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Drop-coating deposition Raman spectroscopy for metabolite profiling

There has been a lot of interest in enhancing the sensitivity of Raman spectroscopy due to the low efficiency of the Raman technique. A pre-concentration technique, drop-coating deposition Raman (DCDR), has been used in recent years to increase the utility of Raman spectroscopy by decreasing the detection limit for non-enhanced Raman detections.

In a typical implementation of DCDR, a small volume (in the μL to nL range) of a dilute solution is preconcentrated by being dried on a special hydrophobic plate. DCDR uses the coffee-ring drying pattern to pre-concentrate the weak Raman scatterers prior to their analysis with Raman.1 The enhancement in the detection limit is obtained due to the formation of concentrated residue upon drying. For maximum efficiency of DCDR, the substrate should have certain properties, such as high solvophobicity (to a wide range of solvents), low optical absorbance, high reflectance, and no background and non-wetting interaction with the deposit.2 The non-wetting property is particularly critical because it is necessary to confine the ring to a small area to create a concentrated deposit. A wetting substrate would spread the solution to a larger area, thus producing a larger ring and resulting in less dense analyte deposits. In the studies presented here, gold-coated substrates with these properties are used.

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