Optical Biosensing Applications Research Articles

Facile synthesis of biomass silica-silver colloidal nanoparticles and its application as highly sensitive fluorescent biosensor

Colloidal inorganic nanoparticles have a significant impact for biosensing due to its precise biomolecular interaction. Herein, we report on the efficiency of silica-silver colloidal nanoparticles towards optical biosensor application. Silica colloids was prepared by the sol-gel method using biomass of rice husk as a precursor and then composited with silver colloids. The size of silica and silver (SiO2-Ag) colloidal nanoparticles was found to be 80 nm and 75 nm, respectively. The SiO2-Ag colloidal nanoparticles have the unique fluorescence at 325 nm with an excitation of 260 nm, which is significant for the excitation of most biomolecules, organelle stains and fluorescent labelling. The biosensing properties were validated against biomolecules such as glucose, uric acid, paracetamol, ascorbic acid and dopamine through plasmon resonance energy transfer (PRET) process by fluorescence spectroscopic technique. The glucose molecules responded with good sensing efficacy and the detection limit was found to be 0.49 µM. The proof of efficient glucose sensing of the SiO2-Ag colloidal nanoparticles also validated on human urine and serum and it gives the maximum recovery of 99.3 % and 98.2 %, respectively. These results support the efficacy of SiO2-Ag colloidal nanoparticles for optical biosensing applications in future.

Influence of Localized Surface Plasmon Polaritons on Silver Nanoparticles

In this article, we present a theoretical study on localized surface Plasmon of spherical Ag nanoparticles (NPs) done by numerical simulation. A plane EM wave was used to determine absorption cross-section and results showed that excitation of LSPPs produced an electric field on the surface of the nanoparticle. This field causes a large cross sectional area that influences higher scattering of incident photon at the surface of an absorber layer. It was concluded that LSPPs excitations in small size spherical particles can be utilized in low-cost solar cells to increase PCE of solar panels and can be expanded to many other fields of optoelectronic technologies ranging from solar cells, through photo diodes to optical bio-sensing applications. 

Porous Silicon-Zinc Oxide Nanocomposites Prepared by Atomic Layer Deposition for Biophotonic Applications.

In the current research, a porous silicon/zinc oxide (PSi/ZnO) nanocomposite produced by a combination of metal-assisted chemical etching (MACE) and atomic layer deposition (ALD) methods is presented. The applicability of the composite for biophotonics (optical biosensing) was investigated. To characterize the structural and optical properties of the produced PSi/ZnO nanocomposites, several studies were performed: scanning and transmission electron microscopy (SEM/TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance, and photoluminescence (PL). It was found that the ALD ZnO layer fully covers the PSi, and it possesses a polycrystalline wurtzite structure. The effect of the number of ALD cycles and the type of Si doping on the optical properties of nanocomposites was determined. PL measurements showed a “shoulder-shape” emission in the visible range. The mechanisms of the observed PL were discussed. It was demonstrated that the improved PL performance of the PSi/ZnO nanocomposites could be used for implementation in optical biosensor applications. Furthermore, the produced PSi/ZnO nanocomposite was tested for optical/PL biosensing towards mycotoxins (Aflatoxin B1) detection, confirming the applicability of the nanocomposites.

Functionalization of silicon dioxide and silicon nitride surfaces with aminosilanes for optical biosensing applications

AbstractThe development of optical biosensors based on silicon dioxide or silicon nitride transducers requires the chemical activation of their surface to achieve stable, repeatable and homogeneous binding of biomolecules. In the present study, the chemical activation of silicon dioxide and silicon nitride surfaces with 3‐aminopropyl‐triethoxysilane (APTES) was optimized so as to enable the immobilization of biomolecules by adsorption or covalent bonding. Chemical activation was performed with either aqueous or organic solution of APTES, and the surfaces were used to immobilize directly protein molecules by physical adsorption or further modified with glutaraldehyde to allow covalent binding of protein molecules. The protein immobilization capacity of the chemically activated silicon dioxide and silicon nitride surfaces was evaluated through incubation with mouse γ‐globulins and reaction with a fluorescently labelled goat antimouse IgG antibody. By determining the surface fluorescence signal intensity, it was found that modification with 5% (v/v) APTES solution in ethanol followed by modification with glutaraldehyde provided 30% higher fluorescence signals than all the other protocols tested. In addition, this method provided the lower signal variation between different chips. To test the possible advantages of the chemical activation protocols for optical biosensing applications, they were also applied to a label‐free white light interference spectroscopy sensor and evaluated through (a) real‐time monitoring of the reaction between immobilized on the sensor surface mouse γ‐globulins with an unlabelled goat antimouse IgG antibody and (b) a non‐competitive immunoassay for the determination of C‐reactive protein. The results showed that in case of antibody, physical absorption provided marginally higher binding capacity to covalent bonding.

