The Effect Of Second Layer Matrix On Target Spots...

The Influence of Second Layer Matrix on Target Spots Unclassified by MALDI-TOF Although MALDI-TOF MS has been widely used in routine clinical microbiology laboratories, it is generally acknowledged that the appropriate sample-matrix preparation, a homogenous deposition on the target plate, is not very simple for successful MALDI-TOF measurement as well as microbial identification. (1) MALDI-TOF MS manufacturers introduced manually direct smear preparation protocols (2) in a convenient way for analysis of the large amounts microorganism colonies in microbiology laboratories, but they are called â€Å"black art† because of the unpredictability to find the dispersed â€Å"sweet-spots† due to the heterogeneous co-crystallization.(3) Regarding to those unclassified â€Å"no peaks found† samples, further purity cultures have to be inoculated for the second day remeasurement, which are costly in terms of labor, material and turnaround time. To date, many preparation methods, such as dried-droplet, thin layered, etc., have been developed to overco me the challenges.(4) However, all of them are â€Å"wet† preparation, in which sample solutions are used in analysis and thus they are impractical in â€Å"real† clinical microbiology scenario where semi-solid colonies are smeared on target directly. Based on an interesting MALDI-TOF phenomena, i.e., a significant improved mass spectrum can be obtained when analytes are mixed with matrix in a relative high mole ratio,(5) the influence of an second layer matrix