Upconversion (UC) luminescence sensing is a technique to improve the detection limit of conventional fluorescence in biosensing that is commonly limited by the autofluorescence-generated background signal. The main limitation of UC materials is their low wavelength conversion efficiency. Many studies have been made to enhance the efficiency of UC materials by optimizing light absorption and energy transfer processes. However, rather low efficiency remains an issue limiting the practical usage of UC materials in biosensors. Plasmon enhancement is a way to improve UC photoluminescence by enhancing the excitation and emission rates. In this study, we modeled and fabricated gold gratings for exciting surface plasmon polaritons (SPPs) at 976-nm wavelength. We aim at increasing the local optical intensity at the locations of UC nanoparticles on a nano-structured plasmonic surface. The UC nanoparticles were adsorbed on the gratings via biomolecule conjugation. UC photoluminescence on the gratings was compared with flat gold surfaces. Experimentally, we achieved UC enhancement up to 70, which is relatively high in comparison with other plasmon-enhanced UC techniques presented in the literature. The results of our work can be applied in various biosensing applications in which low excitation intensity is preferred.
Monitoring and verification of structural changes in mining areas is necessary for mining operators - especially in terms of what events are taking place in the mining area and tailing ponds. Emptying or enriching a pond requires up-to-date information on the shape of the pond and amount of contained material. Increasing accurate measurements interests mining operators. Novel monitoring technologies include possibility of imaging spectroscopic optical measurements - such as hyperspectral imaging - with drone-based scanning feature. At Pyhäsalmi Mine in Finland, we established field trials with drone-based near-infrared multispectral imaging of mine tailing ponds and their dam structures. These field trials were part of the European Union’s Horizon 2020 project called ‘Goldeneye’, which aims to develop a data-acquisition and processing platform combining remote sensing and positioning technologies to produce actionable intelligence for mine operators.
The goal of the SensApp FET-Open project is to develop an innovative super-sensor that will be able to detect Alzheimer’s disease (AD) biomarkers (β-amyloid, Tau and pTAU) in peripheral blood. Considering that nowadays an accurate diagnosis of AD requires the highly invasive withdrawal and analysis of cerebrospinal fluid, SensApp will represent a breakthrough in the field of AD diagnosis thanks to the ability to detect the early stage of the disease by a simple blood collection. We call Droplet-Split-and-Stack (DSS) the new technology that will emerge from SensApp. The achievement of SensApp goal is enabled by the interdisciplinary cooperation between different research institutions and one company involved in the key fields of the project, Vrije Universiteit Brussels, VTT Technical Research Centre of Finland, University of Linz, Ginolis Ltd, IRCCS Centre “Bonino Pulejo”, under the coordination of CNR-Institute of Applied Sciences and Intelligent Systems. This communication will illustrate the progress of the activities.
The effective detection of very low abundant biomarkers can enable fast diagnosis of many severe and disabling diseases (e.g. Alzheimer’s Disease) at an early stage. To develop a cost-efficient, super-sensitive optical fluorescence detection microscope, we have proposed an optical modelling approach to predict the signal-noise-ratio that considers various noise sources introduced by the components of the detection system. After the optimal design is identified, a tolerance analysis regarding typical perturbations is performed for further mechanical design and assembly. Finally, experiments have demonstrated a limit of detection at a low abundant concentration reaching 0.05 pmol/ml.
A remote and heat-resistant Raman measurement probe has been developed for timegated PicoRaman utilizing a 532 nm pulsed laser and SPAD detector. The probe has 400 mm measuring distance with automated focus detection. The focus detection enables a fast auto-focusing to a varying sample surface distance – an obligatory requirement in many industrial applications including ore mineral scanning above conveyor belts in raw material sector or the inspection of metal product consistency in metal industry lines. In addition, the Raman probe has been designed to withstand thermal loads to be suitable for hot industrial process control.
In food industry, detection of spoilage yeasts such as W. anomalus and B. bruxellensis and pathogens such as certain Listeria and E. coli species can be laborious and time-consuming. In the present study, a simple and repeatable technique was developed for rapid yeast detection using a combination of patterned gold coated polymer SERS substrates and gold nanoparticles [1−4]. For the first time, a state-of-the-art time-gated Raman detection approach was used as a complementary technique to show the possibility of using 532-nm pulsed laser excitation and avoid the destructive influence of induced fluorescence [3].
Conventional nanoparticles synthesized by colloidal chemistry are typically contaminated by non-biocompatible by-products (surfactants, anions), which can have negative impacts on many live objects under examination (cells, bacteria) and thus decrease the precision of bioidentification. Here, we explore novel ultrapure laser-synthesized Au-based nanomaterials, including Au NPs and Au Si hybrid nanostructures, as mobile SERS probes in tasks of bacteria detection [3].
