The analysis of Caffeine in oral fluid using Surface-Enhanced Raman Spectroscopy and High-Performance Liquid Chromatography

摘要

Surface-Enhanced Raman spectroscopy (SERS) is a technique that is preferred over conventional Raman spectroscopy. The main advantage of SERS is that the intensity of the Raman signal is enhanced up to 104 to 106 fold thus allowing low concentrations of the analyte to be detected. The use of oral fluid for detecting drugs of abuse is increasing in popularity as the methods of collecting saliva are not as invasive as other biological fluids (blood or urine). As SERS can detect low limits of substances, the use of this technique coupled with the analysis of oral fluid for the detection of drugs is becoming popular. This technique could have applications in roadside testing, drug testing and medical care. The constant appearance of caffeine present in new psychoactive substances is becoming increasingly common. There are a lot of the drugs that are being sold on the market that only contain caffeine rather than the stated drug. A market is opening up for the detection of drugs in saliva using a rapid portable testing kit. This work focuses on the analysis of caffeine as it is a common adulterant that it found in illegal and legal drugs of abuse. A reproducible silver colloid with strong surface-enhancement and good shelf life was used to optimise a method capable of analysing caffeine. The colloid was produced by the reduction of silver nitrate with hydroxylamine phosphate. An optimised SERS method was developed that was capable of detecting caffeine in methanolic solutions, however when analysing caffeine in saliva there were problems that meant a spectrum could not be obtained. A HPLC method was developed for the quantification of caffeine. The HPLC method was successfully able to detect and quantify caffeine in saliva using 8 independent participants, the participants were asked to go 24 hours without any form of caffeine, and they were then required to give a saliva sample before and after the consumption of caffeine. The caffeine concentrations ranged between 1.51-1.94 μg/mL. The HPLC results show that caffeine was present at levels that should have been detected by the SERS method. Further investigation is needed to determine why SERS couldn’t detect caffeine in saliva; this could be due to other substances present in saliva.