Loss Of Sensitivity Research Articles

Evaluation of the in-situ performance of neutron detectors based on EJ-426 scintillator screens for spent fuel characterization

The reliable detection of neutrons in a harsh gamma-ray environment is an important aspect of establishing non-destructive methods for the characterization of spent nuclear fuel. In this study, we present results from extended in-situ monitoring of detector systems consisting of commercially available components: EJ-426, a 6Li-enriched solid-state scintillator material sensitive to thermal neutrons, and two different types of Hamamatsu photomultiplier tubes (PMT). Over the period of eight months, these detectors were operated in close vicinity to spent nuclear fuel stored at the interim storage facility CLAB, Oskarshamn, Sweden. At the measurement position the detectors were continuously exposed to an estimated (moderated) neutron flux of approx. 280n/scm2 and a gamma-ray dose rate of approximately 6Sv/h.Using offline software algorithms, neutron pulses were identified and characterized in the data. Over the entire investigated dose range of up to 35kGy, the detector systems were functioning and were delivering detectable neutron signals. Their performance as measured by the number of identified neutrons degrades down to about 30% of the initial value. Investigations of the irradiated components suggest that this degradation is a result of reduced optical transparency of the involved materials as well as a reduction of PMT gain due to the continuous high currents. Increasing the gain of the PMT through step-ups of the applied high voltage allowed to partially compensate for this loss in detection sensitivity even when the detectors were highly irradiated.The integrated neutron fluence during the measurement was experimentally verified to be in the order of 5×109ncm−2. The results were interpreted with the help of MCNP6.2 simulations of the setup and the neutron flux.

Relationship Between Flicker Modulation Sensitivity and Retinal Ganglion Cell Related Layer Thicknesses.

PurposeEarly detection of structural changes in retinal ganglion cells (RGCs) and corresponding changes in visual function is important in early degenerative diseases of the retina, but the sensitivity of both measurements is limited by the inherent variability in healthy subjects. This study investigates the relationships between RGC-related layer thicknesses and foveal and parafoveal flicker modulation sensitivity (FMS) across photopic and mesopic light levels in healthy subjects.MethodsPhotopic and mesopic FMS was measured in 56 young adults, at the point of fixation and at an eccentricity of 5 degrees, in each of the four quadrants. Spectral-domain optical coherence tomography (SD-OCT) was used to measure retinal thicknesses. Relationships between foveal and parafoveal FMS and the retinal thickness in the corresponding region were examined after adjusting for confounding variables.ResultsTotal macular and inner retinal layer (IRL) thicknesses in the parafoveal ring were significant predictors of photopic (P = 0.034) and mesopic (P = 0.034) parafoveal FMS, respectively. The superior peripapillary retinal nerve fiber layer (pRNFL) thickness was a contributing factor to the inferior parafoveal FMS (photopic: P = 0.006 and mesopic: P = 0.021) and the inferior pRNFL thickness was also a contributing factor to the superior parafoveal FMS (photopic: P < 0.001 and mesopic: P = 0.015).ConclusionsThe pRNFL thicknesses predict parafoveal FMS for both mesopic and photopic conditions in healthy eyes.Translational RelevanceThe measurement of rapid flicker sensitivity in the parafoveal retina together with the pRNFL thickness profiles measured before the onset of disease, may provide a more sensitive biomarker for detecting loss of sensitivity caused by the earliest neurodegenerative changes in the eyes.

Minimizing the need for coil attenuation correction in integrated PET/MRI at 1.5 T using low-density MR-linac receive arrays

