Research

Open AccessArticle Modeling of Nanoparticular Magnetoresistive Systems and the Impact on Molecular Recognition

by Lisa Teich, Daniel Kappe, Thomas Rempel, Judith Meyer, Christian Schröder and Andreas Hütten

Sensors 2015, 15(4), 9251-9264; doi:10.3390/s150409251

Received: 27 February 2015 / Revised: 7 April 2015 / Accepted: 14 April 2015 / Published: 20 April 2015

Cited by 3 | PDF Full-text (2943 KB) | HTML Full-text | XML Full-text

Abstract

The formation of magnetic bead or nanoparticle superstructures due to magnetic dipole dipole interactions can be used as configurable matter in order to realize low-cost magnetoresistive sensors with very high GMR-effect amplitudes. Experimentally, this can be realized by immersing magnetic beads or [...] Read more.

The formation of magnetic bead or nanoparticle superstructures due to magnetic dipole dipole interactions can be used as configurable matter in order to realize low-cost magnetoresistive sensors with very high GMR-effect amplitudes. Experimentally, this can be realized by immersing magnetic beads or nanoparticles in conductive liquid gels and rearranging them by applying suitable external magnetic fields. After gelatinization of the gel matrix the bead or nanoparticle positions are fixed and the resulting system can be used as a magnetoresistive sensor. In order to optimize such sensor structures we have developed a simulation tool chain that allows us not only to study the structuring process in the liquid state but also to rigorously calculate the magnetoresistive characteristic curves for arbitrary nanoparticle arrangements. As an application, we discuss the role of magnetoresistive sensors in finding answers to molecular recognition. Full article

(This article belongs to the Special Issue Nanoparticle-Based Biosensors)

Open AccessArticle Rapid Immunoenzyme Assay of Aflatoxin B1 Using Magnetic Nanoparticles

by Alexandr E. Urusov, Alina V. Petrakova, Maxim V. Vozniak, Anatoly V. Zherdev and Boris B. Dzantiev

Sensors 2014, 14(11), 21843-21857; doi:10.3390/s141121843

Received: 29 September 2014 / Revised: 5 November 2014 / Accepted: 14 November 2014 / Published: 18 November 2014

Cited by 9 | PDF Full-text (843 KB) | HTML Full-text | XML Full-text | Supplementary Files

Abstract

The main limitations of microplate-based enzyme immunoassays are the prolonged incubations necessary to facilitate heterogeneous interactions, the complex matrix and poorly soluble antigens, and the significant sample dilutions often required because of the presence of organic extractants. This study presents the use [...] Read more.

The main limitations of microplate-based enzyme immunoassays are the prolonged incubations necessary to facilitate heterogeneous interactions, the complex matrix and poorly soluble antigens, and the significant sample dilutions often required because of the presence of organic extractants. This study presents the use of antibody immobilization on the surface of magnetic particles to overcome these limitations in the detection of the mycotoxin, aflatoxin B1. Features of the proposed system are a high degree of nanoparticle dispersion and methodologically simple immobilization of the antibodies by adsorption. Reactions between the immobilized antibodies with native and labeled antigens are conducted in solution, thereby reducing the interaction period to 5 min without impairing the analytical outcome. Adsorption of immunoglobulins on the surface of magnetic nanoparticles increases their stability in aqueous-organic media, thus minimizing the degree of sample dilution required. Testing barley and maize extracts demonstrated a limit of aflatoxin B1 detection equal to 20 pg/mL and total assay duration of 20 min. Using this method, only the 3-fold dilution of the initial methanol/water (60/40) extraction mixture in the microplate wells is necessary. The proposed pseudo-homogeneous approach could be applied toward immunodetection of a wide range of compounds. Full article

(This article belongs to the Special Issue Nanoparticle-Based Biosensors)

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Open AccessArticle Magnetic Bead-Based Colorimetric Immunoassay for Aflatoxin B1 Using Gold Nanoparticles

by Xu Wang, Reinhard Niessner and Dietmar Knopp

Sensors 2014, 14(11), 21535-21548; doi:10.3390/s141121535

Received: 11 October 2014 / Revised: 7 November 2014 / Accepted: 11 November 2014 / Published: 14 November 2014

Cited by 11 | PDF Full-text (901 KB) | HTML Full-text | XML Full-text

Abstract

A competitive colorimetric immunoassay for the detection of aflatoxin B1 (AFB) has been established using biofunctionalized magnetic beads (MBs) and gold nanoparticles (GNPs). Aflatoxin B1-bovine serum albumin conjugates (AFB-BSA) modified MBs were employed as capture probe, which could specifically bind with GNP-labeled [...] Read more.

