Approaches to Assure Similarity between Pharmaceutical Heparins from Two Different Manufacturers

Pharmaceutical heparins from different manufacturers may present heterogeneities due to particular extraction and purification procedures or even variations in the raw material manipulation. Heparins obtained from different tissues also differ in their structure and activity. Nevertheless, there is an increased demand for more accurate assessments to ensure the similarities of pharmaceutical heparins. We propose an approach to accurately assess the similarity of these pharmaceutical preparations based on well-defined criteria, which are verified with a variety of refined analytical methods. We evaluate six commercial batches from two different manufacturers which were formulated with Brazilian or Chinese active pharmaceutical ingredients. Biochemical and spectroscopic methods and analysis based on digestion with heparinases were employed to evaluate the purity and structure of the heparins. Specific assays were employed to evaluate the biological activity. We observed minor but significant differences between the constitutive units of the heparins from these two manufacturers, such as the content of N-acetylated α-glucosamine. They also have minor differences in their molecular masses. These physicochemical differences have no impact on the anticoagulant activity but can indicate particularities on their manufacturing processes. The protocol we propose here for analyzing the similarity of unfractionated heparins is analogous to those successfully employed to compare low-molecular-weight heparins.

Fluorescence Polarization-Based Bioassays: New Horizons

Fluorescence polarization holds considerable promise for bioanalytical systems because it allows the detection of selective interactions in real time and a choice of fluorophores, the detection of which the biosample matrix does not influence; thus, their choice simplifies and accelerates the preparation of samples. For decades, these possibilities were successfully applied in fluorescence polarization immunoassays based on differences in the polarization of fluorophore emissions excited by plane-polarized light, whether in a free state or as part of an immune complex. However, the results of recent studies demonstrate the efficacy of fluorescence polarization as a detected signal in many bioanalytical methods. This review summarizes and comparatively characterizes these developments. It considers the integration of fluorescence polarization with the use of alternative receptor molecules and various fluorophores; different schemes for the formation of detectable complexes and the amplification of the signals generated by them. New techniques for the detection of metal ions, nucleic acids, and enzymatic reactions based on fluorescence polarization are also considered.

A label-free RTP sensor based on aptamer/quantum dot nanocomposites for cytochrome c detection

Given the outstanding room-temperature phosphorescence (RTP) of Mn–ZnS quantum dots (QDs) and the specific recognition performance of the aptamer, we built phosphorescent composites from aptamers conjugated with polyethyleneimine quantum dots (PEI-QDs) and applied them to cytochrome c (Cyt c) detection. Specifically, QDs/CBA composites were generated from the electrostatic interaction between the positively-charged PEI-QDs and the negatively-charged Cyt c binding aptamer (CBA). With the presence of Cyt c, the Cyt c can specifically bind with the QDs/CBA composites, and quench the RTP of QDs through photoinduced electron-transfer (PIET). Thereby, an optical biosensor for Cyt c detection was built, which had a detection range of 0.166–9.96 μM and a detection limit of 0.084 μM. This aptamer-mediated phosphorescent sensor with high specificity and operational simplicity can effectively avoid the interference of scattering light from complex substrates. Our findings offer a new clue for building biosensors based on QDs and aptamers.

In this study, the nanocomposites from polyethyleneimine-capped Mn-doped ZnS QDs (PEI-QDs) and Cyt c binding aptamer (CBA) were prepared and used as Cyt c RTP sensors..

-Phosphorescent Mesoporous Surface Imprinting Microspheres: Preparation and Application for Transferrin Recognition from Biological Fluids

The relationship between the thickness of surface molecularly imprinted polymers (MIPs) and specific recognition performance of transferrin (Trf) as well as the quantitative relation between the grafting amount of Mn-ZnS room-temperature phosphorescence (RTP) quantum dots (QDs) (short for PQDs) and RTP signals for recognition of Trf was analyzed in this study. Based on analysis results, RTP protein mesoporous imprinting microspheres (SiO₂-PQDs-MIPs) with high specificity and strong interference resistance were developed using a mesoporous SiO₂ nanomaterial that can create more three-dimensional precise recognition sites as the matrix and using PQDs with strong resistance to background fluorescence interference as the luminescent materials. A discriminatory analysis of Trf was realized by the phosphorescence quenching principle based on light quenching caused by the photoinduced electron transfer. The concentration range, limit of detection, relative standard deviation, and imprinting factor of Trf detection under pH 7.4 are 0.05-1.0 μM, 0.014 μM, 3.23%, and 3.09, respectively. Although the sensing signals of SiO₂-PQDs-MIPs for proteins are based on the phosphorescence of PQDs, they are particularly suitable for specific recognition and accurate quantitative detection of proteins in biological fluids. Research conclusions are expected to realize high-efficiency recognition of target proteins in actual biological samples.

Enzymatic cleavage and mass amplification strategy for small molecule detection using aptamer-based fluorescence polarization biosensor

Fluorescence polarization (FP) assays incorporated with fluorophore-labeled aptamers have attracted great interest in recent years. However, detecting small molecules through the use of FP assays still remains a challenge because small-molecule binding only results in negligible changes in the molecular weight of the fluorophore-labeled aptamer. To address this issue, we herein report a fluorescence polarization (FP) aptamer assay that incorporates a novel signal amplification strategy for highly sensitive detection of small molecules. In the absence of adenosine, our model target, free FAM-labeled aptamer can be digested by nuclease, resulting in the release of FAM-labeled nucleotide segments from the dT-biotin/streptavidin complex with weak background signal. However, in the presence of target, the FAM-labeled aptamer-target complex protects the FAM-labeled aptamer from nuclease cleavage, allowing streptavidin to act as a molar mass amplifier. The resulting increase in molecular mass and FP intensity of the aptamer-target complex provides improved sensitivity for concentration measurement. The probe could detect adenosine from 0.5 μM to 1000 μM, with a detection limit of 500 nM, showing that the sensitivity of the probe is superior to aptamer-based FP approaches previously reported for adenosine. Importantly, FP could resist environmental interferences, making it useful for complex biological samples without any tedious sample pretreatments. Our results demonstrate that this dual-amplified, aptamer-based strategy can be used to design fluorescence polarization probes for rapid, sensitive, and selective measurement of small molecules in complicated biological environment.

Aminophenylboronic-acid-conjugated polyacrylic acid-Mn-doped ZnS quantum dot for highly sensitive discrimination of glycoproteins

Discrimination of glycoproteins with different glycans is a significant but difficult issue. We presented here a new strategy for strengthening the discrimination of glycoproteins by introducing a new signaling channel, fluorescence polarization (FP), into a "single probe with three signaling channels" sensor array. The single probe was aminophenylboronic-acid-conjugated poly(acrylic acid)-Mn-doped ZnS quantum dots, and the three signaling channels were FP, room temperature phosphorescence and light scattering. Ten glycoproteins, including ovalbumin, fibrinogen, transferrin, horseradish peroxidase, vascular endothelial growth factor, immunoglobulin G, avidin, hyaluronidase, cellulase R-10, and glucose oxidase, were involved for evaluating the discriminating capability. The introduction of the FP signaling channel improved the discriminating power of the sensor array, so that the 10 glycoproteins at 0.15 μM could be well discriminated both in PBS buffer and in the presence of human serum sample. The identification accuracy of the unknown samples was 96.25% (77 out of 80) at the 0.15 μM level and 97.50% (78 out of 80) at the 0.2 μM level. The integration of the signaling patterns with different responsive principles was demonstrated as the promising way to enhance the discrimination power of the single-probe-based sensor arrays.