Biosensor technology for real-time detection of the cystic fibrosis W1282X mutation in CFTR

PNA Molecular Beacons Assembled by Post-Synthetic Click Chemistry Functionalization

To avoid the tedious synthesis of functionalized peptide nucleic acid (PNA) monomers for probe development, we proposed a simple approach to modify PNA oligomers by post-synthetic on-resin click chemistry. PNA molecular beacons (MBs) were prepared by incorporation of azide-containing monomers into the oligomer by automatic solid-phase peptide synthesis and subsequent derivatization with pyrene moieties by copper-catalyzed azide-alkyne cycloaddition. Two pyrene-based quencher-free PNA molecular beacons, a stemless MB and one possessing a stem-loop structure, targeting a portion of the cystic fibrosis gene, were successfully synthesized by using this method. Fluorescence studies showed that the stem-loop MB exhibited better discrimination of changes in excimer/monomer ratios as compared to the stemless MB construct.

Label-free efficient and accurate detection of cystic fibrosis causing mutations using an azimuthally rotated GC-SPR platform

Plasmonic nanosensors are candidates for the development of new sensors with low detection limits, high sensitivity, and specificity for target detection: these characteristics are of critical importance in the screening of mutations responsible for inherited diseases. In this work, we focused our study on the detection of some of the most frequent mutations responsible for cystic fibrosis (CF) among the Italian population. For the detection of the CF mutations we adopted a recently developed and highly sensitive Grating Coupled-Surface Plasmon Resonance (GC-SPR) enhanced spectroscopy method for label-free molecular identification exploiting a conical illumination configuration. Gold sinusoidal gratings functionalized with heterobifunctional PEG were used as sensing surfaces, and the specific biodetection was achieved through the coupling with DNA hairpin probes designed for single nucleotide discrimination. Such substrates were used to test unlabeled PCR amplified homozygous wild type (wt) and heterozygous samples, deriving from clinical samples, for the screened mutations. Hybridization conditions were optimized to obtain the maximum discrimination ratio (DR) between the homozygous wild type and the heterozygous samples. SPR signals obtained from hybridizing wild type and heterozygous samples show DRs able to identify univocally the correct genotypes, as confirmed by fluorescence microarray experiments run in parallel. Furthermore, SPR genotyping was not impaired in samples containing unrelated DNA, allowing the platform to be used for the concomitant discrimination of several alleles also scalable for a high throughput screening setting.

Rational targeting of subclasses of intermolecular interactions: elimination of nonspecific binding for analyte sensing

The ability to target and control intermolecular interactions is crucial in the development of several different technologies. Here we offer a tool to rationally design liquid media systems that can modulate specific intermolecular interactions. This has broad implications in deciphering the nature of intermolecular forces in complex solutions and offers insight into the forces that govern both specific and nonspecific binding in a given system. Nonspecific binding still continues to be a problem when dealing with analyte detection across a range of different detection technologies. Here, we exemplify the problem of nonspecific binding on model membrane systems and when dealing with low-abundance protein detection on commercially available SPR technology. A range of different soluble reagents that target specific subclasses of intermolecular interactions have been tested and optimized to virtually eliminate nonspecific binding while leaving specific interactions unperturbed. Thiocyanate ions are used to target nonpolar interactions, and small reagents such as glycylglycylglycine are used to modulate the dielectric constant, which targets charge-charge and dipole interactions. We show that with rational design and careful modulation these reagents offer a step forward in dissecting the intermolecular forces that govern binding, alongside offering nonspecific binding elimination in detection systems.

Surface plasmon resonance applications in clinical analysis

In the last 20 years, surface plasmon resonance (SPR) and its advancement with imaging (SPRi) emerged as a suitable and reliable platform in clinical analysis for label-free, sensitive, and real-time monitoring of biomolecular interactions. Thus, we report in this review the state of the art of clinical target detection with SPR-based biosensors in complex matrices (e.g., serum, saliva, blood, and urine) as well as in standard solution when innovative approaches or advanced instrumentations were employed for improved detection. The principles of SPR-based biosensors are summarized first, focusing on the physical properties of the transducer, on the assays design, on the immobilization chemistry, and on new trends for implementing system analytical performances (e.g., coupling with nanoparticles (NPs). Then we critically review the detection of analytes of interest in molecular diagnostics, such as hormones (relevant also for anti-doping control) and biomarkers of interest in inflammatory, cancer, and heart failure diseases. Antibody detection is reported in relation to immune disorder diagnostics. Subsequently, nucleic acid targets are considered for revealing genetic diseases (e.g., point mutation and single nucleotides polymorphism, SNPs) as well as new emerging clinical markers (microRNA) and for pathogen detection. Finally, examples of pathogen detection by immunosensing were also analyzed. A parallel comparison with the reference methods was duly made, indicating the progress brought about by SPR technologies in clinical routine analysis.