A competitive colorimetric immunoassay for the detection of aflatoxin B1 (AFB) has been established using biofunctionalized magnetic beads (MBs) and gold nanoparticles (GNPs). Aflatoxin B1-bovine serum albumin conjugates (AFB-BSA) modified MBs were employed as capture probe, which could specifically bind with GNP-labeled anti-AFB antibodies through immunoreaction, while such specific binding was competitively inhibited by the addition of AFB. After magnetic separation, the supernatant solution containing unbound GNPs was directly tested by UV-Vis spectroscopy. The absorption intensity was directly proportional to the AFB concentration. The influence of GNP size, incubation time and pH was investigated in detail. After optimization, the developed method could detect AFB in a linear range from 20 to 800 ng/L, with the limit of detection at 12 ng/L. The recoveries for spiked maize samples ranged from 92.8% to 122.0%. The proposed immunoassay provides a promising approach for simple, rapid, specific and cost-effective detection of toxins in the field of food safety. Full article

(This article belongs to the Special Issue Nanoparticle-Based Biosensors)

Open AccessArticle Using Bio-Functionalized Magnetic Nanoparticles and Dynamic Nuclear Magnetic Resonance to Characterize the Time-Dependent Spin-Spin Relaxation Time for Sensitive Bio-Detection

by Shu-Hsien Liao, Kuen-Lin Chen, Chun-Ming Wang, Jen-Jie Chieh, Herng-Er Horng, Li-Min Wang, C. H. Wu and Hong-Chang Yang

Sensors 2014, 14(11), 21409-21417; doi:10.3390/s141121409

Received: 12 September 2014 / Revised: 24 October 2014 / Accepted: 29 October 2014 / Published: 12 November 2014

Cited by 3 | PDF Full-text (868 KB) | HTML Full-text | XML Full-text

Abstract

In this work, we report the use of bio-functionalized magnetic nanoparticles (BMNs) and dynamic magnetic resonance (DMR) to characterize the time-dependent spin-spin relaxation time for sensitive bio-detection. The biomarkers are the human C-reactive protein (CRP) while the BMNs are the anti-CRP bound [...] Read more.

In this work, we report the use of bio-functionalized magnetic nanoparticles (BMNs) and dynamic magnetic resonance (DMR) to characterize the time-dependent spin-spin relaxation time for sensitive bio-detection. The biomarkers are the human C-reactive protein (CRP) while the BMNs are the anti-CRP bound onto dextran-coated Fe₃O₄ particles labeled as Fe₃O₄-antiCRP. It was found the time-dependent spin-spin relaxation time, T₂, of protons decreases as time evolves. Additionally, the ΔT₂ of of protons in BMNs increases as the concentration of CRP increases. We attribute these to the formation of the magnetic clusters that deteriorate the field homogeneity of nearby protons. A sensitivity better than 0.1 μg/mL for assaying CRP is achieved, which is much higher than that required by the clinical criteria (0.5 mg/dL). The present MR-detection platform shows promise for further use in detecting tumors, viruses, and proteins. Full article

(This article belongs to the Special Issue Nanoparticle-Based Biosensors)

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Open AccessArticle Optical Fiber Sensor Based on Localized Surface Plasmon Resonance Using Silver Nanoparticles Photodeposited on the Optical Fiber End

by J. Gabriel Ortega-Mendoza, Alfonso Padilla-Vivanco, Carina Toxqui-Quitl, Placido Zaca-Morán, David Villegas-Hernández and Fernando Chávez

Sensors 2014, 14(10), 18701-18710; doi:10.3390/s141018701

Received: 1 July 2014 / Revised: 19 September 2014 / Accepted: 25 September 2014 / Published: 9 October 2014

Cited by 13 | PDF Full-text (1730 KB) | HTML Full-text | XML Full-text

Abstract

This paper reports the implementation of an optical fiber sensor to measure the refractive index in aqueous media based on localized surface plasmon resonance (LSPR). We have used a novel technique known as photodeposition to immobilize silver nanoparticles on the optical fiber [...] Read more.

This paper reports the implementation of an optical fiber sensor to measure the refractive index in aqueous media based on localized surface plasmon resonance (LSPR). We have used a novel technique known as photodeposition to immobilize silver nanoparticles on the optical fiber end. This technique has a simple instrumentation, involves laser light via an optical fiber and silver nanoparticles suspended in an aqueous medium. The optical sensor was assembled using a tungsten lamp as white light, a spectrometer, and an optical fiber with silver nanoparticles. The response of this sensor is such that the LSPR peak wavelength is linearly shifted to longer wavelengths as the refractive index is increased, showing a sensitivity of 67.6 nm/RIU. Experimental results are presented. Full article

(This article belongs to the Special Issue Nanoparticle-Based Biosensors)

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Open AccessArticle Development of an Immunochromatographic Strip Test for Rapid Detection of Ciprofloxacin in Milk Samples

by Liqiang Liu, Liju Luo, Steven Suryoprabowo, Juan Peng, Hua Kuang and Chuanlai Xu

Sensors 2014, 14(9), 16785-16798; doi:10.3390/s140916785

Received: 30 June 2014 / Revised: 20 August 2014 / Accepted: 5 September 2014 / Published: 10 September 2014

Cited by 18 | PDF Full-text (475 KB) | HTML Full-text | XML Full-text

Abstract

A rapid, simple, and sensitive immunochromatographic test strip has been developed for testing residues of ciprofloxacin (CIP). A specific and sensitive monoclonal antibody (mAb) for CIP was generated by immunizing BALB/c mice with well-characterized CIP-Keyhole limpet haemocyanin. Under the optimized conditions, the [...] Read more.

