Orbiting Light Around the Outer Surface of Dielectric Microspheres

Circulating light in the total internal reflection within dielectric spheres or disks is called the whispering gallery mode (WGM), which by itself is highly sensitive to its surface and capable of detecting viruses and single atomic ions. The detection site of the sensors using WGM is created by the evanescent light from the circulating light inside spheres. On the other hand, there have been no reports of observation or discussion of the light orbiting outside the surface of dielectric microspheres. Here we report light orbiting the outer surface of a dielectric microspheres different from the WGM. We observed anomalously enhanced Raman spectrum at the periphery of 3 μm diameter polystyrene (PS) microspheres on a silicon nitride (SiN) film using Raman microscopy. The wavelength intensity of this enhanced Raman spectrum was accompanied by periodic changes due to interference. These features may lead to the development of high-sensitive sensors and optical devices.

Sensitive and In Situ Hemoglobin Detection Based on a Graphene Oxide Functionalized Microfiber

The determination of hemoglobin (Hb) level is indispensable in the pathological study of many blood diseases. Graphene oxide (GO), with its excellent optical properties and great biocompatibility, has attracted significant attention and been widely utilized in biochemical detection. Here, we report an ultrasensitive Hb sensor based on a graphene oxide (GO)-coated microfiber. The GO was utilized as a linking layer deposited on the microfiber surface, which can provide an enhanced local evanescent light field and abundant bonding sites for Hb molecules. The optical microfiber with a compact structure and a strong evanescent light field served as the platform for biosensing. The surface morphology characterized by optical microscope, scanning electron microscope, and Raman spectroscopy offers detailed evidence for the success of GO deposition. The dynamic bonding between GO and target Hb molecules was monitored in real-time through an optical spectrum analyzer. An ultrahigh sensitivity of 6.02 nm/(mg/mL) with a detection limit of 0.17 μg/mL was achieved by tracking the resonant wavelength shift of spectra. It is important to highlight that the detection limit of GO-coated microfiber is 1–2 orders of magnitude lower than other reported fiber optic Hb sensors. Benefiting from high sensitivity, low cost, small size, and fast response, the proposed sensing microfiber coated with GO could be a competitive alternative in the diagnosis of blood diseases and a subject of further research in the medical field.

Sensitive Detection of C-Reactive Protein by One-Step Method Based on a Waveguide-Mode Sensor

One-step biosensing methods enable the quick and simplified detection of biological substances. In this study, we developed a sensitive one-step method on the basis of a waveguide-mode sensor, which is an optical sensor utilizing waveguide-mode resonance and evanescent light. Streptavidin-conjugated and gold-nanoparticle-conjugated antibodies were reacted with a target substance and applied onto a biotinylated sensing plate. The target substance was detected by observing changes in sensor signals caused by binding the immunocomplex to the sensing surface. Performance of the developed one-step method was examined using a C-reactive protein (CRP) as a target substance. A sensor signal corresponding to the concentration of CRP was obtained. The minimal detectable CRP concentration of the developed method was 10 pM. The developed method greatly simplifies quantitative protein detection without reducing sensitivity.