Label-free, single molecule detection of cytokines using optical microcavities

Interleukin-2 (IL2) is a cytokine that regulates T-cell growth and is used in cancer therapies. By sensitizing a microcavity sensor surface with anti-IL2 and monitoring the resonant frequency, single molecules of IL2 can be detected

Label-free detection of cytokines using optical microcavities

Ultra-high-Q microresonators have demonstrated sensitive and specific chemical and biological detection. The sensitivity is derived from the long photon lifetime inside the cavity and specificity is achieved through surface functionalization. Here, ultra-high-Q microcavities demonstrate label-free, single molecule detection of Interleukin-2 (IL-2) in fetal bovine serum (FBS). IL-2 is a cytokine released in response to immune system activation. The surface of the microtoroids was sensitized using anti-IL-2. The detection mechanism relies upon a thermo-optic mechanism to enhance resonant wavelength shifts induced through binding of a molecule

Chemical and biological detectors using ultra-high-Q microresonators

Recently, a method for fabricating planar arrays of optical microtoroid resonators with quality factors greater than 500 million was developed. These devices have previously demonstrated Raman and OPO lasing and radiation pressure induced oscillations. When immersed in an aqueous environment, these devices are able to maintain their ultra-high Q factors by operating in the visible wavelength band, enabling very sensitive chemical and biological detection. The fabrication and optical properties of these devices will be described. These devices have performed both chemical and biological detection. Systems which have been detected include D_2O in water and a variety of biological molecules. Sensitivity limits will also be discussed

Electrical thermo-optic tuning of ultrahigh-Q microtoroid resonators

The ability to tune resonant frequency in optical microcavities is an essential feature for many applications. Integration of electrical-based tuning as part of the fabrication process has been a key advantage of planar microresonant devices. Until recently, the combination of these features has not been available in devices that operate in the ultrahigh-Q regime where device quality factors (Q) can exceed 100 million. In this letter, we demonstrate an electrically tunable resonator on a chip with ultrahigh-quality factors. Futhermore, the devices have demonstrated tuning rates in excess of 85 GHz/V2 and are capable of tuning more than 300 GHz

Multiphoton Label-Free ex-vivo imaging using a custom-built dual-wavelength microscope with chromatic aberrations compensation

Label-Free Multiphoton Microscopy is a very powerful optical microscopy that can be applied to study samples with no need for exogenous fluorescent probes, keeping the main benefits of a Multiphoton approach, like longer penetration depths and intrinsic optical sectioning, while opening the possibility of serial examinations with different kinds of techniques. Among the many variations of Label-Free MPM, Higher Harmonic Generation (HHG) is one of the most intriguing due to its generally low photo-toxicity, which enables the examination of specimens particularly susceptible to photo-damages. HHG and common Two-Photon Microscopy (TPM) are well-established techniques, routinely used in several research fields. However, they require a significant amount of fine-tuning in order to be fully exploited and, usually, the optimized conditions greatly differ, making them quite difficult to perform in parallel without any compromise on the extractable information. Here we present our custom-built Multiphoton microscope capable of performing simultaneously TPM and HHG without any kind of compromise on the results thanks to two, separate, individually optimized laser sources with full chromatic aberration compensation. We also apply our setup to the examination of a plethora of ex vivo samples in order to prove the significant advantages of our approach

Low threshold Er³⁺/Yb³⁺ co-doped microcavity laser

An Erbium:Ytterbium codoped microcavity-based laser which is lithographically fabricated from sol-gel is demonstrated. Both single-mode and multimode lasing is observed in the C band (1550nm). The quality factor and pump threshold are experimentally determined for a series of erbium and ytterbium doping concentrations, verifying the inter-dependent relationship between the two dopants. The lasing threshold of the optimized device is 4.2 μW

Characterization of high-Q optical microcavities using confocal microscopy

Confocal microscopy was initially developed to image complex circuits and material defects. Previous imaging studies yielded only qualitative data about the location and number of defects. In the present study, this noninvasive method is used to obtain quantitative information about the Q factor of an optical resonant cavity. Because the intensity of the fluorescent signal measures the number of defects in the resonant cavity, this signal is a measure of the number of surface scattering defects, one of the dominant loss mechanisms in optical microcavities. The Q of the cavities was also determined using conventional linewidth measurements. Based upon a quantitative comparative analysis of these two techniques, it is shown that the Q can be determined without a linewidth measurement, allowing for a noninvasive characterization technique

Label-free single-molecule all-optical sensor

Recently, quality factors greater than 100 million were demonstrated using planar arrays of silica microtoroid resonators. These high Q factors allow the toroidal resonators to perform very sensitive detection experiments. By functionalizing the silica surface of the toroid with biotin, the toroidal resonators become both specific and sensitive detectors for Streptavidin. One application of this sensor is performing detection in lysates. To mimic this type of environment, additional solutions of Streptavidin were prepared which also contained high concentrations (nM and μM) of tryptophan

Simultaneous measurement of quality factor and wavelength shift by phase shift microcavity ring down spectroscopy

Optical resonant microcavities with ultra high quality factors are widely used for biosensing. Until now, the primary method of detection has been based upon tracking the resonant wavelength shift as a function of biodetection events. One of the sources of noise in all resonant-wavelength shift measurements is the noise due to intensity fluctuations of the laser source. An alternative approach is to track the change in the quality factor of the optical cavity by using phase shift cavity ring down spectroscopy, a technique which is insensitive to the intensity fluctuations of the laser source. Here, using biotinylated microtoroid resonant cavities, we show simultaneous measurement of the quality factor and the wavelength shift by using phase shift cavity ring down spectroscopy. These measurements were performed for disassociation phase of biotin-streptavidin reaction. We found that the disassociation curves are in good agreement with the previously published results. Hence, we demonstrate not only the application of phase shift cavity ring down spectroscopy to microcavities in the liquid phase but also simultaneous measurement of the quality factor and the wavelength shift for the microcavity biosensors in the application of kinetics measurements