Ultrasensitive and rapid detection of nano‐objects is crucial in both fundamental studies and practical applications. Optical sensors using evanescent fields in microcavities, plasmonic resonators, ...and nanofibers allow label‐free detection down to single molecules, but practical applications are severely hindered by long response time and device reproducibility. Here, an on‐chip dense waveguide sensor to monitor single unlabeled nanoparticles in a strong optical evanescent field is demonstrated. The spiral nanowaveguide design enables two orders of magnitude enhancement in sensing area compared to a straight waveguide, significantly improving the particle capture ability and shortening the target analysis time. In addition, the measurement noise is suppressed to a level of 10−4 in the transmitted power, pushing the detection limit of single particles down to the size of 100 nm. The waveguide sensor on the silicon‐on‐isolator platform can be fabricated reproducibly by the conventional semiconductor processing and compatible with surface functionalization chemistries and microfluidics, which could lead to widespread use for sensing in environmental monitoring and human health.
An on‐chip spiral waveguide is demonstrated to perform rapid and ultrasensitive detection of nano‐objects. Optimization in field distributions and noise suppression pushes the detection limit of single particles down to the size of 100 nm. This silicon spiral waveguide provides superior efficiency to capture the targets, drastically decreasing the target analysis time and the sample consumption volumes.
The optofluidic laser has become an important platform for biological sensing and medical diagnosis. To date, fluorescent dyes and proteins have been widely utilized as gain materials for biological ...analysis due to their good biocompatibility, but the limited photostability restricts their reliability and sensitivity. Here, an optofluidic microlaser with an ultralow threshold down to 7.8 µJ cm−2 in the ultrahigh‐Q whispering‐gallery microcavity, which is filled with a biocompatible conjugated polymer, is demonstrated. This conjugated polymer exhibits a significant enhancement in the lasing stability compared with a typical laser dye (Nile red). In the experiment, after 20 min of illumination with the excitation intensity of 23.2 MW cm−2, the lasing intensity of the conjugated polymer experiences a decrease of less than 10%, while the lasing feature of Nile red completely disappears. Additionally, by mechanically stretching the resonator, the lasing frequency can be fine‐tuned with the range of about 2 nm, exceeding the free spectral range of the resonator.
Tunable optofluidic microlasers with an ultralow threshold down to 7.8 μJ cm−2 are demonstrated in an ultrahigh‐Q whispering‐gallery microcavity filled with a biocompatible conjugated polymer. Compared with typical laser dyes, the conjugated polymer exhibits a significant enhancement in lasing stability. This low‐threshold laser with excellent photostability could find widespread use in aqueous environments for biological sensing and medical diagnosis.
Optical evanescent sensors can non-invasively detect unlabeled nanoscale objects in real time with unprecedented sensitivity, enabling a variety of advances in fundamental physics and biological ...applications. However, the intrinsic low-frequency noise therein with an approximately 1/f-shaped spectral density imposes an ultimate detection limit for monitoring many paramount processes, such as antigen-antibody reactions, cell motions and DNA hybridizations. Here, we propose and demonstrate a 1/f-noise-free optical sensor through an up-converted detection system. Experimentally, in a CMOS-compatible heterodyne interferometer, the sampling noise amplitude is suppressed by two orders of magnitude. It pushes the label-free single-nanoparticle detection limit down to the attogram level without exploiting cavity resonances, plasmonic effects, or surface charges on the analytes. Single polystyrene nanobeads and HIV-1 virus-like particles are detected as a proof-of-concept demonstration for airborne biosensing. Based on integrated waveguide arrays, our devices hold great potentials for multiplexed and rapid sensing of diverse viruses or molecules.
The ability to track individual cells in space over time is crucial to analyzing heterogeneous cell populations. Recently, microlaser particles have emerged as unique optical probes for massively ...multiplexed single-cell tagging. However, the microlaser far-field emission is inherently direction-dependent, which causes strong intensity fluctuations when the orientation of the particle varies randomly inside cells. Here, we demonstrate a general solution based on the incorporation of nanoscale light scatterers into microlasers. Two schemes are developed by introducing either boundary defects or a scattering layer into microdisk lasers. The resulting laser output is omnidirectional, with the minimum-to-maximum ratio of the angle-dependent intensity improving from 0.007 (-24 dB) to > 0.23 (-6 dB). After transfer into live cells in vitro, the omnidirectional laser particles within moving cells could be tracked continuously with high signal-to-noise ratios for 2 h, while conventional microlasers exhibited frequent signal loss causing tracking failure.
