Developing localized surface plasmon resonance biosensor chips and fiber optics via direct surface modification of PMMA optical waveguides

A review of Optical Point-of-Care devices to Estimate the Technology Transfer of These Cutting-Edge Technologies

Despite the remarkable development related to Point-of-Care devices based on optical technology, their difficulties when used outside of research laboratories are notable. In this sense, it would be interesting to ask ourselves what the degree of transferability of the research work to the market is, for example, by analysing the relation between the scientific work developed and the registered one, through patent. In this work, we provide an overview of the state-of-the-art in the sector of optical Point-of-Care devices, not only in the research area but also regarding their transfer to market. To this end, we explored a methodology for searching articles and patents to obtain an indicator that relates to both. This figure of merit to estimate this transfer is based on classifying the relevant research articles in the area and the patents that have been generated from these ones. To delimit the scope of this study, we researched the results of a large enough number of publications in the period from 2015 to 2020, by using keywords "biosensor", "optic", and "device" to obtain the most representative articles from Web of Science and Scopus. Then, we classified them according to a particular classification of the optical PoC devices. Once we had this sampling frame, we defined a patent search strategy to cross-link the article with a registered patent (by surfing Google Patents) and classified them accordingly to the categories described. Finally, we proposed a relative figure called Index of Technology Transference (IoTT), which estimates to what extent our findings in science materialized in published articles are protected by patent.

Ion-Imprinted Chitosan-Based Localized Surface Plasmon Resonance Sensor for Ni2+ Detection

Heavy metals are important sources of environmental pollution and cause disease in organisms throughout the food chain. A localized surface plasmon resonance sensor was proposed and demonstrated to realize Ni2+ detection by using ion-imprinted chitosan. Au nanoparticles were coated on the multimode fiber to excite the local surface plasmon resonance, and Ni2+-imprinted chitosan was then functionalized by using the dip coating technique. Ethylene diamine tetra-acetic acid was used to release the Ni2+ ions and hence form countless voids. Ni2+ was refilled into the voids to increase the refractive index of the sensing material, thus realizing the measurement of Ni2+ by monitoring the wavelength shift in the localized surface plasmon resonant peak. The coating thickness of the Ni2+-chitosan gel was optimized to obtain greater sensitivity. Experimental results show that the proposed Ni2+ sensor has a sensitivity of 185 pm/μM, and the limit of detection is 0.512 μM. The comparison experiments indicated that the ion-imprinted chitosan has better selectivity than pure chitosan.

Highly Sensitive Biosensor Based on Partially Immobilized Silver Nanopillars in the Terahertz Band

In this paper, a highly sensitive biosensor based on partially immobilized silver nanopillars is proposed. The working frequency of this sensor is in the terahertz band, and the range of the detected refractive index is 1.33 to 1.38. We set air holes of two different sizes on the cross-section of the optical fiber and arranged them into a hexagon. In order to improve the sensitivity, silver nanopillars were immobilized on part of the surface of the fiber cladding. The method for detecting the change of refractive index of the bio-analyte was based on local surface plasmon resonance properties of noble metal. The research recorded valuable data about the values of loss peak and full width at half maximum as well as resonance frequency shift under different setting conditions. The data present the biosensor’s final sensitivity as 1.749 THz/RIU.

All-POF coupling ratio-imbalanced Sagnac interferometer as a refractive index sensor

A polymer optical Sagnac interferometer is proposed as a compact and low-cost refractive index sensor for the first time to our best knowledge. The Sagnac interferometer is fabricated by only one piece of fiber to facilitate its fabrication and to avoid losses due to misalignment or fusion. The coupler was developed based on chemical and twisting techniques of ∼5cm of fiber. We modified the coupling ratio by varying the refractive index of media surrounding the coupler and consequently modified the transmission. For several values of mass percent concentration of sugar solutions surrounding the coupler, we found that transmittance decreases as the mass concentration increases. However, the decay is faster for the low concentration, while the decay is slower for higher concentrations. Two sets of experiments were carried out, at high (≥ 1 gm/100 ml) and low (<1gm/100ml) mass concentration of sugar solutions. The calibration of the sensor was done at 733 nm, where the response of the interferometer displays larger transmission variations for different solutions. The refractive index estimation was possible by correlation of the transmittance function (calculated by fitting the experimental data) with a linear refractive index model. The estimated resolution of the system is 0.057 weight percent of sugar solution, determined by the noise of the system.

