Biomedical subjects

L M Lechuga

Publications and source records attributed to L M Lechuga.

7 recordsLinked to original sources

PubMed2006

Multi-analyte SPR immunoassays for environmental biosensing of pesticides.

Multi-analyte detection of environmentally relevant pesticides is performed by using a two-channelled surface plasmon resonance (SPR) biosensor. The special design of the SPR instrument allows the determination of several analytes (DDT, chlorpyrifos and carbaryl) via different immobilization formats. First, simultaneous pesticide monitoring is possible by flowing chlorpyrifos, carbaryl or DDT samples separately over each channel of the SPR system, wherein their corresponding recognition element was previously immobilized. The second approach is based on the multiple and combined immobilization of several analyte recognition elements on the sensing surface of one individual flow cell. In this format, the analysis time for all three pesticides varied from 40 to 60 min depending on the number of regeneration cycles. In most cases, similar detection limits were attained for the target analyte irrespective of the assay format, with sensitivity values at the nanogram per litre level (18-50 ng L(-1)). The assay reproducibility was proved through the repeated use of the same sensor surface for over more than 200 assay cycles, whereas the absence of biosensor response to non-related analytes showed the specificity and reliability of the analysis. The SPR instrument, including optics, electronics and microfluidics, is already commercialised by the company SENSIA, SL.

Antibodies↗

PubMed2006

Optical immunosensor for fast and sensitive detection of DDT and related compounds in river water samples.

A surface plasmon resonance (SPR) based immunosensor has been developed for the monitoring of environmentally persistent pollutants like DDT, its metabolites and analogues in real water samples. A reusable immunosurface is provided via the covalent attachment of the analyte derivative to a self-assembled alkanethiol monolayer formed onto the SPR gold-thin layer. The regeneration of the sensor surface allowed the performance of 270 assay cycles within an analysis time of 20 min for each assay cycle. Immunoassays based on a binding inhibition format were performed by using two monoclonal antibodies (MAbs) with different selectivity. Low limits of detection (LODs), in the sub-nanogram per litre range, were attained for DDT-selective (15 ng L-1) and DDT group-selective immunoassays (31 ng L-1). Both assays were carried out in spiked river water samples without significant effect of the matrix. SPR measurements were validated using gas-chromatography-mass spectrometry. The comparison between methods was in good agreement showing an excellent correlation coefficient (r2=0.995). The SPR analysis of DDT proved to be three times more sensitive than colorimetric ELISAs without the need of labelling and a much lower time of response. Our SPR biosensor portable platform (beta-SPR) is already commercialised by the company SENSIA, S.L. (Spain).

Antibodies↗

PubMed2006

Highly sensitive detection of biomolecules with the magneto-optic surface-plasmon-resonance sensor.

The characteristics of a novel magneto-optic surface-plasmon-resonance (MOSPR) sensor and its use for the detection of biomolecules are presented. This physical transduction principle is based on the combination of the magneto-optic activity of magnetic materials and a surface-plasmon resonance of metallic layers. Such a combination can produce a sharp enhancement of the magneto-optic effects that strongly depends on the optical properties of the surrounding medium, allowing its use for biosensing applications. Experimental characterizations of the MOSPR sensor have shown an increase in the limit of detection by a factor of 3 in changes of refractive index and in the adsorption of biomolecules compared with standard sensors. Optimization of the metallic layers and the experimental setup could result in an improvement of the limit of detection by as much as 1 order of magnitude.

Biopolymers↗

PubMed2006

Light coupling into an optical microcantilever by an embedded diffraction grating.

By measuring the excitation efficiency of an optical waveguide on a diffraction grating one can accurately register the changes in the incidence angle of the exciting light beam. This phenomenon was applied to detect ultrasmall deflections of silicon dioxide cantilevers of submicrometer thickness that were fabricated with corrugation on top to act as diffraction grating couplers. The power of light coupled into the cantilevers was monitored with a conventional photodetector and modulated using mechanical vibration of the cantilever, thus changing the spatial orientation of the coupler with respect to the incident light beam. The technique can be considered as an alternative to the methods known for detection of cantilever deflection.

