Surface Plasmon Resonance Biosensors: A Review of Molecular Imaging with High Spatial Resolution

Surface plasmon resonance (SPR) is a powerful tool for determining molecular interactions quantitatively. SPR imaging (SPRi) further improves the throughput of SPR technology and provides the spatially resolved capability for observing the molecular interaction dynamics in detail. SPRi is becoming more and more popular in biological and chemical sensing and imaging. However, SPRi suffers from low spatial resolution due to the imperfect optical components and delocalized features of propagating surface plasmonic waves along the surface. Diverse kinds of approaches have been developed to improve the spatial resolution of SPRi, which have enormously impelled the development of the methodology and further extended its possible applications. In this minireview, we introduce the mechanisms for building a high-spatial-resolution SPRi system and present its experimental schemes from prism-coupled SPRi and SPR microscopy (SPRM) to surface plasmonic scattering microscopy (SPSM); summarize its exciting applications, including molecular interaction analysis, molecular imaging and profiling, tracking of single entities, and analysis of single cells; and discuss its challenges in recent decade as well as the promising future.

A New Approach to the Quantification of Fibroblast Growth Factor 23-An Array Surface Plasmon Resonance Imaging Biosensor

A new biosensor based on the "surface plasmon resonance imaging (SPRi)" detection technique for the quantification of "fibroblast growth factor 23 (FGF23)" has been developed. FGF23 is mainly produced in bone tissues as a phosphaturic hormone that forms a trimeric complex with "fibroblast growth factor receptor 1 (FGFR1)" and αKlotho upon secretion. FGF23 stimulates phosphate excretion and inhibits the formation of active vitamin D in the kidneys. FGF23 has been shown to play a role in bone carcinogenesis and metastasis. The newly developed method, based on the array SPRi biosensor, was validated-the precision, accuracy, and selectivity were acceptable, and yielded less than ±10% recovery. The rectilinear response of the biosensor ranges from 1 to 75 pg/mL. The limit of detection was 0.033 pg/mL, and the limit of quantification was 0.107 pg/mL. The biosensor was used to determine FGF23 concentrations in the blood plasma of healthy subjects and patients with "clear cell" renal cell carcinoma (ccRCC). The obtained results were compared with those measured through an "enzyme-linked immunosorbent assay (ELISA)". The determined Pearson correlation coefficients were 0.994 and 0.989, demonstrating that the newly developed biosensor can be used as a competitive method for the ELISA.

Semi-Selective Array for the Classification of Purines with Surface Plasmon Resonance Imaging and Deep Learning Data Analysis

In process analytics or environmental monitoring, the real-time recording of the composition of complex samples over a long period of time presents a great challenge. Promising solutions are label-free techniques such as surface plasmon resonance (SPR) spectroscopy. They are, however, often limited due to poor reversibility of analyte binding. In this work, we introduce how SPR imaging in combination with a semi-selective functional surface and smart data analysis can identify small and chemically similar molecules. Our sensor uses individual functional spots made from different ratios of graphene oxide and reduced graphene oxide, which generate a unique signal pattern depending on the analyte due to different binding affinities. These patterns allow four purine bases to be distinguished after classification using a convolutional neural network (CNN) at concentrations as low as 50 μM. The validation and test set classification accuracies were constant across multiple measurements on multiple sensors using a standard CNN, which promises to serve as a future method for developing online sensors in complex mixtures.

Plasmonic Effect of Gold-Patchy Silica Nanoparticles on Green Light-Photopolymerizable Dental Resin

A low ratio of polymerization is a major problem in resin-based composites. In this paper, the plasmonic effect of gold-covered silica nanoparticles on the physicochemical and mechanical properties of bisphenol A diglycidyl dimethacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA) and urethane dimethacrylate (UDMA) green light-photopolymerizable dental resin was investigated at an intensity of 1.4 mW/cm2 for 40 s. Transmission electron microscopy (TEM) showed silica of about 350 nm covered with 12-15 nm gold nanoparticles (Au NPs) at 100% nominal coverage. Five different concentrations of bare and patchy silica particles were used; in the latter composite, the calculated Au wt% were 0.0052 wt%, 0.0104 wt%, 0.0208 wt%, 0.04160 wt%, and 0.0823 wt%. The plasmon peak of patchy silica-filled nanocomposite overlapped with the absorption of Irgacure 784 photoinitiator and green LED light emission peak. The effect of plasmon-enhanced polymerization achieved with green light illumination was analyzed using diametral tensile strength (DTS), differential scanning calorimetry (DSC), surface plasmon resonance imaging (SPRi), and degree of conversion (DC) based on Raman spectroscopy. The values of the Au NP with 0.0208 wt% was found to be maximum in all the measured data. Based on our result, it can be concluded that the application of patchy silica particles in dental resin can improve the polymerization ratio and the mechanical parameters of the composite.

