Larry D. Stephenson

Silicon nanoparticle-functionalized fiberglass pads for sampling

We used wet treatment to immobilize luminescent silicon nanoparticles on industrial glass fibers to impart optical and chemical functions to the fiber. Carpets or pads consisting of thousands of fibers are processed in parallel, enhancing the sensitivity of detection and the sampled volume. Treated pads exhibit strong luminescence, characteristic of the luminescence of the particles; showing no shift, broadening, or reduction of quantum efficiency. We demonstrate that drawing material by the pad due to physical adsorption can be reversed. We also demonstrate that allylamine can be covalently attached by photoinduced irradiation reactions, which results in imprinting the amine emission spectrum, providing spectral recognition. The imprint accompanied with a blue-shifting of the luminescence spectrum of the probe, allowing examination of the effect of termination on the nanoparticle structure. The shift is found to be consistent with an increase in the bandgap of the Si nanoparticle and is consistent with Q...

Measurement of the photostability of silicon nanoparticles under UVA and near infrared irradiation

We examine the photostability of silicon nanoparticles when they are dispersed in liquid or immobilized in gels or on surfaces. We show that the photoluminescence in static solution develops, under UV irradiation, a long-term stability at the 50% level. Under the same conditions, common dye molecules such as coumarin and stilbene quench with time at rates 8 and 50 fold faster, and exhibit no long-term stability. For the case of immobilized particles in agarose gel as well as on a quartz substrate we used two-photon near infrared femtosecond excitation at 780 nm to induce the blue luminescence. “Parking” the excitation beam, focused on such stationery particles shows that they, unlike similarly immobilized dye molecules, are highly photostable at more than 80%–90% level and do not bleach. The photostability is discussed in terms of excited state interactions and structuring of the silicon outer shell.

Accelerated long-term assessment of thermal and chemical stability of bio-based phase change materials

Thermal energy storage systems incorporated with phase change materials have potential applications to control energy use by building envelopes. However, it is essential to evaluate long-term performance of the phase change materials and cost-effectiveness prior to full-scale implementation. For this reason, we have used the accelerated long-term approach for studying the thermal performance and chemical stability of a commercially available bio-based phase change material during thermal cycling over a simulated period of 20 years. The phase change material was subjected to accelerate thermal aging under controlled environmental conditions. Small samples of the phase change material were periodically removed to measure its latent heat, thermal decomposition, and chemical stability using various analytical methods such as differential scanning calorimetry, thermogravimetry analysis, and infrared spectroscopy. The topographic changes in the phase change material due to the aging process were observed using scanning electron microscopy. The differential scanning calorimetry data indicate a significant reduction of 12% in the latent heat during heating and cooling cycles during the initial 6.2 years remain nearly constant thereafter. The thermogravimetry analysis results showed that the phase change material has excellent thermal stability within the working temperature range and also shows long-term decomposition temperature stability. The Fourier transform infrared spectra of the phase change material indicate absorption of moisture but the phase change material was chemically stable over the duration of accelerated aging cycles. After several aging cycles, the baseline surface morphology appeared to be changed from uniform mix of phase change material with microstructures to segregated microstructures as evidenced by the observation of the scanning electron micrographs.

Detection of liposome lysis utilizing an enzyme-substrate system.

A novel optical reporter system was developed to verify encapsulation and subsequent release of a foreign molecule in liposomes. The protocol utilizes a single enzyme and substrate. We encapsulate o-nitrophenyl-β,d-galactopyranoside (ONPG) and measure its release by detecting the levels of o-nitrophenol created when the encapsulated ONPG is released and hydrolyzed by β-galactosidase. Using this method, liposome formation and subsequent lysis with Triton X-100 were verified. This new protocol eliminates the complications of multiple reaction enzyme detection methods, along with the chance for false negatives and unreliable data seen when using fluorescent particles as reporters.