Continuous-flow photochemistry in microreactors receives a lot of attention from researchers in academia and industry as this technology provides reduced reaction times, higher selectivities, straightforward scalability, and the possibility to safely use hazardous intermediates and gaseous reactants. In this review, an up-to-date overview is given of photochemical transformations in continuous-flow reactors, including applications in organic synthesis, material science, and water treatment. In addition, the advantages of continuous-flow photochemistry are pointed out and a thorough comparison with batch processing is presented.

Applications of Continuous-Flow Photochemistry in Organic Synthesis, Material Science, and Water Treatment

Optofluidics - the synergistic integration of photonics and microfluidics - has recently emerged as a new analytical field that provides a number of unique characteristics for enhanced sensing performance and simplification of microsystems. In this review, we describe various optofluidic architectures developed in the past five years, emphasize the mechanisms by which optofluidics enhances bio/chemical analysis capabilities, including sensing and the precise control of biological micro/nanoparticles, and envision new research directions to which optofluidics leads.

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Optofluidic microsystems for chemical and biological analysis

In order to enable optical systems to operate with a high degree of compactness and reliability it is necessary to combine large number of optical functions in small monolithic structures. A development, somewhat reminiscent of that that took place in Integrated Electronics, is now beginning to take place in optics. The initial challenge in this emerging field, known appropriately as "Integrated Optics", is to demonstrate the possibility of performing basic optical functions such as light generation, coupling, modulation, and guiding in Integrated Optical configurations. The talk will review the main theoretical and experimental developments to date in Integrated Optics. Specific topics to be discussed include: Material considerations, guiding mechanisms, modulation, coupling and mode losses. The fabrication and applications of periodic thin film structures will be discussed.

Integrated optics

Inorganic semiconductor nanostructures are ideal systems for exploring a large number of novel phenomena at the nanoscale and investigating the size and dimensionality dependence of their properties for potential applications. The use of such nanostructures with tailored geometries as building blocks is also expected to play crucial roles in future nanodevices. Since the discovery of carbon nanotubes much attention has been paid to exploring the usage of inorganic semiconductor nanostructures as field-emitters due to their low work functions, high aspect ratios and mechanical stabilities, and high electrical and thermal conductivities. This article provides a comprehensive review of the state-of-the-art research activities in the field. It mainly focuses on the most widely studied inorganic nanostructures, such as ZnO, ZnS, Si, WO3, AlN, SiC, and their field-emission properties. We begin with a survey of inorganic semiconductor nanostructures and the field-emission principle, and then discuss the recent progresses on several kinds of important nanostructures and their field-emission characteristics in detail and overview some additional inorganic semiconducting nanomaterials in short. Finally, we conclude this review with some perspectives and outlook on the future developments in this area.

Inorganic semiconductor nanostructures and their field-emission applications

Organic dyes have been used as gain medium for lasers since the 1960s, long before the advent of today’s organic electronic devices. Organic gain materials are highly attractive for lasing due to their chemical tunability and large stimulated emission cross section. While the traditional dye laser has been largely replaced by solid-state lasers, a number of new and miniaturized organic lasers have emerged that hold great potential for lab-on-chip applications, biointegration, low-cost sensing and related areas, which benefit from the unique properties of organic gain materials. On the fundamental level, these include high exciton binding energy, low refractive index (compared to inorganic semiconductors), and ease of spectral and chemical tuning. On a technological level, mechanical flexibility and compatibility with simple processing techniques such as printing, roll-to-roll, self-assembly, and soft-lithography are most relevant. Here, the authors provide a comprehensive review of the developments in the...

