Internally amplified stimulated Raman spectroscopy

Internally amplified stimulated Raman scattering is developed as a novel approach to study concentrational thresholds in stimulated Raman scattering (SRS). In the proposed physical model, amplifier molecules are used to bridge the spatial gaps among analyte molecules distributed distantly from each other throughout a dilute solution. As a result, Stokes photons can more effectively reach the next target molecules down the pump light path to sustain and amplify the desirable SRS process. The model has been verified by experimental results which give a better understanding of the threshold phenomenon in SRS. The technique of internal amplification is practically useful to lower concentrational thresholds, leading to improved detection limits in analytical SRS measurements.     

Activatable imaging probes with amplified fluorescent signals

Current optical imaging probe applications are hampered by poor sensitivity and specificity to the target, but molecular-level fluorescent signal activation strategies can efficiently overcome these limitations. Recent interdisciplinary research that couples the imaging sciences to fluorophore, peptide, polymer, and inorganic-based chemistry has generated novel imaging probes that exhibit high sensitivity and low background noise in both in vitro and in vivo applications. This feature article introduces and discusses the various approaches described by the term "fluorescent signal activation methods" with respect to their unique imaging probe design strategies and applications.     

On collision-induced amplified emission of alkali atoms

The recently discovered amplified emission of alkali atoms resonantly excited to theP _3/2 state by intense laser beam is analyzed theoretically. This effect is caused essentially by collisions with buffer gas atoms building up a population inversion of theP _1/2 state with respect to theS _1/2 ground state. Our theoretical calculations based on dressed-atom density matrix analysis agree with most experimental results.     

Methacrylic silicon-containing tercopolymers for chemically amplified resists

Tercopolymers of methyl methacrylate with methacrylic acid and dimethylphenyl (methyldiphenyl)silyl methacrylates are synthesized and investigated as components of chemically amplified resistive formulations with sulfonium and iodonium salts as photoacid generators for UV lithography in the 254-nm range. The surface behavior and the kinetics of dissolution of resistive films in an aqueous solution of tetraethylammonium hydroxide in relation to the concentration of onium salts and the temperatures of postapply and postexposure bakes are studied. The introduction of sulfonium salt into the resistive formulation brings about an increase in the solubility of unexposed films, thereby erasing the difference in dissolution rates of exposed and unexposed areas of a resist and preventing image formation. The iodonium salt plays the role of an inhibitor for dissolution of unexposed films of both copolymers, which makes it possible to obtain a high-contrast positive image in resists.     

Studies of the chemically amplified development-free vapor photolithography

Development-free vapor photolithography (DFVP) is a unique all-dry pattern transfer technique, which is based on the reaction of SiO₂ with HF vapor under a polymer film in the presence of accelerators at a temperature of above 100°C. In this paper, we found that the etching reaction could be catalyzed by superacids. Based on this discovery, a novel, chemically amplified, development-free vapor photolithography technique was developed, and has benn successfully applied to power electronic device manufacture.     

A cationic tetrahedral chromophore for amplified DNA detection

The tetrahedral cationic chromophore, tetrakis [4-(9,9-bis(6′-(N,N,N-trimethylammonium)hexyl)-2-fluorenyl)phenyl]methane (1) shows better fluorescence resonance energy transfer (FRET) to the fluorescein (Fl) attached to the 5′-terminus of double-stranded DNA (dsDNA-Fl) as compared to the linear oligomers 2 and 3 and also provides efficient DNA hybridization detection.     

Complexation amplified pH oscillation in metal involved systems

A novel mechanism of amplifying pH oscillations by pH-dependent EDTA-metal ion complexation is proposed. If there is a metal ion involved in the H(+) consuming reactions in the pH oscillator and the metal's complex formation constant is big enough, the nonlinear coupling of the original oscillator with the complexation induced metal ion oscillation can finally amplify the pH oscillation. This effect is demonstrated in H(2)O(2)-S(2)O(3)(2-)-Cu(2+) system and further discussed in three other systems. Since pH oscillation is widely used in many areas as a spontaneous periodical driving force at the molecular level, this work may help to broaden the driving range of pH oscillators.     

Tunable amplified spontaneous emissions by dimensional-controlled microcrystal synthesis

One-dimensional (1D) microwires and 2D microdisks of DMF-HPPO have been selectively prepared by controlling the solution polarity. Tunable amplified spontaneous emissions are achieved and 1D microwire demonstrates sharp splitting photoluminescence peaks around 618 nm, while 2D microdisk shows a red-shifted emission central at 650 nm.     

