Eliminating viscosity bias in lateral flow tests

Consumer-Led Investigation into Potential Issues That Arise When Testing Dairy Matrixes for Gluten With the NIMA Sensor

BACKGROUND

Some consumers with celiac disease use personal, point-of-use gluten detection devices to test food. False-positive results may occur due to sampling, matrix effects, and sensor issues.

OBJECTIVE

The purpose of the present study was to determine if the positive gluten results some users were obtaining when testing cream cheese and materials of similar consistency were false positives and, if so, what might be causing them to occur.

METHODS

Cream cheese, soft cheese, and yogurt were tested for gluten using the Ridascreen Gliadin R7001 sandwich R5 ELISA and the Ridascreen Gliadin R7021 competitive R5 ELISA. Two test portions were taken, extracted, and tested from each homogenized material. Materials were also analyzed for gluten using a NIMA sensor, a personal, point-of-use gluten detection device. Multiple test portion weights were tested beginning at 0.13 to 0.17 g (the ideal weight of the test portion according to the NIMA sensor development team).

RESULTS

Using the sandwich R5 ELISA and the competitive R5 ELISA, all materials tested below the lower LOD for gluten. Using a NIMA sensor, as the weight of the test portion tested increased, sensor results went from no gluten found, to gluten found, to no test result.

CONCLUSION

The gluten found results using the NIMA sensor are likely false positives that appear to correspond with the weight and volume of the material tested, as well as the viscosity. There is also an apparent disconnect between the gluten found result reported by the sensor and an interpretation of the lateral flow device (LFD) strip result when assessed by eye which should also be taken into account. Ideally, NIMA sensor users should be advised on the weight amount of material to analyze and test portions should be weighed before being used with the NIMA sensor. However, this is not a practical solution when testing in many environments, including restaurants.

HIGHLIGHTS

Slight variations in weight and volume of test materials can result in false positive results when testing dairy matrixes for gluten using the Nima sensor.

Quantitative injection strip platform using water-soluble paper and magnet based on a lateral flow assay

Quantitative analysis for lateral flow immunoassay (LFA) strips was conducted continuously. Quantitative analysis means measuring concentration, which represents the number of molecules per unit volume. In this study, we designed a quantitative injection (QI) strip by modifying the structure of general LFA strips to inject the same unit volume. To achieve the injection of the same unit volume, we used water-soluble paper and magnet. In addition, the QI strip was fabricated to enable the physical separation of the gold conjugate pad from the nitrocellulose membrane (NC membrane) at the optimized time after sample injection. The optimized time refers to the time from the point at which the sample started flowing on the NC membrane to the point at which the strip was separated. At the samples of same concentration, the LFA strip increases detection signals as the volume of injected sample increases. In contrast to the LFA strip, the QI strip maintained consistent detection signals even with increasing volume of injected sample. Furthermore, the QI strip demonstrated an 11-fold lower deviation compared to the LFA strip. These results are attributed to the separation function of the QI strip. In conclusion, the QI strip is more suitable for quantitative analysis compared to the LFA strip due to the same unit volume without additional equipment such as a pipette. This study is expected to contribute to the development of user-friendly POCT and strip-based quantitative analysis.

Rapid and Simple Buffer Exchange Using Cation-Exchange Chromatography to Improve Point-of-Care Detection of Pharmacological Agents

