Study of substrate-enzyme interaction between immobilized pyridoxamine and recombinant porcine pyridoxal kinase using surface plasmon resonance biosensor

2D material-based surface plasmon resonance biosensors for applications in different domains: an insight

The design of surface plasmon resonance (SPR) sensors has been greatly enhanced in recent years by the advancements in the production and integration of nanostructures, leading to more compact and efficient devices. There have been reports of novel SPR sensors having distinct nanostructures, either as signal amplification tags like gold nanoparticles (AuNPs) or as sensing substrate-like two-dimensional (2D) materials including graphene, transition metal dichalcogenides (TMDCs), MXene, black phosphorus (BP), metal-organic frameworks (MOFs), and antimonene. Such 2D-based SPR biosensors offer advantages over conventional sensors due to significant increases in their sensitivity with a good figure of merit and limit of detection (LOD). Due to their atomically thin structure, improved sensitivity, and sophisticated functionalization capabilities, 2D materials can open up new possibilities in the field of healthcare, particularly in point-of-care diagnostics, environmental and food monitoring, homeland security protection, clinical diagnosis and treatment, and flexible or transient bioelectronics. The present study articulates an in-depth analysis of the most recent developments in 2D material-based SPR sensor technology. Moreover, in-depth research of 2D materials, their integration with optoelectronic technology for a new sensing platform, and the predicted and experimental outcomes of various excitation approaches are highlighted, along with the principles of SPR biosensors. Furthermore, the review projects the potential prospects and future trends of these emerging materials-based SPR biosensors to advance in clinical diagnosis, healthcare biochemical, and biological applications.

An LSPR Sensor Integrated with VCSEL and Microfluidic Chip

The work introduces a localized surface plasmon resonance (LSPR) sensor chip integrated with vertical-cavity surface-emitting lasers (VCSELs). Using VCSEL as the light source, the hexagonal gold nanoparticle array was integrated with anodic aluminum oxide (AAO) as the mask on the light-emitting end face. The sensitivity sensing test of the refractive index solution was realized, combined with microfluidic technology. At the same time, the finite-difference time- domain (FDTD) algorithm was applied to model and simulate the gold nanostructures. The experimental results showed that the output power of the sensor was related to the refractive index of the sucrose solution. The maximum sensitivity of the sensor was 1.65 × 106 nW/RIU, which gives it great application potential in the field of biomolecular detection.

Theoretical and experimental study of a highly sensitive SPR biosensor based on Au grating and Au film coupling structure

A high-sensitivity surface plasmon resonance (SPR) sensor based on the coupling of Au grating and Au film is investigated through simulations and experiments. The SPR sensor is designed by using a hybrid method composed of genetic algorithm (GA) and rigorous coupled wave analysis (RCWA). The numerical results indicate the sensor has an angular sensitivity of 397.3°/RIU (refractive index unit), which is approximately 2.81 times higher than the conventional Au-based sensor and it is verified by experiments. Theoretical analysis, by finite-difference time-domain (FDTD) method, demonstrates the co-coupling between surface plasmon polaritons (SPPs) propagating on the surface of Au film and localized surface plasmons (LSPs) in the Au grating nanostructure, improving the sensitivity of the SPR sensor. According to the optimized structural parameters, the proposed sensor is fabricated using e-beam lithography and magnetron sputtering. In addition, the proposed sensor is very sensitive to the detection of small molecules. The limit of detection (LOD) for okadaic acid (OA) is 0.72 ng/mL based on an indirect competitive inhibition method, which is approximately 38 times lower than the conventional Au sensor. Such a high-sensitivity SPR biosensor has potential in the applications of immunoassays and clinical diagnosis.

