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Biosensors, Volume 5, Issue 1 (March 2015) , Pages 1-130

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Open AccessArticle
Whispering Gallery Mode Resonators for Rapid Label-Free Biosensing in Small Volume Droplets
Biosensors 2015, 5(1), 118-130; https://doi.org/10.3390/bios5010118
Received: 5 February 2015 / Revised: 8 March 2015 / Accepted: 11 March 2015 / Published: 23 March 2015
Cited by 11 | Viewed by 2450 | PDF Full-text (494 KB) | HTML Full-text | XML Full-text
Abstract
Rapid biosensing requires fast mass transport of the analyte to the surface of the sensing element. To optimize analysis times, both mass transport in solution and the geometry and size of the sensing element need to be considered. Small dielectric spheres, tens of [...] Read more.
Rapid biosensing requires fast mass transport of the analyte to the surface of the sensing element. To optimize analysis times, both mass transport in solution and the geometry and size of the sensing element need to be considered. Small dielectric spheres, tens of microns in diameter, can act as label-free biosensors using whispering gallery mode (WGM) resonances. WGM resonances are sensitive to the effective refractive index, which changes upon analyte binding to recognition sites on functionalized resonators. The spherical geometry and tens of microns diameter of these resonators provides an efficient target for sensing while their compact size enables detection in limited volumes. Here, we explore conditions leading to rapid analyte detection using WGM resonators as label-free sensors in 10 μL sample droplets. Droplet evaporation leads to potentially useful convective mixing, but also limits the time over which analysis can be completed. We show that active droplet mixing combined with initial binding rate measurements is required for accurate nanomolar protein quantification within the first minute following injection. Full article
(This article belongs to the Special Issue Label-Free Biosensors: Exploring the Field)
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Open AccessArticle
Label-Free Detection of Rare Cell in Human Blood Using Gold Nano Slit Surface Plasmon Resonance
Biosensors 2015, 5(1), 98-117; https://doi.org/10.3390/bios5010098
Received: 30 December 2014 / Revised: 7 March 2015 / Accepted: 10 March 2015 / Published: 23 March 2015
Cited by 8 | Viewed by 3353 | PDF Full-text (1096 KB) | HTML Full-text | XML Full-text
Abstract
Label-free detection of rare cells in biological samples is an important and highly demanded task for clinical applications and various fields of research, such as detection of circulating tumor cells for cancer therapy and stem cells studies. Surface Plasmon Resonance (SPR) as a [...] Read more.
Label-free detection of rare cells in biological samples is an important and highly demanded task for clinical applications and various fields of research, such as detection of circulating tumor cells for cancer therapy and stem cells studies. Surface Plasmon Resonance (SPR) as a label-free method is a promising technology for detection of rare cells for diagnosis or research applications. Short detection depth of SPR (400 nm) provides a sensitive method with minimum interference of non-targets in the biological samples. In this work, we developed a novel microfluidic chip integrated with gold nanoslit SPR platform for highly efficient immunomagnetic capturing and detection of rare cells in human blood. Our method offers simple yet efficient detection of target cells with high purity. The approach for detection consists of two steps. Target cells are firs captured on functionalized magnetic nanoparticles (MNPs) with specific antibody I. The suspension containing the captured cells (MNPs-cells) is then introduced into a microfluidic chip integrated with a gold nanoslit film. MNPs-cells bind with the second specific antibody immobilized on the surface of the gold nanoslit and are therefore captured on the sensor active area. The cell binding on the gold nanoslit was monitored by the wavelength shift of the SPR spectrum generated by the gold nanoslits. Full article
(This article belongs to the Special Issue Label-Free Biosensors: Exploring the Field)
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Open AccessArticle
Label-Free Sensing of Adenosine Based on Force Variations Induced by Molecular Recognition
Biosensors 2015, 5(1), 85-97; https://doi.org/10.3390/bios5010085
Received: 9 January 2015 / Revised: 25 February 2015 / Accepted: 11 March 2015 / Published: 19 March 2015
Cited by 7 | Viewed by 2785 | PDF Full-text (579 KB) | HTML Full-text | XML Full-text
Abstract
We demonstrate a simple force-based label-free strategy for the highly sensitive sensing of adenosine. An adenosine ssDNA aptamer was bound onto an atomic force microscopy (AFM) probe by covalent modification, and the molecular-interface adsorption force between the aptamer and a flat graphite surface [...] Read more.