The current COVID-19 pandemic has highlighted the power, speed, and simplicity of point-of-care (POC) diagnostics. POC diagnostics are available for a wide range of targets, including both drugs of abuse as well as performance-enhancing drugs. For pharmacological monitoring, minimally invasive fluids such as urine and saliva are commonly sampled. However, false positives or negatives caused by interfering agents excreted in these matrices may confound results. For example, false positives have, in most cases, prevented the use of POC diagnostics for pharmacological agent detection; the consequence is that centralized labs are instead tasked to perform these screenings, resulting in significant delays between sampling and testing. Thus, a rapid, simple, and inexpensive methodology for sample purification is required for the POC to reach a field-deployable tool for the pharmacological human health and performance assessments. Buffer exchange is a simple, rapid approach to remove interfering agents, but has traditionally been difficult to perform on small pharmacological molecules. Therefore, in this communication, we use salbutamol, a performance-enhancing drug, as a case example to demonstrate the efficacy of ion-exchange chromatography as a technique to perform buffer exchange for charged pharmacological agents. This manuscript demonstrates the efficacy of this technique leveraging a commercial spin column to remove interfering agents found in simulant urines, such as proteins, creatinine, and urea, while retaining salbutamol. The utility and efficacy of the method was then confirmed in actual saliva samples. The eluent was then collected and run on the lateral flow assays (LFAs), improving the reported limit of detection by over 5× (new lower limit of detection of 10 ppb compared to reported 60 ppb by the manufacturer) while simultaneously removing noise due to background interfering agents.

Disposable and low-cost pen-like sensor incorporating nucleic-acid amplification based lateral-flow assay for at-home tests of communicable pathogens

Rapid at-home test is a good alternative to the gold standard quantitative polymerase chain reaction (qPCR) for early identification and management of infected individuals in pandemic. However, the currently available at-home rapid antigen kits and nucleic acid tests (NATs) are prone to false results. Although some CRISPR-mediated NATs enhanced accuracy, long turnaround time (ca. 1 h) and aerosol contamination due to additional open-lid reaction hinder its applicability for self-tests. Moreover, the accuracy of at-home NATs is also impacted by interference of sample matrix due to lack of sample purification. Here we report a Fast, Low-cost, Aerosol contamination-free and Sensitive molecular assay for at-Home tests of communicable pathogens (FLASH) incorporating oLAMP, a recently reported isothermal and target-specific NATs by our group, and a visible lateral-flow readout. The integrated platform enabled sample-to-result SARS-CoV-2 RNA detection in 20-30 min achieving a sensitivity of 0.5 copies/μL in a blinded experiment with a high accuracy comparable with the qPCR. Its prototype consists of two disposable pen-like instruments for single-step sample preparation and contamination-free NATs, respectively. The simplified workflow of the FLASH enabled detection to be readily conducted by untrained users for at-home tests. All in all, the FLASH prototype demonstrates itself to be a promising home-use assay platform for effective mitigation of the pandemic.

Highly portable quantitative screening test for prostate-specific antigen at point of care

Prostate cancer (PCa) is the second most diagnosed cancer among men. Targeted PCa screening may decrease PCa-specific mortality. Prostate-specific antigen (PSA) is the most reliable and widely accepted tumor biomarker for screening and monitoring PCa status. However, in many settings, quantification of serum PSA requires access to centralized laboratories. In this study, we describe a proof-of-concept rapid test combined with a highly portable Cube^™ reader for quantification of total PSA from a drop of serum within 20 min. We demonstrated the application of gold nanoshells as a label for lateral flow assay with significant increase in the measured colorimetric signal intensity to achieve five times lower detection limit when compared to the traditionally used 40 nm gold nanosphere labels, without a need for any additional signal amplification steps. We first optimized and evaluated the performance of the assay with commercially available total PSA calibrators. For initial validation with commercially available ACCESS Hybritech PSA calibrator, a detection range of 0.5-150 ng/mL was achieved. We compared the performance of our total PSA test with IMMULITE analyzer for quantification of total PSA in archived human serum samples. On preliminary testing with archived serums samples and comparison with IMMULITE total PSA assay, a correlation of 0.95 (p < .0001) was observed. The highly portable quantitative screening test for PSA described in this study has the potential to make PCa screening more accessible where diagnostic labs and automated immunoassay systems are not available, to reduce therapeutic turnaround time, to streamline clinical care, and to direct patient care for both initial screening and for post-treatment monitoring of patients.