Recent Advances in Rapid and Highly Sensitive Detection of Proteins and Specific DNA Sequences Using a Magnetic Modulation Biosensing System

In early disease stages, biomolecules of interest exist in very low concentrations, presenting a significant challenge for analytical devices and methods. Here, we provide a comprehensive overview of an innovative optical biosensing technology, termed magnetic modulation biosensing (MMB), its biomedical applications, and its ongoing development. In MMB, magnetic beads are attached to fluorescently labeled target molecules. A controlled magnetic force aggregates the magnetic beads and transports them in and out of an excitation laser beam, generating a periodic fluorescent signal that is detected and demodulated. MMB applications include rapid and highly sensitive detection of specific nucleic acid sequences, antibodies, proteins, and protein interactions. Compared with other established analytical methodologies, MMB provides improved sensitivity, shorter processing time, and simpler protocols.

Exploring Graphene and MoS2 Chips Based Surface Plasmon Resonance Biosensors for Diagnostic Applications

Until now, two-dimensional (2D) nanomaterials have been widely studied and applied in the biosensor field. Some of the advantages offered by these 2D materials include large specific surface area, high conductivity, and easy surface modification. This review discusses the use of 2D material in surface plasmon resonance (SPR) biosensor for diagnostic applications. Two-dimensional material reviewed includes graphene and molybdenum disulfide (MoS2). The discussion begins with a brief introduction to the general principles of the SPR biosensor. The discussion continues by explaining the properties and characteristics of each material and its effect on the performance of the SPR biosensor, in particular its sensitivity. This review concludes with some recent applications of graphene- and MoS2-based SPR biosensor in diagnostic applications.

Graphene-MoS2 with TiO2-SiO2 layers based surface plasmon resonance biosensor: Numerical development for formalin detection

In this article, numerically a surface plasmon resonance (SPR) biosensor is developed based on Graphene-M_OS₂with TiO₂—SiO₂ hybrid structure for the detection of formalin. Based on attenuated total reflection (ATR) method, we used angular interrogation technique to sense the presence the formalin by observing the change of “minimum reflectance with respect to SPR angle” and “maximum transmittance with respect to surface plasmon resonance frequency (SPRF)”. Here, we used Chitosan as probe analyte to perform chemical reaction with formalin (formaldehyde) which is consider as target analyte. Simulation results show a negligible variation of SPRF and SPR angle for improper sensing of formalin that confirms absence of formalin whereas for proper sensing is considerably countable that confirms the presence of formalin. Thereafter, a comparison of sensitivity for different sensor structure is made. It is observed that the sensitivity without TiO₂, SiO₂, MoS₂ and Graphene (conventional structure) is very poor and 73.67% whereas the sensitivity with graphene but without TiO₂, SiO₂ and MoS₂ layers is 74.67% consistently better than the conventional structure. This is due to the electron loss of graphene, which is accompanying with the imaginary dielectric constant. Furthermore, the sensitivity without TiO₂, SiO₂ and graphene but with MoS₂ layer is 79.167%. After more if both graphene and MoS2 are used and TiO₂ and SiO₂ layers are not used then sensitivity improves to 80.5%. This greater than before performance is due to the absorption ability and optical characteristics of graphene biomolecules and high fluorescence quenching ability of MoS₂. Further again, if TiO₂—SiO₂ composite layer is used with the Graphene-MoS2 then the sensitivity enhances from 80.5% to 82.5%. Finally, the sensitivity for the proposed structure has been carried out, and result is 82.83%, the highest value among all the previous structures to integrate the advantages of graphene, MoS₂, TiO₂ and SiO₂.

Immobilized Enzymes in Biosensor Applications

Enzyme-based biosensing devices have been extensively developed over the last few decades, and have proven to be innovative techniques in the qualitative and quantitative analysis of a variety of target substrates over a wide range of applications. Distinct advantages that enzyme-based biosensors provide, such as high sensitivity and specificity, portability, cost-effectiveness, and the possibilities for miniaturization and point-of-care diagnostic testing make them more and more attractive for research focused on clinical analysis, food safety control, or disease monitoring purposes. Therefore, this review article investigates the operating principle of enzymatic biosensors utilizing electrochemical, optical, thermistor, and piezoelectric measurement techniques and their applications in the literature, as well as approaches in improving the use of enzymes for biosensors.