Interfacial charge-transfer transitions in ZnO induced exclusively by adsorption of aromatic thiols.

Interfacial charge-transfer transitions (ICTTs) between organic compounds and inorganic semiconductors have recently gained increasing interest as a new visible light absorption mechanism for optical biosensing via direct visualization, surface enhanced Raman scattering (SERS), and circular dichroism (CD) and also as a direct charge separation mechanism for photoenergy conversions such as photocatalytic reactions. So far, ICTTs have been observed with various organic compounds, while inorganic materials are almost limited to titanium oxides such as TiO2. Although SERS via ICTTs has been reported with several kinds of inorganic semiconductors, their ICTT bands have not been observed directly except for TiO2. From these viewpoints, the direct observation of ICTT bands in inorganic semiconductors other than TiO2 is an important issue. In this study, we demonstrate ICTTs in ZnO induced by the adsorption of aromatic thiols. ICTTs take place from the HOMO of the adsorbed thiol compounds to the conduction band of ZnO via a Ti-S linkage. Notably, ZnO selectively shows ICTTs with aromatic thiols, but almost no ICTT with oxygen-linkage-type organic compounds such as phenol. In addition, the wide-range control of ICTTs was achieved by the chemical modification of aromatic thiols. Our research not only opens up a new way for the research of ICTTs but also supports the reported ICTT-based SERS in ZnO.

Emerging Applications of Optical Bio-Sensors

In the simplest words, a bio-sensor is an analytic device. In recent years, bio-sensors have shown emerging contribution in medical diagnosis, drug discovery, and treatment process. In this regards, continuous research is ongoing and many more features are being added in the sensing technologies. Optical sensing technology is no more bound in research area but also in the commercial use for the betterment of mankind. There are different types of bio-sensors particularly optical which have already been developed and research is going to expand many more of them. Sensing applications are not limited in glucose, DNA, cancer cell detection, drug discovery, immunological, Hepatitis B virus, and enzyme detection but also many more development is knocking at the door. Therefore, this review paper is focused on the applications and functions of bio-sensors (especially optical) in medical diagnostics and treatment.

Ultra-small dye-doped silica nanoparticles via modified sol-gel technique

In modern biosensing and imaging, fluorescence-based methods constitute the most diffused approach to achieve optimal detection of analytes, both in solution and on the single-particle level. Despite the huge progresses made in recent decades in the development of plasmonic biosensors and label-free sensing techniques, fluorescent molecules remain the most commonly used contrast agents to date for commercial imaging and detection methods. However, they exhibit low stability, can be difficult to functionalise, and often result in a low signal-to-noise ratio. Thus, embedding fluorescent probes into robust and bio-compatible materials, such as silica nanoparticles, can substantially enhance the detection limit and dramatically increase the sensitivity. In this work, ultra-small fluorescent silica nanoparticles (NPs) for optical biosensing applications were doped with a fluorescent dye, using simple water-based sol-gel approaches based on the classical Stöber procedure. By systematically modulating reaction parameters, controllable size tuning of particle diameters as low as 10 nm was achieved. Particles morphology and optical response were evaluated showing a possible single-molecule behaviour, without employing microemulsion methods to achieve similar results.Graphical abstractWe report a simple, cheap, reliable protocol for the synthesis and systematic tuning of ultra-small (< 10 nm) dye-doped luminescent silica nanoparticles.

