Higher LODs Research Articles

Multiplexed electrochemical liposomes applied to the detection of nucleic acids for Influenza A, Influenza B and SARS-CoV-2

Multiplexing is a relevant strategy for biosensors to improve accuracy and decision-making due to the increased amount of simultaneously obtained information. Liposomes offer unique benefits for label-based multiplexing since a variety of different marker molecules can be encapsulated, leading to intrinsic signal amplification and enabling a variety of detection formats. We successfully developed an electrochemical (EC) liposome-based platform technology for the simultaneous detection of at least three analytes by studying parameters to ensure specific and sensitive bioassay performance. Influenza A and B and SARS-CoV-2 sequences served as model system in a standard sandwich hybridization assay. Studies included encapsulants, probe distribution on liposomes and capture beads, assay setup and interferences between liposomes to also ensure a generalization of the platform. Ruthenium hexamine(III), potassium hexacyanoferrate(II) and m-carboxy luminol, when encapsulated separately into a liposome, provided desirable long-term stability of at least 12 months and no cross-signals between liposomes. Through the optimization process, low limits of detections of 1.6 nmol L−1, 125 pmol L−1 and 130 pmol L−1, respectively, were achieved in a multiplexed assay setup, which were similar to singleplex assays. Non-specific interactions were limited to 25.1%, 7.6% and 7.5%, respectively, through sequential liposome incubations and singleplex capture bead designs. Here, ruthenium hexamine liposomes had only mediocre performance so that low overall signal strength translated into higher LODs and worse specificity. A different marker such as ferroin may be an option in the future. The identification of further electrochemical markers will provide new opportunities for liposomes to function as multiplex, orthogonal or internal standard labels in electrochemical bioassays.Graphical

The Limit of Detection Matters: The Case for Benchmarking Severe Acute Respiratory Syndrome Coronavirus 2 Testing.

BackgroundResolving the coronavirus disease 2019 (COVID-19) pandemic requires diagnostic testing to determine which individuals are infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The current gold standard is to perform reverse-transcription polymerase chain reaction (PCR) on nasopharyngeal samples. Best-in-class assays demonstrate a limit of detection (LoD) of approximately 100 copies of viral RNA per milliliter of transport media. However, LoDs of currently approved assays vary over 10,000-fold. Assays with higher LoDs will miss infected patients. However, the relative clinical sensitivity of these assays remains unknown.MethodsHere we model the clinical sensitivities of assays based on their LoD. Cycle threshold (Ct) values were obtained from 4700 first-time positive patients using the Abbott RealTime SARS-CoV-2 Emergency Use Authorization test. We derived viral loads from Ct based on PCR principles and empiric analysis. A sliding scale relationship for predicting clinical sensitivity was developed from analysis of viral load distribution relative to assay LoD.ResultsCt values were reliably repeatable over short time testing windows, providing support for use as a tool to estimate viral load. Viral load was found to be relatively evenly distributed across log10 bins of incremental viral load. Based on these data, each 10-fold increase in LoD is expected to lower assay sensitivity by approximately 13%.ConclusionsThe assay LoD meaningfully impacts clinical performance of SARS-CoV-2 tests. The highest LoDs on the market will miss a majority of infected patients. Assays should therefore be benchmarked against a universal standard to allow cross-comparison of SARS-CoV-2 detection methods.

Characteristics of wipe sampling methods for antineoplastic drugs in North America: comparison of six providers

Abstract Objectives Several societies have published guidelines to limit the occupational exposure of workers. Several of these guidelines recommend periodic (once or twice a year) environmental monitoring of specific sites where antineoplastic drugs are prepared and administered. However, most of the guidelines provide no guidance concerning which antineoplastic drugs should be monitored, the preferred sampling sites, appropriate test methods or limits of detection. The aim of this study was to characterize providers that quantify antineoplastic drug measured on surfaces. Methods This was a cross-sectional descriptive study. To identify service providers offering environmental monitoring tests, we searched the PubMed database and used the Google search engine. We contacted each service provider by email between June 3rd and June 15th, 2020. We specified the objective of our study and described the information needed and the variables of interest with standardized questions. Additional questions were sent by emails or via teleconferences. No statistical analyses were performed. Results We identified six providers offering services to Canadian hospitals, either based in Canada or in the United States. Five of these providers were private companies and one was a public organization. Each service provider was able to measure trace contamination of 3–17 antineoplastic drugs. Five of the providers quantified drugs using ultra performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MSMS), which allowed for lower LODs. The sixth provider offered quantification by immunoassay, which has higher LODs, but offers near real-time results; the surface area to be sampled with this method was also smaller than with UPLC-MSMS. The services offered varied among the service providers. The information about LODs supplied by each provider was often insufficient and the units were not standardized. A cost per drug quantified could not be obtained, because of variability in the scenarios involved (e.g. drug selection to be quantified, number of samples, nondisclosure of ancillary costs). Four of the six service providers were unable to report LOQ values. Conclusions Few data are available from Canadian service providers concerning the characteristics of wipe sampling methods for antineoplastics. This study identified six north-American providers. Their characteristics were very heterogeneous. Criteria to consider when choosing a provider include the validation of their analytical method, a low limit of detection, the choice of drugs to be quantified and the sites to be sampled, obtaining details about the method and understanding its limits, and price. This should be part of a structured multidisciplinary approach in each center.

Simultaneous determination of legacy and emerging organophosphorus flame retardants and plasticizers in indoor dust using liquid and gas chromatography-tandem mass spectrometry: method development, validation, and application.