Interaction between Nanoparticles, Membranes and Proteins: A Surface Plasmon Resonance Study

Regardless of the promising use of nanoparticles (NPs) in biomedical applications, several toxic effects have increased the concerns about the safety of these nanomaterials. Although the pathways for NPs toxicity are diverse and dependent upon many parameters such as the nature of the nanoparticle and the biochemical environment, numerous studies have provided evidence that direct contact between NPs and biomolecules or cell membranes leads to cell inactivation or damage and may be a primary mechanism for cytotoxicity. In such a context, this work focused on developing a fast and accurate method to characterize the interaction between NPs, proteins and lipidic membranes by surface plasmon resonance imaging (SPRi) technique. The interaction of gold NPs with mimetic membranes was evaluated by monitoring the variation of reflectivity after several consecutive gold NPs injections on the lipidic membranes prepared on the SPRi biochip. The interaction on the membranes with varied lipidic composition was compared regarding the total surface concentration density of gold NPs adsorbed on them. Then, the interaction of gold and silver NPs with blood proteins was analyzed regarding their kinetic profile of the association/dissociation and dissociation constants (k_off). The surface concentration density on the membrane composed of 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine and cholesterol (POPC/cholesterol) was 2.5 times higher than the value found after the injections of gold NPs on POPC only or with dimethyldioctadecylammonium (POPC/DDAB). Regarding the proteins, gold NPs showed preferential binding to fibrinogen resulting in a value of the variation of reflectivity that was 8 times higher than the value found for the other proteins. Differently, silver NPs showed similar interaction on all the tested proteins but with a variation of reflectivity on immunoglobulin G (IgG) 2 times higher than the value found for the other tested proteins.

Surfactant-like Peptide Self-Assembled into Hybrid Nanostructures for Electronic Nose Applications

An electronic nose (e-nose) utilizes a multisensor array, which relies on the vector contrast of combinatorial responses, to effectively discriminate between volatile organic compounds (VOCs). In recent years, hierarchical structures made of nonbiological materials have been used to achieve the required sensor diversity. With the advent of self-assembling peptides, the ability to tune nanostructuration, surprisingly, has not been exploited for sensor array diversification. In this work, a designer surfactant-like peptide sequence, CG₇-NH₂, is used to fabricate morphologically and physicochemically heterogeneous "biohybrid" surfaces on Au-covered chips. These multistructural sensing surfaces, containing immobilized hierarchical nanostructures surrounded by self-assembled monolayers, are used for the detection and discrimination of VOCs. Through a simple and judicious design process, involving changes in pH and water content of peptide solutions, a five-element biohybrid sensor array coupled with a gas-phase surface plasmon resonance imaging system is shown to achieve sufficient discriminatory capabilities for four VOCs. Moreover, the limit of detection of the multiarray system is bench-marked at <1 and 6 ppbv for hexanoic acid and phenol (esophago-gastric biomarkers), respectively. Finally, the humidity effects are characterized, identifying the dissociation rate constant as a robust descriptor for classification, further exemplifying their efficacy as biomaterials in the field of artificial olfaction.

Clinical significance of S100B protein in pregnant woman with early- onset severe preeclampsia

OBJECTIVES

Preeclampsia is one of the most feared complications of pregnancy, which can progress rapidly to serious complications such as death of both mother and fetus. To present, the leading cause of preeclampsia is still debated. The purpose of this article was to explore the clinical significance of S100B protein, a kind of Ca2+ -sensor protein, in the early-onset severe preeclampsia.

MATERIAL AND METHODS

Nine pregnant women with early-onset severe preeclampsia (the study group) and 13 healthy pregnant women (the control group) were included in this study. The level of S100B in the amniotic fluid, maternal blood, and umbilical cord blood were detected by enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance imaging (SPRi) methods. Diagnostic values of S100B for early-onset severe preeclampsia were assessed by Receiver Operating Characteristic (ROC) curve analysis.

RESULTS

The levels of S100B in maternal blood and amniotic fluid in the study group were higher than those in the control group (p < 0.05). ROC curve analysis showed that S100B detected by SPRi method (SPRi-S100B) showed a cut-off level of 181 ng/mL with sensitivity of 100%, a specificity of 84.6%, and a Youden index of 0.846 in the maternal blood, which had better clinical significance and diagnostic value (at than that detected by ELISA (ELISA-S100B).