Recent Advances in Porous Silicon Based Optical Biosensors

Abstract PSi structures have unique physical and optical properties, which are being exploited for a numerous biomedical applications including biosensing, bioimaging, tissue engineering, and drug delivery. Different PSi optical structures can be fabricated to improve the sensitivity of the optical measurements. A very high surface area per volume of PSi can be used for the higher loading of target analytes in a small sensor area, which helps in increasing sensitivity and allows the miniaturization of biosensor. The specificity of PSi biosensor to the target analyte can be inferred by immobilizing the corresponding bioreceptor such as DNA, enzyme, or antibody via different conjugation chemistries. Finally, PSi is biocompatible material that offers additional advantage in comparison to other sensing platforms for in vivo implantable biosensing applications. This paper reviews fabrication, surface modification, biofunctionalization, and optical biosensing applications of PSi structures with special emphasis on in vivo and PSi photonic particles biosensing.

Recent advances in emerging 2D nanomaterials for biosensing and bioimaging applications

Abstract The great success of graphene throws new light on discovering more two-dimensional (2D) layered nanomaterials that stem from atomically thin 2D sheets. Compared with a single element of graphene, emerging graphene-like 2D materials composed of multiple elements that possess more versatility, greater flexibility and better functionality with a wide range of potential applications. In this review, we provide insights into the rapidly emerging 2D materials and their biosensing and bioimaging applications in recent three years, including 2D transition metal nanomaterials, graphitic nitride materials, black phosphorus, and emerging 2D organic polymers. We first briefly highlight their unique 2D morphology and physicochemical properties and then focus on their recent applications in electrochemical biosensing, optical biosensing and bioimaging. The challenges and some thoughts on future perspectives in this field are also addressed.

Hidden symmetries in plasmonic gratings

Plasmonic gratings constitute a paradigmatic instance of the wide range of applications enabled by plasmonics. While subwavelength metal gratings find applications in optical biosensing and photovoltaics, atomically thin gratings achieved by periodically doping a graphene monolayer perform as metasurfaces for the control of terahertz radiation. In this paper we show how these two instances of plasmonic gratings inherit their spectral properties from an underlying slab with translational symmetry.We develop an analytical formalism to accurately derive the mode spectrum of the gratings that provides a great physical insight.

Noncovalent Protein and Peptide Functionalization of Single-Walled Carbon Nanotubes for Biodelivery and Optical Sensing Applications.

The exquisite structural and optical characteristics of single-walled carbon nanotubes (SWCNTs), combined with the tunable specificities of proteins and peptides, can be exploited to strongly benefit technologies with applications in fields ranging from biomedicine to industrial biocatalysis. The key to exploiting the synergism of these materials is designing protein/peptide-SWCNT conjugation schemes that preserve biomolecule activity while keeping the near-infrared optical and electronic properties of SWCNTs intact. Since sp2 bond-breaking disrupts the optoelectronic properties of SWCNTs, noncovalent conjugation strategies are needed to interface biomolecules to the nanotube surface for optical biosensing and delivery applications. An underlying understanding of the forces contributing to protein and peptide interaction with the nanotube is thus necessary to identify the appropriate conjugation design rules for specific applications. This article explores the molecular interactions that govern the adsorption of peptides and proteins on SWCNT surfaces, elucidating contributions from individual amino acids as well as secondary and tertiary protein structure and conformation. Various noncovalent conjugation strategies for immobilizing peptides, homopolypeptides, and soluble and membrane proteins on SWCNT surfaces are presented, highlighting studies focused on developing near-infrared optical sensors and molecular scaffolds for self-assembly and biochemical analysis. The analysis presented herein suggests that though direct adsorption of proteins and peptides onto SWCNTs can be principally applied to drug and gene delivery, in vivo imaging and targeting, or cancer therapy, nondirect conjugation strategies using artificial or natural membranes, polymers, or linker molecules are often better suited for biosensing applications that require conservation of biomolecular functionality or precise control of the biomolecule's orientation. These design rules are intended to provide the reader with a rational approach to engineering biomolecule-SWCNT platforms, broadening the breadth and accessibility of both wild-type and engineered biomolecules for SWCNT-based applications.

High Numerical Aperture Hexagonal Stacked Ring-Based Bidirectional Flexible Polymer Microlens Array.

