Development of a highly sensitive sensor chip using optical diagnostic based on functionalized plasmonically active AuNPs

Highly sensitive regenerable immunosensor for label-free detection of 2,4-dichlorophenoxyacetic acid at ppb levels by using surface plasmon resonance imaging

This paper presents low-cost, multi-channel, nano-grating SPR (Surface Plasmon Resonance) sensor chips for applications to disposable biomolecule detection. The present SPR sensor chip consists of two fluidic channels, including a sample channel and a reference channel, each having 833 nm-pitch PDMS gratings. The SPR signals from each channel are coupled by an external mirror and the SPR dip shift in the coupled signals is detected by a single spectrometer. Compared to the previous multi-channel SPR sensors using fiber-optic switches or special prisms, the present SPR sensor chips with PDMS nanogratings result in more compact and less expensive SPR detectors. We have designed and fabricated the SPR sensor chips with two channel gratings having the refractive index sensitivity of 321.78 nm/RI and 514.26 nm/RI, respectively. From the fabricated SPR sensor chips, we measure the SPR dip shift of 1.13±0.16 nm for the target biomolecules of 0.5 μM streptavidin binded on a 10% biotinylated surface. The real-time binding reaction rates of m-antibiotin has been monitored for the fixed concentration of 0.2 μM streptavidin as well as for the varying concentration range of 2-50 nM; thus obtaining the results for the fixed and varying concentration in good agreement with those obtained from a commercialized SPR sensor. It is demonstrated that the polymer nanograting SPR sensor chips offer simple and disposable biomolecule detection methods for point-of-care applications. [DOI: 10.1380/ejssnt.2009.750]

The paper presents a multi-channel real-time monitoring of biomolecule binding using a disposable SPR (Surface Plasmon Resonance) sensor chip integrated with nano-scale pitch grating. The sensor chip has two fluidic channels for sample delivery and gratings in each fluidic channel for SPR sensing. An external mirror makes an incidence of light at different angles on each sensing channel, thus generating two SPR dip at different spectral band. The gratings on the SPR sensor chip are fabricated by micromolding process for disposable application. We monitor the biotin-streptavidin binding reaction in real-time. The binding reaction using 0.2 muM streptavidin solution on the biotinylated surface is saturated in 30 min. The refractive index sensitivity of the SPR sensor chip is also characterized as 321.78 nm/RI at the sensing wavelength of 607 nm and 512.26 nm/RI at 704 nm.

Localized surface plasmon resonance biosensor chip surface modification and signal amplifications toward rapid and sensitive detection of COVID-19 infections

Novel surface plasmon resonance sensor chip functionalized with organic silica compounds for antibody attachment

The RNA folding variation due to one or more mutations leads to different RNA splicing, RNA processing, and translational controls as a result of differences in the primary and higher-ordered structures that interact with other cellular molecules. Thus, distinguishing RNA folding is one of the guides to detect the gene functions related to disease and drug responses. We found, previously, a small Ca(2+)-dependent deoxyribozyme with its site-specific RNA cleavage [Sugimoto, N., Okumoto, Y., and Ohmichi, T. (1999) J. Chem. Soc., Perkin Trans. 2, 1382-1388]. In this study, we report the potential of this deoxyribozyme as a useful tool to distinguish RNA foldings. It is found that the immobilized deoxyribozyme using avidin-biotin interaction cleaves the target site within only single-stranded RNAs. The systematic design for the target RNA hairpin loops shows that the immobilized deoxyribozyme is able to cleave them with a > or =17 nucleotide loop size at only one site under single-turnover conditions. Furthermore, an RNA cleavage reaction is detected using the immobilized deoxyribozyme on a surface plasmon resonance (SPR) sensor chip. These results show that the immobilized deoxyribozymes on a column and on an SPR sensor chip become a novel and useful tool to distinguish the RNA foldings.

Site specific biotinylated antibody functionalized Ag@AuNIs LSPR biosensor for the ultrasensitive detection of exosomal MCT4, a glioblastoma progression biomarker

We have developed novel surface plasmonresonance (SPR) sensorchips whose surfaces bear newly synthesized functional self-assembledmonolayer (SAM) anchoring lignin through covalent chemical bonds.The SPR sensor chips are remarkably robust and suitable for repetitiveand accurate measurement of noncovalent lignin–peptide interactions,which is of significant interest in the chemical or biochemical conversionof renewable woody biomass to valuable chemical feedstocks. The lignin-anchoredSAMs were prepared for the first time by click chemistry based onan azide–alkyne Huisgen cycloaddition: mixed SAMs are fabricatedon gold thin film using a mixture of alkynyl and methyl thioalkyloligo(ethyleneoxide) disulfides and then reacted with azidated milled wood ligninsto furnish the functional SAMs anchoring lignins covalently. The resultingSAMs were characterized using infrared reflection–absorption,Raman, and X-ray photoelectron spectroscopies to confirm covalentimmobilization of the lignins to the SAMs via triazole linkages andalso to reveal that the SAM formation induces a helical conformationof the ethylene oxide chains. Further, SPR measurements of the noncovalentlignin–peptide interactions using lignin-binding peptides havedemonstrated high reproducibility and durability of the prepared lignin-anchoredsensor chips.