The Alkaline Phosphatase (ALPL) Locus Is Associated with B6 Vitamer Levels in CSF and Plasma

The active form of vitamin B6, pyridoxal phosphate (PLP), is essential for human metabolism. The brain is dependent on vitamin B6 for its neurotransmitter balance. To obtain insight into the genetic determinants of vitamin B6 homeostasis, we conducted a genome-wide association study (GWAS) of the B6 vitamers pyridoxal (PL), PLP and the degradation product of vitamin B6, pyridoxic acid (PA). We collected a unique sample set of cerebrospinal fluid (CSF) and plasma from the same healthy human subjects of Dutch ancestry (n = 493) and included concentrations and ratios in and between these body fluids in our analysis. Based on a multivariate joint analysis of all B6 vitamers and their ratios, we identified a genome-wide significant association at a locus on chromosome 1 containing the ALPL (alkaline phosphatase) gene (minimal p = 7.89 × 10⁻¹⁰, rs1106357, minor allele frequency (MAF) = 0.46), previously associated with vitamin B6 levels in blood. Subjects homozygous for the minor allele showed a 1.4-times-higher ratio between PLP and PL in plasma, and even a 1.6-times-higher ratio between PLP and PL in CSF than subjects homozygous for the major allele. In addition, we observed a suggestive association with the CSF:plasma ratio of PLP on chromosome 15 (minimal p = 7.93 × 10⁻⁷, and MAF = 0.06 for rs28789220). Even though this finding is not reaching genome-wide significance, it highlights the potential of our experimental setup for studying transport and metabolism across the blood–CSF barrier. This GWAS of B6 vitamers identifies alkaline phosphatase as a key regulator in human vitamin B6 metabolism in CSF as well as plasma. Furthermore, our results demonstrate the potential of genetic studies of metabolites in plasma and CSF to elucidate biological aspects underlying metabolite generation, transport and degradation.

Binding Kinetics of Methylene Blue on Monolayer Graphene Investigated by Multiparameter Surface Plasmon Resonance

In this paper, we study the interaction of a small dye molecule, namely, methylene blue (MB) with graphene surfaces using surface plasmon resonance (SPR). We show that by utilizing all of the parameters of the SPR angular dip and exploiting the fact that MB absorbs light at the operating wavelength, it is possible to detect the binding of small molecules that would otherwise not give a significant signal. The binding of MB to unmodified graphene is found to be stronger than that for gold. By studying the interaction at modified surfaces, we demonstrate that electrostatic effects play a dominant role in the binding of MB on to graphene. Furthermore, following the binding kinetics at various concentrations allows us to estimate apparent equilibrium binding and rate constants for the interaction of MB with graphene.

Surface plasmon resonance: a versatile technique for biosensor applications

Surface plasmon resonance (SPR) is a label-free detection method which has emerged during the last two decades as a suitable and reliable platform in clinical analysis for biomolecular interactions. The technique makes it possible to measure interactions in real-time with high sensitivity and without the need of labels. This review article discusses a wide range of applications in optical-based sensors using either surface plasmon resonance (SPR) or surface plasmon resonance imaging (SPRI). Here we summarize the principles, provide examples, and illustrate the utility of SPR and SPRI through example applications from the biomedical, proteomics, genomics and bioengineering fields. In addition, SPR signal amplification strategies and surface functionalization are covered in the review.

Application of optical biosensors in small-molecule screening activities

The last two decades have seen remarkable progress and improvements in optical biosensor systems such that those are currently seen as an important and value-adding component of modern drug screening activities. In particular the introduction of microplate-based biosensor systems holds the promise to match the required throughput without compromising on data quality thus representing a sought-after complement to traditional fluidic systems. This article aims to highlight the application of the two most prominent optical biosensor technologies, namely surface plasmon resonance (SPR) and optical waveguide grating (OWG), in small-molecule screening and will present, review and discuss the advantages and disadvantages of different assay formats on these platforms. A particular focus will be on the specific advantages of the inhibition in solution assay (ISA) format in contrast to traditional direct binding assays (DBA). Furthermore we will discuss different application areas for both fluidic as well as plate-based biosensor systems by considering the individual strength of the platforms.

