Design Strategy for Nanostructured Arrays of Metallodielectric Cuboids to Systematically Tune the Optical Response and Eliminate Spurious Bulk Effects in Plasmonic Biosensors

Plasmonic biosensors are a powerful tool for studying molecule adsorption label-free and with high sensitivity. Here, we present a systematic study on the optical properties of strictly regular nanostructures composed of metallodielectric cuboids with the aim to deliberately tune their optical response and improve their biosensing performance. In addition, the patterns were tested for their potential to eliminate spurious effects from sensor response, caused by refractive index changes in the bulk solution. Shifts in the plasmonic spectrum are exclusively caused by the adsorbing molecules. For this purpose, nanopatterns of interconnected and separated cubes with dimensions ranging from 150 to 600 nm have been fabricated from poly(methyl methacrylate) using electron-beam lithography followed by metallization with gold. It is shown that a small lateral pattern size, a high aspect ratio, and short connection lengths are favorable to generate extinction spectra with well-separated and pronounced peaks. Furthermore, for selected nanostructures, we have been able to identify reflection angles for which the influence of the bulk refractive index on the position of the plasmonic peaks is negligible. It is shown that sensor operation under these angles enables monitoring of in situ biomolecule adsorption with high sensitivity providing a promising tool for high-throughput applications

Polymer-induced swelling of solid-supported lipid membranes

In this paper, we study the interaction of charged polymers with solid-supported 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membranes by in-situ neutron reflectivity. We observe an enormous swelling of the oligolamellar lipid bilayer stacks after incubation in solutions of poly(allylamine hydrochloride) (PAH) in DO. The positively charged polyelectrolyte molecules interact with the lipid bilayers and induce a drastic increase in their d-spacing by a factor of ~4. Temperature, time, and pH influence the swollen interfacial lipid linings. From our study, we conclude that electrostatic interactions introduced by the adsorbed PAH are the main cause for the drastic swelling of the lipid coatings. The DMPC membrane stacks do not detach from their solid support at T > T. Steric interactions, also introduced by the PAH molecules, are held responsible for the stabilizing effect. We believe that this novel system offers great potential for fundamental studies of biomembrane properties, keeping the membrane's natural fluidity and freedom, decoupled from a solid support at physiological conditions

Poly-acrylic Acid Brushes and Adsorbed Proteins

Planar polyelectrolyte brushes are prepared by Langmuir-Schaefer based grafting of perdeuterated (styrene)49-b-(acrylic acid)222 block copolymer (dPS-b-PAA) to dPS pre-coated silicon supports with grafting density σPAA from 0.07 to 0.11 nm-2. The structure of the solvent-swollen brushes, i. e. the volume fraction profile of polymer segments, ϕPAA, as a function of altitude z from the grafting plane into the liquid phase is extracted from neutron reflectivity measurements. We find that for all cases investigated ϕPAA(z) resembles a Gaussian profile. Although very condensed, the PAA brushes can be loaded with bovine serum albumin (BSA). The integral amount of adsorbed BSA scales linearly with grafting density. We compare our z-resolved volume fraction profile ϕBSA(z) of BSA on PAA brushes with existing literature on that system. It is found that a cross-over takes place in the adsorption scheme from ternary compressive, where proteins can approach the grafting surface only by compressing the brush, to ternary insertive, where proteins enter the brush with only local perturbation of the concentration profile, as a function of RP/Hmax, where RP is the Stokes-Radius of the protein, and Hmax is the experimentally determined maximum height of the brush

Surface Generated Acoustic Wave Biosensors for the Detection of Pathogens: A Review

