Improving The Desorption/Ionization Efficiency Of SALDI-MS Based On Silicon Nanostructures

Surface-assisted laser desorption/ionization mass spectrometry(SALDI-MS),which is a soft ionization technology,has been widely used in the analysis of small molecules.This analytical technology uses inorganic materials instead of organic matrix,which has low interference of background signals and high detection sensitivity.The main materials used for SALDI-MS substrates are:carbon,silicon,metal and metal oxide,these materials have high stability in vacuum and excellent absorption under ultraviolet light.Among them,silicon-based micro/nano-materials have unique properties of optics,electricity,and surface chemistry.With the advanced and flexible synthesis and fabrication technology based on silicon,various structures with controllable morphology can be prepared.In addition,the surface of silicon is easy to derivatization and functionalization.With these advantages,the silicon-based SALDI-MS substrate can provide various surface morphology and adjustable surface chemical properties,which can lead to the improvement of detection sensitivity,repeatability,specificity,and therefore improving the detection performance of SALDI-MS.In addition,the technology of desorption/ionization on silicon has the advantages of simple preparation,fast-speed analysis,and high detection repeatability,it has been widely used in the detection of various analytes.With the fast developing of modern society,detection of trace analyte is playing an increasingly important role in various fields.Therefore,improving the desorption/ionization efficiency of SALDI-MS is the key to making this technology widely used for in various fields.In order to enhance the desorption/ionization efficiency and improve the detection performance of silicon-based SALDI-MS,this paper has made the following investigations by combining various micro/nano-structures fabrication techniques and surface functionalization methods:Firstly,a superhydrophobic-assisted concentration method was proposed to improve the detection sensitivity in SALDI-MS.In this method,the silver nanoparticles/superhydrophobic coating(AgNPs/SHC)substrate was fabricated by combined AgNPs with unique optical properties and the superhydrophobic fluorosilane-coated silica nanoparticles.The AgNPs/SHC substrate has the following advantages:(1)It can provide good detection reproducibility,the relative standard deviation(RSD)of signal intensity ? 9.4%for detection 1 pmol/?L of rhodamine 6G(R6G);and a good linearity(R2>0.99)of concentration and its signal intensity is shown over the concentration ranges from 1 to 50 fmol/?L.(2)It is suitable for detecting various species of trace analytes,including amino acid,fatty acid,dye molecule,polypeptide,and polymer.(3)Moreover,it can also be used for the analysis of malachite green in lake water and bradykinin 1-7 in human serum.Secondly,a new method was proposed for improving the desorption/ionization efficiency of SALDI-MS by adjusting the laser energy deposition in nanostructure with changing its tilt angle.The slant silicon nanopillar arrays(SSNA)were fabricated using the technology of reactive ion etching,and then we prepared the AgNPs/SSNA substrate by deposited AgNPs on the surface of SSNA substrate.The theoretical simulation results show that the laser energy deposited in the nanostructure can be increased by modifying AgNPs and adjusting its tilt angle.By detection R6G in SALDI-MS,the results show that:(1)after modifying AgNPs on SSNA,the signal intensity of analyte has increased about 5 times;(2)with the tilted angle of AgNPs/SSNA substrate increased from 0° to 15°,the signal intensity of analyte gradually increased.In summary,with modifying AgNPs and adjusting the tilt angle of nanopillars,the deposition of laser energy in silicon nanopillar arrays can be improved,and thereby enhanced the desorption/ionization efficiency of silicon-based SALDI-MS.This work provides a new idea for improving the detection performance of SALDI-MSThirdly,the ordered silicon nanopillar arrays with controllable morphology parameters were fabricated by combined the technologies of self-assembly and reactive ion etching,and the effects of the surface morphology on ion-desorption efficiency and internal energy transfer in SALDI-MS were systematically investigated.The results suggest that:(1)the increasing optical absorption of substrate can improve ion-desorption efficiency by enhancing internal energy transfer and promoting the restructuring of the silicon surface;(2)the high surface voidage of silicon nanopillar arrays can cause the surface temperature increasing,and thereby promote ion-desorption.This research work reveals that enough optical absorption,high surface voidage are vital for silicon-based SALDI-MS substrate to achieve high ion-desorption efficiency.