In the present study, an analytical method has been developed and validated for the simultaneous detection and quantification of 19 PFRs (14 legacy organophosphorus flame retardants (PFRs) and 5 emerging PFRs (ePFRs)) and 20 plasticizers (7 legacy plasticizers (LPs) and 13 alternative plasticizers (APs)). Sample preparation was based on the combination of previously validated analytical protocols including ultrasonic extraction and Florisil fractionation/cleanup. The analysis was performed by using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for all targeted compounds, except for bis (2-ethylhexyl) phthalate (DEHP) and bis (2-ethylhexyl) terephthalate (DEHT), for which the separation of the isomers resulted in more favorable gas chromatography-electron ionization-mass spectrometry (GC-EI-MS). The new method was in-house validated by applying two levels of fortification in dust. The achieved linearity (R2) ranged between 0.993 and 0.999. Limits of detection and quantification (LODs and LOQs) ranged between 1 and 265ng/g and between 1 and 870ng/g for all analytes, respectively, except for DEHP and DEHT, for which relatively higher LODs (665 and 1100ng/g, respectively) and LOQs (2100 and 3500ng/g, respectively) were observed. Accuracy ranged between 75 and 125% for most of the targeted analytes, and repeatability was good with relative standard deviation (RSD) < 15% for most compounds. Finally, the method was applied for the determination and quantification of the targeted chemicals in house dust samples (n = 10) from the megacity of Guangzhou (China). Median values ranged from 3 to 210ng/g for PFRs, from 4 to 165ng/g for ePFRs, from 30 to 100,000ng/g for LPs, and from 6 to 34,000ng/g for APs. Main contributors to the total contamination were LPs 63% and APs 37% in total plasticizers, whereas PFRs and ePFRs contributed 90% and 10% in total flame retardants. Graphical abstract.

A UNIFIED APPROACH FOR 3D GENERALIZATION OF BUILDING MODELS IN CITYGML

Abstract. Task-specific applications demand abstractions (generalized) 3D scenes of 3D models to be used for visualization and analysis purposes. Therefore, lower LoDs (level-of-details) from higher LoDs need to be made available to these applications. A unified generalization framework is proposed to derive multiple LoDs (LoD3-LoD1) taking both semantics and geometric aspects of 3D buildings modelled in CityGML (City Geography Markup Language) into account. For this purpose, interior structures of 3D objects at LoD4 are removed to derive LoD3 and openings (door, windows) are removed from LoD3 to derive LoD2. Remaining parts such as outer installations and walls are projected onto the ground and simplified based on CityGML generalization specifications. Algorithms for simplification with the aim to derive LoD1 from LoD2 are implemented and tested on a number of buildings of Putrajaya city, Malaysia.The experiments shows that elimination of important part (s) or merging could be avoided by applying semantic-based removal of objects at different LoDs.

Atmospheric pressure gas chromatography with quadrupole time of flight mass spectrometry for simultaneous detection and quantification of polycyclic aromatic hydrocarbons and nitro-polycyclic aromatic hydrocarbons in mosses

Within the family of polycyclic aromatic hydrocarbons (PAHs), nitrated derivatives are of particular interest in environmental science because they have well-known carcinogenic and mutagenic effects. They are in fact more toxic than their parent PAHs. One valuable diagnosis of atmospheric pollution can be obtained using biomonitors such as mosses. These biomonitors can provide information about air pollution over long periods of time in wilderness areas. Thus, they can serve as monitors of the atmospheric transport of pollutants. In this study, atmospheric pressure gas chromatography coupled to a quadrupole hyphenated to a time of flight mass spectrometer (APGC–MS/Q-TOF) has been examined for the identification of target analytes (15 PAHs and 8 NPAHs) for subsequent use in the analysis of mosses. Working ranges in low μgg−1 concentration levels were obtained with most correlation coefficients higher than 0.999. All LODs were in the 0.007–0.035μgg−1 range and higher LODs (0.035μgg−1) were obtained for the less volatile PAHs with higher mass and retention times: benzo(g,h,i)perylene, dibenz(a,h)anthracene and indeno(1,2,3-c,d)pyrene. These LODs are of importance for the intended use, biomonitoring, especially taking into account that NPAHs are commonly found at very low concentration levels. Recoveries from mosses ranged from 75 to 98%. Intraday and interday precision ranged from 1.8 to 11.1% RSD and from 2.4 to 16.7% RSD, respectively. Very low concentrations of NPAHs were found in mosses compared to those of PAHs. All these data were used for pattern recognition of the pollutant source. The results are shown and discussed.

Comparison of Imaging Techniques for Tracking Cardiac Stem Cell Therapy

<h3>Abstract</h3> Resolving the COVID-19 pandemic requires diagnostic testing to determine which individuals are infected and which are not. The current gold standard is to perform RT-PCR on nasopharyngeal samples. Best-in-class assays demonstrate a limit of detection (LoD) of ~100 copies of viral RNA per milliliter of transport media. However, LoDs of currently approved assays vary over 10,000-fold. Assays with higher LoDs will miss more infected patients, resulting in more false negatives. However, the false-negative rate for a given LoD remains unknown. Here we address this question using over 27,500 test results for patients from across our healthcare network tested using the Abbott RealTime SARS-CoV-2 EUA. These results suggest that each 10-fold increase in LoD is expected to increase the false negative rate by 13%, missing an additional one in eight infected patients. The highest LoDs on the market will miss a majority of infected patients, with false negative rates as high as 70%. These results suggest that choice of assay has meaningful clinical and epidemiological consequences. The limit of detection matters.