Nanosphere metal-coated

Figure 3. Various type of SERS active metallic nanostructures (a) metal-island films (b) metal-coated nanospheres (semi-nanoshells) (c) metal-coated random nanostructures and (d) polymer coatings embedded with metal nanoparticles. Inset An SEM image of silver-coated polystyrene spheres.

Instrumentation. In both cases, a near field probe is employed—either a metal-coated fiber (aperture-based) or a metal tip (apertureless). Distance regulation, as used with scanning probe methods (see Sect. 7.2), controls the probe-surface gap it may also be used to obtain a topographic mapping of the studied surface. Scattered light is collected and guided to a Raman spectrometer. In a (non-electrochemical) study, dye-labeled DNA that had adsorbed onto evaporated silver layers on FIFE nanospheres was observed [531]. Special surface sites with particularly high enhancement could be identified. 

Because the forces of attraction prevail when molecules are brought into sufficiently dose proximity under normal conditions, release is best effected if both the strength of the interaction and the degree of contact are minimized. Aliphatic hydrocarbons and fluorocarbons achieve the former effect, finely divided solids the latter. Materials such as microcrystalline wax [64742 42-3] and hydrophobic silica [7631-86-9] combine both effects. Some authors refer to this combined effect as the ball bearing mechanism. A perfluoroalkylated fullerene nanosphere would perhaps be the ultimate example of this combined effect (17). These very general mechanistic remarks can be supplemented by publications on the mechanism of specific classes of release agents such as metallic stearates (18), fatty acids and fluorinated compounds (19), and silicone-coated rdease papers (20,21). The mechanism of release of certain problem adherents, eg, polyurethanes, has also been addressed (22,23). 

Copper 18 mm diameter discs were utilized as substrates for glucose detection. After cleaning, approximately 10 lL of the nanosphere suspension (4% solids, 390 nm diameter) was drop coated onto each copper substrate and allowed to dry in ambient conditions.58 The substrates were then mounted into an electron beam deposition system for metal deposition (Kurt J. Lesker, Clairton, PA). Silver metal films (dm = 200 nm) were deposited over and through the sphere masks on the substrates.58 59... 

Figure 2. Schematic ilhistiatian of the nanoq)here lithography Cabricatioo technique. A small vohime of nanosphere solution is diop-coated onto the clean substrate. As die solvent evaporates, die nanoqiheres assemble into a two-dimensional colloidal crystal mask. The desired noble metal is then dqpodted in a hi vacuum thin film vapor deposition tem. In the last step of the sam de prqnratioii, the lift-off step, the nanospheres are removed by sonication in absolute ethanol.

Glass and copper substrates for anthrax detection and glucose detection respectively were pretreated as described previously (10, II). Approximately 2 pL of the nanosphere suspension (4% solids) was drop-coated onto each glass substrate and 10 pL of the nanosphere suspension was drop-coated onto each copper substrate and allowed to dry in ambient conditions. The metal films were deposited in a modified Consolidated Vacuum Corporation vapor deposition system with a base pressure of 10" Ton. The deposition rates for each film (10 A/sec) were measured as described previously (10). AgFON surfaces were stored in the dark at room temperature prior to use. 

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