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How to use Klarite substrates

To achieve the maximum benefit from using Klarite, samples should be deposited onto the active surface and analysed with a standard Raman instrument.  Many sample deposition techniques are possible ranging from dip coating to multi array spotting. 

A pipette dropping method is described here for basic analysis, although other techniques may be better suited to your applications. For illustration purposes the amino acid L-Alanine is used as an example throughout.  However, the methodology described here can be applied to many other compounds and solvent.

Preparation of the sample on the Klarite substrate is done in the three steps described below.

1. Deposition

Using a pipette, a liquid sample of typically 1 microlitre or less is deposited onto the active area of the Klarite chip shown.  If the drop does not detach from the pipette, carefully let the drop touch the substrate and then transfer the drop onto the substrate.

Avoid touching the chip with the tip of the pipette – a scratch to the gold surface on the chip will adversely affect the measurement results.

The solution used in this example was obtained by diluting 7.5mg of L-Alanine (Sigma-Aldrich A7469) in 15ml of ultra filtered water (Sigma-Aldrich 95289). 

2. Evaporation

In general the evaporation process of any liquid on a surface produces one of three main types of patches: coffee rings, crystalline capillaries or spot-like stains. The evaporation result depends on the interplay of adhesive forces of the substrate and cohesive forces of the fluid.

The L-Alanine used in this example was left at room temperature in a clean lab environment for about 30 minutes for the water solvent to evaporate.  Typically the evapourated L-Alanine will appear as shown.

3. Measurement

Once the sample is dry, Raman measurement can be carried out across the deposited patch.  The patch will appear formed by many concentric rings of different colours. Crystalline islands can also form inside the patch for concentration typically >1mM.  In general the size and characteristics of the film patch and crystalline islands depend on the concentration of the solution, the purity of the solvent and the polar nature of both the analytes and the solution.

Typical Raman spectra of L-Alanine across the film patch are shown below.  The spectra were acquired in 10 sec of CCD exposure time with 15mW laser power at 785nm excitation with a standard micro Raman instrument.  No normalisation and baseline subtraction was performed on the spectra.  Quantitative data on film composition and molecular interaction can be obtained by probing the Raman features across the patch.