The further development of “lab on fiber” technology demands more powerful optical microsystems and optical fibers with special functions to create sensors with better performance. Whispering gallery ...microcavities (WGMs) made of different materials with high quality factors show very good sensitivity to gases, nanoparticles, and biocomponents. However, realizing the excitation and detection of the resonant modes of WGMs on the facets of optical fibers is still a great challenge. This work employs the advanced 3D manufacturing technology of two‐photon lithography to fabricate an optical microsystem on the end facet of a multicore optical fiber, which enables excitation and detection of whispering gallery modes on the end facet of an optical fiber. Whispering gallery modes with high quality factors are observed, and the sensing characterization of this device for vapors of three types of volatile organic compounds is investigated. Such optical fiber vapor sensors can be applied in the fields of medical care, environmental monitoring and chemical manufacturing. Additionally, the out‐of‐plane light coupling strategy may be useful for the design of integrated optical circuits on chips.
High‐Q polymer whispering gallery microcavities (WGMs) with receptacle‐type ports on a multicore fiber facet for vapor sensing applications have been achieved. Just like the diodes in the integrated circuits, such a configuration design of the optical microsystem may be a building block for more compact devices which are based on integrated WGMs sensing array.
Biomarker detection is key to identifying health risks. However, designing sensitive and single-use biosensors for early diagnosis remains a major challenge. Here, we report submonolayer lasers on ...optical fibers as ultrasensitive and disposable biosensors. Telecom optical fibers serve as distributed optical microcavities with high Q-factor, great repeatability, and ultralow cost, which enables whispering-gallery laser emission to detect biomarkers. It is found that the sensing performance strongly depends on the number of gain molecules. The submonolayer lasers obtained a six-order-of-magnitude improvement in the lower limit of detection (LOD) when compared to saturated monolayer lasers. We further achieve an ultrasensitive immunoassay for a Parkinson's disease biomarker, alpha-synuclein (α-syn), with a lower LOD of 0.32 pM in serum, which is three orders of magnitude lower than the α-syn concentration in the serum of Parkinson's disease patients. Our demonstration of submonolayer biolaser offers great potentials in high-throughput clinical diagnosis with ultimate sensitivity.
Label-free sensors are highly desirable for biological analysis and early-stage disease diagnosis. Optical evanescent sensors have shown extraordinary ability in label-free detection, but their ...potentials have not been fully exploited because of the weak evanescent field tails at the sensing surfaces. Here, we report an ultrasensitive optofluidic biosensor with interface whispering gallery modes in a microbubble cavity. The interface modes feature both the peak of electromagnetic-field intensity at the sensing surface and high-
factors even in a small-sized cavity, enabling a detection limit as low as 0.3 pg/cm
The sample consumption can be pushed down to 10 pL due to the intrinsically integrated microfluidic channel. Furthermore, detection of single DNA with 8 kDa molecular weight is realized by the plasmonic-enhanced interface mode.
We report enhanced optical nonlinear effects at the surface of an ultrahigh-Q silica microcavity functionalized by a thin layer of organic molecules. The maximal conversion efficiency of third ...harmonic generation reaches ∼1680%/W2 and an absolute efficiency of 0.0144% at pump power of ∼2.90 mW, which is approximately 4 orders of magnitude higher than that in a reported silica microcavity. Further analysis clarifies the elusive dependence of the third harmonic signal on the pump power in previous literature. Molecule-functionalized microcavities may find promising applications in high-efficiency broadband optical frequency conversion and offer potential in sensitive surface analysis.
Optical microcavities have emerged as promising platforms for ultrasound detection. One of the main tendencies in recent studies is to develop high-
Q
microresonators for ultrasensitive ultrasound ...detection, while the nonlinear optical effects become significant but are generally neglected. Here, we propose a thermal-assisted microcavity Raman laser for ultrasound detection. Acoustic waves modulate the resonant frequency of the cavity mode, altering the coupled efficiency of a fixed-wavelength input laser, and therefore the output Raman power. Experimentally, the noise equivalent pressure reaches as low as 8.1 Pa at 120 kHz in air. Besides, it is found that the thermal effect involved in high-
Q
microcavities can compensate for the low-frequency noises, while without degrading their sensitivity to high-frequency acoustic waves above hundreds of kilohertz. Therefore, it enables long-standing stability during the measurements due to the natural resistance to laser frequency drifts and environmental disturbances, which holds great potential in practical applications of ultrasound sensing and imaging.
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