CONCLUSIONS

The levels of S100B detected by SPRi in maternal blood can indicate early-onset severe preeclampsia and perinatal brain injury.

The Interactome of Cancer-Related Lysyl Oxidase and Lysyl Oxidase-Like Proteins

The members of the lysyl oxidase (LOX) family are amine oxidases, which initiate the covalent cross-linking of the extracellular matrix (ECM), regulate ECM stiffness, and contribute to cancer progression. The aim of this study was to build the first draft of the interactome of the five members of the LOX family in order to determine its molecular functions, the biological and signaling pathways mediating these functions, the biological processes it is involved in, and if and how it is rewired in cancer. In vitro binding assays, based on surface plasmon resonance and bio-layer interferometry, combined with queries of interaction databases and interaction datasets, were used to retrieve interaction data. The interactome was then analyzed using computational tools. We identified 31 new interactions and 14 new partners of LOXL2, including the α5β1 integrin, and built an interactome comprising 320 proteins, 5 glycosaminoglycans, and 399 interactions. This network participates in ECM organization, degradation and cross-linking, cell-ECM interactions mediated by non-integrin and integrin receptors, protein folding and chaperone activity, organ and blood vessel development, cellular response to stress, and signal transduction. We showed that this network is rewired in colorectal carcinoma, leading to a switch from ECM organization to protein folding and chaperone activity.

Immunoassay Biosensing of Foodborne Pathogens with Surface Plasmon Resonance Imaging: A Review

Surface plasmon resonance imaging (SPRi) has been increasingly used in the label-free detections of various biospecies, such as organic toxins, proteins, and bacteria. In combination with the well-developed microarray immunoassay, SPRi has the advantages of rapid detection in tens of minutes and multiplex detection of different targets with the same biochip. Both prism-based and prism-free configurations of SPRi have been developed for highly integrated portable immunosensors, which have shown great potential on pathogen detection and living cell imaging. This review summarizes the recent advances in immunoassay biosensing with SPRi, with special emphasis on the multiplex detections of foodborne pathogens. Additionally, various spotting techniques, surface modification protocols, and signal amplification methods have been developed to improve the specificity and sensitivity of the SPRi biochip. The challenges in multiplex detections of foodborne pathogens in real-world samples are addressed, and future perspectives of miniaturizing SPRi immunosensors with nanotechnologies are discussed.

Cancer-ID: Toward Identification of Cancer by Tumor-Derived Extracellular Vesicles in Blood

Extracellular vesicles (EVs) have great potential as biomarkers since their composition and concentration in biofluids are disease state dependent and their cargo can contain disease-related information. Large tumor-derived EVs (tdEVs, >1 μm) in blood from cancer patients are associated with poor outcome, and changes in their number can be used to monitor therapy effectiveness. Whereas, small tumor-derived EVs (<1 μm) are likely to outnumber their larger counterparts, thereby offering better statistical significance, identification and quantification of small tdEVs are more challenging. In the blood of cancer patients, a subpopulation of EVs originate from tumor cells, but these EVs are outnumbered by non-EV particles and EVs from other origin. In the Dutch NWO Perspectief Cancer-ID program, we developed and evaluated detection and characterization techniques to distinguish EVs from non-EV particles and other EVs. Despite low signal amplitudes, we identified characteristics of these small tdEVs that may enable the enumeration of small tdEVs and extract relevant information. The insights obtained from Cancer-ID can help to explore the full potential of tdEVs in the clinic.

Identification of amino acid residues involved in the interaction between peste-des-petits-ruminants virus haemagglutinin protein and cellular receptors

Peste-des-petits-ruminants virus (PPRV) haemagglutinin (H) protein mediates binding to cellular receptors and then initiates virus entry. To identify the key residues of PPRV H (Hv) protein of the Nigeria 75/1 strain involved in binding to receptors, interaction of the Hv and mutated Hv (mHv) proteins with receptors (SLAM and Nectin 4) and their mutants (mSLAM1, mSLAM2, mSLAM3 and mNectin 4) was investigated using surface plasmon resonance imaging (SPRi) and coimmunoprecipitation (co-IP) assays. The results showed that the Hv protein failed to interact with mSLAM3, but interacted at a strong or medium intensity with SLAM, mSLAM2, Nectin 4 and mNectin 4, and at a low level with mSLAM1. The mHv protein was unable to interact with SLAM and its mutants, but bound to Nectin 4 and mNectin 4 with medium and weak intensity, respectively. Further analysis showed that the Hv protein could precipitate mSLAM1, mSLAM2 and mNectin 4, but not mSLAM3. The mHv protein failed to coprecipitate with SLAM and its mutants. The binding activities of mNectin 4 and Nectin 4 to mHv were less than 30.36 and 51.94 % of the wild-type levels, respectively. Based on the results obtained, amino acids at positions R389, L464, I498, R503, R533, Y541, Y543, F552 and Y553 of H protein and I61, H62, L64, K76, K78, E123, H130, I210, A211, S226 and R227 in SLAM were identified to be essential for the specificity of H-SLAM interaction, while the critical residues of H-Nectin 4 interaction require further study. These findings would improve our understanding of the invasive mechanisms of PPRV.