The simultaneous use of positron emission tomography (PET) and magnetic resonance imaging (MRI) requires attenuation correction (AC) of photon-attenuating objects, such as MRI receive arrays. However, AC of flexible, on-body arrays is complex and therefore often omitted. This can lead to significant, spatially varying PET signal losses when conventional MRI receive arrays are used. Only few dedicated, photon transparent PET/MRI arrays exist, none of which are compatible with our new, wide-bore 1.5 T PET/MRI system dedicated to radiotherapy planning. In this work, we investigated the use of 1.5 T MR-linac (MRL) receive arrays for PET/MRI, as these were designed to have a low photon attenuation for accurate dose delivery and can be connected to the new 1.5 T PET/MRI scanner. Three arrays were assessed: an 8-channel clinically-used MRL array, a 32-channel prototype MRL array, and a conventional MRI receive array. We experimentally determined, simulated, and compared the impact of these arrays on the PET sensitivity and image reconstructions. Furthermore, MRI performance was compared. Overall coil-induced PET sensitivity losses were reduced from 8.5% (conventional) to 1.7% (clinical MRL) and 0.7% (prototype MRL). Phantom measurements showed local signal errors of up to 32.7% (conventional) versus 3.6% (clinical MRL) and 3.5% (prototype MRL). Simulations with data of eight cancer patients showed average signal losses were reduced from 14.3% (conventional) to 1.2% (clinical MRL) and 1.0% (prototype MRL). MRI data showed that the signal-to-noise ratio of the MRL arrays was slightly lower at depth (110 versus 135). The parallel imaging performance of the conventional and prototype MRL arrays was similar, while the clinical MRL array’s performance was lower. In conclusion, MRL arrays reduce in-vivo PET signal losses >10×, which decreases, or eliminates, the need for coil AC on a new 1.5 T PET/MRI system. The prototype MRL array allows flexible coil positioning without compromising PET or MRI performance. One limitation of MRL arrays is their limited radiolucent PET window (field of view) in the craniocaudal direction.

Assessment of Clinical and Laboratory Use of the Cutaneous Direct Immunofluorescence Assay

Dermatologists submit direct immunofluorescence (DIF) biopsies on a daily basis, using an assay detecting immunoreactant deposition with a panel that has traditionally comprised immunoglobulin (Ig) G, IgA, IgM, C3, and fibrin, with or without albumin antibodies. To evaluate and compare the frequency of immunoreactants in DIF biopsies submitted over an 8-year period and assess use by dermatologists based on clinical impression. A quality improvement study was conducted in a community outreach reference laboratory associated with a large academic medical center. Results of 2050 consecutive DIF skin biopsies submitted to the laboratory between April 1, 2012, and June 12, 2020, were analyzed by final pathologic diagnosis and antibody subtype positivity, in comparison with clinical impression. Biopsies in which the submitting physician had not performed the biopsy were excluded. Histopathologic findings and the results of DIF biopsies using the standard 6-antibody panel were evaluated in correlation with the submitted clinical diagnosis to assess immunoreactivity of the assay. Of 2050 DIF biopsies submitted, 367 (17.9%) were positive; IgG, IgA, and C3 alone identified all primary immunobullous disease cases (pemphigoid, pemphigus, linear IgA, and dermatitis herpetiformis), and IgA, C3, and fibrin antibodies alone identified all vasculitis cases. A panel of IgG, IgA, IgM, and fibrin identified all cases of lupus erythematosus. DIF results were positive in less than half of cases of hematoxylin and eosin biopsy-confirmed lupus erythematosus (23 of 47 [49%]). A total of 247 biopsies were submitted for clinical diagnoses not optimally supported on DIF: lichen planus, porphyria, and connective tissue disease. The findings of this study suggest that there is a knowledge gap among dermatologists relating to the opportunity for high-value, cost-conscious use of DIF. The practice of reflexive antibody testing using a 6-antibody panel for all DIF biopsies is likely unnecessary. DIF protocols tailored to the clinical diagnosis may enhance cost-effectiveness without loss of test sensitivity or specificity.

Sensitivity limitations of high-resolution perfusion-based human fMRI at 7 Tesla

The study of the brain's functional organization at laminar and columnar level of the cortex with blood oxygenation-level dependent (BOLD) functional MRI (fMRI) is affected by the contribution of large veins downstream from the microvascular response to brain activity. Blood volume- and especially perfusion-based techniques may reduce this problem because of their reduced sensitivity to venous effects, but may not allow the same spatial resolution because of smaller signal changes associated with brain activity. Here we investigated the practical resolution limits of perfusion-weighted fMRI in human visual stimulation experiments. For this purpose, we used a highly sensitive, single-shot perfusion labeling (SSPL) technique at 7 T and compared sensitivity to detect visual activation at low (2 mm, n = 10) and high (1 mm, n = 8) nominal isotropic spatial, and 3 s temporal, resolution with BOLD in 5½-minute-long experiments. Despite the smaller absolute signal change with activation, 2 mm resolution SSPL yielded comparable sensitivity to BOLD. This was attributed to a superior suppression of physiological noise with SSPL. However, at 1 mm nominal resolution, SSPL sensitivity fell on average at least 42% below that of BOLD, and detection of visual activation was compromised. This is explained by the fact that at high resolution, with both techniques, typically thermal noise rather than physiological noise dominates sensitivity. The observed sensitivity loss implies that to perform 1-mm resolution, perfusion weighted fMRI with a robustness similar to BOLD, scan times that are almost 3 times longer than the comparable BOLD experiment are required. This is in line with or slightly better than previous comparisons between perfusion-weighted fMRI and BOLD. The lower sensitivity has to be weighed against the spatial fidelity advantages of high-resolution perfusion-weighted fMRI.

