Molecular inversion probe-based SPR biosensing for specific, label-free and real-time detection of regional DNA methylation

DNA methylation has the potential to be a clinically important biomarker in cancer. This communication reports a real-time and label-free biosensing strategy for DNA methylation detection in the cancer cell line. This has been achieved by using surface plasmon resonance biosensing combined with the highly specific molecular inversion probe based amplification method, which requires only 50 ng of bisulfite treated genomic DNA

Metamirrors based on arrays of silicon nanowires with height gradients

Arrays of silicon nanowires with height gradients fabricated using metal-assisted chemical etching act as tunable metamirrors enabling light focusing the reflected light in arbitrary shapes. Metamirrors with non-cylindrical nanowires can simultaneously focus the reflected light and induce strong polarization conversion effect.The authors acknowledge the financial support of the Spanish Ministerio de Economia y Competitividad (MINECO) projects MAT2013-48628-R, FIS2013-49280-EXP, and MAT2011-12645-E and Comunidad the Madrid project S2013/MIT-2740. ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295).Peer Reviewe

Identification of the optimal spectral region for plasmonic and nanoplasmonic sensing

This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in ACS Nano, copyright © American Chemical Society after peer review. To access the final edited and published work see http://pubs.acs.org/articlesonrequest/AOR-jfCkKFwsJwtEYkHTFzG7We present a theoretical and experimental study involving the sensing characteristics of wavelength interrogated plasmonic sensors based on Surface Plasmon Polaritons (SPP) in planar gold films and on Localized Surface Plasmon Resonances (LSPR) of single gold nanorods. The tunability of both sensing platforms allowed us to analyze their bulk and surface sensing characteristics as a function of the plasmon resonance position. We demonstrate that a general figure of merit (FOM), which is equivalent in wavelength and energy scales, can be employed to mutually compare both sensing schemes. Most interestingly, this FOM has revealed a spectral region for which the surface sensitivity performance of both sensor types is optimized, which we attribute to the intrinsic dielectric properties of plasmonic materials. Additionally, in good agreement with theoretical predictions, we experimentally demonstrate that, although the SPP sensor offers a much better bulk sensitivity, the LSPR sensor shows an approximately 15% better performance for surface sensitivity measurements when its FOM is optimized. However, optimization of the substrate refractive index and the accessibility of the relevant molecules to the nanoparticles can lead to a total 3-fold improvement of the FOM in LSPR sensors.This research was carried out with the support of the Commission for Universities and Investigation belonging to the Department of Innovation, Universities and Companies of the Generalitat de Catalunya, and the Social European Fund. Financial support of the M. Botn Foundation and the Nanomag CIBER-BBN Project is also greatly acknowledged. L.M.L.-M. acknowledges financial support from Ministerio de Ciencia e Innovacin (MAT2007-62696 and PCI2005-A7-0075).Peer reviewe

Trends and challenges of refractometric nanoplasmonic biosensors: A review

Motivated by potential benefits such as sensor miniaturization, multiplexing opportunities and higher sensitivities, refractometric nanoplasmonic biosensing has profiled itself in a short time span as an interesting alternative to conventional Surface Plasmon Resonance (SPR) biosensors. This latter conventional sensing concept has been subjected during the last decades to strong commercialization, thereby strongly leaning on well-developed thin-film surface chemistry protocols. Not surprisingly, the examples found in literature based on this sensing concept are generally characterized by extensive analytical studies of relevant clinical and diagnostic problems. In contrast, the more novel Localized Surface Plasmon Resonance (LSPR) alternative finds itself in a much earlier, and especially, more fundamental stage of development. Driven by new fabrication methodologies to create nanostructured substrates, published work typically focuses on the novelty of the presented material, its optical properties and its use - generally limited to a proof-of-concept - as a label-free biosensing scheme. Given the different stages of development both SPR and LSPR sensors find themselves in, it becomes apparent that providing a comparative analysis of both concepts is not a trivial task. Nevertheless, in this review we make an effort to provide an overview that illustrates the progress booked in both fields during the last five years. First, we discuss the most relevant advances in SPR biosensing, including interesting analytical applications, together with different strategies that assure improvements in performance, throughput and/or integration. Subsequently, the remaining part of this work focuses on the use of nanoplasmonic sensors for real label-free biosensing applications. First, we discuss the motivation that serves as a driving force behind this research topic, together with a brief summary that comprises the main fabrication methodologies used in this field. Next, the sensing performance of LSPR sensors is examined by analyzing different parameters that can be invoked in order to quantitatively assess their overall sensing performance. Two aspects are highlighted that turn out to be especially important when trying to maximize their sensing performance, being (1) the targeted functionalization of the electromagnetic hotspots of the nanostructures, and (2) overcoming inherent negative influence that stem from the presence of a high refractive index substrate that supports the nanostructures. Next, although few in numbers, an overview is given of the most exhaustive and diagnostically relevant LSPR sensing assays that have been recently reported in literature, followed by examples that exploit inherent LSPR characteristics in order to create highly integrated and high-throughput optical biosensors. Finally, we discuss a series of considerations that, in our opinion, should be addressed in order to bring the realization of a stand-alone LSPR biosensor with competitive levels of sensitivity, robustness and integration (when compared to a conventional SPR sensor) much closer to reality.We thank the financial support from the national projects MULTIBIOPLAS (TEC2099-08729) and INNBIOD (INNPACTO Subprogram, IPT-2011-1429-010000) from Spanish Ministry of Economy and Competitiveness.Peer Reviewe