We demonstrate a simple force-based label-free strategy for the highly sensitive sensing of adenosine. An adenosine ssDNA aptamer was bound onto an atomic force microscopy (AFM) probe by covalent modification, and the molecular-interface adsorption force between the aptamer and a flat graphite surface was measured by single-molecule force spectroscopy (SMFS). In the presence of adenosine, the molecular recognition between adenosine and the aptamer resulted in the formation of a folded, hairpin-like DNA structure and hence caused a variation of the adsorption force at the graphite/water interface. The sensitive force response to molecular recognition provided an adenosine detection limit in the range of 0.1 to 1 nM. The addition of guanosine, cytidine, and uridine had no significant interference with the sensing of adenosine, indicating a strong selectivity of this sensor architecture. In addition, operational parameters that may affect the sensor, such as loading rate and solution ionic strength, were investigated. Full article
(This article belongs to the Special Issue Label-Free Biosensors: Exploring the Field)
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Open AccessArticle
Optimization of Electrically Active Magnetic Nanoparticles as Accurate and Efficient Microbial Extraction Tools
Biosensors 2015, 5(1), 69-84; https://doi.org/10.3390/bios5010069
Received: 5 November 2014 / Revised: 18 December 2014 / Accepted: 23 January 2015 / Published: 5 February 2015
Cited by 1 | Viewed by 2727 | PDF Full-text (709 KB) | HTML Full-text | XML Full-text
Abstract
Food defense requires the means to efficiently screen large volumes of food for microbial pathogens. Even rapid detection methods often require lengthy enrichment steps, making them impractical for this application. There is a great need for rapid, sensitive, specific, and inexpensive methods for [...] Read more.
Food defense requires the means to efficiently screen large volumes of food for microbial pathogens. Even rapid detection methods often require lengthy enrichment steps, making them impractical for this application. There is a great need for rapid, sensitive, specific, and inexpensive methods for extracting and concentrating microbial pathogens from food. In this study, an immuno-magnetic separation (IMS) methodology was developed for Escherichia coli O157:H7, using electrically active magnetic nanoparticles (EAMNPs). The analytical specificity of the IMS method was evaluated against Escherichia coli O55:H7 and Shigella boydii, and was improved over previous protocols by the addition of sodium chloride during the conjugation of antibodies onto MNPs. The analytical sensitivity of the IMS method was greatest when a high concentration of antibodies (1.0 mg/mL) was present during conjugation. EAMNP concentrations of 1.0 and 0.5 mg/mL provided optimal analytical sensitivity and analytical specificity. The entire IMS procedure requires only 35 min, and antibody-conjugated MNPs show no decline in performance up to 149 days after conjugation. This analytically sensitive and specific extraction protocol has excellent longevity and shows promise as an effective extraction for multiple electrochemical biosensor applications. Full article
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Open AccessArticle
Escherichia coli O-Antigen Gene Clusters of Serogroups O62, O68, O131, O140, O142, and O163: DNA Sequences and Similarity between O62 and O68, and PCR-Based Serogrouping
Biosensors 2015, 5(1), 51-68; https://doi.org/10.3390/bios5010051
Received: 9 December 2014 / Revised: 24 January 2015 / Accepted: 30 January 2015 / Published: 5 February 2015
Cited by 6 | Viewed by 2490 | PDF Full-text (454 KB) | HTML Full-text | XML Full-text
Abstract
The DNA sequence of the O-antigen gene clusters of Escherichia coli serogroups O62, O68, O131, O140, O142, and O163 was determined, and primers based on the wzx (O-antigen flippase) and/or wzy (O-antigen polymerase) genes within the O-antigen gene clusters were designed and used [...] Read more.