Sensitivity of two SARS-CoV-2 variants with spike protein mutations to neutralising antibodies

SARS-CoV-2 infections elicit a humoral immune response capable of neutralising the virus. However, multiple variants have emerged with mutations in the spike protein amongst others, the key target of neutralising antibodies. We evaluated the neutralising efficacy of 89 serum samples from patients, infected with SARS-CoV-2 in the beginning of 2020, against two virus variants isolated from acutely infected patients and harbouring spike protein mutations. One isolate was assigned to lineage B.1.351 (MUC-IMB-B.1.351) whilst the other (MUC-484) was isolated from an immunocompromised patient, sharing some but not all mutations with B.1.351 and representing a transitional variant. Both variants showed a significant reduction in neutralisation sensitivity compared to wild-type SARS-CoV-2 with MUC-IMB-B.1.351 being almost completely resistant to neutralisation. The observed reduction in neutralising activity of wild-type-specific antibodies against both variants suggests that individual mutations in the spike protein are sufficient to confer a potent escape from the humoral immune response. In addition, the effect of escape mutations seems to accumulate, so that more heavily mutated variants show a greater loss of sensitivity to neutralisation up to complete insensitivity as observed for MUC-IMB-B.1.351. From a clinical point of view, this might affect the efficacy of (monoclonal) antibody treatment of patients with prolonged infections as well as patients infected with variants other than the donor. At the same, this could also negatively influence the efficacy of current vaccines (as they are based on wild-type spike protein) emphasising the need to thoroughly surveil the emergence and distribution of variants and adapt vaccines and therapeutics accordingly.

Antibody orientational labeling via staphylococcus A protein to improve the sensitivity of gold immunochromatography assays

The Cry1Ab toxin is usually expressed in genetically modified crops in order to control chewing pests. Although the gold immunochromatography assay (GICA) based on the double-antibody sandwich method has been developed to detect this toxin, its detection sensitivity needs improvement. In this study, Cry1Ab-51 antibodies were immobilized orientationally in a simple and effective way on colloidal gold nanoparticles (CGNPs) using the affinity of staphylococcal protein A (SPA) towards the fragment crystallizable (FC) fragment of mouse immunoglobulin G (IgG). Lateral flow detection test strips, assembled with probes labeled with orientational methods under optimal operational conditions (new probe), were 10 times more sensitive than test strips assembled with probes labeled by adsorption (conventional probe). Experiments showed that the affinity of the new probe was much higher than the conventional probe. The immunochromatography gold strip (ICG strip) assembled using the new probe was highly specific to Cry1Ab with no cross-reaction with other transgenic proteins, and it was proved that the specificity of the new probe had no change. Furthermore, the ICG strips assembled with the new probe could be stored for 12 months under dry conditions without a significant loss of sensitivity. The orientational labeling of the antibodies with SPA on colloidal gold proved to be suitable for improving the sensitivity of the ICG strips.

Sensitivity-Enhanced Moisture Sensor Based on θ-Shape Bending Fiber Coated With Copper-Polyvinyl Alcohol Thin Film