Substrate effect on the refractive index sensitivity of silver nanoparticles

The bulk refractive index (RI) sensitivity of dispersed and immobilized silver nanoparticles of three different shapes (spheres, cubes, and plates) is investigated. We demonstrate, both experimentally and theoretically, that the influence of immobilization on the RI sensitivity is highly dependent on the shape of the nanoparticles. A strong correlation is seen between the fraction of the particle surface area in direct contact with the substrate and the decrease in RI sensitivity when the particles are immobilized on a glass substrate. The largest decrease (-36%) is seen for the most sensitive nanoparticles (plates), drastically reducing their advantage over other nanoparticle shapes. The shape-dependent substrate effect is thus an important factor to consider when designing nanoplasmonic sensors based on colloidal noble-metal nanoparticles.D.A. and E.M. gratefully acknowledge financial support from the Swedish Research Council (VR) and the Swedish Foundation for Strategic Research (SSF). During this study, E.M. was enrolled in the graduate school Forum Scientium. B.S. and M.A.O acknowledge the financial support of the Spanish project MAT2011-12645-EPeer Reviewe

Tailored Height Gradients in Vertical Nanowire Arrays via Mechanical and Electronic Modulation of Metal-Assisted Chemical Etching

In current top-down nanofabrication methodologies the design freedom is generally constrained to the two lateral dimensions, and is only limited by the resolution of the employed nanolithographic technique. However, nanostructure height, which relies on certain mask-dependent material deposition or etching techniques, is usually uniform, and on-chip variation of this parameter is difficult and generally limited to very simple patterns. Herein, a novel nanofabrication methodology is presented, which enables the generation of high aspect-ratio nanostructure arrays with height gradients in arbitrary directions by a single and fast etching process. Based on metal-assisted chemical etching using a catalytic gold layer perforated with nanoholes, it is demonstrated how nanostructure arrays with directional height gradients can be accurately tailored by: (i) the control of the mass transport through the nanohole array, (ii) the mechanical properties of the perforated metal layer, and (iii) the conductive coupling to the surrounding gold film to accelerate the local electrochemical etching process. The proposed technique, enabling 20-fold on-chip variation of nanostructure height in a spatial range of a few micrometers, offers a new tool for the creation of novel types of nano-assemblies and metamaterials with interesting technological applications in fields such as nanophotonics, nanophononics, microfluidics or biomechanics.Authors acknowledge the financial support of Spanish MINECO projects MAT2011–12645-E, TEC2012–34280, MAT2011–29194-C02–01, CSD2008-00023, and MAT2013–48628-R. V. Solis-Tinoco acknowledges financial support from The National Council for Science and Technology (CONACyT), Mexico. ICN2 acknowledges support of the Spanish MINECO through the Severo Ochoa Centers of Excellence Program under Grant No. SEV-2013–0295.Peer reviewe

Molecular inversion probe-based SPR biosensing for specific, label-free and real-time detection of regional DNA methylation

DNA methylation has the potential to be a clinically important biomarker in cancer. This communication reports a real-time and label-free biosensing strategy for DNA methylation detection in the cancer cell line. This has been achieved by using surface plasmon resonance biosensing combined with the highly specific molecular inversion probe based amplification method, which requires only 50 ng of bisulfite treated genomic DNA.This work was supported by the UQ fellowship (2012001456) awarded to LGC, ARC DECRA (DE120102503) awarded to MJAS, and National Breast Cancer Foundation (NBCF) of Australia (CG-08-07 and CG-12-07) awarded to MT.Peer Reviewe

Highly sensitive dendrimer-based nanoplasmonic biosensor for drug allergy diagnosis