Diagnosis of Mild Cognitive Impairment and Alzheimer's Disease by the Plasma and Serum Amyloid-beta 42 Assay through Highly Sensitive Peptoid Nanosheet Sensor

Alzheimer's disease (AD) is the most common neurodegenerative disorder with a continuous pathophysiological process starting from the preclinical and mild cognitive impairment (MCI) phases to the dementia phase. Early diagnosis is prerequisite for the early intervention of AD but meanwhile challenging. Amyloid-beta 1-42 (Aβ₄₂) plays a crucial part in AD pathology. Positron-emission tomography (PET) imaging of Aβ₄₂ in the brain and the measurement of Aβ₄₂ in the cerebrospinal fluid (CSF) have been adopted for the auxiliary diagnosis of AD, but their widespread clinical application has been limited due to the radiation and the high-cost of PET and the invasive lumbar puncture for collecting CSF. Noninvasive and cost-effective blood-based assay is desirable for the early diagnosis of AD. Here, a label-free assay for the quantification of blood Aβ₄₂ was developed using the high-throughput surface plasmon resonance imaging method with the aid of an antibody-mimetic peptoid nanosheet equipping Aβ₄₂-recognizing loops. We demonstrated that this nanosheet-based sensor system could distinguish the plasma and sera from normal individuals and patients suffering AD and amnestic MCI with high sensitivity and specificity, preceding the diagnostic performance of the Aβ₄₂-recognizing molecule and the antibody specific to Aβ₄₂. This work provides a label-free, cost-effective, highly sensitive, and high-throughput blood-based assay for early detection of AD.

Plasma aromatase as a sensitive and selective potential biomarker of bladder cancer and its role in tumorigenesis

Bladder cancer (BCa) is the ninth most common cancer in the world and its early detection is crucial for successful therapy. Unfortunately, there are no satisfactory tools to detect BCa at early stages and BCa's confirmation muscle-invasive. The search for a suitable biomarker is therefore necessary and aromatase is a potential candidate. The purpose of the current study was to determine if aromatase serves as a biomarker of BCa. A Surface Plasmon Resonance Imaging biosensor was applied for the quantification and determination of aromatase. A total of 3 µl blood plasma was used for a single measurement. The results revealed that the aromatase concentration in the plasma of patients with BCa (n=78) ranged from 17.41-57.44 ng/ml. The range determined in healthy donors (n=18) was 2.59-7.74 ng/ml. Additionally, it was revealed that muscle invasive BCa samples exhibited elevated, statistically significant (P=0.01) average aromatase concentrations in blood plasma (38.64 ng/ml) when compared with non-muscle invasive samples (29.83 ng/ml). The results demonstrated that plasma aromatase may serve as an excellent bimarker of BCa with 100% sensitivity, 100% selectivity and an area under the curve value of the reciever operating characteristic curve equal to 1.0. Furthermore, the marker differenciated between muscle-invasive and non muscle-invasive BCa with a sensitivity of 60% and a specificity of 81%. In conclusion, aromatase may serve a role in bladder tumorigenesis.

Influence of Fixation and Permeabilization on the Mass Density of Single Cells: A Surface Plasmon Resonance Imaging Study

Fixation and permeabilization of cells and tissues are essential processes in biological techniques like immunofluorescence and immunohistochemistry for cell biology studies. In typical procedures, the biological samples are treated by paraformaldehyde and Triton X-100 to achieve cellular fixation and permeabilization, respectively, prior to the incubation with specific antibodies. While it is well-known that the integrity of cell membrane has been broken during these processes, quantitative studies on the loss of cellular mass density and the enhancement of molecular accessibility at single cell level are still rare. In this study, we employed the surface plasmon resonance (SPR) imaging technique to monitor the mass density change of single cells during sequential fixation and permeabilization processes. We further utilize the osmotic responses of single cells to sugar molecules as an indicator to evaluate the integrity of cell membranes. It was found that, while fixation initially destructed the integrity of cell membranes and increased the permeability of intra- and extra-cellular molecules, it was permeabilization process that substantially induced significant loss in cellular mass density.

