Conventional Quenchers Research Articles

Galactose-Functionalized, Colloidal-Fluorescent Nanoparticle from Aggregation-Induced Emission Active Molecule via Polydopamine Coating for Cancer Cell Targeting

Aggregation-induced emission (AIE) active molecules emerge as new generation fluorescent probes, and their transformation to functional nanoparticle can greatly extend the application potential. Here we report an approach for transforming AIE active tetraphenylethene (TPE) molecule to galactose-functionalized colloidal nanoparticle that can be used for targeting/labeling of cancer cells. The approach involves polydopamine coating around aggregated TPE or TPE–chitosan conjugate followed by covalent linking with thiolated galactose. Resultant nanoparticles have 50–200 nm hydrodynamic size with good colloidal stability at physiological condition and 6–12% fluorescence quantum yield, and they selectively label cells with overexpressed galactose receptors. The unique advantage of this nanoprobe is that fluorescence remains intact in the presence of conventional quenchers. This approach may be extended for making AIE-active molecule-based various functional nanoprobes.

Shot noise limit of chemically amplified resists with photodecomposable quenchers used for extreme ultraviolet lithography

In lithography using high-energy photons such as an extreme ultraviolet (EUV) radiation, the shot noise of photons is a critical issue. The shot noise is a cause of line edge/width roughness (LER/LWR) and stochastic defect generation and limits the resist performance. In this study, the effects of photodecomposable quenchers were investigated from the viewpoint of the shot noise limit. The latent images of line-and-space patterns with 11 nm half-pitch were calculated using a Monte Carlo method. In the simulation, the effect of secondary electron blur was eliminated to clarify the shot noise limits regarding stochastic phenomena such as LER. The shot noise limit for chemically amplified resists with acid generators and photodecomposable quenchers was approximately the same as that for chemically amplified resists with acid generators and conventional quenchers when the total sensitizer concentration was the same. The effect of photodecomposable quenchers on the shot noise limit was essentially the same as that of acid generators.

Theoretical study on effects of photodecomposable quenchers in line-and-space pattern fabrication with 7 nm quarter-pitch using chemically amplified electron beam resist process

The line width roughness (LWR) is a significant issue in the development of chemically amplified resists. The increase in sensitizer concentration is inevitable for the suppression of LWR in the sub-10 nm fabrication. In this study, we investigated the effects of photodecomposable quenchers from the viewpoint of the excluded volume effect, assuming line-and-space patterns with 7 nm quarter-pitch (7 nm space width and 28 nm pitch). The pattern formation of chemically amplified electron beam resists with photodecomposable quenchers was calculated and compared with those with conventional quenchers. It was found that the sum of the concentrations of acid generators and quenchers (photodecomposable or conventional quenchers) can be reduced without decreasing the chemical gradient (an indicator of LWR) by using the photodecomposable quenchers. The photodecomposable quenchers are considered essential in the high-resolution fabrication.

Conformational studies on δ-crystallin, the core protein of the bird eye lens

Proteins that perform other functions elsewhere appear to be recruited for structural purposes in the eye lens. The lens being a tissue with very little metabolic activity and little or no turnover, the lens proteins, crystallins, are long lived. In an effort to understand whether their recruitment might be related to their conformation and structural stability, we have examined these features of the avian lens protein δ-crystallin. The native molecule is a tetramer (molecular mass 200 kDa) that is highly α-helical in conformation, and with an unusually blue tryptophan fluorescence (315,325 nm), which is only partially quenched by conventional quenchers. We show that the fluorescence doublet arises due to Trp residues that are effectively buried inside the rigid hydrophobic core of the tetrameric aggregate. The protein is heat stable up to 91°C. Guanidinium chloride (GuHCl) effects the complete denaturation of δ-crystallin, whereas heat or urea treatment results in only partial unfolding or dissociation. The initial transition is the disruption of the quaternary structure by perturbing the intersubunit interactions, leading to exposure of hydrophobic contact surfaces (as monitored by extrinsic probe fluorescence). This initial transition is seen upon heating to 60°C as well as in 1 M GuHCl and 4 M urea. We show that in 2.2 M GuHCl the molecule is swollen but is still largely helical with the Trp residues being present in a somewhat more polar environment than in the native molecule. Beyond 4 M GuHCl there is a gradual unfolding of the molecule, which is complete in 6 M GuHCl. This structural robustness of δ-crystallin might be important in its recruitment as the core protein of the avian lens.