Bovine serum albumin (BSA) protein is widely used to fabricate antifouling coatings for nanobiotechnology applications. Numerous BSA protein options are commercially available and obtained through different purification methods, however, there is no guidance on which ones are preferable for antifouling coatings. Herein, we investigate the real-time fabrication of antifouling coatings composed of BSA proteins obtained through different purification methods, and report significant differences in ultrathin film coating properties and ability to mitigate serum biofouling and to prevent nanoparticle-induced immune reactions. Mechanistic studies unravel the source of these performance variations, which are related to some BSA proteins containing fatty acid stabilizers while other BSA proteins are fatty acid-free depending on the purification method. Fatty acid-free BSA proteins exhibit greater conformational flexibility and less charge repulsion, which allow them to form more rigidly attached and tightly packed coatings on flat surfaces and nanoparticles that result in superior application performance.

Continuous flow immunosensor for highly selective and real-time detection of sub-ppb levels of 2-hydroxybiphenyl by using surface plasmon resonance imaging

Model Protein Adsorption on Polymers Explained by Hansen Solubility Parameters

In this paper, optical fiber sensors, based on both surface plasmon resonance (SPR) and localized SPR (LSPR) approaches, have been successfully developed and cross-compared. The SPR sensor has been constructed by coating a thin layer of gold film on a piece of an optical fiber with the cladding having first been removed. Several LSPR sensors, however, have been configured in a slightly different way through coating several unclad fibers, each with a thin layer of gold-nanorods (GNRs) with a different aspect ratio. Subsequently, both SPR and LSPR sensors are exposed to solutions with different refractive index and their corresponding plasmon resonance wavelength shifts have been recorded and cross-compared. The experimental results obtained confirm that the SPR sensor has demonstrated a much higher sensitivity than that of any of the LSPR sensors, irrespective of the variation of the aspect ratio of GNRs coated. The LSPR sensors, however, have demonstrated a much better linearity compared to that of the SPR sensor.

Natural proteins such as bovine serum albumin (BSA) are readily extracted from biological fluids and widely used in various applications such as drug delivery and surface coatings. It is standard practice to dope BSA proteins with an amphipathic stabilizer, most commonly fatty acids, during purification steps to maintain BSA conformational properties. There have been extensive studies investigating how fatty acids and related amphiphiles affect solution-phase BSA conformational properties, while it is far less understood how amphipathic stabilizers might influence noncovalent BSA adsorption onto solid supports, which is practically relevant to form surface coatings. Herein, we systematically investigated the binding interactions between BSA proteins and different molar ratios of caprylic acid (CA), monocaprylin (MC), and methyl caprylate (ME) amphiphiles-all of which have 8-carbon-long, saturated hydrocarbon chains with distinct headgroups-and resulting effects on BSA adsorption behavior on silica surfaces. Our findings revealed that anionic CA had the greatest binding affinity to BSA, which translated into greater solution-phase conformational stability and reduced adsorption-related conformational changes along with relatively low packing densities in fabricated BSA adlayers. On the other hand, nonionic MC had moderate binding affinity to BSA and could stabilize BSA conformational properties in the solution and adsorbed states while also enabling BSA adlayers to form with higher packing densities. We discuss physicochemical factors that contribute to these performance differences, and our findings demonstrate how rational selection of amphiphile type and amount can enable control over BSA adlayer properties, which could lead to improved BSA protein-based surface coatings.

Localized surface plasmon resonance (LSPR) biosensors show great potential for practical/commercial use in clinical diagnosis, home healthcare, environmental analysis, and public healthcare. However, two main issues, that is, low refractometric sensitivity and low reproducibility (large-area uniformity and batch-to-batch consistency), hinder the extensive applications of LSPR biosensors. Therefore, plasmonic nanostructures with high sensitivity and excellent reproducibility are desirable for preparing reliable LSPR sensors. Herein, we have fabricated plasmonic nanopyramid arrays (NPAs) for several batches with reproducible morphology and optical properties by elastic soft lithography and metal thermal evaporation. NPAs of various metals (i.e., Al, Au, and Ag) were also prepared by thermal evaporation with the according metals. The transmission spectra of these NPAs showed several narrow LSPR peaks in the visible-infrared wavelength region. The refractometric sensitivities of the LSPR peaks were systematically studied, and high refractometric sensitivities of 774.0, 472.8, and 421.0 nm/RIU were achieved on Al, Au, and Ag NPAs, respectively. To demonstrate the potential of the NPAs for multiplex applications, we first applied this highly sensitive Al NPA biosensor to monitoring the process of proliferation of HeLa cancer cells, in situ and in real time. Then, we demonstrated that the Au NPA was able to identify the absorbed analytes on its surface through the surface-enhanced Raman scattering spectrum. In addition, the finite difference time domain simulations were performed to reveal the electromagnetic field enhancement on NPAs. Because of the properties of high sensitivity and excellent reproducibility of the metal NPA LSPR substrates, as well as the simplicity and cost efficiency of the fabrication method, our proposed work will accelerate the practical use of LSPR sensors.

Adsorption of bovine serum albumin on amorphous carbon surfaces studied with dip pen nanolithography