The ElectroSpray Ionization (ESI) allows to bring intact and isolated units of large organic molecules in the gas phase. The technique uses a solution of the molecule of interest flowing in a small capillary held at high voltage (HV, typically a few kV) with respect to a grounded counter electrode placed few cm away. The HV produces a spray of charged droplets whose size continues to decrease by solvent evaporation and Coulombic explosion until a gas of molecular ions is formed. The ESI process usually takes place in air and then the jet can be transported into a vacuum chamber for the analysis or deposition.
A device based on an ESi source is under construction at the CNR-ISM Montelibretti. Presently, it consists of i) a heated capillary to transport the charged species in vacuum and ii) a first differential pumping stage equipped with an octupole ion guide. A vacuum chamber housing a quadrupole mass spectrometer for m/z selection of the species, followed by a quadrupolar deflector to direct them towards a deposition chamber is being designed and will soon be commissioned for ‘soft-landing’ deposition of large biomolecular species . All in all, this is quite complex and costly set-up, which may suffer of severe limitations due to the low fluency of the m/z selected species. The long term goal of the project is to increase the intensity of the ESI source in a custom apparatus in order to make ‘soft landing’ a competitive technique for nanotechnology applications such as the production of biosensors and organic devices.
In parallel to the design of the in-vacuum apparatus, the potentiality of the ESI technique for the deposition of active enzymes is being tested using a set-up for ‘in-air’ deposition. This approach provides an effective removal of the solvent, the advantage to operate at ambient pressure or in controlled atmosphere, a significant reduction of costs and times of the process, the possibility to be easily automatized and a direct scale-up.
Laccase, a well-known enzyme used for the detection of polyphenols in different matrices [2,3] is used for these studies. Preliminary results showing the applicability of the ESI deposition on screen printed electrodes will be presented.
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 M.M. Rodríguez-Delgado et al. Trends in Anal. Chem. 74 (2015) 21
 M. Verrastro et al. Talanta 154 (2016) 438