Mesoporous silica thin films as a spatially extended probe of interfacial electric fields for amplified signal transduction in surface plasmon resonance spectroscopy

The transformation behaviour of "alucones", deposited by molecular layer deposition, in nanoporous Al2O3 layers

Nanoporous alumina films can be synthesized from hybrid organic-inorganic "alucone" films deposited by molecular layer deposition (MLD) by wet etching in deionized water or calcination in air at 500 °C. This transformation process was systematically investigated for two alucone chemistries based on ethylene glycol (EG) and glycerol (GL). Ellipsometric porosimetry (EP) was used for the characterization of the porous alumina structures that are formed as a result of the treatments. Etching in deionized water transforms both EG- and GL-alucones into porous alumina with a porosity of about 40%, albeit with a different pore structure: cylindrical pores for EG-alucones and ink-bottle structures for GL-alucones. Calcination in air up to 500 °C only successfully transformed EG-alucones into porous alumina if the chosen heating and cooling rate was lower than 200 °C h-1. Below this ramp rate, a relationship between the resulting porosity and the ramp rate was found. At the lowest investigated ramp rate of 20 °C h-1, the highest porosity of 36% was achieved. For this treatment type, the pore shape was of the ink-bottle type for all investigated ramp rates with narrow 1 nm-sized pores. Infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy revealed that the final chemistry of the porous structures was slightly different for both treatments due to trace amounts of carbon left behind by water etching. This suggests that the internal surface of the porous structure has a different termination depending on the chosen treatment. The precise thickness control and conformal nature inherent to MLD combined with the wet and heat treatments enables the coating of complex 3D structures with a porous alumina film with a well-defined thickness and pore structure.

Evanescent Field Based Photoacoustics: Optical Property Evaluation at Surfaces

Here, we present a protocol to estimate material and surface optical properties using the photoacoustic effect combined with total internal reflection. Optical property evaluation of thin films and the surfaces of bulk materials is an important step in understanding new optical material systems and their applications. The method presented can estimate thickness, refractive index, and use absorptive properties of materials for detection. This metrology system uses evanescent field-based photoacoustics (EFPA), a field of research based upon the interaction of an evanescent field with the photoacoustic effect. This interaction and its resulting family of techniques allow the technique to probe optical properties within a few hundred nanometers of the sample surface. This optical near field allows for the highly accurate estimation of material properties on the same scale as the field itself such as refractive index and film thickness. With the use of EFPA and its sub techniques such as total internal reflection photoacoustic spectroscopy (TIRPAS) and optical tunneling photoacoustic spectroscopy (OTPAS), it is possible to evaluate a material at the nanoscale in a consolidated instrument without the need for many instruments and experiments that may be cost prohibitive.

In situ monitoring of atomic layer deposition in nanoporous thin films using ellipsometric porosimetry

Ellipsometric porosimetry (EP) is a handy technique to characterize the porosity and pore size distribution of porous thin films with pore diameters in the range from below 1 nm up to 50 nm and for the characterization of porous low-k films especially. Atomic layer deposition (ALD) can be used to functionalize porous films and membranes, e.g., for the development of filtration and sensor devices and catalytic surfaces. In this work we report on the implementation of the EP technique onto an ALD reactor. This combination allowed us to employ EP for monitoring the modification of a porous thin film through ALD without removing the sample from the deposition setup. The potential of in situ EP for providing information about the effect of ALD coating on the accessible porosity, the pore radius distribution, the thickness, and mechanical properties of a porous film is demonstrated in the ALD of TiO(2) in a mesoporous silica film.

Poly(amidoamine)-dendrimer-modified gold surfaces for anomalous reflection of gold to detect biomolecular interactions

Label-free protein detecting chip technology has encouraged a number of discoveries, as it is a powerful analytical tool in the postgenomic era. In particular, we have focused on a unique characteristic of anomalous reflection of gold (AR) as a new class of label-free detection method for a protein chip system. In this paper, in order to improve the sensitivity of detection of biomolecular interactions by the AR method, we have constructed three-dimensional (3D) nanostructures on gold surfaces with a series of well-defined structures of poly(amidoamine) dendrimers (PAMAMs) from generation 2 to 4 (G2, G3, and G4) tethering biotin moieties as capturing agents for avidin and antibiotin IgG. Comparison of features of such 3D nanostructured surfaces with a diamine-modified flat-like surface revealed a 2-fold increase in the amount of avidin for 3D surfaces relative to the flat surface, and surface-assisted nonspecific interactions were significantly suppressed. We thus obtained 91% coverage for avidin detection on the PAMAM G4-modified surface, indicating a theoretically maximum attainable absorption considering a hexagonal-packed arrangement as a saturated monomolecular layer. In the antibiotin IgG assay, the PAMAM G4-modified surface clearly improved the amount of proteins captured compared to that for the flat surface, indicating that an appropriate density of capturing agents played a more important role in the interaction of larger molecular-sized proteins such as antibiotin IgG, which requires more space for interaction than the medium-sized avidin. These findings should assist in the development of a simple and practical tool for high-throughput protein detection, particularly with the AR method.