Water Pollutants p-Cresol Detection Based on Au-ZnO Nanoparticles Modified Tapered Optical Fiber

In this work, a localized plasmon-based sensor is developed for para-cresol (p-cresol) - a water pollutant detection. A nonadiabatic [Formula: see text] of tapered optical fiber (TOF) has been experimentally fabricated and computationally analyzed using beam propagation method. For optimization of sensor's performance, two probes are proposed, where probe 1 is immobilized with gold nanoparticles (AuNPs) and probe 2 is immobilized with the AuNPs along with zinc oxide nanoparticles (ZnO-NPs). The synthesized metal nanomaterials were characterized by ultraviolet-visible spectrophotometer (UV-vis spectrophotometer) and transmission electron microscope (HR-TEM). The nanomaterials coating on the surface of the sensing probe were characterized by a scanning electron microscope (SEM). Thereafter, to increase the specificity of the sensor, the probes are functionalized with tyrosinase enzyme. Different solutions of p-cresol in the concentration range of [Formula: see text] - [Formula: see text] are prepared in an artificial urine solution for sensing purposes. Different analytes such as uric acid, β -cyclodextrin, L-alanine, and glycine are prepared for selectivity measurement. The linearity range, sensitivity, and limit of detection (LOD) of probe 1 are [Formula: see text] - [Formula: see text], 7.2 nm/mM (accuracy 0.977), and [Formula: see text], respectively; and for probe 2 are [Formula: see text] - [Formula: see text], 5.6 nm/mM (accuracy 0.981), and [Formula: see text], respectively. Thus, the overall performance of probe 2 is quite better due to the inclusion of ZnO-NPs that increase the biocompatibility of sensor probe. The proposed sensor structure has potential applications in the food industry and clinical medicine.

Bimetallic Thin-Film Combination of Surface Plasmon Resonance-Based Optical Fiber Cladding with the Polarizing Homodyne Balanced Detection Method and Biomedical Assay Application

In this work, we present the optical birefringence properties of the optical fiber cladding that exists as an evanescent field where the refractive index (RI) of the analysis solution is applied for optical sensor aspiration. To enhance the performance of the sensor, we have investigated the sensor with different thicknesses of TiO₂ coating and bimetallic (Ag-Al) film alloy combinations by thermal evaporation coating. We described a special balanced homodyne detection method for the intensity difference change between the p- and s-polarization lights in the surface plasmon resonance sensing systems, which is strongly determined by the RI of the test medium. The plasmonic optical fiber can measure a very small change of the RI of a glycerol solution, which is a resolution of 4.37 × 10^-8 RI unit (RIU). This method has great advantages of a small-sized optical setup, high stability, high selectivity, easy chemical modification, and low cost. Furthermore, because of the experiment results, we observe that our approach can also eliminate the surrounding noise in the Mach-Zehnder interferometer, which shows the feasibility of this proposed technique. We demonstrate the fluorescence enhancement in detecting the C-reactive protein antibody conjugated with fluorescein isothiocyanate by means of near-field coupling between surface plasmons and fluorophores at spectral channels of emission. This technique can also be extended for application in a biomedical assay and in biochemical science, including molecular diagnostics relying on multichannels that require a small volume of the analyte at each channel which would suffer from the weakness of fluorescence if it were not for the enhancement technology.

Hg2+ Optical Fiber Sensor Based on LSPR with PDDA-Templated AuNPs and CS/PAA Bilayers

An optical fiber localized surface plasmon resonance (LSPR) sensor was proposed and experimentally demonstrated to detect Hg2+ ions by functionalizing the optical fiber surface with gold nanoparticles (AuNPs) and chitosan (CS)/poly acrylic acid (PAA) bilayers. A flame-brushing technology was proposed to post-process the polydimethyl diallyl ammonium chloride(PDDA)-templated nanoparticles, avoiding the aggregation of AuNPs and achieving well-dispersed AuNPs arrays. LSPR stimulated by the AuNPs is sensitive to changes in the refractive index induced by Hg2+ ions absorption on the CS/PAA bilayers. Experimental results demonstrated that the LSPR peak wavelength linearly shifts with the concentrations of Hg2+ ions from 1 to 30 μM with a sensitivity of around 0.51 nm/ppm. The sensor also exhibits good specificity and longtime stability.

Fiber Optic Particle Plasmon Resonance Biosensor for Label-Free Detection of Nucleic Acids and Its Application to HLA-B27 mRNA Detection in Patients with Ankylosing Spondylitis

We developed a label-free, real-time, and highly sensitive nucleic acid biosensor based on fiber optic particle plasmon resonance (FOPPR). The biosensor employs a single-strand deoxyoligonucleotides (ssDNA) probe, conjugated to immobilized gold nanoparticles on the core surface of an optical fiber. We explore the steric effects on hybridization affinity and limit of detection (LOD), by using different ssDNA probe designs and surface chemistries, including diluent molecules of different lengths in mixed self-assembled monolayers, ssDNA probes of different oligonucleotide lengths, ssDNA probes in different orientations to accommodate target oligonucleotides with a hybridization region located unevenly in the strand. Based on the optimized ssDNA probe design and surface chemistry, we achieved LOD at sub-nM level, which makes detection of target oligonucleotides as low as 1 fmol possible in the 10-μL sensor chip. Additionally, the FOPPR biosensor shows a good correlation in determining HLA-B27 mRNA, in extracted blood samples from patients with ankylosing spondylitis (AS), with the clinically accepted real-time reverse transcription-polymerase chain reaction (RT-PCR) method. The results from this fundamental study should guide the design of ssDNA probe for anti-sense sensing. Further results through application to HLA-B27 mRNA detection illustrate the feasibility in detecting various nucleic acids of chemical and biological relevance.

