Mass spectrometry-based biosensing using pencil graphite rods

Pencil graphite rods are inexpensive, eco-friendly, and readily available materials that can be useful as probes for biosensing using mass spectrometry (MS). In this sense, we developed a method named graphite-MS in which a pencil graphite rod is used to collect a small amount of sample and is subsequently submitted to MS analysis. The method was optimized and applied for the analysis of several analytes in solution, including creatinine in human urine samples. Figures of merits were obtained by analyzing the insecticide chlorpyrifos in tomato peel extracts, and a calibration curve with R2 > 0.99 was achieved, along with a limit of detection of 80 ?g L-1 and limit of quantification of 200 ?g L-1. Values of accuracy and precision were below 5%. In tests with solid samples, apples were analyzed by simply puncturing the fruits for 10 s and submitting the rods for MS analysis. Mouse brains were also analyzed (ex vivo and in vivo) without any sample preparation. Discrimination between regions of the mouse brain such as cortex, cerebellum, and ventricle, as well as differentiation between female and male mice, were successfully achieved by using lipid profiles in combination with principal component analysis. In summary, this study increases the range of knowledge about simple and readily available materials that can be used by the scientific community specializing in analytical chemistry and biosensors.