Development of High Surface Area Organosilicate Nanoparticulate Thin Films for Use in Sensing Hydrophobic Compounds in Sediment and Water.

The scope of this study was to apply advances in materials science, specifically the use of organosilicate nanoparticles as a high surface area platform for passive sampling of chemicals or pre-concentration for active sensing in multiple-phase complex environmental media. We have developed a novel nanoporous organosilicate (NPO) film as an extraction phase and proof of concept for application in adsorbing hydrophobic compounds in water and sediment. We characterized the NPO film properties and provided optimization for synthesis and coatings in order to apply the technology in environmental media. NPO films in this study had a very high surface area, up to 1325 m2/g due to the high level of mesoporosity in the film. The potential application of the NPO film as a sorbent phase for sensors or passive samplers was evaluated using a model hydrophobic chemical, polychlorinated biphenyls (PCB), in water and sediment. Sorption of PCB to this porous high surface area nanoparticle platform was highly correlated with the bioavailable fraction of PCB measured using whole sediment chemistry, porewater chemistry determined by solid-phase microextraction fiber methods, and the Lumbriculus variegatus bioaccumulation bioassay. The surface-modified NPO films in this study were found to highly sorb chemicals with a log octanol-water partition coefficient (Kow) greater than four; however, surface modification of these particles would be required for application to other chemicals.

Modular design of paper based switches for autonomous lab-on paper micro devices.

This paper presents a new approach towards the design of paper based autonomous microfluidic devices. Autonomy in the device operation is achieved through the incorporation of mechanically actuated microfluidic switches that are versatile in their design and may be configured to be simple time triggered ON or OFF switches or more complex switches that can be timed to be in multiple states (timed ON, followed by timed OFF). These switches are self-contained and require no external power for their operation, deriving their functionality solely through stored elastic energy. This paper presents the design and fabrication of these switches as fluidic analogs of electronic transistors, and their integration into microfluidic paper based circuit demonstrating their operation as a programmable paper-based microfluidic device.

Re-usable PDMS stamps for non-destructive fluorescence evaluation and imaging of thin film photonic structures.

We report on a non-destructive method for evaluating fluorescence emission from fluorophores placed upon engineered photonic structures. Our method utilizes re-usable, fluorescent thin film coated polydimethylsiloxane (PDMS) stamps. We harness the inherent characteristics of PDMS slabs; their ability to form conformal contact through van der Waals interactions in bringing the coated fluorescent layer on PDMS into close proximity of the photonic structure of interest. Fluorescence measurements are performed using the PDMS slab while in conformal contact with the test structure, allowing one to re-use these stamps for reliable evaluation over multiple samples. Transfer of the fluorescent film from the PDMS to the test structures is mitigated by the use of appropriate cross linkers that covalently bond the fluorescent film to the PDMS surface. To demonstrate the application potential of this approach, we report on the evaluation of fluorescence emission modulation from patterned nanoporous thin films, which are particularly challenging to evaluate using traditional approaches, and from plasmonic gratings supporting metal enhanced fluorescence. Comparison with traditional evaluation approaches has been made to showcase the superiority of the reported technique.

Nanomaterial processing using self-assembly-bottom-up chemical and biological approaches.

Nanotechnology is touted as the next logical sequence in technological evolution. This has led to a substantial surge in research activities pertaining to the development and fundamental understanding of processes and assembly at the nanoscale. Both top-down and bottom-up fabrication approaches may be used to realize a range of well-defined nanostructured materials with desirable physical and chemical attributes. Among these, the bottom-up self-assembly process offers the most realistic solution toward the fabrication of next-generation functional materials and devices. Here, we present a comprehensive review on the physical basis behind self-assembly and the processes reported in recent years to direct the assembly of nanoscale functional blocks into hierarchically ordered structures. This paper emphasizes assembly in the synthetic domain as well in the biological domain, underscoring the importance of biomimetic approaches toward novel materials. In particular, two important classes of directed self-assembly, namely, (i) self-assembly among nanoparticle-polymer systems and (ii) external field-guided assembly are highlighted. The spontaneous self-assembling behavior observed in nature that leads to complex, multifunctional, hierarchical structures within biological systems is also discussed in this review. Recent research undertaken to synthesize hierarchically assembled functional materials have underscored the need as well as the benefits harvested in synergistically combining top-down fabrication methods with bottom-up self-assembly.

Femtogram-level detection of Clostridium botulinum neurotoxin type A by sandwich immunoassay using nanoporous substrate and ultra-bright fluorescent suprananoparticles.

We report a simple, robust fluorescence biosensor for the ultra-sensitive detection of Clostridium botulinum Neurotoxin Type A (BoNT/A) in complex, real-world media. High intrinsic signal amplification was achieved through the combined use of ultra-bright, photostable dye-doped nanoparticle (DOSNP) tags and high surface area nanoporous organosilicate (NPO) thin films. DOSNP with 22 nm diameter were synthesized with more than 200 times equivalent free dye fluorescence and conjugated to antibodies with average degree of substitution of 90 dyes per antibody, representing an order of magnitude increase compared with conventional dye-labeled antibodies. The NPO films were engineered to form constructive interference at the surface where fluorophores were located. In addition, DOSNP-labeled antibodies with NPO films increased surface roughness causing diffuse scattering resulting in 24% more scattering intensity than dye-labeled antibody with NPO films. These substrates were used for immobilization of capture antibodies against BoNT/A, which was further quantified by DOSNP-labeled signal antibodies. The combination of optical effects enhanced the fluorescence and, therefore, the signal-to-noise ratio significantly. BoNT/A was detected in PBS buffer down to 21.3 fg mL(-1) in 4 h. The assay was then extended to several complex media and the four-hour detection limit was found to be 145.8 fg mL(-1) in orange juice and 164.2 fg mL(-1) in tap water, respectively, demonstrating at least two orders of magnitude improvement comparing to the reported detection limit of other enzyme-linked immunosorbent assays (ELISA). This assay, therefore, demonstrates a novel method for rapid, ultra-low level detection of not only BoNT/A, but other analytes as well.