The DNA sequence of the O-antigen gene clusters of Escherichia coli serogroups O62, O68, O131, O140, O142, and O163 was determined, and primers based on the wzx (O-antigen flippase) and/or wzy (O-antigen polymerase) genes within the O-antigen gene clusters were designed and used in PCR assays to identify each serogroup. Specificity was tested with E. coli reference strains, field isolates belonging to the target serogroups, and non-E. coli bacteria. The PCR assays were highly specific for the respective serogroups; however, the PCR assay targeting the O62 wzx gene reacted positively with strains belonging to E. coli O68, which was determined by serotyping. Analysis of the O-antigen gene cluster sequences of serogroups O62 and O68 reference strains showed that they were 94% identical at the nucleotide level, although O62 contained an insertion sequence (IS) element located between the rmlA and rmlC genes within the O-antigen gene cluster. A PCR assay targeting the rmlA and rmlC genes flanking the IS element was used to differentiate O62 and O68 serogroups. The PCR assays developed in this study can be used for the detection and identification of E. coli O62/O68, O131, O140, O142, and O163 strains isolated from different sources. Full article
(This article belongs to the Special Issue Biosensors in Agroecosystems)
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Open AccessArticle
Direct Determination of a Small-Molecule Drug, Valproic Acid, by an Electrically-Detected Microcantilever Biosensor for Personalized Diagnostics
Biosensors 2015, 5(1), 37-50; https://doi.org/10.3390/bios5010037
Received: 14 November 2014 / Revised: 17 December 2014 / Accepted: 21 January 2015 / Published: 27 January 2015
Cited by 4 | Viewed by 2882 | PDF Full-text (639 KB) | HTML Full-text | XML Full-text
Abstract
Direct, small-molecule determination of the antiepileptic drug, valproic acid, was investigated by a label-free, nanomechanical biosensor. Valproic acid has long been used as an antiepileptic medication, which is administered through therapeutic drug monitoring and has a narrow therapeutic dosage range of 50–100 μg·mL [...] Read more.
Direct, small-molecule determination of the antiepileptic drug, valproic acid, was investigated by a label-free, nanomechanical biosensor. Valproic acid has long been used as an antiepileptic medication, which is administered through therapeutic drug monitoring and has a narrow therapeutic dosage range of 50–100 μg·mL1 in blood or serum. Unlike labeled and clinically-used measurement techniques, the label-free, electrical detection microcantilever biosensor can be miniaturized and simplified for use in portable or hand-held point-of-care platforms or personal diagnostic tools. A micromachined microcantilever sensor was packaged into the micro-channel of a fluidic system. The measurement of the antiepileptic drug, valproic acid, in phosphate-buffered saline and serum used a single free-standing, piezoresistive microcantilever biosensor in a thermally-controlled system. The measured surface stresses showed a profile over a concentration range of 50–500 μg·mL1, which covered the clinically therapeutic range of 50–100 μg·mL1. The estimated limit of detection (LOD) was calculated to be 45 μg·mL−1, and the binding affinity between the drug and the antibody was measured at around 90 ± 21 μg·mL1. Lastly, the results of the proposed device showed a similar profile in valproic acid drug detection with those of the clinically-used fluorescence polarization immunoassay. Full article
(This article belongs to the Special Issue Label-Free Biosensors: Exploring the Field)
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Open AccessArticle
Kinetic Analyses of Data from a Human Serum Albumin Assay Using the liSPR System
Biosensors 2015, 5(1), 27-36; https://doi.org/10.3390/bios5010027
Received: 9 September 2014 / Revised: 26 September 2014 / Accepted: 19 December 2014 / Published: 19 January 2015
Cited by 1 | Viewed by 2669 | PDF Full-text (633 KB) | HTML Full-text | XML Full-text
Abstract
We used the interaction between human serum albumin (HSA) and a high-affinity antibody to evaluate binding affinity measurements by the bench-top liSPR system (capitalis technology GmbH). HSA was immobilized directly onto a carboxylated sensor layer, and the mechanism of interaction between the [...] Read more.