Time-resolved microspectrofluorometry and fluorescence imaging techniques: study of porphyrin-mediated cellular uptake of oligonucleotides

Time-resolved confocal microspectrofluorometry and fluorescence microscopy imaging were applied to monitor the cellular uptake of fluorescent-labeled oligonucleotides (ONs) delivered by a porphyrin molecule. The fate of porphyrin-ON complexes inside living cells has also been monitored. Due to intrinsic fluorescence of the porphyrin and sensitivity of its characteristics to microenvironment, multicomponent analysis of time-resolved fluorescence provides unique information about stability of the porphyrin-ON complexes, ON interactions with their target sequences, and ON and porphyrin distributions after delivery inside the cells. Time-resolved confocal microspectrofluorometry indeed delivers additional information compared with fluorescence confocal microscopy imaging widely employed to study ON uptake.

In situ phosphorylation of immobilized receptors on biosensor surfaces: application to E-cadherin/beta-catenin interactions

Phosphorylation is a key posttranslational modification for modulating biological interactions. Biosensor technology is ideally suited for examining in real time the role of phosphorylation on protein-protein interactions in signaling pathways. We have developed processes for on-chip phosphorylation of immobilized receptors on biosensor surfaces. These processes have been used to analyze E-cadherin/beta-catenin interactions. Phosphorylation of the intracellular domain (ICD) of E-cadherin modulates its affinity to beta-catenin and consequently the strength of cell-cell adhesion. We have phosphorylated immobilized E-cadherin ICD in situ using casein kinase 1 (CK1), casein kinase 2 (CK2), and src. On-chip phosphorylation of E-cadherin was confirmed using anti-phosphoserine and anti-phosphotyrosine antibodies. The binding of beta-catenin to E-cadherin was analyzed quantitatively. CK1 phosphorylation of E-cadherin increased the binding affinity to beta-catenin from approximately 230 to 4 nM. A similar increase in affinity, from 260 to 4 nM, was obtained with CK2 phosphorylation of E-cadherin. However, phosphorylation by src kinase decreased the affinity constant from approximately 260 nM to 4 microM. Interestingly, phosphorylation of E-cadherin by CK1 or CK2 prevented the inhibition of beta-catenin binding by src phosphorylation.

Expression, purification, and kinetic constants for human and Escherichia coli pyridoxal kinases

Pyridoxal kinase is an ATP dependent enzyme that phosphorylates pyridoxal, pyridoxine, and pyridoxamine forming their respective 5'-phosphorylated esters. The kinase is a part of the salvage pathway for re-utilizing pyridoxal 5'-phosphate, which serves as a coenzyme for dozens of enzymes involved in amino acid and sugar metabolism. Clones of two pyridoxal kinases from Escherichia coli and one from human were inserted into a pET 22b plasmid and expressed in E. coli. All three enzymes were purified to near homogeneity and kinetic constants were determined for the three vitamin substrates. Previous studies had suggested that ZnATP was the preferred trinucleotide substrate, but our studies show that under physiological conditions MgATP is the preferred substrate. One of the two E. coli kinases has very low activity for pyridoxal, pyridoxine, and pyridoxamine. We conclude that in vivo this kinase may have an alternate substrate involved in another metabolic pathway and that pyridoxal has only a poor secondary activity for this kinase.

A survey of the year 2002 commercial optical biosensor literature

We have compiled 819 articles published in the year 2002 that involved commercial optical biosensor technology. The literature demonstrates that the technology's application continues to increase as biosensors are contributing to diverse scientific fields and are used to examine interactions ranging in size from small molecules to whole cells. Also, the variety of available commercial biosensor platforms is increasing and the expertise of users is improving. In this review, we use the literature to focus on the basic types of biosensor experiments, including kinetics, equilibrium analysis, solution competition, active concentration determination and screening. In addition, using examples of particularly well-performed analyses, we illustrate the high information content available in the primary response data and emphasize the impact of including figures in publications to support the results of biosensor analyses.