Confeito-like assembly of organosilicate-caged fluorophores: ultrabright suprananoparticles for fluorescence imaging.

We report ultrabright, photostable, sub-25 nm nanoparticle agglomerates (suprananoparticles) assembled from a few hundred 3.3 ± 0.9 nm units, each hosting on average a single rhodamine 6G (Rh6G) dye molecule encased in a thin organosilicate cage. These individual Rh6G-doped nanoparticle (DOSNP) units consist of a hydrophobic core containing the dye and an ultrathin, conformal silicate shell modified by CO(2) plasma to confer a beneficial 'cage effect' as well as surface hydrophilicity. The isolation of the dye within individual DOSNP units in the final 22 ± 5 nm agglomerate avoids dimerization and related spontaneous molecular interactions that otherwise lead to self-quenching in closely co-localized fluorophores. The resulting suprananoparticles are over 200 times brighter than the free Rh6G molecules in the same volume. There is no observable dye leaching, and the labels are 20-fold more resistant to photobleaching than free Rh6G in solution. We demonstrate the attractive features of DOSNPs as labels in bioimaging applications.

Sub-minute formation of supported nanoporous mesoscale patterns programmed by surface energy.

We demonstrate an original and powerful concept for elaborating spontaneous, high fidelity patterns of nanoporosity from nanoscale building blocks using patterned surface chemistry (i.e., "surface energy gating") to corral the growth of colloidal structures at a solid surface. Composite films consisting of polymethylsilsesquioxane nanoparticles uniformly dispersed in polypropylene glycol polymer were examined at temperatures beyond the decomposition of the polymer as a function of the substrate surface energy to clarify nanoparticulate ensemble behavior. The principle behind this colloidal assembly can be understood by taking into consideration the entropy and enthalpy dictating the mutual interactions between substrate surface, polymeric solvent, and dispersed colloids in the decomposition regime. The relevance of this research is shown by demonstrating how the principle of surface energy gating can be utilized to achieve spontaneous and controllable spatial patterns of nanoporous, high surface area thin films in a cost-effective and energy-efficient manner via brief thermal exposure. The simplicity and general nature of this methodology are further exemplified by showing the facility with which high-contrast fluorescent bioconjugate arrays can be prepared from nanoporous organosilicate patterns.

A comparative evaluation of microarray slides as substrates for the development of protease assay biosensors.

The application of commercially available microarray slides as substrates for fluorogenic protease assays has been explored in terms of binding efficiency, stability, and activity. A fluorescent, biotinylated substrate for botulinum neurotoxin A (BoNTA) was attached via self-assembled monolayer of Streptavidin to amine-reactive aldehyde, epoxy, hydrogel, and polymer slides. Nexterion Slide P® was found to have optimal protein binding efficiency and stability of the slides examined. Addition of glycerol to the printing buffer improved spot morphology significantly and polyvinylpyrrolidone provided long-term stability, allowing chips to be stored for up to 1 month with good viability. Detection of a recombinant BoNTA light chain was then carried out at 37°C and a sub-lethal dose was detected in 2 hours.

Entropy driven spontaneous formation of highly porous films from polymer-nanoparticle composites.

Nanoporous materials have become indispensable in many fields ranging from photonics, catalysis and semiconductor processing to biosensor infrastructure. Rapid and energy efficient process fabrication of these materials is, however, nontrivial. In this communication, we describe a simple method for the rapid fabrication of these materials from colloidal dispersions of Polymethyl Silsesquioxane nanoparticles. Nanoparticle-polymer composites above the decomposition temperature of the polymer are examined and the entropic gain experienced by the nanoparticles in this rubric is harnessed to fabricate novel highly porous films composed of nanoparticles. Optically smooth, hydrophobic films with low refractive indices (as low as 1.048) and high surface areas (as high as 1325 m(2) g(-1)) have been achieved with this approach. In this communication we address the behavior of such systems that are both temperature and substrate surface energy dependent. The method is applicable, in principle, to a variety of nanoparticle-polymer systems to fabricate custom nanoporous materials.

Characterization of a novel ultra low refractive index material for biosensor application.

Nanoporous materials can provide significant benefits to the field of biosensors. Their size and porous structure makes them an ideal tool for improving sensor performance. This study characterized a novel ultra low index of refraction nanoporous organosilicate (NPO) material for use as an optical platform for fluorescence-based optical biosensors. While serving as the low index cladding material, the novel coating based on organosilicate nanoparticles also provides an opportunity for a high surface area coating that can be utilized for immobilizing biological probes. Biological molecules were immobilized onto NPO, which was spin-coated on silicon and glass substrates. The biological molecule was composed of Protein A conjugated to AlexaFluor 546 fluorophore and then immobilized onto the NPO substrate via silanization. Sample analysis consisted of spectrofluorometry, FT-IR spectroscopy, scanning electron microscopy, contact angle measurement and ellipsometry. The results showed the presence of emission peaks at 574 nm, indicating that the immobilization of Protein A to the NPO material is possible. When compared to Si and glass substrates not coated with NPO, the results showed a 100X and 10X increase in packing density with the NPO coated films respectively. Ellipsometric analysis, FT-IR, contact angle, and SEM imaging of the surface immobilized NPO films suggested that while the surface modifications did induce some damage, it did not incur significant changes to its unique characteristics, i.e., pore structure, wettability and index of refraction. It was concluded that NPO films would be a viable sensor substrate to enhance sensitivity and improve sensor performance.