We used the interaction between human serum albumin (HSA) and a high-affinity antibody to evaluate binding affinity measurements by the bench-top liSPR system (capitalis technology GmbH). HSA was immobilized directly onto a carboxylated sensor layer, and the mechanism of interaction between the antibody and HSA was investigated. The bivalence and heterogeneity of the antibody caused a complex binding mechanism. Three different interaction models (1:1 binding, heterogeneous analyte, bivalent analyte) were compared, and the bivalent analyte model best fit the curves obtained from the assay. This model describes the interaction of a bivalent analyte with one or two ligands (A + L ↔ LA + L ↔ LLA). The apparent binding affinity for this model measured 37 pM for the first reaction step, and 20 pM for the second step. Full article
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Open AccessEditorial
Acknowledgement to Reviewers of Biosensors in 2014
Biosensors 2015, 5(1), 25-26; https://doi.org/10.3390/bios5010025
Received: 7 January 2015 / Accepted: 7 January 2015 / Published: 7 January 2015
Viewed by 1938 | PDF Full-text (21 KB) | HTML Full-text | XML Full-text
Abstract
The editors of Biosensors would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2014:[...] Full article
Open AccessArticle
Tracking Traction Force Changes of Single Cells on the Liquid Crystal Surface
Biosensors 2015, 5(1), 13-24; https://doi.org/10.3390/bios5010013
Received: 26 August 2014 / Accepted: 2 December 2014 / Published: 5 January 2015
Cited by 2 | Viewed by 2471 | PDF Full-text (597 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Cell migration is a key contributor to wound repair. This study presents findings indicating that the liquid crystal based cell traction force transducer (LCTFT) system can be used in conjunction with a bespoke cell traction force mapping (CTFM) software to monitor cell/surface traction [...] Read more.
Cell migration is a key contributor to wound repair. This study presents findings indicating that the liquid crystal based cell traction force transducer (LCTFT) system can be used in conjunction with a bespoke cell traction force mapping (CTFM) software to monitor cell/surface traction forces from quiescent state in real time. In this study, time-lapse photo microscopy allowed cell induced deformations in liquid crystal coated substrates to be monitored and analyzed. The results indicated that the system could be used to monitor the generation of cell/surface forces in an initially quiescent cell, as it migrated over the culture substrate, via multiple points of contact between the cell and the surface. Future application of this system is the real-time assaying of the pharmacological effects of cytokines on the mechanics of cell migration. Full article
(This article belongs to the Special Issue Label-Free Biosensors: Exploring the Field)
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Open AccessCommunication
A Laser Photoacoustic Analysis of Residual CO2 and H2O in Larch Stems
Biosensors 2015, 5(1), 1-12; https://doi.org/10.3390/bios5010001
Received: 25 September 2014 / Accepted: 2 December 2014 / Published: 23 December 2014
Cited by 4 | Viewed by 2115 | PDF Full-text (750 KB) | HTML Full-text | XML Full-text
Abstract
Every so often, the results obtained from investigations into the effects of varying environmental conditions on the tree growth rate at the same sites and on the change in the carbon balance in plants, using traditional methods, are found to differ widely. We [...] Read more.
Every so often, the results obtained from investigations into the effects of varying environmental conditions on the tree growth rate at the same sites and on the change in the carbon balance in plants, using traditional methods, are found to differ widely. We believe that the reason for the ambiguity of the data has to do with failure to account for the role of the residual CO2 (and H2O) in the tree wood exhibiting a climate response. In our earlier work, the results of a laser photoacoustic gas analysis of CO2 and H2O vacuum-desorbed from disc tree rings of evergreen conifer trees were presented. In this paper, laser photoacoustic measurements of tree ring gases in deciduous conifer trees and CO2 carbon isotope composition determined by means of a mass spectrometer are given. Conclusions are made regarding the response of annual larch CO2 disc tree ring distributions to climatic parameters (temperatures and precipitation). The data about the CO2 disc content for different sites are compared. Full article
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