Detection of Parkinson's Disease through the Peptoid Recognizing α-Synuclein in Serum

Parkinson's disease (PD) is a severe neurodegenerative disease and there is great need for developing a biochemical detection method to precisely diagnose it. Alpha-synuclein (α-syn) participates in the main pathology of PD and serves as an important biomarker of PD. Here, we identified peptoid ASBP-7 that had high affinity and specificity to α-syn by screening a peptoid library using the high-throughput surface plasmon resonance imaging method. We confirmed that ASBP-7 could significantly distinguish PD sera from the normal ones through identifying α-syn in the serum. We also demonstrated the high sensitivity of this system in detecting PD serum. This work provides a method for the blood-based, label-free, high-throughput analysis of PD serum, and holds great potential for the early diagnosis and dynamic monitoring of PD.

Utility of cystatin C as a potential bladder tumour biomarker confirmed by surface plasmon resonance technique

Background & objectives:

The determination of cystatin C (cysC) may be helpful in diagnosis and monitoring of cancer because the pathogenesis of cancer is linked with an increased activity of cysteine peptidases (cathepsins) and a decrease of cysC concentration. This study was aimed to examine the utility of cysC as a marker of bladder cancer (BCa) to be used in the diagnosis.

Methods:

This study was conducted with 90 patients with BCa and 27 healthy people. Patients with other cancers, inflammation process and impaired renal function were excluded from the study. The concentrations of cysC in the plasma and urine were measured by surface plasmon resonance imaging technique.

Results:

The concentration of cysC in the serum taken from the patients with BCa [0.35±0.02 μg/ml (range: 0.20-0.78 μg/ml)] was significantly (P <0.001) lower than the serum cysC concentration of the healthy people [0.68±0.05 μg/ml (range: 0.52-0.89 μg/ml)]. The urinary cysC concentration of the BCa patients [0.19±0.01 μg/ml (range: 0.09-0.34 μg/ml)] was not significantly different from the urinary cysC concentration of the healthy people [0.24±0.02 μg/ml (range: 0.16-0.33 μg/ml)]. Receiver operating characteristic (ROC) curve showed that BCa patients with cysC concentration <0.54 μg/ml [sensitivity: 87%; specificity: 92%; area under the curve (AUC) of ROC: 0.927; P =0.02] could be optimally separated from healthy people. The ROC curve further showed that superficial low-grade patients with cysC concentration lower than 0.36 μg/ml (sensitivity: 0.63%; specificity: 0.58%; AUC of ROC: 0.635; P =0.08) could not be optimally separated from high-risk tumour patients.

Interpretation & conclusions:

BCa patients have lower serum cysC concentration than the control group. Serum cysC may be considered as a potential marker of BCa but not its aggressiveness.

Automatic Spot Identification Method for High Throughput Surface Plasmon Resonance Imaging Analysis

An automatic spot identification method is developed for high throughput surface plasmon resonance imaging (SPRi) analysis. As a combination of video accessing, image enhancement, image processing and parallel processing techniques, the method can identify the spots in SPRi images of the microarray from SPRi video data. In demonstrations of the method, SPRi video data of different protein microarrays were processed by the method. Results show that our method can locate spots in the microarray accurately regardless of the microarray pattern, spot-background contrast, light nonuniformity and spotting defects, but also can provide address information of the spots.

Quantitative Analysis of Interaction Between CADM1 and Its Binding Cell-Surface Proteins Using Surface Plasmon Resonance Imaging

The cell adhesion molecule (CADM) family of the immunoglobulin superfamily (IgSF) comprises four members, CADM1-CADM4, and participates in the formation of epithelial and synaptic adhesion through cell-cell homophilic and heterophilic interactions. To identify the partners that interact with each member of the CADM family proteins, we set up a platform for multiple detection of the extracellular protein-protein interactions using surface plasmon resonance imaging (SPRi) and analyzed the interactions between the CADM family proteins and 10 IgSF of their structurally related cell adhesion molecules. SPRi analysis identified a new interaction between CADM1 and CADM4, where this heterophilic interaction was shown to be involved in morphological spreading of adult T-cell leukemia (ATL) cells expressing CADM1 when incubated on CADM4-coated glass. Moreover, class-I MHC-restricted T-cell-associated molecule (CRTAM) was identified to show the highest affinity to CADM1 among its binding partners by comparing the dissociation constants calculated from the SPR sensorgrams. These results suggest that the SPRi platform would provide a novel screening tool to characterize extracellular protein-protein interactions among cell-surface and secreted proteins, including IgSF molecules.

