Microfluidic Detection of Vitamin D₃ Compounds Using a Cylindrical Optical Microcavity

Abstract

This paper explores the detection of vitamin D 3 (VD3) using a fluorescent microcavity sensor. There is currently a high demand for measurement and analysis of this vitamin, whose deficiency may result in several different pathologies; however, the standard methods, predominantly based on mass spectroscopy and liquid chromatography require large equipment and must be done remotely. In contrast, measurement of solvent concentrations via microcavity-based optical systems can be sensitive to small changes and require miniscule analyte volumes. However, the refractive effect of VD3 (cholecalciferol) in different solvents has not been widely investigated. This paper shows that VD3 can be detected in an optofluidic setup consisting of a fluorescent capillary with a high-refractive-index quantum-dot coating. Detection and quantification were performed both in pure ethanol and food-grade soy oil solvents. While the refractive detection limits (∼1 mg/mL) were higher than in current standards for D 3 analysis, specific VD3 binding could lower these values. Since cholecalciferol is almost certainly too small (mass 384 Da) to be measured by attempting to treat the cavity surface for its −OH functionality, binding of the VD3 carrier protein is shown instead. This suggests practical routes toward specific microfluidic detection of VD3.

Fluorescent and lasing whispering gallery mode microresonators for sensing applications

“…This work demonstrated that microgoblets can be used as biolasers for the detection of anti‐2,4‐Dinitrophenol . Other examples of biosensing include polystyrene microspheres embedded with CdSe/ZnS QDs for thrombin detection , dye‐doped polymer coated microcapillaries for detecting Vitamin D Binding Protein , fluorescent microspheres for the detection of unlabeled oligonucleotide targets , and the multiplexed quantification of ovarian cancer markers . In terms of reaching the same single‐molecule detection capability of passive resonators, a self‐referenced and self‐heterodyned WGM Raman microlaser was recently demonstrated .…”

Advances of Optofluidic Microcavities for Microlasers and Biosensors

“…Even if a single bio-particle of nanoscale is locally attached to the cavities’ surface, it would also rearrange the electric field distribution because of highly enhanced light-particle interaction. Recently, much research attention has been put on the WGM-based detection of single particles, such as virus, DNA and single proteins [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 ]. Some reviews had made detailed descriptions of the theories and the recent biosensing applications of optical microresonators [ 27 , 28 , 67 , 68 ].…”

“…An external light source (white source or tunable laser) is used to couple photons into the cavities by the taper fiber or the waveguide. By monitoring the shift or splitting the resonant peaks of transmission spectra, analyte concentration or molecule attaching can be detected [ 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 ]. As the optical confinement elements, the cavities with high Q factor would greatly enhance the light-matter interaction and would result in high sensitivity.…”

Whispering Gallery Mode Devices for Sensing and Biosensing

“…A physisorption-based surface functionalization process, using bovine serum albumin (BSA) directly deposited onto the sensor surface and subsequently cross-linked with antibodies [107], has been used with fluorescent polystyrene microspheres, while a PE-based surface functionalization process has also been used with both fluorescent polystyrene microspheres [108] and glass capillaries [118,119], demonstrating the applicability of such approach for biosensing applications involving whispering gallery modes. Biomolecule immobilization, non-specific binding, and specific orientation The deposition of either silanes or PE multilayers is merely the first step of a complex process.…”