Abstract
We present an automated droplet microfluidic system (DMF) to generate monitored nanoliter aqueous droplets in oil and their deposition on a commercial stainless steel plate for MALDI-TOF analysis of peptides or protein digests. We demonstrate that DMF-MALDI combination focuses the analyte on the MALDI plate, increasing considerably the homogeneity of the dried material. This results in a 30times enhanced MALDI-TOF MS signal for a model peptide, allowing a significant improvement of the detection sensitivity limit (down to few tens of attomoles). Moreover, positive detection can be achieved from sub-nanomolar peptides solutions and better overall protein sequence coverages are obtained from few tens attomoles of protein digest. These results make DMF-MALDI a promising approach for the treatment of peptides samples as well as a key component for an integrated approach in the proteomic field.
Highlights
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is recognized as a powerful tool in biological studies, especially in biomarker discovery and in the proteomic field[1]
A one-step droplet deposition method was envisaged by creating droplets from a mixture of sample containing a model peptide (Ang II) including the classical hydroxy-cinnamic acid (HCCA) matrix preparation acidified by 0.1% Trifluoroacetic Acid (TFA)
In this study we engineered a droplet based microfluidic (DMF) device dedicated to MALDI-TOF peptide analysis
Summary
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is recognized as a powerful tool in biological studies, especially in biomarker discovery and in the proteomic field[1]. Dittrich’s group developed a novel interface to monitor the enzymatic conversion of Angiotensin I to Angiotensin II by ACE (Angiotensin Converting Enzyme)[24] In their automatized interface, nanoliter aqueous droplets immersed in oil are created in a microfluidic T-junction and deposited on a home-made hydrophobic MALDI plate with 26000 hydrophilic areas. The assays have been performed with tens of femtomoles of Angiotensin peptides spotted on dried matrix This detection range is intrinsically linked to the parameters of this enzymatic study implying substrate degradation by ACE. The device comprises a PDMS microchip in which few nL droplets are created before being automatically spotted on a commercial MALDI stainless steel plate Thanks to this DMF system, we develop a spotting method for the analysis of peptides or protein (through protein digest) encapsulated in microdroplets which leads to a higher detection sensitivity by MALDI-TOF MS compared to conventional droplet deposition
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