RESUMEN
Time-of-flight secondary ion mass spectrometry is one of the most promising techniques for label-free analysis of biomolecules with nanoscale spatial resolution. However, high-resolution imaging of larger biomolecules such as phospholipids and peptides is often hampered by low yields of molecular ions. Matrix-enhanced SIMS (ME-SIMS), in which an organic matrix is added to the sample, is one promising approach to enhancing the ion yield for biomolecules. Optimizing this approach has, however, been challenging because the processes involved in increasing the ion yield in ME-SIMS are not yet fully understood. In this work, the matrix α-cyano-4-hydroxycinnamic acid (HCCA) has been combined with cluster primary ion analysis to better understand the roles of proton donation and reduced fragmentation on lipid molecule ion yield. A model system consisting of 1:100 mol ratio dipalmitoylphosphatidylcholine (DPPC) in HCCA as well as an HCCA-coated mouse brain cryosection have been studied using a range of Bi and Ar cluster ions. Although the molecular ion yield increased with an increase in cluster ion size, the enhancement of the signals from intact lipid molecules decreased with an increase in cluster ion size for both the model system and the mouse brain. Additionally, in both systems, protonated molecular ions were significantly more enhanced than sodium and potassium cationized molecules for all of the primary ions utilized. For the model system, the DPPC molecular ion yield was increased by more than an order of magnitude for all of the primary ions studied, and fragmentation of DPPC was dramatically reduced. However, on the brain sample, even though the HCCA matrix reduced DPPC fragmentation for all of the primary ions studied, the matrix coating suppressed the ion yield for some lipids when the larger cluster primary ions were employed. This indicated insufficient migration of the lipids into the matrix coating, so that dilution by the matrix overpowered the enhancement effect. This study provides strong evidence that the HCCA matrix both enhances protonation and reduces fragmentation. For imaging applications, the ability of the analytes to migrate to the surface of the matrix coating is also a critical factor for useful signal enhancement. This work demonstrates that the HCCA matrix provides a softer desorption environment when using Bi cluster ions than that obtained using the large gas cluster ions studied alone, indicating the potential for improved high spatial resolution imaging with ME-SIMS.
RESUMEN
N-Heterocyclic carbene (NHC)-modified planar gold surfaces (NHC@Au) were found to be more susceptible toward wet chemical etching than undecorated surface areas. Site-selective decoration of NHCs on Au was achieved by microcontact printing (µCP) of the NHC precursors 1,3-bis(diisopropylphenyl)imidazol-3-ium hydrogen carbonate (IPr(H)[HCO3]) or 1,3-dimethylbenzimidazol-3-ium hydrogen carbonate (BIMe(H)[HCO3]). Strikingly, BIMe@Au showed concentration-dependent etching behavior, tunable from a positive resist to a negative resist. Surface patterning was verified by time-of-flight secondary-ion mass spectrometry and Kelvin probe force microscopy. Moreover, orthogonal µCP enabled the patterned functionalization of planar Au with both IPr and 1-eicosanethiol and the subsequent formation of three-dimensional structures with a single etching step. The selective removal of Au by functionalization with a surface ligand is unprecedented and enables novel applications of NHCs in materials chemistry and nanofabrication.
RESUMEN
Nanoparticles offer unique physical and chemical properties. Dip pen nanolithography of nanoparticles enables versatile patterning and nanofabrication with potential application in electronics and sensing, but is not well studied yet. Herein, the patterned deposition of various nanoparticles onto unmodified silicon substrates is presented. It is shown that aqueous solutions of hydrophilic citrate and cyclodextrin functionalized gold nanoparticles as well as poly(acrylic) acid decorated magnetite nanoparticles are feasible for writing nanostructures. Both smaller and larger nanoparticles can be patterned. Hydrophobic oleylamine or n-dodecylamine capped gold nanoparticles and oleic acid decorated magnetite nanoparticles are deposited from toluene. Tip loading is carried out by dip-coating, and writing succeeds fast within 0.1 s. Also, coating with longer tip dwell times, at different relative humidity and varying frequency are studied for deposition of nanoparticle clusters. The resulting feature size is between 300 and 1780 nm as determined by scanning electron microscopy. Atomic force microscopy confirms that the heights of the deposited structures correspond to a single or double layer of nanoparticles. Higher writing speeds lead to smaller line thicknesses, offering possibilities to more complex structures. Dip pen nanolithography can hence be used to pattern nanoparticles on silicon substrates independent of the surface chemistry.
RESUMEN
Surface patterning of functional materials is a key technology in various fields such as microelectronics, optics, and photonics. In micro- and nanofabrication, polymers are frequently employed either as photoreactive or thermoresponsive resists that enable further fabrication steps, or as functional adlayers in electronic and optical devices. In this article, a method is presented for imprint lithography using low molecular weight arylazoisoxazoles photoswitches instead of polymer resists. These photoswitches exhibit a rapid and reversible solid-to-liquid phase transition upon photo-isomerization at room temperature, making them highly suitable for reversible surface functionalization at ambient conditions. Beyond photo-induced imprint lithography with multiple write-and-erase cycles, prospective applications as patterned matrix for nanoparticles and etch resist on gold surfaces are demonstrated.