Ultrasensitive antibody-aptamer plasmonic biosensor for malaria biomarker detection in whole blood

Development of plasmonic biosensors combining reliability and ease of use is still a challenge. Gold nanoparticle arrays made by block copolymer micelle nanolithography (BCMN) stand out for their scalability, cost-effectiveness and tunable plasmonic properties, making them ideal substrates for fluorescence enhancement. Here, we describe a plasmon-enhanced fluorescence immunosensor for the specific and ultrasensitive detection of Plasmodium falciparum lactate dehydrogenase (PfLDH)—a malaria marker—in whole blood. Analyte recognition is realized by oriented antibodies immobilized in a close-packed configuration via the photochemical immobilization technique (PIT), with a top bioreceptor of nucleic acid aptamers recognizing a different surface of PfLDH in a sandwich conformation. The combination of BCMN and PIT enabled maximum control over the nanoparticle size and lattice constant as well as the distance of the fluorophore from the sensing surface. The device achieved a limit of detection smaller than 1 pg/mL (<30 fM) with very high specificity without any sample pretreatment. This limit of detection is several orders of magnitude lower than that found in malaria rapid diagnostic tests or even commercial ELISA kits. Thanks to its overall dimensions, ease of use and high-throughput analysis, the device can be used as a substrate in automated multi-well plate readers and improve the efficiency of conventional fluorescence immunoassays

¿Psicología de la Educación o Psicología Escolar? Esa es la cuestión

Este artigo apresenta alguns dados oriundos da tese de doutorado sobre a história do campo de conhecimento e prática da Psicologia em sua relação com a Educação no Brasil. Este estudo foi conduzido baseado no fundamento epistêmico-filosófico do materialismo histórico dialético e na nova história, utilizando fontes bibliográficas históricas e cinco relatos orais de personagens da Psicologia Educacional e Escolar. Os depoimentos e o material das fontes escritas constituíram o corpus documental cuja organização seguiu a metodologia da história oral e historiografia plural. Foi realizada análise descritivo-analítica compreendida em duas etapas: a) análise documental (fontes não orais) e b) construção de indicadores e núcleos de significação dos registros orais. A partir das análises, compôs-se uma periodização da história da Psicologia Educacional e Escolar brasileira por meio de marcos históricos da área. No presente artigo destaca-se a discussão acerca da conceituação e terminologias utilizadas pela Psicologia Educacional e Escolar ao longo do tempo e de como essas mudanças nas nomenclaturas da área refletem questões epistemológicas, ideológicas e políticas

Sensing small neurotransmitter-enzyme interaction with nanoporous gated ion-sensitive field effect transistors

Ion-sensitive field effect transistors with gates having a high density of nanopores were fabricated and employed to sense the neurotransmitter dopamine with high selectivity and detectability at micromolar range. The nanoporous structure of the gates was produced by applying a relatively simple anodizing process, which yielded a porous alumina layer with pores exhibiting a mean diameter ranging from 20 to 35 nm. Gate-source voltages of the transistors demonstrated a pH-dependence that was linear over a wide range and could be understood as changes in surface charges during protonation and deprotonation. The large surface area provided by the pores allowed the physical immobilization of tyrosinase, which is an enzyme that oxidizes dopamine, on the gates of the transistors, and thus, changes the acid-base behavior on their surfaces. Concentration-dependent dopamine interacting with immobilized tyrosinase showed a linear dependence into a physiological range of interest for dopamine concentration in the changes of gate-source voltages. In comparison with previous approaches, a response time relatively fast for detecting dopamine was obtained. Additionally, selectivity assays for other neurotransmitters that are abundantly found in the brain were examined. These results demonstrate that the nanoporous structure of ion-sensitive field effect transistors can easily be used to immobilize specific enzyme that can readily and selectively detect small neurotransmitter molecule based on its acid-base interaction with the receptor. Therefore, it could serve as a technology platform for molecular studies of neurotransmitter-enzyme binding and drugs screening. (C) 2011 Elsevier B.V. All rights reserved.311157163research training group of biointerface (RWTH, Aachen