This review presents a deep insight into the Surface Generated Acoustic Wave (SGAW) technology for biosensing applications, based on more than 40 years of technological and scientific developments. In the last 20 years, SGAWs have been attracting the attention of the biochemical scientific community, due to the fact that some of these devices - Shear Horizontal Surface Acoustic Wave (SH-SAW), Surface Transverse Wave (STW), Love Wave (LW), Flexural Plate Wave (FPW), Shear Horizontal Acoustic Plate Mode (SH-APM) and Layered Guided Acoustic Plate Mode (LG-APM) - have demonstrated a high sensitivity in the detection of biorelevant molecules in liquid media. In addition, complementary efforts to improve the sensing films have been done during these years. All these developments have been made with the aim of achieving, in a future, a highly sensitive, low cost, small size, multi-channel, portable, reliable and commercially established SGAW biosensor. A setup with these features could significantly contribute to future developments in the health, food and environmental industries. The second purpose of this work is to describe the state-of-the-art of SGAW biosensors for the detection of pathogens, being this topic an issue of extremely importance for the human health. Finally, the review discuses the commercial availability, trends and future challenges of the SGAW biosensors for such applications

Applications of Lithium Niobate acoustic plate mode devices as sensors for liquids

The operation principles of acoustic wave sensors for liquids are summarized and results are reported on the use of ZX-LiNbO3 acoustic plate mode (APM) devices as detectors for dilute electrolyte and metal ion solutions. The APM is a slow shear wave having a relatively strong acousto-ionic interaction, and thus allows to measure the liquid electrical properties by the perturbation of the wave propagation characteristics. To utilize the APM device as a selective chemical sensor for liquids, the surface is derivatized in order to covalently couple a chemical selective film onto it. For the development of a selective sensor, the surface cleaning and derivatization of the LiNbO3 surface proved to be a major obstacle. We will summarize our recent results on the derivatization of LiNbO3 with alkylaminosilanes. To understand the relationship between the state of the oxide substrate surface and the homogeneity and structural aspects of aminosilane monolayers further, model experiments with different aminosilanes on a Si(100) surface covered with a native oxide layer are described

Proteinnachweis mit akustischen Sensoren

Die hohe Spezifität von Antigen/Antikörper‐Wechselwirkungen ist in den vergangenen Jahrzehnten intensiv genutzt worden, um präzise Nachweismethoden für Makromoleküle zu entwickeln. Hauptziel hierbei war der Nachweis von Krankheitserregern sowie infektionsspezifischer und Stoffwechsel‐bestimmender Proteine. Trotz ihrer hohen Empfindlichkeit besitzen diese Analysetechniken einige Nachteile. So sind sie in der Regel zeitintensive Mehrschrittverfahren, die für eine direkte Beobachtung von Prozeßabläufen nicht geeignet sind, und sie erfordern den Einsatz von Markierungsstoffen. Ein neuer Forschungszweig beschäftigt sich daher mit der Entwicklung alternativer Nachweistechniken, die — bei hoher Empfindlichkeit und Selektivität — eine on‐line Detektion unmarkierter Moleküle ermöglichen. Bisher gewonnene Ergebnisse zeigen, daß akustische Sensoren einen vielversprechenden Ansatz zur Realisierung eines derartigen Konzeptes bieten

In situ detection of cells and biochemical reactions by optical diffraction

The combination of mesoscopic surface patterning and Fourier diffraction optics represents a new sensor concept for (bio)chemical applications. Antibodies have been covalently linked to microstructures formed by μCP and provide the basis for the in situ detection of cells, which serve as scattering elements for the incident laser beam

Experimental determination of mass sensitivity of APM sensors by CVD thin films

Acoustic wave devices have been used as gravimetrical sensors in both gas and liquid environments. In case of corrosive analytes the use of acoustic plate modes (APMs) has proved to be a promising concept as sensor electrodes and analyte are strictly separated. While mass sensitivity of quartz microbalances and surface acoustic waves has been studied in detail both theoretically and experimentally, there are only few data on the mass sensitivity of APMs. In order to overcome this lack of information we determined the mass sensitivity of APMs on ZX-LiNbO 3 using a chemical vapour deposition (CVD) method. Results are reported on the frequency dependence of mass sensitivity and the effects of metallization thickness and applied constant strain. The obtained data are compared to liquid-phase measurement