Flexible imprinted photonic nanostructures that are able to diffract/focus narrow-band light have potential applications in optical lenses, filters, tunable lasers, displays, and biosensing. Nanophotonic structures through holography and roll-to-roll printing may reduce fabrication complexities and expenses and enable mass production. Here, 3D photonic nanostructures of a stacked ring array were imprinted on acrylate polymer (AP) over poly(ethylene terephthalate) (PET) substrate through holography and lift-off processes to create a microlens array (MLA). The surface structure of the array consisted of circular nonostepped pyramids, and repeated patterns were in hexagonal arrangements. Stacked-ring-based MLA (SMLA) on a flexible AP-PET substrate showed efficient bidirectional light focusing and maximum numerical aperture (NA = 0.60) with a reasonable filling factor. The nanostructures produced a well-ordered hexagonally focused diffraction pattern in the far field, and power intensities were measured through angle-resolved experiments. The variation of nanostep dimensions (width and height) and the number of steps resulted in different photonic bandgaps, and the arrays produced distance-dependent narrow-band light focusing. The validation of the SMLA was demonstrated through the text, image, and hologram projection experiments. It is anticipated that imprinted bidirectional SMLA over flexible substrates may find applications in optical systems, displays, and portable sensors.

Biofunctionalization Effectiveness of Titanium Oxide Thin Films Obtained with Physical and Chemical Vapour Deposition Methods for Optical Label-free Biosensing Applications

An influence of titanium oxide (TiOx) deposition method, i.e., chemical (atomic layer deposition, ALD) and physical (reactive magnetron sputtering, RMS) vapor deposition, on the optical properties and surface chemical modification were investigated. TheTiOx film was used as a functional coating for enhancing sensing properties of two types of label-free optical sensors, i.e., localized surface plasmon resonance (LSPR) sensors based on gold nanoparticles and induced in optical fibre long-period gratings (LPGs) working in visible and infrared spectral range, respectively. We have found that independently on deposition method the films increase the sensitivity of LPG and enhance biofunctionalization capabilities.

Patternable polymer microstructure for optical biosensing

Introduction: Applications of rapid sensing and detection of biological analytes are growing due to the significant environmental monitoring, health screening, cell growth and bio/chemical sensors. These factors influence the research and development on simple, cheap and sensitive functional biomolecular device. The interest in the label-free optical detection has been increased as the optical waveguide has a direct light interaction with surrounding analytes, easy integration with microfluidic system and the capability to provide specific interaction. Methods: In this work, we demonstrate the potential of microstructure as an optical biosensor. Visible wavelength is utilized because it is commonly used in biological and chemical sensing for both label and label-free sensing. The SU8 polymer microstructures waveguides were fabricated on 3.5 µm oxide. The microstructures are simulated using COMSOL Multiphysics. Simulation was recorded based on refractive index that mimic the bioanalytes solution and biological binding. Then the experimental setup is developed to control the optical component and manipulate the liquid samples. The fabricated devices were characterized by using the end-facet technique. Meanwhile, microfluidic channel system was also constructed in order to inject the liquid sample into the sensor surface. Results: The wavelength shift for microresonator structure approximately 41.2 nm for 0.1 increments of surrounding refractive index. The experiments demonstrate that the shift occurred approximately 22.5 nm. In other hand, simulated Bragg grating structure gained the shift at 63.2 nm. Meanwhile, the experimental results achieve approximately 20.3 nm. Conclusions: Thus, both simulation and experimental results strongly indicate that patternable polymer microstructure has a huge potential for optical biosensing applications at visible region.

Rigid Rod-Based FRET Probes for Membrane Sensing Applications.

Oligospirothioketal (OSTK) rods are presented as an adjustable scaffold for optical membrane probes. The OSTK rods are readily incorporated into lipid bilayers due to their hydrophobic backbones. Because of their high length-over-diameter aspect ratio, only a minimal disturbance of the lipid bilayer is caused. OSTK rods show outstanding rigidity and allow defined labeling with fluorescent dyes, yielding full control of the orientation between the dye and OSTK skeleton. This allows the construction of novel Förster resonance energy transfer probes with highly defined relative orientations of the transition dipole moments of the donor and acceptor dyes and makes the class of OSTK probes a powerful, flexible toolbox for optical biosensing applications. Data on steady-state and time-resolved fluorescence experiments investigating the incorporation of coumarin- and [1,3]dioxolo[4,5-f][1,3]benzo-dioxole-labeled OSTKs in large unilamellar vesicles are presented as a show case.

