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Suebka S, McLeod E, Su J. Ultra-high-Q free-space coupling to microtoroid resonators. LIGHT, SCIENCE & APPLICATIONS 2024; 13:75. [PMID: 38490984 PMCID: PMC10942989 DOI: 10.1038/s41377-024-01418-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2023] [Revised: 02/20/2024] [Accepted: 02/28/2024] [Indexed: 03/18/2024]
Abstract
Whispering gallery mode (WGM) microtoroid resonators are one of the most sensitive biochemical sensors in existence, capable of detecting single molecules. The main barrier for translating these devices out of the laboratory is that light is evanescently coupled into these devices though a tapered optical fiber. This hinders translation of these devices as the taper is fragile, suffers from mechanical vibration, and requires precise positioning. Here, we eliminate the need for an optical fiber by coupling light into and out from a toroid via free-space coupling and monitoring the scattered resonant light. A single long working distance objective lens combined with a digital micromirror device (DMD) was used for light injection, scattered light collection, and imaging. We obtain Q-factors as high as 1.6 × 10 8 with this approach. Electromagnetically induced transparency (EIT)-like and Fano resonances were observed in a single cavity due to indirect coupling in free space. This enables improved sensing sensitivity. The large effective coupling area (~10 μm in diameter for numerical aperture = 0.14) removes the need for precise positioning. Sensing performance was verified by combining the system with the frequency locked whispering evanescent resonator (FLOWER) approach to perform temperature sensing experiments. A thermal nonlinear optical effect was examined by tracking the resonance through FLOWER while adjusting the input power. We believe that this work will be a foundation for expanding the implementation of WGM microtoroid resonators to real-world applications.
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Affiliation(s)
- Sartanee Suebka
- Wyant College of Optical Sciences, University of Arizona, Tucson, AZ, USA
| | - Euan McLeod
- Wyant College of Optical Sciences, University of Arizona, Tucson, AZ, USA
| | - Judith Su
- Wyant College of Optical Sciences, University of Arizona, Tucson, AZ, USA.
- Department of Biomedical Engineering, University of Arizona, Tucson, AZ, USA.
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Xu Y, Stanko AM, Cerione CS, Lohrey TD, McLeod E, Stoltz BM, Su J. Low Part-Per-Trillion, Humidity Resistant Detection of Nitric Oxide Using Microtoroid Optical Resonators. ACS APPLIED MATERIALS & INTERFACES 2024; 16:5120-5128. [PMID: 38240231 DOI: 10.1021/acsami.3c16012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2024]
Abstract
The nitric oxide radical plays pivotal roles in physiological as well as atmospheric contexts. Although the detection of dissolved nitric oxide in vivo has been widely explored, highly sensitive (i.e., low part-per-trillion level), selective, and humidity-resistant detection of gaseous nitric oxide in air remains challenging. In the field, humidity can have dramatic effects on the accuracy and selectivity of gas sensors, confounding data, and leading to overestimation of gas concentration. Highly selective and humidity-resistant gaseous NO sensors based on laser-induced graphene were recently reported, displaying a limit of detection (LOD) of 8.3 ppb. Although highly sensitive (LOD = 590 ppq) single-wall carbon nanotube NO sensors have been reported, these sensors lack selectivity and humidity resistance. In this report, we disclose a highly sensitive (LOD = 2.34 ppt), selective, and humidity-resistant nitric oxide sensor based on a whispering-gallery mode microtoroid optical resonator. Excellent analyte selectivity was enabled via novel ferrocene-containing polymeric coatings synthesized via reversible addition-fragmentation chain-transfer polymerization. Utilizing a frequency locked optical whispering evanescent resonator system, the microtoroid's real-time resonance frequency shift response to nitric oxide was tracked with subfemtometer resolution. The lowest concentration experimentally detected was 6.4 ppt, which is the lowest reported to date. Additionally, the performance of the sensor remained consistent across different humidity environments. Lastly, the impact of the chemical composition and molecular weight of the novel ferrocene-containing polymeric coatings on sensing performance was evaluated. We anticipate that our results will have impact on a wide variety of fields where NO sensing is important such as medical diagnostics through exhaled breath, determination of planetary habitability, climate change, air quality monitoring, and treating cardiovascular and neurological disorders.
