Efficient antifouling surface for quantitative surface plasmon resonance based biosensor analysis

Detection of Biomarker Using Aptasensors to Determine the Type of Diabetes

Diabetes mellitus (DM) is a metabolic disorder characterized by elevated blood glucose levels. This disease is so serious that many experts refer to it as the "silent killer". The early detection of diabetes mellitus, whether type 1, type 2 or mitochondrial, is crucial because it can improve the success of treatment and the quality of life for patients. Aptamer-based biosensor diagnosis methods have been widely developed because they have high sensitivity and selectivity in detecting biomarkers of various diseases. Aptamers are short sequences of oligonucleotides or proteins that recognize specific ligands and bind to various target molecules, ranging from small ions to large proteins. They are promising diagnostic molecules due to their high sensitivity and selectivity, ease of modification, low toxicity, and high stability. This article aims to summarize the progress of detection methods, including detection principles, sensitivity, selectivity, and the performance of detection devices, to distinguish between types of diabetes mellitus using electrochemical aptasensors with biomarkers such as glucose, insulin, HbA1c, GHSA, and ATP.

Recent progress on developing of plasmon biosensing of tumor biomarkers: Efficient method towards early stage recognition of cancer

Cancer is the second most extended disease with an improved death rate over the past several time. Due to the restrictions of cancer analysis methods, the patient's real survival rate is unknown. Therefore, early stage diagnosis of cancer is crucial for its strong detection. Bio-analysis based on biomarkers may help to overcome the problem Biosensors with high sensitivity and specificity, low-cost, high analysis speed and minimum limit of detection are practical alternatives for laboratory tests. Surface plasmon resonance (SPR) is reaching a maturity level sufficient for their application in detection and determination cancer biomarkers in clinical samples. This review discusses main concepts and performance characteristics of SPR biosensor. Mainly, it focuses on newly emerged enhanced SPR biosensors towards high-throughput and ultrasensitive screening of cancer biomarkers such as PSA, α-fetoprotein, CEA, CA125, CA 15-3, HER2, ctDNA, ALCAM, hCG, VEGF, TNF, Interleukin, IFN-γ, CD24, CD44, Ferritin, COLIV using labeling processes with focusing on the future application in biomedical research and clinical diagnosis. This article reviews current status of the field, showcasing a series of early successes in the application of SPR for clinical bioanalysis of cancer related biomolecules and detailing a series of considerations regarding sensing schemes, exposing issues with analysis in biofluids, while providing an outlook of the challenges currently associated with plasmonic materials, bioreceptor selection, microfluidics, and validation of a clinical bioassay for applying SPR biosensors to clinical samples. Research opportunities are proposed to further advance the field and transition SPR biosensors from research proof-of-concept stage to actual clinical usage.

Reflector-less nanoparticles doped optical fiber biosensor for the detection of proteins: Case thrombin

A miniature biosensing platform based on MgO-based nanoparticle doped optical fiber was developed for the biomolecule detection. The technology used a single mode fiber with MgO-based nanoparticles doped core. The detection was based on collecting the Rayleigh backscattering signatures with increased gain upon the etching of the fiber 1-2 mm away from the tip. The shift from the backscattered signal with the maximum value of the cross-correlation was used to report the results. The sensor exhibited a sensitivity range from 0.75 nm/refractive index unit up to 19.63 nm/refractive index unit for a refractive index range from 1.3329 up to 1.37649. The deposition of the thin gold layer increased the overall sensitivity of the biosensor by 3.7 times for the etched part of the fiber with diameter 8-9 μm. The proposed biosensor was tested for the detection of thrombin molecule concentrations ranging from 0.625 μg/ml to 20 μg/ml. Thiol modified DNA specific aptamers were used to functionalize the gold coated surface of the fiber for the detection. The sensor showed detectable sensitivity and specificity as compared to the other control proteins. The proposed biosensing platform could be multiplexed and can be used in vivo for the detection in clinical settings due to its miniature size, biocompatibility of silica glass and reflector less set up.

