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Track membranes (TM) were used as the matrixes for replication:ensembles with stable standing copper microwires (needles) were made by electrochemical replication of TM. Samples with microwires of two main shapes were obained- conical (with the lower base 0.5-1.5 mcm and high up to 5-10 mcm) and cylindrical (with diameter 0.1-2.0 mcm, high up to 10 mcm). Surface densities of wires were 10**8 -10**9 /sq.cm.
Obtained structures were used as a substrate for deposition of analyte for mass-spectrometry. The test object - polypeptide (gramicidin, MW 1142 Da) was used as an analyte which was deposited on the surface of obtained substrates and put into the ion source of mass-spectrometer. Irradiation of this sample by short pulse of nitrogen laser stimulate the emission (ejection) of the polypeptide ions from the surface which were then analyzed by time of flight mass analyzer (Vision-2000). Using this technique we obtained rather intensive mass-spectra - it should be mentioned that flat copper substrate at the same condition has not give detectable signal. We also found out multi-mers formation which increased with increase of surface density and decrease of wires diameter.
For cylindrical wires comparison of substrates with different diameters and surface density of microwires was made. For conical microwires substrate the number of ejected ions was 5-10 times greater. It can be explained by the role of lightning rod effect, effect of enhanced of electric field in the local area near the top of microwire. Estimation gives the factor of electric field enhancement close to 10. Moreover, high electric field gradient induces moving of dipoles to the area of higher field. It also increase the effect of ionization and desorption of big organic molecules. In our mind in the case of electromagnetic field stimulation (during the laser pulse irradiation) resonance mechanism of local field amplification is also take place. The effectiveness of this method was compared with the same for up-to-date methods MALDI and SALDI.
Metallic replicas of TM is already known as effective electron emitters-here we demonstrated that such surfaces (with artificially made roughness) could be used for stimulation of ion emission.
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