This paper presents a compact and easy fabrication of a moisture sensing probe based on macro-bending loss induces in a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta $ </tex-math></inline-formula> -shaped Mach-Zehnder interferometer (MZI) for the first time. The interferometer configuration was simply fabricated by bending a segment of single-mode fiber (SMF) into two elliptical loops divided by a fiber bridge to form a shape of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta $ </tex-math></inline-formula> symbol without any splicing. The sensing mechanism is reliant on the optical path difference among the core and cladding modes in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta $ </tex-math></inline-formula> -shaped configuration induces by appropriately adjusting the SMF bending diameters, which causes the resonance wavelength to shift towards relative humidity (RH) variation. Two sensing probes based on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta $ </tex-math></inline-formula> -shaped bend structure with an optimized bending diameter of 1.5 cm were fabricated to investigate the effect of Copper-Polyvinyl Alcohol (Cu/PVA) coatings, which served as a moisture-sensitive layer on the sensor sensitivity. The coated macro-bend structure exhibits an excellent sensitivity of −1.469 nm/RH% with a polynomial fitting coefficient of 99.645% in the 55%-97% relative humidity (RH) range, which is 1.4 times higher than that of an uncoated structure. This result presents a feasible and practical method to construct excellent sensitive optical fiber moisture sensors based-bending loss and Cu/PVA nanostructured coatings.

Reducing unnecessary thyroid fine needle aspirations using American College of Radiology's thyroid imaging reporting and data system: A 5‐year retrospective audit

AbstractBackgroundWith the growing investigative imaging techniques available in medicine, increasing numbers of thyroid lesions are being identified, either symptomatically or as incidental findings. Ultrasonography remains a key first‐line investigation into evaluating these lesions, and accurately stratifying whether further investigation or management is required.MethodsThis study retrospectively analysed a 5‐year patient cohort (2013–2017) who underwent fine needle aspirate (FNA) investigation of thyroid lesions at a large regional public hospital in Victoria, Australia. We aimed to identify whether using the American College of Radiology's thyroid imaging reporting and data system (ACR TI‐RADS) in grading the initial ultrasound (US) images would have resulted in a reduction in the number of patients undergoing invasive testing and if all malignant lesions would still have been captured.ResultsApplication of TI‐RADS criteria retrospectively to the audited population demonstrated a theoretical 56.16% (n = 164) reduction in FNAs with 0.00% of malignant nodules missed (n = 14). Sensitivity for referral to FNA testing based on ACR TI‐RADS grading was high (100%) with a moderately low specificity (58.99%).ConclusionFurther management of thyroid lesions guided by ACR TI‐RADS grading on initial US assessment is recommended, due to significant potential reduction in FNAs performed without loss of sensitivity for malignant nodules.

Auditory Tests for Characterizing Hearing Deficits in Listeners With Various Hearing Abilities: The BEAR Test Battery.

The Better hEAring Rehabilitation (BEAR) project aims to provide a new clinical profiling tool—a test battery—for hearing loss characterization. Although the loss of sensitivity can be efficiently measured using pure-tone audiometry, the assessment of supra-threshold hearing deficits remains a challenge. In contrast to the classical “attenuation-distortion” model, the proposed BEAR approach is based on the hypothesis that the hearing abilities of a given listener can be characterized along two dimensions, reflecting independent types of perceptual deficits (distortions). A data-driven approach provided evidence for the existence of different auditory profiles with different degrees of distortions. Ten tests were included in a test battery, based on their clinical feasibility, time efficiency, and related evidence from the literature. The tests were divided into six categories: audibility, speech perception, binaural processing abilities, loudness perception, spectro-temporal modulation sensitivity, and spectro-temporal resolution. Seventy-five listeners with symmetric, mild-to-severe sensorineural hearing loss were selected from a clinical population. The analysis of the results showed interrelations among outcomes related to high-frequency processing and outcome measures related to low-frequency processing abilities. The results showed the ability of the tests to reveal differences among individuals and their potential use in clinical settings.

Two-Stage Hierarchical Group Testing Strategy to Increase SARS-CoV-2 Testing Capacity at an Institution of Higher Education: A Retrospective Analysis

