JOURNAL OF MASS SPECTROMETRY J. Mass Spectrom. 2003; 38: 1259–1264 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jms.580 Two-dimensional microfabricated sources for nanoelectrospray † S´ everine Le Gac, 1 Steve Arscott, 1,2 C´ ecile Cren-Oliv ´ e 1 and Christian Rolando 1* 1 Laboratoire de Chimie Organique et Macromol ´ eculaire, Universit ´ e des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq, France 2 Institut d’Electronique, de Micro ´ electronique et de Nanotechnologie (IEMN), Cit ´ e Scientifique, Avenue Poincar ´ e, 59652 Villeneuve d’Ascq Cedex, France Received 10 June 2003; Accepted 10 November 2003 The idea of a novel two-dimensional (2D) nanoelectrospray ionization emitter tip with the shape of a nib is explored here. This novel planar design is studied as an alternative to the needle-like standard emitter tips that suffer from a lack of reproducibility and robustness and from an inherent incompatibility with high- throughput analysis. The composition of the micro-nib sources is analogous to the working of a simple fountain pen, with a liquid reservoir linked to a micro-nib tip from which the sample is electrosprayed via a capillary slot. The micro-nib prototypes described here were fabricated using microtechnology techniques and using the epoxy-based negative photoresist SU-8. The resulting free-standing micro-nib structure was supported by a silicon wafer. We present here two series of such micro-nib sources, the latter series exhibiting improved characteristics such as a 8 μm source width of the nib tip. They were tested in mass spectrometry experiments on an ion trap mass spectrometer (LCQ Deca XP+, Thermo Finnigan) using standard peptide samples having concentrations down to 1 μM and with a high voltage (HV) supply around 1 kV for the second series of micro-nib sources. In addition to the stability of the spray, the obtained mass spectra showed the reliability of these sources for peptide analysis; the signal of the spectra was as intense and the signal-to-noise ratio (S/N) as high as that obtained with the use of standard emitter tips. Copyright  2003 John Wiley & Sons, Ltd. KEYWORDS: electrospray ionization; microfabricated emitter tip; 2D ionization sources; microfluidics INTRODUCTION Nanoelectrospray ionization is currently performed using fused-silica or glass emitter tips. 1–3 These emitter tips have the shape of a needles with a typical inner diameter at the end of 1–5 μm. 3 They are manufactured using pulling and heat- ing techniques. 3,4 However, this fabrication process is not very well controlled and consequently leads to the produc- tion of sources with critical dimensions which are not always reproducible. This drawback can be reduced by including a laser micromachining step during the fabrication of the emit- ter tips 5 as this technique increases the source reproducibility and quality; however, this quality enhancement increases the cost of the sources. As a result, the laser-micromachined sources are rare and not used routinely in laboratories for infusion analysis. The second drawback of these needle-like ionization sources is the method of employment that requires L Correspondence to: Christian Rolando, Universit´ e des Sciences et Technologies de Lille (Lille 1), Bˆ atiment C4, 2` eme ´ etage, UPRESA CNRS 8009, Chimie Organique et Macromol´ eculaire, 59655 Villeneuve d’Ascq Cedex, France. E-mail: Christian.Rolando@univ-lille1.fr † Paper presented at the 21st Informal Meeting on Mass Spectrometry, Antwerp, 11–15 May 2003. Contract/grant sponsor: French Network for Micro- and Nanotechnologies. † Paper presented at the 21st Informal Meeting on Mass Spectrometry, Antwerp, 11–15 May, 2003. skilled users for the analysis preparation. 5 The emitter tip is first loaded with the sample using a micro-pipette and a gel-loader. Following this, the air bubbles inside the tip must be removed by careful agitation, the source is then introduced in the inlet of the mass spectrometer and broken open to allow the infusion of the sample into the inlet for analysis. 3,4 Again, the breaking step of the source is a random process suffering from a lack of reproducibility and results in a non-calibrated flow rate of the sample. 6 Currently, the field of MS-based analysis is rapidly expanding, especially with the soft ionization modes such as electrospray ionization (ESI) 1,3 and matrix-assisted laser desorption/ionization (MALDI), 7–9 as these processes are suitable for the analysis of biological samples. 2 The rapid evolution in MS reflects the increasing number of biological samples to be analyzed today. Indeed, MS techniques are currently the most powerful detection and analysis techniques for protein samples, 10 – 15 as they allow the identification, characterization and sequencing of proteins and peptides. In addition, MS is a very sensitive analytical tool which is well adapted for the low quantities of biological material to be analyzed after the sample extraction and processing steps. MS is hence the last step in the usual process of protein samples, also called the proteomic approach. 12,14,15 The result of this emerging field of protein and proteomic analysis is a current need for high-throughput analysis; this Copyright  2003 John Wiley & Sons, Ltd.