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We conduct DNA high-resolution melting (HRM) analysis using optofluidic lasers based on a Fabry-Pérot microcavity. Compared to the fluorescence-based HRM, the laser-based HRM has advantages of higher emission intensity for better signal-to-noise ratio and sharper transition for better temperature resolution. In addition, the melting temperature can be lowered by optimizing the laser conditions such as external pump and cavity Q-factor. In this work, we first theoretically analyze the laser-based HRM. Then experiments are performed on three long DNA sequences as model systems, one being 99 bases and the other two being 130 bases long but with different GC contents. We show that the laser-based HRM is able to distinguish the target and the single-base mismatched DNA as long as 130 bases and with nearly 50% GC content. The dependence of laser threshold on the temperature for each DNA sample is first experimentally investigated and by optimizing the external pump, the melting temperature is reduced by more than 10 °C, compared to the fluorescence-based HRM for long DNA sequences up to 130 bases. Finally, we demonstrate an alternative method of using the laser-based HRM for rapid DNA screening that does not exist for the fluorescence-based HRM, in which laser excitation is scanned at a fixed temperature to distinguish the target and the base-mismatched DNA sequences. It is shown that the 130-bases-long DNA with nearly 50% GC content can have as much as 20% difference in the laser threshold and 40% difference in the laser output slope between the target and the single-base mismatched sequences, despite only 0.5 °C difference in their melting temperature, indicating that the laser-excitation-scanning method can also be suitable for long DNA sequences with higher GC content.

We report the development of an optofluidic laser array fabricated on a chip using stable plano-concave Fabry-Pérot (FP) microcavities, which are far less susceptible to optical misalignment during device assembly than the commonly used plano-plano FP microcavities. The concave mirrors in our FP microcavities were created by first generating an array of microwells of a few micrometers in depth and a few tens of micrometers in diameter on a fused silica chip using a CO2 laser, followed by coating of distributed Bragg reflection (DBR) layers. The plano-concave FP microcavity had a Q-factor of 5.6 × 10(5) and finesse of 4 × 10(3), over 100 times higher than those for the FP microcavities in existing optofluidic lasers. 1 mM R6G dye in ethanol was used to test the plano-concave FP microcavities, showing an ultralow lasing threshold of only 90 nJ mm(-2), over 10 times lower than that in the corresponding unstable plano-plano FP microcavities formed by the same DBR coatings on the same chip. Simultaneous laser emission from the optofluidic laser array on the chip and single-mode lasing operation were also demonstrated. Our work will lead to the development of optofluidic laser-based biochemical sensors and novel on-chip photonic devices with extremely low lasing thresholds (nJ mm(-2)) and mode volumes (fL).

In article number 1805553, Yanxia Cui, Shengzhong Liu, and co‐workers report a record‐low‐threshold laser based on atomically smooth triangular nanoplatelet perovskite. Such perovskite nanoplatelets are obtained by fabricating atomically smooth PbI2 nanoplates and converting them to atomically smooth perovskites. The laser emissions have record‐low‐thresholds and high‐quality factors, thus making the scheme suitable for implementation of semiconductor nano‐lasers in a wide range of applications. [ABSTRACT FROM AUTHOR]

Single‐crystalline perovskites are ideal candidates for lasing and other optoelectronic applications. Although significant efforts have been made to grow both bulk single‐crystalline perovskites in liquid solution, their dimensions are still too large to make nanoscale whispering‐gallery‐mode (WGM) resonator based lasers that possess high quality (Q) factor and small volume. Besides, most reported perovskite resonators do not possess atomically smooth surfaces and facets, which limits the Q and thereby increases the lasing threshold. Here, atomically smooth triangular PbI2 templates are fabricated on a mica substrate by the vapor phase deposition method and are converted to atomically smooth perovskites which have regular and unwrinkled facets with average surface roughness less than 2 nm. By using a CH3NH3PbI3 nanoplatelet with a side length of 27 µm and thickness of 80 nm, room temperature WGM lasing with a Q up to 2600 is demonstrated, the highest reported for hybrid organic–inorganic perovskite nanoplatelets. In addition, the volume of the WGM mode is reduced significantly in comparison with the prior reports. The realized high‐quality triangular CH3NH3PbI3 perovskite nanoplatelets with high Q factor and small volume are expected to perform as ideal cavities for long pulse durations lasers and would find potential applications in integrated optoelectronic devices. Resonators that possess atomically smooth surfaces and facets are of critical importance for low‐threshold lasers. Here, atomically smooth CH3NH3PbI3 perovskite nanoplatelets with an average surface roughness less than 2 nm, which exhibit room temperature whispering gallery mode lasing with quality factors up to 2600, the highest reported for hybrid organic–inorganic perovskite nanoplatelets, are fabricated. [ABSTRACT FROM AUTHOR]