Population testing for severe acute respiratory syndrome coronavirus 2 is necessary because of the potential for viral transmission from asymptomatic cases, yet the scarcity of reagents and equipment has increased the cost-prohibitive implementation of screening campaigns at institutions of higher education. Significant analytical sensitivities of nucleic acid amplification methods permit sample pooling to increase testing capacity. Statistical models compared optimal testing configurations for pools of 3, 5, and 10 samples. Assessment of pooling using the TaqPath COVID-19 Combo Kit multiplex assay (ORF1ab, N, and S gene targets) involved a limit-of-detection study, matrix-effect study, and clinical comparison of neat with pooled samples. A limit of detection of 135.02 (ORF1ab; 95% CI, 117.21–155.52), 373.92 (N; 95% CI, 257.05–437.64), and 1001.32 (S; 95% CI, 896.62–1118.33) gene copy equivalents per milliliter was resolved. Seventy-two randomly selected samples showed slight suppression owing to a negative sample matrix. The resulting mean cycle threshold shifts were 2.09 (ORF1ab), 1.76 (N), and 2.31 (S) for the 3-sample pool, 2.83 (ORF1ab), 2.45 (N), and 3.24 (S) for the 5-sample pool, and 3.99 (ORF1ab), 3.46 (N), and 4.07 (S) for the 10-sample pool. Despite a quantitative sensitivity loss trend, the qualitative result was unaffected in each pool. According to the range of disease prevalence observed at the testing site (0.03% to 7.32%), a pool of five samples was deemed an optimal and cost-effective option for monitoring the Northeastern University community.

The Role of Tapered Light-Diffusing Fibers in Plasmonic Sensor Configurations.

In this work, we experimentally analyzed the effect of tapering in light-diffusing optical fibers (LDFs) when employed as surface plasmon resonance (SPR)-based sensors. Although tapering is commonly adopted to enhance the performance of plasmonic optical fiber sensors, we have demonstrated that in the case of plasmonic sensors based on LDFs, the tapering produces a significant worsening of the bulk sensitivity (roughly 60% in the worst case), against a slight decrease in the full width at half maximum (FWHM) of the SPR spectra. Furthermore, we have demonstrated that these aspects become more pronounced when the taper ratio increases. Secondly, we have established that a possible alternative exists in using the tapered LDF as a modal filter after the sensible region. In such a case, we have determined that a good trade-off between the loss in sensitivity and the FWHM decrease could be reached.

Psychometric Curves Reveal Three Mechanisms of Vigilance Decrement

The vigilance decrement is a decline in signal detection rate that occurs over time on a sustained-attention task. The effect has typically been ascribed to conservative shifts of response bias and losses of perceptual sensitivity. Recent work, though, has suggested that sensitivity losses in vigilance tasks are spurious, and other findings have implied that attentional lapses contribute to vigilance failures. To test these possibilities, we used Bayesian hierarchical modeling to compare psychometric curves for the first and last blocks of a visual vigilance task. Participants were a convenience sample of 99 young adults. Data showed evidence for all three postulated mechanisms of vigilance loss: a conservative shift of response bias, a decrease in perceptual sensitivity, and a tendency toward more frequent attentional lapses. Results confirm that sensitivity losses are possible in a sustained-attention task but indicate that mental lapses can also contribute to the vigilance decrement.

Multichannel Approach for Arrayed Waveguide Grating-Based FBG Interrogation Systems.

In this manuscript, an optically passive fiber Bragg grating (FBG) interrogation system able to perform high-frequency measurement is proposed. The idea is mainly based on the use of an arrayed waveguide grating (AWG) device which is used to discriminate the fiber optic sensor (FOS) wavelength encoded response under test in function of its output channels. As made clear by the theoretical model studied in the proposed manuscript, the Bragg wavelength shift can be detected as in linear dependence with the proposed interrogation function which changes with the voltage produced by two (or more) adjacent AWG output channels. To prove the feasibility of the system, some experimental analyses are conducted with a custom electrical module characterized by high-speed and low-noise operational amplifiers. As static measurements, three FBGs with different full width at half maximum (FWHM) have been monitored under wide-range wavelength variation; while, as dynamic measurement, one FBG, glued onto a metal plate, in order to sense the vibration at low and high frequency, was detected. The output signals have been processed by a digital acquisition (DAQ) board and a graphical user interface (GUI). The presented work highlights the characteristics of the proposed idea as competitor among the entire class of interrogation systems currently used. This is because here, the main device, that is the AWG, is passive and reliable, without the need to use modulation signals, or moving parts, that affect the speed of the system. In addition, the innovative multi-channel detection algorithm allows the use of any type of FOS without the need to have a perfectly match of spectra. Moreover, it is also characterized by a high dynamic range without loss of sensitivity.

