No abstract

Near-infrared (NIR) light-triggered release from polymeric capsules could make a major impact on biological research by enabling remote and spatiotemporal control over the release of encapsulated cargo. The few existing mechanisms for NIR-triggered release have not been widely applied because they require custom synthesis of designer polymers, high-powered lasers to drive inefficient two-photon processes, and/or coencapsulation of bulky inorganic particles. In search of a simpler mechanism, we found that exposure to laser light resonant with the vibrational absorption of water (980 nm) in the NIR region can induce release of payloads encapsulated in particles made from inherently non-photo-responsive polymers. We hypothesize that confined water pockets present in hydrated polymer particles absorb electromagnetic energy and transfer it to the polymer matrix, inducing a thermal phase change. In this study, we show that this simple and highly universal strategy enables instantaneous and controlled release of payloads in aqueous environments as well as in living cells using both pulsed and continuous wavelength lasers without significant heating of the surrounding aqueous solution.

An activation mechanism based on encapsulated ultra-small gadolinium oxide nanoparticles (Gd oxide NPs) in bioresponsive polymer capsules capable of triggered release in response to chemical markers of disease (i.e., acidic pH, H2O2) is presented. Inside the hydrophobic polymeric matrices, the Gd oxide NPs are shielded from the aqueous environment, silencing their ability to enhance water proton relaxation. Upon disassembly of the polymeric particles, activation of multiple contrast agents generates a strong positive contrast enhancement of more than one order of magnitude.

This paper reports the development of spherical Ag@SiO 2 nanocomposites in which fluorescein isothiocyanate molecules have been incorporated using a silane coupling agent and a straightforward microemulsion-based synthesis procedure. The photophysical characteristics of core-shell and coreless nanostructures with similar silica shell thickness and fluorophore densities are measured and compared, and show unequivocally that the presence of the silver core decreases the fluorophore lifetime by a factor as high as 4 and that the steady-state fluorescence intensity is increased by a factor as high as 3. The relationship between the enhancement in fluorescence yield and the influence of the silver core on resonance energy transfer processes was examined by fluorescence lifetime and anisotropy measurements. These Ag@SiO 2 core-shell nanoparticles provide higher detectability and lower self-quenching, whereas the faster recycling time offers more robustness toward photobleaching.

The influence of metallic silver nanoparticles on F€ orster resonance energy transfer (FRET) between a watersoluble cationic conjugated polymer and fluorescent multilayer Ag@SiO 2 @SiO 2 þFiTC core-shell nanoparticles was characterized using a combination of light scattering and luminescence techniques. Positioning the fluorescent polymer 7 nm away from the surface of a 45 nm silver nanoparticle with a silica spacing layer increases its quantum yield to 77%, as compared to 3% when measured as an isolated emitter. In the presence of the metallic core, the luminescence of the nanoparticle-bound acceptor fluorophore is increased at the expense of the polymer donor luminescence, and time-resolved fluorescence measurements indicate an enhancement of FRET efficiency from 4 to 50%, an increase in the F€ orster distance from 50 to 85 Å, and a resonant transfer rate between donors and acceptors more than 2 orders of magnitude higher than that measured in the absence of the metal core. The strong influence of plasmonic coupling in these multilayer nanocomposites offers great potential for signal amplification schemes in polymer-based and FRET-based biosensors.

This study describes the preparation and characterization of a DNA sensing architecture combining the molecular recognition capabilities of a cationic conjugated polymer transducer with highly fluorescent core-shell nanoparticles (NPs). The very structure of the probe-labeled NPs and the polymer-induced formation of NP aggregates maximize the proximity between the polymer donor and acceptor NPs that is required for optimal resonant energy transfer. Each hybridization event is signaled by a potentially large number of excited reporters following the efficient plasmon-enhanced energy transfer between target-activated polymer transducer and fluorophores located in the self-assembled core-shell aggregates, resulting in direct molecular detection of target nucleic acids at femtomolar concentrations.

Controlling chemistry in space and time has offered scientists and engineers powerful tools for research and technology. For example, on-demand photo-triggered activation of neurotransmitters has revolutionized neuroscience. Non-invasive control of the availability of bioactive molecules in living organisms will undoubtedly lead to major advances; however, this requires the development of photosystems that efficiently respond to regions of the electromagnetic spectrum that innocuously penetrate tissue. To this end, we have developed a polymer that photochemically degrades upon absorption of one photon of visible light and demonstrated its potential for medical applications. Particles formulated from this polymer release molecular cargo in vitro and in vivo upon irradiation with blue visible light through a photoexpansile swelling mechanism.

Inspired by the spontaneous cyclization of ornithine in peptides, polyesters containing protected ornithine (Orn) side chains along the backbone were synthesized and shown to degrade rapidly upon deprotection through intramolecular cyclization. A new ornithine-based poly(ester amide) PEA 1 and a lysine-based control PEA 2, both bearing the light-sensitive protecting group o-nitrobenzyl alcohol (ONB), were synthesized. Tert-butyl carbamate (Boc)-protected versions 1-Boc and 2-Boc were also synthesized for proof of concept. GPC confirmed that 1-Boc degrades over 40 times faster than 2-Boc following deprotection into the designed intramolecular cyclization products. Finally, TEM visualization of particles made from 1 encapsulating iron oxide nanoparticles reveals complete disruption of nanoparticles and release of payload within a day upon UV irradiation.