An integrated microchip-based nanoelectrospray device for high-throughput mass spectrometry

The emerging field of microfluidics may provide for the rapid, automated analysis of samples. Here we describe the microfabrication and operation of a nanoelectrospray device formed from the planar surface of a monolithic silicon substrate for electrospray (ESI) mass spectrometry (MS) sample analysis at low nanoliter per minute flow rates. To generate a useful electrospray from a microchip, a high aspect ratio nozzle structure of small dimensions is required. Deep reactive ion etching (DRIE) technologies allow these high aspect ratio structures to be fabricated in parallel and are widely available for the etching of silicon. DRIE methods originally developed for making microelectromechanical systems (MEMS) are increasingly being applied to the fabrication of microfluidic devices, allowing for creation of low-cost, highly reproducible devices. This work demonstrates the feasibility of using a microfabricated nozzle structure for the nanoelectrospray of solutions for rapid MS sample analysis of both large and small molecules. Specifically, protein and tryptic digests using both infusion experiments and deposition of samples in on-chip reservoirs followed by automated "on-the-fly" reconstitution nanoelectrospray MS. Using this microchip-based device, detection of sample amounts of 10 fmole for cytochrome c tryptic digest and 10 fmole for whole protein were achieved. This method was also applied to determine sequence coverage for novel proteins. Protein digests analyzed on this ESI chip demonstrated sequence coverage better than 70 perscent. rising this method, MS sample analysis may be conducted at rates exceeding 3 samples/min.