique vibrational modes. Inelastic scattering of light from the sample is measured, with distinct shifts in the energy of the scattered photons being representative of the sample chemistry. Information from an array of points on – or in – the sample can be visually represented as images (1D, 2D or 3D), with the brightness, contrast and colour of the image used to convey the science of the sample.
The LabRAM HR system can be used as a traditional Raman spectrometer to provide vibrational spectra of chemicals, but the most powerful feature of this instrument is its ability to quickly produce confocal images. Four different laser wavelengths are available spanning the UV-Visible-NIR regions giving the user access to an excitation source to match their sample.
The confocal set-up of the microscope gives rise to both clearer images (by reducing contributions from out-of-focus background regions) and the ability to perform depth profiling studies of samples. This instrument is ideally suited for materials and pharmaceutical characterisation, tissue imaging and chemical identification.
- Confocal depth profiling.
- Four excitation wavelengths available: 325, 532, 660 and 785 nm.
- SWIFT and DuoScan mapping options for fast mapping applications.
- Choice of standard CCD or EM-CCD detectors.
- Variable temperature stage (-196 to 450 oC).
- Choice of gratings for standard or high resolution spectroscopy.
- Flow cell for 'in-situ' dissolution and elution studies.
- Vibrational spectral analysis of substrate chemistry in ambient or controlled conditions.
- Confocal component mapping and depth profiling.
- UV-Visible-IR excitation analysis.
- Temperature and time dependent chemical and physical state change identification.
One-dimensional mapping: chemical damage to hair
Hair is susceptible to changes and damage induced by a number of factors, including the application of bleaching and colouring treatments. Using Raman microscopy it is possible to spatially locate differences in the composition of (blonde) hair and thus evaluate the extent of damage induced by such chemical treatments. In this study, we line-mapped cross-sections of treated and untreated hair and using the intensity of diagnostic band at 540 cm-1 associated with S-S cross-linkages determined that whilst bleaching does destabilise the structure of the hair at the surface (cuticle), it does not penetrate significantly into the centre (cortex).
Two-dimensional mapping: mechanical exfoliation of graphite
Graphene has been hailed as the wonder material of the twenty-first century. It can be readily procured by simple exfoliation of bulk graphite using sticky tape with the properties of the resultant material dependant on the number of graphitic layers present. Using Raman microscopy it is possible to spatially locate the presence of mono-, bi-, tri- and tetra-layer graphene using the position and symmetry of the diagnostic band at ~2600 cm-1 (2D band). In this study, we used two-dimensional mapping to probe the layering in this few-layer graphene sample and found it to comprise a mixture of layers, a fact that would have been indeterminable from the optical image alone.
Three-dimensional mapping: phase distribution in chocolate
The size, shape and distribution of fats and sugars in confectionary has a remarkable impact on its textural properties which is of high importance to the modern-day consumer. Using Raman microscopy it is possible to spatially locate the presence of the individual ingredients of chocolate based on their diagnostic chemical signatures. In this study, we used three-dimensional mapping to show that the white chocolate under examination comprised small 10-20 micron-sized domains of sugars dispersed within a continuum of fats and milk