Evaluation of Molecularly Imprinted Polymers for Point-of-Care Testing for Cardiovascular Disease

Molecular imprinting is a rapidly growing area of interest involving the synthesis of artificial recognition elements that enable the separation of analyte from a sample matrix and its determination. Traditionally, this approach can be successfully applied to small analyte (<1.5 kDa) separation/ extraction, but, more recently it is finding utility in biomimetic sensors. These sensors consist of a recognition element and a transducer similar to their biosensor counterparts, however, the fundamental distinction is that biomimetic sensors employ an artificial recognition element. Molecularly imprinted polymers (MIPs) employed as the recognition elements in biomimetic sensors contain binding sites complementary in shape and functionality to their target analyte. Despite the growing interest in molecularly imprinting techniques, the commercial adoption of this technology is yet to be widely realised for blood sample analysis. This review aims to assess the applicability of this technology for the point-of-care testing (POCT) of cardiovascular disease-related biomarkers. More specifically, molecular imprinting is critically evaluated with respect to the detection of cardiac biomarkers indicative of acute coronary syndrome (ACS), such as the cardiac troponins (cTns). The challenges associated with the synthesis of MIPs for protein detection are outlined, in addition to enhancement techniques that ultimately improve the analytical performance of biomimetic sensors. The mechanism of detection employed to convert the analyte concentration into a measurable signal in biomimetic sensors will be discussed. Furthermore, the analytical performance of these sensors will be compared with biosensors and their potential implementation within clinical settings will be considered. In addition, the most suitable application of these sensors for cardiovascular assessment will be presented.

Surface plasmon resonance imaging reveals multiple binding modes of Agrobacterium transformation mediator VirE2 to ssDNA

VirE2 is the major secreted protein of Agrobacterium tumefaciens in its genetic transformation of plant hosts. It is co-expressed with a small acidic chaperone VirE1, which prevents VirE2 oligomerization. After secretion into the host cell, VirE2 serves functions similar to a viral capsid in protecting the single-stranded transferred DNA en route to the nucleus. Binding of VirE2 to ssDNA is strongly cooperative and depends moreover on protein–protein interactions. In order to isolate the protein–DNA interactions, imaging surface plasmon resonance (SPRi) studies were conducted using surface-immobilized DNA substrates of length comparable to the protein-binding footprint. Binding curves revealed an important influence of substrate rigidity with a notable preference for poly-T sequences and absence of binding to both poly-A and double-stranded DNA fragments. Dissociation at high salt concentration confirmed the electrostatic nature of the interaction. VirE1–VirE2 heterodimers also bound to ssDNA, though by a different mechanism that was insensitive to high salt. Neither VirE2 nor VirE1–VirE2 followed the Langmuir isotherm expected for reversible monomeric binding. The differences reflect the cooperative self-interactions of VirE2 that are suppressed by VirE1.

Detection of embryonic stem cell lysate biomarkers by surface plasmon resonance with reduced nonspecific adsorption

Surface plasmon resonance imaging (SPRi) has emerged as a versatile biosensor to detect a wide range of biomolecular interactions with divergent potential applications. However, the use of this advanced-level technology for stem cell lysate study is still not much explored. Cell lysates are significant biological analytes used for disease diagnostics and proteomic studies, but their complex nature limits their use as an analyte for SPRi biosensors. Here, we review the problems associated with the use of SPRi for stem cell lysate study and examine the role of surface chemistry, running buffer, and blocking solution in order to minimize nonspecific adsorption (NSA). We detect the expression of Oct4, Sox2, Nanog, Rex1, and Lin28 biomarkers present in mouse embryonic stem cell (mESC) lysate against their corresponding antibodies immobilized on the sensor surface with reduced NSA. The current study shows that the conjunction of SPRi and microarray can be used as a label-free, high-throughput, and rapid technique for detection of biomarkers and their relative abundance in stem cell lysate study.

Nanoscale engineering of low-fouling surfaces through polydopamine immobilisation of zwitterionic peptides

We report a versatile approach for the design of substrate-independent low-fouling surfaces via mussel-inspired immobilisation of zwitterionic peptides. Using mussel-inspired polydopamine (PDA) coatings, zwitterionic glutamic acid- and lysine-based peptides were immobilised on various substrates, including noble metals, metal oxides, polymers, and semiconductors. The variation of surface chemistry and surface wettability upon surface treatment was monitored with X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Following peptide immobilisation, the surfaces became more hydrophilic due to the strong surface hydration compared with PDA-coated surfaces. The peptide-functionalised surfaces showed resistance to human blood serum adsorption and also effectively prevented the adhesion of gram-negative and gram-positive bacteria (i.e., Escherichia coli and Staphylococcus epidermidis) and mammalian cells (i.e., NIH 3T3 mouse embryonic fibroblast cells). The versatility of mussel-inspired chemistry combined with the unique biological nature and tunability of peptides allows for the design of low-fouling surfaces, making this a promising coating technique for various applications.

