A significant amount of noteworthy articles reviewing different label-free biosensors are being published in the last years. Most of the times, the comparison among the different biosensors is limited by the procedure used of calculating the limit of detection and the measurement uncertainty. This article clarifies and establishes a simple procedure to determine the calibration function and the uncertainty of the concentration measured at any point of the measuring interval of a generic label-free biosensor. The value of the limit of detection arises naturally from this model as the limit at which uncertainty tends when the concentration tends to zero. The need to provide additional information, such as the measurement interval and its linearity, among others, on the analytical systems and biosensor in addition to the detection limit is pointed out. Finally, the model is applied to curves that are typically obtained in immunoassays and a discussion is made on the application validity of the model and its limitations.
In this article we report a new, simple, and reliable optical read-out detection method able to assess Rotavirus present in human sera as well as in the viral pollution sources. It is based on the interference of two interferometers used as biophotonic transducers. The method significantly improves the optical label-free biosensing response measuring both, the concentration of the AgR and its corresponding size. Two different immunoassays were carried out: Bovine Serum Albumin (BSA), and the recognition by its antibody (anti-BSA); and Rotavirus (AgR) and the recognition by its antibody (anti-AgR). In the cases studied, and using as model interferometer a simple Fabry-Perot transducer, we demonstrate a biosensing enhancement of two orders of magnitude in the Limit of Detection (LoD). In fact, this read-out optical method may have significant implications to enhance other optical label-free photonic transducers reported in the scientific literature.
This work reports the synthesis and hydrogenation of polynorbornenes with functionalized imide
side groups, specifically, poly(N-phenyl-exo,endo-norbornene-5,6-dicarboximide), as well as the sulfonation of
the hydrogenated polymer. The gas transport characteristics and permselectivity of membranes prepared from
the three separated polymers were thoroughly investigated. The results show that hydrogenation of the starting
polymer promotes packaging efficiency, which is even enhanced by further sulfonation of the hydrogenated chains.
The economy of free volume is reflected in the permeation and permselectivity coefficients of membranes prepared
from the polymers. The study of electromotive forces of concentration cells with the sulfonated membrane separating
hydrochloric solutions of different concentration suggests that the membranes exhibit high permselectivity to
protons that decreases as concentration increases. However, a sharp increase in the electromotive force occurs at
high concentrations. The fact that this increase is not observed in the electromotive forces of concentration cells
with sodium chloride in the compartment cells suggests the formation of pair ions between protonated imide
groups and chloride ions at high concentration that restrains co-ions mobility in the membrane. The membranes
exhibit pretty good permselectivity to protons and sodium ions which makes them useful for ionic separation
applications, such as electrodialysis. However, owing to the low water uptake, the protonic conductivity of the
membranes equilibrated with water is nearly 2 orders of magnitude below that reported for Nafion membranes.
We have recently developed a new type of porous silicon we name as porous silicon colloids. They consist of almost perfect spherical silicon nanoparticles with a very smooth surface, able to scatter (and also trap) light very efficiently in a large-span frequency range. Porous silicon colloids have unique properties because of the following: (a) they behave as optical microcavities with a high refractive index, and (b) the intrinsic photoluminescence (PL) emission is coupled to the optical modes of the microcavity resulting in a unique luminescence spectrum profile. The PL spectrum constitutes an optical fingerprint identifying each particle, with application for biosensing. In this paper, we review the synthesis of silicon colloids for developing porous nanoparticles. We also report on the optical properties with special emphasis in the PL emission of porous silicon microcavities. Finally, we present the photonic barcode concept.
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