A label-free biosensing strategy for amoxicillin (AX) allergy diagnosis based on the combination of novel dendrimer-based conjugates and a recently developed nanoplasmonic sensor technology is reported. Gold nanodisks were functionalized with a custom-designed thiol-ending-polyamido-based dendron (d-BAPAD) peripherally decorated with amoxicilloyl (AXO) groups (d-BAPAD–AXO) in order to detect specific IgE generated in patient's serum against this antibiotic during an allergy outbreak. This innovative strategy, which follows a simple one-step immobilization procedure, shows exceptional results in terms of sensitivity and robustness, leading to a highly-reproducible and long-term stable surface which allows achieving extremely low limits of detection. Moreover, the viability of this biosensor approach to analyze human biological samples has been demonstrated by directly analyzing and quantifying specific anti-AX antibodies in patient's serum without any sample pretreatment. An excellent limit of detection (LoD) of 0.6 ng/mL (i.e. 0.25 kU/L) has been achieved in the evaluation of clinical samples evidencing the potential of our nanoplasmonic biosensor as an advanced diagnostic tool to quickly identify allergic patients. The results have been compared and validated with a conventional clinical immunofluorescence assay (ImmunoCAP test), confirming an excellent correlation between both techniques. The combination of a novel compact nanoplasmonic platform and a dendrimer-based strategy provides a highly sensitive label free biosensor approach with over two times better detectability than conventional SPR. Both the biosensor device and the carrier structure hold great potential in clinical diagnosis for biomarker analysis in whole serum samples and other human biological samples.M. Soler and P. Mesa-Antunez acknowledges financial support from “Programa de Formación de Personal Investigador (FPI)” from the Spanish Ministry of Economy and Competitiveness. The authors acknowledge the Red De Investigación de Reacciones Adversas a Alergenos y Fármacos (RIRAAF) (RD12/0013/0003), the Consejería de Salud from Junta de Andalucía (PI-0159-2013), Junta de Andalucía (CTS 06603), ISCIII (09/01768, PI12/02529), the former Spanish Ministry of Science and Innovation (CTQ2010-20303) and the Spanish Ministry of Economy and Competitiveness (MULTIBIOPLAS project, TEC2099-08729) for the financial support. ICN2 is the recipient of Grant SEV-2013-0295 from the >Severo Ochoa Centers of Excellence> Program of Spanish MINECO.Peer Reviewe

Guiding Light in Monolayers of Sparse and Random Plasmonic Meta-atoms

Encouraged by the capacity of surface plasmons to confine and propagate electromagnetic fields, waveguiding concepts have been developed, including combinations of continuous metal films or ordered arrays of metal nanoparticles. So far, waveguiding in the latter systems has been based on near-field or diffractive coupling. Herein, we show that monolayers of sparse and disordered gold nanoparticles support a novel transverse-electric guided mode that, contrary to previous work, relies on the strong enhancement of the polarizability upon excitation of the nanoparticle LSPR, creating an effective refractive index sufficiently high to support light guidance over a large range of frequencies. Excitation of this guided mode offers interesting nanophotonics features and applications such as a tunable total absorption spectral band, attractive for light harvesting applications, or the generation of a large amplification of the sensitivity to changes of refractive index accompanied with striking enhancement of the limit of detection in real biosensing experiments. © 2011 American Chemical Society.This work was done with financial support from MULTIBIOPLAS of the Spanish Ministry of Science and Innovation (TEC2009-08729), the M. Botín Foundation, and EU MC2Access program. M. A. Otte acknowledges the “Programa de Formación de Profesorado Universitario (FPU)” of the Spanish Ministry of Education; B. Sepúlveda acknowledges the “Ramón and Cajal” program from Spanish Ministry of Science and Innovation for financial support; and David Regatos acknowledges financial support from “Programa de Formación de Investigadores del Departamento de Educación, Universidades e Investigación” of the Gobierno Vasco (Spain).Peer Reviewe

Direct Detection of Protein Biomarkers in Human Fluids Using Site-Specific Antibody Immobilization Strategies

Design of an optimal surface biofunctionalization still remains an important challenge for the application of biosensors in clinical practice and therapeutic follow-up. Optical biosensors offer real-time monitoring and highly sensitive label-free analysis, along with great potential to be transferred to portable devices. When applied in direct immunoassays, their analytical features depend strongly on the antibody immobilization strategy. A strategy for correct immobilization of antibodies based on the use of ProLinker™ has been evaluated and optimized in terms of sensitivity, selectivity, stability and reproducibility. Special effort has been focused on avoiding antibody manipulation, preventing nonspecific adsorption and obtaining a robust biosurface with regeneration capabilities. ProLinker™-based approach has demonstrated to fulfill those crucial requirements and, in combination with PEG-derivative compounds, has shown encouraging results for direct detection in biological fluids, such as pure urine or diluted serum. Furthermore, we have implemented the ProLinker™ strategy to a novel nanoplasmonic-based biosensor resulting in promising advantages for its application in clinical and biomedical diagnosis