Noise and transport characteristics of silicon nanowire field effect transistors with liquid gate

Silicon nanowire field effect transistors (Si NW FETs) are promising structures for the development of new biosensors due to their ability to directly translate interactions with target molecules into readable signals. These structures are highly sensitive and selective and are capable of real-time response and label-free detection. However, there are challenges: the stability and reproducibility of the operation of such sensors in a liquid environment due to the property changes of the thin gate dielectric when exposed to an electrolyte for a long time. In this contribution, noise spectroscopy was employed to characterize the performance of the devices in the electrolyte and without it. Noise spectra were measured and analyzed for Si NW FETs with a width of 500nm and a variety of lengths (2-16µm) and a thin SiO2 passivation layer (10nm thickness) in air and phosphate-buffered saline (PBS) at different back-gate voltages, VG. Figure 1 shows the normalized current noise spectral density (NCNSD), SI / I2, at sub-threshold and above-threshold voltages measured in air and PBS. In the sub-threshold region, NCNSD in the device decreased when PBS was introduced to the sample. This decrease can be mainly explained by the changing of the surface charge state in the sample’s top dielectric due to PBS electrolyte adsorption and screening effect as well as only partial contribution of the increased sub-threshold current. Above the threshold voltage, submerging the sample in PBS results in a small increase in the amount of fluctuations in the sample. The lower value of the current at VG-VTh = 1.0 V in PBS only partially influences the normalized noise level behavior. Our results show that exposing the nanowire samples to PBS not only affects the number of charge carriers, but also most likely results in a change in the mobility of charge carriers

Double-Resonant Nanostructured Gold Surface for Multiplexed Detection

A novel double-resonant plasmonic substrate for fluorescence amplification in a chip-based apta-immunoassay is herein reported. The amplification mechanism relies on plasmon-enhanced fluorescence (PEF) effect. The substrate consists of an assembly of plasmon-coupled and plasmon-uncoupled gold nanoparticles (AuNPs) immobilized onto a glass slide. Plasmon-coupled AuNPs are hexagonally arranged along branch patterns whose resonance lies in the red band (∼675 nm). Plasmon-uncoupled AuNPs are sprinkled onto the substrate, and they exhibit a narrow resonance at 524 nm. Numerical simulations of the plasmonic response of the substrate through the finite-difference time-domain (FDTD) method reveal the presence of electromagnetic hot spots mainly confined in the interparticle junctions. In order to realize a PEF-based device for potential multiplexing applications, the plasmon resonances are coupled with the emission peak of 5-carboxyfluorescein (5-FAM) fluorophore and with the excitation/emission peaks of cyanine 5 (Cy5). The substrate is implemented in a malaria apta-immunoassay to detect Plasmodium falciparum lactate dehydrogenase (PfLDH) in human whole blood. Antibodies against Plasmodium biomarkers constitute the capture layer, whereas fluorescently labeled aptamers recognizing PfLDH are adopted as the top layer. The fluorescence emitted by 5-FAM and Cy5 fluorophores are linearly correlated (logarithm scale) to the PfLDH concentration over five decades. The limits of detection are 50 pM (1.6 ng/mL) with the 5-FAM probe and 260 fM (8.6 pg./mL) with the Cy5 probe. No sample preconcentration and complex pretreatments are required. Average fluorescence amplifications of 160 and 4500 are measured in the 5-FAM and Cy5 channel, respectively. These results are reasonably consistent with those worked out by FDTD simulations. The implementation of the proposed approach in multiwell-plate-based bioassays would lead to either signal redundancy (two dyes for a single analyte) or to a simultaneous detection of two analytes by different dyes, the latter being a key step toward high-throughput analysis

Randomly positioned gold nanoparticles as fluorescence enhancers in apta-immunosensor for malaria test