• Melting analysis of DNA methylation based on laser-emission in a Fabry-Pérot microcavity was proposed. • DNA molecules were distinguished by the melting temperature from the laser-based melting curves. • The method of laser slope was proposed to discriminate DNA molecules at a constant temperature. • Five mixes of methylated and non-methylated DNA samples were discriminated by the laser slope. In this paper, we first analyzed the DNA methylation by using the method of laser-based melting in a Fabry-Pérot (FP) microcavity. Pumped with an external intensity, four types of artificially synthesized DNA sequences with/without cytosine methylation in each strand were first analyzed and distinguished by the melting temperatures of the laser-based high-resolution melting (HRM) curves. Meanwhile the dependance of the laser threshold on the melting temperature for each sample was investigated; the experimental result indicates that, by optimizing the pump intensity, a lower melting temperature can be obtained for each sample. On the other hand, by setting the melting temperature at an optimized value, the samples can be distinguished by the laser behaviors above the threshold; this provides a new way for DNA analysis, and cannot be realized in the fluorescence-based melting analysis. For example, the four types of DNA samples were distinguished with an obvious difference in the laser slope coefficients when the melting temperature was set at 60 °C. Finally, five mixes of methylated and non-methylated DNAs with different mole percentages were analyzed by the laser slope coefficients. [ABSTRACT FROM AUTHOR]

In the study, we investigate the generation of optofluidic laser in stable planar-concave Fabry–Pérot (FP) microcavities. The concave mirror is created on the end-facet of a fiber using the method of CO 2 laser ablation and subsequent coating with dielectric layers. Coumarin 6 in ethanol is used as the gain solution to test the FP microcavities. For comparison, we first test the laser generation in a stable FP microcavity formed by a concave mirror on a fiber and a planar mirror on the substrate of a fused silica without cavity assembly. In this configuration, we can obtain the laser emission with an ultralow pumping energy of 25.5 μ J/ mm2 at the gain concentration of 10 μ M and a detection limit of gain solution as low as 2 μ M. Then, the generation of optofluidic laser is explored in a polymeric optofluidic chip integrated with a stable fiber FP microcavity in the format of planar-concave mirrors and a microfluidic channel. Laser results in this configuration show a laser threshold of 36.9 μ J/mm2 at the gain concentration of 10 μ M and a deduced Q-factor of 7.8 × 105 of the FP microcavity. • We investigate the generation of optofluidic laser in a stable planar-concave fiber Fabry–Pérot microcavity. • Optofluidic laser with low laser threshold of 36.9 μ J/mm2 at the gain concentration of 10 μ M is obtained. • Calculation shows a deduced Q-factor of 7. 8 × 1 0 5 of the FP microcavity. [ABSTRACT FROM AUTHOR]

Enzyme-linked immunosorbent assay (ELISA) is a powerful analytical method for biomolecular analysis due to high sensitivity and specificity. The large background fluorescence can be eliminated by using optofluidic laser-based ELISA. However, the detection time is too long, especially for the detection of low concentration of analyte. Such a drawback can potentially be overcome by using particle with high surface-to-volume ratio. The effect of particle on the lasing threshold of optofluidic laser based on Fabry–Pérot microcavity was demonstrated, which is a fundamental issue on magnetic particle-based optofluidic laser ELISA. The 1 mM R6G ethanol solution and different concentrations of magnetic particles (Fe 3 O 4) solution (5, 10, 20, 40 and 80 μ g/ml) with the diameter 30 or 100 nm was be tested the effect of particle on optofluidic laser. The results show that the lasing threshold increases with the concentration and diameter of particles increasing, but the adverse effect is very small for the detection of low concentration of analyte. Our work will lead to the development of magnetic particle-based optofluidic laser ELISA, which can shorten the detection time and push the detection limit. [ABSTRACT FROM AUTHOR]