SPRi-Based Biosensing Platforms for Detection of Specific DNA Sequences Using Thiolate and Dithiocarbamate Assemblies

The framework of presented study covers the development and examination of the analytical performance of surface plasmon resonance-based (SPR) DNA biosensors dedicated for a detection of model target oligonucleotide sequence. For this aim, various strategies of immobilization of DNA probes on gold transducers were tested. Besides the typical approaches: chemisorption of thiolated ssDNA (DNA-thiol) and physisorption of non-functionalized oligonucleotides, relatively new method based on chemisorption of dithiocarbamate-functionalized ssDNA (DNA-DTC) was applied for the first time for preparation of DNA-based SPR biosensor. The special emphasis was put on the correlation between the method of DNA immobilization and the composition of obtained receptor layer. The carried out studies focused on the examination of the capability of developed receptors layers to interact with both target DNA and DNA-functionalized AuNPs. It was found, that the detection limit of target DNA sequence (27 nb length) depends on the strategy of probe immobilization and backfilling method, and in the best case it amounted to 0.66 nM. Moreover, the application of ssDNA-functionalized gold nanoparticles (AuNPs) as plasmonic labels for secondary enhancement of SPR response is presented. The influence of spatial organization and surface density of a receptor layer on the ability to interact with DNA-functionalized AuNPs is discussed. Due to the best compatibility of receptors immobilized via DTC chemisorption: 1.47 ± 0.4 · 10¹² molecules · cm^-2 (with the calculated area occupied by single nanoparticle label of ~132.7 nm²), DNA chemisorption based on DTCs is pointed as especially promising for DNA biosensors utilizing indirect detection in competitive assays.

Rapid screening of IgG quality attributes - effects on Fc receptor binding

The interactions of therapeutic antibodies with fragment crystallizable γ (Fcγ) receptors and neonatal Fc receptors (FcRn) are measured in vitro as indicators of antibody functional performance. Antibodies are anchored to immune cells through the Fc tail, and these interactions are important for the efficacy and safety of therapeutic antibodies. High‐throughput binding studies on each of the human Fcγ receptor classes (FcγRI, FcγRIIa, FcγRIIb, FcγRIIIa, and FcγRIIIb) as well as FcRn have been developed and performed with human IgG after stress‐induced modifications to identify potential impact in vivo. Interestingly, we found that asparagine deamidation (D‐N) reduced the binding of IgG to the low‐affinity Fcγ receptors (FcγRIIa, FcγRIIb, FcγRIIIa, and FcγRIIIb), while FcγRI and FcRn binding was not impacted. Deglycosylation completely inhibited binding to all Fcγ receptors, but showed no impact on binding to FcRn. On the other hand, afucosylation only impacted binding to FcγRIIIa and FcγRIIIb. Methionine oxidation at levels below 7%, multiple freeze/thaw cycles and short‐term thermal/shake stress did not influence binding to any of the Fc receptors. The presence of high molecular weight species, or aggregates, disturbed measurements in these binding assays; up to 5% of aggregates in IgG samples changed the binding and kinetics to each of the Fc receptors. Overall, the screening assays described in this manuscript prove that rapid and multiplexed binding assays may be a valuable tool for lead optimization, process development, in‐process controls, and biosimilarity assessment of IgGs during development and manufacturing of therapeutic IgGs.

Molecular modeling and SPRi investigations of interleukin 6 (IL6) protein and DNA aptamers

Interleukin 6 (IL6), an inflammatory response protein has major implications in immune-related inflammatory diseases. Identification of aptamers for the IL6 protein aids in diagnostic, therapeutic, and theranostic applications. Three different DNA aptamers and their interactions with IL6 protein were extensively investigated in a phosphate buffed saline (PBS) solution. Molecular-level modeling through molecular dynamics provided insights of structural, conformational changes and specific binding domains of these protein-aptamer complexes. Multiple simulations reveal consistent binding region for all protein-aptamer complexes. Conformational changes coupled with quantitative analysis of center of mass (COM) distance, radius of gyration (R_g), and number of intermolecular hydrogen bonds in each IL6 protein-aptamer complex was used to determine their binding performance strength and obtain molecular configurations with strong binding. A similarity comparison of the molecular configurations with strong binding from molecular-level modeling concurred with Surface Plasmon Resonance imaging (SPRi) for these three aptamer complexes, thus corroborating molecular modeling analysis findings. Insights from the natural progression of IL6 protein-aptamer binding modeled in this work has identified key features such as the orientation and location of the aptamer in the binding event. These key features are not readily feasible from wet lab experiments and impact the efficacy of the aptamers in diagnostic and theranostic applications.

