A team of Chinese researchers, led by the Central China Normal University in Wuhan, has come up with a graphene-based extraction method for aldehydes from breath, which could aid in diagnosing lung cancer. This method can effectively extract hydrophobic small molecules such as aldehydes from breath while ignoring large biomolecules such as proteins, and it can also direct the extracted aldehydes straight to an HPLC system to determine its concentration.
The extraction method is based on in-tube solid-phase microextraction (IT-SPME), in which the inside of a thin tube is coated with an adsorbent material, usually some form of polymer. When a liquid sample is injected into this tube, the analytes of interest are adsorbed by the coating as the sample flows through, after which the analytes are released by a desorber for subsequent analysis. Critical to the whole process is finding a material that will effectively adsorb the analyte of interest while ignoring everything else.
The researchers decided to base their adsorbent coating on polypyrrole, which is commonly used to extract hydrophobic small molecules, but to try enhancing its performance by combining it with graphene. By taking advantage of the high surface area and strength of graphene, they hoped to produce a nanocomposite that was both tougher than polypyrrole and offered a greater area for adsorption.
With this system, the scientists saw that the aldehydes could be detected at concentrations below 5nmol/litre. When they added a couple of proteins to the mixture, they found that the pyrrole-graphene coating could still extract the aldehydes while hardly adsorbing any of the proteins.
Finally, they tested the coating on samples of breath collected from eight lung cancer patients and eight healthy subjects. In total, the whole extraction and analysis process took just half an hour for each subject, and revealed that the concentrations of four aldehydes butanal, heptanal, octanal and nonanal were substantially higher in breath from the lung cancer patients. Confirming whether this finding can form the basis for a practical diagnosis technique will require further studies with many more subjects, but the method poses a hopeful new way of potential diagnosis.