Abstract
Laser Desorption Ionization Mass Spectrometry employs matrix which is co-crystallised with the analyte to achieve "soft ionization" that is the formation of ions without fragmentation. A variety of matrix-free and matrix-assisted LDI techniques and matrices have been reported to date. LDI has been achieved using ultra fine metal powders (UFMPs), desorption ionisation on silicon (DIOS), sol-gel assisted laser desorption/ionization (SGALDI), as well as with common MALDI matrices such as 2,5-dihydroxy benzoic acid (DHB), 3,5-dimethoxy-4-hydroxycinnamic acid (SA), α-cyano-4-hydroxycinnamic acid (CHCA) to name a few. A variety of matrix additives have been shown to improve matrix assisted desorption, including silicon nanowires (SiNW), carbon nanotubes (CNT), metal nanoparticles and nanodots. To our knowledge no evidence exists for the application of highly fluorescent CdSe/ZnS quantum dots to enhance MALDI desorption of biological samples. Here we report that although CdSe/ZnS quantum dots on their own can not substitute matrix in MALDI-MS, their presence has a moderately positive effect on MALDI desorption, improves the signal-to-noise ratio, peak quality and increases the number of detected peptides and the overall sequence coverage.
Highlights
The term 'MALDI' was first introduced by Karas et al [1] who documented the advantage of using a highly absorbing matrix that reduces the threshold irradiance required to generate ions in Laser Desorption Ionization Mass Spectrometry (LDI-MS)
Characterisation of quantum dot preparations CdSe/ZnS Core/Shell "EviDots" from Evident Technologies were first characterised by TEM imaging
TEM images obtained for all other "EviDots" preparations are provided as Supporting Information
Summary
The term 'MALDI' (matrix assisted laser desorption ionization) was first introduced by Karas et al [1] who documented the advantage of using a highly absorbing matrix that reduces the threshold irradiance required to generate ions in Laser Desorption Ionization Mass Spectrometry (LDI-MS). The presence of a matrix results in a larger degree of "soft ionization", that is the formation of ions without fragmentation. This soft laser desorption increases the ratio of molecular-to-fragment ions which is of great benefit in the detection of sample-specific ions. Matrix selection depends on the particular sample being analysed and can often be a case of trial and error to determine the one best suited, it is typically a low molecular weight compound that is able to undergo phase transition upon excitation with laser. Because the matrix is co-crystallised with the analyte sample, this phase transition extends to the sample itself. Tanaka's "monumental blunder" when he unwittingly suspended his ultra fine metal powders (UFMPs) matrix in glycerol instead of acetone, and subsequently deviated from his standard protocol a further three times, only to stumble across a significant discovery [2] was an essential step and a breakthrough in the development of macromolecule (page number not for citation purposes)
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