Photonic crystal cavity-enhanced emission from silicon vacancy centers in polycrystalline diamond achieved without postfabrication fine-tuning.

Diamond optical centers have recently emerged as promising single-photon sources for quantum photonics. Particularly, negatively charged silicon vacancy (SiV-) centers show great promise due to their narrow zero-phonon emission line present also at room temperature. However, due to fabrication tolerances it is challenging to prepare directly photonic structures with optical modes spectrally matching the emission of SiV- centers. To reach the spectral overlap, photonic structures must typically undergo complicated post-processing treatment. In this work, suspended photonic crystal cavities made of polycrystalline diamond are engineered and more than 2.5-fold enhancement of the SiV- center zero-phonon line intensity via coupling to the cavity photonic mode is demonstrated. The intrinsic non-homogeneous thickness of the diamond thin layer within the sample is taken as an advantage that enables reaching the spectral overlap between the emission from SiV- centers and the cavity modes without any post-processing. Even with lower optical quality compared to monocrystalline diamond, the fabricated photonic structures show comparable efficiency for intensity enhancement. Therefore, the results of this work may open up a promising route for the application of polycrystalline diamond in photonics.

Determination of 1-methylhistidine and 3-methylhistidine by capillary and chip electrophoresis with contactless conductivity detection.

CE with capacitively coupled contactless detection (C4D) was used to determine 3-methylhistidine (3-MH) and 1-methylhistidine (1-MH). The C4D response to 3-MH was studied in a BGE consisting of 500 mM acetic acid and ammonia at varying concentration and the results were compared with the theory. Complete separation of a model mixture of 3-MH, 1-MH, and histidine (His) was attained in two optimized BGEs, one containing 500 mM HAc, 20 mM NH4OH, and 0.1 % m/v hydroxyethylcellulose (HEC), pH 3.4 (I) and the other consisting of 100 mM morpholinoethanesulfonic acid (MES), 25 mM LiOH, and 0.1 % m/v HEC, pH 5.5 (II). These optimized BGEs were tested in CE/C4D analyses of urine. Promising results were obtained for separation and determination of 3-MH, 1-MH, and His on a silicon microchip, using aluminum strips as the C4D electrodes; the three analytes were baseline-separated within less than 30 s with a separation channel effective length of 38 mm. The LOD were satisfactory and amounted to 26.4 microM for 3-MH and 18.3 microM for 1-MH.

Fabrication of poly(methyl methacrylate) microfluidic chips by atmospheric molding.

A greatly simplified method for fabricating poly(methyl methacrylate) (PMMA) separation microchips is introduced. The new protocol relies on UV-initiated polymerization of the monomer solution in an open mold under ambient pressure. Silicon microstructures are transferred to the polymer substrate by molding a methyl methacrylate solution in a sandwich (silicon master/Teflon spacer/glass plate) mold. The chips are subsequently assembled by thermal sealing of the channel and cover plates. The new fabrication method obviates the need for specialized replication equipment and reduces the complexity of prototyping and manufacturing. Variables of the fabrication process were assessed and optimized. The new method compares favorably with common fabrication techniques, yielding high-quality devices with well-defined channel and injection-cross structures, and highly smoothed surfaces. Nearly 100 PMMA chips were replicated using a single silicon master, with high chip-to-chip reproducibility (relative standard deviations of 1.5 and 4.7% for the widths and depths of the replicated channels, respectively). The relatively high EOF value of the new chips (2.12 x 10(-4) cm(2) x V(-1) x s(-1)) indicates that the UV polymerization process increases the surface charge and hence enhances the fluidic transport. The attractive performance of the new CE microchips has been demonstrated in connection with end-column amperometric and contactless-conductivity detection schemes. While the new approach is demonstrated in connection with PMMA microchips, it could be applied to other materials that undergo light-initiated polymerization. The new approach brings significant simplification of the process of fabricating PMMA devices and should lead to a widespread low-cost production of high-quality separation microchips.