A rapid, simple, and sensitive immunochromatographic test strip has been developed for testing residues of ciprofloxacin (CIP). A specific and sensitive monoclonal antibody (mAb) for CIP was generated by immunizing BALB/c mice with well-characterized CIP-Keyhole limpet haemocyanin. Under the optimized conditions, the cut-off limits of test strips for CIP were found to be 5 ng/mL in phosphate-buffered saline and 2.5 ng/mL in milk samples. Each test can be evaluated within 3 min. The cross-reactivities of the CIP test strip to enrofloxacin (ENR), norfloxacin (NOR), nadifloxacin (NDF), danofloxacin (DANO), pefloxacin (PEX), lomefloxacin (LOME), enoxacin (ENO), and sarafloxacin (SAR) were 71.4%, 71.4%, 66%, 50%, 33%, 20%, 12.5%, and 6.25%, respectively. The data indicate that the method is sensitive, specific, and has the advantages of simplicity and speed, therefore, this test strip is a useful screening method for the detection of CIP residues in milk samples. Full article

(This article belongs to the Special Issue Nanoparticle-Based Biosensors)

Open AccessArticle Development of an ELISA and Immunochromatographic Strip for Highly Sensitive Detection of Microcystin-LR

by Liqiang Liu, Changrui Xing, Huijuan Yan, Hua Kuang and Chuanlai Xu

Sensors 2014, 14(8), 14672-14685; doi:10.3390/s140814672

Received: 25 June 2014 / Revised: 3 August 2014 / Accepted: 6 August 2014 / Published: 12 August 2014

Cited by 19 | PDF Full-text (2624 KB) | HTML Full-text | XML Full-text

Abstract

A monoclonal antibody for microcystin–leucine–arginine (MC-LR) was produced by cell fusion. The immunogen was synthesized in two steps. First, ovalbumin/ bovine serum albumin was conjugated with 6-acetylthiohexanoic acid using a carbodiimide EDC (1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride)/ NHS (N-hydroxysulfosuccinimide) reaction. After dialysis, the protein was [...] Read more.

A monoclonal antibody for microcystin–leucine–arginine (MC-LR) was produced by cell fusion. The immunogen was synthesized in two steps. First, ovalbumin/ bovine serum albumin was conjugated with 6-acetylthiohexanoic acid using a carbodiimide EDC (1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride)/ NHS (N-hydroxysulfosuccinimide) reaction. After dialysis, the protein was reacted with MC-LR based on a free radical reaction under basic solution conditions. The protein conjugate was used for immunization based on low volume. The antibodies were identified by indirect competitive (ic)ELISA and were subjected to tap water and lake water analysis. The concentration causing 50% inhibition of binding of MC-LR (IC₅₀) by the competitive indirect ELISA was 0.27 ng/mL. Cross-reactivity to the MC-RR, MC-YR and MC-WR was good. The tap water and lake water matrices had no effect on the detection limit. The analytical recovery of MC-LR in the water samples in the icELISA was 94%–110%. Based on this antibody, an immunochromatographic biosensor was developed with a cut-off value of 1 ng/mL, which could satisfy the requirement of the World Health Organization for MC-LR detection in drinking water. This biosensor could be therefore be used as a fast screening tool in the field detection of MC-LR. Full article

(This article belongs to the Special Issue Nanoparticle-Based Biosensors)

Open AccessArticle The Optical Property of Core-Shell Nanosensors and Detection of Atrazine Based on Localized Surface Plasmon Resonance (LSPR) Sensing

by Shaobo Yang, Tengfei Wu, Xinhua Zhao, Xingfei Li and Wenbin Tan

Sensors 2014, 14(7), 13273-13284; doi:10.3390/s140713273

Received: 22 April 2014 / Revised: 17 June 2014 / Accepted: 17 July 2014 / Published: 23 July 2014

Cited by 1 | PDF Full-text (1428 KB) | HTML Full-text | XML Full-text

Abstract

Three different nanosensors with core-shell structures were fabricated by molecular self-assembly and evaporation techniques. Such closely packed nanoparticles exhibit fine optical properties which are useful for biochemical sensing. The refractive index sensitivity (RIS) of nanosensors was detected by varying the refractive index [...] Read more.

Three different nanosensors with core-shell structures were fabricated by molecular self-assembly and evaporation techniques. Such closely packed nanoparticles exhibit fine optical properties which are useful for biochemical sensing. The refractive index sensitivity (RIS) of nanosensors was detected by varying the refractive index of the surrounding medium and the decay length of nanosensors was investigated using a layer-by-layer polyelectrolyte multilayer assembly. The results showed that the thickness of the Au shell plays an important role in determining the RIS and the decay length. A system based on localized surface plasmon resonances (LSPR) sensing was constructed in our study. The core-shell nanosensors can detect 10 ng/mL atrazine solutions and are suitable for pesticide residue detection. Full article

(This article belongs to the Special Issue Nanoparticle-Based Biosensors)

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