A methodology for enabling biochemical sensing applications using porous polymer photonic bandgap structures is presented. Specifically, we demonstrate an approach to encapsulation of chemical and biological recognition elements within the pores of these structures. This sensing platform is built on our recently demonstrated nanofabrication technique using holographic interferometry of a photo-activated mixture that includes a volatile solvent as well as monomers, photoinitiators, and co-initiators. Evaporation of the solvent after polymerization yields nanoporous polymeric 1D photonic bandgap structures that can be directly integrated into optical sensor systems that we have previously developed. More importantly, these composite structures are simple to fabricate, chromatically tunable, highly versatile, and can be employed as a general template for the encapsulation of biochemical recognition elements. As a specific example of a prototype device, we demonstrate an oxygen (O2) sensor by encapsulating the fluorophore (tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) within these nanostructured materials. Finally, we report initial results of extending this technique to the development of a hydrophilic porous polymer photonic bandgap structure for sensing in aqueous environments. The ability to control the hydrophilic/hydrophobic nature of these materials has direct impact on chemical and biological sensing.
The development of porous nanostructured materials, such as polymer Bragg gratings, offer an attractive and unique platform for chemical and biological recognition elements. Much of the efforts in polymeric gratings have been focused on holographic polymer dispersed liquid crystal (H-PDLC) gratings with demonstrated applications in switching, lasing, and display devices. Here, we present the application of porous polymer photonic bandgap structures produced using a modified holographic method that includes a solvent as a phase separation fluid. The resulting gratings are simple to fabricate, stable, tunable, and highly versatile. Moreover, these acrylate porous polymer photonic bandgap structures were generated using a simple one-beam setup. In this paper, we describe the application of these nanoporous polymer gratings as a general template for biochemical recognition elements. As a prototype, we developed an oxygen (O2) sensor by encapsulating the fluorophore (tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) within these nanostructured materials. Thus, the obtained O2 sensors performed through the full-scale range (0%-100%) with a response time of less than 1 second. Most importantly, the use of the inherent property of these gratings to transmit or reflect a particular wavelength spectrum, based on the grating spacing, enables us to selectively enhance the detection efficiency for the wavelengths of interest.
This presentation focuses on the synthesis and characterization of luminescent silicon nanoparticles that have potential as components of hybrid inorganic/organic materials for photonic and biophotonic applications. In our lab, silicon nanoparticles with bright visible photoluminescence are being prepared by a new combined vapor-phase and solution-phase process, using only inexpensive commodity chemicals. CO2 laser-induced pyrolysis of silane is used to produce Si nanoparticles at high rates (20 to 200 mg/hour). Particles with an average diameter as small as 5 nm can be prepared directly by this method. Etching these particles with mixtures of hydrofluoric acid (HF) and nitric acid (HNO3) reduces the size and passivates the surface of these particles such that they exhibit bright visible luminescence at room temperature. The wavelength of maximum photoluminescence (PL) intensity can be controlled from above 800 nm to below 500 nm by controlling the etching time and conditions. Particles with blue and green emission are prepared by rapid thermal oxidation of orange-emitting particles. These particles have exciting potential applications in optoelectronics, display technology, chemical sensing, biological imaging, and other areas. The availability of relatively large quantities of these particles is allowing us to begin to functionalize particles for these applications, as well as to study the optical, electronic, and surface chemical properties of them. All of these potential applications require inorganic/organic hybrid materials, in the sense that the nanoparticles must have their surfaces coated with organic molecules that mediate the interaction of the particles with the polymeric or biological host matrix. The particle synthesis methods, photoluminescence measurements on the particles, the stability of the photoluminescence properties with time, chemical quenching of photoluminescence, and functionalization of the particles for incorporation into different organic matrices or for specific interaction with small molecules or biomolecules are
discussed in the context of applications to photonics and biophotonics.
Optical properties of silicon and indium phosphide nanoparticles with emission throughout the visible wavelength range are presented. The peak emission wavelength of these nanoparticles is controlled by the reaction time and by post-growth etching treatments. Ultrafast spectroscopy is used to determine the photoluminescence lifetime in order to correlate the spectral response with the structural and chemical characterization of these nanoparticles. The measured lifetimes are used to identify surfactant, surface, and core nanoparticle emission. The nanoparticles exhibit efficient emission that is quenched when embedded within particular polymeric matrices.