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Organic Lasers: Recent Developments on Materials, Device Geometries, and Fabrication Techniques

This letter reports the measurement of single living cells’ refractive index (RI) using an on-chip fiber-based Fabry-Perot cavity by a differential method. In experiment a single cell is captured into the cavity, then the spectral shift in response to the buffer change and the cell presence/absence can be used to determine the cell’s RI and size. Experiment on kidney cancer cells measures an effective RI of 1.399 at 0.1% accuracy. Compared with other approaches, the differential method eliminates uncertain factors and thus ensures high accuracy. The microchip facilitates automatic detection and makes it promising for label-free drug screening.

https://nocweba.ntu.edu.sg/laq_mems/journal%20papers/2006/Refractive%20index%20measurement%20of%20single%20living%20cells%20using%20on-chip%20Fabry-Perot%20cavity.pdf

Refractive index measurement of single living cells using on-chip Fabry-Pérot cavity

This paper reports experimental studies using the photoelectrocatalytic effect to eliminate a fundamental limit of photocatalysis – the recombination of photo-excited electrons and holes. The fabricated reactor has a planar reaction chamber (10 × 10 × 0.1 mm3), formed by a blank indium tin oxide glass slide, an epoxy spacer and a BiVO4-coated indium tin oxide glass substrate. A blue light-emitting diode panel (emission area 10 × 10 mm2) is mounted on the cover for uniform illumination of the reaction chamber. In the experiment, positive and negative bias potentials were applied across the reaction chamber to suppress the electron/hole recombination and to select either the hole-driven or electron-driven oxidation pathway. The negative bias always exhibits higher performance. It is observed that under −1.8 V the degradation rate is independent of the residence time, showing that the accompanying electrolysis can solve the oxygen deficiency problem. The synergistic effect of photocatalysis and electrocatalysis is observed to reach its maximum under the bias potential of ± 1.5 V. The photoelectrocatalytic microreactor shows high stability and may be scaled up for high-performance water purification.

Microfluidic photoelectrocatalytic reactors for water purification with an integrated visible-light source

We demonstrate an optofluidic evanescent laser based on a solid circular distributed feedback grating with the dye solution acting as the cladding layer. The laser mode is confined within the grating and experiences optical gain via the interaction between its evanescent component with the dye solution. Above a pump energy of 9.5 µJ/pulse, the laser exhibited single mode operation at 571 nm. Stable, narrow-linewidth emission was observed for a wide range of fluid refractive indices, even for those lower than of polydimethylsiloxane. We attribute this property to the evanescent coupling of the laser mode with the fluidic gain

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Optofluidic evanescent dye laser based on a distributed feedback circular grating

We report the demonstration of low order distributed feedback (DFB) optofluidic dye lasers with reduced threshold. The laser chips were realized in polydimethylsiloxane using replica molding with two masters. A comparison between first, second, and third order DFB dye lasers was performed, while the second order DFB dye laser exhibited the lowest pump threshold of 78 nJ/pulse. Compared to previous reports on higher order Bragg grating structures, the pump threshold in this work is approximately 30-fold lower than the state of the art due to the reduction in the cavity losses and the more efficient pumping configuration.

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Low-order distributed feedback optofluidic dye laser with reduced threshold

Optical trapping using plasmonic nanoapertures has proven to be an effective means for the contactless manipulation of nanometer-sized particles under low optical intensities. These particles have included polystyrene and silica nanospheres, proteins, coated quantum dots and magnetic nanoparticles. Here we employ fluorescence microscopy to directly observe the optical trapping process, tracking the position of a polystyrene nanosphere (20 nm diameter) trapped in water by a double nanohole (DNH) aperture in a gold film. We show that position distribution in the plane of the film has an elliptical shape. Comprehensive simulations are performed to gain insight into the trapping process, including of the distributions of the electric field, temperature, fluid velocity, optical force, and potential energy. These simulations are combined with stochastic Brownian diffusion to directly model the dynamics of the trapping process, that is, particle trajectories. We anticipate that the combination of direct particle...

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Wuzhou Song

Papers

Refractive index measurement of single living cells using on-chip Fabry-Pérot cavity

Microfluidic photoelectrocatalytic reactors for water purification with an integrated visible-light source

Optofluidic evanescent dye laser based on a distributed feedback circular grating

Low-order distributed feedback optofluidic dye laser with reduced threshold

Direct Particle Tracking Observation and Brownian Dynamics Simulations of a Single Nanoparticle Optically Trapped by a Plasmonic Nanoaperture