Apathy in caregiving –

Over the years little attention has been given to a practical theology of compassion. Even in the discussion on theopaschitic theology, and the implication of a theology of the cross for theory formation in practical theology and the praxis of ministry, the emphasis was mainly on reconciliation, forgiveness, and the notion of restorative justice. Ethical and moral issues dominated the discourse. In the meantime, it seems that people in their quest for a humane society, social justice and human dignity are exposed to a gradual inflation of compassion. The migrant crisis has become a crisis of replacement and apathy; xenophobia represents and antipathy of local communities towards strangers. The emphasis on wealth and importance in affluent societies create carelessness, insensitivity and even antipathy against the demands of strangers and poor people. Zygmunt Bauman (2013) refers to “moral blindness and the loss of sensitivity in liquid modernity”. At the same time, disillusionment breeds a kind of antipathetic anger, captured in a very poignant and harsh expression: “F*ck you” (Manson 2016). This phenomenon of antipathy and indifferentism had already been identified as a huge stumbling block for ministry in medieval times and life in monasteries. Sloth had been earmarked as one of the seven deadly sins. How then should a theology of compassion and the praxis of pastoral caregiving respond to these very challenging phenomena of apathy, indifferentism, sloth, and life fatigue?

Minimizing Pervasive Artifacts in 4D Covariance Maps for Protein Side Chain NMR Assignments.

Nuclear magnetic resonance (NMR) is a mainstay of biophysical studies that provides atomic level readouts to formulate molecular mechanisms. Side chains are particularly important to derive mechanisms involving proteins as they carry functional groups, but NMR studies of side chains are often limited by challenges in assigning their signals. Here, we designed a novel computational method that combines spectral derivatives and matrix square-rooting to produce reliable 4D covariance maps from routinely acquired 3D spectra and facilitates side chain resonance assignments. Thus, we generate two 4D maps from 3D-HcccoNH and 3D-HCcH-TOCSY spectra that each help overcome signal overlap or sensitivity losses. These 4D maps feature HC-HSQCs of individual side chains that can be paired to assigned backbone amide resonances of individual aliphatic signals, and both are obtained from a single modified covariance calculation. Further, we present 4D maps produced using conventional triple resonance experiments to easily assign asparagine side chain amide resonances. The 4D covariance maps encapsulate the lengthy manual pattern recognition used in traditional assignment methods and distill the information as correlations that can be easily visualized. We showcase the utility of the 4D covariance maps with a 10 kDa peptidyl carrier protein and a 52 kDa cyclization domain from a nonribosomal peptide synthetase.

Quantitative Real-Time PCR Assay for the Detection of Pectobacterium parmentieri, a Causal Agent of Potato Soft Rot.

Pectobacterium parmentieri is a plant-pathogenic bacterium, recently attributed as a separate species, which infects potatoes, causing soft rot in tubers. The distribution of P. parmentieri seems to be global, although the bacterium tends to be accommodated to moderate climates. Fast and accurate detection systems for this pathogen are needed to study its biology and to identify latent infection in potatoes and other plant hosts. The current paper reports on the development of a specific and sensitive detection protocol based on a real-time PCR with a TaqMan probe for P. parmentieri, and its evaluation. In sensitivity assays, the detection threshold of this protocol was 102 cfu/mL on pure bacterial cultures and 102–103 cfu/mL on plant material. The specificity of the protocol was evaluated against P. parmentieri and more than 100 strains of potato-associated species of Pectobacterium and Dickeya. No cross-reaction with the non-target bacterial species, or loss of sensitivity, was observed. This specific and sensitive diagnostic tool may reveal a wider distribution and host range for P. parmentieri and will expand knowledge of the life cycle and environmental preferences of this pathogen.

SARS-CoV-2 B.1.617 Mutations L452R and E484Q Are Not Synergistic for Antibody Evasion.

The SARS-CoV-2 B.1.617 variant emerged in the Indian state of Maharashtra in late 2020. There have been fears that 2 key mutations seen in the receptor-binding domain, L452R and E484Q, would have additive effects on evasion of neutralizing antibodies. We report that spike bearing L452R and E484Q confers modestly reduced sensitivity to BNT162b2 mRNA vaccine-elicited antibodies following either first or second dose. The effect is similar in magnitude to the loss of sensitivity conferred by L452R or E484Q alone. These data demonstrate reduced sensitivity to vaccine-elicited neutralizing antibodies by L452R and E484Q but lack of synergistic loss of sensitivity.