Solid-supported single- and multi-enzyme amplified assays for clostridiopeptidase A

A rapid and sensitive spectrophotometric assay for Clostridium histolyticum clostridiopeptidase A (collagenase) was accomplished by measuring the activity of an alkaline phosphatase indicator enzyme released into solution from insoluble, covalently linked alkaline phosphatase indicator enzyme released into solution from activity of the alkaline phosphatase was monitored spectrophotometrically using either p-nitrophenyl phosphate as substrate or more sensitively by a signal amplification system consisting of NAD⁺, alcohol dehydrogenase, diaphorase and INT-Violet. Under the reaction conditions the amount of indicator enzyme produced is directly proportional to the concentration of collagenase. With p-nitrophenyl phosphate as substrate the magnitude of the signal was 0.003 abs. min^?1 per 100 ng ml^?1 collagenase whereas with the multienzyme amplification system it was 0.035 abs. min^?1, i.e. approximately as 12-fold increase. The method consists in first incubating the substrate with the bacterial collagenase for 20 min, then up to 96 samples of the released alkaline phosphatase can be analysed in 2 min using a microtitre plate reader run in the kinetic mode.     

Observation of collision-induced amplified emission in Na-noble gas system

A stimulated resonance emission and stimulated Raman scattering signals have been generated in an atomic sodium and rare gas mixture by a laser tuned to the 3² S_1/2-3² P_3/2 transition. The intensity dependence of these effects on the buffer gas pressures is obtained in the experiment. We demonstrate good qualitative agreement between experimental observations and a simple theoretical model. A new method using stimulated emission is applied to measure the cross section for the J mixing of 3P states of sodium due to collisions with noble gas atoms. Good agreement between our results and the measurements of Pitre and Krause is obtained for Ar and Kr perturbers     

Quantification of amplified quenching for conjugated polymer microsphere systems

A series of nonaggregating carboxylate-functionalized poly(phenylene ethynylene)s (PPEs) have been synthesized for immobilization via electrostatic adsorption onto Eu3+-polystyrene microspheres with a mean diameter of 0.2 microm. This system is shown to constitute a ratiometric system that measures fluorescence quenching with high fidelity. The fluorescence quenching properties of the polymer-coated particles in response to methyl viologen and a naphthyl-functionalized viologen have been investigated in aqueous solutions to study the influence of electrostatic and hydrophobic interactions with pentiptycene-incorporated as well as macrocycle-containing polymers.     

Aggregation-induced amplified quenching in conjugated polyelectrolytes with interrupted conjugation

A pair of anionic conjugated polyelectrolytes that contain three-ring (phenylene ethynylene) units linked by a single -CH(2)- or -O- tether (P1 and P2, respectively) are studied. The linkers serve to interrupt the π conjugation along the polymer backbone. Fluorescence spectroscopy reveals that P2 forms a fluorescent aggregate in methanol and water; however, the fluorescence of P1 is much weaker in water, and P1 exhibits only weak aggregate fluorescence. Fluorescence quenching of the polymers was examined using methyl viologen (MV(2+)) as a cationic quencher. P1 shows only a weak amplified quenching effect, with a Stern-Volmer quenching constant of K(SV) ≈ 6 × 10(5) M(-1) in methanol. Interestingly, for P2 in methanol, the aggregate emission is strongly quenched with K(SV) ≈ 5 × 10(6) M(-1), which is comparable to the highest quenching efficiency observed for fully π-conjugated polyelectrolytes. By contrast, the monomer emission is quenched much less efficiently, with K(SV) ≈ 2 × 10(5) M(-1). The results are explained by a model in which -O- linked polymer P2 is able to fold into a helical conformation in solution, which facilitates the formation of extended π-stacked aggregates allowing long-distance exciton transport.     

Optical modulation of amplified emission in a polyfluorene-diarylethene blend

A novel system for the modulation of amplified emission based on a polyfluorene/diarylethene (namely F8BT/DTP) blend is shown. The high sensitivity of amplified spontaneous emission (ASE) is exploited to achieve efficient emission modulation with a low-intensity control signal. Modulation is then characterized by photoluminescence (PL) lifetime measurements, photocurrent experiments, and density functional theory calculations. This system can also act as a photocurrent switch based on the same principle. This technique may represent a useful tool for fluorescence quenching and sensing as well as find application in organic photonics.     

Formation of deprotected fuzzy blobs in chemically amplified resists

The requirement of nanometer dimensional control in photolithographic patterning underlies the future of emerging technologies, including next-generation semiconductors, nanofluids, photonics, and microelectromechanical systems. For chemically amplified resists, dimensional control is mediated by the diffusion and reaction of photogenerated acids within a polymer-based photoresist matrix. The complex nature of the combined processes of reaction and diffusion prohibit the routine measurement of this phenomenon. Using small-angle neutron scattering, we have measured the form of the diffusion–reaction path of a photogenerated acid within a model photoresist matrix with a labeled protection group on the polymer side group. During the deprotection reaction, changes in the scattering form factor result from the shape and form of the deprotected regions. The individual volumes or blobs of reacted material are diffuse, with a fuzzy boundary between the reacted and unreacted regions. The impact of these results on the pattern quality is also discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3063–3069, 2004     

Aptamer-functionalized Au nanoparticles for the amplified optical detection of thrombin

The catalytic enlargement of aptamer-functionalized Au nanoparticles amplifies the optical detection of aptamer-thrombin complexes in solution and on surfaces.