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Affiliation(s)
- Yinchao Xu
- Wyant College of Optical Sciences, The University of Arizona, Tucson, Arizona 85721, United States
- Department of Biomedical Engineering, The University of Arizona, Tucson, Arizona 85721, United States
| | - Allison M Stanko
- The Warren and Catherine Schlinger Laboratory for Chemistry and Chemical Engineering, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Chloe S Cerione
- The Warren and Catherine Schlinger Laboratory for Chemistry and Chemical Engineering, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Trevor D Lohrey
- The Warren and Catherine Schlinger Laboratory for Chemistry and Chemical Engineering, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Euan McLeod
- Wyant College of Optical Sciences, The University of Arizona, Tucson, Arizona 85721, United States
- Department of Biomedical Engineering, The University of Arizona, Tucson, Arizona 85721, United States
| | - Brian M Stoltz
- The Warren and Catherine Schlinger Laboratory for Chemistry and Chemical Engineering, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Judith Su
- Wyant College of Optical Sciences, The University of Arizona, Tucson, Arizona 85721, United States
- Department of Biomedical Engineering, The University of Arizona, Tucson, Arizona 85721, United States
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Gin A, Nguyen PD, Melzer JE, Li C, Strzelinski H, Liggett SB, Su J. Label-free, real-time monitoring of membrane binding events at zeptomolar concentrations using frequency-locked optical microresonators. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.20.558657. [PMID: 37786702 PMCID: PMC10541581 DOI: 10.1101/2023.09.20.558657] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/04/2023]
Abstract
Binding events to elements of the cell membrane act as receptors which regulate cellular function and communication and are the targets of many small molecule drug discovery efforts for agonists and antagonists. Conventional techniques to probe these interactions generally require labels and large amounts of receptor to achieve satisfactory sensitivity. Whispering gallery mode microtoroid optical resonators have demonstrated sensitivity to detect single-molecule binding events. Here, we demonstrate the use of frequency-locked optical microtoroids for characterization of membrane interactions in vitro at zeptomolar concentrations using a supported biomimetic membrane. Arrays of microtoroids were produced using photolithography and subsequently modified with a biomimetic membrane, providing high quality (Q) factors (> 10 6 ) in aqueous environments. Fluorescent recovery after photobleaching (FRAP) experiments confirmed the retained fluidity of the microtoroid supported-lipid membrane with a diffusion coefficient of 3.38 ± 0.26 μm 2 ⋅ s - 1 . Utilizing this frequency-locked membrane-on-a-chip model combined with auto-balanced detection and non-linear post-processing techniques, we demonstrate zeptomolar detection levels The binding of Cholera Toxin B- monosialotetrahexosyl ganglioside (GM1) was monitored in real-time, with an apparent equilibrium dissociation constant k d = 1.53 nM . The measured affiny of the agonist dynorphin A 1-13 to the κ -opioid receptor revealed a k d = 3.1 nM using the same approach. Radioligand binding competition with dynorphin A 1-13 revealed a k d in agreement (1.1 nM) with the unlabeled method. The biosensing platform reported herein provides a highly sensitive real-time characterization of membrane embedded protein binding kinetics, that is rapid and label-free, for toxin screening and drug discovery, among other applications.
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Affiliation(s)
- Adley Gin
- Wyant College of Optical Sciences, The University of Arizona, Tucson, AZ 85721
| | - Phuong-Diem Nguyen
- Department of Biomedical Engineering, The University of Arizona, Tucson, AZ 85721
| | - Jeffrey E. Melzer
- Wyant College of Optical Sciences, The University of Arizona, Tucson, AZ 85721
| | - Cheng Li
- Wyant College of Optical Sciences, The University of Arizona, Tucson, AZ 85721
| | - Hannah Strzelinski
- Department of Medicine, University of South Florida Morsani College of Medicine, Tampa, FL 33612
| | - Stephen B. Liggett
- Department of Medicine, University of South Florida Morsani College of Medicine, Tampa, FL 33612
| | - Judith Su
- Wyant College of Optical Sciences, The University of Arizona, Tucson, AZ 85721
- Department of Biomedical Engineering, The University of Arizona, Tucson, AZ 85721
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