Implementation of an efficient SARS-CoV-2 specimen pooling strategy for high throughput diagnostic testing

The rapid identification and isolation of infected individuals remains a key strategy for controlling the spread of SARS-CoV-2. Frequent testing of populations to detect infection early in asymptomatic or presymptomatic individuals can be a powerful tool for intercepting transmission, especially when the viral prevalence is low. However, RT-PCR testing—the gold standard of SARS-CoV-2 diagnosis—is expensive, making regular testing of every individual unfeasible. Sample pooling is one approach to lowering costs. By combining samples and testing them in groups the number of tests required is reduced, substantially lowering costs. Here we report on the implementation of pooling strategies using 3-d and 4-d hypercubes to test a professional sports team in South Africa. We have shown that infected samples can be reliably detected in groups of 27 and 81, with minimal loss of assay sensitivity for samples with individual Ct values of up to 32. We report on the automation of sample pooling, using a liquid-handling robot and an automated web interface to identify positive samples. We conclude that hypercube pooling allows for the reliable RT-PCR detection of SARS-CoV-2 infection, at significantly lower costs than lateral flow antigen (LFA) tests.

Enabling Multiplexed Electrochemical Detection of Biomarkers with High Sensitivity in Complex Biological Samples.

The ability to perform multiplexed detection of various biomarkers within complex biological fluids in a robust, rapid, sensitive, and cost-effective manner could transform clinical diagnostics and enable personalized healthcare. Electrochemical (EC) sensor technology has been explored as a way to address this challenge because it does not require optical instrumentation and it is readily compatible with both integrated circuit and microfluidic technologies; yet this approach has had little impact as a viable commercial bioanalytical tool to date. The most critical limitation hindering their clinical application is the fact that EC sensors undergo rapid biofouling when exposed to complex biological samples (e.g., blood, plasma, saliva, urine), leading to the loss of sensitivity and selectivity. Thus, to break through this barrier, we must solve this biofouling problem.In response to this challenge, our group has developed a rapid, robust, and low-cost nanocomposite-based antifouling coating for multiplexed EC sensors that enables unprecedented performance in terms of biomarker signal detection compared to reported literature. The bioinspired antifouling coating that we developed is a nanoporous composite that contains various conductive nanomaterials, including gold nanowires (AuNWs), carbon nanotubes (CNTs), or reduced graphene oxide nanoflakes (rGOx). Each study has progressively evolved this technology to provide increasing performance while simplifying process flow, reducing time, and decreasing cost. For example, after successfully developing a semipermeable nanocomposite coating containing AuNWs cross-linked to bovine serum albumin (BSA) using glutaraldehyde, we replaced the nanomaterials with reduced graphene oxide, reducing the cost by 100-fold while maintaining similar signal transduction and antifouling properties. We, subsequently, developed a localized heat-induced coating method that significantly improved the efficiency of the drop-casting coating process and occurs within the unprecedented time of <1 min (at least 3 orders of magnitude faster than state-of-the-art). Moreover, the resulting coated electrodes can be stored at room temperature for at least 5 months and still maintain full sensitivity and specificity. Importantly, this improved coating showed excellent antifouling activity against various biological fluids, including plasma, serum, whole blood, urine, and saliva.To enable affinity-based sensing of multiple biomarkers simultaneously, we have developed multiplexed EC sensors coated with the improved nanocomposite coating and then employed a sandwich enzyme-linked immunosorbent assay (ELISA) format for signal detection in which the substrate for the enzyme bound to the secondary antibody precipitates locally at the molecular binding site above the electrode surface. Using this improved EC sensor platform, we demonstrated ultrasensitive detection of a wide range of biomarkers from biological fluids, including clinical biomarkers, in both single and multiplex formats (N = 4) with assay times of 37 and 15 min when integrated with a microfluidic system. These biosensors developed demonstrate the vast potential of solving the biofouling problem, and how it can enable potential clinically important diagnostic applications. This Account reviews our antifouling surface chemistry and the multiplexed EC sensor-based biodetection method we developed and places it in context of the various innovative contributions that have been made by other researchers in this field. We are optimistic that future iterations of these systems will change the way diagnostic testing is done, and where it can be carried out, in the future.