A plasmon-enhanced fluorescence-based antibody-aptamer biosensor — consisting of gold nanoparticles randomly immobilized onto a glass substrate via electrostatic self-assembly — is described for specific detection of proteins in whole blood. Analyte recognition is realized through a sandwich scheme with a capture bioreceptor layer of antibodies — covalently immobilized onto the gold nanoparticle surface in upright orientation and close-packed configuration by photochemical immobilization technique (PIT) — and a top bioreceptor layer of fluorescently labelled aptamers. Such a sandwich configuration warrants not only extremely high specificity, but also an ideal fluorophore-nanostructure distance (approximately 10–15 nm) for achieving strong fluorescence amplification. For a specific application, we tested the biosensor performance in a case study for the detection of malaria-related marker Plasmodium falciparum lactate dehydrogenase (PfLDH). The proposed biosensor can specifically detect PfLDH in spiked whole blood down to 10 pM (0.3 ng/mL) without any sample pretreatment. The combination of simple and scalable fabrication, potentially high-throughput analysis, and excellent sensing performance provides a new approach to biosensing with significant advantages compared to conventional fluorescence immunoassays. Graphical abstract: [Figure not available: see fulltext.

In situ fabrication of ultrathin porous alumina and its application for nanopatterning Au nanocrystals on the surface of ion-sensitive field-effect transistors

In situ fabrication in a single step of thin films of alumina exhibiting a thickness of less than 100 nm and nanopores with a highly regular diameter distribution in order to pattern nanostructures over field-effect devices is a critical issue and has not previously been demonstrated. Here we report the fabrication in situ of 50 nm thick ultrathin nanoporous alumina membranes with a regular pore size directly over metal-free gate ion-sensitive field-effect transistors. Depositing thin films of aluminum by an electron beam at a relatively low rate of deposition on top of chips containing the transistors and using a conventional single-step anodization process permits the production of a well-adhering nanoporous ultrathin layer of alumina on the surface of the devices. The anodization process does not substantially affect the electrical properties of the transistors. The small thickness and pore size of ultrathin alumina membranes allow them to be sequentially employed as masks for patterning Au nanocrystals grown by an electroless approach directly on the top of the transistors. The patterning process using a wet chemical approach enables the size of the patterned crystals to be controlled not only by the dimensions of the pores of alumina, but also by the concentration of the reactants employed. Surface modification of these nanocrystals with alkanethiol molecules demonstrates that the electrostatic charge of the functional groups of the molecules can modulate the electrical characteristics of the transistors. These results represent substantial progress towards the development of novel nanostructured arrays on top of field-effect devices that can be applied for chemical sensing or non-volatile memories.2348DFG research training group 'Biointerface' at RWTH Aachen Universit

LSPR-based colorimetric immunosensor for rapid and sensitive 17β-estradiol detection in tap water

We propose a highly sensitive immunosensor based on the Localized Surface Plasmon Resonance (LSPR) for 17β-estradiol (E2) quantification in water. E2 molecules are recognized by polyclonal antibodies immobilized onto gold nanoparticles (AuNPs) and act as linkers that cause nanoparticles aggregation. This leads to the change in the optical properties of the solution visible even by naked eyes. The aggregates were characterized by Dynamic Light Scattering (DLS) and Scanning Transmission Electron Microscopy (STEM) that provided an accurate assessment of the inter-particle distance. The finite-difference time-domain (FDTD) method applied to a Mie problem like workspace allowed us to describe the optical behaviour of the AuNP aggregates with excellent agreement between the experimental and numerical results. The limit of detection (LOD), without any preconcentration step, is 3 pg/mL (11 pM), whereas the detection range extends over five decades up to 105 pg/mL. The proposed E2 immunosensor was tested in tap water, where no significant cross-reaction signal was detected by similar molecules (testosterone, progesterone, estrone and estriol). The device described here represents a significant improvement of low E2 levels determination in terms of affordability, time and measuring simplicity, making it suitable for environmental applications