5-(Acridin-9-ylamino)uracil — A hydrolytically labile nucleobase modification in peptide nucleic acid

5-Aminouracil (5-AU) is a readily available yet underutilized starting material for the synthesis of labelled nucleobase analogues. We have prepared the derivative of 5-AU with the amine-reactive chromophore 9-chloroacridine for the purpose of investigating its potential as a base-discriminating fluorophore. 9-Chloroacridine readily undergoes substitution by reaction with 5-AU to yield a fluorescent nucleobase that after standard manipulations produced a monomer suitable for incorporation into peptide nucleic acid (PNA) by fluorenylmethyloxycarbonyl (Fmoc)-based oligomerization chemistry. Although the monomer was stable in organic solvents, once incorporated into an oligomer the 5-substitution was found to be thermally labile and hydrolyzed to a small degree in neutral aqueous solution during study of its hybridization to cDNA. We have determined that 5-(acridin-9-ylamino)uracil and related derivatives produce the highly fluorescent acridone and 5-AU by hydrolysis in water.

Direct detection of point mutations in nonamplified human genomic DNA

Ultrasensitive detection protocols not requiring polymerase chain reaction (PCR)-mediated target DNA amplification are expected to significantly improve our possibilities in several research and diagnostic applications for which minute cell quantities are available. For this reason we have tested a nanoparticle-enhanced surface plasmon resonance imaging (SPRI) sensing strategy to detect point mutations in nonamplified genomic DNA. We have used genomic DNAs, not subject to costly, time-consuming, and prone to contamination PCR-based amplification procedures, obtained from both healthy individuals and homozygous or heterozygous patients affected by β-thalassemia, in order to demonstrate the specificity and the sensitivity of the described sensing strategy. The assay we describe is ultrasensitive and convenient. Attomolar concentrations of target genomic DNA are detected, DNAs from healthy individuals and homozygous or heterozygous patients affected by β-thalassemia are discriminated, and only simple manipulations of the genetic samples are required before the analysis. The proposed ultrasensitive detection of DNA point mutations involved in genomic disorders possibly represents an important advantage in several biomedical applications.

Surface Plasmon Resonance-Based Molecular Detection of Hb S [β6(A3)Glu→Val, GAG→GTG] at the Gene Level

The surface plasmon resonance (SPR) approach, being a relatively novel biophysical method, is used to detect many different targets by biomolecular interaction. The SPR system uses optical and evanescent wave phenomenon. This approach does not need any labels, such as enzymes or isotopes, and the monitored interactions are in real time. In DNA-DNA interaction, the SPR approach is Tm-independent. Here we report our preliminary results for the molecular detection of the Hb S (GAG -->GTG) mutation at codon 6 of the human beta-globin gene. Our preliminary results show that the SPR approach could be applied as an inexpensive and fast routine test system for the molecular diagnosis of abnormal hemoglobins (Hbs), especially in premarital screening programs.

Systems biology coupled with label-free high-throughput detection as a novel approach for diagnosis of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a treatable and preventable disease state, characterised by progressive airflow limitation that is not fully reversible. Although COPD is primarily a disease of the lungs there is now an appreciation that many of the manifestations of disease are outside the lung, leading to the notion that COPD is a systemic disease. Currently, diagnosis of COPD relies on largely descriptive measures to enable classification, such as symptoms and lung function. Here the limitations of existing diagnostic strategies of COPD are discussed and systems biology approaches to diagnosis that build upon current molecular knowledge of the disease are described. These approaches rely on new 'label-free' sensing technologies, such as high-throughput surface plasmon resonance (SPR), that we also describe.

Technology platforms for molecular diagnosis of cystic fibrosis

Cystic fibrosis (CF) is one of the most common recessive genetic diseases in North America. So far, 1200 mutations causing CF have been identified. Several techniques such as allele specific oligonucleotide (ASO) dot-blot, reverse dot-blot, amplification refractory mutation (ARMS), and an oligo-ligation assay, are available to detect the most common mutations. However, detecting compound heterozygotes between DeltaF508, the most common disease causing mutation, and other mutations which are rare is difficult as some mutations are common only to particular ethnic groups. Therefore, new diagnostic tests such as restriction enzyme assays and single stranded conformational polymorphism (SSCP) have been designed to recognize rare and population-specific mutations. This review will describe the most commonly used CF mutation detecting diagnostic techniques, as well as novel assays and techniques currently in development that might be employed in future.