Preparation and characterizations of poly(2-methyl-2-oxazoline) based antifouling coating by thermally induced immobilization

Poly[(2-methyl-2-oxazoline)-random-glycidylmethacrylate] was immobilized on a silicon/glass surface via a simple annealing procedure to obtain a covalent and cross-linked antifouling coating.

SPRi-based strategy to identify specific biomarkers in systemic lupus erythematosus, rheumatoid arthritis and autoimmune hepatitis

Background

Heterogeneous nuclear ribonucleoprotein (hnRNP) A2/B1 is a target for antinuclear autoantibodies in systemic Lupus erythematosus (SLE), rheumatoid arthritis (RA), and autoimmune hepatitis (AIH).

Aim

To monitor molecular interactions between peptides spanning the entire sequence of hnRNP A2/B1 and sera from patients and healthy controls.

Methods

Sera from 8 patients from each pathology and controls were passed across a surface plasmon resonance Imagery (SPRi) surface containing 39 overlapping peptides of 17 mers covering the human hnRNP B1. Interactions involving the immobilised peptides were followed in real time and dissociation rate constants k_off for each interaction were calculated.

Results

Several significant interactions were observed: i) high stability (lower k_off values) between P_55-70 and the AIH sera compared to controls (p= 0.003); ii) lower stability (higher k_off values) between P_118-133 and P_262-277 and SLE sera, P_145-160 and RA sera compared to controls (p=0.006, p=0.002, p=0.007). The binding curves and k_off values observed after the formation of complexes with anti-IgM and anti-IgG antibodies and after nuclease treatment of the serum indicate that i) IgM isotypes are prevalent and ii) nucleic acids participate in the interaction between anti-hnRNAP B1 and P_55-70 and also between controls and the peptides studied.

Conclusions

These results indicate that P_55-70 of hnRNP B1 is a potential biomarker for AIH in immunological tests and suggest the role of circulating nucleic acids, (eg miRNA), present or absent according to the autoimmune disorders and involved in antigen-antibody stability.

Highly mutagenic exocyclic DNA adducts are substrates for the human nucleotide incision repair pathway

BACKGROUND

Oxygen free radicals induce lipid peroxidation (LPO) that damages and breaks polyunsaturated fatty acids in cell membranes. LPO-derived aldehydes and hydroxyalkenals react with DNA leading to the formation of etheno(ε)-bases including 1,N(6)-ethenoadenine (εA) and 3,N(4)-ethenocytosine (εC). The εA and εC residues are highly mutagenic in mammalian cells and eliminated in the base excision repair (BER) pathway and/or by AlkB family proteins in the direct damage reversal process. BER initiated by DNA glycosylases is thought to be the major pathway for the removal of non-bulky endogenous base damage. Alternatively, in the nucleotide incision repair (NIR) pathway, the apurinic/apyrimidinic (AP) endonucleases can directly incise DNA duplex 5' to a damaged base in a DNA glycosylase-independent manner.

METHODOLOGY/PRINCIPAL FINDINGS

Here we have characterized the substrate specificity of human major AP endonuclease 1, APE1, towards εA, εC, thymine glycol (Tg) and 7,8-dihydro-8-oxoguanine (8oxoG) residues when present in duplex DNA. APE1 cleaves oligonucleotide duplexes containing εA, εC and Tg, but not those containing 8oxoG. Activity depends strongly on sequence context. The apparent kinetic parameters of the reactions suggest that APE1 has a high affinity for DNA containing ε-bases but cleaves DNA duplexes at an extremely slow rate. Consistent with this observation, oligonucleotide duplexes containing an ε-base strongly inhibit AP site nicking activity of APE1 with IC(50) values in the range of 5-10 nM. MALDI-TOF MS analysis of the reaction products demonstrated that APE1-catalyzed cleavage of εA•T and εC•G duplexes generates, as expected, DNA fragments containing 5'-terminal ε-base residue.

CONCLUSIONS/SIGNIFICANCE

The fact that ε-bases and Tg in duplex DNA are recognized and cleaved by APE1 in vitro, suggests that NIR may act as a backup pathway to BER to remove a large variety of genotoxic base lesions in human cells.