A Versatile Electronic Tongue Based on Surface Plasmon Resonance Imaging and Cross-Reactive Sensor Arrays-A Mini-Review

Nowadays, there is a strong demand for the development of new analytical devices with novel performances to improve the quality of our daily lives. In this context, multisensor systems such as electronic tongues (eTs) have emerged as promising alternatives. Recently, we have developed a new versatile eT system by coupling surface plasmon resonance imaging (SPRi) with cross-reactive sensor arrays. In order to largely simplify the preparation of sensing materials with a great diversity, an innovative combinatorial approach was proposed by combining and mixing a small number of easily accessible molecules displaying different physicochemical properties. The obtained eT was able to generate 2D continuous evolution profile (CEP) and 3D continuous evolution landscape (CEL), which is also called 3D image, with valuable kinetic information, for the discrimination and classification of samples. Here, diverse applications of such a versatile eT have been summarized. It is not only effective for pure protein analysis, capable of differentiating protein isoforms such as chemokines CXCL12α and CXCL12γ, but can also be generalized for the analysis of complex mixtures, such as milk samples, with promising potential for monitoring the deterioration of milk.

Simple Nanoimprinted Polymer Nanostructures for Uncooled Thermal Detection by Direct Surface Plasmon Resonance Imaging

We experimentally demonstrate the uncooled detection of long wavelength infrared (IR) radiation by thermal surface plasmon sensing using an all optical readout format. Thermal infrared radiation absorbed by an IR-sensitive material with high thermo-optic coefficient coated on a metal grating creates a refractive index change detectable by the shift of the supported surface plasmon resonance (SPR) measured optically in the visible spectrum. The interface localization of SPR modes and optical readout allow for submicrometer thin film transducers and eliminate complex readout integrated circuits, respectively, reducing form factor, leveraging robust visible detectors, and enabling low-cost imaging cameras. We experimentally present the radiative heat induced thermo-optic action detectable by SPR shift through imaging of a thermal source onto a bulk metal grating substrate with IR-absorptive silicon nitride coating. Toward focal plane array integration, a route to facile fabrication of pixelated metal grating structures by nanoimprint lithography is developed, where a stable polymer, parylene-C, serves as an IR-absorptive layer with a high thermo-optic coefficient. Experimental detection of IR radiation from real thermal sources imaged at infinity is demonstrated by our nanoimprinted polymer-SPR pixels with an estimated noise equivalent temperature difference of 21.9 K.

SPR and SPR Imaging: Recent Trends in Developing Nanodevices for Detection and Real-Time Monitoring of Biomolecular Events

In this paper we review the underlying principles of the surface plasmon resonance (SPR) technique, particularly emphasizing its advantages along with its limitations regarding the ability to discriminate between the specific binding response and the interfering effects from biological samples. While SPR sensors were developed almost three decades, SPR detection is not yet able to reduce the time-consuming steps of the analysis, and is hardly amenable for miniaturized, portable platforms required in point-of-care (POC) testing. Recent advances in near-field optics have emerged, resulting in the development of SPR imaging (SPRi) as a powerful optical, label-free monitoring tool for multiplexed detection and monitoring of biomolecular events. The microarrays design of the SPRi chips incorporating various metallic nanostructures make these optofluidic devices more suitable for diagnosis and near-patient testing than the traditional SPR sensors. The latest developments indicate SPRi detection as being the most promising surface plasmon-based technique fulfilling the demands for implementation in lab-on-a-chip (LOC) technologies.

Mapping single-cell-substrate interactions by surface plasmon resonance microscopy

We report the imaging of the cell-substrate adhesion of a single cell with subcellular spatial resolution. Osmotic pressure was introduced to provide a controllable mechanical stimulation to the cell attached to a substrate, and high-resolution surface plasmon resonance microscopy was used to map the response of the cell, from which local cell-substrate adhesion was determined. In addition to high spatial resolution, the approach is noninvasive and fast and allows for the continuous mapping of cell-substrate interactions and single-cell movements.