Fiber optic sensor based on ZnO nanowires decorated by Au nanoparticles for improved plasmonic biosensor

Fiber-optic-based localized surface plasmon resonance (FO-LSPR) sensors with three-dimensional (3D) nanostructures have been developed. These sensors were fabricated using zinc oxide (ZnO) nanowires and gold nanoparticles (AuNPs) for highly sensitive plasmonic biosensing. The main achievements in the development of the biosensors include: (1) an extended sensing area, (2) light trapping effect by nanowires, and (3) a simple optical system based on an optical fiber. The 3D nanostructure was fabricated by growing the ZnO nanowires on the cross-section of optical fibers using hydrothermal synthesis and via immobilization of AuNPs on the nanowires. The proposed sensor outputted a linear response according to refractive index changes. The 3D FO-LSPR sensor exhibited an enhanced localized surface plasmon resonance response of 171% for bulk refractive index changes when compared to the two-dimensional (2D) FO-LSPR sensors where the AuNPs are fixed on optical fiber as a monolayer. In addition, the prostate-specific antigen known as a useful biomarker to diagnose prostate cancer was measured with various concentrations in 2D and 3D FO-LSPR sensors, and the limits of detection (LODs) were 2.06 and 0.51 pg/ml, respectively. When compared to the 2D nanostructure, the LOD of the sensor with 3D nanostructure was increased by 404%.

Localized surface plasmon resonance modulation of totally encapsulated VO2/Au/VO2 composite structure

We design and fabricate a totally encapsulated VO₂/Au/VO₂ composite structure which is aimed to improve the tunability of the localized surface plasmon resonance (LSPR) peak. In this work, the structure will ensure all the Au NPs' resonant electric field area is filled with VO₂. The modulation range of the totally encapsulated structure is larger than that of the semi-coated structure. To further improve the modulation range, we also explore the VO₂ thickness dependence of the structure's LSPR modulation. With the increase of the top layer VO₂ thin film thickness, the modulation range becomes larger. When the thickness is about 80 nm, the absorption peak achieves a largest shift of 112 nm. FDTD solution and equivalent model of series capacitor are used to explain the phenomenon. These results will contribute to the area of metamaterial electromagnetic wave absorber and other fields.

Facile Functionalization of Polymer Surfaces in Aqueous and Polar Organic Solvents via 3-Mercaptopropylsilatrane

Surface modification of a polymer substrate with a mercapto functionality is crucial in many applications such as flexible circuitry and point-of-care biosensors. We present here a novel bifunctional molecular adhesive, 3-mercaptopropylsilatrane (MPS), as an interface between polymer and metal surfaces. Under ambient conditions, surface modification of polymer surfaces with a mercapto functionality can be achieved with low concentration (0.46 mM) of MPS in aqueous solvent (50% ethanol) in a short time (<30 min). Three popular polymers for optical sensors, polycarbonate, polyethylene terephthalate, and poly(methyl methacrylate), were employed as substrates, and MPS films formed on these substrates were examined and compared with that on a glass substrate. The films were characterized by UV-vis spectroscopy, water contact angle, X-ray photoelectron spectroscopy, and atomic force microscopy. MPS was also used as a bifunctional linker for the construction of a gold nanoparticle (AuNP) sub-monolayer on these polymer surfaces. Under optimized preparation conditions, the absorbance and full width at half-maximum of the plasmon band are comparable to those of a AuNP-modified glass substrate. Hence, MPS may have a potential to be a key component in polymer substrate-based localized surface plasmon resonance sensors. A self-catalytic surface reaction mechanism is also proposed to account for the results. As compared to a glass surface with a high number of silanol groups, the successful formation of an MPS film on polymer surfaces with relatively few reactive sites is probably due to the lateral polymerization of MPS starting from a condensed MPS molecule on a reactive site of a polymer surface.

Superhydrophobic Au/polymer nanocomposite films via AACVD/swell encapsulation tandem synthesis procedure

A synthetic route is presented for creating well-attached Au/polymer nanocomposite thin films on glass which exhibit superhydrophobicity.