We demonstrate successful identification of two types of bacteria (L. innocua and E. coli) and yeast (W. anomalus and B. bruxellensis). They showed several differing characteristic peaks making the discrimination of these yeasts possible without the need for chemometric analysis [2]. The use of composite gold-silicon laser-ablated nanoparticles in combination with the SERS substrate gave distinctive spectra for all the detected species. The detection limit of the studied species varied within 104-107 CFU/ml. The obtained results open up opportunities for non-disturbing investigation of biological systems by profiting from excellent non-disturbing nature of laser-synthesized nanomaterials in combination with outstanding optical detection technologies [2, 3].
[1] Uusitalo et al. 2016, http://pubs.rsc.org/en/content/articlehtml/2016/ra/c6ra08313g
[2] Uusitalo et al. 2017a, https://www.sciencedirect.com/science/article/pii/S0260877417302054
[3] Kögler et al. 2018, https://onlinelibrary.wiley.com/doi/abs/10.1002/jbio.201700225
[4] Uusitalo et al. 2017b, https://www.spiedigitallibrary.org/journalArticle/Download?fullDOI=10.1117/1.OE.56.3.037102
Immunomagnetic separation (IMS) beads with antibody coating are an interesting option for biosensing applications for the identification of biomolecules and biological cells, such as bacteria. The paramagnetic properties of the beads can be utilized with optical sensing by migrating and accumulating the beads and the bound analytes toward the focus depth of the detection system by an external magnetic field. The stability of microbial detection with IMS beads was studied by combining a flexible, inexpensive, and mass producible surface-enhanced Raman spectroscopy (SERS) platform with gold nanoparticle detection and antibody recognition by the IMS beads. Listeria innocua ATCC 33090 was used as a model sample and the effect of the IMS beads on the detected Raman signal was studied. The IMS beads were deposited into a hydrophobic sample well and accumulated toward the detection plane by a neodymium magnet. For the first time, it was shown that the spatial stability of the detection could be improved up to 35% by using IMS bead capture and sample well placing. The effect of a neodymium magnet under the SERS chip improved the temporal detection and significantly reduced the necessary time for sample stabilization for advanced laboratory testing.
We fabricated SU-8 based slab waveguides on surface-modified poly(dimethyl siloxane) PDMS lower claddings for
application in evanescent field sensing. In this application, higher sensitivity is obtained by generating stronger
penetrating power above the waveguide into the analyte. This can be achieved by reducing the refractive index of the
substrate. Compared with glass substrates that have a refractive index of 1.5, PDMS has a refractive index of 1.42 at 633
nm, thus serving as a better lower cladding material for high-sensitivity sensing with an evanescent field or as claddings
in multilayer waveguide applications. In order to increase the adhesion of PDMS surfaces for successful SU-8
application we treated PDMS thin films in low-frequency (40 kHz) oxygen plasma for varied length of exposure time.
The treatment process made PDMS hydrophilic and created nano-structures on the surfaces. The resultant surface
topography with different exposure time was studied by an interferometric profiler on PDMS lower claddings and the
later spin-coated SU-8 waveguides. Measurement results showed that longer plasma treatment on PDMS claddings
significantly improved the uniformity and waviness of the waveguides. Light propagation tests performed with a prism
coupler and an end-butt coupling setup proved that PDMS can be used as a proper material for SU-8 waveguides.
This paper presents a label-free optical biosensor based on a Young's interferometer configuration that uses a vertically
integrated dual-slab waveguide interferometer as sensing element. In this element, linearly polarized light is coupled into
a dual-slab waveguide chip from the input end-face, and the in-coupled zeroth order mode propagates in separated upper
and lower waveguides. At the output end-face, the two closely spaced coherent beams diffract out and produce an
interference fringe pattern. An evanescent wave field, generated on the surface of the upper waveguide, probes changes
in the refractive index of the studied sample, causing a phase shift in the fringe pattern. Compared to a conventional
integrated Young's interferometer utilizing a Y-junction as the beam splitter, the dual-slab waveguide Young's
interferometer has the advantage of easy fabrication and large tolerance to the input-coupling beam. This paper builds a
measurement system to investigate sensor performance using glucose solutions with various concentrations. These
glucose concentration measurements are performed within the physiological range of 30mg/dl ~ 500mg/dl. The results
indicate that a dual-slab waveguide interferometer yields an average phase resolution of 0.002 rad, which corresponds to
an effective refractive index change of 4×10-8 with an interaction path length of 15 mm.
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