Investigation of the magnetic properties of ferritin by AFM imaging with magnetic sample modulation.

Individual ferritin molecules can be sensitively detected using magnetic sample modulation (MSM) combined with contact mode atomic force microscopy (AFM). To generate an oscillating magnetic field, an alternating current (AC) was applied to a solenoid placed within the base of the AFM sample stage. When a modulated electromagnetic field is applied to samples, ferromagnetic and paramagnetic nanomaterials are induced to vibrate. The flux of the AC electromagnetic field causes the ferritin samples to vibrate with corresponding rhythm and periodicity of the applied field. This motion can be detected and mapped using contact mode AFM with a soft, nonmagnetic cantilever. Changes in the phase and amplitude of the periodic motion of the sample are sensed by the tip to selectively map vibrating magnetic nanomaterials. Particle lithography was used to create nanopatterned test platforms of ferritin for MSM measurements. Regularly spaced structures of proteins provide precise reproducible dimensions for multiple successive surface measurements at dimensions of tens of nanometers.

Controlling the surface coverage and arrangement of proteins using particle lithography.

AIMS: The applicability of particle lithography with monodisperse mesospheres is tested with various proteins to control the surface coverage and dimensions of protein nanopatterns. METHODS & MATERIALS: The natural self-assembly of monodisperse spheres provides an efficient, high-throughput route to prepare protein nanopatterns. Mesospheres assemble spontaneously into organized crystalline layers when dried on flat substrates, which supply a structural frame or template to direct the placement of proteins. The template particles are displaced with a simple rinsing step to disclose periodic arrays of protein nanopatterns on surfaces. RESULTS & DISCUSSION: The proteins are attached securely to the surface, forming nanopatterns with a measured thickness of a single layer. The morphology and diameter of the protein nanostructures can be tailored by selecting the diameter of the mesospheres and choosing the protein concentration. CONCLUSIONS: Particle lithography is shown to be a practical, highly reproducible method for patterning proteins on surfaces of mica, glass and gold. High-throughput patterning was achieved with ferritin, apoferritin, bovine serum albumin and immunoglobulin-G. Depending on the ratio of proteins to mesospheres, either porous films or ring structures were produced. This approach can be applied for fundamental investigations of protein-binding interactions of biological systems in surface-bound bioassays and biosensor surfaces.

Achieving precision and reproducibility for writing patterns of n-alkanethiol self-assembled monolayers with automated nanografting.

Nanografting is a high-precision approach for scanning probe lithography, which provides unique advantages and capabilities for rapidly writing arrays of nanopatterns of thiol self-assembled monolayers (SAMs). Nanografting is accomplished by force- induced displacement of molecules of a matrix SAM, followed immediately by the self-assembly of n-alkanethiol ink molecules from solution. The feedback loop used to control the atomic force microscope tip position and displacement enables exquisite control of forces applied to the surface, ranging from pico to nanonewtons. To achieve high-resolution writing at the nanoscale, the writing speed, direction, and applied force need to be optimized. There are strategies for programing the tip translation, which will improve the uniformity, alignment, and geometries of nanopatterns written using open-loop feedback control. This article addresses the mechanics of automated nanografting and demonstrates results for various writing strategies when nanografting patterns of n-alkanethiol SAMs.

Coprecipitation with calcium hydroxide for determination of iron in fish otoliths by collision cell ICP-MS.

A method has been described for the determination of iron from fish otoliths containing high levels of calcium by collision cell technology (CCT) ICP-MS. Iron (Fe) in otolith solutions was quantitatively coprecipitated with small amounts of calcium hydroxide by adding 1.0 M sodium hydroxide solution. The performance of CCT-ICP-MS pressurized with He/H(2) cell gas was investigated on the elimination of Ca-based spectral interferences at m/z 54, 56 and 57. Molecular ion interferences at m/z 54 and 56 were reduced by 2 orders of magnitude. However, the interferences at m/z 57 increased by the same amount in the presence of Ca in solutions owing to the formation of (40)Ca(16) OH(+) through reactions with H(2) in collision cell, indicating that (57)Fe was not suitable for the determination of Fe from otoliths. Results for (56)Fe suffered significantly from interferences of Ca-based molecular ions when the Ca concentration in solution exceeded 100 microg ml(-1), for which matrix-matched calibration was required for accurate determination. CCT with the aid of He/H(2) cell gas proved to be very effective in eliminating the interferences ((40)Ar(14)N(+) and (40)Ca(14)N(+)) at m/z 54. Presence of Ca up to 300 microg ml(-1) had virtually no effect on the ion signals of (54)Fe, which with low background signals, afforded accurate determination of Fe from otoliths by using aqueous external standards.