A general method to determine ionization constants of responsive polymer thin films

A general method has been developed to determine the ionization constants of polymer thin films based on the stimuli-responsiveness of the polymer. Robust polymer films were fabricated on silicon wafers and gold slides using perfluorophenyl azide (PFPA) as the coupling agent. The ionization constants were measured by a number of techniques including ellipsometry, dynamic contact angle goniometry, and surface plasmon resonance imaging (SPRi). Using poly(4-vinylpyridine) (P4VP) as the model system, P4VP thin films were fabricated and the ionization constants of the films were measured taking advantage of the pH responsive property of the polymer. The pK(a) determined by ellipsometry, ~4.0, reflects the swelling of the polymer film in response to pH. The pK(a) value calculated from the dynamic contact angle measurements, ~5.0, relies on the change in hydrophilicity/hydrophobicity of the films as the polymer undergoes protonation/deprotonation. The pK(a) value measured by SPRi, ~4.9, monitors in situ the change of refractive index of the polymer thin film as it swells upon protonation. This was the first example where SPRi was used to measure the ionization constants of polymers.

Evaluation of photochemically immobilized poly(2-ethyl-2-oxazoline) thin films as protein-resistant surfaces

Poly(2-ethyl-2-oxazoline) (PEOX) of various molecular weights were covalently immobilized on silicon wafers and gold slides to form protein-resistant surfaces via a fast and general photocoupling chemistry based on the CH insertion reaction of light-activated perfluorophenyl azide (PFPA). The thicknesses of the immobilized PEOX films ranged from 23 to 80 Å for molecular weight of 5000 to 500,000, and the grafting density reached 3.2 × 10(-3) Å(-2) for PEOX 5000. The protein-resistant property of the films was studied using bovine serum albumin (BSA) by fluorescence imaging, ellipsometry, and surface plasmon resonance imaging (SPRi). The fluorescence imaging and ellipsometry studies showed the largest amount of BSA adsorbed on PEOX 5000 and the smallest on PEOX 500,000. This was consistent with the kinetic analysis of BSA adsorption by SPRi showing that PEOX 5000 exhibited the fastest association rate and the slowest dissociation rate whereas PEOX 500,000 had the slowest association rate and the fastest dissociation rate. The PEOX film was then applied in the fabrication of carbohydrate microarrays to reduce the nonspecific adsorption of lectins and thus the background noises. Results showed that the microarray signals were significantly enhanced when the PEOX film was used.

Development of an SPR imaging biosensor for determination of cathepsin G in saliva and white blood cells

Cathepsin G (CatG) is an endopeptidase that is associated with the early immune response. The synthetic compound cathepsin G inhibitor I (CGI-I) was tested for its ability to inhibit the activity of CatG via a new surface plasmon resonance imaging assay. CGI-I was immobilized on the gold surface of an SPR sensor that was first modified with 1-octadecanethiol. A concentration of CGI-I equal to 4.0 μg·mL-1 and a pH of 8.0 were found to give the best results. The dynamic response of the sensor ranges from 0.25 to 1.5 ng·mL-1, and the detection limit is 0.12 ng·mL-1. The sensor was applied to detect CatG in human saliva and white blood cells.FigureThe synthetic compound cathepsin G inhibitor I (CGI-I) was tested for its ability to inhibit the activity of cathepsin G via a newly developed surface plasmon resonance imaging assay. The sensor was applied to detect cathepsin G in human saliva and white blood cells.

Plasmon resonance methods in GPCR signaling and other membrane events

The existence of surface guided electromagnetic waves has been theoretically predicted from Maxwell's equations and investigated during the first decades of the 20th century. However, it is only since the late 1960's that they have attracted the interest of surface physicists and earned the moniker of "surface plasmon". With the advent of commercially available instruments and well established theories, the technique has been used to study a wide variety of biochemical and biotechnological phenomena. Spectral response of the resonance condition serves as a sensitive indicator of the optical properties of thin films immobilized within a wavelength of the surface. This enhanced surface sensitivity has provided a boon to the surface sciences, and fosters collaboration between surface chemistry, physics and the ongoing biological and biotechnological revolution. Since then, techniques based on surface plasmons such as Surface Plasmon Resonance (SPR), SPR Imaging, Plasmon Waveguide Resonance (PWR) and others, have been increasingly used to determine the affinity and kinetics of a wide variety of real time molecular interactions such as protein-protein, lipid-protein and ligand-protein, without the need for a molecular tag or label. The physical-chemical methodologies used to immobilize membranes at the surface of these optical devices are reviewed, pointing out advantages and limitations of each method. The paper serves to summarize both historical and more recent developments of these technologies for investigating structure-function aspects of these molecular interactions, and regulation of specific events in signal transduction by G-protein coupled receptors (GPCRs).