Journal Article↗

PubMed2005

Determination of carbaryl in natural water samples by a surface plasmon resonance flow-through immunosensor.

The analysis of carbaryl in natural water samples was accomplished using a portable immunosensor based on surface plasmon resonance (SPR) technology. The assay was based on a binding inhibition immunoassay format with the analyte derivative covalently immobilized on the sensor surface. An alkanethiol self-assembled monolayer (SAM) was formed onto the gold-coated sensor surface to allow the reusability of the same sensing surface during 220 regeneration cycles. Reproducibility was evaluated by performing three independent assays in triplicate on 3 different days. The batch-assay variability was also calculated using three different gold-coated sensor surfaces. The intra- and inter-day relative standard deviation were 8.6 and 15.3%, respectively, whilst a variation of 7.4% in assay sensitivity was obtained by employing different sensor chips. The lowest detection limit, calculated as the concentration providing a 10% decrease of the blank signal, was of 1.38 microg L(-1). Matrix effects were also evaluated in different water types, showing I50 values (carbaryl concentrations that produced a 50% decrease of the blank signal) within the range of carbaryl standard curves in distilled water (2.78-3.55 microg L(-1)). The carbaryl immunoassay performance was validated with respect to conventional high-performance liquid chromatography-mass spectrometry (HPLC-MS). The correlation between methods was in good agreement (r2 = 0.998, 0.999 and 0.999) for the three types of natural water samples tested. A complete assay cycle, including regeneration, is accomplished in 20 min. All measurements were carried out with the SPR sensor system (beta-SPR) commercialised by the company SENSIA, SL (Spain). The small size and low-time of response of the beta-SPR platform would allow its utilization in real contaminated locations.

Biosensing Techniques↗

PubMed2005

Highly sensitive polymer-based cantilever-sensors for DNA detection.

We present a technology for the fabrication of cantilever arrays aimed to develop an integrated biosensor microsystem. The fabrication process is based on spin coating of the photosensitive polymer and near-ultraviolet exposure. Arrays of up to 33 microcantilevers are fabricated in the novel polymer material SU-8. The low Young's modulus of the polymer, 40 times lower than that of silicon, enables to improve the sensitivity of the sensor device for target detection. The mechanical properties of SU-8 cantilevers, such as spring constant, resonant frequency and quality factor are characterized as a function of the dimensions and the medium. The devices have been tested for measurement of the adsorption of single stranded DNA and subsequent interstitial adsorption of lateral spacer molecules. We demonstrate that sensitivity is enhanced by a factor of six compared to that of commercial silicon nitride cantilevers.

Biosensing Techniques↗

PubMed2004

Nanomechanics of the formation of DNA self-assembled monolayers and hybridization on microcantilevers.

Biomolecular interactions over the surface of a microcantilever can produce its bending motion via changes of the surface stress, which is referred to nanomechanical response. Here, we have studied the interaction forces responsible for the bending motion during the formation of a self-assembled monolayer of thiolated 27-mer single-stranded DNA on the gold-coated side of a microcantilever and during the subsequent hybridization with the complementary nucleic acid. The immobilization of the single-stranded DNA probe gives a mean surface stress of 25 mN/m and a mean bending of 23 nm for microcantilevers with a length and thickness of about 200 microm and 0.8 microm, respectively. The hybridization with the complementary sequence could not be inferred from the nanomechanical response. The nanomechanical response was compared with data from well-established techniques such as surface plasmon resonance and radiolabeling, to determine the surface coverage and study the intermolecular forces between neighboring DNA molecules anchored to the microcantilever surface. From both techniques, an immobilization surface density of 3 x 10(12) molecules/cm(2) and a hybridization efficiency of 40% were determined. More importantly, label-free hybridization was clearly detected in the same conditions with a conventional sensor based on surface plasmon resonance. The results imply that the nanomechanical signal during the immobilization process arises mainly from the covalent attachment to the gold surface, and the interchain interactions between neighboring DNA molecules are weak, producing an undetectable surface stress. We conclude that detection of nucleic acid hybridization with nanomechanical sensors requires reference cantilevers to remove nonspecific signals, more sensitive microcantilever geometries, and immobilization chemistries specially addressed to enhance the surface stress variations.

Base Sequence↗