In vitro binding of purified NahR regulatory protein with promoter Psal

The NahR regulatory protein activates the naphthalene catabolic operon through binding to the Psal promoter in the presence of salicylate. Here, we investigated in vitro binding interaction between NahR and Psal using purified functional recombinant NahR. The T7-tagged NahR was shown to exist as a monomer in solution. Electrophoretic mobility shift assay (EMSA) showed that purified NahR bound to Psal in 3 different forms, whereas surface plasmon resonance (SPR) showed on an SPR chip at ratios ranging from 1:1 (at 0.42 microM NahR) to 8:1 (at 6.8 microM NahR). The binding was slightly inhibited by salicylate, suggesting that salicylate may not be involved in the binding of NahR to the promoter, but rather may be important in the activation of prebound NahR. An examination of the binding kinetics by SPR for the interaction between NahR and Psal revealed that the equilibrium dissociation constant was approximately 2.44 x 10(-6) M and the association and dissociation rates were 7.82 x 10(4) M(-1) s(-1) and 0.191 s(-1), respectively. These results demonstrate for the first time that purified NahR binds as a monomer to Psal and undergoes multimerization. In addition, we present novel data on the kinetics of NahR binding.

Dendrimer-functionalized self-assembled monolayers as a surface plasmon resonance sensor surface

We report here a multistep route for the immobilization of DNA and proteins on chemically modified gold substrates using fourth-generation NH(2)-terminated poly(amidoamine) dendrimers supported by an underlying amino undecanethiol (AUT) self-assembled monolayer (SAM). Bioactive ultrathin organic films were prepared via layer-by-layer self-assembly methods and characterized by fluorescence microscopy, variable angle spectroscopic ellipsometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FTIR). The thickness of the AUT SAM base layer on the gold substrates was determined to be 1.3 nm from ellipsometry. Fluorescence microscopy and AFM measurements, in combination with analyses of the XPS/ATR-FTIR spectra, confirmed the presence of the dendrimer/biopolymer molecules on the multilayer sensor surfaces. Model proteins, including streptavidin and rabbit immunoglobulin proteins, were covalently attached to the dendrimer layer using linear cross-linking reagents. Through surface plasmon resonance measurements, we found that sensor surfaces containing a dendrimer layer displayed an increased protein immobilization capacity, compared to AUT SAM sensor surfaces without dendrimer molecules. Other SPR studies also revealed that the dendrimer-based surfaces are useful for the sensitive and specific detection of DNA-DNA interactions. Significantly, the multicomponent films displayed a high level of stability during repeated regeneration and hybridization cycles, and the kinetics of the DNA-DNA hybridization process did not appear to be influenced by surface mass transport limiting effects.

Real-time multiplex analysis of four beta-thalassemia mutations employing surface plasmon resonance and biosensor technology

In this paper, biospecific interaction analysis (BIA) employing surface plasmon resonance (SPR) and biosensor technologies was applied to the analysis of multiple mutations of the human beta-globin gene. To this aim, large target polymerase chain reaction (PCR) products were immobilized on sensor chips and then probes detecting beta degrees 39 (C>T), beta degrees IVSI-1 (G>A), beta(+)IVSI-6 (T>C) and beta(+)IVSI-110 (G>A) thalassemia mutations were sequentially injected. In this study, a total of ten normal and seven heterozygous subjects, and six homozygous patients were considered. The results obtained allow to conclude that discrimination between normal subjects, heterozygous, and homozygous patients is readily achieved for all the four mutations by PCR amplification of genomic DNA containing all the regions corresponding to the same mutations, immobilization of the same PCR products, and hybridization. To our knowledge the procedure described here is the first reported on the use of SPR-based BIA and biosensor technology for multiple detections of point mutations.

Surface plasmon resonance and biosensor technology for real-time molecular diagnosis of beta o 39 thalassemia mutation

BACKGROUND

Biospecific interaction analysis (BIA) employing surface plasmon resonance (SPR) and biosensor technologies is of interest in clinical genetics. However, few data are available on its use in hereditary diseases caused by genetic mutations.

AIM

The primary aim of this study was the refinement of BIA technology for use in identifying the beta o 39 mutation of the beta-globin gene, a mutation which causes a common type of beta o thalassemia.

METHODS

Target-biotinylated PCR products were immobilized on streptavidin-coated sensor chips and diagnosed using SPR-based BIA performed by injecting specific oligonucleotide probes into the sensor chip.

