Microstructured Optical Waveguide-Based Endoscopic Probe Coated with Silica Submicron Particles

Thermo-optics of gilded hollow-core fibers

Hollow core fibers, supporting waveguiding in a void, open a room of opportunities for numerous applications owing to an extended light-matter interaction distance and relatively high optical confinement. Decorating an inner capillary with functional materials allows tailoring the fiber's optical properties further and turns the structure into a functional device. Here, we functionalize an anti-resonant hollow-core fiber with 18 nm-size gold nanoparticles, approaching a uniform 45% surface coverage along 10 s of centimeters along its inner capillary. Owing to a moderately low overlap between the fundamental mode and the gold layer, the fiber maintains its high transmission properties; nevertheless, the entire structure experiences considerable heating, which is observed and quantified with the aid of a thermal camera. The hollow core and the surrounding capillary are subsequently filled with ethanol and thermo-optical heating is demonstrated. We also show that at moderate laser intensities, the liquid inside the fiber begins to boil and, as a result, the optical guiding is destroyed. The gilded hollow core fiber and its high thermal-optical responsivity suggest considering the structure as an efficient optically driven catalytic reactor in applications where either small reaction volumes or remote control over a process are demanded.

Ultrasmooth, biocompatible, and removable nanocoating for hollow-core microstructured optical fibers

Functional nanocoatings of hollow-core microstructured optical fibers (HC-MOFs) have extended the domain of their applications to biosensing and photochemistry. However, novel modalities typically come with increased optical losses since a significant surface roughness of functional layers gives rise to additional light scattering, restricting the performance of functionalization. Here, the technique that enables a biocompatible and removable nanocoating of HC-MOFs with low surface roughness is presented. The initial functional film is formed by a layer-by-layer assembly of bovine serum albumin (BSA) and tannic acid (TA). The alkaline etching at pH 9 results in the reduction of surface roughness from 26 nm to 3 nm and decreases fiber optical losses by three times. The nanocoating can be fully removed within 7 min of the treatment. Natural biocompatibility of BSA alongside antibacterial and antifouling properties of TA makes the presented nanocoating promising for biophotonic applications.

Submicron silica particles have cytotoxicities on hepatocellular carcinoma, non-small cell lung cancer and breast cancer by unified regulating the XLOC_001659/miR-98-5p/MAP3K2-mediated pathway

The cytotoxicities of silica (SiO₂s) particles against cancers are still controversial. In this study, the purchased submicron silica particles (SM-SiO₂s) were identified by transmission electron microscopy and energy dispersive spectrometer, and it showed potent cytotoxicities on hepatocellular carcinoma (HCC), non-small cell lung cancer (NSCLC) and breast cancer (BC), which ranked the top in the incidence among the tumor types. Through the microarray assay on long noncoding RNAs (lncRNAs) from the SM-SiO₂s-treated HCC, NSCLC and BC cells, followed by Venn analysis, we found that a series of lncRNAs were significantly regulated by SM-SiO₂s, among of which XLOC_001659 was mostly decreased. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assay confirmed that XLOC_001659 could be decreased in all the SM-SiO₂s-treated HCC, NSCLC and BC cells, coupled to inhibited cell proliferation. Further, XLOC_001659 was recognized as a miR-98-5p sponge and therefore modulates the "pro-inflammatory tumor promoter" MAP3K2 expressions. The XLOC_001659/miR-98-5p/MAP3K2 axis uniformly mediated the regulation of SM-SiO₂s on proliferation of HCC, NSCLC and BC cells. Further clinical experiments demonstrated that XLOC_001659 was negatively correlated with miR-98-5p level and positively correlated with MAP3K2 level, and XLOC_001659/miR-98-5p/MAP3K2 axis was significantly associated with progressions and prognosis in HCC, NSCLC and BC patients. These results provide a new clue for the anti-tumor mechanism of SM-SiO₂s and a new way for drug development by using SM-SiO2s.

Microstructured optical fibers sensor modified by deep eutectic solvent: Liquid-phase microextraction and detection in one analytical device

A sensitive optical sensor based on hollow core microstructure optical fibers modified with deep eutectic solvent was produced for the first time. An easy procedure for the modification of hollow-core microstructure optical fibers with deep eutectic solvent was developed. Deep eutectic solvents based on natural monoterpenoids and fatty acids were investigated for glass surface modification. The sensor was used for the determination of non-steroidal anti-inflammatory drugs (mefenamic acid, diclofenac, flurbiprofen and ketoprofen) in human urine samples. The mechanism of the sensor response was investigated and discussed. Liquid-phase microextraction of non-steroidal anti-inflammatory drugs was implemented in deep eutectic solvent phase supported in the inner surface of hollow-core microstructure optical fibers followed by transmission spectra measurement in one analytical device. The preconcentration step performed directly in the analytical device allowed to obtain high sensitivity and selectivity. The limits of detection calculated from the calibration plots based on 3σ were 3 μg L^-1 for all target analytes.

Multispectral sensing of biological liquids with hollow-core microstructured optical fibres

The state of the art in optical biosensing is focused on reaching high sensitivity at a single wavelength by using any type of optical resonance. This common strategy, however, disregards the promising possibility of simultaneous measurements of a bioanalyte's refractive index over a broadband spectral domain. Here, we address this issue by introducing the approach of in-fibre multispectral optical sensing (IMOS). The operating principle relies on detecting changes in the transmission of a hollow-core microstructured optical fibre when a bioanalyte is streamed through it via liquid cells. IMOS offers a unique opportunity to measure the refractive index at 42 wavelengths, with a sensitivity up to ~3000 nm per refractive index unit (RIU) and a figure of merit reaching 99 RIU-1 in the visible and near-infra-red spectral ranges. We apply this technique to determine the concentration and refractive index dispersion for bovine serum albumin and show that the accuracy meets clinical needs.

Light guidance up to 6.5 µm in borosilicate soft glass hollow-core microstructured optical waveguides

Limited operating bandwidth originated from strong absorption of glass materials in the infrared (IR) spectral region has hindered the potential applications of microstructured optical waveguide (MOW)-based sensors. Here, we demonstrate multimode waveguide regime up to 6.5 µm for the hollow-core (HC) MOWs drawn from borosilicate soft glass. Effective light guidance in central HC (diameter ∼240 µm) was observed from 0.4 to 6.5 µm despite high waveguide losses (0.4 and 1 dB/cm in near- and mid-IR, respectively). Additional optimization of the waveguide structure can potentially extend its operating range and decrease transmission losses, offering an attractive alternative to tellurite and chalcogenide-based fibers. Featuring the transparency in mid-IR, HC MOWs are promising candidates for the creation of MOW-based sensors for chemical and biomedical applications.

Functionalized Microstructured Optical Fibers: Materials, Methods, Applications

Microstructured optical fiber-based sensors (MOF) have been widely developed finding numerous applications in various fields of photonics, biotechnology, and medicine. High sensitivity to the refractive index variation, arising from the strong interaction between a guided mode and an analyte in the test, makes MOF-based sensors ideal candidates for chemical and biochemical analysis of solutions with small volume and low concentration. Here, we review the modern techniques used for the modification of the fiber's structure, which leads to an enhanced detection sensitivity, as well as the surface functionalization processes used for selective adsorption of target molecules. Novel functionalized MOF-based devices possessing these unique properties, emphasize the potential applications for fiber optics in the field of modern biophotonics, such as remote sensing, thermography, refractometric measurements of biological liquids, detection of cancer proteins, and concentration analysis. In this work, we discuss the approaches used for the functionalization of MOFs, with a focus on potential applications of the produced structures.