OPTICAL BIOSENSORS PROSPECTIVE BASED ON BRAGG GRATING POLYMER WAVEGUIDE

In this work, we demonstrate the potential of Bragg grating polymer waveguide as an optical biosensor. Visible wavelength region at 650 nm is used as a centre wavelength because it is commonly used in biological and chemical sensing for both label and label-free sensing. The Bragg polymer waveguide structure is simulated using RSoft optical design and analysis software. The results show that there is a transmission drop with a 3 dB bandwidth of 661.0 nm when the surrounding refractive index is 1.33. The specific wavelength (transmission drop) is shifted to 724.2 nm when we increased the surrounding medium into 1.43 to mimic the bioanalytes solution. Simulation result shows that the wavelength shift was approximately 63.2 nm for every 0.1 increasing of surrounding refractive index. The Bragg grating polymer waveguide was fabricated by using electron beam lithography. Then, the fabricated devices were easily integrated within microfluidic systems in order to validate the wavelength shift. From the experiments, the wavelength shift occurred approximately 20.3 nm over 0.1 increment of refractive index. The discrepancies were likely due to the accumulation of sucrose solution on top and sidewall of the sensing area, the insertion loss between input and output coupling of the waveguide interface that induced the noise to signal ratio. Where we know that, is impossible to happen in simulation. Thus both simulation and experimental results strongly indicate that Bragg grating polymer waveguide structure at visible wavelength region have a potential for label or label-free optical biosensing applications.

Rhodopsin Engineering through Structure-Guided Recombination

Membrane proteins assume key roles in environmental sensing, metabolite uptake, and product efflux. Given the vital connections they facilitate between a cell and its environment, there is great potential to engineer these proteins to modulate cellular activity and productivity. For this project, we focus our efforts on rhodopsins, light-sensing transporters and channels that have applications in optical biosensors, neuronal monitoring and control, and bioenergy. Using structure-guided recombination we have built a library of chimeric rhodopsins. We used a novel assay for membrane protein localization to pre-screen a fraction of the library. A diverse selection of well-expressing variants has been further characterized via electrophysiology. Through machine learning we can associate rhodopsin expression, localization, and functional properties to blocks of structure and make predictions on the properties of untested chimeras.

Preparation of highly luminescent and color tunable carbon nanodots under visible light excitation for in vitro and in vivo bio-imaging

Abstract

Designing Plasmonic Gratings with Transformation Optics

Plasmonic gratings that support both localized and propagating plasmons have wide applications in solar cells and optical biosensing. In this paper, we report on a most unusual grating designed to capture light efficiently into surface plasmons and concentrate their energy at hot spots where the field is resonantly enhanced. The dispersion of the surface plasmons shows degeneracy points at k=0, where, despite a strongly modulated grating, hidden symmetries forbid hybridization of plasmons traveling in opposite directions.Received 9 March 2015DOI:https://doi.org/10.1103/PhysRevX.5.031029This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical Society

Photo-physical characterization of fluorophore Ru(bpy)32+ for optical biosensing applications

We studied absorption, emission and lifetime of the coordination compound tris(2,2′-bipyridyl)ruthenium(II) fluorophore (Ru(bpy)32+) both dissolved in water solutions and dried. Lifetime measurements were carried out using a new detector, the Silicon Photomultiplier (SiPM), which is more sensitive and physically much smaller than conventional optical detectors, such as imager and scanner. Through these analyses and a morphological characterization with transmission electron microscopy, revealed its usability for sensor applications, in particular, as dye in optical DNA-chip technology, a viable alternative to the conventional CY5 fluorophore. The use of Ru(bpy)32+ would solve some of the typical disadvantages related to Cy5’s application, such as self-absorption of fluorescence and photobleaching. In addition, the Ru(bpy)32+ longer lifetime may play a key role in the definition of new optical DNA-chip.