RESULTS

We demonstrated that the beta o 39 mutation can be easily and reproducibly identified during the association phase.

CONCLUSIONS

This should be considered a pilot study demonstrating the ability of SPR-based BIA to detect point mutations in the beta-globin gene by real-time monitoring of hybridization between oligonucleotide probes and target-biotinylated PCR products generated from genomic DNA from normal, heterozygous individuals and homozygous beta o thalassemia patients.

Quantitation of Bt-176 maize genomic sequences by surface plasmon resonance-based biospecific interaction analysis of multiplex polymerase chain reaction (PCR)

Surface plasmon resonance (SPR) based biosensors have been described for the identification of genetically modified organisms (GMO) by biospecific interaction analysis (BIA). This paper describes the design and testing of an SPR-based BIA protocol for quantitative determinations of GMOs. Biotinylated multiplex Polymerase Chain Reaction (PCR) products from nontransgenic maize as well as maize powders containing 0.5 and 2% genetically modified Bt-176 sequences were immobilized on different flow cells of a sensor chip. After immobilization, different oligonucleotide probes recognizing maize zein and Bt-176 sequences were injected. The results obtained were compared with Southern blot analysis and with quantitative real-time PCR assays. It was demonstrated that sequential injections of Bt-176 and zein probes to sensor chip flow cells containing multiplex PCR products allow discrimination between PCR performed using maize genomic DNA containing 0.5% Bt-176 sequences and that performed using maize genomic DNA containing 2% Bt-176 sequences. The efficiency of SPR-based BIA in discriminating material containing different amounts of Bt-176 maize is comparable to real-time quantitative PCR and much more reliable than Southern blotting, which in the past has been used for semiquantitative purposes. Furthermore, the approach allows the BIA assay to be repeated several times on the same multiplex PCR product immobilized on the sensor chip, after washing and regeneration of the flow cell. Finally, it is emphasized that the presented strategy to quantify GMOs could be proposed for all of the SPR-based, commercially available biosensors. Some of these optical SPR-based biosensors use, instead of flow-based sensor chips, stirred microcuvettes, reducing the costs of the experimentation.

Biosensors for DNA sequence detection

DNA biosensors are being developed as alternatives to conventional DNA microarrays. These devices couple signal transduction directly to sequence recognition. Some of the most sensitive and functional technologies use fibre optics or electrochemical sensors in combination with DNA hybridization. In a shift from sequence recognition by hybridization, two emerging single-molecule techniques read sequence composition using zero-mode waveguides or electrical impedance in nanoscale pores.

Survey of the year 2001 commercial optical biosensor literature

We have assembled references of 700 articles published in 2001 that describe work performed using commercially available optical biosensors. To illustrate the technology's diversity, the citation list is divided into reviews, methods and specific applications, as well as instrument type. We noted marked improvements in the utilization of biosensors and the presentation of kinetic data over previous years. These advances reflect a maturing of the technology, which has become a standard method for characterizing biomolecular interactions.

Biosensor technology and surface plasmon resonance for real-time detection of genetically modified Roundup Ready soybean gene sequences

Biospecific interaction analysis (BIA) was performed using surface plasmon resonance (SPR) and biosensor technologies to detect genetically modified Roundup Ready soybean gene sequences. We first immobilized, on SA sensor chips, single-stranded biotinylated oligonucleotides containing soybean lectin and Roundup Ready gene sequences, and the efficiency of hybridization to oligonucleotide probes differing in length was determined. Second, we immobilized biotinylated PCR products from nontransgenic soybeans (genomes carrying only the lectin gene), as well as from genetically modified Roundup Ready soybean, and we injected the oligonucleotide probes. Furthermore, we used the sensor chips carrying either lectin and Roundup Ready soybean PCR products or 21-mer oligonucleotide as probes, and we injected both nonpurified and purified asymmetric PCR products. The results obtained show that 13 and 15 mer oligonucleotides are suitable probes to detect genetically modified Roundup Ready soybean gene sequences (either target oligonucleotides or PCR products) under standard BIA experimental conditions. By contrast, when 11 mer DNA probes were employed, no efficient hybridization was obtained. All the SPR-based formats were found to be useful for detection of Roundup Ready gene sequences, suggesting that these procedures are useful for the real-time monitoring of hybridization between target single-stranded PCR products, obtained by using as substrates DNA isolated from normal or transgenic soybeans, and oligonucleotide or PCR-generated probes, therefore enabling a one-step, nonradioactive protocol to perform detection.